How to improve the working life of the screw barrel of the plastic machine?

Injection screw is long time in high temperature, high pressure, high mechanical torque and high friction environment to work. The first few factors are required by the process conditions, and the loss caused by friction is inevitable. Generally, the screw has been nitriding the surface to improve the surface hardness, that is, to improve the wear resistance. However, if the causes of wear are ignored and the wear is not reduced as far as possible, the working life of the screw will inevitably be greatly reduced.

The following describes the causes of screw wear and ways to reduce wear

1, each plastic, there is an ideal plasticizing processing temperature range, should control the cylinder processing temperature, so that it is close to this temperature range. Granular plastic from the hopper into the barrel, will first reach the feeding section, in the feeding section will inevitably appear dry friction, when these plastics are not heated enough, melting uneven, it is easy to cause the inner wall of the barrel and screw surface wear increase. Similarly, in the compression section and the homogenization section, if the melting state of the plastic is chaotic and uneven, it will also cause increased wear

2, speed should be adjusted properly. Because some plastics are fortified, such as glass fiber, minerals or other fillers. The friction force of these substances on metal materials is often much greater than that of molten plastics. When injection molding these plastics, if the high speed is used, it will increase the shear force on the plastic, but also will strengthen the corresponding production of more torn fibers, torn fibers contain sharp ends, so that the wear force is greatly increased. When inorganic minerals glide at high speed on the metal surface, the scraping effect is not small. So the speed should not be adjusted too high.

3, to check the debris in the plastic. In general, there is no debris in the original purchase of fresh plastic, but after transportation, weighing, drying, mixing color, especially the addition of recycled materials, it is possible to mix debris. As small as metal scraps, as large as heating ring nuts paper clips, and even strings of warehouse keys, mixed into the barrel have occurred, the damage to the screw is self-evident (of course, the barrel will also be damaged at the same time), so it is necessary to install the magnet rack, strict feeding management and monitoring.

4, the moisture contained in the plastic has a certain impact on the wear of the screw surface. If the plastic does not eliminate all the water before injection, the residual water enters the compression section of the screw, forming a "steam particle" with high temperature pressure mixed in the molten plastic, with the advance of the injection process, from the homogenization section to the screw head, these "steam particles", in the shooting process of pressure relief expansion, like a fine impurity of hard particles, Produce friction and damage to the wall surface.

In addition, for some types of plastics, under high temperature and pressure, water may become a catalyst for plastic cracking, producing harmful impurities that can erode the surface of the metal. Therefore, the drying work before plastic injection molding not only has a direct relationship to the quality of the parts, but also affects the working life of the screw.

Injection molding machine screw type shape

The functions and requirements of the screw injection molding machine are selected respectively:

Commonly used are:

Reciprocating screw (three-stage screw) is divided into gradient type, Mi type, general type.

Screw for the production of imitation marble products.

Exhaust injection molding machine screw.

Preplasticizing injection molding machine screw.

Mixing screw.

1, Conventional injection molding screw: The general injection molding machine with a standard medium diameter screw, and with two high and low pressure conventional screw, can be applied to a wide range of general plastics and engineering plastics processing, this screw is also a three-stage: feeding section, compression section, homogenization section, are considering the pre-plastic injection molding machine and injection molding processing of the material characteristics to determine.

2, lengthening injection screw: It is a general injection screw with higher plasticizing ability and better mixing effect. Compared with conventional screw, its characteristics are: The length to diameter ratio is large (20~25), the length of the measuring section is (30%), the measuring section groove is shallow (0.04~0.05D), and the compression ratio is large (0.11~012D), so it is conducive to the cooperation of plasticizing temperature.

3, Type of hard PVC injection screw: This kind of screw is characterized by: the length to diameter ratio is small, the metering section and the conveying section is short, the compression section is long, the screw groove of the i metering section is deep, the compression is relatively small, suitable for injection molding of hard PVC and other plastics with poor thermal stability, in order to reduce the strong shear effect and storage material, to prevent overheating decomposition, The seat screw is suitable for a "Z" type screw head with a melt flow void.

4, No metering section injection screw: light metering injection screw is also known as "ZM" "screw, which is characterized by no metering section, only feeding section and transition section, so this is a two-stage screw, because the non-metering section can reduce melt overheating, increase plasticizing capacity and mixing effect, so it is suitable for injection molding ABS and other non-crystalline materials to prevent shear overheating.

For example, it is used to process flame-retardant impact resistant polyvinyl, polycarbonate, filled polyvinyl, polyvinyl, and filled nylon, etc., the screw length-diameter ratio of the non-metering section is generally 20, the length of the feeding section and the transition section account for 50%, and the depth of the screw groove is recommended for each section.

5, Separation injection screw: (BM screw) Separation injection screw called "BM" screw, In the injection molding has been widely used, the main kind of screw is characterized by the melting section (transition segment, pressure contraction segment) to increase a secondary screw thread, the main screw groove is divided into two parts, when the screw rotates, the main screw scrape the melt film from the gap between the screw edge and the cylinder into the secondary screw groove, so that the solid bed and the molten pool are separated, so as to maintain the fixed body bed and the inner wall of the cylinder good contact, Easy to transport and heat transfer.

6, Wave screw (HPM screw) : wave screw has "single wave" and "double wave" points, single-wave screw is characterized by the bottom diameter of the adjacent screw groove is equal, but it is eccentric, and the eccentricity is equal, and symmetrical open screw axis. Because the depth of the spiral groove changes periodically along the axial direction, the material is subjected to strong extrusion and shearing action during premolding, which absorbs a lot of mechanical energy and converts energy. Heat sensitive materials such as vinyl chloride can be injected to reduce degradation.

7, Mixing injection screw: Mixing injection screw is characterized by setting mixing components in the metering section position. Based on the analysis of common screw; In the transition section, the polymer is initially melted and melted, and a melt film is also formed at the back edge of the thread, so the whole bed is actually surrounded by the melt film, reducing the melting efficiency, so in the transition zone, it is appropriate to emphasize the stable melting and conveying effect, after the material has passed through the transition section, after melting. Barrier type mixing element (straight channel mixing element is also known as Maddook element); Other barrier type mixing element,(shunt type mixing element is also known as DIS type mixing element)

8, Combination screw: combination screw is used in the heart of the screw metering section, according to the different nature of the material to install different functions of the mixing component group, mixing components into the form of a key, and the key and the mind connection, the end face of the set should be precisely matched to prevent melt into.