What are the classifications of plastic moulds?

Fri Feb 24 17:25:45 CST 2023

 Classification of plastic moulds

A. Injection molding mold - TV casing, keyboard buttons, electronic products outside, computer peripheral plastic products, toys, household products (the most common application)

B. Air blowing mold - beverage bottles

C. Compression molding mold - bakelite switches, scientific porcelain dishes

D. Transfer molding mold - integrated circuit products

E. Extrusion molding mold - glue tube, plastic bags

F. Thermoforming mold--transparent molding packaging shell

G. Rotational molding mold - soft rubber doll toys

According to the different types of pouring system can be divided into three types of molds.

(1) Big spout mold: the runner and gate are on the parting line, and the product is demolded together when the mold is opened, the design is the simplest, easy to process, and the cost is low, so more people use the big spout system to work.

(2) Fine spout mold: the runner and gate are not on the parting line, generally directly on the product, so it is necessary to design more than one group of spout parting line, the design is more complicated, the processing is more difficult, generally depending on the product requirements and choose the fine spout system.

(3) hot runner mold: the structure of this kind of mold and the fine spout is largely the same, the biggest difference is that the runner is in one or more hot runner plate and hot spout with constant temperature, no cold material demoulding, runner and gate directly on the product, so the runner does not need to demould, this system is also called no spout system, can save raw materials, suitable for raw materials are more expensive, products require high situation, design and processing difficulties, mold Higher cost.

Hot runner system, also known as hot sprue system, mainly consists of hot sprue sleeve, hot sprue plate and temperature control electric box. Our common hot runner system has two forms: single point hot gate and multi-point hot gate. Single point hot gate is to use single hot gate sleeve to shoot molten plastic into the cavity directly, it is suitable for single cavity single gate plastic mold; multi-point hot gate is to branch the molten material into each sub hot gate sleeve and then into the cavity through the hot gate plate, it is suitable for single cavity multi-point feeding or multi-cavity mold.

Advantages of hot runner system

(1) No water spout material, no post-processing, so that the whole molding process is fully automated, saving working time and improving working efficiency.

(2) Small pressure loss. The hot runner temperature is equal to the injection nozzle temperature, which avoids the surface condensation of the raw material in the sprue, and the injection pressure loss is small.

(3) Repeated use of sprues will degrade the performance of plastic, while using hot runner system without sprues can reduce the loss of raw materials, thus reducing the cost of products. With uniform temperature and pressure in the cavity, the plastic parts have low stress and uniform density, and better products can be injection molded than general injection molding system in a shorter molding time under a smaller injection pressure. For transparent parts, thin parts, large plastic parts or high demand plastic parts can show its advantages, and can use smaller models to produce larger products.

(4) Heat nozzle adopts standardized and serialized design, with various optional nozzle heads and good interchangeability. Unique design and processing of electric heating ring can achieve uniform heating temperature and long service life. The hot runner system is equipped with hot runner plates, temperature controllers, etc., with delicate design, various types, easy to use, stable and reliable quality.

◆The shortcomings of hot runner system application

(1) The overall mold closing height is increased, and the overall height of the mold is increased due to the addition of hot runner plates, etc.

(2) It is difficult to control the heat radiation. The biggest fault of hot runner is the heat loss of the sprue, which is a major issue that needs to be solved.

(3) There is thermal expansion, thermal expansion and contraction is a problem to be considered when we design.

(4) The cost of mold manufacturing increases, and the standard parts of hot sprue system are more expensive, which affects the popularity of hot sprue mold.