DESC:FIELD OF THE INVENTION
The present invention relates to a lab skid testing setup. More importantly the present invention relates to a lab skid testing setup and method thereof for determining the skid characteristics of tyre tread compound using a lab skid testing device with design parameters for the model pavement at lab level.

BACKGROUND OF THE INVENTION
Various devices and methods have been developed to measure skid performance of pavement surface including portable testers like California Skid Tester (CST), the British Pendulum Tester (BPT) and other industrial level testers. Some of these perform the skid test for tyre on pavement, road surface based on laboratory data and some do it through onsite test.

US2008250843A1 discloses a method for calculating a friction-slippage curve for a tire. The method for calculating a mu-slippage curve for a tyre based on laboratory data derived from characteristic values of a used compound, of the road surface and a vehicle without producing a complete tyre, and a method for calculating a mu-slippage curve for a tyre include the steps: calculating a friction force between rubber compound and a rough surface based on a friction coefficient for different slippage values and lateral positions of the tyre wherein the friction coefficient is calculated depending on a sliding velocity between the rough surface and a tread block and on a temperature of the tyre.

The article entitled “Laboratory test to evaluate the effect of contaminants on road skid resistance” talks about a laboratory test method is developed to reproduce the deposit of contaminant particles on the road surface and measure the friction coefficient on dry and wet-contaminated surfaces. It simulates in this way the variation of skid resistance of the road surface due to contaminants during a dry period–precipitation event and the washoff effect of the rain. Protocols are described with respect to the contaminant collection on site and the subsequent preparation in the laboratory, the spreading of contaminant particles on the road specimen and their compaction to simulate the effect of the traffic, the wetting of the test surface to simulate precipitations, and the friction measurement [MT Do, V Cerezo, H Zahouani; Sage Publication Volume 228 Issue 11, April 14, 2014].

“Skid resistance and friction tester” originally developed at the Transport and Research Laboratory, U.K., consists of an adjustable pendulum arm, and a spring loaded rubber slider (see accessories) mounted on the end of the arm. It is used for the measurement of surface friction properties, the apparatus is suitable for both side and laboratory applications and for Polished Stone Value (PSV) using curved specimens from accelerated polishing test with the Accelerated Polishing machine conforming to EN 1097-8. It can also be used for testing Paving Stones (EN 1341, EN 1342) and Paving Blocks (EN 1338).

Accordingly, there exists a need for a lab skid testing setup and a method for determining the tyre skid characteristics of tire tread compound using a lab skid testing device with design parameters for the model pavement at lab level.

SUMMARY OF THE INVENTION
One or more of the problems of the conventional prior art may be overcome by various embodiments of the present invention.

It is the primary object of the present invention to provide a lab skid testing setup and method thereof for determining the skid characteristics of tyre tread compound using a lab skid testing device with design parameters for the model pavement at lab level.

It is another object of the present invention to provide facility to simulate the test conditions using different medium such as water, oil, ice, snow, alcohol, molten asphalt, bitumen and the like.

It is another object of the present invention to provide a sample preparation method to conduct the tests at lab level.
It is another object of the present invention to provide a ready tool to determine the skid characteristics of rubber compounds.

It is another object of the present invention to create an industrially applicable skid test setup and method.

It is another object of the present invention to reduce testing time and cost for testing.

It is another object of the present invention, wherein the pavement sample is pre-prepared based on the friction values of typical road surfaces or can be tailored based on the test requirements.

It is another object of the present invention to provide a method of reporting the skid resistance of the tyre tread compound, comprising:
preparation of tread rubber compound;
molding rubber compound into prespecified size;
adhering molded sample onto the sample holder;
Preparation of pavement;
Preparation of test surface;
Testing the coefficient of friction of the test surface using the standard samples;
Measuring the skid resistance of tread rubber compound on the test surface developed; and
determining the skid resistance of the tyre tread compound.

