Re: Heat -shrinking caps for cordage


Garth Fletcher
 

Common forms of "heat shrink tubing" are designed to shrink down
to 1/2 their original diameter when heated to 250-350F (depending
on the material). When heated they soften slightly and shrink greatly
in diameter but only slightly in length; when cooled they become once
again firm rather slippery plastic, now with a somewhat thicker wall.

The most common and inexpensive kinds are made of polyolefins and are
available in a variety of colors, including clear. One can also get
specialized forms using Kynar, silicone, Teflon, and other materials
for special conditions. I've long used a Teflon version to line
the flexible ear-pieces on my metal rim glasses, Teflon being chosen
because it is biologically inert.

In my experience it is fairly easy to slide a shrunken tube off of a
soft material - the tension during shrinkage is quite low so it only
slightly compresses the cord you are shrinking around. If you are
shrinking around a knot or splice, the most common use, the shrunk tube
will be mechanically locked in place, but when shrunk around a smooth
section of cord, such as the end of a shoelace, it would be quite
likely to slip off.

There are "adhesive lined" versions which include an inner adhesive coating
which becomes semi-liquid at the shrinking temperature. The intent
is to "encapsulate", waterproof, and bond to the thing being shrunk around.

This form might be especially suitable for cords because the liquid inner
coating would penetrate and bond to the fibers... Coated tubing is most
often seen in black, but there isn't any reason to assume that a clear
or colored version could not be found.

Digi-Key (http://www.digikey.com), and many others, carry a variety
of heat shrink tubing, including adhesive lined versions.

Occasionally I've used a different expedient - coat the object with
epoxy ("Devcon 5-Minute Epoxy", etc.), slide over regular heat shrink tubing,
and shrink it. The shrinking heat also helps accelerate the epoxy's cure...

In my 30+ years of using heat shrink tubing I've successfully used just
about every type of heat source imaginable, but hot air guns certainly do
the best job with the least risk. The sooty flame from cigarette lighters
tends to discolor the tubing, but a small butane torch or flame from a gas
stove, used with care, will serve quite well.
--
Garth Fletcher, President, JacqCAD International
288 Marcel Road, Mason, NH 03048-4704
(603) 878-4749 fax: (603) 878-0547
JacqCAD MASTER website: www.JacqCAD.com

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