In an earlier post on tyre machinery industry, I expressed that it’s the rapid pace of change faced by tyre producers that is driving the tyre machinery manufacturers to invest more in R&D, evolve rapidly in technology and offer customized automated solutions for maximum output to their customers.
For tyre manufacturers the consequence of increasing the automation to eliminate human errors will be, that stringent testing on 100 per cent of tyre production will be a binding procedure in future. When Dr.S.N.Chakravarty sent me this informative piece on Tyre Testing, it felt apt to be shared with you for a beginning on this topic and to exchange notes.
Here is Part 1 of his three-part series.
As in all fields of technology, methods of measuring performance is essential for development. Major areas of tyre testing system are:
- Laboratory testing of compounds, cords, bead etc.
- Indoor (Resilometer) endurance testing
- Outdoor or field testing.
After designing and manufacturing, a tyre is then subject to rigorous indoor (endurance) and field test evaluation. (Laboratory testing will be dealt later).
Performance evaluation of a tyre is carried out by mainly
- Plunger strength
- Wheel endurance or Resilometer test and
- Wheel high speed performance tests.
Plunger strength indicates carcass load bearing capability and safety factor whereas endurance and high speed wheel tests give idea about tyre performance.
Endurance test is carried out by freely rotating the tyre on a smooth surface metal wheel or drum at a fixed speed; increasing load step-wise to certain kilometer limit or till failure.
In high speed test, tyre is rotated on drum or wheel at a step wise increasing speed at constant load, holding for a fixed period at every speed step, till failure occurs or to a minimum speed limit.
Resilometers are now being electronically programmed to act as simulators. Further, observations or resilometer testing is being done more efficiently by means of closed circuit TV. Stroboscopic system and high speed cameras capable of producing high resolution pictures are also used for proper observation.
Different specifications for evaluation of tyres are available in various National and Government as well as International standards. Widely known specification is from Department of Transport (DOT), USA.
Another important test that is carried out with tyre is the measurement of heat development by determining the temperature developed in the tyre during resilometer test. A new technique to assist in the indoor evaluation of tyre is a system which utilises infrared to obtain thermal history of the tyre during test.
Besides these, Hydro Burst test (to determine bursting pressure), Rolling resistance of tyre and Static and Dynamic balancing tests are often carried out with the tyre.
For development as well as quality check Holographic Interferometry and Shearographic studies and X-ray analysis for casing flaw is carried out with tyres.
For Passenger tyre uniformity test is an important criteria.
The tyre industry is continuously developing indoor tyre tests to duplicate, at an accelerated pace, the type of performance encountered in service.
Testing machines are becoming increasingly important in the tyre industry. Government and international test institute and certifying bodies use testing machines for R&D and to develop standards. Car manufacturers and the aftermarket require not only technical specifications, but also data from conducted tests according to specified procedures.
Why test ?
Another important factor in tyre development is the ecological aspect. Lower rolling resistance means lower fuel consumption and consequently a reduction in emissions. It is also important to reduce noise pollution. Research vehicles and tests have shown that tyre noise generation is the main source of vehicle noise.
The laboratory test machines can also measure important parameters such as durability (endurance) at high speed; tyre characteristics / force and moment; rolling resistance; noise levels; tyre stiffness; foot-printing, including dynamic; and wheel fatigue.
Economic efficiency of equipment is as important for testing machines as it is in manufacturing.
The endurance tester has been designed to determine the service life of tyres. The test procedures of this machine are in compliance with DOT, SAE and ECE & BIS standards.
Image: Poling Group
The machine can be configured in several ways; one or two car tyre stations, one or two truck tyre stations, or a combination of both. A number of options can be included, for example slip, camber, deflection, temperature / circumference / rolling resistance measurement, pressure regulation or foot-printing.
The traffic noise is an increasingly important issue for tyre and highway industries, with demand from many quarters for quieter products. A necessary property of modern tyres is a low noise level in all situations. As mentioned earlier, tyre noise generation is a major source of vehicle noise.
Two main methods are currently used for direct measurement of tyre / road noise on trafficked roads – statistical pass-by and close-proximity. Of these, the statistical pass-by (SPB) method is used most frequently because of it’s simplicity and the representative-ness of the results. Essentially the method consists of measurement of individual pass-by noise levels of a large number of vehicle traveling through a fixed test area. This is the internationally accepted ISO method and has been adopted by many countries.
The frame and drive train of the noise tester are situated in a pit and the bearing on the road-wheel only develops low running noise, thereby creating the optimum conditions for measuring tyre generated noise.
A trailer has been constructed that allows acoustical dynamic or static tyre testing under the wide variation of parameters – slip angle, camber, torque, speed, wheel load, tyre size, rim size and rim material – on real road surfaces. Generally the acoustical near field of the tested wheel is measure using four microphones.
Force and Moment Tester
The force and moment tester meets all requirements for tyre characteristics, such as dynamic altering of the slip angle, camber angle adjustment and hub drive. All moments and forces are measured, making this equipment suitable for testing tyres as well as for use in their development.
Image: MTS Systems Corporation
A five component measuring hub records all moments and forces in detail. The industrial PC in the control cabinet stores the data. This sophisticated measuring system is ideal for the development of high performance tyres.
Universal Tyre Testing Machine
The universal tyre testing machine can test passenger and truck tyres for four distinct operational characteristic: load deflection, bead unseating, plunger energy, and footprint. Additional tests include tread contact area ration (image scanning by CCD camera) and the dynamic behavior of the tread pattern under load.
Machines to investigate the rolling resistance of various tyres are also part of the range, as are multi-station machines used to test and investigate solid rubber roller compounds.
Standard tyre uniformity is very different from high-speed uniformity, so different machines are needed to do the testing.
The tyre and automobile industries have been successfully using test machines for measuring tyre uniformity for many years. Tests performed with these machines, which include measurements of force and geometry, have now become a standard in quality assurance as well as development, and are completely accepted in these fields. They are therefore often called standard tyre uniformity (STU) tests.
(….to be contd in Part 2)
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