Canadian Plastics

Jim’s Tip of the Month

Choosing a sealing compound

March 1, 2008   Canadian Plastics

Choosing a sealing compound

Many processes, most notably injection molding, use a complex network of cooling channels and tubing to circulate coolant solutions. Threaded joints may be straight or tapered (pipe) and multiple ports may by provided for cleaning or sensor installation. Tapered joints may seal without chemicals, but straight threads are normally installed with “pipe dope”.

What compound should you use? Silicones conform to surface irregularities, but need set up time. Anaerobic joints are usable immediately. Teflon tape is fast and clean, but shouldn’t be used where the presence of bits of tape in the fluid stream could cause trouble.

I prefer pipe dopes specified for the gas fitting trade because they’re heavy bodied, stay in place, and are acid and alkali resistant. That’s important for cooling systems that are occasionally flushed with chemicals. You need less than you think; a thin coating on all threads applied with a finger is my technique.


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