The lithium Polymer battery

The lithium Polymer battery

Structure of Lithium Polymer battery

The cell consists of positive electrode plate, negative electrode plate and separator.
The positive and negative electrode plates are housed in Al foil pouch.

 Lithium Polymer Battery

The lithium-polymer differentiates itself from conventional battery systems in the type of electrolyte used. The original design, dating back to the 1970s, uses a dry solid polymer electrolyte. This electrolyte resembles a plastic-like film that does not conduct electricity but allows ions exchange (electrically charged atoms or groups of atoms). The polymer electrolyte replaces the traditional porous separator, which is soaked with electrolyte.

The dry polymer design offers simplifications with respect to fabrication, ruggedness, safety and thin-profile geometry. With a cell thickness measuring as little as one millimeter (0.039 inches), equipment designers are left to their own imagination in terms of form, shape and size.

Unfortunately, the dry lithium-polymer suffers from poor conductivity. The internal resistance is too high and cannot deliver the current bursts needed to power modern communication devices and spin up the hard drives of mobile computing equipment. Heating the cell to 60°C (140°F) and higher increases the conductivity, a requirement that is unsuitable for portable applications.

To compromise, some gelled electrolyte has been added. The commercial cells use a separator/ electrolyte membrane prepared from the same traditional porous polyethylene or polypropylene separator filled with a polymer, which gels upon filling with the liquid electrolyte. Thus the commercial lithium-ion polymer cells are very similar in chemistry and materials to their liquid electrolyte counter parts.

Lithium-ion-polymer has not caught on as quickly as some analysts had expected. Its superiority to other systems and low manufacturing costs has not been realized. No improvements in capacity gains are achieved - in fact, the capacity is slightly less than that of the standard lithium-ion battery. Lithium-ion-polymer finds its market niche in wafer-thin geometries, such as batteries for credit cards and other such applications. 



 Component of Lithium Polymer battery

Advantages

• Very low profile - batteries resembling the profile of a credit card are feasible.
  
• Flexible form factor - manufacturers are not bound by standard cell formats. With high volume, any reasonable size can be produced economically.
  
• Lightweight - gelled electrolytes enable simplified packaging by eliminating the metal shell.
  
• Improved safety - more resistant to overcharge; less chance for electrolyte leakage.

Limitations

Lower energy density and decreased cycle count compared to lithium-ion.

Expensive to manufacture.

No standard sizes. Most cells are produced for high volume consumer markets.

Higher cost-to-energy ratio than lithium-ion 

A Lithium-Ion Polymer Battery used to power a mobile phone

The lithium-ion battery

Pioneer work with the lithium battery began in 1912 under G.N. Lewis but it was not until the early 1970s when the first non-rechargeable lithium batteries became commercially available. lithium is the lightest of all metals, has the greatest electrochemical potential and provides the largest energy density for weight.

Attempts to develop rechargeable lithium batteries failed due to safety problems. Because of the inherent instability of lithium metal, especially during charging, research shifted to a non-metallic lithium battery using lithium ions. Although slightly lower in energy density than lithium metal, lithium-ion is safe, provided certain precautions are met when charging and discharging. In 1991, the Sony Corporation commercialized the first lithium-ion battery. Other manufacturers followed suit.

The energy density of lithium-ion is typically twice that of the standard nickel-cadmium. There is potential for higher energy densities. The load characteristics are reasonably good and behave similarly to nickel-cadmium in terms of discharge. The high cell voltage of 3.6 volts allows battery pack designs with only one cell. Most of today's mobile phones run on a single cell. A nickel-based pack would require three 1.2-volt cells connected in series.

Lithium-ion is a low maintenance battery, an advantage that most other chemistries cannot claim. There is no memory and no scheduled cycling is required to prolong the battery's life. In addition, the self-discharge is less than half compared to nickel-cadmium, making lithium-ion well suited for modern fuel gauge applications. lithium-ion cells cause little harm when disposed.

Despite its overall advantages, lithium-ion has its drawbacks. It is fragile and requires a protection circuit to maintain safe operation. Built into each pack, the protection circuit limits the peak voltage of each cell during charge and prevents the cell voltage from dropping too low on discharge. In addition, the cell temperature is monitored to prevent temperature extremes. The maximum charge and discharge current on most packs are is limited to between 1C and 2C. With these precautions in place, the possibility of metallic lithium plating occurring due to overcharge is virtually eliminated.

