What Is Dimensional Stability Of Engineering Plastics?

August 05, 2024

What is the dimensional stability of engineering plastics?

Low IQ: warping, deformation, can not be installed, cracking, poor quality, and the following six points ......

High IQ: engineering plastics from parts processing, assembly, product application process, due to processing, the environment and a series of external conditions, will have an impact on the entire life cycle, the product from the material to the parts, whether the function is good operation. The most commonly affected by dimensional stability is the size of the part, due to high humidity or extreme temperature environment, resulting in material expansion or contraction.

Furthermore, even if the part is not exposed to particularly harsh operating environments, when machining parts to precision tolerances, the process is subjected to a great deal of mechanical stress! SO, it is important to consider the dimensional stability of the material.

Schematic diagram of precision plastic parts assembly

How to assess the dimensional stability of engineering plastics?

It can be judged from the following aspects:

Coefficient of Thermal Expansion (CTE): The coefficient of thermal expansion (CTE) indicates the extent to which a material expands in volume when the temperature changes. A low CTE means that the material has less dimensional change when the temperature changes. Due to their chemical structure, plastic materials will expand and contract thermally to varying degrees. This change in material dimensions can lead to fit and clearance problems and can weaken the mechanical properties of the material over time.

Water Absorption: Engineering plastics expand when they absorb water, which can lead to dimensional changes. Different plastics have different water absorption capacities. Plastics with low water absorption have less dimensional change in humid environments and are therefore more dimensionally stable. In addition, water absorption weakens other properties of the material, such as electrical conductivity and mechanical strength.

Low shrinkage, low water absorption LCP in pr

In the face of environmental humidity, or to cope with long-term submergence, wet or steam and exposure to natural environments, such as applications, it is necessary to consider the plastic parts in its life cycle of exposure to moisture, as well as the concentration and temperature of moisture. For example, nylon Pa6, Pa66 has a high water absorption rate, injection molded out of the hard, boil water and leave it for a few days to soften! Easy to hydrolyze. While materials like PPO, PEEK, LCP have lower water absorption, hit out so hard, put in water or hard.

PPO in water treatment wet environment applic

Internal Stress: Internal stresses generated during the injection or molding process can affect the dimensional stability of the material, deform the material, and in severe cases, crack it, inject it out well and then crack it the next day, and in some cases even worse, crack it after delivery. Internal stresses may cause the material to deform or warp during cooling. This is because plastic molecules are cooled from the outside in. Internal stresses can be reduced by appropriate machining processes (e.g. annealing), which can improve dimensional stability.

Crystallinity: The dimensional stability of semi-crystalline plastics such as PP, PA66, and POM is influenced by their crystallinity. Higher crystallinity usually results in lower coefficient of thermal expansion and higher dimensional stability. Amorphous plastics such as PC, PMMA, PPE, PEI usually have better dimensional stability because of their lower coefficient of thermal expansion.

Application of PC fiber reinforcement in cell

Fillers and modifiers: Adding fillers such as glass fibers and carbon fibers can significantly improve the dimensional stability of the material. Modifiers such as lubricants, heat stabilizers, etc. can also affect the high-temperature stability of the material, appropriate toughening can improve the material stress cracking.

Processing conditions: Temperature, pressure and cooling rate during the injection or molding process can affect the dimensional stability of the final product. Optimizing processing parameters can reduce internal stress and improve dimensional stability.

Injection molding process parameter adjustmen

Environmental conditions: in different temperatures, humidity, outdoor, oily, alcohol and other environmental factors. Physical and chemical properties of materials working under extreme conditions, select corrosion resistance, high and low temperature resistance, hydrolysis resistance and other properties of engineering plastics applications.

How to test the dimensional stability of plastics?

Dimensional Change Test (DCT): Measure the dimensional change of the material under different temperature and humidity conditions.

Thermomechanical Analysis (TMA): Measures the dimensional change of a material during heating.

Differential Scanning Calorimetry (DSC): Used to assess the crystallinity and melting point of a material, indirectly reflecting dimensional stability.

Water Absorption Test (WAT): To evaluate the water absorption and dimensional changes of materials under different humidity conditions.

Through the above analysis of plastic Jun, you should have a preliminary understanding of the specific application of plastic components and the environment, in order to decide to decide how to select materials. Such as sealing components require the material size is extremely stable, because the seal size change may lead to leakage. For some parts that need to be regularly cleaned with steam, chemicals or high temperature liquids, whether it will be deformed due to water absorption, corrosion resistance. Only sophisticated equipment, process technology, plus dimensional stability of engineering plastics, to be able to build a small size, strict error complex parts, such as electrical connectors and test sockets.

Get so complicated, why don't you choose metal?

Reduce weight: plastic specific gravity is light, in aerospace, automotive lightweight can improve fuel efficiency and reduce emissions.

Reduced Costs: Reduced processing costs compared to metal in high volume production.

Design Flexibility: Plastics can be injection molded, extruded, and molded in a variety of ways, which provides greater design freedom.

Chemical resistance: Plastics generally have good corrosion resistance, a huge advantage for parts used in harsh environments.

Wear Resistance, Vibration Damping and Insulation: Plastics have a clear advantage in wear resistance and have good vibration damping and insulating properties, which is a significant advantage in electronic equipment and other applications where vibration damping or electrical insulation is required.

Ease of processing: Engineering plastics can be processed into complex shapes through injection molding, extrusion, etc. without the need for expensive metal processing tools and equipment.

Therefore, to fully assess the dimensional stability of an engineering plastic, a number of the above factors need to be considered and verified through experimental testing. For specific applications, other performance indicators of the material, such as strength, toughness, chemical resistance, etc., also need to be considered to ensure that the most appropriate material is selected.

Author:

Ms. Tina

E-mail:

sales@honyplastic.com

Phone/WhatsApp:

+86 18680371609