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Plastic Mold Basic Knowledge And Application Technology
May 26, 2018

1 Introduction 


The various tools and products used in our daily production and life are as large as the base of the machine tool, the shell of the machine body, and the size of a single head screw, button, and shell of various household appliances, all of which are closely related to the mold. The shape of the mold determines the shape of these products. The quality and accuracy of the mold determines the quality of these products. Because of the different materials, appearances, specifications, and uses of various products, molds are divided into non-plastic molds such as casting molds, forging molds, die-casting molds, stamping molds, and plastic molds.


In recent years, with the rapid development of the plastics industry and the continuous improvement in the strength and accuracy of general-purpose and engineering plastics, the application range of plastic products is also expanding, such as: household appliances, instrumentation, construction equipment, automotive industry, and In areas such as hardware, the proportion of plastic products is increasing rapidly. A well-designed plastic part can often replace many traditional metal parts. The trend toward the plasticization of industrial products and household products continues to rise.


2, the general definition of the mold: In industrial production, using a variety of presses and special tools installed on the press, through the pressure of metal or non-metallic materials to produce the desired shape of the parts or products, this special tool is collectively referred to as the mold .


3, injection molding process description: mold is a tool for the production of plastic products. It consists of several sets of parts, which have molding cavities inside. During injection molding, the mold is clamped on the injection molding machine. The molten plastic is injected into the mold cavity, and is cooled and set in the cavity. Then the upper and lower molds are separated, the product is ejected from the mold cavity through the ejector system, and finally the mold is closed again. For the next injection molding, the entire injection molding process is performed cyclically.


4, the general classification of mold: can be divided into plastic mold and non-plastic mold:


(1) Non-plastic molds include: casting molds, forging molds, stamping molds, and die casting molds.


A. Casting mold - faucet, pig iron platform

B. Forging die - car body

C. Stamping die - computer panel

D. Die casting mold - super alloy, cylinder block


(2) Plastic molds are divided into:


A. Injection Molding - TV Case, Keyboard Buttons (Applications Most Common)

B. Blowing mold - beverage bottle

C. Compression Mold - Bakelite Switch, Scientific Porcelain Dishes

D. Transfer Molding - Integrated Circuit Products

E. Extrusion molds - glue pipes, plastic bags

F. Thermoforming molds - transparent molded packaging shell

G. Rotary Molding - Soft Rubber Doll Toy


Injection molding is the most commonly used method in plastics processing. This method is applicable to all thermoplastic plastics and partially thermoset plastics. The large number of plastic products obtained is beyond the reach of other molding methods. As one of the main tools for injection molding processing, the injection molds are used in mass accuracy, manufacturing cycle and injection molding process. The level of production efficiency in China and other countries directly affects the quality, output, cost, and product renewal of products, and at the same time determines the responsiveness and speed of enterprises in market competition.


 


Injection mold is composed of several pieces of steel plate and various parts, basically divided into:


A forming device (die, punch)

B positioning device (guide post, guide sleeve)

C Fixing devices (I-shaped plates, pattern pits)

D cooling system (water hole)

E constant temperature system (heating pipe, heating line)

F runner system (唧 nozzle hole, runner channel, runner hole)

G ejector system (thimble, top stick)


5, according to the different types of casting system can be divided into three categories:


(1) Dashuikou Mould: The runner and the gate are on the parting line, and it is released together with the product when the mold is opened. The design is the simplest, easy to process, and the cost is low, so more people use the large nozzle system operation.


(2) Fine nozzles: The runners and gates are not on the parting line. Generally, they are directly on the product. Therefore, it is necessary to design more than one outlet line. The design is more complicated and the processing is more difficult. Generally, it is selected according to the product requirements. Fine water outlet system.


(3) Hot Runner Mould: This type of die structure is the same as the fine nozzle. The biggest difference is that the runner is in one or more thermostatic hot runner plates and hot nipples. No cold material is used to release the mold, runners and pouring. The mouth is directly on the product, so the runner does not need to be demoulded. This system is also called a waterless system, which can save raw materials. It is applicable to the situation where the raw materials are relatively expensive and the products require high quality. The design and processing are difficult and the mold cost is high.


Hot runner system, also known as hot runner system, is mainly composed of hot sprue bushing, hot runner plate and temperature control electric box. Our common hot runner system has two forms of single hot runner and multiple hot runners. The single-point hot sprue is the use of a single hot sprue bushing to directly inject the molten plastic into the cavity. It is applicable to a single cavity single gate plastic mold; the multi-point hot sprue is used to branch the molten material to each through a hot runner plate. The heat-receiving sprue bushing is then re-entered into the cavity, which is suitable for single-cavity multi-point feeding or multi-cavity molds.


Hot runner system advantages


(1) no water mouth material, no post-processing, so that the entire molding process is fully automated, saving work time, improve work efficiency.


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


3) Repeated use of outlet material will degrade the plastics performance, while the use of hot runner system without outlet material can reduce the loss of raw materials, thereby reducing product costs. In the cavity, the temperature and pressure are uniform, the plastic parts have small stress, and the density is uniform. Under a relatively small injection pressure and a shorter molding time, a better product than the general injection molding system is injected. For transparent parts, thin parts, large-scale plastic parts or high-demand plastic parts can better show its advantages, and can use a smaller model to produce larger products.


(4) The hot nozzle adopts a standardized and serialized design, equipped with various nozzle heads for selection, and has good interchangeability. The uniquely designed and processed electric heating ring can achieve even heating temperature and long service life. The hot runner system is equipped with a hot runner plate, a thermostat, etc. The design of the hot runner system is exquisite, the types are various, the use is convenient, and the quality is stable and reliable.


Disadvantages of hot runner system applications


(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.


(2) Heat radiation is difficult to control. The biggest problem with hot runners is the loss of heat from the runner. This is a major issue that needs to be addressed.


(3) Thermal expansion and thermal expansion and contraction are issues that we must consider when designing.


(4) The cost of mold manufacturing increased, and the price of hot runner system standard parts was relatively high, affecting the popularity of hot runner molds.