The Barcol #935 impresser is identical to the #934 instrument but uses a softer pressure spring. Readings from the 935 impresser are approximately double those recorded by the 934 gauge whist surface penetration and damage is halved. This is particularity useful on lightweight GRP composites where the higher point pressure of the 934 gauge makes it is easy to penetrate gelcoat layers into air voids beneath.
As a guide, using the 935 gauge optimally cured polyester layup or gelcoat resins should give Barcol Hardness readings of approximately 80 ~ 85 at 20 °C. (See manufacturer's data sheets for specific information.) Under-cured resins provide lower mechanical strength than optimally cured examples and are more likely to distort at elevated temperatures. Moisture absorption will also be higher.
Kit includes the Barcol Impresser, two spare indenter points, test disks, wrench and detachable foot all housed in a foam lined carry case. The photographs show the actual instrument offered for sale.
See details of the Barcol #934 and #936 impressers for use on other materials.
Please note that hardness readings from plastics will vary with temperature, dropping significantly as the Glass Transition Temperature (Tg) is approached. Hardness should be measured with the gauge and specimen at 20 °C unless otherwise specified. Surface temperature can be measured with an infra-red thermometer.
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