Joerg wrote:
: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.
Rema patches in action:
https://scontent.ford4-1.fna.fbcdn.n...bb&oe=58E69CCC
https://scontent.ford4-1.fna.fbcdn.n...9c&oe=58E45D94
That tube is still in service, two years later.
:The question is why would be the good ones to buy?
I use rema f1, which are round and 25 mm in diameter. Box of 100
costs ~20 bucks. A half pint bottle of vulcanizing flouid, which will
do hundreds of patches, and last for years (mine has been in my dsk
for five years) costs ~$10 at an auto parts store (very expensive to
ship, buy local.).
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