Forming Large Silicone Hose

Does anyone know how this is done? I am thinking about buying some 2" or 2.25" silicone hose and bending it. I was thinking of marking where you want the bend, then pouring boiling water over the hose to soften it up. Or I could just dunk the section in some boiling water. Then I will bend the hose and shape the bend to be smooth (i.e. no kinks). Then I will dunk that in ice water to quench the silicone to the shape I want. I have no clue if this will work, but figured I could ask around and see if anyone has attempted this. I have heard of people doing this with smaller recirc. hose. Thanks for the input.

Silicone hose can usually withstand high temps, like 350*-500* depending on the hose. Boiling water is 212*. I have never tried it myself, but I would guess that it won't work...

I think it has a "memory effect" so to speak. So it would have to be formed/created/molded into the shape it needs to be. I think it's a manufacturing task.

SciFiMan said:

I think it has a "memory effect" so to speak. So it would have to be formed/created/molded into the shape it needs to be. I think it's a manufacturing task.

Click to expand...

Silicone is moldable post-production. The 'memory' you speak of is orientaition of polymer chains within the silicone. Silicone has a curing temperature which is a function of the polymer chains within it. As you bend the room-temp silicon hose, a level of stress is introduced into the polymer chains. Once a certain temperature is reached (its called the curing temperature I believe), the poymers chains are free to move where they wish (going from a high level of entropy to a low level of entropy), thus relaxing the stresses in the silicone. Once the stresses are relaxed, the part can be quenched and the new orinetation of the polymer chains (i.e. 'memory') is permenant.

That is why hose 'snaps' back after you bend it. When you bend the hose, you increase the level of entropy because the polymer chains are being asked to move when they don't want to. When you release, the chains snap to the lowest level of entropy (i.e. their original position). If you were to hold the hose in the bent position for a long amount of time, the stresses will slowly relax out and it will stay bent permenately. But this could take years. Same reason an old, stretched rubber band will no longer snap back.

DAMN that was a boring post.

You know all that, but not how to form it???? LOL

Everything I stated is theory and science. The process is a delicate one. I don't know if I can get temperatures above the cure temp, unless I steal some 2kW infrared bulbs from work. If I can get the temps I need, it should work just as science says. Places like Samco might just use a plastisizer or something.... I dunno the most efficient way of doing this. If you dunk hard PVC pipe in a bucket of plastisizer it will be flimsy like a shower curtain.

I want a silicone hose turboback exhaust.

I have used this technique to mold PVC pipe although it worked with only moderate efficacy. Some places bend PVC pipe by introducing heated sand inside of the pipe and allowing it to soften the pipe before they bend it to the position they want. Once the desired position is achieved they rapidly cool the pipe in cold water to set the PVC. I also tried heating the pipe with a propane torch and heating it over a stove element.

Of the three techniques, I found the stove element to be the most effective without creating too much heat too rapidly (too high a temp causes the PVC to bubble on the surface. I found that gently rolling the pipe back and forth approx 2 inches above a red hot stove element was effective. Be sure to wear gloves and not to touch the element with the hose.

All of this is to say that it should be fairly easy to bend silicone hose. However, the process takes time, especially if you want the bends to be smooth and if you want to keep the surface of the silicone hose pristine.

Yes the look of the silicone might suck, I dunno how to keep it pretty during the process. I found out that IR bulbs are used to cure silicone, due to their wavelength and intensity. You can heat it up in no time, you just cant look at the bulbs!