Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Viscosity
Patent
1998-03-04
1999-12-14
Larkin, Daniel S.
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Viscosity
73843, G01N 1114
Patent
active
060002794
DESCRIPTION:
BRIEF SUMMARY
This invention relates to methods of testing rubber and apparatus for carrying out such methods.
One of the most, if not the most, significant factors affecting quality and consistency in manufacture of rubber products, is the quality of the raw rubber used. However, the quality and consistency of raw rubber, particularly natural rubber but also to a lesser extent synthetic rubbers, varies considerably. It is accordingly desirable to have a method of testing rubber-quality that can be readily applied before or during the early stages of the manufacturing process, towards achieving assurance of consistency of manufactured product. It is one of the objects of the present invention to provide such a method and also an apparatus for carrying out the method.
According to one aspect of the present invention, there is provided a method of testing rubber wherein a sample of the rubber is entered to fill an annular space defined between coaxial cylindrical surfaces of two relatively-rotatable members, and measurements of the viscous torque of the sample and the force it exerts axially of the annular space during relative rotation of the two members is derived to provide a measure of quality of the sample.
It has been found that the measurements of torque and axially-exerted force of the sample can be used with advantage for assessing the quality of the rubber in relation to its acceptability or otherwise for consistency of manufactured product. In the manufacture of tyres, for example, it is necessary to have reproducibility of properties such as tensile strength and resistance to wear, and the method of the invention has been found to enable criteria of acceptability or suitability for the starting material, whether in the raw or compounded condition, to be established.
A multiplicity of measurements of the viscous torque and the axial force may be derived during a period of relative rotation of the two members so as to provide time-related characteristics dependent, respectively, upon the viscosity and the elasticity of recovery of the sample. Determination of acceptability or otherwise of the sample may then be made in dependence upon the degree of conformity of the characteristics to predetermined criteria.
The measurements may be made for each of a series of samples taken at successive stages of manufacture of a rubber product. For example, the samples may be taken from the raw rubber, from the product of compounding in a primary masticator-mixer, and from the product of extrusion, calendering, or injection-moulding of the compounded rubber.
The method of testing is desirably carried out at a temperature and for a duration comparable with the temperature and duration of the next processing stage to which the rubber from which the sample was taken, is to be submitted. The temperature in primary compounding is generally in the range 130 to 150 degrees Celsius for natural rubber, 140 to 170 degrees Celsius for general-purpose synthetic rubbers, and 100 to 120 degrees Celsius for butyl rubbers, and may exceed 200 degrees Celsius for high temperature rubbers. Moreover, the speed of relative rotation of the two members is desirably such as to give rise to a rate of shear within the sample comparable with that to which the rubber is to be submitted in the next processing stage. The speed of relative rotation of the two members may in this respect be within the range 50 to 1,000 revolutions per minute, or more especially within the range 100 to 500 revolutions per minute.
According to another aspect of the present invention, an apparatus for testing a sample of rubber comprises two relatively-rotatable members having coaxial cylindrical surfaces to define an annular space between the two members for receiving the sample, means for rotating the two members relative to one another, means to derive a measurement dependent upon the viscous torque of the sample, and means to derive a measurement dependent upon the force exerted axially of the annular space during relative rotation of the two members.
The apparatus may incl
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