(1) Continuous extrusion inflation method. The sequence of continuous extrusion and blow molding of hollow plastic products: extrude the melted tube blank that has been mixed and plasticized uniformly from the extruder to a certain length - the product is moved from the inflation and cooling station to the melt tube with the molding die Below the billet → the billet tube material enters the forming mold → the mold is closed, and the tubular feed is cut off → the forming die is moved to the inflation and cooling position (the other forming die moves simultaneously to the bottom of the tube blank) → the mold is opened and the molded plastic product is demolded. The forming die moves reciprocatingly to exchange positions, so that the extrusion and blow molding of hollow plastic products can be carried out continuously. This production method has the advantages of simple equipment structure, low investment, and easy to master the production process and operation. At present, this method of producing hollow plastic products is widely used in small and medium-sized plastic products factories.
(2) Transposition feeding extrusion blowing method. The production method of extruded and inflated hollow plastic products by transposition feeding is basically the same as that of continuous extrusion and inflation, except that the feeding method is controlled by the reversing valve (the forming mold is fixed), and the molten material is alternately supplied to the two forming molds, and then Inflation molded articles.
(3) Rotary disc continuous extrusion blowing method. The continuously extruded plasticized molten blank tubes are respectively supplied to a plurality of molding dies that rotate around the axis of the turntable. With the rotation of the turntable, the actions of clamping the mold, cutting the blank tube, inflating and cooling, and opening the mold to release the plastic product are completed.
In the extrusion and inflation molding of large-scale hollow plastic products, due to the large amount of materials used for one-time molding, the extruded molten material is first stored in a storage cavity during production, and when the amount of material is reached, the molten material is quickly pushed and melted. The material enters the product forming mold through the blank tube, and then blows and cools to form.
Reduce screw wear in blow molding
The blow molding process works under high temperature, high pressure, high mechanical torque and high friction environment for a long time. The first few factors are required by the process conditions, and the loss caused by friction is inevitable.
Generally, the blow molding process has undergone surface nitriding treatment to improve the surface hardness, that is, to improve the wear resistance. However, if the cause of wear is ignored and the wear is not minimized, the working life of blow molding will be greatly reduced.
The following will focus on the causes of blow molding wear and the methods to reduce wear:
Similarly, in the compression section and the homogenization section, if the molten state of the plastic is turbulent, it will also cause increased wear.
The speed should be adjusted properly. Because some plastics are added with reinforcing agents, such as glass fibers, minerals or other fillers. These substances tend to be much more abrasive to metal than molten plastic. When injection molding these plastics, if the high rotational speed is used, the shear force on the plastic will be increased, and at the same time, more shredded fibers will be generated correspondingly. The shredded fibers contain sharp ends, which will cause wear and tear. Power is greatly increased.
Each plastic has an ideal plasticizing temperature range, and the barrel processing temperature should be controlled to make it close to this temperature range. Granular plastic enters the barrel from the hopper, and will first reach the feeding section. Dry friction will inevitably occur in the feeding section. When these plastics are insufficiently heated and melt unevenly, it is easy to cause increased wear on the inner wall of the barrel and the blow molding surface.
Analysis and solution of deformation defects in blow molding products
The greater the degree of deformation of the product processed by the extrusion blow molding machine, the proportional decrease in its appearance satisfaction and performance, and in severe cases, the product will be scrapped. The deformation of blow-molded products is not only detrimental to the quality of the products, but also detrimental to the output and production costs of blow-molded products. Therefore, the treatment of deformation defects of blow-molded products is an important topic discussed by various plastic processing enterprises in terms of skills. There are many reasons for the deformation of blow molding products, and it is far from enough to deal with the adjustment of process parameters. After a long period of practical work experience and the analysis and summary of related materials, the thermophysical properties of plastic materials and the conditions and parameters of the blow molding process have varying degrees of influence on the deformation of blow molding products, and it is necessary to summarize and consider them and deal with them reasonably.
Influence of Thermophysical Properties of Materials on Deformation
(1) The use of cyanide pigments in the processing formula of blow molding machines will affect the crystallinity of polyethylene and cause product deformation;
(2) The primary color blow molding products produced by materials without adding any pigments are not easy to deform, and can improve the quality and output of products;
(3) The use of plastic with low melting point and good fluidity can improve the quality and output of products because of its small shrinkage rate, fast cooling and not easy to deform.