How to Quickly Master the Use and Selection of a Heat Deflection & Vicat Softening Point Tester

1. Device Overview: What Does a Heat Deflection & Vicat Softening Point Tester Actually Measure?

The Heat Deflection & Vicat Softening Point Tester (commonly referred to as an HDT/VST tester) is a precision instrument designed to determine the thermal performance of non-metallic materials under load and elevated temperature. It’s essential for evaluating the heat resistance level of a material to determine its suitability for high-temperature environments.

The device integrates two core test functions:

Heat Deflection Temperature (HDT): The temperature at which a test specimen deforms under a specified stress.

Vicat Softening Point (VST): The temperature at which a flat-ended needle penetrates a test specimen to a depth of 1 mm under a specific load.

These measurements are critical for assessing the thermal stability of thermoplastics, thermosetting plastics, electrical insulation materials, and more.

2. Test Process Overview (Including HDT & VST)

HDT (Heat Deflection Temperature) Test Process

Prepare the specimen according to standard dimensions;

Mount it on a three-point bending fixture and apply a specific load (e.g., 0.45 MPa);

Heat at a constant rate (typically 120°C/h);

Record the temperature when the deformation reaches 0.25 mm—this is the HDT.

VST (Vicat Softening Temperature) Test Process

Fix the specimen horizontally in a holder;

Apply a flat-ended needle with a standard weight (e.g., 10N or 50N);

Heat the oil bath at a constant rate;

Record the temperature when the needle penetrates the specimen to 1 mm.

3.Testing Standards Reference

Ensure that the equipment supports the above standards and features automatic temperature control and displacement measurement for accurate results.

4.Key Components Breakdown (What to Look For When Buying)

5. Application Fields and Typical Users

Material R&D Labs: For analyzing thermoplastic and thermoset performance

Quality Inspection Labs: For batch testing, compliance, and reporting

Educational Institutions: For hands-on training and demonstrations

Third-party Testing Agencies: For issuing certified test reports

6. Operation Essentials

Specimen Requirements

Vicat sample: (10 ± 0.2) mm length, (4 ± 0.1) mm thickness

HDT sample: (127 ± 1) mm length, (13 ± 0.2) mm width, (12.7 ± 0.2) mm thickness

Pre-Test Checklist

Calibrate load and temperature sensors

Check oil level and remove residues from oil bath

Set proper heating rate (commonly 50°C/h or 120°C/h)

Post-Test Data Processing

Auto-identify deformation depth or penetration depth

Graphical data visualization (optional)

Auto-generate PDF reports or print results directly

7. Common Issues & Troubleshooting

8. Recommended Brands for HDT/VST Testers

Domestic Brands:

Jinan Jingji, Zttest, Beijing Beiguang, Huaheng

Pros: Cost-effective, fast after-sales, standards compliant

International Brands:

Zwick/Roell (Germany), Instron (USA)

Pros: High accuracy, robust software, ISO-certified

Conclusion: Focus on the Specs That Matter

When selecting a Heat Deflection & Vicat Softening Point Tester, it’s not just about cost. Focus on the specific materials you're testing, how frequently you use the machine, and which standards apply. A well-matched machine ensures accurate data, high efficiency, and long-term compliance for lab and industrial use.