Injection mold design, you must know this plastics knowledge!

Injection mold design, you must know this plastics knowledge!
1. Molecular structure of plastic

The main component of plastic is resin, which comes in two varieties: natural resin and synthetic resin.

Second, composition of plastic

1. Resin: The main function is to bind other components of plastic and determine type of plastic (thermoplastic or thermoset) and basic properties such as mechanical, physical, electrical and chemical properties. The proportion of resin in plastic is usually 40~65%.

2. Filler: Also known as filler, choosing right filler can improve performance of a plastic and expand its use.

3.Plasticizer: Some resins have little plasticity and poor flexibility.In order to reduce melt viscosity and melting point of resin, improve its molding characteristics, improve flexibility, elasticity and other necessary properties of resin, generally adding compatible non-volatile high-boiling organic resins to resin connections. Such substances are called plasticizers. Plasticizers are usually ester compounds with high boiling liquids or melting point solids.

4. Dye: Also known as dye, it mainly plays an aesthetic and decorative role, including two parts of paint.

5. Stabilizer. Any substance that can slow down degradation of plastic is called a stabilizer, light-splitting stabilizer, heat stabilizer, and antioxidant.

6. Lubrication: Improve plastic melt flow, reduce or avoid friction and sticking on equipment or molds, and improve surface quality of plastic parts.

Injection mold design, you must know this plastics knowledge!
Three ﹑Specifications of plastics

Plastic is in a glassy state at room temperature. If it is heated, it will go into a highly elastic state and then become a viscous liquid state, so it has excellent plasticity. Many high-performance molding methods can be used to produce products that can save raw materials ﹑Save man hours, simplify process, and have low manual technology requirements, easy to arrange mass production.

1. Shrinkage rate or shrinkage rate. Before designing, be sure to check with supplier for degree of shrinkage. When designing a mold, calculate shrinkage rate = mold size at room temperature - plastic part size at room temperature

2. Specific volume and compression ratio.

3. Liquidity. This is a very important factor in plastic injection molding. Good fluidity contributes to easy burr formation, and clearance and air groove depth during design must be calculated according to fluidity of different materials.

4. Hygroscopicity, thermal energy and volatile matter content. Some water-absorbent plastics are placed in water immediately after formation so that they can absorb water before use. Some plastics are especially hygroscopic (1:100 ratio).

5. Crystallinity.

6. Stress cracking and melt cracking.

7. Speed ​​setting.

Four types of plastic:

1. Thermoplastics: All synthetic trees of this type of plastic are linear or branched polymers so they become soft when heated and even turn into a stable and viscous liquid that can flow. retains its existing shape after cooling and can be softened to a different shape when reheated, so it can be repeated many times. There are only physical changes in this process, but no chemical changes, and these changes are reversible. (Re-molding many times)

Injection mold design, you must know this plastics knowledge!

Plastic types: a) Polyvinyl chloride (PVC) is produced in large quantities, it is toxic and cannot be used as food packaging.

b. Polystyrene (PS) is one of first types of plastic that appeared on an industrial scale.

in. Polyethylene (PE) g. Polypropylene (PP)

for example, nylon (PA) f. polyoxymethylene (POM)

g. Polycarbonate (PC) can be used in food packaging, lenses.


I. Polyink Stone (PSU) j. Polyphenylene oxide (PPO)

K. Fluoroplast l. Polyester resin

N. plexiglass (PMMA)

2. Thermosetting plastics: The synthetic resin of this type of plastic is a body-shaped polymer. Therefore, at beginning of heating, since molecules have a linear structure, they have fusibility and plasticity, and can be molded. into plastic parts of a certain shape. When heating continues, molecules form a wind-like structure, and when temperature reaches a certain level, resin becomes an insoluble and non-melting structure of body, so that shape is fixed and will not change. If it is heated, it will not soften and is no longer safe. In a certain process of change, both physical and chemical changes occur, so the process of change is irreversible. (one-time molding)

Type: A. Phenolic plastic PF

B. Aminoplast

C. Epoxy resin EP

D. Phenolic plastic (PF), also known as Bakelite, is used for electrical switches and is a thermoset material.

For more information about renaming and other shapes, you can follow WeChat Public Account: Plastic Shape Learning