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The ability of rubber products to withstand repeated flexing without
developing cracks is of prime importance where such products are used in
conditions undergoing repeated flexing.
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Flexing endurance of rubber products is determined by simulating in the
laboratory the action of flexing repeatedly under standard conditions of
speed, mode, and degree of flexing.
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One of the accepted procedures for determination of flexing resistance makes
use of a De Mattia flexing tester. This tester provides useful information
about the resistance of compounds of vulcanized rubber to flex cracking when
subjected to flexing. Cracks develop in that part of the surface where
stresses are set up during flexing, or if that part of the surface initially
contains a crack, cause this crack to extend in a direction perpendicular to
the stress.
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The PSI De Mattia Flex Tester consists of a set of grips to hold test
specimens in two tiers with their holding faces lying in the same vertical
plane. The flexing and unflexing action is provided by holding one end of
the test specimens in a fixed grip and the other end in a reciprocating
grip.
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The set of grips has two fixed grips and one large reciprocating grip
positioned between them in order to flex half of the test specimens while
the other half are being unflexed. The reciprocating grip is fitted with
gunmetal bushes, which slide on hardened and ground rods made of high carbon
steel. The reciprocating motion is provided by an eccentric and linkage
mechanism driven by an electric motor through a V-belt and pulleys.
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A six digit electronic counter with reset and memory backup is provided for
indicating the number of test cycles undergone.
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The equipment is built on a rigid metallic base plate and finished in grey
hammertone stoving painting and bright chrome / zinc plating to give it a
corrosion resistant finish.
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The standard model of the tester is designed to test up to six test specimens
at one time. A special model capable of testing up to twelve test specimens
at a time can also be offered against specific enquiries.
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Moulding dies for preparing test specimen and jig and punch assembly for
making initial crack in test specimens for crack growth test are available
as optional accessories.
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A special model of the tester, which can test up to twelve rubber specimens at
elevated temperature, is also available. In this model the grips of the
tester are placed inside a double walled oven having a front door fitted
with toughened glass. The inner walls of the oven are made of aluminium
sheet while the outer ones are of CRCA mild steel sheet. The space between
the walls is filled with mineral wool for insulation. An electric heating
element is provided for heating the air in the oven. An air-circulating fan
for uniform temperature distribution in the oven is also provided. The
temperature of the oven is controlled and indicated by a digital temperature
controller cum indicator.
