Maintenance of the hottest plastic injection moldi

Maintenance of plastic injection molding machine

injection molding machine has the ability to form plastic products with complex shape, precise size or dense texture with metal inserts at one time. It is widely used in national defense, electromechanical, automobile, transportation, building materials, packaging, agriculture, culture, education, health and all fields of people's daily life. Injection molding process has good adaptability to the processing of various plastics, high production capacity, and easy to realize automation. Today, with the rapid development of the plastic industry, injection molding machines play an important role in both quantity and variety, so they have become one of the fastest growing and largest production types of plastic machinery

xingluoqibu, a plastic processing enterprise in China, is spread all over the country. The technical level of equipment is uneven, and the equipment of most processing enterprises needs technical transformation. In recent years, the technological progress of China's plastic machine industry has been very significant, especially the gap between the technical level of injection molding machines and foreign famous brand products has been greatly narrowed, and significant improvements have been made in the control level, internal quality and appearance of products. Choosing domestic equipment, with a small investment, we can also produce products with the same quality as imported equipment. These have created conditions for the technological transformation of enterprises

to have good products, we must have good equipment. The wear and corrosion of equipment is a natural law. If people master this law, they can prevent or reduce the wear and corrosion of equipment, prolong the service life of equipment, and ensure the integrity rate of equipment

this paper has written the relevant knowledge and technical data of injection molding machine maintenance, which can be used as a reference for the managers and technicians of equipment management departments and production enterprises.

plastic injection molding technology has developed from the end of the 19th century to the beginning of the 20th century according to the die-casting principle It is one of the most commonly used methods in plastic processing at present. This method is applicable to all thermoplastics and some thermosetting plastics (accounting for about 1/3 of the total plastic)

1.1 working principle of injection molding machine

the working principle of injection molding machine is similar to that of syringe for injection. It is the process of injecting plasticized molten plastic (i.e. viscous flow) into a closed mold cavity with the help of the thrust of screw (or plunger), and obtaining products after curing and shaping

injection molding is a cycle process, and each cycle mainly includes: quantitative feeding - melting and plasticizing - pressure injection - mold filling and cooling - mold opening and taking parts. After taking out the plastic part, close the mold again for the next cycle

1.2 structure of injection molding machine

injection molding machine is divided into plunger injection molding machine and screw injection molding machine according to the plasticization method; According to the transmission mode of the machine, it can be divided into hydraulic type, mechanical type and hydraulic mechanical (connecting rod) type; According to the operation mode, it is divided into automatic, semi-automatic and manual injection molding machines

(1) horizontal injection molding machine: This is the most common type. The mold closing part and the injection part are on the same horizontal centerline, and the mold is opened along the horizontal direction. Its features are: low fuselage, easy to operate and maintain; The center of gravity of the machine is low and the installation is stable; After the products are ejected, they can fall automatically by gravity, which is easy to realize full-automatic operation. At present, injection molding machines in the market mostly adopt this type

(2) vertical injection molding machine: its clamping part and injection part are on the same vertical centerline, and the mold is opened along the vertical direction. Therefore, it covers a small area, easy to place inserts, convenient to load and unload molds, and the materials falling from the hopper can be plasticized more evenly. However, the products are not easy to fall automatically after being ejected, and must be removed by hand, so it is not easy to realize automatic operation. Vertical injection molding machines are suitable for small injection molding machines. Generally, injection molding machines below 60g are widely used, and large and medium-sized machines are not suitable

(3) angle injection molding machine: its injection direction is on the same surface as the mold interface. It is especially suitable for plane products that are not allowed to leave gate traces in the machining center. Its floor area is smaller than that of horizontal injection molding machine, but the inserts placed in the mold are easy to tilt and fall. This type of injection molding machine is suitable for small machines

(4) multi mode rotary table injection molding machine: it is a special injection molding machine with multi station operation. Its feature is that the clamping device adopts a rotary table structure, and the mold rotates around the rotating shaft. This type of injection molding machine gives full play to the plasticizing capacity of the injection device, which can shorten the production cycle and improve the production capacity of the machine. Therefore, it is particularly suitable for the production of large quantities of plastic products with long cooling and finalization time or requiring more auxiliary time due to the placement of inserts. However, due to the large and complex clamping system, the clamping force of the clamping device is often small, so this kind of injection molding machine is widely used in the production of plastic soles and other products

general injection molding machine includes injection device, mold closing device, hydraulic system and electrical control system

the basic requirements of injection molding are plasticization, injection and molding. Plasticization is the premise to realize and ensure the quality of molded products. In order to meet the requirements of molding, injection must ensure sufficient pressure and speed. At the same time, due to the high injection pressure, a high pressure is generated in the mold cavity (the average pressure in the mold cavity is generally between 20~45mpa, see Table 1), so there must be enough clamping force. It can be seen that the injection device and clamping device are the key components of the injection molding machine

1.4 operation of injection molding machine

1.4.1 action procedure of injection molding machine

nozzle advance → injection → pressure maintaining → pre molding → shrinkage → nozzle retreat → cooling → mold opening → ejection → needle withdrawal → door opening → door closing → mold closing → nozzle advance

