About the plastic injection mould design, these knowledge you may not know!
I. Molecular Structure of Plastics
The ain components of plastics are resins, which are natural resins and synthetic resins.
II. Composition of Plastics
1. Resin: The main function is to bind other components of plastics and determine the type (thermoplasticity or thermosetting) and main properties of plastics, such as mechanical, physical, electrical and chemical properties. The proportion of resin in plastics is generally 40-65%.
2. Filler: Also known as filler, correct selection of filler can improve the performance of plastics and expand its application.
3. Plasticizers: Some resins have little plasticity and poor softness. In order to reduce the melting viscosity and melting temperature of resins, improve their processing properties, improve the flexibility, elasticity and other necessary properties of plastics, organic compounds with high boiling point, which are compatible with resins, are usually added. This kind of material is called plasticizer. Plasticization is usually an ester compound with high boiling point liquid nano or melting point solid.
4. Colorant: also known as pigments, mainly plays an aesthetic and decorative role, including two parts of the paint.
5. Stabilizers: Any substance that can slow down the deterioration of plastics is called stabilizer, spectrophotometric stabilizer, thermal stabilizer and antioxidant.
6. Lubricant: Improve the fluidity of plastic melt, reduce or avoid friction and adhesion to equipment or die, and improve the surface finish of plastic parts.
III. PROCESS CHARACTERISTICS OF PLASTICS
Plastics are glassy at room temperature. If heated, they become high elastic state and viscous flow state, so they have excellent plasticity. Many high-productivity forming methods can be used to produce products, which can save raw materials, save man-hours, simplify the process, and have low requirements for artificial technology and easy to organize mass production.
1. Shrinkage rate or shrinkage rate. The shrinkage rate of the supplier must be inquired before the design. The calculated shrinkage rate is used in the design of the mould = the size of the normal temperature mould - the size of the normal temperature plastic parts.
2. Specific volume and compression rate.
3. Liquidity. It is a very important factor in plastic forming. The fluidity of long fur edge, the clearance in design and the depth of air tank should be designed according to the fluidity of different materials.
4. Hygroscopicity, thermal energy and volatile matter content. Some of the absorbent plastics are placed directly in the water after plastic moulding to make it absorb water and then use. Some of the plastics have special moisture absorption properties, with a ratio of 1:100.
6. Stress cracking and melt liquid cracking.
7. Setting speed.
4. Types of plastics:
1. Thermoplastics: The synthetic trees of this kind of plastics are linear or branched-chain polymers, which soften when heated and even become a stable, flowing viscous liquid. In this state, they are plasticized and can be made into plastic parts of a certain shape. After cooling, they retain their existing shape, such as reheating and softening to another shape. It can be repeated many times. In this process, there are only physical changes, but no chemical changes. The changes are reversible. (repeated moulding)
Plastic types: a. Polyvinyl chloride (PVC) production is large, toxic can not be used as food packaging.
B. Polystyrene (PS) is one of the early industrial plastics.
C. Polyethylene (PE) D. Polybine (PP)
E. nylon (PA) F. polyformaldehyde (POM)
G. Polycarbonate (PC) can be used for food packaging and lens.
I. Polyinkstone (PSU) J. Polyphenyl ether (PPO)
K. Fluoroplastics L. Polyester Resin
2. Thermosetting plastics: The synthetic resins of this kind of plastics are bulk polymers, so at the beginning of heating, because the molecule is linear structure with meltability and plasticity, they can be made into plastic parts of a certain shape. When heated continuously, the molecule presents wind-like structure. When the temperature reaches a certain level, the resin becomes insoluble and non-melting body-like junction. The structure fixes the shape and does not change any more. If heated or not softened, it will no longer be available. In a certain process of change, there are both physical and chemical changes, so the process of change is irreversible. (One Forming)
Category: A. Phenolic acid plastics PF
C. Epoxy Resin EP
D. Phenolic plastic (PF), also known as bakelite, is used for electrical switches and thermosetting materials.