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Testing of plastic material for HDT measurements can now be carried out safely

Lloyd Instruments : 30 July, 2006  (Company News)
Testing of plastic material for HDT (Heat Distortion Temperature) and VICAT (a measure of the temperature at which plastic starts to soften rapidly) measurements can now be carried out more safely in the Davenport HDT/VICATPlus instrument from Lloyd Instruments. The tests are carried in a temperature-controlled oil bath, which can rise to a temperature of 300
The testing area consists of 6 independent test stations which allows HDT or VICAT measurements to be made on up to six samples. The weight loading mechanism and test fixture mountings are deigned as a single unit, which is lowered and raised in the oil bath by an electric motor. The assembly moves smoothly up and down on a lead screw to ensure that the mechanism remains exactly horizontal. The bath is completely closed off in both the upper and lower positions.

Electrical heating of the oil bath is carried out completely automatically at 120˚C/hr for HDT measurements and 50˚C/hr for VICAT. Silicon oil is usually used in the bath as a heating medium. This has a flash point of above 300˚C, well above the maximum normally required. Should any tests be carried out at temperatures above 250C, the unit is designed as standard to allow an optional nitrogen blanket to flood the top of the tank, thus excluding oxygen.

Cooling is also carried out automatically, using water circulating round cooling pipes. The test station is interlocked so that it cannot be raised until the temperature of the oil is below 50˚C. An over-temperature safety unit is also fitted which automatically stops the heating and begins cooling in the event of the specified temperature being exceeded.

The instrument can be used as a stand-alone unit or under PC-control using Lloyd InstrumentsNEXYGEN-Davenport control and data analysis software. Test can be carried out to EN ISO 306 and ASTM D1525-98 for VICAT, BS2782 Part 1: Method 120C 1990 for 1/10 VICAT and EN ISO 75-1 and 75-2 and ASTM D648-98C for HDT. Automation of the measurements using NEXYGEN-Davenport software can save time, especially for some VICAT measurements where a delay of 5 minutes is required before the test load is applied. For additional ease of use, the instrument features an automatic weight calculator, which tells the operator which combination of weights from the binary set supplied is required for a particular test.
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