You are being redirected because this document is part of your ASTM Compass® subscription.
    This document is part of your ASTM Compass® subscription.


    An Improved Guarded Hot Plate Thermal Conductivity Apparatus with Automatic Controls

    Published: 0

      Format Pages Price  
    PDF (440K) 15 $25   ADD TO CART
    Complete Source PDF (2.1M) 91 $55   ADD TO CART


    This paper describes an 8-in. guarded hot plate apparatus constructed according to ASTM Standard C 177–45 but with a number of changes that increase the versatility of the apparatus and permit the securing of thermal conductivity values to ±1 per cent by automatic means.

    These improvements include the use of mica for the insulating spacers and heating core in the hot plate permitting use up to 400 F. A new thermopile consisting of a string of 32 junctions made from chromel-constantan wire was woven across the gap, thus making a thinner and a more sensitive hot plate. Automatic controls were added to keep the heater to guard balance to ±0.004 F. This unit consists of a servo system that continually regulates the power to the guard. The cold plates were constructed with a continuous labyrinth instead of the usual manifold type shown in the ASTM method, and commercial constant temperature water baths were used to hold the cold plate temperature within 0.05 F. A frame was designed to hold the hot plate assembly under a constant pressure of 50 lb per sq ft. The completed apparatus was placed in a temperature and humidity controlled cabinet, with the temperature controlled automatically. With the above changes it was found possible to construct a guarded hot plate apparatus using commercially available equipment that will determine thermal conductivity values to within 1 per cent of those determined at the National Bureau of Standards.

    Author Information:

    Zabawsky, Zeno
    Research and Development Center, Armstrong Cork Co., Lancaster, Pa.

    Committee/Subcommittee: C16.30

    DOI: 10.1520/STP43653S