Aging is a concern with most lithium-ion batteries and many manufacturers remain silent about this issue. Some capacity deterioration is noticeable after one year, whether the battery is in use or not. The battery frequently fails after two or three years. It should be noted that other chemistries also have age-related degenerative effects. This is especially true for nickel-metal-hydride if exposed to high ambient temperatures. At the same time, lithium-ion packs are known to have served for five years in some applications.

Manufacturers are constantly improving lithium-ion. New and enhanced chemical combinations are introduced every six months or so. With such rapid progress, it is difficult to assess how well the revised battery will age.

Storage in a cool place slows the aging process of lithium-ion (and other chemistries). Manufacturers recommend storage temperatures of 15°C (59°F). In addition, the battery should be partially charged during storage. The manufacturer recommends a 40% charge.

The most economical lithium-ion battery in terms of cost-to-energy ratio is the cylindrical 18650 (18 is the diameter and 650 the length in mm). This cell is used for mobile computing and other applications that do not demand ultra-thin geometry. If a slim pack is required, the prismatic lithium-ion cell is the best choice. These cells come at a higher cost in terms of stored energy.

Advantages

• High energy density - potential for yet higher capacities.
  
• Does not need prolonged priming when new. One regular charge is all that's needed.
  
• Relatively low self-discharge - self-discharge is less than half that of nickel-based batteries.
  
• Low Maintenance - no periodic discharge is needed; there is no memory.
• Specialty cells can provide very high current to applications such as power tools.

Limitations

• Requires protection circuit to maintain voltage and current within safe limits.
  
• Subject to aging, even if not in use - storage in a cool place at 40% charge reduces the aging effect.
  
• Transportation restrictions - shipment of larger quantities may be subject to regulatory control. This restriction does not apply to personal carry-on batteries. (See last section)
  
• Expensive to manufacture - about 40 percent higher in cost than nickel-cadmium.
  
• Not fully mature - metals and chemicals are changing on a continuing basis.

Here are a few MANDATORY guidelines for charging/using LiPos (Lithium Polymer Batteries).




1. Use only a charger approved for lithium batteries. The charger may be designed for Li-Ion or Li-Poly. Both batteries are charged in exactly the same. Some older cell phone chargers may charge the batteries .1 volt to low (4.1 vs 4.2), but that will not harm the battery. However, inexpensive lithium chargers are widely available and the use of cellphone chargers is highly discouraged.
2. Make certain that the correct cell count is set on your charger. Watch the charger very closely for the first few minutes to ensure that the correct cell count continues to be displayed. If you don't know how to do that, get a charger that you do know how or don't charge the batteries.
3. Use the Taps. Before you charge a new Lithium pack, check the voltage of each cell individually. Then do this after every tenth cycle there after. This is absolutely critical in that an unbalanced pack can explode while charging even if the correct cell count is chosen. If the cells are not within 0.1 volts of each other then charge each cell individually to 4.2 volts so that they are all equal. If after every discharge the pack is unbalanced you have a faulty cell and that pack must be replaced.
Taps are provided on most new lithium packs. Taps give you the ability to check individual cell voltages and charge one cell at a time. Make sure and get the appropriate connector to go into your taps. Don't try to stick you volt meter probes in the taps to measure voltage. They could slip and short your cells. Don't try to charge more than one cell at a time from the taps. Unless you have an isolated ground charging system, you'll short your batteries out. Refer to your individual cell maker for tap pin-outs.
4. NEVER charge the batteries unattended. This is the number one reason for houses and cars being burned to a crisp by lithium fires.
5. Use a safe surface to charge your batteries on so that if they burst into flame no damage will occur. Vented fire safes, pyrex dishes with sand in the bottom, fireplaces, plant pots, are all good options.
6. DO NOT CHARGE AT MORE THAN 1C unless specifically authorized by the pack vendor. I have personally had a fire in my home because of violating this rule. Todays highest discharge batteries can supposedly be safely charged at greater than 1C, however so far in all cases doing so shortens the life of the pack. Better to buy 3 packs than to try to charge 1 pack 3 times quickly. This may change in the future but as of Winter 2005 1C is still the recommended charge rate.
7. DO NOT puncture the cell, ever. If a cell balloons quickly place it in a fire safe place, especially if you were charging it when it ballooned. After you have let the cell sit in the fire safe place for at least 2 hours. Discharge the cell/pack slowly. This can be done by wiring a flashlight bulb of appropriate voltage (higher is voltage is ok, lower voltage is no) up to your batteries connector type and attaching the bulb to the battery. Wait until the light is completely off, then throw the battery away.
8. If you crash with your lithium cells they may be damaged such that they are shorted inside. The cells may look just fine. If you crash in ANY way carefully remove the battery pack from the aircraft and watch it carefully for at least the next 20 min. Several fires have been caused by damaged cells being thrown in the car and then the cells catch fire later and destroys the car completely.
9. Charge your batteries in a open ventilated area. If a battery does rupture or explode hazardous fumes and material will spew from the battery.
10. Keep a bucket of sand nearby when you are flying or charging batteries. This is a cost effective way to extinguish fires. This is very cheap and absolutly necessary.
11. It can happen to you, do not think to yourself that “it won't happen to me” as soon as you do that it you'll be trying to rescue your kids from your burning house or car. I'm very serious about this.


