29 January 2011

FRP RADIATOR GRILL


FRP RADIATOR GRILL



SUBMITTED BY

AJESH.A











CONTENTS


v INTRODUCTION

v OBJECTIVE

v FRP RAW MATERIALS

v FRP TECHNOLOGY

v MANUFACTURING PROCESS

v PODUCTION PROCEDURE

v PRODUCTION FLOW CHART

v COMPARISON WITH OTHER RADIATOR GRILL

v COST ANALYSIS

v PLANT LAYOUT

v CONCLUSION

v REFERENCE




INTRODUCTION

   
Reinforcing plastic matrix with high strength fibre material result in production of what is called fibre reinforced plastic. FRP’S have outstanding properties such as high strength to weight ratio and excellent corrosion resistance and are easy to fabricate. A wide variety of articles are made by the fibre reinforcing process. A remarkably high strength to weight raio is the main feature. Attracting space craft designers. Elegance light weight and corrosion resistant quqlities make it suitable material in a salt water application. Corrosion resistance property of the reinforced plastic is fully utilized when they are employed in huge quantities.


        Different type of Radiator grills are available in the market. But the price of those are very high. FRP Radiator grill has light weight, good finish etc. More over the manufacturing process is simple and it need less manufacturing material.


OBJECTIVE


To produce an FRP Radiator grill

Colour                     :   Black
 
No. of layers           :    2

Weight of product  :     1.650 gm



F R P RAW MATERIALS

1.    POLY ESTER RESIN

2.    M E K P

3.    COBALT NAPHTHANATE SOLUTION

4.    GLASS FIBRE

5.    POLY VINYL ALCHAHOL


A precut glass cloth or mat is then laid over the glass  cloth. Rollers are used to press the glass cloth on the resin uniformly and also remove the air entrapped air bubbles. Alternate layers of resins and glass cloths are laid in a similar sequence until the required thickness is build up. The whole set up is then cured eieher at the ambient on elevated temperature. After curing is completed the reinforced plastic material is thus trimmed and is removed from the mould and subjected to trimming and finishing.



MANUFACTURING PROCESS



The first step in the production of FRP based Radiator grill is cleaning the mould and wax paste to avoid scratches and for surface smoothness. Mould releasing agent PVA applied using sponge. PVA is a water soluble polymer. So mould releasing easy.
After PVA drying gelcoat is applied using laminating brush. For the production of FRP based Radiator grill general purpose resin is used. The gelcoat in the ratio of 1 kg resin for 100 gm of pigment.
It is stirred thoroughly and mixed with Cobalt Naphthanate and MEKP. Gel coat is applied whole of the mould surface with a brush. After that required size fibre adhered to the gelcoat surface by applying resin compound using laminating brush. Process is repeated to get the required thickness and allowed to setting the product.
                        
            Usually within half an hour moulding become cured. Then the product is released from the mould using water with force. 


COMPARISON WITH OTHER RADIATOR GRILL


FRP BASED
CLAY BASED
Light weight
      High weight

Low cost

       High cost
Easy processability
   Processing is complicated
No painting and polishing
required
  Painting and polishing 
   required





APPLICATION

It is used for Automobile purposes.

    

COST ANALYSIS
               
INGRADIENTS
QUANTITY
COST
Glass fibre
100 gm
8.00
Polyester resin
200 gm
18.00
MEKP
3 ml
2.00
Cobalt Naphthanate
5 ml
4.00
PVA
5 ml
3.00
Sand paper 1 sheet
1
3.00
Cotton waste
1
2.00
TOTAL

40.00
          


REQUIREMENTS

         Labours          2 Person

         Mould             1


CONCLUSION

        In modern life FRP based products are more useful. This is used for a variety of application. This is a development of plastic product. Compared to another manufacturing process of plastic products it has more advantages.


    

