Gas monitor accessories injection mold design

Time:2022-11-29 09:03:31 / Popularity: / Source:

Gas monitors are widely used in Internet of Things, petrochemical, sewage treatment, coking coal smelting and other industries, can be used to alarm for toxic and harmful gases. A European brand of gas monitor accessories has 4 plastic parts, namely turning button, pendulum,door bolt button and pawl. 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. Four plastic parts are all plastic parts in same model, and actual number of plastic parts is 1. Plastic material is POM, commonly known as Saigang, which has good mechanical strength and fatigue resistance. Number of cavities specified by customer of this set of molds is 2+2+2+2.
injection mold design 
Figure 1. 4 product diagrams of gas monitor accessories
It can be seen from Figure 1 that four plastic parts are all small in size and in different shapes. Size and shape of plastic parts are quite different, which brings great difficulty to mold design. Multiple plastic parts of same model are arranged on same mold, which is called a family mold. Main points that need to be paid attention to when designing mold are as follows:
1) Quantity of each plastic part matches actual installed quantity;
2) If some of plastic parts are produced separately, a runner switching device needs to be designed in the center of mold.
3) Make runner as balanced or close to balance as possible.
4) Pay attention to position and direction of plastic parts, try to balance parting surface as much as possible, avoid big ups and downs of parting surface.
5) Make slider as far as possible to face outside of mold when ranking.
Mold design cavity ranking is 2+2+2+2, mold base is an inch non-standard mold base, code mode is that there are two code grooves at the bottom of fixed mold base plate, these two grooves are stuck on fixed mold mounting plate of injection molding machine to increase rigidity of code mold. A zero-degree positioning block is designed on four sides of mold base to increase accuracy of mold clamping. Characteristics of British mold are that mold base and standard parts are inch size, size of movable and fixed mold base plate is larger, such as this mold. 3d drawing of mold design is shown in Figure 2. Design of slider and its parting surface is shown in Figure 3.
injection mold design 
Figure 2 3d drawing of mold design
injection mold design 
Figure 3 Slide block and its parting surface design
Ejection method of plastic part adopts ejector pin, and a sensor is designed at the bottom of ejector pin to monitor injection pressure in mold cavity. Cooling of plastic parts adopts long throat cooling, that is, long throat is directly screwed on the front and rear mold cores. This cooling method eliminates need for rubber rings and is suitable for high temperature molds.
injection mold design 
Figure 4 3D drawing of rear mold core
Pressure in mold cavity depends on characteristics of molten plastic, geometry of injection molded part, cavity layout, and other factors. In injection molding process, mold internal pressure measurement system (also known as visualization system inside cavity) is used to measure, record, and manage waveform of mold internal pressure change. By intuitively analyzing dynamic process of injection molding, it provides guidance for improving mold design and improving molding process control, which helps to improve efficiency and quality of injection molding. There are two ways to measure pressure inside mold: direct measurement and indirect measurement using sensors.
injection mold design 
Figure 5 Sensor design under thimble
Currently, there are two types of pressure sensors used in mold cavities, flush mount and indirect. Flush-mount sensor is inserted into mold cavity by drilling a mounting hole in the back of mold cavity, its top is flush with surface of mold cavity, and its cable is passed through mold to connect to monitoring system interface located on outer surface of mold . Advantage of this sensor is that it will not be disturbed by pressure during demolding, but it is easily damaged under high temperature conditions, making installation difficult. Indirect sensors are divided into two types: sliding type and button type. All of them can transmit pressure exerted by plastic melt on ejector or fixed pin to sensor on mold ejector plate or movable platen. Slide sensors are usually mounted on ejector plate of an existing ejector pin. Sensor design under thimble is shown in Figure 5.

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