Injection molding of plastic products - first understand the injection molding machine
First, what is the injection molding machine:
Injection molding machines are also known as injection molding machines or injection machines. It is the main molding equipment for making thermoplastic or thermosetting materials into plastic products of various shapes by using plastic molding dies. Divided into vertical, horizontal, all-electric. The injection molding machine heats the plastic and applies a high pressure to the molten plastic to eject it to fill the mold cavity.
Second, the classification of injection molding machine:
(1) Classification by plasticization
1.Plunger plastic injection molding machine
It has poor mixing and plasticity. It is necessary to install a shuttle device. It is rarely used now.
Relying on the plasticizing and injection of the screw, the mixing and plasticizing properties are very good, and it is used most now.
3. Screw-Plunger Plastic Injection Molding Machine relies on the screw for plasticizing and relying on the plunger for injection. The two processes are separated.
(2) Classification by clamping mode
3. Hydraulic - mechanical
Third, how to choose the injection molding machine:
The correct choice of the type and specification of the injection molding machine before use, has a greater impact on the production cost, quality and production efficiency of injection molded products. Before selecting the specifications of the injection molding machine, first check the performance parameters of the injection molding machine in the product manual provided by the manufacturer of the injection molding machine. These parameter values are the main performance characteristics of the injection molding machine. According to some technical requirements of the plastic products to be produced [such as the type of raw materials used in the products, the grades, the quality (weight) of the products and the external dimensions, etc.] The parameter values of the injection molding machine corresponding to these parameter values are the injection molding machines to be purchased. At the same time, we must also understand the working precision, speed and product accuracy level of the injection molding machine to be purchased, and whether it meets the molding conditions of the product.
The key data in the specification model include: the ratio of the mass (or volume) and the external dimensions of the injection molded product to the parameter values in the equipment, ie the ratio between the mass (weight) of the product and the theoretical injection volume (or volume) of the injection molding machine. Relationship: The dimensional requirements between the length (height) dimension of the article and the dimension of the thickness of the forming die (the thickness of the die on the moving die plate) and the distance traveled by the moving die of the injection molding machine. In addition, it should be verified that the size of the mold to be installed on the injection molding machine is consistent with the conditions of the injection molding machine:
1) The spacing of the tie rods should be larger than the width and height of the mold to facilitate the assembly of the mold.
2) The size of the template meets the dimensional requirements when the molding die is installed and fixed.
3) The width and height dimensions of the mold must conform to the minimum mold size recommended by the injection molding machine.
Fourth, the working principle of the injection molding machine
The working principle of the injection molding machine is similar to that of the syringe for injection. It is to inject the plasticized molten state (ie, the viscous flow state) into the closed cavity by the thrust of the screw (or plunger). The process of obtaining the product after curing and setting.
Injection molding is a cyclic process, and each cycle mainly includes: quantitative feeding - melt plasticizing - pressure injection - filling mold cooling - mold extraction. After removing the plastic part, the mold is closed again for the next cycle.
Injection molding machine operation items: Injection molding machine operation items include three aspects: control keyboard operation, electrical control system operation and hydraulic system operation. The injection process action, the feeding action, the injection pressure, the injection speed, the selection of the ejection type, the monitoring of the temperature of each section of the barrel, the adjustment of the injection pressure and the back pressure are performed.
Generally, the molding process of the screw type injection molding machine is: firstly, the granular or powdered plastic is added into the barrel, and the plastic is melted by the rotation of the screw and the outer wall of the barrel, and then the machine performs the mold clamping and the injection seat forward. The nozzle is placed close to the gate of the mold, and then the pressure oil is introduced into the injection cylinder to advance the screw, thereby injecting the melt into the lower temperature closed mold at a high pressure and a relatively high speed. Time and pressure are maintained (also known as holding pressure), cooled, and solidified, and the product can be opened by mold opening (the purpose of holding pressure is to prevent backflow of molten material in the cavity, replenish material into the cavity, and ensure the product Has a certain density and dimensional tolerance). The basic requirements for injection molding are plasticization, injection and molding. Plasticization is the premise to achieve and guarantee the quality of molded products, and in order to meet the molding requirements, the injection must ensure sufficient pressure and speed.
At the same time, due to the high injection pressure, a correspondingly high pressure is generated in the cavity (the average pressure in the cavity is generally between 20 and 45 MPa), so a sufficient clamping force must be obtained. It can be seen that the injection device and the clamping device are key components of the injection molding machine.
There are three main aspects for the evaluation of plastic products. The first is the appearance quality, including integrity, color, gloss, etc.; the second is the accuracy between size and relative position; the third is the physical properties and chemical properties corresponding to the application. Electrical properties, etc. These quality requirements are different depending on the use of the product. The defects of the product mainly lie in the design, manufacturing precision and wear degree of the mold. But in fact, technicians in plastic processing plants often suffer from the difficult situation of using technology to compensate for the problems caused by mold defects.
Process adjustment during production is a necessary way to improve product quality and yield. Since the injection cycle itself is very short, if the process conditions are not well mastered, the waste will continue to flow. When adjusting the process, it is best to change only one condition at a time, and observe a few more times. If the pressure, temperature, and time are unified and uplifted, it is easy to cause confusion and misunderstanding. If there is a problem, it does not know what it is. The measures and means to adjust the process are various. For example, there are more than a dozen possible solutions to solve the problem of product dissatisfaction. It is necessary to choose one or two major solutions to solve the problem and solve the problem. In addition, attention should be paid to the dialectical relationship in the solution. For example, the product has a depression, sometimes it is necessary to increase the temperature of the material, sometimes to reduce the temperature of the material; sometimes to increase the amount of material, and sometimes to reduce the amount of material. It is necessary to recognize the feasibility of solving the problem of reverse measures.
Five, injection molding machine energy saving
The energy saving of an injection molding machine can be divided into two parts: one is the power part and the other is the heating part.
Power saving: Most of the inverters are used. The energy saving method is to save the residual energy of the motor. For example, the actual power of the motor is 50Hz, and you only need 30Hz in production to produce enough. The excess energy consumption is vain. Wasted, the inverter is to change the power output of the motor to achieve energy saving.
Energy saving in heating part: Most of the energy saving in heating is energy saving by electromagnetic heater, and the energy saving rate is about 30%-70% of the old resistor ring.
1. Compared with resistance heating, the electromagnetic heater has an additional layer of insulation, and the heat utilization rate is increased.
2. Compared with resistance heating, the electromagnetic heater directly acts on the material tube to reduce the heat transfer heat loss.
3. Compared to resistance heating, the heating rate of the electromagnetic heater is faster than one quarter, which reduces the heating time.
4. Compared with resistance heating, the heating speed of the electromagnetic heater is fast, the production efficiency is improved, the motor is in a saturated state, which reduces the power loss caused by high power and low demand.
The above four points are the reason why flying electromagnetic heaters can save up to 30%-70% on injection molding machines.