REFERENCE

    
FRP technology by R.G Whetherhead

01 January 2011

truck tyre compounding

Optimization Of property variation in
truck tyre compound

By
Hiran Mayookh Lal
Abhishek Krishna G


________________________________________





CONTENTS Page number
I. SCOPE OF PROJECT : 1
II. OUTLINE OF WORK : 2
III. COMPANY PROFILE : 4
IV. INTRODUCTION : 5 – 30
GENERAL RUBBER COMPOUNDING : 6
AN INTRODUCTION TO SBR 1712 : 30
V. EXPERIMENTAL DETAILS : 31 – 46
MATERIALS USED : 32
COMPOUNDING : 36
PROCESSABILITY STUDIES : 38
PHYSICAL TESTING OF CURED SAMPLES : 40
VI. TESTS & RESULTS : 47 – 62
VII. CONCLUSION : 63
VIII. RECOMMENDATIONS : 64
IX. REFERENCE & WEBSITES VISITED : 65
I. SCOPE OF THE PROJECT
Natural rubber (NR) is the major raw material for tyre industry. Nowadays the cost of NR is increasing dramatically. So the tyre manufacturers are forced to reduce the amount of NR used in tyre compounds with synthetic rubbers.
SBR 1712 is an economical grade of SBR produced now. It also gives an optimum balance of processing & physical properties. Other advantages of SBR 1712 is high amount of filler loading is possible, that will increase abrasion resistance of compound. Abrasion resistance is prime requirement of tyre tread compound. So we select SBR 1712 to replace some part of NR in heavy duty truck tyre tread cap.
PRICE OF NATURAL RUBBER & SBR 1712 in 2009 (Rupees per quintal)
Month
RSS 4
(Domestic)
SBR 1712
January
7034
-
February
6903
-
March
7583
-
April
9488
8027
May
9805
-
June
9913
-
July
9819
-
August
10250
-
September
10651
-
October
10898
-
November
11302
-
December
13430
8018
Note: Domestic price (RSS 4) refers to Kottayam market.
Courtesy: Monthly Rubber Statistical News - VOL.68 No.7 December 2009
II. OUTLINE OF WORK
The project work is on replacement of NR with SBR 1712. 10 phr of RSS – 4 is replaced with 10 phr SBR 1712 and properties were studied. Master batches were prepared in a banburry mixer. The compound finalization is done in a lab Two – Roll mill. Various accelerator dosages were used and the properties were studied. Various formulations used are given below
INGREDIENT
R
A
B
C
D
E
F
G
RSS - 4
100.0
90.00
90.00
90.00
90.00
90.00
90.00
90.00
SBR 1712
-
13.75
13.75
13.75
13.75
13.75
13.75
13.75
Crumb
(80 mesh)
10.00
10.00
10.00
10.00
10.00
10.00
10.00
10.00
Silica
10.00
10.00
10.00
10.00
10.00
10.00
10.00
10.00
HAF (N330)
55.00
55.00
55.00
55.00
55.00
55.00
55.00
55.00
Aromatic oil
13.00
13.00
13.00
13.00
13.00
13.00
13.00
13.00
Zinc Oxide
5.00
5.00
5.00
5.00
5.00
5.00
5.00
5.00
TQ
0.70
0.70
0.70
0.70
0.70
0.70
0.70
0.70
6PPD
3.00
3.00
3.00
3.00
3.00
3.00
3.00
3.00
Stearic acid
3.00
3.00
3.00
3.00
3.00
3.00
3.00
3.00
Peptiser
0.18
0.18
0.18
0.18
0.18
0.18
0.18
0.18
MBS
0.50
0.55
0.67
0.84
1.00
0.60
0.65
0.70
Sulphur
2.25
2.25
2.25
2.25
2.25
2.25
2.25
2.25
Retarder
-
-
-
-
-
-
-
-
The various properties studied are
1. Process ability studies
2. Tensile Properties (aged & unaged)
3. Tear Strength (aged & unaged)
4. Hardness (aged & unaged)
Based on these studies we selected three compounds (E, F & G) that found matching with regular compound (R). These compounds along with Regular compound were then finalized in banburry mixer. The various properties were studied.
The various properties studied are
1. Process ability studies
2. Tensile Properties (aged & unaged)
3. Tear Strength (aged & unaged)
4. Hardness (aged & unaged)
5. Abrasion Resistance
6. Heat Build Up
7. Resilience
8. Flex – Crack Initiation & Growth
Based on the final results we selected the proper compound (E) to replace the regular compound that is based on NR.
III. COMPANY PROFILE
Apollo Tyres Ltd is the fastest growing top tier tyre manufacturer, with annual revenues of over US$ 1.2 billion (2007-08). It was founded in 1976. Its first plant was commissioned in Perambra in Kerala state. In 2006 the company acquired Dunlop Tyres International of South Africa. The company now has four manufacturing units in India, two in South Africa and two in Zimbabwe. It has a network of over 4,000 dealerships in India, of which over 2,500 are exclusive outlets. In South Africa, it has over 900 dealerships, of which 190 are Dunlop Accredited Dealers. "Apollo Tyres Ltd." has been pioneer in the implementation of "Six Sigma" among all the tyre companies in India, and is in the list of top 15 tyre manufacturers of the world in terms of Revenues.The construction of fully automated plant at chennai with a initial capacity of 6000 TBR and 8000 PCR is under progress. Apollo Tyres has acquired the Netherlands-based Vredestein Banden BV (VBBV) for an undisclosed sum from Russia's bankrupt largest tyre manufacturer Amtel-Vredestein NV.
The company currently produces the entire range of automotive tyres for ultra and high speed passenger cars, truck and bus, farm, Off-The-Road, industrial and specialty applications like mining, retreaded tyres and retreading material. These are produced across Apollo’s eight manufacturing locations in India, Netherlands and Southern Africa. A ninth facility is currently under construction in southern India, and is expected to commence production towards the end of 2009. The major brands produced across these locations are: Apollo, Dunlop, Kaizen, Maloya, Regal and Vredestein.
Apollo is one of the largest corporate investors in developing sporting talent through its Mission 2018, which is focused on nurturing and training youngsters in the sport of tennis to enable an Indian to win a Singles Grand Slam Championship by the year 2018.
IV. INTRODUCTION
GENERAL RUBBER COMPOUNDING
Compounding, a term that has evolved within the tire and rubber industry, is the materials science of modifying a rubber or elastomer or a blend of polymers and other materials to optimize properties to meet a given service application or set of performance parameters. The ingredients available to the materials scientist for formulating a rubber compound can be divided into five categories:
1. Polymers Natural rubber, synthetic polymers
2. Filler systems Carbon blacks, clays, silicas, calcium carbonate
3. Stabilizer systems Antioxidants, antiozonants, waxes
4. Vulcanization system Sulfur, accelerators, activators
components
5. Special materials Secondary components such as pigments, oils,
resins, processing aids, and short fibers
II. Polymers
A. Natural Rubber
General
NR can be isolated from more than 200 different species of plant; including surprising examples such as dandelions. Only one tree source, Hevea Brasiliensis, is commercially significant. Latex is an aqueous colloid of NR, and is obtained from the tree by ‘tapping’ into the inner bark and collecting the latex in cups. The latex typically contains 30-40% dry rubber by weight, and 10-20% of the collected latex is concentrated by creaming, or centrifuging, and used in its latex form. Historically, such latex would be exported to consumer countries, but as it is expensive to ship a product with a high percentage of water, consumer companies are increasingly siting their latex processing plants in the producer countries, where the cheaper labour rates are an additional incentive. The remaining latex is processed into dry rubber as sheets, crepes and bales. There is an International Standard for the Quality and Packing for Natural Rubber grades, the so-called ‘Green Book’, published by the Rubber Manufacturers’ Association. The following grades of NR listed in the ‘Green Book’ are sold to visual inspection standards only:
Ribbed smoke sheets
White and pale crepes
Estate brown crepes
Compo crepes
Thin brown crepes
Thick blanket crepes
Flat bark crepes
Pure smoked crepe
Under each category there are generally up to 5 divisions, e.g., 1RSS, 2RSS, 3RSS, 4RSS, 5RSS for ribbed smoked sheets; the higher the number the more inferior the quality. The Malaysian rubber industry has, however, played a pioneering role in producing NR grades to technical specifications, and this system is being followed by other producer countries. Currently the following countries sell technically specified grades:
SMR - Standard Malaysian Rubber
SIR - Standard Indonesian Rubber
SSR - Specified Singapore Rubber
SLR - Standard Lanka Rubber
TTR - Thai Tested Rubber
NSR - Nigerian Standard Rubber
Field coagulated grades break down quicker on mastication and offer inferior ageing resistance to latex coagulated grades. They also have a higher dirt content. Some of the field coagulated grades can contain a variable mixture of field and latex coagulated materials.
NR is cis-1,4-polyisoprene, of molecular weight 200,000-500,000, but it also contains a small level of highly important non-rubber constituents. Of these, the most important are the proteins, sugars and fatty acids which are antioxidants and activators of cure. Trace elements present include potassium, manganese, phosphorus, copper and iron which can act as catalysts for oxidation.
NR is available in a granular form (powdered rubber), and in oil extended grades.
Two chemically modified types of NR (graft copolymers of NR and polymethylmethacrylate, and epoxidised NR) exhibit useful properties. The former are used in adhesive systems, and for the production of hard compounds, whilst the latter has probably still to find its market niche. As the name suggests, epoxidised NR is prepared by chemically introducing epoxide groups randomly onto the NR molecule. This chemical modification leads to increased oil resistance, greater impermeability to gases, but an increase in the glass transition temperature, Tg, and damping characteristics; the excellent mechanical properties of NR are retained. A 50 mole % epoxidised NR exhibits oil resistance only marginally inferior to that of nitrile rubber. NR can strain crystallise which results in its compounds exhibiting high tensile strength and good tear strength. Although crystallisation can occur at low temperatures, compounding greatly reduces this tendency and it can be effectively prevented from crystallising by using sulphur levels greater than 2.5 phr to cure the compound.
Since the main chain of NR contains unsaturation (residual double bonds) it, along with other unsaturated rubbers, is susceptible to attack by oxygen, ozone and light, and compounds therefore require protection against these agencies. NR is not oil resistant and is swollen by aromatic, aliphatic and halogenated hydrocarbons. It is resistant to many inorganic chemicals, but not to oxidising acids and had limited resistance to mineral acids. It is unsuitable for use with organic liquids in general, the major exception being alcohols of low molecular weight. NR can be crosslinked by the use of sulphur, sulphur donor systems, peroxides, isocyanate cures and radiation, although the use of sulphur is the most common method. The sulphur vulcanisation of NR generally requires higher added amounts of sulphur, and lower levels of accelerators than the synthetic rubbers. Sulphur contents of 2-3 phr, and accelerator levels of 0.2-1.0 phr are considered to be conventional cure systems.
NR can yield a hard rigid thermoplastic with excellent chemical resistance when cured with over 30 phr of sulphur. Such a product is termed ebonite. NR requires a certain degree of mastication (reduction in molecular weight) to facilitate processing,
although the advent of constant viscosity grades, and oil extended grades has substantially reduced the need for mastication. Peptisers are often used to facilitate breakdown of the rubber during mixing, although quantities of greater than 0.6 phr can cause a reduction in the final level of physical properties.
B. Polyisoprene (synthetic) (IR)
General
This synthetic rubber has the same empirical formula as NR and hence closely approximates to the behaviour of its naturally occurring rival. It has the same cis structure as NR, good uncured tack, high gum tensile strength, high resilience and good hot tear strength. Although similar to NR it does exhibit some differences:
i. It is more uniform and lighter in colour than NR.
ii. Due to a narrower molecular weight distribution it exhibits less of a tendency to strain
crystallise, hence green strength is inferior, as are both tensile and tear strength.
In general synthetic IR behaves like NR during processing, and it also requires protection against oxygen, ozone and light due to unsaturation in the main chain. Oil resistance is poor and it is not resistant to aromatic, aliphatic and halogenated hydrocarbons. It is resistant to many inorganic chemicals, but not to oxidising acids and has limited resistance to mineral acids. It is unsuitable for use with organic liquids in general, the major exception being alcohols of low molecular weight. Due to the absence of the non-rubber constituents present in the NR some differences in compounding occur, although, in essence, the principles are the same. An increased level of stearic acid is generally required for cure activation and approximately 10% extra accelerator is necessary to achieve a similar cure rate to NR; similar sulphur levels are, however, used. IR can be cured by the same type of systems as NR
