Author: Gordon (NZ)
Date: 2004-03-21 10:28
1. It is very messy stuff to use. How do you deal with some that oozes out from behind the pad during installation?
2. There are various types. At least some are quite corrosive to copper alloys. I understand that the "neutral-cure" types are safe in this respect.
3. Technicians, and presumably DIYs, want to know when the glue has set. With a hot-melt glue you know it has set when the key is cool. The silicones depend on evaporation, which in this location could take hours or even days. With sprung-closed keys, they could continue oozing glue during this time.
4. One wants the adhesive to set as soon as possible, because it is only after it has set, that one can test for leaks and analyse what should be done in each case.
5. As has been said, no adjustments can be made to the pad alignment AFTER the glue has set. It is not uncommon for adjustments to pad alignment to be needed at a later date after the larger pads have bedded in more with use, because they tend to bed in deeper on the non-pivot side of the key cup, developing leaks here. Also, a technician will want to press firmly on a key, particularly a larger one, to hasten this 'bedding-in' process. This cannot be done until the glue has set.
4. Many (all?) give off ammonia as they set. One would have to know whether this has any adverse affect on timber, silver plating, nickel plating, or even behaving as an electrolyte to enable galvanic corrosion to occur in the microscopic pits in the plating, between the plating and the base metal.
5. It is particularly difficult glue to remove from a surface. What a pain for the NEXT repadding job, to have little chunks of it tenaciously adhering to the key cup.
6. As mentioned, it sets not particularly rigid. If a pad is installed so poorly that 'give' is needed behind the pad, for the pad to seal, then a new technician is definitely needed!
And that is just off the top of my head. Shellac-based adhessive/fillers have got so much going for them that they have been the mainstay for many decades. High temp glue-gun glue has some advantages, and the odd disadvantage.
IMHO, silicone has not got a lot going for it!
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