chinain jection: Recent Episodes
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The combined work quality of the two parts, the screw and the barrel, has an important influence on the plasticization of the material, the quality of the product and the production efficiency. Their quality of work is related to the manufacturing precision and assembly clearance of the two parts. When the two parts are seriously worn and the output of the extruder is reduced, the maintenance of the screw and the barrel should be arranged. First, the cause of damage to the screw and barrel 1. The screw rotates in the barrel, and the friction between the material and the two causes the working surface of the screw and the barrel to wear gradually: the diameter of the screw is gradually reduced, and the diameter of the inner hole of the barrel is gradually increased. . Thus, the matching diameter gap between the screw and the barrel increases little with the gradual wear of the two. However, since the resistance of the front head and the splitter plate of the barrel is not changed, this increases the leakage flow when the extruded material advances, that is, the amount of material flowing from the diameter gap to the feed direction increases.
As a result, the extruder production is reduced. This phenomenon causes the residence time of the material in the barrel to increase, causing the material to decompose. In the case of polyethylene, the decomposition of the gas increases the corrosion of the screw and barrel. 2. If there are fillers such as calcium carbonate and glass fiber in the material, it can accelerate the wear of the screw and the barrel. 3. Since the material is not plasticized evenly, or metal foreign matter is mixed into the material, the torque of the screw is suddenly increased. This torque exceeds the strength limit of the screw, and the screw is broken. This is an unconventional accident damage. Second, the repair of the screw 1, the broken screw should be considered according to the actual inner diameter of the barrel, according to the normal gap with the barrel gives the deviation of the outer diameter of the new screw for manufacturing. 2. After the surface of the thread with the reduced diameter of the wear screw is treated, the wear-resistant alloy is thermally sprayed and then ground to a size. This method is generally processed and repaired by a professional spray factory, and the cost is still relatively low. 3. Surfacing the wear-resistant alloy on the threaded portion of the wear screw. Depending on the degree of wear of the screw, weld 1 to 2 mm thick and then grind the screw to size.
This wear-resistant alloy consists of materials such as C, Cr, Vi, Co, W and B, which increases the anti-wear and corrosion resistance of the screw. Professional surfacing plants have a high cost for such processing, and are rarely used except for special requirements. 4, repair screw can also be surface hard chrome plating method, chromium is also wear-resistant and corrosion-resistant metal, but the hard chrome layer is easier to fall off. Third, the inner surface of the barrel of the repair cylinder is harder than the screw, and its damage is later than the screw. The scrapping of the barrel is such that the diameter of the inner diameter increases due to time wear. Its repair method is as follows: 1. Increase the diameter of the barrel due to wear. If there is a certain nitriding layer, the inner hole of the barrel can be directly bored, ground to a new diameter size, and then prepared according to this diameter. New screw. 2. The inner diameter of the barrel is machined and trimmed to recast the alloy, the thickness is between 1~2mm, and then finished to the size. 3. Under small household appliances OEM factory normal circumstances, the homogenization section of the barrel wears faster. This section (take 5~7D length) can be trimmed by the boring hole, and then a nitriding alloy steel bushing is used. The diameter of the inner hole is referenced to the diameter of the screw. Normally fit the gap and process and prepare. It is emphasized here that the two important parts of the screw and the barrel are an elongated threaded rod and a small diameter and long hole. The machining and heat treatment processes are complicated and the precision is difficult to guarantee. . Therefore, after the wear of these two parts is repaired or replaced with new ones, it must be comprehensively analyzed from an economic perspective. If the repair cost is lower than the replacement screw cost, it is decided to repair, this is not necessarily the correct choice, the comparison of repair costs and update costs is only one aspect. Also depends on the ratio of repair costs to screw time and renewal costs after repair and updated screw usage time.
It is economical to adopt a scheme with a small ratio and is the right choice. 4, screw and barrel manufacturing materials to manufacture screws and barrels, the current domestic commonly used materials are 45, 40Cr and 38CrMoAlA. The manufacturing materials of the screw and barrel in the imported extruder, commonly used alloy steel are 34CrAINi7 and CrMoV9. The yield strength of this material is about 900 MPa. After nitriding treatment, the hardness is above 1000 HV, which is both wear-resistant and has good corrosion resistance.
The main task of the hot runner plate is to thermostatically feed the melt from the main flow path to each individual nozzle. During melt transfer, the melt pressure drop should be as small as possible and no material degradation is allowed. The flow of the melt to each nozzle should be as uniform as possible. In order to save heating power, the volume is small, but if it is too small, the heat capacity is too small and the temperature is not stable. The hot runner plate should be processed in a thick plate. The surface of the runner that is in contact with the melt is drilled and then re-polished with a reamer. The end points of the flow path are not allowed to have blind holes, and the shape of the corner should be smoothly transitioned with the flow path. The hot runner plate should be made of a material that is smaller than heat and has a high thermal conductivity.
Hot runner plates are typically fabricated from steel and nozzles are made of beryllium copper or copper to maintain a uniform temperature. In recent years, it has been recommended to use a finished, high-quality stainless steel tube with an inner wall to make a hot runner for a large product mold, which is fixed with cast copper around it. A support pad having a high strength contact area is used at the support portion or an air gap is used between the hot runner plate and the fixed plate. The hot runner system is generally divided into two categories according to the heating method of the hot runner plate: 1. Heating type: The heating channel system also has two designs: an inner heating channel and an outer heating channel: 1. an inner heating channel: an inner heating stream The road features an internally heated annular flow path. Heating is provided by a probe in the flow channel and a heating shuttle (also known as a distributor tube). This system utilizes the insulating effect of molten plastic to reduce heat transfer and loss elsewhere in the mold. Despite the annular heater in the distributor tube, there is still a condensation of material between the heating shuttle and the flow channel wall. The material must flow between the insulation wall and the heating shuttle, which, combined with the annual flow effect, causes a drop in pressure within the system, so the importance of balance is critical. In view of this problem, the internal heating system is most suitable for Thin-wall injection molding processing a wide range of materials and equidistant flow paths to the gates.
This system is not suitable for the use of heat sensitive plastics. Internal heating provides improved heat distribution relative to the insulation system, but the system is more costly and more complex to design. Such systems require careful balancing and complex thermal control. 2, external heating system: Another design of the hot runner is the external heating system. This design consists of an annular heating header with internal flow channels. The header is designed with a variety of insulation configurations that are isolated from the rest of the mold. The advantage of this system is better temperature control, but the cost is higher and the equipment is complicated. The latest technology development has reduced the size of the header and made the installation easier. The external heating system can also be balanced by diameter rather than by length. Second, the heat insulation type: the heat insulation flow channel mold has an excessively large flow path composed of a template. The flow channel is not heated, but the size of the flow channel is large enough to be combined with the heat generated by the plastic that is condensed on the flow channel wall under working conditions to maintain the melt in the flow channel. Unblocked. This kind of system is earlier and simpler in two categories. The advantage is that the design is not so complicated and the manufacturing cost is low. The disadvantage is that condensation sometimes forms at the gate; in order to maintain the molten state, a very fast duty cycle is required; in order to achieve a stable melting temperature, a long preparation time is required. Another major problem is that it is difficult to achieve consistency in injection molding, or it cannot be guaranteed. Also, because there is no heating in the system, a high injection pressure is required, which often causes deformation or bending of the cavity plate.