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Rubber & Plastics News ● December 10, 2007 15www.rubbernews.com
CUSTOM MIXING• Largest Custom Mixer on West Coast
• All Solid Polymers • Black and Non-blacks• Slabs, Strips, Preforms, Calendered Rubber & Fabrics
• Your Formula or Ours
Valley ProcessingDiv. of Mitchell Rubber Prod.491 Wilson Way • City of Industry, CA 91744(626) 961-0311 • FAX (626) 968-2026Contact: Sy Hasan or Kevin Sarcone-mail: [email protected]
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By Uday Karmarkar and Edward Terrill
Akron Rubber Development Laboratory Inc.
P.K. Mohamed and Arup K. ChandraApollo Tyres, Limda Village
Eight tires were received at AkronRubber Development Laboratory. Eachof the tires is subjected to complete re-verse engineering reconstruction usingthe techniques of dynamic characteriza-tion, modulus profiling and chemical de-construction. All tests are data analyzedto understand the design philosophywith respect to the dynamic propertiesas well as the raw material composition.
Physical propertiesTensile testingDumbbell specimens were die-cut us-
ing an ASTM D 638 Type V dumbbelldie and tested per ASTM D 412. Sam-ples were tested at 2 inches per minute(50.08 cm/minute).
Testing was done in a controlled envi-ronmental space maintained at 50-per-cent relative humidity and at 70°F. Testoutput includes elongation to break,stress at break, modulus at 25 percent,
Technical
See Winter, page 16Table I. The seven tires used to con-duct a winter tire survey.
Table II. Data on three types of compounds formulated designated by letters A, Band C differentiating the level of antioxidants used 0.5, 1.25 and 2 phr. All slabs arecompression molded to a uniform thickness of 40 thousandths of an inch.
Fig.1 Two tires used in the winter tire survey as identified in Table I.
Fig 2. The remaining six tires used inthe winter tire survey as per Table I.
Fig 3. The dimensions of the different layers used in the tires.
Executive summaryThis paper presents the development of winter tire tread formulations using
a variety of material testing techniques. Winter tire tread compounds have to perform adequately under conditions of
ice and snow. Tread compound formulation strategies encompass several fac-tors, such as microscopic analysis, dynamic characteristics, filler interactions,traction and friction testing, geometric conditions of tread design.
We have focused on obtaining the tread formulation that will provide ade-quate traction under ice and snow conditions using laboratory bench testingtechniques developed in-house.
We present the development of the ARDL bench top traction tester to per-form testing to duplicate traction at cold temperatures to exact laboratory con-ditions.
Additional testing on the dynamic characteristics of the material provides in-sight into the tread rubber formulations. The laboratory testing provides thebasis for production of winter tires and testing under ice and snow conditionsby Apollo Tyres, India.
Testing tires for ice and snow performance is done using maneuverabilitytesting and braking performance in the field.
Winter tires: Tread material test innovations
50 percent, 100 percent, 200 percent,300 percent and 400-percent elongation.
Pulsed proton Nuclear MagneticResonance
The ARDL NMR instrument is aBruker Minispec mq 20 MHz PulsedProton Unit. This instrument has beenused as a chemical structure probe tool.
The solid state NMR pulsed proton in-
strument is used for measuring thetransversal relaxation decay curves toprobe the changes in the chemical struc-ture. This in principle can be used toidentify the changes in the structureswith aging as well as with changes inthe formulations of rubber products.
ARDL Benchtop Traction TestThe traction tester is used to compare
the traction properties of the materialsthat are used in the tread formulations.The inputs are 65 mph speed axial loadthat equates to the load based on footprint analysis.
DiscussionAs stated in the introduction, com-
plete analysis of the winter tires used inthe study provides us with a good under-standing of the critical components, di-mensions and formulations.
The study also provides a new trac-See Winter, page 16
TECHNICAL NOTEBOOKEdited by Harold Herzlichh
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16 Rubber & Plastics News ● December 10, 2007 www.rubbernews.com
tion test that helps with the under-standing of the traction capabilities ofthe compounds under dynamic condi-tions. Tire component testing and re-search can be a very effective tool in de-veloping tire durability tests as well astire properties to help develop a wintertire with superior properties.
Winter Tire treads compounds have toperform adequately under conditions ofice and snow. Tire traction as well as thetire wear is important to a winter tiretread formulation. Understanding oftire traction and the transfer of forces onlow coefficient of friction material aswell as regular concrete is important fortread formulations.
Tread compound formulation strate-
gies encompass several factors, such asmicroscopic analysis, dynamic charac-teristics, filler interactions, traction andfriction testing and geometric conditionsof tread design.
This task was divided into three steps:1) winter tire survey, 2) traction andwear and 3) tire prototyping. The firststep was conducted on eight tires asshown in Table I.
Dimensional analysis, dynamic test-ing and chemical deconstruction wereperformed to understand the existingranges of material and sizes used in thewinter tires.
All tests are data analyzed to under-stand the design philosophy with re-spect to the dynamic properties as wellas the raw material composition.
Figs. 1 and 2 indicate the differentlayers in the tires. The different tireshave varying thicknesses as well as con-struction characteristics depending on
Technical
WinterContinued from page 15
Fig 5. The comparative data between the tread formulations based on the wintersurvey and the two formulations developed. The data indicates an identical trans-fer of torque under dynamic conditions.