C. Polybutadiene (BR)
General
Polybutadiene is produced by solution polymerisation, and one important feature governing the performance of the resultant polymer is the cis 1,4, and 1, 2 vinyl contents. High cis 1,4 polymers (>90%) have a Tg around –90 °C, and hence exhibit excellent low temperature flexibility only exceeded by the phenyl silicones. They also exhibit excellent resilience and abrasion resistance; unfortunately the high resilience gives poor wet grip in tyre treads, and hence this rubber finds limited use as the sole base for such compounds.
As the cis 1,4 content decreases, and 1,2 vinyl content increases, the low temperature properties, abrasion resistance and resilience become inferior.
The polymerisation of butadiene results in a polymer with a narrow molecular weight distribution which can be difficult to process. Indeed, commercially available grades present a compromise between processibility and performance. Most polybutadiene rubbers are inherently difficult to break down during mixing and milling, have low inherent tack, and the inherent elasticity of the polymer gives poor extrudability. Peptisers can be used to facilitate breakdown and hence aid processing.
Due to the unsaturation present in the main chain, protection is required against oxygen, UV and ozone. Oil resistance is poor and the polymer is not resistant to aromatic, aliphatic and halogenated hydrocarbons. Polybutadiene based compounds can be cured by sulphur, sulphur donor systems and peroxides. Less sulphur and a higher level of accelerators are required when compared to NR. The cure of polybutadiene by peroxides is highly ‘efficient’ in that a large number of crosslinks are produced per free radical, the resultant highly crosslinked rubber exhibiting high resilience; this factor is utilised in the manufacture of ‘superballs’. Compounds based on this polymer only give optimum properties at high filler and oil loadings.
D. Styrene-Butadiene Rubber (SBR)
General
When the USA and Germany were cut off from the supplies of natural rubber during the Second World War both countries sought to produce a synthetic alternative; SBR was the result, and at one stage it was the most commonly used synthetic rubber. It can be produced by both emulsion and solution polymerisation techniques, with the emulsion grades being the most widely used.
Emulsion polymerisation yields a random copolymer, but the temperature of the polymerization reaction also controls the resultant properties obtained. ‘Cold’ polymerisation yields polymers with superior properties to the ‘hot’ polymerised types.
Solution polymerisation can yield random, di-block, tri-block or multi-block copolymers. It is important to note that the tri-block, or multi-block copolymers, belong to that class of material termed thermoplastic elastomers and it is only the random copolymer types that are considered here. Both random emulsion and solution polymerised SBR contain about 23% styrene.
SBR continues to be used in many of the applications where it earlier replaced natural rubber, even though it requires greater reinforcement to achieve acceptable tensile and tear strengths, and durability. SBR exhibits significantly lower resilience than NR, so that it has a higher heat build-up on flexing which restricts its use in lorry tyres with their thicker sections. This inferior resilience to natural rubber is an advantage in passenger car tyre treads because the higher hysteresis loss gives increased wet grip and this, combined with the good abrasion resistance that can be obtained from tyre tread compounds, ensures that SBR has a high volume use in tyre production. The oil resistance of SBR is poor, and the polymer is not resistant to aromatic, aliphatic or halogenated solvents. Due to the unsaturation in the main chain, protection is required against oxygen, ozone and UV light.
Oil extended SBR, and SBR carbon black masterbatches are supplied by the polymer producers and such grades give the advantage of reducing the necessity of further additions of filler and oil at the mixing stage. SBR can be cured by the use of sulphur, sulphur donor systems and peroxides. Sulphur cures generally require less sulphur (1.5-2.0 phr) and more accelerator than is normally required to cure natural rubber.
E. Butyl Rubbers (IIR)
General
Commercial grades of IIR (butyl rubber) are prepared by copolymerising small amounts of isoprene with polyisobutylene. The isoprene content of the copolymer is normally quoted as the ‘mole percent unsaturation’, and it influences the rate of cure with sulphur, and the resistance of the copolymer to attack by oxygen, ozone and UV light. The polyisobutylene, being saturated, however, naturally confers on the polymer an increased level of resistance to these agencies when compared to natural rubber. Commercial butyl rubbers typically contain 0.5-3.0% mole unsaturation. The close packing of the isobutylene chain confers on the polymer a high degree of impermeability
to gases, but also results in a very ‘lossy’ rubber. The high hysteresis loss can be utilised in some circumstances to provide good friction in wet conditions. Chlorobutyl (CIIR) and bromobutyl (BIIR) are modified types containing 1.2% wt of chlorine or bromine, the isoprene unit being the site of halogenation. Introduction of the halogen gives greater cure flexibility, and enhanced cure compatibility in blends with other diene rubbers. It also confers increased adhesion to other rubbers and metals. Butyl rubber is not oil resistant.
Butyl, and the halogenated butyls, can be cured by sulphur, dioxime and resin cure systems. In addition, the halogenated types can be crosslinked with zinc oxide, and diamines. Peroxides cannot be used because they tend to depolymerise the polyisobutylene. Due to the low level of unsaturation in the main chain, sulphur cures require the more active thiuram and dithiocarbamate accelerators to achieve an adequate state of cure. Dioxime cures yield vulcanisates with good ozone resistance and moisture impermeability and, as such, are frequently used for curing electrical insulating compounds. Resin cures utilise phenol-formaldehyde resins with reactive methylene groups and a small added amount of either a chlorinated rubber, e.g., polychloroprene, or stannous chloride. If halogenated phenolic resins are used the additional source of a halogen may not be required. Resin cures give butyl compounds excellent heat stability and are used to good effect where this is required, e.g., in tyre curing bags which have to resist service at 150 °C in a steam atmosphere. Calcium stearate has to be added to stabilise the chlorobutyl during processing.
F. Ethylene-Propylene Rubber (EPM/EPDM)
General
The copolymerisation of ethylene and propylene yields useful copolymers, the crystallisation of both polymers being prevented if the ethylene content is in the range 45-60%; grades with higher ethylene contents, 70-80%, can partially crystallise. The lower ethylene types are generally easier to process, whilst green strength and extrudability improve as the ethylene content increases. One disadvantage of the copolymer is that it cannot be crosslinked with sulphur due to the absence of unsaturation in the main chain. To overcome this difficulty a third monomer with unsaturation is introduced, but to maintain the excellent stability of the main chain the unsaturation is made pendant to it. The three types of third monomer used commercially are dicyclopentadiene, ethylidene norbornene, and 1,4-hexadiene. Generally 4-5% of the termonomer will give acceptable
cure characteristics, whilst 10% gives fast cures; dicyclopentadiene gives the slowest cure rate and ethylidene norbornene the highest.
Since the main chain of both EPM and EPDM rubbers is saturated, both co- and terpolymers exhibit excellent stability to oxygen, UV light, and are ozone resistant. EPM and EPDM are not oil resistant, and are swollen by aliphatic and aromatic hydrocarbons, and halogenated solvents. They have excellent electrical properties and stability to radiation. Their densities are the lowest of the synthetics, and they are capable of accepting large quantities of filler and oil. They exhibit poor tack, and even if tackifiers are added, it still is not ideal for building operations. Adhesion to metal, fabrics and other materials, can be difficult to accomplish.
The copolymers can only be cured by peroxides or radiation, whilst the terpolymers can be cured with peroxides, sulphur systems, resin cures and radiation. The dicyclopentadiene terpolymer can give higher states of cure with peroxides than the copolymer, although in peroxide curing of both the copolymer and terpolymer it is common practice to add a coagent, to increase the state of cure. Triaryl isocyanurate or sulphur are the most common coagents. Bloom can be a problem in sulphur cures, so selection of the accelerator system is important. Resin cures utilise the same resins that are used for butyl rubber, but more resin (ca. 10-12 phr) and a halogen donor (10 phr), typically bromobutyl, or polychloroprene, are required. Although heat stability is slightly improved by resin curing when compared to sulphur cures, the effect is not as marked as in the resin curing of butyl.
FILLER SYSTEMS
Fillers, or reinforcement aids, such as carbon black, clays, and silicas are added to rubber formulations to meet material property targets such as tensile strength and brasion resistance.
Carbon Black
Carbon blacks are principally made by the chemical decomposition of natural gas or oil. Two classes predominate: the furnace blacks (95% of black usage) which are active, and thermal blacks (5% of usage) which are inactive. There are a substantial number of blacks for special applications such as electrically conducting and printing ink blacks. The latter are of too fine a particle size for rubber use. The nomenclature used for carbon blacks includes the ASTM designation and the industry type as illustrated in the next table.
The size of the carbon black particle has a profound influence on its dispersion characteristics within a rubber matrix and determines the final vulcanisate properties of the rubber compound. Blacks of very fine particle size are difficult to disperse adequately and when dispersion is achieved give a high reinforcement. Large particle size blacks are easily completely dispersed, but do not give reinforcement. The structure of the black affects the processing properties of the rubber compound, but generally does not have great significance in the reinforcement.
The structure of a carbon black depends on the original nature of the oil/gas feedstock. Thermal blacks have little or no structure. The higher the structure of the carbon black, the more irregular is the shape of the aggregate. The aggregates cling together to form agglomerates. In this form, carbon black is a fluffy, difficult-tohandle product, unsuitable for automatic weighing. Pelletisation produces a roughly spheroidal, easily broken pellet which will contain a large number of aggregates.
Mixing of carbon black into rubber consists essentially of two phases:
Incorporation - the carbon black is distributed into the rubber matrix but not into the desired state for complete reinforcement. At this stage of mixing the rubber penetrates the voids in the large agglomerates of carbon black. It is also at this stage that strong interaction between the rubber and black surface occurs in the case of small particle sized blacks with low structure, which makes the next step of dispersion difficult to achieve.
Dispersion - the large carbon black agglomerates become broken down and ‘wetted out’ under the influence of the mixing shear forces into discretely dispersed small aggregates/particles. The rubber becomes occluded into the remaining small aggregates, penetrates the voids within and between the aggregates and enters any cavities, resulting in an increase in viscosity as the available free volume of rubber is diminished. The result of the rubber occlusion is an effective increase in black loading. High surface area, low structure blacks are difficult to disperse as their dense packing and low void volume gives them the ability to rapidly interact with the rubber. As a result of the strong adhesion between the black and rubber, good random spatial dispersion is difficult to achieve.
Silica
Silica fillers offered to the rubber industry are of three specific types
• ground mineral silica,
• precipitated silica, and
• fumed or pyrogenic silica.
Ground Mineral Silica
Ground silica, generally available below 300 mesh in size (5 m 2 /g), is used as a cheap heat resistant filler for a variety of compounds. There is no effect on the rate or state of cure.
Hydrated Precipitated Silica
