Ask Dr. Dave / Finished Adhesives and Sealants / Columns

Ask Dr. Dave: January 2013

QUESTION: We have a lab freezer that goes down to -32°C, and the seals are torn and need replaced. What do you recommend?

ANSWER: Exposure to low temperature affects most elastomeric materials, resulting in decreased compression and possible leakage. Extreme cold also affects seals by making them less flexible and more brittle. You will find, however, that most silicones will still give some flexibility at the low temperature of your freezer.

Although silicone manufacturers do offer special low-temperature grades, I would be surprised if a window and door sealant grade will not work for you. You should certainly make sure that the silicone is fully cured at room temperature before exposing it to the low temperature.

QUESTION: Can I use a threadlocking adhesive for assembling screws into plastics?

ANSWER: You have to be very careful in using the “anaerobic” type of sealants on plastics. Although they don’t usually have any problem in contact with thermoset plastics (e.g., fiberglass or epoxy), they can often cause crazing and cracking when the liquid is in contact for a period of time with several thermoplastics.

The secret to preventing this is to convert the liquid to a solid very quickly by using them together with an activator. In extreme cases, or where it is not possible or convenient to use an activator, you can use a cyanoacrylate-based threadlocker. Some solvent-based threadlockers (non-curing types) also seem to work well on thermoplastics.

Any views or opinions expressed in this column are those of the author and do not represent those of Adhesives & Sealants Industry, its staff, Editorial Advisory Board or BNP Media.

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