Now that we have covered that important topic let's move on to lighter matters:


2. Lithium What?
Lithium Polymer batteries are used in many electronic devices. Cell Phone, Laptops, PDA's, Hearing Aids just to name a few. Most, if not all, lithium polymer batteries are not designed for RC use, we use them in different applications than they were designed for. They are similar to Lithium Ion batteries in that they each have a nominal voltage of 3.6 volts, but dissimilar in that they do not have a hard metal casing but rather a flexible material encloses the chemicals inside. The "normal" lithium polymer batteries are thin rectangle shapes with two tabs on the top one positive one negative. The reason we use Lithium cells is that they are significantly lighter than comparable NiCad or NiMH batteries, which makes our planes fly longer and better.


3. Voltage and Cell Count:
LiPolys act differently than NiCad or NiMH batteries do when charging and discharging. Lithium batteries are fully charged when each cell has a voltage of 4.2 volts. They are fully discharged when each cell has a voltage of 3.0 volts. It is important not to exceed both the high voltage of 4.2 volts and the low voltage of 3.0 volts. Exceeding these limits can harm the battery.
The way to ensure that you do not go below 3.0 volts while flying is to set the low voltage cutoff (LVC) of your electronic speed control (ESC). It important to use a programmable ESC since the correct voltage cutoff is critical to the life of your batteries. Use the ESC's programming mode to set the LVC to 3.0 volts per cell with a hard cutoff, or 3.3 volts per cell with a soft cutoff. If your ESC does not have hard or soft cutoff, use 3.0 volts per cell. You will know when flying that it is time to land when you experience a sudden drop in power caused by the LVC.
If your ESC has an automatic lithium mode. Use it, it will correctly sense the number of cells and set the auto cutoff appropriately.
If you have previously been flying with NiCad or NiMH batteries, switching over to lithium polymer will result in a different number of cells being used. If you had 6 to 7 round cells then 2 lithium polymer cells will correctly duplicate the voltage of those cells. If you had 10-11 cells then 3 lithium polymer cells would be right for you. There are a lot of 8 cell flyer's out there that are stuck between 2 and 3 cells. In my experience the best option is to determine how many watts you were using before and duplicate that with your LiPos, Motor, and Prop. For example. If you were running 8 cells (9.6volts) at 10 amps on a speed 400 airplane, then you have 9.6 x10, 96 watts. So if you went with 2 lithium polymer cells (7.2 volts nominal) then you'd need to change your prop such that you used 13 amps. If you went to 3 LiPoly's (10.8 volts nominal) then you'd need to reduce the amperage to 8.9 amps. These estimates are approximate, and some experimentation is required for best results but conserving Watts is a good way to start.


