MTS Series 653 High-Temperature Furnaces - Manual (Page 33)

Achieving a Low-Temperature Gradient
Series 653 High-Temperature Furnace Operation 33
Achieving a Low-Temperature Gradient
Several factors affect the specimen thermal gradient. To establish and ensure
temperature uniformity, some experimentation should be done prior to
performing a test.
The following factors should be considered:
• Position of the heater element.
• To minimize chimney effect, make sure that the insulation inserts closely fit
the specimen geometry.
• Reduce excessive water flow through the extensometer heat shield and through
the extensometer and grips. However, do not reduce the water flow below the
requirements of each water cooled device. Each water cooled device that may
be used with the furnace has minimum requirements for flow, pressure, and/or
constant cooling water temperature. Refer to the specifications for each water
cooled device. The grip water cooling manifold has flow switches that will
shut off the furnace if cooling water drops below a safe level.
• The furnace should be situated in a controlled environment which is free of
drafts and temperature changes.
• The position of the feedback thermocouple affects how close the furnace
tracks the programmed temperature setting. Positioning the thermocouple
on the specimen provides the most accurate specimen temperature reading.
• The temperature reading near the heating element may not be the same as
the temperature reading near the specimen. This is due to the thermal losses
caused by the process of radiating heat between the heating elements and the
specimen.
• Deteriorated thermocouples can produce inaccurate readings.