Heat Resistance of Plastics: Overview

  • Plastics have important heat resistance properties.
  • Temperature resistance is measured using:
    • Vicat Softening Temperature (VST)
    • Heat Deflection Temperature (HDT)
  • Both methods use an oil bath heated at a defined temperature increase over time.
  • The device measures the temperature at which:
    • A specific deflection (HDT) or
    • A specific indentation depth (VST) is reached, as defined by relevant standards.

Standards Complied with by VICAT / HDT Testers

  • ISO 2507: Thermoplastics pipes and fittings — Vicat Softening Temperature
  • ISO 75: Heat Deflection Temperature (HDT)
  • ISO 306: Vicat Softening Temperature
  • ASTM D1525: Vicat Softening Temperature of Plastics
  • ASTM D648: Deflection Temperature of Plastics Under Flexural Load (Edgewise Position)

Vicat Softening Temperature (VST) – ISO 306

  • Measures the temperature at which an indenter penetrates the plastic sample to a depth of 1 mm.
  • Procedure:
    • Plastic sample placed in holder under a predefined weight.
    • Sample is lowered into heated oil bath.
    • Oil is heated at a defined rate.
    • Temperature is recorded once 1 mm penetration is achieved.

Test Methods Defined in ISO 306:

  • Method A 50: 10 N weight, heating rate of 50 K/h
  • Method A 120: 10 N weight, heating rate of 120 K/h
  • Method B 50: 50 N weight, heating rate of 50 K/h
  • Method B 120: 50 N weight, heating rate of 120 K/h

Heat Deflection Temperature (HDT) – ISO 75

  • Indicates material behavior under flexural load at elevated temperatures.
  • Applicable for:
    • Thermoplastics
    • Hard rubber
    • Duroplastic laminates

Test Procedure:

  • Sample is placed in a 3-point bending fixture.
  • Loaded with a defined weight (per Standard).
  • Heated in an oil bath at 120 K/h.
  • HDT is the temperature where deflection reaches specified limit.

Deflection Standards:

  • ISO: 0.2% increase in flexural strain.
  • ASTM: Absolute deflection of 0.25 mm.

Specimen Orientation:

  • Standards specify specimen position: flatwise or edgewise.

Flexural Stress Levels (ISO 75):

  • Method HDT A: 1.8 MPa
  • Method HDT B: 0.45 MPa
  • Method HDT C: 8.0 MPa

Flexural Stress Levels (ASTM D648):

  • 1.82 MPa and 0.455 MPa
  • For duroplastic laminates: 1/1000 of flexural Young’s modulus

BAYERTEQ HDT / VICAT Model A

  • Model A features:
    • 3, 4, 5, or 6 testing stations
    • Each station equipped with individual temperature measuring points.
Number of test stations3, 4, 5 or 6
automatic weight loading
Lifting of the test stations automatic
Controltouchscreen or Pc control
Room temp– 300 °C
Heating rate120°C/H or 50°C/H
Heating rate accuracymax 1% / 6 min
Temperature accuracymax 0,5 °C
Number of temperature measuring pointsfor each station an individual measuring point
Thermal expansion coefficient of test stations 0,005 mm / 100 °C
Deformation measuring devicedigital gauge with interface
Span of sample supports64 mm, 100mm
Max deformation measuring error0,005 mm
Mediummethyl silicon oil
Coolingnatural cooling
Equipped with temperature protective circuit
Software included
Power supply 220 V, 50 Hz

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