4.10C from 3S4P? Naming conventions explained.
How fast a battery can discharge is it's maximum current capacity. Current is generally rated in C's for the battery. C is how long it takes to discharge the battery in fractions of an hour. For instance 1 C discharges the battery in 1/1 hours or 1 hour. 2 C discharges the battery in ½ or half an hour. All RC batteries are rated in milli Amp hours. If a battery is rated at 2000 mAh and you discharge it at 2000mA (or 2 amps, 1 amp = 1000mA) it will be completely discharged in one hour. The C rating of the battery is thus based on its capacity. A 2000mAh cell discharged a 2 amps is being discharged at 1C (2000mA x 1), a 2000mAh cell discharged at 6 amps is being discharged at 3C( 2000mA x 3).
All batteries have limitations on how fast they can discharge. Because of this many LiPoly batteries are put in parallel to increase the current capacity of the battery pack. When 2 batteries are wired positive to positive and negative to negative they become like one battery with double the capacity. If you have 2 2000mAh cells and you wire them in parallel then the result is the same as 1 4000mAh cell. This 4000mAh cell has the same C rating as the original 2000mAh cells did. Thus if the 2000mAh cells could discharge at a maximum of 5C, or 10 amps then the new 4000mAh cell can also discharge at 5C or (4000mA x 5) 20 amps. This method of battery pack building allows us to use LiPoly batteries at higher currents than single cells could produce.
The naming convention that allows you to decipher how many cells are in parallel and how many are in series is the XSXP method. The number in front of the S represents the number of series cells in the pack so 3S means it's a 3 cell pack. The number in front of P means the number of cells in parallel. So a 3S4P pack of 2100mAh cells has a total of 12 cells inside. It will have the voltage of any other 3S pack since the number of cells in series determines the voltage. It will have the current handling of 4 times the maximum C rating of the 12 individual cells. So say our 3S4P pack had a maximum discharge of 6C. That means that it has a nominal voltage of 10.8 volts (3x3.6) and a maximum discharge rate of 50.4 amps (2100mAh x 6Cx4P ).


5. Which battery should you buy?
With so many choices out there it is difficult to decipher what is marketing hype, what is brand
loyalty, and what is outright lies. Battery manufacturers are constantly trying to one up one another. While capitalism can drive prices down, it also can give cause to false claims about products.
One great way to find out what the best battery is, is to look at graphs of the batteries performance. Looking at how low the voltage of the cell drops at various amperages will give you a metric to compare that battery to similar size/weight batteries.
If graphs aren't your thing then simply look at what other people are using in successful setups that are similar to your application. If a lot of people are reporting long flight times and lots of power from airplane X, with power system Y, and battery Z and you do the same, then if your setup is similar the same battery will probably work well for you.
It pays to learn something about Watts, Volts, and Amps. Understanding these concepts is beyond the scope of this document, but can serve you well in not only figuring out what battery is best but also in your electric aircraft hobby.
I'm not convinced that a 30C battery is really any better than a 10 or 20C battery. Sure a higher C rating means it can discharge faster. But at the same time a battery discharged at 20C continuously will be empty in 3 minutes. Do you really only want to use the battery for 3 minutes? I love having burst power in helicopters and boats, but in almost all other applications actually running a battery at or above 20C is useless to me. I prefer to run batteries at 8-10 C and have a little headroom if I need it.
A final note on choosing a battery. Don't cheap out. Confirm that your batteries are capable of running that the amperage level you plan to use them at. Running a cell at a higher C rating than the battery can handle can not only damage your batteries, but it can also damage your speed control. Castle Creations has an excellent article on how using a weak battery can destroy a perfectly good speed control of any brand. Better to buy a bit better battery than you need than to destroy your electronics.


6. Dealing with temperature.
Lithium batteries like heat, but not too much. In the winter time, try to keep your batteries from the cold as much as possible. Leave them in the car while your flying, or keep them in your cargo pants... etc. At the same time don't let them heat up too much. Try to keep your batteries from reaching 160F after use. This will prolong the life of the cells. A good way to measure temperature is a handheld IR meter, they can be found for around $50.00 at most hobby shops.









