- temperature of 250ºC
- a system pressure of 1.1 psi when at roasting temperature
- Hot rolled flanges, not machined surfaces
- it must provide a barrier to very acrid smoke
- must resist suction
- must not out gas after burn in
Silicone sheet was touted to withstand the temperatures but over the years it crystallized and became brittle. Some Teflons have a fairly high temperature ceiling but most are not nearly as capable and durable as the claims make them out to be. We attempted to use high temperature ceramic paper but by itself it turned out to be too porous.
Out of curiosity we added a ring of packing material which would further compress the ceramic fibers but it still leaked.
It was possible to seal machined faces with High Temperature paste, some of which was "scaringly" smelly but most of the flanges are cut from hot rolled sheet material. Better sealing capacity was required over a slightly wavy surface which is exacerbated by the weld to the tubing.
Samples were cut from various materials that were either on the shelf or purchased. The initial tests consisted of about four times as many gaskets as shown in the picture above. A rather simple device was salvaged from the "steel pile" to pressurize the gaskets. An arbitrary 1.5 atmospheres was selected as the testing pressure. A soap mixture (sorry I forget the soap's brand-name which pretty well ruins an endorsement contract) was used to dramatize the results for the camera. The relative size of the bubbles is proportional to the size of the leak.
We looked for sealing ability especially after being subjected to repeated hot/cool cycles but also the material had to resist extrusion.
Many of the gaskets sealed until they were subjected to periods at 325°C a temperature that was also arbitrarily chosen to represent heat damage over an extended period. Some people might complain that this is not a fair test. It might not be but since their product is not named they will not know that they should complain about the procedures.
To the right is the outside view of the testing oven. A PID Autonics temperature controller was added with a RTD sensor. As mentioned above the Set Point is 325°C. This little throw together may not win an award (it is from the same design studio as the testing jig to the left) but it keeps a stable temperature.
Seal progress was made through the combination of various products but further work is required to determine the mixture and the method of application so that a uniform gasket is produced.
