Drip pot + tee + handle is an infusion product in the category of medical device products. Drip pot + tee + handle product is shown in Figure 1. Maximum dimension of drip pot product is 65.51 mm * ø17mm, average thickness of plastic part is 0.82 mm, plastic part material is PVC, shrinkage rate is 1.03, and plastic part weight is 3.10 grams. Maximum dimension of three-way product is 18.94 mm * 17.51 mm * 4.74 mm, plastic part material is PC, shrinkage rate is 1.005, and plastic part weight is 0.25 grams. Maximum external dimension of handle product is 14.36 mm * 8.08 mm * 4.74 mm, plastic part material is PC, shrinkage rate is 1.005, and plastic part weight is 0.14 grams. Technical requirements for plastic parts are that there shall be no defects such as peaks, underfilling, flow lines, pores, warpage deformation, silver lines, cold materials, and spray lines.

 

Figure 1 Product map of drip pot + tee + handle
Drip pot, tee and handle are assembled together to form a set of infusion device. As can be seen from Figure 1, drip pot is a long cylindrical plastic part with a circle of protruding buckles inside, and protruding height is 0.3, which needs to be designed for forced demoulding. Both inclined hole and center hole of three-way plastic parts need to be designed with slider core pulling, neutron mating part of slider needs to be tightly sealed, and there should be no slight sharpening. Any small batches will enter human body through infusion medicine, which will increase possibility of medical risks. Therefore, cooperation of the two slider neutrons needs to have higher precision requirements.
Mold design cavity ranking is 1+1+1, and each of three plastic parts has one cavity. Since materials of plastic parts are PVC and PC, respectively, injection molding needs to be separately injected, and switching runner device is used to realize injection respectively. Mold design diagram is shown in Figure 2. Mold base is standard mold base GAI2525, gate is side gate, and gate of drip pot is located on shoulder.
Core pulling of central part of slider of tee adopts oil cylinder core pulling, and neutron in slope direction adopts inclined guide column core pulling. Core pulling of oil cylinder can insert neutron in place in advance before mold is closed, and then insert neutron in oblique direction when mold is closed. In this way, neutrons are inserted in order to ensure precise coordination of two neutrons and prevent neutrons from being damaged.
Ejection of dripping pot is ejection of cylinder. Due to larger diameter of plastic part, longer movable mold core and more heat, a cooling circuit needs to be designed in the center of cylinder needle. Cylinder needle water transport connection board is shown in Figure 5 and shown in Figure 6.

 

Figure 2 Mold diagram of drip pot + tee + handle

 

Figure 3 Parting surface runner diagram
Since PVC is a corrosive plastic, its mold steel must be stainless steel. Therefore, S136H is used for front and rear core steel of this set of molds. PVC is a heat-sensitive material, and its injection molding process is poor. Reason is that too high melting temperature or too long heating time can easily decompose PVC, so controlling melting temperature is the key to injection molding PVC products.
Heat source for melting PVC raw materials comes from two aspects: shear heat generated by screw movement and resistance wire heating of outer wall of barrel, but mainly shear heat of screw movement, and external heating of barrel is mainly to provide heat source when machine is started.

 

Figure 4 3D drawing of the moving mold

 

Figure 5 Cylinder needle water transport connection board
Following points should be paid attention to in design of PVC products and molds:
1. Product should not have sharp corners or sudden changes as much as possible, and thickness should not change much to prevent degradation of PVC.
2. Injection port of mold should be slightly larger than nozzle hole, and larger than diameter of staggered part of main channel, so that PVC material flows into mold cavity without stagnation and pressure can be balanced.
3. Gate should be designed at the thickest wall of product, width is sufficient, and length is preferably between 6-8mm, so that PVC material can flow smoothly.
4. In order to make plastic part easy to demould, runner should preferably be circular, and diameter should be selected between 6-10mm according to size and weight of product.
4. Mold temperature should have a cooling water control device, so that mold temperature can be controlled between 30℃ and 60℃.
5. Mold should have a smooth surface and be chrome-plated to prevent corrosion.

 

Figure 6 Dimensions and specifications of cylinder needle water transport connection plate