High Temperature Exposure FM tests
We confirmed the snug fitting of the gasket in the ductile iron housings. We conducted lab tests to determine parameters as per test standards. We kept pipe assembly samples in the oven at 140 degrees C for 7 days as per the stipulated test procedure. The samples were subsequently cooled to room temperature. As per the stipulated test procedure, we pressure tested the gasket assembly to detect any leakage at the joints.
The American gaskets did not leak at all. Our gaskets leaked profusely at the joints. I investigated to find the cause of leakage. The gaskets were subject to 140 degrees C for one hour instead of 7 days. Our gaskets leaked, and the American gaskets were intact. This proved long exposure for one hour at 140 degrees C was not necessary at all. Our gaskets were exactly as per the American gaskets. Nevertheless our gaskets failed badly.
A prominent bulged seam formed at the chamfered edge at the split axis of the ductile iron housing. The deep cavity at the split axis of the housing is due to local shrinkage. The gasket periphery shows a concave profile due to shrinkage on cooling. The split axis is the line of least resistance for rubber contraction in the cooling process.
The material properties with respect to thermal coefficient of expansion is the main criterion. This information was not given to us in the patented design, and this data was not disclosed to us. I contacted the Canadian Research Institute. They gave us the general data for rubbers. It is 7 to 20 times the value of ductile iron and steel pipe materials.
The value of ductile iron and steel pipe material is 10 to 13. Our EPDM gaskets failed in the 140 degrees C exposure due to higher value of thermal coefficient of expansion. It was not matching with the properties of ductile iron and steel. We prepared some samples of EPDM rubber of different composition. We molded gaskets out of it. We subjected these gaskets to temperature of 140 degrees C for one hour.
This was the best way to determine the coefficient of linear thermal expansion of EPDM gaskets. We got gaskets that matched closely with iron and steel thermal properties. We solved our quality problems without offending patentee copyrights.
Rubber Products Manufacturers - Please Note
The value of thermal expansion coefficient of Rubbers, EPDM, and Elastomers is not specified in any Standards. Its value is 7 to 20. Rubber products are used in combination with SG Iron and Steel parts. The value of thermal expansion coefficient of Steel and SG Iron is 10 to 13. Rubber parts meant for gasket seals, rubber mounts, and so on must have its composition that matches with the thermal expansion coefficient within 10 and 13.