What is the common sense of using injection molding machine?

What is the common sense of using injection molding machine? There are many things that need to be paid attention to when using injection molding machine. Haisen Machinery has compiled some common sense of using injection molding machine:

　　 1. Opening and closing of the mold

Generally speaking, the mold opening and closing time used by most injection molding machines is slower than the quoted time (about 100-359%). This difference is related to the weight, size and complexity of the mold, and is also related to the safety protection of the mold (in opening Prevent damage to the mold during the combined operation).

　　The typical mold opening and closing time is as follows (tcm: time unit quoted by the injection molding machine):

　　Traditional double plate mold: 1-2tcm

　　Composite mold (including the use of side mold core and screw-out device) and multi-plate mold: 2-3.5tcm

　　 If the mold opening and closing time is 15% longer than the actual operation time, then you need to modify the pet preform mold or use another injection molding machine to shorten the time. Newer injection molding machines can provide faster opening and closing speeds, and use low mold opening and closing (mold sensing) pressure to activate the clamping force to close the mold.

　　Injection molding machine operators often do not pay attention to the speed or time of a particular injection molding machine's board, and use personal experience to set the mold opening and closing time, which often leads to a long operating time. If you reduce one second in a ten-second operation, you will get a 10% improvement immediately. This improvement often constitutes the difference between profit and loss.

　　 2. The function of back pressure

The application of 　　 back pressure can ensure that the screw can generate enough mechanical energy to melt and mix the plastic when the screw is rotated and reset. Back pressure also has the following uses:

Exhaust volatile gases, including air, out of the injection cylinder; mix additives (such as toner, color, antistatic agent, talc, etc.) and melt uniformly; make the melt flowing through the length of the screw uniform ; Provide uniform and stable plasticized materials to obtain precise finished product weight control. The selected back pressure value should be as low as possible (for example, 4-15bar, or 58-217.5psi), as long as the melt has proper density and uniformity, and there are no bubbles, volatile gases and incomplete plastics in the melt. Modified plastic will do.

　　The use of back pressure increases the pressure temperature and melt temperature of the injection molding machine. The magnitude of the increase is related to the set back pressure value. Larger injection molding machines (screw diameters over 70mm/2.75in) can have oil back pressure as high as 25-40bar (362.5-580psi). However, it should be noted that too high back pressure causes the temperature of the melt in the shooting barrel to be too high, which is destructive to the production of heat-sensitive plastics.

　　 And too high back pressure also causes the screw to be too large and irregular offside, which makes the injection volume extremely unstable. The amount of offside is affected by the viscoelastic properties of the plastic. The more energy stored in the melt, the screw will suddenly jump backwards when it stops rotating. Some thermoplastics have more jumps than others, such as ldpe, hdpe, pp, eva, pp/epdm composites and ppvc Compared with gpps, hips, pom, pc, ppo-m and pmma, it is more prone to beating.

　　In order to obtain the best production conditions, the correct back pressure setting is very important, so that the melt can be properly mixed, and the screw's offside range will not exceed 0.4mm (0.016in).

What are the types of injection molding machine screws?

The screw is an important part of the injection molding machine. Its function is to transport, compact, melt, stir and press the plastic. What are the types of injection molding machine screws? Injection molding machine screws are divided into: mutation type screw, gradual change type screw, general purpose Type screw.

　　1, mutant screw:

　　 The process of screw groove depth changing from deep to shallow is completed within a short axial distance. It is mainly used to process crystalline plastics with obvious viscosity and melting point, such as polyethylene and polypropylene.

　　2, general-purpose screw:

　　 The length of the compression section is between the abrupt type screw and the gradual type screw, but the plasticization quality and energy consumption are worse than the dedicated ones. In order to meet the requirements of crystalline and amorphous plastics melted into plastics.

　　3. Gradual screw:

　　 means that the depth of the screw groove gradually transitions from the deep screw groove of the feeding section to the screw groove of the homogenization section. Mainly used for processing non-crystalline plastics with a wide softening temperature range and high viscosity, such as polyvinyl chloride.

　　4, injection screw compression ratio:

　　The screw groove of the homogenization section of the injection screw is deeper, the compression ratio is small, and vice versa, the compression ratio is large.

　　 5. Injection screw length to diameter ratio:

　　 Compared with the extrusion screw, the screw of the injection molding machine has a smaller L/D ratio. The screw length-diameter ratio of domestic injection molding machines is mostly between 17-22, and usually around 20:1. The length-to-diameter ratio of foreign screws is mostly between 21-33, and the common length-to-diameter ratios are 20, 25, 30, etc.

The selection of the depth of the screw groove is mainly based on the factors of the processed plastic: specific heat capacity, thermal conductivity, stability, viscosity, and pressure during plasticization. But it should not be too deep, too deep will cause the screw due to excessive torque Twisting, or stalling due to overload, over to the groove of the homogenization section. The compression ratio of the injection screw is usually (1.5-3.5):1. The screw with a high compression ratio should rotate slowly, and the screw with a compression ratio of less than 2:1 can work at a higher speed.

　　 There are these types of screws for injection molding machines. When the screw rotates, the plastic will produce friction and mutual movement on the inner wall of the barrel, the bottom surface of the screw groove, the screw edge advancement surface, and the plastic and the plastic.