Fig 6. The data from NMR and traction transferred on the traction and wear tester.Generally the higher the crosslink density, the lower the traction.
Fig 7. The simultaneous measurement of the wear rates indicates that the modelcompound aged at 70°C has a reversal in trend in comparison to the traction rates.This data demonstrates the capability of the test to differentiate the sample chem-istry.
The authorsUday Prakash Karmarkar is a business development manager for Akron
Rubber Development Laboratory Inc. Karmarkar has been active in new testdevelopment and aging research in tires. He holds two U.S. patents and haspublished several scientific articles and presentations on the subject of tires,automotive, aerospace, medical products and predictive materials research. E-mail him at [email protected].
Ed Terrill worked more than 20 years with Goodyear in the Polyester, TirePhysics and Compound Science departments and DuPont n the Textile FibersPioneering Research Laboratory. He joined ARDL in March of 2003. He hasthree patents, two trade secrets and six publications in polymer science. He canbe reached at [email protected].
the usage and application. Five of theseven tires have cap ply overlays.
Detailed cross sectional microscopy isessential to accurate measurement ofthe thicknesses. Tire A and C indicate asubtread and tread interface that is onlyvisible with color shaded optical mi-croscopy images assisted with freshcross section visual observations.
Tire A has a subtread that in the cen-terline has a physical connection to theroad surface.
The second step was to conduct a trackable traction and wear test on a labora-tory materials scale. We focused on ob-taining the tread formulation that willprovide adequate traction under ice andsnow conditions using laboratory benchtesting techniques developed in house.Figs. 4 and 5 shows the development ofthe ARDL Traction and Wear Tester.
A survey of the existing techniquessuch as Tabor abrasion ASTM 3389,DIN 53576, ISO 4649, ASTM 5963,PICO Index abrasion ASTM D2228,
NBS abrasion test 1630, Slip and cam-ber wear testing, flat track testing indi-cated a need for a simultaneous meas-urement of traction and wear on alaboratory scale.
The ARDL test equipment consists ofa mechanism to apply a known axialforce to the “donut” specimen against aknown frictional surface at a known ro-tational speed. Footprint analysis of atypical tire used in service is conductedas a basis for the load.
Polished basalt tiles are used to simu-late very slick icy conditions. All the testparameters are fed to a lab view pro-gram that allows accurate and high scanrate monitoring of the torsional force,axial load as well as temperature of thespecimen.
The sprocket and the sample, the fric-tion surface and the loading block, andthe collection pan for wear particles areall accurately measured for weight beforeand after the 15-second test is complete.
Fig. 4. The “ARDL Benchtop Traction Tester” and sample dimensions. See Winter, page 20
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20 Rubber & Plastics News ● December 10, 2007 www.rubbernews.com
Studies were conducted on compound-ed rubber samples aged in tire reactorsunder various conditions of thermo ox-idative aging.
Table II shows the comparison ofpulsed proton NMR data and traction.Figs. 6 and 7 indicate the unusual phe-nomenon where the high temperatureaged sample and a trend reversal be-tween traction and wear compared tocrosslink density.
The blue shaded symbols indicatesamples aged in lower oxygen concen-
trations that the lower change in crosslinking for these specimens also ismatched by a lower drop in tractionforces. The greater the thermo oxidativeaging, the greater the loss of traction.The wear rate, however, depends on thetemperature of aging. This might possi-bly be from the formation of certain sul-fur linkages compared with others.
The third step of novel tire tread com-pound prototyping was started using thetraction and wear tester. Fig. 5 indi-cates comparison of the traction ratesfor two tires compared to two experi-mental tread formulations. A variety oftechniques will be utilized for compar-ing the new formulations to existingtread formulations.
ConclusionA new test method is under develop-
ment at ARDL to measure tractionforces transferred.
Testing of winter tire tread materialformulations can be performed on mold-ed model compounds as well as on sam-ples from tires.
New winter tires are being developedwith material testing
The ARDL Benchtop Traction testercan be used to measure information ontraction and wear and to study wearparticle morphology.
Detailed cross section analysis, dy-namic testing and winter traction test-ing are used to develop a benchmarkedwinter tire formulation
The next phase of this study is tomanufacture tires with this tread for-mulation and conduct on the road iceand snow testing for correlations
References1. Shoop, S., Kestler, K. and Haehnel, R., “ FiniteElement Modelling of Tires on Snow, “ Tire Scienceand Technology. TSTCA, Vol. 34, No. 1, January-March 2006, pp.2-372. Lacombe, James, “Tire Model for simulations ofvehicle motion on high and low friction road sur-faces., US ARMY REL, Hannover, N.H.3. Nakajima, Yukio, “Analytical model of longitudinaltire traction in snow,” Journal of Terramechanics,Vol. 40, Issue 1, January 2003. pp. 63-82.4. Hofstetter, K.; Grohs, Ch.; Eberhardsteiner, J.;Mang, H.A.; “Sliding behaviour of simplified tiretread patterns investigated by means of FEM Com-puters and Structures,” Vol. 84, Issue 17-18, June2006. pp. 1151-1163
Technical
WinterContinued from page 16
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