Patent Application
20150323437
This disclosure pertains to an apparatus and its method of use in measuring indentation hardness of rubber materials at, above or below room temperature according to the standard test method ASTM D2240.
Hardness is the most important and widely measured and reported property of rubber materials. This is due to it being inexpensive to measure and it serving as a proxy for the Young's Modulus of the rubber material.
Measuring hardness of rubber materials is often done according to the standard test method ASTM D2240. This method basically involves using a durometer for measuring the durometer hardness of the rubber materials.
Durometers are designed for use at room temperature. Therefore, the durometer hardness according to ASTM D2240 can only be measured at room temperature.
The apparatus and method of this disclosure measures indentation hardness of rubber materials at, above or below room temperature using the durometer method described in the standard test method ASTM D2240. The apparatus combines together a testing instrument called a dynamic mechanical analyzer (DMA) and a durometer indentor.
The dynamic mechanical analyzer is of a type having co-axially aligned upper and lower shafts with specimen holders positioned between the two shafts. In the apparatus of this disclosure, the specimen holders are removed from the upper and lower shafts.
A platen is attached to the lower shaft. The platen has a flat, horizontal surface that is dimensioned to receive and support a rubber specimen to be tested.
A durometer indentor is attached to the upper shaft with the indentor tip directed toward the platen surface.
The rubber specimen to be tested is positioned on the platen surface. The specimen is centered below the indentor tip.
The dynamic mechanical analyzer temperature chamber is then closed around the test specimen. The control system or control software of the dynamic mechanical analyzer is then activated by an operator. The temperature chamber then brings the test specimen to the desired temperature.
The control system then controls the indentor to move toward the platen surface and the test specimen supported on the platen surface. The indentor tip is moved into the test specimen a predetermined distance at a constant speed for a predetermined period of time in accordance with the standard test method ASTM D2240 for durometer hardness. The control system could alternatively, or additionally, move the specimen toward the indentor tip.
A position sensor of the dynamic mechanical analyzer measures the indentor movement and a load sensor measures the specimen reaction force periodically during the test time period. The control system of the dynamic mechanical analyzer provides an electronic data file with values of force, indentor displacement, and the time period of the test along with a force-displacement chart for the specimen.
In this manner, the apparatus and its method of use are capable of measuring the hardness of rubber materials at, above and below room temperature according to the standard test method ASTM D2240.
The features, functions, and advantages that have been discussed can be achieved independently in various embodiments or may be combined in yet other embodiments further details of which can be seen with reference to the following description and drawings.
As stated earlier, the apparatus and method of this disclosure measure indentation hardness of rubber materials at, above or below room temperature (23 degrees Celsius) according to the standards set forth by the American Society for Testing and Materials at ASTM D2240, which is incorporated herein by reference. The apparatus 12 combines together a dynamic mechanical analyzer (DMA) 14 and a durometer indentor 16.
The dynamic mechanical analyzer 14 is represented in
The dynamic mechanical analyzer 14 of the apparatus 12 is set to operate in a tension and compression mode. In this mode a drive mechanism 24 of the analyzer. is selectively operable to move the upper shaft 18 downwardly toward the lower shaft 22 and to move the upper shaft 18 upwardly away from the lower shaft 22.
The dynamic mechanical analyzer 14 also includes a load sensor device 26 and a position sensor device 28. The position sensor device 28 is operatively connected with the upper shaft 18 and is operable to measure the movement of the upper shaft 18, the rate of upper shaft 18 movement or the speed of the upper shaft 18. The load sensor device 26 is operatively connected with the upper shaft 18 and is operable to measure a reaction force exerted by the specimen on the upper shaft 18 opposing the downward movement of the upper shaft 18.
The dynamic mechanical analyzer 14 also includes a temperature chamber 30. The temperature chamber 30 is basically a forced convection laboratory oven. It includes top and bottom coiled heaters that are capable of heating the interior of the temperature chamber 30 to an accurate and precise temperature desired by a user of the apparatus. Closed loop controls of the analyzer 14 control the temperature inside the chamber 30. Additionally, the temperature chamber 30 is also provided with means for cooling the interior of the chamber. Again, the closed loop controls of the analyzer 14 control the cooling of the interior of the temperature chamber 30 to an accurate and precise temperature desired by the user. The temperature chamber 30 is positioned to one side of the upper shaft 18 and lower shaft 22. A door 32 of the temperature chamber is movable between an open position represented in
The dynamic mechanical analyzer 14 also includes a closed loop control system 36 or control software that controls the operations of the analyzer 14 yet to be described.
