Product diagram of channel cover is shown in Figure 1. Maximum size of product is 228.00 mm * 107.30 mm * 29.40 mm, average thickness of plastic part is 1.30 mm, material of plastic part is MBS, shrinkage rate is 1.004, and weight of plastic part is 37 grams. Technical requirements for plastic parts are that there must be no defects such as peaks, underfilling of injection molding, flow lines, pores, warpage deformation, silver streaks, cold materials, jet lines, bubbles and so on. This article takes channel cover as an example to introduce key points of needle valve type adiabatic runner injection mold design.

 

Figure 1 Product Picture of Channel Cover
It can be seen from Figure 1 that plastic part is a flat shape with a flange on one side, and a slider needs to be designed here. Channel cover is appearance part of printer, its surface appearance is required to be high, and it is mostly formed by hot runner molds.
Material of plastic part is MBS, commonly known as transparent ABS. ABS material is a ternary blend of acrylonitrile, styrene and butadiene. Replace acrylonitrile of ABS material with polymethyl methacrylate (PMMA, plexiglass, acrylic), ABS becomes MBS, material has transparency. In addition to being transparent, MBS has other properties similar to ABS.
Size of plastic part is large, and mold cavity is ranked as 2 cavities. Mold base is a non-standard mold base 5065, which is mainly due to different coding modes. Coding method of Japanese molds is slightly different from that in China. For large-scale molds, in order to increase safety and reliability of mold coding, increase stability of mold injection, code mode combining V-groove and bolt is adopted. V-shaped groove is opened on the side of mold and matched with V-shaped block on injection molding machine. Mold design drawing is shown in Figure 2. Panel and bottom plate are each added with 4 bolt holes, which are screwed on mold plate of injection molding machine.
Front and rear mold cores are large in size, are processed in two parts separately, are positioned and installed with a compression block. When arranging cavity, it is necessary to design side with sliding block of plastic part on both sides of mold world. Glue feeding method of mold is that a hot nozzle enters glue in a runner in the middle of mold. Single hot nozzle of this runner is essentially an adiabatic runner. After molten plastic flows out from heating nozzle, it enters runner and enters plastic part through two side gates.
Front and back sides of plastic part of printer shell are exterior parts, so there should be no obvious ejection marks. Therefore, 3 top blocks are designed on the edge of plastic part, one straight top and one lifter.

 

Mold cooling is designed for fixed mold to pass water directly, forming 3 U-shaped loops. Movable mold is a cooling method that combines direct water transport and ponds.
Needle valve nozzle uses valve needle to mechanically close gate. Common needle valve gate is shown in Figure 3. (a) is a needle valve hot nozzle with a sprue sleeve. In addition to valve needle mark on the surface of plastic part, there is also a large concentric circle mark. (B) is a needle valve hot nozzle without a sprue sleeve, and surface of plastic part has only valve needle marks. (C) is a large needle valve type hot nozzle with sprue sleeve, and gate imprint is same as (a). (D) and (e) are hot nozzles with lengthened sprue sleeves, lengthened part can be shortened according to shape of plastic part or processed into a shape suitable for plastic part. (F) End surface of sprue sleeve is processed into a shallow spherical surface to facilitate flow of plastic.
Geometric parameters of valve needle head directly affect quality of injection molded parts. Valve needle closing method is shown in Figure 4. Matching shapes of gate and valve needle are cone-shaped and cylindrical. Tapered fit is shown in Figures (a) and (c). It is necessary to pay attention to taper matching of valve needle and gate. The two cannot have same taper, that is, inclined surfaces of the two cannot be completely fitted. Contact between the two should be line contact, so that valve needle can pass through gate and squeeze excess molten plastic from narrow gap behind contact line to rear. If two angles are same, valve needle will squeeze plastic into gap between gates, and valve needle will also be difficult to close. If closing force of valve needle is increased, gate will be crushed and mold will be damaged. Taper of gate should be greater than taper of valve needle. Gate taper is generally 36゜～40゜degree, and valve needle taper is 22゜～38゜degree.

 

 

 

 

 

Figure 2 Die diagram of channel cover

 

Figure 3 Several ways of needle valve gate

 

Figure 4 Valve needle closing method