Surface hardness of a cricket bat after ‘knock-in’ |
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Authors: | Prof A T Sayers M Koumbarakis S Sobey |
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Institution: | (1) Department of Mechanical Engineering, University of Cape Town, 7700 Rondebosch, South Africa |
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Abstract: | New cricket bats need to be ‘knocked in’ prior to use, but just what this process does to the surface fibres of the bat is
unknown and unquantified. One quantitative measurement of knock-in is the resultant surface hardness of the bat, and this
paper describes knock-in tests to determine the surface hardness following differing durations of knock-in. The design of
a cricket bat knock-in machine is first described. This takes the form of a cradle in which a cricket bat can be secured horizontally
and then traversed at constant speeds in two mutually perpendicular directions while at the same time being struck with constant
force by a cricket ball. The traverses are driven by lead screws, the motors of which can be independently switched on or
off. The traverse distance can be varied with adjustable limit switches and relays that reverse the direction of rotation
of the lead screws when activated. The cricket ball is attached to a rod that is lifted cyclically by a cam against a coil
spring extension, and then allowed to fall under that force to impact on the bat surface. The impact (knocking-in) force was
measured by a previously calibrated strain gauge attached to the rod holding the cricket ball. By judicious setting of the
limit switches, selected areas of the bat surface were continuously knocked in for periods varying from 1 to 4 hours. After
knocking in, the surface hardness was measured in accordance with British Standard 373 using a penetrator designed in accordance
with the same standard. Analysis of the load/penetration curves shows an increase in surface hardness with knock duration.
Photographs of the cell structure of the surface wood, obtained using a scanning electron microscope, show that under knock-in
conditions, the wood cells collapse to form a mesh-like hardened layer which increases in hardness with increase in knock-in
duration. |
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Keywords: | cricket bat knock-in hardness |
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