Originally Posted by
Eclectus
Okay, you're right. Applying pressure, such as using a C-clamp does, however eliminate the void spaces between tire and patch, which will improve the seal and bond-strength. If you repair on the road, inflating the tube against the tire casing generates similar high pressure. It's physics. It may be unnecessary. It can't hurt for at-home repairs. I used to patch on road, no problems, but replacing with a fresh tube is faster, then repairing at home at my convenience has been fine.
On the "glue", I don't think it is actually dissolving the butyl, as occurs with styrene model airplanes and toluene-solvent cement, which is a "chemical weld". For example, if this were the case, when you apply the compound to the tube, the ridge should soften. I've never seen this happen.
You are correct that the solvent isn't involved in the process. That's why you
have to let it evaporate. The solvent keeps the cold vulcanization from occurring. If you rush the job, you end up with a poor bond and a patch failure. That's the reason so many people can't patch a tube. They try to get the whole job done in 30 seconds which is not nearly enough time.
The process of cold vulcanization is about chemistry, not physics. The vulcanizing agent forms a chemical bond between the rubber of the tube and the rubber of the patch. Properly dried, the bond between the two pieces of rubber is nearly instantaneous and completely irreversible. Pressure isn't needed because the process doesn't require pressure to make a better bond. Hand pressure is more then enough to hold the pieces together when the process starts and once started, it will go on it's own. Try peeling a patch off if you get it in the wrong spot even without pressure. It won't come off.
I agree that patching on the road is not optimal. I don't do it unless I absolutely have to...see my post about 27 flats
By the way, physics gets waaaay too much credit for the universe. It's all chemistry. Without chemistry to make the stuff that physicists play with, you couldn't have physics
