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Stronger rubber cement?
On 2017-01-03 18:47, David Scheidt wrote:
John B. wrote: :On Tue, 03 Jan 2017 17:04:40 -0800, Joerg :wrote: :Gentlemen, : :Is there something stronger than the usual rubber cement in the patch :kits? Ideally something that won't dry out so fast or where multiple :cheap small tubes are available. : :The reason is that I sometimes have larger holes from side wall :blow-outs. Not inch-long gashes but one or two tenths of an inch long. :The tubes I use are super thick and, therefore, expensive. $15-20 each :and that's not something to be thrown out lightly. Instead of the li'l :REMA patches I need to use thicker rubber from an older sacrified tube :but this has to be vulcanized/cemented really well. :My LBS usually has small sealed tubes of glue. When I see them I buy :four or five and when I open a sealed tube, in the kit on the bike, I :replace it with another sealed one as find the glue has dried up is :not quite so much of a catastrophe at home :-) :Or you might try contact cement what I suspect is what is in the usual :tire patching kit. :By the way, "vulcanizing" implies the use of heat, and sulphur, and I Vulcanizing may have the connotation of involving heat, but it's a chemical reaction, which results in the sulphur in the rubber becoming crosslinked. That's how I also remember it. ... Patches, at least the good ones such as Rema and park, are a multi-layered assembly. The top layers are for strength, the bottom (closest to the tube) consists of unvulcanized rubber, mixed with a vulcanizing ultra-accelerator (there are a number of zinc thiols that are suitable, which ones are used are trade secrets. ZDDP is typical, though). vulcanizing cement consists of a unvulcanized rubber particles, a solvent to carry them, and a vulcanizing activator. Cyclohexylamine is common, but there are others that will work, and are less toxic. The activator reacts with the zinc thiol, and causes the patch, the rubber in the cement, and the surface of tube to become vulcanized. There's not much free sulphur in the tube, because it's vulcanized, which is one of the reasons that it's important to properly scarify the tube surface before patching; it greatly increases the surface area of the patch. The reaction is not instant, but it happens pretty fast at room temperature, and continues for some time, until all the sulphur available has linke.d Ever since I began using REMA patches and the cement that comes with them my result were less stellar than in Europe with the classic kits. Those contain much thicker patches that looked like round chunks of tube, sometimes slightly beveled. Can't find those here in the US. Currently I have two tubes of the thick expensive kinds where REMA patches partially came off after test-inflating outside the tire. Despite being very diligent with sanding and applying. The accelerator in the cement is one reason that tubes of glue sometimes are just rubber, and not cement. The question is why would be the good ones to buy? I am usually only doing tube repairs at home, carrying thinner spare tubes for the road. Except when helping other riders which is the only reason I even carry a patch kit. -- Regards, Joerg http://www.analogconsultants.com/ |
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