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Out-soles
of footwear or other flexing components may suffer cracking due to flexing in
use. Cracks usually develop at points of high surface strain resulting from
the design of the sole pattern, without there are being any cuts due to grit
etc. to initiate them.
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The belt flex tester is designed to flex complete
soles with their patterns intact in a way similar to flexing in actual use.
Tests carried out using it provide a guide to the risk of such cracks
developing during use.
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In this test, test specimens are attached to the
outside of a continuous belt, which is driven round two rollers. The larger
roller drives the belt, while movement of the belt round the smaller roller
provides the main flexing action. The radius of the smaller roller is chosen
to make the flexing either more severe or less severe than in actual use.
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This form of flexing also copies the wear
conditions at each step as it produces a short period of rapid flexing
followed by a longer period when the specimen is not being flexed. A normal
test consists of a number of flexing runs up to a total of 50,000 flexes, with
an examination for cracking at the end of each run.
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The PSI Belt Flex Tester consists of two
rollers on which a flat belt moves. The larger roller, which is the driving
roller, rotates at a desired speed with the help of an electric motor and
V-belt arrangement to give the specified frequency of flexing. The second
roller, which is the flexing roller, rotates with the movement of the belt.
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The flexing rollers are slightly barreled shaped
so as to minimize sideways movement of the belt. A hand wheel is attached to
the front end of these rollers to enable the belt to be moved by hand. The
equipment is supplied with three flexing rollers, one for normal soles, the
second for very flexible soles, and the third for very hard soles.
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The distance between the two rollers can be
adjusted with the help of a screw arrangement to enable the belt to be mounted
over different flexing rollers and to allow for small differences in belt
length. This is done by turning a hand wheel on the side of the tester.
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The tester is provided with an acrylic front
cover and a sheet metal safety guard, which allows adequate circulation of
cooling air round the test specimens during the test. The motor can be started
only when the acrylic cover is closed.
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A six digit pre-set type electronic counter with
memory backup and an inductive sensor are provided to record the total numbers
of cycles completed by the belt and thus the number of flexes undergone by the
test specimens mounted on it. The motor stops automatically on completion of
the set number of flexes.
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The apparatus is finished in grey hammertone
stoving painting and bright chrome / zinc plating to give it a corrosion
resistant finish.