The dynamic mechanical analyzer 14 is modified with a platen 42 that is attached to the upper end of the lower shaft 22. The platen 42 can be removably attached to the lower shaft 22 by a screw threaded connection or any other equivalent mechanical connection that securely holds the platen 42 to the lower shaft 22. The platen 42 is represented in
The dynamic mechanical analyzer 14 of the apparatus 12 is also modified with an indentor 16. Specifically, the indentor 16 is a durometer indentor that is compliant with the standards of ASTM D2240. In the example of the indentor 16 shown, the indentor 16 has a tip 54 with a conical configuration. This is only one example of the configuration of the indentor tip 54. The indentor 16 could have a tip 54 designed as a type A, D, B, C, DO, E, M, O, OO, OOO, OOO-S, R, or any other type included in the standard test method for example ASTM D2240. The indentor 16 is removably attached to the upper shaft 18 by screw threading or any other equivalent mechanical attachment with the indentor tip 54 directed downwardly toward the center of the platen top surface 44. The length of the indentor 16 attached to the upper shaft 18 is coaxial with the coaxial upper 18 and lower 22 shafts. With the indentor 16 attached to the upper shaft 18, the center axis of the indentor 16 is perpendicular to the platen top surface 44.
The method of using the apparatus 12 involves a sequence of steps taken by an operator of the apparatus 12 to set up the test parameters on the dynamic mechanical analyzer 14, place the test sample on the platen surface 44, perform the test and analyze the results.
The test specimen 62 is represented in
The apparatus 12 is then controlled by the operator and the apparatus control system 36 to bring the temperature of the test specimen 62 in the temperature chamber 30 to the desired temperature for the test. The test specimen 62 is kept at the predetermined temperature for a period of time to allow the test specimen 62 to reach thermal equilibrium throughout its volume. The temperature of the specimen 62 is reported by a display of the dynamic mechanical analyzer 14. The temperature of the specimen 62 could also be checked by a thermocouple attached to the specimen 62. A consistent temperature of the specimen 62, either above room temperature or below room temperature, is reached by the dynamic mechanical analyzer 14. The heating or cooling source of the temperature chamber 30, the insulation of the chamber, the chamber small size, and adequate dwell time result in the consistent temperature throughout the entire specimen.
With the test specimen 62 at the predetermined temperature, the upper shaft 18 is then controlled to move the indentor 16 downward toward the platen top surface 44 and the test specimen 62 supported on the surface. The indentor tip 54 is moved into the test specimen 62 at a constant speed. The speed is set to have the indentor tip 54 penetrate the test specimen 62 to the selected distance in approximately 1 second, as in a durometer hardness test, or any other time chosen.
The position sensor device 28 of the dynamic mechanical analyzer 14 measures the movement distance of the indentor tip 54 and the load sensor device 26 measures the reacting force exerted by the test specimen 62 on the indentor tip 54 within a predetermined time frequency, preferably every second or less. The control system 36 of the dynamic mechanical analyzer 14 creates an electronic data file with the values of force, indentor tip displacement, and time during the test, along with a force-displacement chart.
When the test is complete the control system 36 controls the drive mechanism 24 to raise the indentor 16. The door 32 of the temperature chamber 30 can then be opened and the specimen 62 removed.
The apparatus 12 enables measuring hardness of rubber materials at, above and below room temperature in an accurate and precise way according to the standard test method ASTM D2240 for rubber hardness measurements. It minimizes operator variation because the load is applied to the specimen 62 by the dynamic mechanical analyzer 14 in a machine controlled way. The apparatus 12 can operate at a wide range of temperatures, for example −150 C to +610 C. The apparatus 12 permits the design of rubber components for high and/or low-temperature applications with better service performance and longer service life.
As various modifications could be made in the construction of the apparatus and its method of operation herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present disclosure should not be limited by any of the above described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.