Silica used as a filler for rubbers is silicon dioxide, with particle sizes in the range of 10-40 nm. The silica has a chemically bound water content of 25% with an additional level of 4-6% of adsorbed water. The surface of silica is strongly polar in nature, centring around the hydroxyl groups bound to the surface of the silica particles. In a similar fashion, other chemical groups can be adsorbed onto the filler surface. This adsorption strongly influences silica’s behaviour within rubber compounds. The groups found on the surface of silicas are principally siloxanes, silanol and reaction products of the latter with various hydrous oxides. It is possible to modify the surface of the silica to improve its compatibility with a variety of rubbers.
The retention of water on the silica filler surface has significant effects on the processing of the compound and vulcanisation reactions. Despite rigorous drying procedures there is always a monomolecular layer of water retained on the surface of the filler. Silica fillers are sold with a known level of water content, generally 3-6%, but this can change markedly with changes in ambient humidity. Silicas with less than 3% water content do not achieve adequate dispersion in the rubber. Conversely, dispersion of the silica during mixing becomes progressively worse with rising moisture content. Similarly, vulcanisation rates are affected by increased moisture. Failure to control the humidity of the storage area for the silica will obviously result in variable compound behaviour. This phenomenon is not observed with thiuram disulphide and peroxide cures.
Silica fillers also react with the rubber causing an increase in viscosity and ‘dry’ and unmanageable processing behaviour. Filler activators need to be added to silica-reinforced compounds to overcome these problems. The usual filler activators used are diethylene glycol, polyethylene glycol and amines such as triethanolamine. Some of these activators not only overcome the problems of processing and accelerator absorption, but depending on the cure system used, will also act as vulcanisation activators Other additives such as silanes, titanates and zirconates are also used to overcome the processing characteristics of silica fillers. Silanes not only give improved processability of silica-filled compounds, but also provide improved ‘crosslinks’ between the silica particle surface and the rubber molecular chains giving increased physical properties. The use of silane coupling agents at a2-5% level will improve the reinforcing performance of the silica to that of a similar size carbon black.
Fumed Silica
Fumed silica is prepared by burning volatile silicon compounds such as silicon tetrachloride. This type of silica contains less than 2% combined water and generally no free water. It reacts readily with hydroxyl groups. The particle size is in the region 5-10 nm. Fumed silicas are not generally used in conventional rubber compounding but find application with silicone rubber. The recognized surface area values for best reinforcement of silicone rubber by an amorphous silica lies between 150-400 m 2 /g.
Particle size of the silica and tight control of its size distribution decides the ability of the
compounded silicone rubber to be optically clear, even at quite high levels of addition. This feature can be used to advantage in a number of medical applications such as intraocular and contact lenses, medical tubing, flexible lights and a number of other industrial applications where sustained clarity of transparency is important.
Isolated hydroxyl groups on the silica surface lead to hydrogen bonding between the silicone rubber and the filler surface. This bonding produces strong elastic rubbers. During storage, the rubber/filler bonds continue to form and the compound stiffens giving the effect known as ‘crepe hardening’. This is a similar effect to that seen with other rubbers containing carbon black fillers, in which a ‘structure’ forms during storage. Before further processing, the structure will need to be broken down by milling to ensure good flow in down-line processes. The degree of moisture present affects the properties of the silicone rubber vulcanisate. Moisture levels also determine the ease with which the filler is incorporated into the silicone rubber. Low moisture levels improve the final physical properties but definitely detract from the incorporation speed of the silica filler.
A silicone oil plasticiser is desirable to facilitate dispersion and to prevent undesirable polymerfiller interaction prior to vulcanisation.
STABILIZER SYSTEMS
The unsaturated nature of an elastomer accounts for its unique viscoelastic properties. However, the presence of carbon–carbon double bonds renders elastomers susceptible to attack by oxygen, ozone, and also thermal degradation. Retardation of oxidative degeneration and the effects of ozone attack can be mitigated but not totally overcome by the use of chemicals which, unfortunately, in the case of the most effective types, carry the penalty of causing staining of the rubber compound or surfaces with which it comes into contact.
Antioxidants
Oxidative ageing of rubbers is limited by the rate of diffusion of oxygen into the rubber product and is usually confined to the outer 3 mm. Antioxidants are used to protect rubbers from the effects of thermal oxidation and the vast majority of compounds will contain one or more. Peroxide vulcanisates are usually protected with dihydroquinolines. Other antioxidants react adversely with the peroxide inhibiting the crosslinking reaction. The durability of the antioxidant can be affected by a number of factors, the most important being the amount present in the compound. The process of vulcanisation can result in the loss of migratory or volatile antioxidants. Over long periods of service, the antioxidant will decrease in concentration at ambient temperatures due to reaction with oxygen. Loss by volatility is usually only a problem with antioxidants such as the mono-phenolics. The most effective antioxidants for light coloured rubber compounds are the hindered bisphenols, but these offer little ozone and flex cracking resistance.
Strongly Staining Antioxidants
Aryl naphthylamine derivatives are good general antioxidants with moderate volatility and negligible effect on cure. These give a small degree of fatigue protection in natural and polyisoprene rubbers, but little in styrene-butadiene and butadiene vulcanisates. Diphenylamine derivatives are very good antioxidants and provide fatigue activity and good metal poison protection.
Moderately Staining Antioxidants
Dihydroquinoline derivatives offer moderate antioxidant and flex cracking activity with excellent metal poison protection.
Non-Staining Antioxidants
Benzimidazole derivatives are excellent antioxidants, with limited fatigue activity. They offer excellent metal poison protection. Bisphenol derivatives show very good antioxidant activity and are the best materials for light coloured articles. Selected materials are FDA approved. These derivatives have low volatility and no effect on cure rate and do not give a bloom. A slight pink discoloration can occur after prolonged exposure to light in white or light coloured products. Hydroquinones show very good antioxidant activity, but offer limited fatigue and metal poison protection. Alkylphenol derivatives show medium antioxidant activity, but provide limited fatigue and metal poison activity.
Antiozonants
para-Phenylenediamine (PPD)
Ozone attack on rubbers takes the form of cracking which takes place perpendicular to the direction of the strain. Ozone attack occurs mainly at the olefinic double bond of a diene rubber and, if not protected against, will result in loss of physical integrity for thin sectioned articles and surface cracking on larger mass products. Too high a dosage of antiozonant can result in the formation of unsightly blooms on the rubber surface. Too little antiozonant can lead to worse attack than when none is present.
VULCANIZATION SYSTEM
Vulcanization, named after Vulcan, the Roman God of Fire, describes the process by which physically soft, compounded rubber materials are converted into high-quality engineering products. The vulcanization system constitutes the fourth component in an elastomeric formulation and functions by inserting crosslinks between adjacent polymer chains in the compound. A typical vulcanization system in a compound consists of three components: (1) activators; (2) vulcanizing agents, typically sulfur; and (3) accelerators.
Activators
The vulcanization activator system consisting of zinc oxide and stearic acid has received much less research effort than other components in the rubber compound. Stearic acid and zinc oxide levels of 2.0 and 5.0 phr, respectively, are accepted throughout the rubber industry as being adequate for achievement of optimum compound physical properties when in combination with a wide range of accelerator classes and types and also accelerator-to-sulfur ratios.
Vulcanizing Agents
Three vulcanizing agents find extensive use in the rubber industry: sulfur, insoluble sulfur, and peroxides. Rhombic sulfur is the most common form of sulfur used in the rubber industry and, other than normal factory hygiene and operational procedures, does not require any special handling or storage. Sulfur is soluble in natural rubber at levels up to 2.0 phr. Above this concentration, insoluble sulfur must be used to prevent migration of sulfur to the compound surface, i.e., sulfur bloom.
Sulphur in its amorphous form is known in the rubber industry as ‘insoluble sulphur’. Insoluble sulphur is used by the rubber industry as, if not converted to the rhombic form by excessive processing heat, it will remain undissolved in the rubber and thus cannot bloom to the surface of the unvulcanised rubber compound. This is a factor which is very important for products which require a number of processing assembly steps in their manufacture. Normal rhombic sulphur has differing degrees of solubility in the different rubber types. In NR and SBR the required proportion for crosslinking dissolves relatively rapidly at room temperature. In stereospecific rubbers such as polybutadiene and nitrile it does not solubilise so readily. As one would expect, the solubility of the sulphur within the rubber increases with temperature increase.
Accelerators
Accelerators are products which increase both the rate of sulfur crosslinking in a rubber compound and crosslink density. Secondary accelerators, when added to primary accelerators, increase the rate of vulcanization and degree of crosslinking, with the terms primary and secondary being essentially arbitrary. A feature of such binary acceleration systems is the phenomenon of synergism. Where a combination of accelerators is synergistic, its effect is always more powerful than the added effects of the individual components.
Accelerators can be readily classified by one of two techniques:
1. Rate of vulcanization: Ultra-accelerators include dithiocarbamates and xanthates. Semiultra-accelerators include thiurams and amines. Fast accelerators are thiazoles and sulfenamides. A medium-rate system is diphenylguanidine. A slow accelerator is thiocarbanilide.
2. Chemical classifications: Most accelerators fall into one of eight groups.
Aldehydeamines Sulfenamides
Thioureas Dithiocarbamates
Guanidines Thiurams
Thiazoles Xanthates
Sulfenamide accelerators represent the largest class of accelerators consumed on a global basis:
PROCESS OILS
Mineral oils
Mineral oils are the most frequently used plasticisers for both natural and synthetic rubbers. They are high boiling fractions obtained in refining crude oil. The oils are comprised mainly of ring structures: unsaturated (aromatics), saturated (naphthenes) and ring structures possessing saturated side chains (paraffins). They are classified accordingly as aromatic, naphthenic and paraffinic depending on the predominant structure of the oil. The choice of oil depends largely on the compatibility with the elastomer. As a general rule paraffinic oils are best used with low polarity polymers whilst aromatics are more suited to the more polar polymers.
Petroleum waxes
About 90% of all waxes used for commercial purposes are recovered from petroleum. Petroleum waxes are generally classified into three principle types: paraffinic, microcrystalline and petrolatum. Paraffin wax is a solid, colourless substance composed of alkanes up to 30 carbon atoms in length with a low level of branching. As a consequence of the regular structure, paraffin wax crystallises relatively easily into large plates or needles. Microcrystalline paraffin wax differs from paraffin wax in having a higher MW and, therefore, a higher softening temperature. The molecular structure is more branched resulting in a microcrystalline material. Petrolactum is a semi-solid substance, substantially a mixture of a high MW hydrocarbon, ceresine and oils.
Peptising agents
Peptising agents are substances that act as chain terminating agents during the mastication of rubber. They may also act as pro-oxidants during the mastication process. This significantly reduces the time necessary to lower the viscosity of the rubber to a workable level, which in turn brings savings in mixing time and energy.
