The exhaust system should ensure that the gas in the cavity is smoothly discharged, and also prevent the material from entering and exhausting channels from causing flashing of the product or blockage of the gas channel during mass production, most plastic mold factories and plastic mold suppliers only know that they need to open an exhaust slot, but they don’t how large is reasonable. So the cross-sectional size design at the entrance of the exhaust system is very important, in order to meet the above requirements, the inlet section of the exhaust system is usually designed as a gap with a larger aspect ratio (h/w) (see pictue 1), and the gap depth (exhaust gap or exhaust slot depth) h, which is less than the overflow value of the material into the mold is limited, generally 0.02-0.05mm; the gap width w is determined according to the gap depth H and the cross-sectional area A of the exhaust passage required to discharge the gas in the mold cavity during the filling time (w≥A /h).
The cross-sectional area A of the exhaust channel is calculated as follows: A=0.05V/N
In the formula: A exhaust channel cross-sectional area mm²
V—total volume of cavity and pouring system, cm³
n——the number of exhaust slots
The overflow value is the smallest gap that the material can flow into, the overflow value of the molding material depends on the fluidity of the material determined by the material characteristics and process conditions. The better the fluidity, the smaller the overflow value, tThe overflow values of commonly used plastics and conventional molding conditions are shown in picture 2 in the following table.
Picure 3 shows the design standard of the exhaust slot, and picture 4 shows the wrong opening method of the exhaust slot.