Maya Ellison
Heat deflection temperature (HDT) is a measure of a plastic's ability to withstand high temperatures without deforming. This property is essential in determining a plastic's suitability for various applications, particularly in engineering, design, and manufacturing. HDT is measured by applying a specific load to a plastic sample and gradually increasing the temperature until the sample deflects by a predefined amount, typically 0.25 mm. While HDT does not account for long-term exposure, it is a critical parameter in selecting the right plastic for specific applications, ensuring the material maintains its shape and rigidity under high-temperature conditions. Various plastics offer different heat resistance properties, with some, like polyetheretherketone (PEEK), capable of retaining their mechanical properties at temperatures above 250°C (482°F).
| Characteristics | Values |
|---|---|
| Other Names | Deflection temperature under load (DTUL), heat deflection temperature under load (HDTUL), heat distortion temperature (DTUL) |
| Definition | Temperature at which a polymer or plastic sample deforms under a specified load |
| Test Procedure | Specimen is loaded in three-point bending in the edgewise direction, with outer fiber stress of 0.455 MPa or 1.82 MPa, and temperature increased at 2 °C/min until specimen deflects 0.25 mm |
| Standard Measuring System | ASTM D 648, comparable to ISO 75 |
| Sample Size | 127 x 13 x 12 mm |
| Sample Deflection | 0.25 mm |
| Flexural Stress | 0.46 MPa (67 psi) for soft plastics like polyethylene (PE), low-density PE, and general-use polymers |
| Importance | Determines plastic's ability to remain rigid and maintain its shape under high temperatures and constant loads, essential for engineering, design, and manufacturing of plastic products |
| Heat-Resistant Plastics | Continuous-use temperature above 150°C (302°F) or short-term exposure resistance of at least 250°C (482°F) |
| Amorphous vs Semi-Crystalline Plastics | Amorphous plastics slowly soften with increasing temperature and do not have a defined melting point; semi-crystalline plastics have a sharp melting point |
| Examples of Heat-Resistant Plastics | Polyetherimide (PEI), polyether ether ketone, PTFE, Ultem, PEEK, PerFORM stereolithography resin, Accura 5530 |
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What You'll Learn
- Heat deflection temperature HDT is a test to determine the temperature at which plastic will deform under a predefined load
- HDT is valuable for the engineering, design, and manufacturing of plastic products
- HDT is a polymer property that determines its ability to remain rigid and maintain its shape under high temperatures
- HDT is sensitive to stress experienced by the component, which is dependent on the component’s dimensions
- HDT is not the only measure of a plastic's heat resistance. Glass Transition Temperature (Tg) and Continuous Use Temperature (CUT) are also important
Heat deflection temperature HDT is a test to determine the temperature at which plastic will deform under a predefined load
Heat deflection temperature (HDT) is a test that determines the temperature at which a plastic sample will deform under a specified load. This test is crucial for the design, engineering, and manufacturing of products containing thermoplastic components. The HDT value is influenced by the plastic's composition, dimensions, and stress history.
The standard test method for HDT is ASTM D648, which involves a three-point bending test on a specimen in the edgewise direction. The specimen is heated at a rate of 2°C/min until it deflects by 0.25 mm, which is considered an arbitrary value with no particular physical significance. This deflection is measured under a specified load, typically with an outer fiber stress of 0.455 MPa or 1.82 MPa. The HDT value is then recorded as the temperature at which the specimen deflects by the specified amount.
A plastic with a high HDT will maintain its rigidity at higher temperatures, while a low HDT plastic will not. For example, polypropylene begins to lose strength at 82°C, while polyethylene can withstand temperatures up to 130°C. This makes HDT a critical factor in choosing the right plastic for a particular application.
It is important to note that HDT does not account for the long-term effects of sustained high temperatures on the plastic. Other measures, such as the glass transition temperature (Tg) and continuous use temperature (CUT), are also considered when evaluating a plastic's heat resistance. These measures provide insights into the plastic's mechanical properties and long-term performance under different temperature conditions.
By understanding the HDT and other heat resistance characteristics of plastics, manufacturers can make informed decisions about the suitability of different materials for specific applications, ensuring the final product meets the required performance standards.
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HDT is valuable for the engineering, design, and manufacturing of plastic products
Heat deflection temperature (HDT) is a critical factor in the engineering, design, and manufacturing of plastic products. It refers to the temperature at which a plastic sample deforms under a specific load. This property is essential for maintaining the shape and rigidity of plastic products under high-temperature conditions.
HDT is particularly relevant in industries where plastic products need to withstand heat and pressure without warping or deforming. For example, in packaging, containers must be stacked, squashed, and sometimes exposed to heat without losing their shape. Similarly, vehicle parts like dashboards must be able to withstand direct sunlight without sinking when weight is placed on them.
The HDT of a plastic material is determined through a standardised test procedure outlined in ASTM D648, which involves heating, loading, and measuring the sample's deflection under stress. This information is crucial for engineers and designers when selecting the most suitable plastic material for a specific application.
Additionally, HDT plays a significant role in the manufacturing process, especially in injection moulding. It helps determine the process cycle time and the suitability of a plastic for structural components. Manufacturers can also use resins with higher HDT to achieve faster moulding processes while maintaining dimensional stability.
In summary, HDT is invaluable for the engineering, design, and manufacturing of plastic products. It ensures that plastic components can withstand the desired temperature and pressure conditions without deforming, thereby enhancing the performance and functionality of the final product.