Prevulcanisation Inhibitors
Sulphur vulcanisation of rubber is catalysed by the presence of alkali materials. This activation of the vulcanisation system can result in unwanted short scorch times. The addition of weak acids to the rubber compound results in retardation of the crosslinking mechanism. The common materials used for retardation are
• salicylic acid,
• benzoic acid, and
• phthalic anhydride.
These materials are crystalline solids with high melting points which result in their poor dispersing qualities. Their addition also results in reduction of the cure state and lowering of compound modulus.
N-Cyclohexylthiophthalimide (CTP) functions as an effective retarder of vulcanisation for accelerators in the sulphenamide classes. It produces scorch retardation without effect on compound modulus. It is not effective, however, in other classes of vulcanisation systems, notably those based on thiazoles, thiurams and dithiocarbamates.
Resins
Resins fall into one of three functional categories: (1) extending or processing resins, (2) tackifying resins, and (3) curing resins. Resins have been classified in an almost arbitrary manner into hydrocarbons, petroleum resins, and phenolic resins. Hydrocarbon resins tend to have high glass transition temperatures so that at processing temperatures they melt, thereby allowing improvement in compound viscosity mold flow. They will, however, harden at room temperature, thus maintaining compound hardness and modulus. Within the range of hydrocarbon resins, aromatic resins serve as reinforcing agents, aliphatic resins improve tack, and intermediate resins provide both characteristics. Coumarone-indene resin systems are examples of such systems. These resins provide:
1. Improved tensile strength as a result of stiffening at room temperature
2. Increased fatigue resistance as a result of improved dispersion of the
fillers and wetting of the filler surface
3. Retardation of cut growth by dissipation of stress at the crack tip (as a
result of a decrease in compound viscosity)
Petroleum resins are a by-product of oil refining. Like hydrocarbon resins, a range of grades are produced. Aliphatic resins which contain oligomers of isoprene tend to be used as tackifiers, whereas aromatic resins, which also contain high levels of dicyclopentadiene, tend to be classed more as reinforcing systems.
Phenolic resins are of two types, reactive and nonreactive. Nonreactive resins tend to be oligomers of alkyl-phenyl formaldehyde, where the paraal-kyl group ranges from to C4 to C9. Such resins tend to be used as tackifying resins. Reactive resins contain free methylol groups. In the presence of methylene donors such as hexamethylenetetramine, crosslink networks will be created, enabling the reactive resin to serve as a reinforcing resin and adhesion promoter.
COMPOUND PREPARATION
MIXING
The basic design of all commonly-used batch mixers consists of two rotors contra rotating in a close fitting chamber, with an arrangement to feed the raw materials into a machine, pressurizing them into the mixing chamber using a ram, and with a door in the bottom of the machine to discharge the mixed batch.
Fill factor - The amount of the total free volume available in an internal mixer occupied by the mixed compound at the end of the mixing cycle.
Friction ratio - The ratio between the differences in rotational speed of two rotors in a tangential internal mixer, or between the rolls of a two-roll mill.
In a modern tire or general products production facility, rubber compounds are prepared in internal mixers. Internal mixers consist of a chamber to which the compounding ingredients are added. In the chamber are two rotors that generate high shear forces, dispersing the fillers and other rawmaterials in the polymer. The generation of these shear forces results in the production of a uniform, quality compound.After a defined mixing period, thecompound is dropped onto a mill or extruder where mixing is completed and the stock sheeted out for ease of handling. Alternatively, the compound can be passed into a pelletizer. Depending on the complexity of the formulation, size of the internal mixer, and application for which the compound is intended, the mix cycle can
be divided into a sequence of stages. For an all-natural-rubber compound containing 50 phr carbon black, 3 phr of aromatic oil, an antioxidant system, and a semi-EV vulcanization system, a typical Banbury mix cycle will be as follows:
Stage 1 Add all natural rubber; add peptizer if required. Drop into a mill at 165°C.
Stage 2 Drop in carbon black, oils, antioxidants, zinc oxide, stearic acid, and miscellaneous pigments such as flame retardants at 160°C.
Stage 3 If required to reduce compound viscosity, pass the compound once again through the internal mixer for up to 90 seconds or 130°C.
Stage 4 Add the cure system to the compound and mix it up to a temperature not exceeding 115°C.
Computer monitoring of the internal mixer variables such as power consumption, temperature gradients through the mixing chamber, and mix times enables modern mixers to produce consistent high-quality compounds in large volumes. The mixed compound is then transported to either extruders for production of extruded profiles, calenders for sheeting, or injection molding.
Cross-section of a tangential rotor internal mixer
SPECFICATION OF BANBURRY USED(11D)
TYPE OF ROTOR - Tangential rotor, Mixers which are arranged such that the predominant mixing action is to shear the mixing compound against the sides of the mixer.
ROTOR SPEED – 40 RPM for final batch & 60 RPM for Master batch
CAPACITY – 235 Ltrs.
DISCHARGE – Drop Door
An idealised internal mixer power profile for a conventional, single-stage
mixing cycle
An idealised internal mixer ram position profile for a conventional, singlestage mixing cycle
AN INTRODUCTION TO SBR 1712
SBR 1712 is a cold polymerized, 23.5% styrene staining type SBR, extended with 37.5 parts of highly aromatic oil. Raw materials for this elastomer are carefully chosen to produce the best physical properties and processing characteristics at economical cost.
The aromatic oil used is an efficient plasticizer for high molecular weight SBR and results in superior physical and processing properties compared to other oil-extended rubbers.
End Use
Application possibilities for SBR 1712 include tire and mechnical goods compounds where color and staining are not decisive factors.
Features
· Dark brown colour
· High abrasion resistance
· Easy vulcanization and stable scorch properties
· Excellent processability compared to natural rubber)
Raw Polymer: Chemical Analysis
Property Unit Typical Specification
Bound Styrene
%
23.5
23.5 target
Volatile Matter
%
0.2
0.5 max
Ash
%
0.2
1.0 max
Organic Acid
%
5.0
-
Specific Gravity
0.95
-
Mooney Viscosity*
ML1
49
-
* ML 1+4 (100°C)
Test Compound Properties
Property Unit Typical Test Method
Tensile
kg/cm2
245
ASTM D412*
Elongation
%
600
ASTM D412*
300% Modulus
kg/cm2
105
ASTM D412*
ts1
min
5.2
ASTM D5289**
t’50
min
9.0
ASTM D5289**
t’90
min
15.0
ASTM D5289**
* Cure: 35 minutes at 145°C ** 160°C, 1°Arc
COURTESY FROM Astlett Rubber Inc.
V. EXPERIMENTAL DETAILS
MATERIALS USED
NATURAL RUBBER
RSS-4 grade was used throughout. It is visually inspected for its quality.
SBR 1712
SBR 1712 is a cold polymerized, 23.5% styrene staining type SBR, extended with 37.5 parts of highly aromatic oil.
Specification of SBR 1712 is
Oil content (%) - 25.8 – 28.8
Bound styrene (%) - 22.5 – 24.5
CRUMB RUBBER
Specification
Sieve – 60 mesh - 95 % min.
80 mesh - 80 % min.
Acetone extract - 8 – 18 %
Ash content - 12.5 % max.
CARBON BLACK (N330)
High Abrasion Furnace black was used. Its average particle size range is 26nm – 30 nm.
Specification
Iodine adsorption number - 77 – 87
DBP Absorption number - 97 – 107
Heat loss @ 1250c - 2 % max.
PRECIPITATED SILICA
Specification
Heat loss @ 1050c, 2hr. - 4 – 7 %
pH value - 5.8 – 6.8
Heat loss @ 9500c (coarse sample) - 3 – 6 %
AROMATIC OIL
Specification
Sp.Gravity @ 15.50c - 0.982 – 1.012
Aniline point - 30 – 54.40c
Say bolt viscosity @ 98.890c - 97 – 132 sec.
ZINC OXIDE
Specification
Zinc oxide content - 99 % min.
Ash content @ 9500c - 99 % min.
Heat loss @ 1050c - 0.4 % max.
TQ
Specification
Heat loss @ 700c, 2hr - 0.5 % max.
Sofening point - 85 – 950c
Ash content @ 7500c - 0.3 % max.
6 PPD
Specification
Melting point - 46 – 520c
Heat loss @ 700c, 2hr - 0.5 % max.
STEARIC ACID
Specification
Acid no. - 195 – 213
Iodine no. - 8 max
Solidification point - 50 – 630c
Ash content @ 7500c - 0.1 % max.
PCTP (peptizer)
Specification
Heat loss @ 1050c, 2hr - 1 % max.
Ash content - 0.48 % max.
MBS
Specification
Melting point - 75 – 900c
Moisture content - 0.5 % max.
Ash content - 0.5 % max.
SOLUBLE SULPHUR
Specification
Solubility in CS2 - 99 % min.
Acidity - 0.01 % max.
Sieve – 100 mesh - 0.5 % max.
325 mesh - 3 – 9 % max.
CTP (retarder)
Specification
Melting point - 89 – 94 0c
Heat loss @ 70 0c, 2hr - 0.4 % max.
Ash content @ 750 0c - 0.2 % max.
Toluene insoluble - 1 % max.
COMPOUNDING
8 compounds were master batch mixed and finalized for various dosages of accelerator levels in lab two-roll mill. Formulations are given below
INGREDIENT
R
A
B
C
D
E
F
G
RSS - 4
100.0
90.00
90.00
90.00
90.00
90.00
90.00
90.00
SBR 1712
-
13.75
13.75
13.75
13.75
13.75
13.75
13.75
Crumb
10.00
10.00
10.00
10.00
10.00
10.00
10.00
10.00
Silica
10.00
10.00
10.00
10.00
10.00
10.00
10.00
10.00
HAF (N330)
55.00
55.00
55.00
55.00
55.00
55.00
55.00
55.00
Aromatic oil
13.00
13.00
13.00
13.00
13.00
13.00
13.00
13.00
Zinc Oxide
5.00
5.00
5.00
5.00
5.00
5.00
5.00
5.00
TQ
0.70
0.70
0.70
0.70
0.70
0.70
0.70
0.70
6PPD
3.00
3.00
3.00
3.00
3.00
3.00
3.00
3.00
Stearic acid
3.00
3.00
3.00
3.00
3.00
3.00
3.00
3.00
Peptiser
0.18
0.18
0.18
0.18
0.18
0.18
0.18
0.18
MBS
0.50
0.55
0.67
0.84
1.00
0.60
0.65
0.70
Sulphur
2.25
2.25
2.25
2.25
2.25
2.25
2.25
2.25
Retarder
-
-
-
-
-
-
-
-
Based on physical & rheo studies, we selected three of the above compounds matched with regular compound & finalized in banburry.Selected compounds were E, F & G.
INGREDIENT
R1
R2
E1
E2
F1
F2
G1
G2
RSS - 4
100.00
100.00
90.00
90.00
90.00
90.00
90.00
90.00
SBR 1712
-
-
13.75
13.75
13.75
13.75
13.75
13.75
Crumb
10.00
10.00
10.00
10.00
10.00
10.00
10.00
10.00
Silica
10.00
10.00
10.00
10.00
10.00
10.00
10.00
10.00
HAF (N330)
55.00
55.00
55.00
55.00
55.00
55.00
55.00
55.00
Aromatic oil
13.00
13.00
13.00
13.00
13.00
13.00
13.00
13.00
Zinc Oxide
5.00
5.00
5.00
5.00
5.00
5.00
5.00
5.00
TQ
0.70
0.70
0.70
0.70
0.70
0.70
0.70
0.70
6PPD
3.00
3.00
3.00
3.00
3.00
3.00
3.00
3.00
Stearic acid
3.00
3.00
3.00
3.00
3.00
3.00
3.00
3.00
Peptiser
0.18
0.18
0.18
0.18
0.18
0.18
0.18
0.18
MBS
0.50
0.50
0.60
0.60
0.65
0.65
0.70
0.70
Sulphur
2.25
2.25
2.25
2.25
2.25
2.25
2.25
2.25
Retarder
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
Compounding has been carried out in two stages.
Stage 1
At master batch mixing, rubber & chemicals except sulphur & accelerator were intimately mixed. 60 rpm rotor speed was used & dump temperature of 1680c was maintained.
Load Rubber, Chemicals & black under ram, 6 kg/cm2 - 0 – 22 sec.
Add oil @ 1300c, 4.5 kg/cm2 - 60 – 62 sec.
Ram Float, 4.5 kg/cm2 - 90 – 92 sec.
Discharge @ 1680c - 120 sec.
Stage 2
In this stage, master batches are converted into final compounds. This is usually mixed around 1050c - 1070c. In final stage mixing, curatives like sulphur, accelerator, retarder etc. are added to the master batch.Discharge time are 95 – 98 sec.
PROCESSABILITY STUDIES
RHEOMETER STUDIES (AS PER ASTM D 2084)
The rheometer study was done in oscillating disc rheometer (ODR) with following specification.
Temperature °C
141
Range
100
Arc
10
The sample is subjected to an oscillating shearing action of constant amplitude. The torque required to oscillate the rotor, which is confined in the die cavity under pressure and controlled at a desired vulcanization temperature, is noted. As the vulcanization proceeds the torque required to shear the rubber increases and a curve of Torque versus curing time can be generated. From the data, Tc90, ML, MH, TS2 of compounds were found out.
From the plot of Torque Vs time, scorch time (TS2), time for 90% cure (Tc90) and cure rate can be calculated.
1. Cure rate
MH − ML / Tc90 − TS2
Cure rate is the rate at which stiffness (modulus) develops after the scorch point. During this period, compound changes from a soft plastic to a tough elastic material, owing to the introduction of cross-links.
2. Minimum torque (ML)
It is a measure of the viscosity of the stock at the test temperature. The rheometer minimum Torque is proportional to the Mooney viscosity when both the tests are conducted at same temperature.
3. Maximum torque (MH)
It is the measure of the stiffness or shear modulus of the test specimen at the test temperature. It is also an effective measure of the changes in tensile modulus and cross-link density.
4. Induction time (TS2)
