How to use the continuous injection molding machine

Introduction to the application of the continuous injection molding machine;

In terms of thermoplastic, the injection molding machine transforms the plastic particles into the final plastic parts through the circulation of melting, injection, pressure maintaining, cooling, etc. The injection molding machine of thermoplastic usually uses clamping tonnage or shot size as a simple machine specification identification. Other parameters that can be used include injection rate, injection pressure, screw design, die thickness and guide rod spacing, etc.

According to the function, there are three kinds of injection molding machines

(1) General purpose ejectors;

(2) Precise and tight matching injection machine;

(3) High speed, thin and thick injection machine.

The main auxiliary equipment of the injection molding machine includes resin dryer, material processing and conveying equipment, crusher, mold temperature control machine and condenser, mechanical arm for plastic part withdrawal, and plastic part processing equipment. The typical injection molding machine for injection machine components is shown in Figure 2-1, which mainly includes five units, including injection system, die system, oil pressure system, control system, and die locking system. The injection system includes a hopper, a rotating screw and a barrel combination, and a nozzle. The function of the injection system is to store and transport the plastic, so that the plastic goes through the stages of feeding, compression, exhaust, melting, injection and pressure maintaining.

(1) Hopper thermoplastic is usually supplied to the forming plant as small particles. The hopper of the ejector can store plastic particles. By gravity, the plastic particles pass through the neck of the hopper and enter the combination of the barrel and the screw.

(2) The barrel of the barrel ejector can accommodate the rotary screw and heat the plastic with electric heater banks.

(3) Rotary screw can compress plastic, melt plastic and transport plastic. The screw includes three sections: feeding area, compression area, transfer area and metering area. The outer diameter of the screw is a fixed value. The groove depth of the screw decreases gradually from the feeding area to the starting point of the metering area. The change of the groove depth causes the plastic to compress relative to the inner diameter of the barrel, resulting in shear heat and providing the main heat for melting the plastic.

The heating plate outside the barrel helps the plastic to maintain the melting state. Generally, there are three or more groups of heating plates in the ejector, so as to set different temperature ranges.

The nozzle connects the barrel and the sprue liner. When the barrel moves to the front forming position, the outer diameter of the nozzle must be wrapped in the locating ring of the vertical sprue to form a seal. The temperature of the nozzle shall be set at or slightly lower than the melting temperature of the plastic recommended by the material supplier. Thus, when cleaning the barrel, as long as the barrel is backward away from the vertical sprue, the removed plastic can fall freely from the nozzle.

The mold system includes guide rod, fixed formwork, movable formwork, and formwork to accommodate mold cavity, vertical sprue, runner system, ejector pin and cooling pipeline. Basically, the mold is a heat exchanger, which makes the melt glue of thermoplastics solidify into the required shape and size in the mold cavity. The mold system shapes the molten plastic in the mold cavity and ejects the plastic part after cooling.

The injection forming die system is a combination of installation template and forming template, which is usually made of tool steel. The fixed mounting plate is connected to one side of the barrel of the forming machine, and is connected with the moving template through the guide rod. The female template is usually locked on the fixed template and connected to the nozzle; the male template is locked on the movable mounting plate and moves along the guide rod. In some applications, the female template will be locked on the mobile template, and the male template and the hydraulic ejector will be installed on the fixed template.

(1) Most of the two plate molds are composed of two templates, which are often used in the design of the gate of the plastic part just located at or close to the edge of the plastic part, and the flow channel is also designed on the parent template.

(2) Three plate die three plate die is usually used to design the gate away from the edge of the plastic part, and its flow channel is designed on the stripper plate separating the male die and the female die.

(3) Cooling pipeline (loop) cooling pipeline is the channel of the mold body, and the refrigerant (generally water, steam or oil) circulates through the cooling pipeline to adjust the mold wall temperature.

The cooling line can also be used with other temperature control devices, such as baffle tube, spoiler or heat pipe.

The hydraulic system of the ejector provides the power to open and close the die, accumulates and maintains the ton of locking force, rotates and propels the screw, actuates the ejector pin, and moves the die side.

The components of the oil pressure system include pump, valve, oil pressure motor, oil pressure pipe fitting, oil pressure joint, oil pressure tank, etc.

The control system provides consistent repetitive operation of the forming machine, and monitors process parameters such as temperature, pressure, injection speed, screw speed and position, and oil pressure position.

Process control directly affects the quality of plastic parts and the economic benefits of the process. The control system includes simple on / off relay control to complex microprocessor closed loop controller. The mold locking system is used to open / close the mold, support and move the mold components, and generate enough force to prevent the mold from being pushed away by the injection pressure. The mold locking mechanism can be a toggle mechanism locking, an oil pressure mechanism locking, or a combination of the two basic forms.

The typical injection forming system of the injection forming system includes the melt conveying system and the forming parts. The melt conveying system provides a channel for the melt to flow from the ejector nozzle to the mold cavity, which usually includes: vertical sprue, cold well, main sprue, branch runner, and gate. The design of conveying system has a very important influence on filling mode and quality of plastic parts. Therefore, the runner system should be designed to maintain the required filling mode and transport the melt to the cavity. After the injection molding, the cold runner conveying system will be cut to recycle waste, so the conveying system should be designed to produce the least waste. The hot runner or non runner forming process maintains the runner at high temperature, so that the melt glue in the runner remains in the molten state. Because the hot runner is not demoulded together with the plastic part, it will not cause waste and save the process of plastic part secondary cutting.