It is another aspect of the present invention to provide a lab level skid testing setup for tyre tread compound, comprising of steps:
molding of the test sample to an aluminum sample holder by molding and bonding to a predefined dimension to provide a rubber slider block;
conditioning the adhered rubber slider block at a temperature of 23 ± 2°C and 50 ± 5% relative humidity for around 24 hours;
preparation of test pavement [201] comprising preparation of test surface [202] and positioning in the tray;
determining [203] the co-efficient of friction of the test surface using the standard samples;
measuring the skid resistance of the tyre tread compound on the test surface [204] and simulation [301] of road conditions;
optionally filling [302] the tray with fill medium and leveled using the adjustable legs and reference spirit level fixture [4];
measuring [303] the thickness of the medium layer over the pavement surface using measuring scale fixture [5]; and
measuring [304] the temperature of the medium and surrounding atmosphere; of the test pavement using temperature measuring unit [6],
wherein the pavement is a concrete base comprises of cement, M-sand, coarse aggregates (blue metal) and water in the ratio of 1: 1.5: 2: 5 respectively,
wherein the tyre rubber skid testing setup comprises of pendulum tester, a tray [1] and the test pavement [2] and the elastomeric composition of the tyre rubber is tested for skid resistance on the pavement, and
wherein the test method comprises of placing skid test device over the tray [1], slider holder of the skid test device is then released for the rubber slider block to slide over the designed pavement / platform.

It is another aspect of the present invention to provide a lab level skid testing setup for tyre tread compound wherein the tray [1] is made of stainless steel, and comprises of control rod [3], spirit level fixture [4], a measuring scale fixture [5] and a temperature measurement unit[6] for positioning of the pavements [2] developed for measuring skid resistance.

It is another aspect of the present invention to provide a lab level skid testing setup for tyre tread compound wherein the tyre tread compound is an elastomeric composition and is molded and bonded with aluminum sample holder wherein the bonding agent is acrylic based, epoxy based, polyurethane based, silicone based, cyanoacrylate based or latex based.
It is another aspect of the present invention to provide a lab level skid testing setup for tyre tread compound wherein the tyre rubber for testing is NR based, SBR based and blends of SBR / NR and SBR / BR rubber.

It is another aspect of the present invention to provide a lab level skid testing setup for tyre tread compound wherein the elastomers further comprise of SSBR or ESBR or ENR or NBR or PU based or its blends.

It is another aspect of the present invention to provide a lab level skid testing setup for tyre tread compound wherein elastomeric composition in claim 3 is molded to the dimension of 75mm x 25mm x 6mm (Length x Width x Thickness).

It is another aspect of the present invention to provide a lab level skid testing setup for tyre tread compound wherein the elastomeric composition consists of reinforcing fillers like carbon black, silica or other inorganic fillers or nanofillers or its mixtures.

It is another aspect of the present invention to provide a lab level skid testing setup for tyre tread compound wherein the filling medium can be water or oil or ice or snow.

It is another aspect of the present invention to provide a lab level skid testing setup for tyre tread compound wherein the pavement comprises a concrete base comprises of cement, M-sand, coarse aggregates (blue metal) and water in the ratio of 1: 1.5: 2: 5 respectively.

It is another aspect of the present invention to provide a lab level skid testing setup for tyre tread compound wherein the pavement surface comprises of asphalt based, mud based and sand based.

It is another aspect of the present invention to provide a lab level skid testing setup for tyre tread compound wherein the wet skid resistance value on elastomeric composition tested on test pavement for NR based compound ranges from 86-89, for SBR based compound ranges from 95-97, for SBR / BR blend compound ranges from 89-91 and for SBR / NR blend compound ranges from 98-102.

It is another aspect of the present invention to provide a lab level skid testing setup for tyre tread compound wherein the dry skid resistance value on elastomeric composition tested on pavement in claim 10 for NR based compound ranges from 125-128, for SBR based compound ranges from 117-121, for SBR / BR blend compound ranges from 115-121 & for SBR / NR blend compound ranges from 124-128.

DESCRIPTION OF DRAWINGS
Figure 1: depicts the lab skid testing setup according to one embodiment of the present invention.
Figure 2: illustrates the flowchart of the method of reporting the skid resistance of the tyre tread compound according to another embodiment of the present invention.
Figure 3: illustrates the preparation of the test sample setup (a) Molded sample, (b) Aluminium holder and (c) Bonded rubber slider block.

DETAILED DESCRIPTION OF THE INVENTION:
The present invention relates to a lab level skid testing setup for tyre tread compound. This set up comprises of apparatus and method that aims to determine or measure the skid resistance of the tyre tread compound on the test surface that simulates road conditions. The invention comprises of test sample and method of preparation, test pavement preparation and evaluation of the tyre tread composite using the test set up of the present invention. The test sample comprises of elastomeric composition for the tire tread.