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HDT is a polymer property that determines its ability to remain rigid and maintain its shape under high temperatures
Heat deflection temperature (HDT) is a critical property of polymers that determines their ability to maintain rigidity and shape under high temperatures and constant loads. It is the temperature at which a polymer or plastic sample begins to deform under a specified load. A material with a high HDT will remain rigid at higher temperatures, while a low HDT material will not. This property is particularly important when selecting materials for engineering, design, and manufacturing processes, especially when using thermoplastic components.
The HDT of a material is determined through a standardised test procedure, such as the American Society for Testing and Materials (ASTM) D 648 or the ISO 75 international standard. The test specimen, typically a bar with specific dimensions, is subjected to a three-point bending test in the edgewise direction. The outer fibre stress used for testing can be either 0.455 MPa or 1.82 MPa, and the temperature is increased at a rate of 2 °C/min until the specimen deflects by 0.25 mm. This deflection value is arbitrary and has no particular physical significance.
The HDT is an essential consideration when choosing a plastic for a specific application. For example, if a product needs to maintain its shape and size under high temperatures, selecting a plastic with an appropriate HDT is crucial. Additionally, HDT is a deciding factor in determining whether a plastic is suitable for use as a structural component, as these components must withstand high temperatures without deforming.
Some plastics, such as polypropylene, begin to lose strength at relatively low temperatures. For instance, polypropylene's strength starts to diminish at 180°F (82°C). On the other hand, polyethylene can withstand higher temperatures, maintaining its integrity up to 266°F (130°C). However, even "high-heat" polycarbonate has a limited temperature range, with a rating of 284°F (140°C). These variations in HDT values among different plastics highlight the importance of selecting the appropriate material for specific applications.
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HDT is sensitive to stress experienced by the component, which is dependent on the component’s dimensions
The heat deflection temperature (HDT) is a measure of the temperature at which a plastic sample deforms under a specified load. It is an important factor in the design, engineering, and manufacturing of products with thermoplastic components. HDT is a polymer property that determines a plastic's ability to remain rigid and maintain its shape under high temperatures and constant loads.
The HDT of a material is influenced by various factors, including the component's dimensions and the stress experienced by the component. The dimensions of the component play a crucial role in determining its HDT. The standard specimen used for HDT testing has specific dimensions, typically 127 x 13 x 12 mm, and deflects by 0.25 mm under a specified load. This deflection value is selected arbitrarily and does not hold any physical significance. However, the HDT value can vary depending on the thickness of the specimen, as thicker samples may contain a temperature gradient.
The stress experienced by the component can also impact its HDT. This stress is dependent on the component's dimensions and can affect the deformation behaviour of the material. When a plastic part is injection-molded, it is considered "safe" to remove from its mold when the temperature is near or below the HDT. This ensures that the deformation of the part remains within acceptable limits after removal.
In addition to the component's dimensions and stress, other factors such as printing specifications can influence the HDT of plastics. For example, in 3D printing, the light power, wavelength, energy dosage, and printing orientation can affect the HDT values of the printed resins. These variables can impact the mechanical properties of the plastic, including its stiffness and rigidity. Therefore, it is important to consider the component's dimensions and the associated stress when determining the HDT of a plastic material.
Overall, the HDT of a plastic material is sensitive to the stress experienced by the component, which in turn depends on the component's dimensions. This relationship between HDT, stress, and dimensions plays a crucial role in understanding the deformation behaviour of plastics under high temperatures and specified loads.
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HDT is not the only measure of a plastic's heat resistance. Glass Transition Temperature (Tg) and Continuous Use Temperature (CUT) are also important
Heat deflection temperature (HDT) is the temperature at which a plastic sample deforms under a specified load. However, HDT is not the only measure of a plastic's heat resistance. Glass Transition Temperature (Tg) and Continuous Use Temperature (CUT) are also important factors to consider.
Glass Transition Temperature (Tg) is the temperature at which the physical properties of plastics change from a glassy or crystalline state to a rubbery or molten state. Tg is typically applicable to wholly or partially amorphous plastics, and the value of Tg depends on the strain rate and cooling or heating rate. Amorphous polymers, such as polystyrene (PS) and polymethyl methacrylate (PMMA), are used in their glassy state well below their Tg. Semi-crystalline polymers have both crystalline and amorphous regions, and the amorphous regions will exhibit the same transition as amorphous polymers. However, the crystalline regions retain their structure, providing stability to the bulk material.
Continuous Use Temperature (CUT) is the maximum ambient service temperature that a material can withstand while maintaining 50% of its initial physical properties after long-term service, defined as 100,000 hours of service or approximately 11 years. CUT is important for designers, engineers, and users to consider during the design phase, as it helps with initial material selection and predicting the lifespan of a part. The base material polymer structure affects the CUT, and additives and reinforcements can also impact the maximum CUT value.
While HDT is a critical factor in the design, engineering, and manufacturing of products with thermoplastic components, Tg and CUT also play significant roles in understanding the heat resistance and long-term performance of plastics. Tg affects polymer moldability and characteristics such as tensile strength and transparency, while CUT provides information about the maximum temperature a material can withstand over an extended period. Therefore, when considering the heat resistance of plastics, it is essential to look beyond just HDT and also take into account the Tg and CUT values.
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Frequently asked questions
Heat deflection temperature (HDT) is the temperature at which a plastic sample deforms under a specified load.
The standard measuring system for HDT is the American Society for Testing and Materials (ASTM) D 648. The test specimen is loaded in three-point bending in the edgewise direction. The temperature is increased at 2 °C/min until the specimen deflects 0.25 mm.
Polypropylene begins to lose strength at 180°F (82°C).