Lithium ion polymer rechargeable battery similar to the Lithium-ion but with a solid polymer as electrolyte. Some gelled conductive material is added to promote conductivity. It utilizes the latest technology to become available for consumer use in products such as portable computers, PDA, cellular phones, blue tooth, portable DVD and military electronics etc. Lithium-ion polymer batteries have high voltage per cell, and excellent energy on both a weight and volume basis. Additionally, they can be made in very thin and large footprint configurations. Lithium-ion polymer batteries use liquid Lithium-ion electrochemistry in a matrix of conductive polymers that eliminate free electrolyte within the cell. For operating effectively over a broad range of temperatures and conditions, Lithium-ion polymer batteries contain no metallic Lithium anodes.

Lithium polymer: A rechargeable battery using solid polymer as electrolyte. Most Lithium polymer batteries require heat to promote conductivity.

What is the difference between Lithium-Ion and Lithium-ion polymer?
Lithium-ion technology uses a liquid or gel type electrolyte that requires substantial secondary packaging to safely contain flammable active ingredients. This additional packaging not only increases the weight and cost, but it also limits the size flexibility. There is no free liquid electrolyte in Lithium-ion polymer batteries, which leads to stable and less vulnerable to problems caused by overcharge, damage or abuse.

• Gaston Narada Lithium-ion polymer batteries demonstrate the characteristics of high energy density, low impedance, long cycle life, flexible shape and excellent safety and reliability. Our Lithium-ion polymer batteries are ideal for lightweight notebook computers, PDA, cellular phones, blue tooth devices, portable DVD, handheld computer, MP3, smart card, watch, earpiece, emergency lighting, scooter and military electronics and other portable equipments. Because of the many benefits that Lithium-ion polymer has over other battery chemistries, this technology may be used in additional markets in the future.
• Advantages:
  Thinness and form factor flexibility
  Higher energy on both a weight and volume basis
  Higher voltage than NiCd or NiMH --- fewer cells are required to achieve application voltage levels
  Ability to create battery with large "footprint" for thin, high capacity applications
  Improved safety-more resistant to overcharge; less change for electrolyte leakage
• Applications to design:
  Has a high level of technology with new and exciting functionality,
  Needs to be light weight, portable and thin,
  Has either a large or very small footprint,
  And needs the maximum amount of energy available to achieve its purpose.

IMPROVEMENT OF BREAKER OFFCENTERING

IMPROVEMENT OF BREAKER

OFF CENTERING

By

RENJITH. P.R

 

          

STUDY OF OFFCENTREING OF BREAKERS

BREAKERS:

            These are short plies with low EPI (ends per inch) cut at an angle and are positioned centrally between tire casing and tread to strengthen carcass against impact.  They also provide cushioning effect and increase the modulus of tread area.  They are made by rubberizing dipped fabric on calendar and then cutting them by bias cutting machine. Breakers are used mainly in biased tires where as in radial tires they are replaced by steel belts.

            During rotation the carcass transmits all the forces on to the ground through the tread at contact patch.  The tread being a rubber mass undergoes considerable deformation while transmitting these forces as well as engaging on the road deformities.  This deformation of tread cause excessive stress strain concentration at tread to carcass interface and consequent premature failures.  In order to dilute this concentration, a graded structure is opted for biased carcass in which the outer most layer in contact with tread are low modulus suspended plies, or breakers with high gauge of rubber insulation (Low EP (840/2) followed by intermediate layer and real pressure bearing inner plies.

            The EPI (ends per inch), i.e. number of cords per unit area is much lower than carcass plies. This helps for rubber compound penetration between the cards which help in achieving better bond between tread and carcass as well as it provides impact resistance.

           

In general the function of breakers can be summarized as

i)                   It provides stability to the tread and helps in distributing forces uniformly throughout the tire structure.

ii)                Breakers hold the tread firmly to carcass and also help in providing impact resistance to tread region.

OFFCENTERING

Off centering is actually the displacement of breaker from the central position in a band or a tire building drum. This defect can occur mainly during two stages of tyre construction; they are band building and tire building.

Off centering of breakers in tires can lead to;

1) Tread shoulder separation

2) Reduction in tyre life due to early failures.

To study about off centering of breakers mainly we deal with 2 departments

1)                 Band building department

2)                 Tire building department

Band building

In band building department the components of carcass, i.e. the inner liner plies and ply squeegees are assembled to form bands.  Usually for a truck tire mainly 3 bands are employed.

