A multitude of testing methods have heretofore been available for measuring the curing characteristics of elastomeric materials. These devices generally measure to change in visco-elastic properties of the material as the cure proceeds, that is, they measure how the crosslinking of the molecular chains alters viscosity and elastic properties. Two of the most widely accepted and useful devices for measuring cure rate are the Mooney Viscometer and the Monsanto Oscillating Disk Rheometer.
The Mooney device measures shear viscosity, utilitizing a disc which rotates in a shallow cavity to produce a shearing action. The disc contains a number of serrated edges which aid in gripping the rubber. Uncured rubber placed in the cavity is heated to curing temperature. The increase in viscosity caused by the crosslinking during the cure is reflected in a measurably increased resistance to rotation of the disc. As the cure proceeds further, the integrity of the rubber sample is lost because the increased elasticity results in tearing of the sample where it contacts the rotating disc.
The Oscillating Disk Rheometer, on the other hand, is capable of measuring the complete curing characteristics of a rubber sample. As the name implies, a disc embedded in the sample oscillates rather than rotates to produce a shear strain in the rubber. The torque needed to produce the oscillation is proportional to the shear modulus or stiffness of the material which naturally increases during cure. A torque transducer relates the measured torque to a signal which is than plotted on a "rheograph".
Both these devices have certain drawbacks, not the least being their high initial cost and maintenance. The rubber samples tend to adhere to the disc, making turnaround time on either device high because all material from a previous test must be removed prior to subsequent testing. With the oscillating disc, provisions must be made for varying the amplitude of the oscillations so that torque requirements remain within acceptable limits regardless of sample stiffness.
U.S Pat. No. 4,337,646 to the instant inventor, addresses the problem of rubber adhering to the disc but does not discuss what will hereinafter be disclosed, namely, a device for combining the functions of a Mooney Viscometer and an oscillating disc in one device, and an improved design for torque adjustment which does not involve amplitude variation.
USPTO Backgrounds
USPTO Backgrounds