Air purifiers, also known as "air cleaners", air purifiers, purifiers, are products that can adsorb, decompose or convert various air pollutants(generally including PM2.5, dust, pollen, odor, formaldehyde, etc.) and effectively improve air cleanliness. There are many different technologies and media in air purifier that enable it to provide clean and safe air to user.
Air purifiers are used in home, medical, and industrial fields. In home appliance field, single-type household air purifier is mainstream product in the market. Use of air purifiers to purify indoor air is one of internationally recognized methods for improving indoor air quality due to persistence and uncertainty of release of air pollutants in relatively closed spaces. This paper introduces key points of molding design for circular complex products through air purifier body products.

Product diagram of air purifier body is shown in Figure 1. Plastic material is PC, shrinkage rate is 1.005, wall thickness of plastic part is 1.80mm, and size of plastic part is ¢183mm X 230mm.

 

 

As can be seen from air purifier body product drawing, plastic part has a large size, and there are 5 inverted buckles (two round holes are combined on one slider). There are complex rubbings near two sliders, both to avoid interference with slider, but also to consider its craftability and strength.

Size of plastic part is large, structure is complex, core is inclined at a plurality of places, and cavity 1 is out of 1. Non-standard mold base LKM 640x640 A330 B205.5 C175, AB board is round, easy to turn. Front and back sets of guide pillar guide bushes are symmetrically distributed around AB plate, and AB plate is designed with a frustum as a secondary positioning. Customer-specified injection machine is a 530-ton machine, clamping force and plasticizing capacity can fully meet requirements.
Rigidity of mold base of a large mold is very important, a positioning pin is added between each template to increase rigidity. A positioning pin 23 between square iron and bottom plate is disposed near bolt.

For cylindrical parts, parting surface is definitely a plane, no suspense. Difficulty is to first determine which side is in front mold and which side is in back mold. In combination with ejection mode of plastic part, big end is left in movable mold, which is easy to eject after mold is opened. See molding design drawing 2.

PC material has poor fluidity. In order to facilitate filling, a single hot nozzle system is designed. Molten plastic flows from hot nozzle to top surface of plastic part, dives through split flow path, and injection at 4 points. Main parameters for selecting a single hot nozzle are plastic brand, wall thickness of plastic part and quality (weight) of plastic part. It is often necessary to consult hot runner supplier.

Plastic parts are cylindrical parts, and clamping force of core is large. The best way to get out of this plastic part is to push board out. Push plate is designed in the form of a pusher ring, that is push plate insert 17, pusher insert is pushed out by four push rods, and guide sleeve is guided. Insert 18 and insert 19 are made of beryllium copper. Beryllium copper has less friction when draft angle is small or rubbing distance is long. This is a performance that other steels do not have. In extreme cases , it can achieve zero degree of draft angle. Therefore, choice of beryllium copper can effectively prevent plastic parts from dragging, which is good for demolding.

Mold needs to design 4 sliders. Slider 1 and slide 4 are driven by a cylinder, slider 2 is driven by a T-slot, and slider 3 is driven by a slanted guide. Mold opening is divided into two molds. First, panel is separated from A board. AB board is locked with a button 38, front mold sliders 1 and 2 are cored, spring 10 assists in opening mold and limit screw 9 is limited. Immediately after parting surface is opened, AB plate is separated, slider 3 and slider 4 are finished. Wear plates 25, 31, 33 are added to bevel and bottom of slider. Cylinder-driven slider requires a stroke switch to control start and end points of slider.
Button 38 is a typical European common mold opening control component, the most common being STRACK brand and EOC brand (now acquired by DME), mechanically controlled, accurate and reliable.

Front mold cavity has a cooling channel along circumference. A cooling spiral water path is arranged in the middle of rear model core to ensure that injection production is carried out normally.

Considering circular shape of plastic part, front part cavity and back model core, push plate insert and other main parts are round, which is convenient for CNC lathe machining and heat treatment after grinding. Mold base is made of 718H. All mold cores and slider inserts are made of imported S136 steel and heat treated HRC48-52.