Preparation of the tire tread compound:
The present invention relates to a rubber composite wherein the polymer can possibly be natural rubber or synthetic rubber or its blend. An embodiment of the present invention discloses a composition as exemplified in the table no 1 for testing in the Lab skid testing setup of the present invention.
The below composition is an exemplification and is not to limit the scope of the present invention.
Table 1: Compound formulations
Ingredients* Trial 1 Trial 2 Trial 3 Trial 4
RSS 5 100.00 30.00
SBR 1502 100.00 70.00 70.00
BR 30.00
N330 63.00 63.00 63.00 63.00
TDAE Oil 12.00 12.00 12.00 12.00
Zinc Oxide 5.00 5.00 5.00 5.00
Stearic acid 3.00 3.00 3.00 3.00
TMQ 1.00 1.00 1.00 1.00
6PPD 2.00 2.00 2.00 2.00
Microcrystalline wax 1.50 1.50 1.50 1.50
SULPHUR 2.00 2.00 2.00 2.00
PVI 0.15
CBS 1.50 1.50 1.50 1.50
Total 191.00 191.00 191.00 191.15

Ingredients* dosage expressed in Phr (parts per hundred rubber)
1. RSS5 (Ribbed Smoked Sheets)- used as a base polymer from KURIAN ABRAHAM ML (1+4) @ 100°C is 70 - 85 (massed)
2. SBR1502 (styrene-butadiene rubber) - used as a base polymer from KUMHO PETROCHEMICALS. ML (1+4) @ 100°C ranges between 45-55.
3. BR (Polybutadiene rubber) – used as a base polymer from KUMHO PETROCHEMICALS ML (1+4) @ 100°C is 40-50
4. N330 – black used as a reinforcing filler from BIRLA CARBON.
5. TDAE Oil (Treated Distillate Aromatic Extract) – used as a processing aid from REPSOL.
6. Zinc Oxide – used as an activator from PONDY OXIDES & CHEMICALS.
7. Stearic Acid – used as a processing aid from GODREJ INDUSTRIES.
8. Sulphur – used as a curative from STANDARD SULPHUR
9. PVI (Pre-vulcanization inhibitors) - used as a retarder from SHANDONG
10. CBS N-cyclohexyl benzothiazolesulfenamide– used as an accelerator for faster curing from NOCIL LTD.
11. TMQ (Trimethyl Dihydro Quinoline),6PPD (Para-phenylene Diamine) -used as an anti-degradant from LANXESS.
12. Microcrystalline wax -used as process aid from GPL.

Master batch mixing process
The ingredients are initially mixed in Banbury mixer. The rotor speed is maintained constantly around 50-70 rpm. The temperature of mixing is maintained around 60-80°C. The batch weight is decided based on the chamber volume of the mixer. The fill factor of the chamber is 0.70-0.90. The total mixing time of the master batch compound is around 4-8 minutes. Rubber / Blend of Rubber is initially masticated for 20-60 seconds.

Further, the chemicals are loaded in the following order: cure activators, anti-degradants, carbon black and processing oil to the masticated Rubber / Blend of Rubber. The mixing process is carried out for 180-250 seconds. This is followed by sweeping off the chemicals from the chamber walls and again the mixing is continued up to 80-160 seconds. Finally, the mixed rubber composite is dumped. The dump temperature of the rubber composite is 145-165°C.

Final Batch Mixing Process
Rotor speed is maintained at 30-60 rpm and the starting temperature of mixing is 30°C-50°C. The master batch is warmed for 15-45 seconds. The vulcanizing agent and accelerator are added further and mixed for 50-100 seconds. The dump temperature varies between 105°C-120°C.

Preparation of test sample
Separate mold has been designed to mold the tread rubber piece based on the standard rubber provided with skid tester. Then the molded tread rubber piece of dimension 75x25x6 mm (length x width x thickness) is fixed with the aluminum holder using acrylic adhesive to form rubber slider block (Figure 3 a, b, and c). The adhered rubber slider block is conditioned at a temperature of 23±2 °C and 50±5 % relative humidity for 24 hrs.

Preparation of test pavement:
Step 1: Frame work preparation
A wooden square frame / mould of dimensions 70cm X 10cm are prepared. The wooden frame dimension is finalized based on the pavement size to be developed.
Step 2: Rebar preparation
Based on the required size of the pavement initially iron bars are cut into number of bars of 10mm each. These iron bars are placed longitudinally with an equal spacing of 6inch in between. In order, to reinforce these bars, balance bars (also iron bars) are placed transverse (perpendicular) to the iron bars. The two bars are then attached using binding wires or clamps or by welding. The rebar, thus developed, serves as a skeleton and structural reinforcement. This rebar is placed inside the wooden mould.
Step 3: Preparation of Concrete Base:
The concrete base is a mixture consisting of different ingredient materials. The materials include cement, M-sand, coarse aggregates (Blue metal) and water taken in the ratio of 1:1.5:2: 5 respectively. The cement grade used is Ramco 43. The coarse aggregates used for making the pavement are of particle size 18mm. The quantity of the total mixture depends on the size of the pavement required.

