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What can be expected from good liners

By Purushothama Kini *

Purushothama KiniLiners were commodity and now the industry has started understanding that liner can also contribute in process and quality improvement. To have perfection in tyres and better uniformity, we also need to concentrate on components quality. Liner are play a major role in this. First we need to understand the different kinds of liners available in market.

Different kinds of liners
  • Multi -multi liners
  • Multi -Mono liners
  • Flexi mono liners
  • Treated liners
  • Laminated liners
Material used for liners
  • Polypropylene
  • Polyester
  • Polyethylene
  • Cotton
Yarns used in liners
  • Multi filament – Multiple filaments twisted together.
  • Mono filament – Extruded single stiff yarns.
  • Flexi mono filament (profiled, flexible mono filament yarns)

What to expect from a good liner?

Green tack retention – This is major property of liners that can contribute to the improvement of quality and productivity. We have seen that cotton liners eat most of the green tack whereas Polyethylene provides maximum green tack retention. Hence it is always advisable to use PE liners.

Wrinkling – There should not be any permanent wrinkle in liners. It is very important that liner should provide good resistance to wrinkle and should not keep those wrinkle in its memory. This is important to avoid the waste or scrap. Multi -multi and Flexi mono liners can provide wrinkle less service or in other words it won’t keep the wrinkle in its memory. Whereas multi-mono liners give permanent wrinkle. This is not good for components in longer run. Hence it is advisable to use flexi mono liners.

Moisture absorption – Majority of liners available in market absorb 3% to 10% of moisture, irrespective of fact that it has multi- multi or multi mono construction. Whereas Flexi-mono liners from PE wont absorb any moistures. This is very important property because whatever moisture absorbed by liners will be partially or fully passed on to the components. This moisture absorption on standard fabric or steel fabric can create problem in process as well as in service. It could be the one of the reason for rusting of steel fabrics. Hence this makes PE based Flexi -mono liners technically more suitable for the liner application to store steel, fabric or compound sheets.

Good release: – Good release is needed to achieve the uniformity, productivity and good quality tires. PE liners provides best release compare to all other material like PP, PES and cotton. Multi-filament and mono filament construction may not resist the rubber penetration between two yarns placed next to each other, due its round /oval shape. Hence these liners may not provide excellent release in long run. Whereas Flexi mono yarn can provide better release. Hence the combination of PE and flexi mono liners are recommended one for liners to have excellent release.

Impacts on liner release property

Silicon treatment: It has become a new trend in market to use surface treated liners for achieving better release. Generally, it is treated with silicon to achieve the good release property. This silicon is not good for tire components, as eventually this will get transferred on the components. Hence silicon treated liners are not safe liners. We should try to avoid silicon treated liners, in view of safety of tires.
Base material used for liner manufacturing: Liners are produced using Poly propylene, Poly cotton, Cotton, Polyester and polyethylene. Out of these Polyethylene has highest tack retention as well as release property. Good release and good tack retention is the basic property of the PE.
Yarn design: Usage of multifilament’s in yarn gives scope for rubber penetration within yarn, which will eventually lead to rubber sticking. Whereas monofilament yarns avoid rubber penetration within yarn (raw material used is also important here). But mono filament available in market cannot be used in warp direction due to its stiff nature. Hence Flexi mono yarns are better and also resist rubber penetration too.
Weaving pattern: Open weaving or gaps within warp & weft will provide scope for rubber penetration, which will create the problem of rubber sticking eventually. It has to be close weaving to avoid rubber penetration.
Surface: Slight embossed surface will be better for release of rubber. Higher embossing structure may create problem. This embossed surface also can help in air bleeding in case of inner liner.
Combination of yarns: When multi and mono used in same liners, as both yarns behaves in different way, this may lead to gaps within the multi-filaments which can lead to rubber penetration in due course of time. Also when both side muti filament yarns used, it will also lead to penetration of rubber. Flexi mono yarns are better here.
Release is also relative term: When soft, high tack, thin rubber compound needs to be released it is better to go for thicker stiff liners. In same way when stiff thick product (fabric, steel) needs to be released thinner liners could give similar release. At least either of product or liner should be stiff enough to give release.
Durability: – Specialty liners are not cheaper but they prove to be economical if it has high durability. Repeat ordering involves lot of man-hours and cost to disposal those scrap liners. Hence we need to look for the liner that provides durability of at least 10 plus years. This will help in very stable process. Liners with such durability available in market, if not we need to insist for such liners.

Staining: We need to choose a liner that stains less as we want to use it for longer period of time. Having said this, we need to use poly-cotton lead liners to protect the liners from external dust and dirt. These lead liners are also helpful to provide good stretch and tension during liner usage in process. Normally multi-multi and multi-mono are more prone for the staining as it could help in rubber penetrations. By choosing right liners we can avoid cleaning of liners which is additional non-productive job.

Tear resistance: Liner should have good tear resistance, which is normally provided by weaving pattern used by the liner manufacturer.

Edge integrity: It is very important to have good edge integrity. It is not important what kind of system used by liner manufacturer and name it differently, it is very important to have long durability in edge integrity too. This is directly related to durability of the liners. When multi and mono used in same liners, as both yarns behaves in different way, could lead to failure of the edge integrity too. Flexi mono liners could show better edge integrity due to design of yarn.

Colours: We can use different color of liners for making system proofing or fool proof of the system. But we need to be careful as majority of color liners available in mkt is not providing permanent colors on liners. It is dyed over white liners and will be eventually transferred to the components. Hence these liners are not safer to use. It is better to use those liners from the manufacturer, who use the pigments in polymeric stage itself. Also can add colored header at both ends to make process bit robust to provide the guidance for calender operator when to start booking. This will reduce the wrinkle formation and waste generation.

We need to be very careful in liner selection as it impacts on the process performance. We have seen that lot of latest most modern TBM’s that can provide high productivity and better quality green tires, are not able to reach desired goal due to wrong selection of the liners. Wrong selection of liners will never provide the perfection in components that we need to build perfect green tires. It is always advisable to use original liners than copied versions as copied version may not have all the specialties for which original one designed.
In conclusion, we need to select liners that provides combination of higher green tack retention, does not absorb moisture, provides high durability, does not keep wrinkle in memory, safe for tire component without any silicon treatments and that provides color without dyeing.
* Purushothama Kini is Director Sales & Business Development – Asia Pacific, Middle east, Africa – at Bernauer Group of companies, Germany

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