The right instrument
The Shore durometer is an instrument used to measure hardness of rubber and plastic. In commerce there are analogical and digital versions each with different variations indicated to work with particular hardness.
Digital and analogical - Which one to choose?
The main differences between analog and digital Shore durometers reside in reading and calibration modes , both closely related . In the first case, reading occurs by a graduated dial where a needle indicates the value given by the spring , generally moving ring nut to value 0th. In the case of digital shore durometers calibration occurs according to procedures involving a double control , to zero and at full scale , for higher accuracy.
The shore A scale is the most commonly used in hardness measurement of thermoplastic elastomers . A value 0th reading indicates that penetrator came up to maximum depth , while a reading of 100th indicates a lack of penetration in the sample . Above 90th Shore A durometers are less reliable . Therefore for harder materials , it’s preferable to use a Shore D durometer , equipped with a sharper penetrator respect to Shore A durometer . For softer plastic elastomers , Shore A hardness less than 5th , is recommend the use of a Shore E.
Shore A, E, D - the differences
United by the same operating principle , Shore durometers differ in relation to probe shape.
Shore A probe has a pyramid trunk , Shore E has an half – sphere and Shore D a sharp element.
The importance of method
In order to get comparable measurements it’s necessary to apply an uniform method for data collecting . Is to establish the unity of time during which the load will be applied on the sample surface , on Shore durometry is generally spoken of load application for 10 seconds .
The longer the time of application , lower the hardness found , because material will be subjected to a more considerable penetration and relaxation stress.
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