Step 4: Preparation of Pavement:
The concrete base mixture thus prepared is poured into the wooden mould to the required thickness of the pavement. This mixture is left undisturbed and allowed to set for 3 days. This is the time given for the concrete mixture to dry completely. After a period of 3 days, the pavement is ready and removed from the wooden mould.

Test method for skid measurement
The test pavement on which the skid resistance of the tyre tread compound to be determined is placed and test medium is filled on the pavement surface. The developed rubber slider block for which the skid resistance values to be tested is then placed on the slider holder of the testing device. The testing device is placed over the pavement (platform) and it is leveled using the adjustable legs with reference to the spirit level fixture present in the testing device. Then the slider holder is released for the rubber slider block to slide over the designed pavement (platform). Totally 8 swings are to be made and the skid values are noted from the measuring scale fixture. The initial 3 swings are considered for sample conditioning and the next 5 swings are the actual skid resistance measurement. The average value of the skid resistance is arrived at based on these latter 5 readings. The skid resistance of the tyre tread compound is directly measured from the tester scale. The skid resistance of the tyre tread compound relates to the grip, braking, and handling characteristics of the tyre and can be used for comparative evaluation of different compounds.

Results and discussions:
Initially the standard rubber sample (TRL55) provided along with skid tester is tested on the developed pavement surface. The hardness of the standard rubber is in the range of 55±5 IRHD.

Same procedure is followed for the standard rubber sample as well as the trial rubber samples. Totally 8 swings are made and the skid values are noted from the measuring scale fixture. The initial 3 swings are considered for sample conditioning and the next 5 swings are the actual skid resistance measurement. The average value of the skid resistance is arrived at based on these latter 5 readings.

The readings of the standard test sample are noted and the average value of skid resistance is 84 (PTV). Thus, from the skid resistance value it is found that the coefficient of friction of developed pavement test surface is 0.84.

This pavement with the coefficient of friction of 0.84 is further used for testing the trial samples.

Table:2
Wet skid test resistance value on the sample obtained by forming water film on the pavement surface:

The results are expressed as Pendulum Test Value (PTV)
S.No Trial 1 Trial 2 Trial 3 Trial 4
1 88 97 90 100
2 88 96 90 102
3 89 97 91 100
4 86 96 89 100
5 86 95 89 98
Average 87 96 90 100

It is observed that Trial-4 (SBR/NR blend) with average value of 100 has the highest wet skid resistance followed by Trial-2 (100% SBR) with average value of 96. This is followed by Trial-3 (SBR/BR Blend) with average value of 90. Trial-1(100%NR) has the lowest wet skid resistance with an average value of 87.

From Table: 2, it can be concluded that SBR rubber improves wet skid resistance better than NR & BR.

Table:3
Dry skid resistance test value on the sample obtained on the pavement surface:

The results are expressed as Pendulum Test Value (PTV)
S.No Trial 1 Trial 2 Trial 3 Trial 4
1 125 117 115 124
2 127 119 117 125
3 127 120 121 127
4 126 121 120 128
5 128 121 121 127
Average 127 120 119 126

It is observed that Trial-1 (100% NR) & Trial-4(SBR/NR blend) with an average value of 127 &126 respectively have high dry skid resistance. Trial-2 (100% SBR) & Trial-3 (SBR/BR Blend) with an average value of 120&119 respectively have low dry skid resistance.

From Table: 3, it can be concluded that NR rubber improves dry skid resistance better than SBR & BR.

Standard Test Methods:
ASTM E 1859 is taken as the standard reference for this particular test.
This standard test method covers the measurement of the longitudinal friction coefficient with a measurement device that imposes braking-slip between a tire and a surface for the full range of braking-slip speed values. This test method utilizes a series of incremental single measurements of friction force on a braked test wheel as it is pulled over a wetted or contaminated pavement surface. The values measured represent the friction properties obtained with the equipment used only. The values also indicate the evaluation of the braking friction forces on a pavement relative to that of other pavements.

