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What Is The Principle Of Foam Plastic Injection Molding?

Foamed plastics are based on thermoplastic or thermosetting resins and have numerous tiny pores in their interior. Foaming is one of the most important methods for plastics processing. Foamed plastic foams contain gas-solid two-gas and solids. Gases are present in the foam in the form of foam cells. The cells and cells that are isolated from each other are called closed cells. The communication is called open cell, and thus there is a distinction between closed cell foam and open cell foam. The open or closed cells of a foam structure are determined by the properties of the raw material and its processing technology.

Plastic foam technology has a long history. Foam bakelite, which was first used in the early 1920s, was made using a method similar to the production of foam rubber; rigid polyurethane foam and polystyrene foam appeared in the 1930s; polyethylene, polyvinyl chloride, epoxy resin, and phenolic foam in the 1940s; 50 In the era, there were expandable polystyrene foams and flexible polyurethane foams.

Now, virtually all plastics, including both thermoplastic and thermosetting, can be foamed into foam. Industrial preparation methods include: extrusion foaming, injection foaming, molded foaming, calendering, powder foaming, spray foaming, and the like. Among them, injection foaming is one of the most important molding methods. Here, we focus on injection molding foaming.

Foaming principle

The foaming method of plastics can be divided into physical foaming and chemical foaming according to the different foaming agents used. Here is a brief introduction to the blowing agent.

Foaming agent

The foaming agent can be roughly divided into physical foaming agents and chemical foaming agents. The requirements for physical foaming agents are: non-toxic, odorless, non-corrosive, non-flammable, good thermal stability, no chemical reaction in the gaseous state, and a lower diffusion rate in the plastic melt in the gaseous state than in air Diffusion rate. The commonly used physical foaming agents are air, nitrogen, carbon dioxide, hydrocarbons, freon, etc.;

A chemical foaming agent is a substance that releases gases such as nitrogen, carbon dioxide and the like from heat energy. The requirements for a chemical foaming agent are: the gas released by its decomposition should be non-toxic, non-corrosive, non-flammable, and non-flammable. Forming and physical and chemical properties have no effect, the rate of release of gas should be controlled, and the blowing agent should have good dispersion in plastics. Among the more widely used are inorganic blowing agents such as sodium bicarbonate and ammonium carbonate, organic blowing agents such as azoformamide and azobisisobutyronitrile.


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