What glue for secondary heater

[blinky]

As the title says, what is the best glue to use to stick a couple of resistors to the back of my secondary mirror?  Can I use a bit of standard clear silicone?

[MarkyD]

This - carefull you don't get in on the leads

https://www.overclockers.co.uk/arctic-silver-premium-silver-thermal-adhesive-7g-th-004-ac.html

or I used this to stick the sensors to the backs of the mirrors

https://www.overclockers.co.uk/akasa-ak-tt12-80-thermal-adhesive-tape-th-001-ak.html

[Physopto]

If you do use silicon to glue them on and something goes wrong, it is an awful job to remove the silicon afterwards. The surface will have to be thoroughly cleaned and possibly abraded to remove any residue, or you will not be able to bond onto the surface again.

Derek

[faulksy]

i have just bought a kendrick dew heater for my secondary and it says use clear silicone ?

[Physopto]

If you have to remove anything glued on with silicon it always leaves a deposit. If not completely cleaned off you cannot silicon or glue anything onto it again. Silicon glue will not stick to silicon. Nor will anything else.

It is usually the easiest method that most people use, as it is widely available and cheep. Silicon can take temperatures up to around 150 Deg C and using specialized silicon compounds this  can be higher. But you do not need anything like that. If Kendrick say use silicon then I suppose you should, but I would look for another solution. It may well be a special base on the heater pad that requires silicon to stick properly. Try asking Kendrick directly.

Derek

[MarkyD]

I didn't think silicon was a good heat conductor unless additives have been introduced like silver

[Physopto]

Just a note on silicon adhesive if you do use it. Do not let it touch any copper component anywhere. It reacts and eats copper! Many have found their household heating systems leaking because of that. There is a special type of silicon for that purpose.

 

[L8-Nite]

The overall best and most reliable bonding agent I have "ever" used over the last forty years is an archery product called " FletchTite ". It grips like a vice, doesn't become brittle, sets in about 15 minutes, and cures in a day, but can be removed with a razor knife and a little effort

[Physopto]

I had a look on the Kendrick website. The types I saw were orange in colour. This suggests that they are like a dew heater band I bought some years ago from America, for a 12" Meade SCT.  It was made of an orange silicon type covering with its own special bonding glue already applied to one side. This glue only melted and went off when the heater was switched on, so it had to be held initially in place until this bond was firm.  I still have it unused as I never got around to the job.  This could be the reason for the Kendrick statement to use silicon bonding. I would still ask them.

[MarkyD]

24 minutes ago, Physopto said:

I had a look on the Kendrick website. The types I saw were orange in colour.

This would probably be RTV Silicon.  It is a very flexible mould silicon that can withstand up to 300deg C.  I have used it to mould castings in molten lead

[Physopto]

RTV is just a high temperature silicone sealant mostly used on car seals/gaskets I think. That is what I used it for anyway. I did have the correct sealant many years ago which I purchased from Radio Spares, but cannot remember the name now. You can use a Advanced Modified Polymer Adhesive & Sealant like Sikaflex 512 or Soudal Fixall.

[mapstar]

Kendrick do recommend silicone sealant to bond their heaters on. I have used it myself although as Derek point's out if you do get it right the first time.

[eatabean]

RTV stands for Room Temperature Vulcanized, and refers to the fact that you do not need to heat it up in order to cure it fully. It has nothing to do with the temps that compound will withstand. That said, if your glue lets go when you heat the mirror up, it is most likely due to a contamination of the surfaces being glued. Clean both the mirror and the resistors with isopropanol and that should help form a better bond. There is no reason to heat that mirror to the point that the glue releases. Who would push that 150 deg max just for a dew heater?

Silicones are used in electronics to absorb heat and re-radiate it very quickly, that is why the low temp ratings. Engine silicones have higher breakdown temps and are oil resistant. Some silicones will cure fully under water... am I starting to sound like Bubba Gump? LOL I worked with the stuff for ten years, gluing many different materials and testing what works and what doesn't. There are so many different variations in this material, it has become ubiquitous. I was called "Lim Jim" which means "glue Jim" in Swedish

RULE: if it ain't clean to start with (like surgically clean) it won't stick.

Jim in Sweden