First band – it consists of the inner liner, plies and ply squeegees.  First the inner liner is applied to drum followed by 3 plies with 3 ply squeegees in between.

Second band – It consists of 3 plies with 3 ply squeegees in between

Third band – it consists of 2 plies, 2 ply squeegees and 2 breakers.

            Band is usually constructed in a band building machine.  Band building machine consists of a metallic drum driven by a shaft, containing a canvas that is held by a tension bar beneath it. During construction of bands the plies are placed in opposite direction. This is same in case of breakers also. The placement of breakers in 3^rd band should be in such a way that distance of breaker from both ends of ply should be zero or less than 5. When the difference is more than 5 which is the tolerable value the band is said to be offcentred. 

Off centering of breaker in band building machine can occur mainly because of

1.         Machine related problems like

a)                 Canvas shift

b)                 Tension bar alignment

c)                 Light setting vibration

2.         Material related problems like

a)                 Variation in width of incoming material

3.         Worker related problems like

a)                 Error in adjustment of light setting

b)                 Stretching of plies and breaker during band building

Tire Building

            In tire building process all the components of a tire are assembled to make a raw tire called green tire. The building machine consists of a metallic drum, which is mounted on a drive shaft. The ends of the drum are flanged to suit the bead configuration of the tire to be built. In all cases the overall diameter of the drum exceeds the nominal tire diameter. This difference is known as drum crown height and varies from tire type & size. Radial ply tire require complex and costlier machinery having inflatable textile reinforced diaphragms, overlying a skeletal metal drum shell, to shape the carcass plies and other components up to the diameter for belt fitting.

 

                                      In tire building machine there is located a bead carrier ring on either side of the drum. This ring is concentric with the drum and is capable of moving inwardly to provide an interference contact with the drum shoulders and there by transfer and consolidate the tire beads against the partly build casing structure. In the carrier ring frame, there are inbuilt spring steel fingers, which forms a circle turn the plies down the contact shoulder of the drum immediately before the beads make contact.  Attach to the building machine base plate and to the rear of the drum are two pneumatically operated component consolidating assemblies each comprising two pairs of shaped disc rollers. The rollers of one assembly are located on either side of the drum and pivot around the tire bead area for the purpose of turning and interlocking various components around the bead. The pair of rollers forming the second assembly traverses laterally, out word from the central line of the drum to consolidate the sidewall elements of to the carcass.  In case of ply building system servicer is placed at the rear of the machine. More common is to build bands of plies before building tire. Bands with 3 to for plies are assembled together on band building machine. No of plies in a band depends upon the service requirements. No. of bands in a tire also depends upon the service requirements. The diameter of the band is kept lower than that of the drum.

                

                                            Drum is collapsed, the two beads are placed on the carrier rings and the drum is expanded. A rubber base adhesive is applied to the drum shoulders. First band is then slipped over the drum under rotation with the help of the stick to apply pressure at the edges. The bead carrier ring assemblies then automatically turn down the ply edges around the drum and consolidate the beads.   This is followed by the other bands and the second bead, in between the ply edges are turned around the beads. Then the chafer strips are applied and down with the ply edges. After this tread is applied and consolidated followed by applying of side walls on both sides. Final consolidation is done by traversing rollers. On completion drum is collapsed and green tire is removed from the building machine.

                             In case of radial ply construction (which differs from biased ply construction in the angle of orientation of chord in the plies) different approaches are followed. Earlier building and shaping operations were carried out on different machines. But in modern industries both the operations are carried out in the same machine.

           

Offcentring of breaker in tire building can occur mainly because of 

1.         Error in light setting

        

             

REASONS FOR OFFCENTERING IN BAND BUILDING

Machine Related  problems.

1.         Canvas Shift

            In a band building machine, bands are constructed over an in extensible canvas that holds the tension bar and the drum. Depending upon the nature of bands to constructed different canvas is used. The canvas lies holding the building drum and the tension bar. During band construction first the canvas is inserted over the drum by keeping the tension bar in closed position. After insertion on the drum, the tension bar is lowered; this keeps the canvas held tightly over machine. Now plies are rolled over canvas and then made into a band.  For the proper construction of a band it is necessary that the canvas should have the same perimeter in both the side (machine side and operator side).  In case there is variation in perimeter in both side (i.e., difference between perimeter in both sides is greater than 10) then canvas shifting will occur.  I.e. canvas during construction of band will move from one side to another over the building drum.  (That is canvas moves from area having lesser perimeter to be having more perimeters).  In such cases when the builder places the breaker on to the drum, over the plies this shifting movement causes breaker to be placed in such way that distance of breaker from ply ends unequal.

