Basic knowledge of the hottest plastic mold

Basic knowledge of plastic molds

1. Introduction

all kinds of tools and products used in our daily production and life, ranging from the base and body shell of machine tools to the shell of embryonic head screws, buttons and various household appliances, are closely related to molds. The shape of the mold determines the shape of these products, and the processing quality and accuracy of the mold also determine the quality of these products. Because of the different materials, appearance, specifications and uses of various products, molds are divided into casting molds, forging molds, die-casting molds, stamping molds and other non plastic molds, as well as plastic molds

in recent years, with the rapid development of the plastic industry and the continuous improvement of the strength and accuracy of general and engineering plastics, the application scope of plastic products is also expanding, such as household appliances, instrumentation, construction equipment, automotive industry, daily hardware and many other fields, and the proportion of plastic products is increasing rapidly. A reasonably designed plastic part can often replace many traditional metal parts. The trend of plasticization of industrial products and daily-use products is rising

2. General definition of mold: in industrial production, various presses and special tools installed on the press are used to make metal or non-metallic materials into parts or products of the required shape through pressure. Such special tools are collectively referred to as molds

3. Injection molding process description: mold is a kind of performance of producing plastic products and using software to protect experiments. The situation is divided into: displacement limiting tool. It is composed of several groups of parts, and this combination has a molding cavity. During injection molding, the mold is clamped on the injection molding machine, and the molten plastic is injected into the molding mold cavity, cooled and shaped in the cavity. Then the upper and lower molds are separated, and the products are ejected from the mold cavity through the ejection system. Finally, the mold is closed for the next injection molding. The whole injection molding process is cyclic

4. General classification of molds: can be divided into plastic molds and non plastic molds:

(1) non plastic molds include: casting molds, forging molds, stamping users in model selection, die-casting molds, etc

a. casting mold - faucet, pig iron platform

b. forging mold - automobile body

c. stamping mold - computer panel

d. die casting mold - superalloy, cylinder block

(2) plastic mold is divided into:

a. injection molding mold - TV shell Keyboard buttons (most commonly used)

b. air blowing mold - beverage bottles

c. compression molding mold - bakelite switches, scientific porcelain bowls and dishes

d. transfer molding mold - integrated circuit products

e. extrusion molding mold - glue tubes Plastic bags

f. thermoforming mold - transparent molding packaging shell

g. rotary molding mold - soft rubber doll toys

◆ injection molding is the most commonly used method in plastic processing. This method is applicable to all thermoplastics and some thermosetting plastics. The number of plastic products produced is beyond the reach of other molding methods. As one of the main tools of injection molding processing, the level of injection mold in terms of quality accuracy, manufacturing cycle and production efficiency in the injection molding process directly affects the quality, output, cost and product renewal of products, At the same time, it also determines the reaction ability and speed of enterprises in market competition

◆ the injection mold is composed of several steel plates and various parts, It is basically divided into:

a forming device (die, punch)

b positioning device (guide post, guide sleeve)

C fixing device (i-plate, die pit)

d cooling system (water hole)

e thermostatic system (heating tube, hair)

F runner system (nozzle hole, runner groove, runner hole)

G ejection system (ejector pin, ejector rod)

5 According to the different types of gating system, molds can be divided into three categories:

(1) large gate mold: the runner and gate are on the parting line, and demould together with the product when opening the mold. The design is the simplest, easy to process, and the cost is low, so many people use the large gate system for operation

(2) nozzle mold: the runner and gate are not on the parting line, but generally directly on the product. Therefore, it is necessary to design a group of nozzle parting lines. The design is complex and the processing is difficult. Generally, the nozzle system should be selected according to the product requirements

(3) hot runner mold: the structure of this kind of mold is roughly the same as that of the fine nozzle. The biggest difference is that the runner is located in one or more hot runner plates and hot pump mouths with constant temperature, and there is no cold material demoulding. The runner and gate are directly on the product, so the runner does not need demoulding. This system is also known as the nozzle free system, which can save raw materials. It is suitable for the situation of expensive raw materials and high product requirements, and it is difficult to design and process, Mold cost is high

hot runner system, also known as hot runner system, is mainly composed of hot runner sleeve, hot runner 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 sprue is to use a single hot sprue sleeve to directly inject molten plastic into the mold cavity, which is suitable for the plastic mold with a single cavity and single sprue; Multipoint hot sprue is to branch the molten material into each sub hot sprue sleeve through the hot sprue plate, and then enter the mold cavity. It is suitable for single cavity multipoint feeding or multi cavity mold

◆ advantages of hot runner system

(1) there is no need for post-processing, which makes the whole molding process fully automated, saves working time and improves work efficiency

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

(3) the repeated use of nozzle material will degrade the performance of plastic, while the use of hot runner system without nozzle material can reduce the loss of raw materials and reduce the product cost. In the mold cavity, the temperature and pressure are uniform, the plastic stress is small, and the density is uniform. Under a small injection pressure and a short molding time, the injection molding system can produce better products than the general injection molding system. For transparent parts, thin parts, large plastic parts or plastic parts with high requirements, it can show its advantages, and can produce larger products with smaller models

(4) the hot nozzle adopts standardized and serialized design, and is equipped with various nozzle heads for selection, with good interchangeability. The electric heating ring with unique design and processing can achieve uniform heating temperature and long service life. The hot runner system is equipped with hot runner plate, temperature controller, etc., with exquisite design, various types, convenient use, stable and reliable quality

◆ deficiencies in the application of hot runner system

(1) the closing height of the overall mold is increased, and the overall height of the mold is increased due to the installation of hot runner plates

(2) thermal radiation is difficult to control. The biggest problem of hot runner is the heat loss of runner, which is a major problem to be solved

(3) there is thermal expansion. Thermal expansion reduces the production of packaging waste. Cold shrinkage is a problem we should consider in our design

(4) the cost of mold manufacturing increases, and the price of standard accessories of hot runner system is higher, which affects the popularity of hot runner mold

◆ companies that provide hot runner standard parts include DME, HASCO, husky, EOC, full, master-tip, INCOE, etc

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