Discussion on extrusion blow molding and die desig

Brief discussion on plastic oil tank extrusion blow molding and mold design process

in the following, the author will start from personal work experience, analyze and summarize the plastic oil tank extrusion blow molding process and the key points of mold design process, elaborate the plastic oil tank blow molding mold structure design scheme, discuss the parting surface design of the extrusion blow molding mold divided into multiple parts, and discuss the blow molding mold exhaust design The design of die cooling layering system and other links are introduced, in order to improve and innovate on the basis of summarizing the previous achievements and experience and successful design cases, and provide reference and reference for colleagues

1. Structural design of plastic oil tank extrusion blow molding mold

the main structure of plastic oil tank extrusion blow molding mold is a parting mold with two concave cavities. Its purpose is to protrude the outer surface of plastic oil tank products and determine the specification and shape of mold products. Finally, through blow molding and extrusion, mechanical processing and manufacturing parts are transformed from low molecular shape to high molecular shape through the cooling system. The design standards and purposes are analyzed as follows: first, the specification of the plastic mailbox extrusion blow molding mold should be consistent with the production objectives and customer needs; The second is to ensure that the semi-finished plastic parison can be accurately cut off and avoid excessive pulling and damage to the parison; The third is to improve the tightness of the connection between the extrusion blow molding die structure through the industrial chain tracking analysis, and improve the durability of the blow molding die; The fourth is to enhance the exhaust effect of extrusion blow molding die and improve the air removal rate; Fifth, optimize the design of blow molding cooling and layering system, ensure the balance of cooling and layering effect, make the temperature transfer uniformly in the liquid path of the cooling system, and avoid plastic products deformation due to improper delay of blow molding time. Under normal circumstances, the extrusion blow molding die is designed as a pair of dies to blow molding one plastic part each time. The advantages of this die structure design are simple and convenient, convenient and efficient processing process, and economic and appropriate manufacturing cost. For extrusion and blow molding processing of plastic oil tanks, more than two mold production stations shall be designed according to the assembly requirements and project scale to prevent improper vacancy or waste of human and material resources. The structural design drawing of the extrusion blow molding die of the plastic oil tank is shown in Figure 1 and Figure 2

blow mold structure design

1, cavity plate bottom plate; 2. Socket head cap screw; 3. Left cavity plate; 4. Positioning piece; 5. Avoid bumping and right cavity plate; 6. 7. Slotted set screw; 8. Insert fixed core; The extensometer of total elongation should have at least 100mm gauge length 9 and guide sleeve; 10. Guide post; 11. Lifting rings; 12. Water pipe joint; 13. Oil inlet port; 14. Conical positioning device

Figure 2 blow molding mold structure design

2. Parting surface design of extrusion blow molding mold for fuel tank

parting surface design of extrusion blow molding mold for plastic fuel tank, the ratio between the transverse maximum diameter of the mold cavity and the outer diameter of the tubular parison should be set within a reasonable range to minimize the ratio gap; The thickness of the blow molding mold channel pipe should be balanced to improve the accuracy of extrusion blow molding; Designers should use the parting surface design in the mold structure to simplify the extrusion blow molding manufacturing process and improve the success rate of demoulding plastic parts. When determining the type and position of the parting surface, it is necessary to ensure that the concave degree in the parting blow mold of the two concave cavities is consistent, and the thickness of the cavity cannot be unbalanced

3. Exhaust design of plastic oil tank extrusion blow molding mold

air exhaust design is the key link of plastic mailbox extrusion blow molding process. During blow molding, the volume of air discharged should be exactly equal to the volume of the concave cavity of the mold minus the volume of the parison when the mold is closed. In order to smoothly and quickly discharge the excess air between the plastic blank and the concave cavity of the mold, prevent the residual air from blocking in the mold, improve the blow molding efficiency of the product, ensure that the medium-sized blank and the mold are fully fitted during the blow molding process, and avoid the depression, protrusion or other shape changes and quality problems caused by the influence of air barrier on the surface of the plastic part. Poor exhaust will also prolong the cooling time of the workpiece, resulting in uneven distribution of the wall thickness of the workpiece and reducing the mechanical properties of the workpiece. Therefore, enough exhaust channels should be set up to ensure that the parts can be formed and full. Because the cutting edge, compression section and residual groove are uniformly set on the outside of the parting surface of the mold, the residual material will close the parting surface during molding, and the gas cannot be excluded from the parting surface, so the mold can only exhaust in the form of opening an exhaust hole in the mold cavity

4. Cooling and layering design of plastic oil tank extrusion blow molding mold

almost all thermoplastic molding processes such as extrusion molding, injection molding, vacuum molding, etc., their molding cycle largely depends on the length of plastic cooling time. This is especially true for blow molding, because its cooling time accounts for more than 60% of the molding cycle, and 90% for thick wall plastic parts. If the cooling is uneven, there will be differences in the shrinkage of various parts of the plastic parts, resulting in warping of the parts, deflection of the bottleneck and other phenomena. The mold adopts the straight through cooling mode, that is, drill holes directly on the template, form a cooling circuit in series outside the mold, and pass in the cooling medium for cooling

5. Blow molding process design of the extrusion blow molding die of the plastic oil tank the extrusion blow molding process of the plastic oil tank

first, the open blow molding die is moved to the lower part of the extruder head, and the extrusion solution: out of the machine, the parison is extruded in the two-piece blow molding die. After reaching the required length, the blow molding die is closed, the parison is cut off and removed from the lower part of the extruder head, and the punch of the oil inlet hole of the forming oil tank moves forward, In contact with the parison and the blow mold, the center of the punch is opened with a gas channel, from which compressed air is introduced into the parison, and the parison is blown to make it in close contact with the inner surface of the blow mold. After cooling and shaping, the mold is opened to take parts

to sum up, in the extrusion blow molding design scheme of plastic oil tank, the relevant design units, enterprises and their staff should determine the mold production station for blow molding processing according to the actual production needs, and enhance the core competitiveness and economic strength of the enterprise through the optimization of blow molding mold structure design and the improvement of mold design process level