Torsional rheometer that maintains a more uniform cavity pressure
A method and apparatus is disclosed for compensating for a reduction of die cavity pressure in a torsional rheometer caused by shrinkage of the test sample. In one embodiment, a compliant member is placed in series with load-bearing components of the rheometer. This compliant member deflects when pressure in the die cavity is reduced resulting in the die cavity becoming smaller to increase the pressure within the die cavity.
1. A torsional rheometer comprising:
a first die assembly having a first bearing surface;
a second die assembly having a second bearing surface facing the first bearing surface on the first die assembly to form a die cavity therebetween for placement of a test sample;
a first seal plate associated with the first die assembly;
a second seal plate associated with the second die assembly, the first and second seal plates being configured to capture and hold the test sample therebetween;
a force applicator configured to apply a load to urge the first die assembly against the second die assembly and to urge the first seal plate against the second seal plate to capture and hold the test sample in the die cavity; and
at least one compliant member coupled to the second seal plate, the at least one compliant member placed in series with other load-bearing components associated with the second die assembly, the at least one compliant member configured to deflect in response to a load being applied by the force applicator to the second seal plate.
2. The torsional rheometer of claim 1 , wherein a gap is located between the second seal plate and the second die assembly to permit movement of the second die assembly toward and away from the first die assembly when the test sample is captured and held in the die cavity.
3. The torsional rheometer of claim 1 , wherein the at least one compliant member includes a plurality of compliant members.
4. The torsional rheometer of claim 3 , wherein the plurality of compliant members are arranged in parallel with each other.
5. The torsional rheometer of claim 1 , further comprising a housing assembly supporting the second seal plate, the housing assembly configured to bear at least part of the load applied by the force applicator to the second seal plate through the first seal plate, the housing assembly including the at least one compliant member.
6. The torsional rheometer of claim 5 , wherein the housing assembly includes an upper plate, a lower plate and a middle plate located between the upper and lower plates.
7. The torsional rheometer of claim 6 , wherein the at least one compliant member is located between the upper plate and the middle plate.
8. The torsional rheometer of claim 7 , further comprising an indicator configured to measure deflection between the upper and middle plates.
9. The torsional rheometer of claim 1 , wherein the at least one compliant member includes a spring.
10. The torsional rheometer of claim 9 , wherein the spring includes a spring washer.
11. The torsional rheometer of claim 10 , wherein the spring washer includes a Belleville washer.
12. The torsional rheometer of claim 10 , wherein the spring includes a compression spring.
13. The torsional rheometer of claim 12 , wherein the compression spring includes a coil spring.
14. A torsional rheometer comprising:
a first die assembly;
a second die assembly, the second die assembly having a bearing surface facing a bearing surface on the first die assembly to form a die cavity therebetween for placement of a test sample;
a first seal plate associated with the first die assembly;
a second seal plate associated with the second die assembly, the first and second seal plates being configured to capture and hold the test sample therebetween;
a force applying apparatus for applying a load to urge the first die assembly and second die assembly against one another and the first seal plate against the second seal plate to capture and hold the test sample in the die cavity; and
a housing assembly supporting the second seal plate, and bearing at least part of the load applied by the force applying apparatus to the second seal plate through the first seal plate, the housing assembly comprising a compliant member that is placed in series with the other load-bearing components associated with the second die assembly and that deflects when a load is applied by the force applying apparatus.
15. A method for compensating for reduction of cavity pressure due to shrinkage of a test sample in a die cavity of a torsional rheometer, the method comprising the steps of:
placing a compliant member in series with load-bearing components of the rheometer such that when pressure drops in the die cavity, the compliant member deflects causing a size of the die cavity to become smaller and a pressure in the die cavity to increase, wherein the compliant member is disposed between one of an upper plate and a middle plate, the middle plate and a lower plate, the upper plate and an insulator ring, or the lower plate and a table.