It is the time corresponding to two units rise in torque about ML. It is a measure of the time available for mould flow. At lower temperatures Ts2 is a processability measure similar to Mooney scorch.
5. Optimum cure (Tc 90)
It is the time to achieve 90% of the maximum Torque.
Tc90 = [(MH-ML) X 90/100] + ML
MOULDING OF TEST SPECIMENS
The moulding of test specimens were done on a steam heated single day light press (INDEX PELL).
The moulding specifications for the various test samples were as follows.
Type of test
Temperature
0c
Time (min)
Pressure
(Kg/CM2)
press size
Physical
141
45
75
24"X24"
Abrasion Resistance
141
55
35
18"X18"
Heat build up
141
60
35
18"X18"
Resilience
141
60
75
24"X24"
PHYSICAL TESTING OF CURED SAMPLES
MEASURING OF TENSILE PROPERTIES (ASTM D 412-83)
Modulus of rubber compounds is very important because it is a measure of the shear stresses that will exist at the interface of two different compounds. It is also an indication of the deflection of the materials under load. Here the modulus is the stress required to stretch the test specimen from 0% strain to a specified strain (100% and 300% elongation).
Tensile strength is the tensile stress per unit cross sectional area required to stretch the piece to breaking point.
Elongation at break is the tensile strength in the test piece at the breaking point. In the tyre industry, these tests are carried out in the area of identification and quality control.
TEST PIECE SPECIFICATIONS:
Total length
115.00 mm
Width of ends
25 + 1.0 mm
Width of the narrow parallel portion
06 + 0.4 mm
Length of the narrow parallel portion
33 + 2.0 mm
The tensile properties of the samples were tested using dumb-bell test piece of above specification. All these tests were carried out at 23 ± 2°c. Dumb—bell specimens were punched from vulcanized sheets parallel to the grain direction using dumb-bell die [Die C]. Thickness of the narrow portion was measured by a bench thickness gauge. The samples were conditioned before testing for 24 hours. The samples were placed in the grips often Instron Universal Testing Machine [4301] with care, so that the specimen can distribute tension uniformly over the cross—section. The rate of separation of the grip was 500 mm/mm. The machine is modern sophisticated equipment. There were two grips 1" apart. They were fixed to the sample in the narrow region to locate the elongation. The areas corresponding to the thickness were fed into the microprocessor. This is connected to a printer. After testing the tensile strength, 300% modulus, Elongation at Break etc was printed out. The samples were aged for 48 hours at 100°c in an oven. Later they were conditioned and then tested for the tensile proper ties. The values were compared. Tensile strength and 300% modulus were expressed in pounds per square inch (lb/in2) and Elongation at break is given as percentage.
TEAR STRENGTH (ASTM D 624)
The tear resistance is defined as the force required per unit thickness to initiate tearing in a direction normal to the direction of stress. Tear resistance of tyre compounds reflect not only their ability to resist cutting from foreign objects, but also reflects the compounds ability to resist the propagation of a cut once it is formed. Tear strength was tested using Instron 4301 at a crosshead speed of 500mm/min.
HARDNESS (ASTM D 2240)
Hardness, as applied to rubber, may be defined as the resistance to indentation under conditions that do not puncture the rubber The hardness was tested standard using a durometer of Type-A. Shore -A hardness is a measure of the resistance to the penetration of an indenter of specified size and shape forced in to the test specimen. The hardness is measured in Shore A hardness units ranging from 0 to 100. This test method permits hardness measurements based on either initial indentation or indentation after a specified period of time, or both.
Equipment: - Shore A hardness tester with calibrated test spring or approved equipment.
Test Specimens
  1. 1. The minimum dimension of the specimen is 30mm (1.2inch) diameter and 6mm (0.25) thick. Tensile pads may be tested for hardness by stacking 3 pads of similar hardness.
  2. Surface of specimens must be flat and as free of surface irregularities as possible.
  3. Condition the specimen at 23°C ± 2°C (73.4 + 3.6°F) for a minimum of 16 hours before testing.
Procedure
  1. Test two test specimens for each sample
  2. Test the specimens at room temperature, 23°C + 2°C (73.4 ± 3.6°F)
  3. Place the specimen on a hard, flat surface.
  4. Position the durometer such that the indenter is 12mm (0.5inch) from the edge of the specimen and at least 6mm (0.25") between measuring points.
  5. Apply the pressure foot to the specimen rapidly without shock, with sufficient pressure to obtain firm contact between pressure foot and the specimen
  6. Read the indicator on the durometer three seconds after firm contact has been made.
  7. Take three measurements at different positions on each of the two specimens.
  8. Record the two median values and report the average of the two median values.
ABRASION RESISTANCE (ASTM D 1630)
This method is used to determine the abrasion resistance of cured rubber compound. Test should be carried out only 16 hrs after vulcanization.
Equipment: - DIN Abrader.
Sample preparation:
  1. Prepare rubber compounds in accordance with ASTM D
  2. Sheet out stock to obtain a thickness of 0.27"
  3. Make out 16mmx 6mm cylindrical type samples.
  4. Clearly identify each samples with silver lead or silver ink
  5. Carefully place samples in the pre-heated mold with identification up.
  6. Cure samples in accordance with instructions supplied.
  7. Start timer when pressure has been fully applied. It is important to ensure that air is not trapped in samples or mold while curing. Apply full pressure and release three times to allow trapped air to escape.
  8. Carefully remove samples from the mould using the brass screw driver,
  9. Place all samples at room temperature or cooler water for 10 minutes.
  10. Trim the edges of each specimen to remove any overflow.
  11. Condition samples at room temperature for 24 hours prior to testing. Weight the test piece prior to testing.
Procedure
  1. Fit the sample in the sample holder of the Din abrader machinery.
  2. "ON" the machinery and allow the sample to abrade.
  3. Stop the machinery, when the sample get 20 meter run.
  4. Remove the sample from the holder and remove the loose material then weigh it again (initial weight) accurately.
  5. Take the weight after 40 meter run.
  6. Remove the sample from the holder and remove the loose material then weigh it again (final weight) accurately.
  7. Find the mass loss(Initial weight – final weight)
  1. Find the specific gravity of the sample.
Specific gravity = Weight in air / Loss of weight in water
Abrasion loss = mass loss / Specific gravity
HEAT BUILD UP (ASTM D 623 - 78)
These tests are used to compare the rate of heat generation of different rubber vulcanisates when they are subjected to dynamic compressive strains .the Goodrich flexometer as per ASTM D 623-78was used for measuring the property. Tests were carried out with cylindrical samples of 1" height and 0.7" in diameter. The oven temperature was kept constant at 50°c. The samples were preconditioned to the oven temperature for 15". The samples were subjected to flexing for 18". The heat build up at the base of the sample was relayed to the micro voltmeter. The temperature rise (A T°c) at the end of 18" was taken as the heat build up.
RESILIENCE (ISO -R -1767)
Standard tests mostly measured the rebound of a pendulum from the rubber test piece.
Apparatus: - Lupke pendulum
Test specimen of 12.5mm thick was molded as per specification
In this machine the striker is a steel bar suspended so as to remain horizontal. It was released from a position, 100mm above its rest position, the height of the rebound was measured (usually indirectly from the horizontal return swing) and expressed as percentage of the 100mm fall, the result was measured as rebound resilience.
FLEX RESISTANCE
CRACK INITIATION (ASTM D430 – 95)
Equipment used : De Mattia Flexing Machine
Procedure
After adjustment of the apparatus and specimens is completed, start the machine and record the time. Continue the test until, by frequent inspection, the appearance of the first minute sign of cracking is detected. At this point, again record the time. The first cracking may be evidenced as either very fine hairline cracks or as slight pinholes. After this time, observe the specimens very closely until the test is discontinued, and record the final time when the cracks have developed sufficiently to permit grading the degree of the cracking in all specimens as described in Section 25. It is not desirable to run the specimens until actual complete rupture occurs when this can be avoided. When testing specimens of which the dynamic fatigue properties are approximately known, run the test for a known predetermined number of cycles and then make the grading comparison.
Evaluation of De Mattia Bend Flexing Specimens
Grade 0 No cracking has occurred.
Grade 1 Cracks at this stage appear as pin pricks to
the naked eye. Grade as 1 if the pin pricks are less than 10 in number and less than 0.5 mm in length.
Grade 2 Assess as Grade 2 if either of the following
applies:
(1) The pin pricks are in excess of 10 in num­ber, or
(2) The number of cracks is less than 10 but one or more cracks have developed beyond the pin prick stage, that is, they have percep­tible length without much depth, but their length is still less than 0.5 mm.
Grade 3 Assess as Grade 3 if one or more of the pin pricks have become obvious cracks with a length greater than 0.5 mm but not greater than 1.0 mm.
Grade 4 The length of the largest crack is greater than
1.0 mm but not greater than 1.5 mm (0.06 in.).
Grade 5 The length of the largest crack is greater than
1.5mm but not greater than 3.0mm (0.12 in.).
Grade 6 The length of the largest crack is greater than
3.0 mm but not greater than 5.0 mm (0.20 in.).
Grade 7 The length of the largest crack is greater than
5.0 mm but not greater than 8.0 mm (0.31 in.).
Grade 8 The length of the largest crack is greater than
8.0 mm but not greater than 12.0 mm (0.47 in.).
Grade 9 The length of the largest crack is greater than 12.0 mm but not greater than 15.0 mm (0.60 in.).
Grade 10 The length of the largest crack is greater than 15.00 mm. This indicates complete failure of the specimen.
CRACK GROWTH (ASTM D 813 – 95)
Equipment used : De Mattia Flexing Machine
Procedure
After adjustments of the apparatus and specimens have been completed, start the machine and record the time. At the end of any period of operation, calculate the number of flexing cycles by multiplying the observed time in minutes by the machine rate of 5 Hz (300 cpm). This shall also be checked by means of a counter on the machine. Since the rate of crack growth is important, take frequent readings early in the test. Stop the machine after 1000, 3000, and 5000 cycle periods, observe the specimens, and measure the length of the developed crack to the nearest 0.3 mm (0.01 in.) with an accurate scale. For improved precision, make the observation with the aid of a low-powered magnifying glass while the grips are separated 65.0 mm (2.56 in.). Continue the test with readings at regular intervals until a crack at least 12.5 mm (0.5 in.) in length is developed. Continuation to break may be desirable when testing aged specimens or when operating at elevated temperatures. Use of a metric scale for measuring crack growth is recommended. The initial cut produced by the puncturing spear is 2 6 0.1 mm (0.08 ± 0.002) in width.
VI. TESTS & RESULTS
RHEO PROPERTIES
Cc
ML
TS1
TS2
MH
TC15
TC25
TC50
TC90
Cure rate
R
5.34
6.55
8.53
29.39
10.03
11.62
15.10
26.78
1.31
A
5.69
7.82
10.20
28.35
11.78
13.45
17.20
29.57
1.17
B
5.46
7.13
9.93
29.86
11.80
13.22
16.28
26.65
1.46
C
5.75
8.65
11.18
30.85
12.83
14.03
16.45
24.60
1.87
D
6.04
8.47
10.85
32.94
12.68
13.77
15.87
23.18
2.18
E
5.75
7.50
9.95
29.98
11.68
13.30
16.75
28.05
1.34
F
6.10
7.13
9.62
30.61
11.35
12.77
15.93
26.47
1.45
G
5.81
7.68
10.12
31.25
11.85
13.18
16.13
26.20
1.58
CURE RATE
SCORCH TIME
STUDIES OF CURE PROPERTIES
Compound E was found matching with R based on cure rate. TS2 of E is higher than R. Compound F was having less TS2 than E. TC90 of B, F & G were also found matching with R. But TC15 of all experimental compounds were found higher values than R.
PHYSICAL TEST RESULT
COMPOUND
R
A
B
C
D
E
F
G
UNAGED
M100
274.1
245.2
260.8
278.5
303.4
274
297
298
M300
1316
1178
1252
1371
1469
1334
1436
1432
TS
3272
3109
3366
3285
3268
3153
3299
3198
EB%
572.9
554
569
529.5
510.3
526
527
515
HARDNESS
60
58
59
60
61
60
60
60
TEAR
614
460
495
483
460
465
488
534
AGED
M100
405.5
373.2
429.5
427.8
M300
1641
1574
1809
1793
TS
2167
2135
2288
2278
EB%
392.5
395
429
374
HARDNESS
65
62
66.5
65
TEAR
234.9
259
261
291
% RETENTION
M100
148
136
144
143
M300
125
118
126
125
TS
66
68
69
71
EB%
69
75
81
73
HARDNESS
108
103
111
108
TEAR
38
56
53
54




