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   IndiaRubberDirectory.com > Rubber Article > Technical Papers

Articles - Rubber Technical Papers

INTRODUCTION

One of the key technological areas in which new advances are impacting the rubber industry, is that of new physical testing and analytical tools. With technological development in electronic sensors, data acquisition and data analysis systems, enhancements and ew developmentarebeing made continuously in material testing and analytical equipment.

In this paper I have selected a total of ten (10) key examples of recent development in physical testing and analytical instruments for our discussion. Because of time constraints, I will highlight here only the significance of these developments and their applications to rubber industry. Additionally, Appendices A and B, are included here listing commonly used physical tests and analytical instruments by polymer / rubber R&D Laboratories.

ADVANCES IN PHYSICAL PROPERTY TESTS

DYNAMIC STRESS RELAXOMETER (DSR)

Rubber industry continously looks for tests that can determine/predict processing characteristics of rubber compounds in manufacturing plants. A successful and practical test should entail measurement of nervy nature of materials and how they recover/relax when applied stress is released, be simple, have short test time, and provide quality control information.

The DSR, a Uniroyal Goodrich patented tester, is such an insrument for testing the responise of an elastomeric material after the application of applied stress. The sample is put into the conical mould cavity and is squeezed to a fixed thickness (1/4”). It is heated to the desired temperature during a fixed time after which a small twist is applied on the rotor to impart a sudden strain on the sample. The standard twist angle is 20, however, the magnitude of the twist can be varied. The entire test takes only 70 seconds.

Peak torque (TM) is measured after the strain application, and the sample relaxes. The area under the torque-time at two seconds is called torque Summation (S 3). First time constant, t1, is the time at which torque is reduced to 37% of TM. Second time constant, t2 is the time when torque is reduced to 13% of TM Both, t1 and t1 are expressed in millieseconds. See Figure 1. The DSR has on-board data acquistion and analysis system and printer.

DSR OUTPUT

 

 


The DSR has proved to be very useful in many R&D and factory Processing applications. Since it measures the elastic (nerve) and relaxation responses of materials, it has shown excellent correlation between prediction and actual processing behavior. Some examples are given here.

Two polybutadienes with idential Mooney values showed different processing behavior in factory. The DSR measurements on raw polymers showed that t2 and other long term relaxation times were different for those elastomers. The DSR prediction agreed with factory processing.

 

 

Figure 2. Mooney Viscosity Versus DSR t2 of Raw Rubber
Figure 2 shows several natural rubber samples showing ML-4 values fairly close to each other, say between 90-100 range. One might conclude that these would process alike. The DSR t2 data showed much greater differences which agreed with the factory processing experience.

extent of variabillity of natural rubber polybutadienes for a six week period at a tyre plant. For this reason, we now use DSR to classify incoming natural rubber shipments into three categories; easy, moderatend difficult (to process).

Observations of Variability of Natural Rubber and
PolybutadienceforSixweekPeriod at a Tire Plant.
relationship (1) between the Wallace Plasticity, Po and the DSR t2 values. The DSR classification has considerably reduced any processing problem due to NR variability.

 

data obtained over a three-month period on an NBR hose compound. Processi ng difficulty was experienced after mid-February. The Ì2 DSR data on raw rubber explained the change; Ì2 has increaseed from 8.5 to 10.8 N.m.s. indicating changes in relaxation properties. Money values, however, did not show change. DSR was able to differentiate, and the Problem was corrected.

   

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