OT: Silicone rubber?

[N_Cook]

I thought I'd found a source of small dimension silicone rubber drive
bands. Vibrant colours like all that kitchen utensil stuff. For a given
cross-section , the same degree of stretch. But laying against a
soldering iron barrel , it melts, slowly, but does melt , unlike proper
silicone rubber. Low grade "silicone" with admixture of some sort of
plastic?

 

Well for one there are thermoplastics and thermosets. A thermoset will not remelt once it is hardened. Silicone seems to have alot of the properties of a thermoset.

Some things just do not melt they burn. Like you can't melt a tree for example. However the flash point of most sinlicones seem to be quite high.

On old Zenith TVs that had triplers, for example the 25GC45Z chassis (I am sure you've never seen one but I gave the chassis number in case you care to look it up). They used this black silicone on the input wire which carried about 9 KV AC, 70 KJz half sine pumped at 15.734 KHz and had some current behind it and as such was quite dangerous, they used this black silicone that was tough as nails. I had to use the BIG cutters to get enough off to pull the wire out and then practically drill through it with the soldering GUN to get the wire off, and I am talking a Weller 8200 which was 100/140 watts. Sometimes bent the tip getting through that shit.

I imagine that with some of the properties of the "good" silicone made the manufacturing process more expensive so they decided to use a low grade. Look at the application, it is not an insulator and not made to exposed to high voltage or high heat. Why would they use top grade stuff when it is not needed ?

I remember talking with an aircraft engineer as I was working on his PC. We got to bullshitting a bit and he explained that part of what he does is the stress formulae so they can shave off a little material here and there and save some weight. I was not as learned at the time and asked "Why not just make the whole thing out of titanium" and he said it doesn't work that way. One of the main reasons is that it is a bitch to machine.

However my engineer buddy I met a couple years ago does this stuff, actually designed dies and molds to make the impellers for jet engines. Recently he had a gig improving of all things, pain spray heads. He was surprised to find out how involved it is. they had a falling out and I think he is going to wind up doing contract work for Alcoa next but, the things he told me about what seems like a simple thing were quite interesting.

This is not a can of fucking Rustoleum here. This is what paints new cars and refrigerators or what have you. It is done with the electrostatic process which the charge literally pulls the paint to the piece, there is no overspray. But then this spray head turns at 70,000 RPM. So it is whipping the pain all around and the electrical charge reconcentrates it. Each spray head is thousads of dollars and that company rebuilds them. He redesigned them and made the process a whole lot easier and I think now they manufacture them, using his design. Like I said they had a falling out, he gave them a two week notice and they said don't bother. Probably because he was in a very good position to sabotage them. Not that he would, but how do they know that ?

Back to the subject, I agree, I have never seen any type of silicone melt. I have seen it burn but it take a hell off alot to get it going. But if these things work then they do. Being low grade most likely I would not expect them to last alot longer, but then if you are putting belts for the first time on something that is ten years old who cares ? As long as you don't put a soldering iron to them they will probably work fine.

 

[N_Cook]

On 14/09/2016 00:48, jurb6006@gmail.com wrote:

Well for one there are thermoplastics and thermosets. A thermoset will not remelt once it is hardened. Silicone seems to have alot of the properties of a thermoset.

Some things just do not melt they burn. Like you can't melt a tree for example. However the flash point of most sinlicones seem to be quite high.

On old Zenith TVs that had triplers, for example the 25GC45Z chassis (I am sure you've never seen one but I gave the chassis number in case you care to look it up). They used this black silicone on the input wire which carried about 9 KV AC, 70 KJz half sine pumped at 15.734 KHz and had some current behind it and as such was quite dangerous, they used this black silicone that was tough as nails. I had to use the BIG cutters to get enough off to pull the wire out and then practically drill through it with the soldering GUN to get the wire off, and I am talking a Weller 8200 which was 100/140 watts. Sometimes bent the tip getting through that shit.

I imagine that with some of the properties of the "good" silicone made the manufacturing process more expensive so they decided to use a low grade. Look at the application, it is not an insulator and not made to exposed to high voltage or high heat. Why would they use top grade stuff when it is not needed ?

I remember talking with an aircraft engineer as I was working on his PC. We got to bullshitting a bit and he explained that part of what he does is the stress formulae so they can shave off a little material here and there and save some weight. I was not as learned at the time and asked "Why not just make the whole thing out of titanium" and he said it doesn't work that way. One of the main reasons is that it is a bitch to machine.

However my engineer buddy I met a couple years ago does this stuff, actually designed dies and molds to make the impellers for jet engines. Recently he had a gig improving of all things, pain spray heads. He was surprised to find out how involved it is. they had a falling out and I think he is going to wind up doing contract work for Alcoa next but, the things he told me about what seems like a simple thing were quite interesting.

This is not a can of fucking Rustoleum here. This is what paints new cars and refrigerators or what have you. It is done with the electrostatic process which the charge literally pulls the paint to the piece, there is no overspray. But then this spray head turns at 70,000 RPM. So it is whipping the pain all around and the electrical charge reconcentrates it. Each spray head is thousads of dollars and that company rebuilds them. He redesigned them and made the process a whole lot easier and I think now they manufacture them, using his design. Like I said they had a falling out, he gave them a two week notice and they said don't bother. Probably because he was in a very good position to sabotage them. Not that he would, but how do they know that ?

Back to the subject, I agree, I have never seen any type of silicone melt. I have seen it burn but it take a hell off alot to get it going. But if these things work then they do. Being low grade most likely I would not expect them to last alot longer, but then if you are putting belts for the first time on something that is ten years old who cares ? As long as you don't put a soldering iron to them they will probably work fine.

I can just give it a go. People are just so grateful to find someone who
will look at their old cassette unit, let alone repair it. Tell them its
a trial material and may not last the 30 years of their original. For
this use of silicone, I wonder about its continuing flexing in a dynamic
use, but returning units the bands I've replaced in perhaps 5 years are
fine, its other problems t5hat have emerged.
I usually find silicone rubber ges friable on escessive heating and
then breaks up, rather than melting