Heat Deflection Temperature

property

The temperature at which a polymer specimen deflects a specified distance under a controlled load, measured according to ASTM D648 or ISO 75 standards.

In Simple Terms

Heat deflection temperature tells you how hot a plastic can get before it starts to bend or warp under stress. It's like finding out at what temperature a plastic part will lose its shape when supporting weight or under mechanical load.

Why It Matters

HDT is crucial for resin traders and processors selecting materials for high-temperature applications. It directly impacts part performance in automotive under-hood components, electronics housings, and industrial applications where thermal stability is essential.

Technical Details

HDT is measured by applying either 0.45 MPa or 1.8 MPa stress to a test specimen while gradually increasing temperature at 2°C/min. The test ends when the specimen deflects 0.25mm. Results vary significantly between the two stress levels, with 1.8 MPa typically 20-40°C lower than 0.45 MPa values for the same material.

Real-World Examples

Automotive connector housing selection

A resin trader specifies PPA with HDT >200°C at 1.8 MPa for engine bay connectors, ensuring parts won't deform under hood temperatures and vibration stress.

Electronics enclosure material verification

Quality control tests incoming PC resin lots to confirm HDT meets 135°C minimum at 1.8 MPa for laptop housings that must withstand internal heat generation.

Appliance component grade comparison

A processor compares PP copolymer grades with HDT values of 95°C vs 110°C to select optimal material for dishwasher pump housings exposed to hot water cycles.