Product of irradiation lamp holder is shown in Figure 1. Maximum size of product is 98.30 mm * 70.00 mm * 68.40 mm, average thickness of plastic part is 2.00 mm. Material of plastic part is liquid crystal polymer LCP, T130 or T150, UL94-V0, shrinkage rate is 1.0035, density is 1.7, and weight of plastic part is 42.17 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, etc.

 

Figure 1 Product Picture of Irradiation Lamp Stand
It can be seen from Figure 1 that plastic part is shaped as a complex shell formed by a regular planar rectangular structure. One side and one end surface respectively have a place to form undercut of mold. It is necessary to design core pulling of slider. Core pulling direction of two sliders is shown in Figure 3. There is a circular arc surface at the bottom of end slider. Here, a reset device needs to be designed to reset ejection system first and then close mold to avoid interference between thimble at the bottom of eject pin and slider.
When irradiation lamp holder is in use, plastic parts need to withstand high temperatures. According to performance requirements of plastic parts, plastic parts need to use LCP, and fire rating is UL94-V0.
There are 12 fire protection classes in UL94: HB, V-0, V-1, V-2, 5VA, 5VB, VTM-0, VTM-1, VTM-2, HBF, HF1, HF2. Among them, HB, V-0, V-1, V-2, 5VA, 5VB are suitable for general hard plastics. Flame retardant grades of plastics increase gradually from HB, V-2, V-1 to V-0. V-0 is the highest requirement. Criterion is that flame is extinguished within 30 seconds after two 10-second combustion tests are performed on sample. No burning objects should fall. Judging whether there is a burning material falling, is based on whether it can ignite medical absorbent cotton as standard.

 

Liquid crystal polymer LCP has hot melt LCP and thermotropic LCP. Hot-melt LCP is mostly used for spinning. As an engineering plastic, thermally induced LCP is used. Appearance of liquid crystal polymer is generally beige, and there are also white opaque solid powders with a density of 1.4 to 1.7 g/cm3. Liquid crystal polymer has characteristics of high strength and high modulus. Because of its self-reinforcement, liquid crystal plastics that are not reinforced can reach or exceed level of mechanical strength and modulus of ordinary engineering plastics reinforced with glass fibers; if it is reinforced with glass fiber, carbon fiber, etc., it is far more than other engineering plastics. Liquid crystal polymers also have excellent thermal stability, heat resistance and chemical resistance. For most plastics, creep defects of liquid crystal materials are negligible, they have excellent wear resistance and anti-friction properties. Heat distortion temperature of LCP is 275～350℃, which is one of the highest heat distortion temperatures among thermoplastics. Liquid crystal plastics have high thermal stability, and LCP decomposes at 560℃ in the air. It is solder-resistant and can be immersed in solder at 320℃ for 5 minutes without change. Liquid crystal plastic has good weather resistance and radiation resistance, has excellent flame retardancy. After flame is extinguished, it will not continue to burn. Its flame retardant rating reaches UL94V-0 level. LCP is one of special engineering plastics with the best fire safety. LCP also has excellent electrical insulation properties and outstanding corrosion resistance. Molding temperature of LCP is high. Because of its different varieties, melting temperature is in the range of 300～425℃. LCP has low melt viscosity and good fluidity, similar to olefin plastics. LCP has a very small linear expansion coefficient and good dimensional stability.
LCP can be used in electronic and electrical industry, and can be used to make office machinery, precision instruments, auto parts, etc. In addition, LCP has been used in microwave oven containers, this kind of stove must be resistant to high and low temperatures, LCP can fully meet requirements. It can also be used for printed circuit boards, satellite electronic components, jet engine parts, plastic containers, sporting goods, films, fibers and medical supplies. New applications include: high-filled liquid crystal plastics can be used as integrated circuit packaging materials to replace epoxy resins as packaging materials for coil skeletons; used as fiber optic cable joint sheaths and high-strength components; instead of ceramics, it is used as filling material in separation tower for chemical industry. At present, price of TLCP is still high, and it is mainly used in electronics industry. Demand is small and market is small. When it is used as an intensifier of polymer structural materials, demand, market and output are large, its cost and price will follow. Benefits brought by decline will be immeasurable, which is potential of TLCP and its alloy applications. Although there are almost no TLCP products in our country, some are only in research and test stage, above-mentioned potential and international trends urge us to keep up with pace of international TLCP alloy research and development. It is expected that in the near future, with development of my country's economic construction, it is believed that country will also break through difficulties and realize localization.
LCP has good processing performance, and commonly used molding processing conditions are shown in Table 1.

 

According to existing tonnage of injection molding machine, mold design cavity ranking is determined to be 1 cavity, two sliders are designed on ground side and opposite operation side. Mold design diagram is shown in Figure 2. Gating system is designed as a three-plate mold, and glue is injected at the point of gate. Number of gates is 3 points, and location is on the top of plastic part. Mold base is standard simplified nozzle FCI3540. Opening and closing movement of three-platen mold is controlled by limit screw and driven by pulling plate.
Water transportation of front and back molds, sliding block of mold is all straight-through water transportation, with a faster flow rate and a higher cooling efficiency.
Ejector of plastic part is ejected by a thimble, and thimble plate is guided by center toss.
Both sliders are driven by oblique guide pillars, and glue position is designed with slider inserts, which is convenient for designing water transportation and flying molds.

 

There is a thimble at the bottom of slider of mold, and a reset mechanism must be designed. When designing the first reset mechanism, care must be taken not to affect operation of manipulator. This device is built-in, occupies a small space, and is easy to install. Even if ejector stroke of push rod is large, it can fully realize the first return effect of ejector plate, and it can also be installed upside down for secondary ejection. When installing, you need to pay attention to choosing stroke to determine reset rod and length of straight-body guide sleeve.
When there is a thimble in the stroke range of side core slider, even if reset lever is used, slider may collide with thimble before mold clamping and return process, causing great damage; in general, even if reset lever and spring are used to ensure reset of thimble plate, some undesirable situations may occur, such as: a. Thimble or reset lever is jammed b. Spring is broken or aging c. Stroke of thimble is too long and spring force is not enough to cause thimble plate to completely reset, etc. For above mold opening problems, we need to increase thimble plate first reset mechanism to prevent these problems.

 

 

Figure 2 Mould diagram of irradiation lamp holder

 

Figure 3 Slider analysis

 

Table 1 Common LCP injection molding conditions