            When the canvas shifts whole ply which is placed over the canvas also shifts then builder places. The breaker onto the ply according to the light setting which is incorrect then.  The result will be huge difference in distance of breaker from both ply ends.  The region of canvas with higher perimeter will have distance of breaker from ply ends greater than the other region of canvas with lower perimeter.  The ultimate result will be off centering of breaker.

b)        Tension bar alignment

Every band building machine consists of a iron bar with a rubberized coating over it placed below the building drum.  The main function of tension bar is to hold the canvas in position. The tension bar is usually placed as a cant lever.  Now the alignment of tension bar is critical for production of an okay band.  The correctly aligned tension bar will have same distance from building drum with canvas in open position that is difference in distance between tension bar and building drum should be zero.  If the difference exceeds 10mm then it will put more pressure on 10 the canvas inducing canvas shifting. This will lead to off centering.

c)         Light setting vibration

Every band building machine consists of a light setting (which consists two to three laser beams)

Three laser beams are placed with respect to the edge of band building drum

1.                  First beam for correct placement of plies.

2.                  Second and third for correct placement of I and II breakers worker places the breakers and plies to form a band based on this light setting if there is vibration in this light setting because of some kind of machine problems then it will induce the worker to make an off band or offcentred band. Since vibration causes variation in distance set on drum.

2.         Material related problems

            a)        Variation in Incoming material

                        Fort he purpose of making an ok band, it is necessary that the plies and breakers should have some specified dimensions.  When plies and breakers are concerned width forms main area of concern.  It is based on this width that light setting in done in band building machine.  For example is apply is having a width of 845mm, first breaker – 415mm and 2^nd breaker 210 mm the light setting is adjusted in such a way that distance of first breaker from ply ends is 317.5mm and that of 2^nd breaker is 215mm.  But this speficaition work only if width of all these components comes in the tolerable range (ie ±5m).  Whenever the width of breakers and plies exceeds more than 5mm, it becomes difficult to centre the breaker correctly on the band building drum.

[Even if builder changes to set the breaker correctly on onside because of incoming material width variation the distance of breaker may very badly on other side, leading to off centering]

            The breakers and plies are given a tolerance of ±5mm when the width exceeds 5mm or goes down below 5mm it may lead to off centering.  In coming material variation occur mainly due to problems in bias cutting.

3.         Worker related problems

            i)  Error in light setting adjustment

                        Each band building machine consists of a light setting comprising of three laser beams over the drum. Three laser beams are provided over the drum with respect to drum edges.  First beam for placement of ply, 2^nd and 3^rd for placement of breakers. For the purpose of building a correct band it is necessary that this light setting adjustment is done correctly by the builder.  When the builder creates some error in this light setting the result will be variation from specification, which will ultimately lead to an offcentred band. 

2)        Ply stretch during band building

            Since plies and breakers are rubberized fabric they are likely to be deformed when they are excursively stretched when plies or breakers are stretched it will lead to reduction in width of both plies and breakers.  When width reduces below a tolerable limit say 5mm, it becomes impossible to centre the breaker on the band building drum. The ultimate result will be correct reference distance on. One side of the band and incorrect distance on other side.  (That is huge difference in distance between breakers from ply ends)

REASONS FOR OFFCENTERING IN TIRE BUILDING

            In tyre building the only chance of error likely to occur is in light setting.

After bands are made they are inserted on to the tire building drum for making green tire. During insertion of band care should be taken to see that the breaker comes exactly in the centre of the drum i.e., distance of band edges from either side of building drum should be equal. In order to center the band perfectly, light setting is provided at both the ends of the building drum. Light setting consists of a laser beam fitted on to the top of a steel rod placed parallel to axis of building drum.  For the perfect centering of band on the tire building drum the edge of band inserted should coincide with the laser beam. As the distance of band edge from light setting increases off centering also increases. 

