Controller connector is controller element of gas station output device. This article introduces design points of controller joint automatic thread removal mold. Maximum size of product is ø33.2 mm * 17.8 mm, average plastic thickness of plastic parts is 1.65 mm, material of plastic parts is PP, shrinkage is 1.018, and quality of plastic parts is 2.6 grams. Technical requirements for plastic parts are that there must be no defects such as peaks, dissatisfaction with injection molding, flow lines, pores, warpage, silver lines, cold materials, and spray lines. Shape of plastic part is similar to bottle cap, top opening is ø19.5, there is a ring of anti-rotation groove on the edge of mouth, and there are 4 rings of thread inside. It is necessary to design a fully automatic thread removal device. Mold design drawing is shown in Figure 1.

 

Production volume of plastic parts is very large, and it is necessary to design a fully automatic thread removal mold. For small plastic parts similar to bottle caps, before mold design, it is necessary to make a strong thread removal judgment. If it is not possible to force demoulding, a thread-releasing device needs to be designed. Basic principle for judging whether it can be detached is pitch size and tooth height. If pitch is too small or height of tooth pattern is large, it is difficult to take off when tooth pattern is sharp. Another is accuracy of thread. High-precision threads cannot be demoulded.
Mold cavity is arranged in four cavities, and four cavities are arranged in a circle, which is conducive to central gear drive. There are four kinds of power sources for thread-removing mold, which are driven by cylinder, rack with opening force, screw rod, and hydraulic motor (motor). Automatic thread demoulding mechanism using motor as power source is difficult to control limit of mechanism, so it is difficult to meet requirements of high-precision thread products. Automatic injection mold for internal thread removal introduced in this article uses a low-speed high-torque cycloid hydraulic motor to drive chain through a rotary motion to drive sprocket. Gear core rotates and retracts thread core through gear transmission to complete thread removal of plastic parts. Mold has a simple structure, stable control and reliable operation.
Because of its unique technical advantages in power-to-weight ratio, stepless speed regulation, automatic control, and overload protection, hydraulic transmissions are increasingly used by designers and producers. Hydraulic motor used in automatic thread removal mold is a cycloid hydraulic motor, which has following advantages:
1. Small size and light weight, its external dimensions are much smaller than other types of hydraulic motors with same torque.
2. Wide speed range, stepless speed regulation, minimum stable speed up to 15 rpm, easy installation and layout, low investment cost.
3. Rotating inertia is small, easy to start under load, both forward and reverse can be used, and there is no need to stop when changing direction.

 

Gating system of mold is designed to be injected by submerged front mold of latent gate. Nozzle material is pulled by pulling rod 7 and pulling rod 9. Latent gate was broken during mold opening. Nozzle material and plastic parts are left in moving mold.
Common way of traditional demoulding is elastic push plate structure, cavity is set on the side of  fixed mold, and threaded core is set on the side of movable mold. After mold is opened, reduction gear motor drives sprocket transmission gear, and gear drives screw core for rotational movement. Rotational movement generates axial thrust (generally, in order to increase thrust effect, 4 springs need to be installed under thrust plate) to push thrust plate, plastic part moves axially relative to screw core, and under anti-rotation effect of convex stripe, screw core rotates and plastic part moves axially, thereby demoulding inner thread of plastic part. But this thread demoulding method, at the moment when thread is disengaged, due to elastic force of spring and position of tooth shape is not easy to accurately control, tail teeth are often strained and cannot fully meet high precision requirements of product. Simple summary of this springboard structure is that threaded core only rotates and does not retreat, and plastic parts move forward.

 

Figure 1 Controller connector mold drawing

Threading mould of controller joint introduced in this article adopts structure that thread core rotates and retreats while thread is removed by hydraulic motor. Plastic part remains in place until push plate or ejector pin pushes it out. Obviously, this mold design is suitable for molding requirements of high-precision plastic parts.
After mold parting surface is opened, hydraulic motor 15 drives chain 24 to rotate through sprocket 21, then drives gear sleeve 26 to rotate, gear sleeve 26 drives gears of four cavities to rotate, and thread core 34 continuously retreats to complete thread demolding. Rear mold core 33 remains stationary, with a cooling water spacer 42 at the center, and a rubber ring 41 for sealing. After unthreading is completed, under action of travel switch 17, hydraulic motor stops rotating. Ejector rod 28 pushes out ejector pin plate. Ejector pin plate drives center push rod 36 to push out push plate, and pushes plastic part from rotation preventing insert 35. This set of molds cleverly designs ejector rod 28 inside gear sleeve 26. It not only saves space, but also makes mold structure compact and ejection smooth.