1.4.2 injection molding machine operation items: injection molding machine operation items include control keyboard operation, electrical control cabinet operation and hydraulic system operation. Select the injection process action, feeding action, injection pressure, injection speed and ejection type, monitor the temperature, current and voltage of each section of the barrel, and adjust the injection pressure and back pressure

1.4.2.1 action selection in the injection process:

general injection molding machines can be operated manually, semi automatically and fully automatically

manual operation is realized by the operator pulling the operation switch in a production cycle. Generally, it is selected when the machine is tested and the mold is adjusted

during semi-automatic operation, the machine can automatically complete the action of a working cycle, but after each production cycle, the operator must open the safety door, remove the workpiece, and then close the safety door before the machine can continue the production of the next cycle

in fully automatic operation, the injection molding machine can automatically enter the next working cycle after completing the action of one working cycle. In the normal continuous working process, there is no need to stop for control and adjustment. However, it should be noted that if full-automatic operation is required, (1) do not open the safety door midway, otherwise the full-automatic operation will be interrupted; (2) Feed in time; (3) If using electric eye induction, be careful not to cover the electric eye

in fact, it is usually necessary to stop temporarily in the middle of full-automatic operation, such as spraying mold release agent on the machine

in normal production, semi-automatic or full-automatic operation is generally selected. At the beginning of operation, the operation mode (manual, semi-automatic or full-automatic) should be selected according to the production needs, and the manual, semi-automatic or full-automatic switches should be toggled accordingly

the semi-automatic and full-automatic working procedures have been determined by the line itself. The operator only needs to change the size of speed and pressure, the length of time, the number of thimbles, etc. on the electric cabinet, and the working procedure will not be confused because the operator adjusts the wrong keys

before each action in a cycle is not adjusted properly, you should first select manual operation, and then select semi-automatic or full-automatic operation after confirming that each action is normal

1.4.2.2 pre molding action selection

according to whether the injection seat retreats before and after pre molding feeding, that is, whether the nozzle leaves the mold, the injection molding machine is generally equipped with three options. (1) Fixed feeding: the nozzle is always stuck into the mold before and after pre molding, and the injection seat does not move. (2) Front feeding: the nozzle is against the mold for pre molding feeding. After the pre molding is completed, the injection seat retreats, and the nozzle leaves the mold. The purpose of choosing this method is to use the injection hole of the mold to help the nozzle during the pre molding, so as to avoid the melt flowing out of the nozzle when the back pressure is high. After the pre molding, the heat transfer caused by the long-term contact between the nozzle and the mold can be avoided, which affects the relative stability of their respective temperatures. (3) Post feeding: after the injection is completed, the injection seat retreats, the nozzle leaves the mold, and then the pre molding is completed, and then the injection seat advances. This action is applicable to the processing of plastic with a particularly narrow molding temperature. Due to the short contact time between the nozzle and the mold, the loss of heat and the solidification of molten material in the nozzle hole are avoided

after the injection is completed and the cooling timer is timed, the pre molding action begins. The screw rotates to melt the plastic and squeeze it to the front of the screw head. Due to the role of the check valve played by the retaining ring at the front end of the screw, molten plastic accumulated in the front end of the barrel, forcing the screw backward. When the screw retreats to a predetermined position (this position is determined by the travel switch, which controls the distance of the screw retreating to achieve quantitative feeding), the pre molding stops and the screw stops rotating. Then there is the backward contraction action, which means that the screw makes a small amount of axial retreat. This action can relieve the pressure of molten material gathered at the nozzle and overcome the phenomenon of "salivation" caused by the imbalance of internal and external pressure of the barrel. If it is not necessary to shrink, the shrink stop switch should be adjusted to the appropriate position, so that the shrink stop switch is also pressed at the same time that the pre molding stop switch is pressed. When the screw moves backward to press the stop switch, the backward retraction stops. Then the injection seat began to retreat. When the injection seat retreats to press the stop switch, the injection seat stops retreating. If the fixed feeding method is adopted, the position of the travel switch should be adjusted

generally, fixed feeding method is used in production to save the operation time of injection seat advance and retreat and speed up the production cycle

1.4.2.3 injection pressure selection

the injection pressure of the injection molding machine is adjusted by the pressure regulating valve. Under the condition of setting the pressure, the injection pressure of the front and rear stages is controlled through the on-off of the high-pressure and low-pressure oil circuits

ordinary injection molding machines above medium-sized have three pressure options, namely, high pressure, low pressure and high pressure before low pressure. High pressure injection is realized by injecting high pressure oil into the injection cylinder. Due to the high pressure, the plastic enters the mold cavity at high pressure and high speed from the beginning. During high-pressure injection, the plastic enters the mold quickly, and the reading of the pressure gauge of the injection cylinder rises rapidly. Low pressure injection is realized by injecting low pressure oil into the injection cylinder. The reading of the pressure gauge rises slowly during the injection process, and the plastic enters the mold cavity at low pressure and low speed. High pressure first and then low pressure is achieved by controlling the pressure of the pressure oil into the oil cylinder in time according to the actual requirements of the plastic type and mold

in order to meet the requirements of different plastics, there are different injection pressures, and the method of replacing screws or plungers with different diameters can also be used, so