ACTIVITIES

BAND BUILDING

Studies for off centering were carried out on 4 band building machines building the 3^rd band.

1)           Machine related problems

a)           Canvas shift

i)             All the machines were examined for any kind of technical defects which could affect off centering.

ii)          Perimeter of canvas was taken in both machine side and operator’s side. [Dimensions are measured after removing canvas from the band building drum]

iii)        Shifting of canvas for 3 revelations of drum are noted.  (3 revelations forward and backward)

b)           Tension bar alignment

Distance of tension bar form the band building drum is noted with canvas and without canvas.  3 check points are made i.e., perimeter of canvas in operators side, middle and machine side).  The distance between drum and tension bar is noted in closed and open position without canvas also.

c)      Light setting vibration

i)      Light setting is checked continuously after every 3 bands made.

ii)     Material related problems

-                     Breakers and plies from bias cutting departments are continuously checked for width variation.

                  For every breaker and ply both upper and lower part are examined for width variation.  Cut to cut variation is noted.

3.      Worker Related issues

a)     Light setting variation

Error in Light setting is a worker related issue so every worker is examined for any kind of variation in light setting.  So each worker is examined for correct light setting every machine is surveyed for minimum 3 workers.

b)     Stretching of plies and breaker closing band building

- The process of band building requires some kind of force to be applied on to the plies and breakers for the purpose of making a band.  Plies from conveyer are pulled on to the building drum to form the band.  The breakers are also applied in the same way. To see whether stretching has any affect on off centering first points are marked on the ply before it is made into a band and its width is noted.  The dimensions are again checked after the ply is made into a band at the same point marked. The same procedure is carried out for breakers also.

Tire building

            Light setting validation is done in tyre building section studies conducted include:

            Centering of breaker on tyre building drum.

 

RESULTS

Band building

The following conclusions were made from the study

.

1) Incoming material width variation

a) Variation in width of incoming ply material were found to be 7mm more than the specified value.

b) Variation in width of incoming 1^st breaker was found to be 10 mm more than the specified value. Rare cases recorded shows deviation of 8mm lower than that of specified value.

c) Width of 2^nd breaker was found to vary badly when compared to plies and first breaker. The deviation of actual values from the specified values was found to be about 10 mm.

The above mentioned variations were sufficient to cause breaker off centering.

2) Machine related problems

a) Survey was conducted on four band building machines.

Out of four machines two machines showed higher canvas shift of about 12 to 15mm which is very high.

This data pinpoints the role of canvas shift in off centering.

3) Worker related problems

a) Ply stretch during band building

Stretching of plies during band building could cause only around 2mm to 3mm reduction in width which is negligible.

Both first and second breaker width was found to reduce by 2mm to3 mm during band formation

Studies conducted indicate that ply stretching has no significant role in off centering of breakers in band building.

b) Error in light setting

Light setting variation for first and second breakers was checked for 6 operators.

For first breaker, out of 6 operators, 2 to 3 operators were found to vary reference distance by more than 5mm from spec value.

For second breaker 1to 2 operators were found to vary reference distance by about 5mm more than specified value.

The above data clearly indicates the error in light setting which shows that it has a significant role in breaker off centering.

Tire building

Light setting validation was done in tire building section.

Data collected from tire building did not show any kind of variation

From the above data it could be concluded that only source of off centering issue in tire building is off centered bands

 

CONCLUSIONS

The following conclusions were made from the studies conducted

BAND BUILDING

Ø  Incoming material variation seemed to be the main material related problem that caused off centering of breakers

Ø  Out of all machine related problems canvas shift proved to be the main reason for breaker off centering.

Ø  Other machine related issues like light setting vibration and tension bar alignment did not have any effect on off centering.

Ø  Main worker related problem that caused offcentering of breakers was the error in light setting

Ø  Other worker related issues like stretching of plies during band building did not have any significant effect on off centering.

TYRE BUILDING

Ø  Data collected from tire building did not show any kind of variation

Ø  From the above data it could be concluded that only source of off centering issue in tire building is off centered bands

Ø So the best possible option for improvement of breaker off centering is to reduce the above mentioned problems.