STUDIES OF PHYSICAL PROPERTIES
Based on unaged data, M100, M300 & Hardness of compound E was found matching with R. Tensile Strength & EB of E was found less than R. Tear strength of all experimental compounds were found less than that of R. % RETENTION in modulus and tensile strength of E is less than that of R. % RETENTION in tear strength of R is lesser than all experimental compounds. So we selected E, F & G that were found more matching with R for further studies.
RHEO PROPERTIES OF SELECTED COMPOUNDS (2 batches each)
Cc
ML
TS1
TS2
MH
TC15
TC25
TC50
TC90
Cure rate
R1
7.42
9.46
11.57
30.88
13.22
14.59
17.88
28.21
1.40
R2
7.44
9.55
11.63
31.78
13.27
14.80
17.90
28.28
1.46
E1
8.37
11.00
13.13
32.01
14.82
16.42
19.78
31.03
1.32
E2
8.40
11.06
13.14
32.03
14.84
16.43
19.81
31.02
1.32
F1
8.19
10.35
12.60
32.18
14.35
15.98
19.22
30.18
1.36
F2
7.96
10.18
12.63
31.49
14.57
16.37
19.87
31.52
1.24
G1
8.07
10.82
12.97
31.54
14.53
16.00
18.97
29.00
1.46
G2
8.12
10.85
13.01
31.59
14.50
15.96
18.92
28.97
1.47
CURE RATE
SCORCH TIME
STUDIES OF CURE PROPERTIES
Compounds G1 & G2 were having higher cure rate than the rest of the compounds. Compounds R1 & R2 were found having less TS2 than others. TC15 of R1 & R2 was also found less than others. But TC90 of G1 & G2 was found matching with R1 & R2. So based on rheological studies we concluded that G1 & G2 were found matching with R1 & R2 in all aspects.
PHYSICAL TEST RESULT
COMPOUND
R1
R2
E1
E2
F1
F2
G1
G2
UNAGED
M100
328.6
334.4
334.1
314.7
316.4
313.6
314.9
318.2
M300
1624
1656
1586
1509
1549
1480
1508
1558
TS
3286
3258
3126
3025
3161
3136
3300
3209
EB%
502.6
501.1
485.5
488.8
504.2
514.7
512.3
494.5
HARDNESS
61
61.5
61
60
60
60
60
60
TEAR
558
570
482.5
517.33
502.75
514.5
512
532
AGED
M100
546.1
555.6
538.1
540.4
526.7
530
541
534.3
M300
2214.5
2228
2168
2183
2131
2140
2214
2253
TS
2564
2579
2636
2644
2654
2672
2571
2512
EB%
349.1
347
362.6
380.4
371.7
375
381
372
HARDNESS
65
66
67
68
67
67
66
67
TEAR
264
266
234.2
248
253.6
254.1
264.4
278
% RETENTION
M100
139.8
139.8
137.9
141.7
139.9
140.8
141.7
140.4
M300
126.6
125.6
126.8
130.8
127.3
130.8
131.8
130.8
TS
72
74
82
86
81
83
72
73
EB%
57
56
67
72
65
63
66
68
HARDNESS
106.1
106.8
108.9
111.7
110.4
110.4
109
110.4
TEAR
53
54
52.5
53
50.6
51
49
48.6




