EXPERIMENT – 9
HEAT DISTORTION TEMPERATURE
AIM: To determine the temperature at which an arbitrary deformation occurs when plastics
are subjected to an arbitrary set of testing conditions, in accordance with ASTM D 648.
PRINCIPLE:
A bar of rectangular cross section is tested as a simple beam with the load applied at its center
to give maximum fibre stress of 455 kPa or 1820 kPa. The specimen is immersed in a heat
transfer medium with a means of raising the temperature at 2 ± 0.20C/min. the temperature is
recorded when the test bar has deflection 0.25 mm, which is the HDT of the test specimen.
SIGNIFICANCE AND USE:
This test is particularly suited to quality control and research and development work and
ranking materials for short term heat resistance.
APPARATUS:
The equipment essentially consists of the following:
Immersion bath: for heat transfer liquid with stirrer and heaters with controller to permit
manual or automatic control of temperature raise at a uniform rate of 2 ± 0.20C/min.
Heat transfer liquid: Liquids such as silicone oil, mineral oil shall be used as heat transfer
media. The liquid chosen should not affect the material being tested.
Specimen supports: A suitable stand with two metal supports for the specimen which is 100
mm apart, allowing load to be applied on top of the specimen vertically and midway between
the supports
Deflection measurement device: A dial gage or any other device capable of measuring
differences of 0.01 mm or better may be used.
Temperature measuring device: A thermometer or thermocouple adequate to cover the range
being tested may be used.
Weights: A set of weights of suitable sizes so that the specimen can be loaded to a maximum
fiber stress of 1820 or 455 ± 2.5 % kPa. The weight of the rod and force exerted by the spring
or dial gage is determined and included as part of the total load.
The load is calculated using the equation:
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P= 2Sbd2/3L and P’ = P/9.80665 …………..(1)
Where,
P = load, N
S = maximum fiber stress in the specimen, N/mm2
b = width of specimen, mm
d = depth of specimen, mm
L= width of span between supports, mm
and P’ = load in kgf, when P is in N
TEST SPECIMEN:
The dimensions of test specimen shall be 127 mm in length, 13 mm in depth by any width
from 3.17 to 13 mm. test at least two specimens from each sample and report the average
value.
PROCEDURE:
• Measure the depth and width of the test specimen.
• Place the specimen on specimen support assembly with its 13mm dimension vertical.
• Immerse the assembly in oil bath.
• Place the thermometer such that the bulb of the thermometer should be within 3.2mm
distance from the specimen and does not touch it. The bath temperature should be
about room temperature at the start of test, unless previous tests have shown that for
the particular material under test, no error is introduced by starting at a higher
temperature.
• Adjust the load as calculated using equation (1).
• 5 minutes after applying the load, set the dial gage to zero. Switch on the heater and
stirrer. This waiting period may be omitted when testing materials that show no
appreciable creep during the initial 5 min.
• Record the temperature when the indicator reads 0.25 mm deflection which is the
HDT of the test specimen at the specified fiber stress.
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OBSERVATIONS:
Sl. No. Material Depth Width Fiber Load Rate of raise
(mm) (mm) stress, used (kg) of temperature HDT
(kPa) (0C/min) (0C)
RESULT:
The Heat Distortion Temperature (HDT) of ____________ material is __________ 0C
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