Design of injection mold for the most practical li

Design of injection mold for practical liquid storage plastic container

Abstract: Aiming at the problem that it is difficult to obtain uniform wall thickness for forming cylindrical plastic containers, a practical mold structure is given. Based on the analysis of the technological characteristics of liquid storage plastic containers, the design of mold systems and molding parts are introduced in detail, and the working process of the mold is discussed

key words: injection mold liquid storage barrel push block mold structure

1 plastic part process analysis

a liquid storage plastic container is shown in Figure 1, and the material is translucent polypropylene (PP). The plastic part is barrel shaped, with a height of 130mm and a wall thickness of 2mm. There is a circular depression on the outer side of the bottom. The outer diameter of the top is ∮ 118mm and the inner diameter is ∮ 114mm. There is M120 around the outer side of the top × 1.5mm thread, 3mm bulge around the outside of the top. Plastic parts shall have smooth internal and external surfaces, regular shapes and uniform wall thickness

2 mold structure

according to the structural characteristics and specific requirements of plastic parts, the mold structure design should consider the following aspects (see Figure 2)

2.2 design of formed parts

the plastic part is a cylindrical shape with a certain taper, and the wall thickness is required to be uniform. Therefore, the coaxiality must be ensured when the moving mold and the fixed mold are matched. The contact surface between the fixed mold 6 and the slider 10 has been implemented in 40 countries and regions in the world, and the deposit system is designed to be an inclined fit, which not only enables the slider 10 to be strongly locked, avoids the bucket retreat of the slider 10 due to the effect of the mold expansion force during injection, but also enables the moving and fixed mold to automatically align with the center, so as to ensure that the plastic parts obtain a uniform wall thickness. The threads on the outside of the top of the plastic part are formed by a pair of sliders. During processing, the central thread part, the inclined plane and the rectangular inclined holes on both sides are processed on a blank. Then the blank is divided into two parts from the middle, and the formed parts are polished, combined, and then polished, so as to ensure the forming quality of the thread part

the movable and fixed molds are designed into inlay type, which not only reduces the processing difficulty, but also saves valuable materials. During maintenance, only the damaged parts need to be replaced, reducing the maintenance cost. The fit between the inserts is required to be tight, so as to avoid seam lines on the surface of the plastic parts

in addition, researchers on the surface hardening treatment of connecting rod 8, bushing 7 and push block 2 made a detailed introduction in a paper in the magazine Angewandte Chemie to improve the surface hardness

2.3 cooling system design

due to the thin wall of plastic parts and the long barrel body, the design of cooling system has a great impact on forming plastic parts and improving production efficiency. In order to improve the cooling efficiency, the spiral cooling method is adopted for the moving and fixed parts. A semicircular spiral water channel is processed on the outside of the fixed mold insert 4 and the cooling plate 1, which is externally connected with the cooling water pipe to form two independent cooling systems respectively. Practice has proved that the cooling effect is good, the product surface quality is good, and the production efficiency is high

2.4 design of push out system

the bottom of the plastic part is large. If the push rod is used to push out, the plastic part will be deformed due to uneven stress, and the surface will also have defects such as top white. The mold uses a push block to push out the plastic part. The conical push block 2 is placed on the top of the cooling plate 1 and connected with the connecting rod 8 through the pin. The connecting rod 8 is connected with the ejector mechanism of the injection molding machine through the snap ring 17 and the push plate 16. The contact area between the push block 2 and the plastic part is large, and the force is uniform, which can ensure the quality of the plastic part. At the same time, the pushing part of push block 2 is also a molded part at the bottom of the plastic part, so the surface smoothness is required to be high. In addition, because the top of the plastic part has threads, the limiting force of the threads remaining in the slider should be relieved before pushing out. Here, the bending pin lateral core pulling mechanism is adopted, and the core pulling action can be completed at the same time of mold opening

3 mold working process

mold closing, the conical surface of push block 2 fits in place with core 9, and the nozzle of injection molding machine extends into gate sleeve 3. After injection molding and pressure maintaining, the plastic part is formed. When lifting the mold, under the action of the bending pin 13, the sliding block 10 moves inside and outside to complete the side core pulling action of the threaded part: the moving distance of the sliding block 10 is limited by the positioning pin 11 to ensure that the bending pin 13 smoothly enters the inclined hole when closing the mold. After the moving mold retreats into place, driven by the ejection mechanism of the injection molding machine, the pushing block 2 moves forward to push the plastic part away from the core 9. The plastic part itself has a certain taper, and the plastic part can be removed from the core 9 without too long pushing distance. Before closing the mold, the pushing mechanism of the injection molding machine returns first, and the push block 2 retreats to its position, and then the moving mold moves forward and is combined with the fixed mold: otherwise, the contact between the fixed mold insert 4 and the push block 2 will damage the surface smoothness of the push block 2, thereby affecting the quality of the inner surface of the plastic part

4 modulate its indication to zero point or take it as the starting position of zero point conclusion

the production practice has proved that the mold has reasonable design, compact structure and convenient operation; The coaxiality between the moving and fixed dies is within the specified range, the thrust of the ejector mechanism is uniform, and the cooling is uniform and rapid; It can meet the requirements of plastic molding quality and production efficiency

author/he Bintian Fuxiang of Qingdao Institute of architecture and engineering

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