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What materials do we usually use in injection molding?

November 01,2022

Most of the plastic products we see in our life are finished by injection molding. Different products use different materials.

 So, what materials do we usually use in injection molding?

General basic requirements for injection mold materials are as follows.


1.Easy-to-process injection mold parts are mostly made of metal materials, and some structures and shapes are complicated. In order to shorten the production cycle and improve the efficiency, it is required that the mold materials be easily processed into the shapes and precision required by the drawings.

2.The gloss and precision of the surface of the plastic parts with good wear resistance are directly related to the wear resistance of the mold cavity surface. Especially, when glass fiber, inorganic filler and some pigments are added to some plastics, they flow together with the plastic melt in the runner and the mold cavity at a high speed, causing great friction on the surface of the mold cavity. If the materials are not wear-resistant, they will soon wear out and damage the quality of the plastic parts.

3.High corrosion resistance. Many resins and additives have corrosive effects on the surface of the cavity. This kind of corrosion causes the metal on the surface of the cavity to dissolve and peel off, the surface condition becomes worse, and the quality of plastic parts becomes worse. Therefore, it is best to use corrosion-resistant steel, or to treat the surface of the cavity with chromium plating and cymbal nickel.

4.Good dimensional stability During injection molding, the temperature of the injection mold cavity should reach above 300℃. Therefore, it is best to choose tool steel (heat-treated steel) which has been tempered properly. Otherwise, the microstructure of the material will be changed, resulting in the change of mold size.

5.The impact of heat treatment is small. In order to improve the hardness and wear resistance, generally, the mold should be heat-treated, but this treatment should make its size change very small. Therefore, it is best to use pre-hardened steel that can be machined.

6.Plastic parts with good polishing performance usually require good gloss and surface state, so the roughness of the cavity surface is very small. In this way, the surface of the cavity must be processed, such as polishing and grinding. Therefore, the selected steel should not contain rough impurities, pores, etc.

 

Polystyrene (PS). Commonly known as hard glue, it is a colorless, transparent and shiny granular polystyrene with the following properties:

Good optical performance, excellent electrical performance, easy molding and processing, and good coloring performance. The biggest disadvantages are brittleness, low heat-resistant temperature (the highest service temperature is 60~80 degrees Celsius) and poor acid resistance.

Polypropylene (PP). It is a colorless, transparent or shiny granular material, referred to as PP for short, commonly known as hundred percent soft glue. It is a crystalline plastic. The properties of polypropylene are as follows:

Good fluidity and excellent moldability. Excellent heat resistance, and can be boiled and disinfected at 100 degrees Celsius. High yield strength and good electrical performance. Poor fire safety; Poor weather resistance, sensitivity to oxygen, easy to be affected by ultraviolet rays and aging.

Nylon (PA). It is an engineering plastic, which is made of polyamide resin, referred to as PA for short. There are PA6 PA66 PA610 PA1010, etc. The properties of nylon are as follows:

Nylon has high crystallinity, high mechanical strength, good toughness, high tensile strength and compressive strength. Outstanding fatigue resistance, wear resistance, corrosion resistance, heat resistance, non-toxicity, and excellent electrical performance. Poor light resistance, easy to absorb water, and not acid-resistant.

1.Polyoxymethylene (POM). Also known as Saigang material, it is an engineering plastic. Characteristics and uses of polyoxymethylene:

Polyoxymethylene has a high crystal structure, excellent mechanical properties, high elastic modulus, high rigidity and high surface hardness, so it is called “the competitor of metals”. Small friction coefficient, excellent wear resistance and self-lubrication, second only to nylon, but cheaper than nylon. Good solvent resistance, especially organic solvents, but not strong acid, alkali and oxidant. Good dimensional stability, and can manufacture precision parts. Large molding shrinkage, poor thermal stability and easy decomposition when heated.

2.ABS (propylene moon green-butadiene-styrene). ABS is a kind of high-strength modified polystyrene, which is composed of acrylonitrile, butadiene and styrene in a certain proportion. It is light ivory, opaque, non-toxic and tasteless. Features and uses:

High mechanical strength; Strong impact resistance; Good creep resistance; It has the characteristics of hardness, tenacity and rigidity. The surface of ABS plastic parts can be electroplated, and ABS can be blended with other plastics and rubber to improve its performance, such as (ABS +PC).

3.PC (polycarbonate). Commonly known as bulletproof glass, it is a non-toxic, tasteless, odorless, transparent material, which is flammable, but can extinguish itself after leaving the fire. Features and uses:

It has special toughness and hardness, and its impact strength is the best among all thermoplastic materials. Excellent creep resistance, good dimensional stability and high molding accuracy; Good heat resistance (120 degrees). The disadvantages are low fatigue strength, large internal stress, easy cracking and poor wear resistance of plastic parts.

4.PC+ABS(PC+ABS alloy). The advantages of PC (engineering plastic) and ABS (general plastic) are integrated, and their properties are improved. They contain chemical components of ABS and PC, and have good fluidity and processability of ABS, and PC is resistant to impact and cold-hot cycle changes. Features:

Die design of dispensing nozzle/large nozzle. The surface can be sprayed with oil, electroplating and metal spraying film. Pay attention to surface exhaust. Materials are commonly used in hot runner molds, and have been used in more and more consumer communication products, such as mobile phone cases/computer cases.