A large part of a pneumatic tyre skid resistance (or anti-skid) properties lies in the rubber compound employed in the tyre tread (the portion that contacts the road). The invention relates to the prediction of the tyre skid characteristics by evaluating the tyre tread compound. The skid resistance of the tyre tread compound can be directly measured using a British Pendulum Tester (BPT). The present invention discloses the pavement surface (concrete, asphalt, sand, mud etc.) and filling medium (water, snow, ice, oil, etc.). The pavement sample can be tailored based on the test requirements. ,CLAIMS:WE CLAIM:
1. A lab level skid testing setup for tyre tread compound, comprising of steps:
molding of the test sample to an aluminum sample holder by molding and bonding to a predefined dimension to provide a rubber slider block;
conditioning the adhered rubber slider block at a temperature of 23 ± 2°C and 50 ± 5% relative humidity for around 24 hours;
preparation of test pavement [201] comprising preparation of test surface [202] and positioning in the tray;
determining [203] the co-efficient of friction of the test surface using the standard samples;
measuring the skid resistance of the tyre tread compound on the test surface [204] and simulation [301] of road conditions;
optionally filling [302] the tray with fill medium and leveled using the adjustable legs and reference spirit level fixture [4];
measuring [303] the thickness of the medium layer over the pavement surface using measuring scale fixture [5]; and
measuring [304] the temperature of the medium and surrounding atmosphere; and coefficient of friction of the test pavement using temperature measuring unit [6],
wherein the pavement is a concrete base comprises of cement, M-sand, coarse aggregates (blue metal) and water in the ratio of 1: 1.5: 2: 5 respectively,
wherein the tyre rubber skid testing setup comprises of pendulum tester, a tray [1] and the test pavement [2] and the elastomeric composition of the tyre rubber is tested for skid resistance on the pavement, and
wherein the test method comprises of placing skid test device over the tray [1], slider holder of the skid test device is then released for the rubber slider block to slide over the designed pavement / platform.

2. The tyre rubber skid testing setup as claimed in claim 1, wherein the tray [1] is made of stainless steel, and comprises of control rod [3], spirit level fixture [4], a measuring scale fixture [5] and a temperature measurement unit[6] for positioning of the pavements [2] developed for measuring skid resistance.

3. The tyre rubber skid testing setup as claimed in claim 1, wherein the tyre tread compound is an elastomeric composition and is molded and bonded with aluminum sample holder wherein the bonding agent is acrylic based, epoxy based, polyurethane based, silicone based, cyanoacrylate based or latex based.

4. The elastomeric composition as claimed in claim 3, wherein the tyre rubber for testing is NR based, SBR based and blends of NR/SBR and SBR/PBR rubber.

5. The elastomeric composition as claimed in claim 3, wherein the elastomers further comprise of SSBR or ESBR or ENR or NBR or PU based or its blends.

6. The elastomeric composition as claimed in claim 3, wherein the tyre tread compound is molded to the dimension of 75mm x 25mm x 6mm (Length x Width x Thickness).

7. The elastomeric composition as claimed in claim 3, consists of reinforcing fillers like carbon black, silica or other inorganic fillers or nanofillers or its mixtures.

8. The skid testing setup for tyre tread compound as claimed in claim 1, wherein the filling medium can be water or oil or ice or snow.

9. The skid testing setup for tyre tread compound as claimed in claim 1, wherein the pavement comprises a concrete base comprises of cement, M-sand, coarse aggregates (blue metal) and water in the ratio of 1: 1.5: 2: 5 respectively.

10. The skid testing setup for tyre tread compound by a tyre rubber skid testing apparatus as claimed in claim 1, wherein the pavement surface comprises of asphalt based, mud based and sand based.

11. The skid testing setup for tyre tread compound by a tyre rubber skid testing apparatus as claimed in claim 1, wherein the wet skid resistance value on elastomeric composition tested on test pavement for NR based compound ranges from 86-89, for SBR based compound ranges from 95-97, for SBR / BR blend compound ranges from 89-91 and for SBR / NR blend compound ranges from 98-102.

12. The skid testing setup for tyre tread compound by a tyre rubber skid testing apparatus as claimed in claim 1, wherein the dry skid resistance value on elastomeric composition tested on pavement in claim 10 for NR based compound ranges from 125-128, for SBR based compound ranges from 117-121, for SBR / BR blend compound ranges from 115-121 & for SBR / NR blend compound ranges from 124-128.