STUDIES OF PHYSICAL PROPERTIES
Based on unaged data R2 and E1 were found matching. Tensile Strength & EB of E1 were found less than R2. Tear strength of all experimental compounds were found less than that of R1 & R2. % RETENTION in modulus and hardness of F1 & E1 were less than that of R1 & R2. % RETENTION in tear strength of R1 & R2 was lesser than all experimental compounds. So based on physical studies we concluded that E1 & F1 were found matching with R1 & R2 in all aspects.
TEST FOR ABRASION RESISTANCE
Abrasion Loss
(mm3)
R
122.70
E
126.065
F
127.00

TEST FOR RESILIENCE
RESILIENCE
R
42.2
E
42.5
F
42.8
TEST FOR HEAT BUILD UP
HEAT BUILD UP
(0C)
R
22
E
17
F
14
TESTS CRACK INITIATION & CRACK GROWTH
CRACK INITIATION
(no. of cycles)
CRACK GROWTH
(no. of cycles)
R
57,618
2,52,419
E
51,727
2,53,437
F
53,209
3,36,115
STUDIES OF ABRASION RESISTANCE, RESILIENCE, HEAT BUILDUP & FLEX LIFE
Based on test data it was seen that the compound R has better abrasion resistance & better in crack initiation. But F is superior in heat build up & crack growth; it has less heat built up than others.
VII. CONCLUSION
Our project work is on replacement of NR with SBR 1712 in a heavy duty truck tyre tread cap compound. The aim of the project was cost reduction with optimized properties. Experiment results shown the following positive remarks
· % retention of M100 & M300 in E & F are comparable with R
· % retention of HARDNESS in E & F are also comparable with R
· Heat Build Up of E & F are less than that of R
· Crack Growth resistance of E & F are higher than that of R
· EB % of F is comparable with R
The negative remarks are
· Abrasion resistance of E & F is less than that of R
· Crack initiation resistance of E & F are lower than that of R
· Tensile strength of E & F are lower than that of R
· Tear strength of E & F are lower than R
VIII. RECOMMENDATIONS
  • Abrasion resistance is prime requirement of a tread cap compound. We used SBR 1712 which is capable of high filler loading, that capability is not used here. We recommend that increase the black loading & thereby improvement in abrasion resistance.
  • Tear resistance of E & F can be improved by a slight increase in silica addition.
  • Tensile strength can also be improved by increasing the filler loading.
  • The cost was reduced to some extend by the use of SBR 1712; the increase in black loading can also reduce the cost with improvement in abrasion resistance & tensile strength.
  • Tyre should be build & tested for pulley wheel test, plunger test etc…
IX. REFERENCE
1. THE VANDERBILT RUBBER HANDBOOK- Edited by Robert F. Ohme, 1990
2. RUBBER TECHNOLOGY AND MANUFACTURE- Edited by C.M. Blow, C. Hepburn, Butterworths London, 1982
3. RUBBER PRODUCTS MANUFACTURING TECHNOLOGY- Edited by Anil K. Bhowmick, Malcolm M. Hall, Henry A. Benarey, Marcel Dekker, Inc. 1984
4. RUBBER TECHNOLOGY HANDBOOK, Werner Hofmann
5. RUBBER TECHNOLOGIST’S HANDBOOK, Edited by Sadhan K. De and Jim R. White, RAPRA, 2001
6. SCIENCE & TECHNOLOGY OF RUBBER- Edited by James E Mark, Burak Erman, Frederick R. Elrich, ELSEVIER ACADEMIC PRESS, 2005
7. ASTM INTERNATIONAL – volume 09.01
WEBSITES VISITED

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