Hydraulic diameter conversion of runners in plastic mold gating system design
Hydraulic diameter refers to 4 times the ratio of the flow cross-sectional area to the perimeter, as the wall shear stress of non-circular pipes is not even distributed along the surrounding walls, only the average value of the surrounding walls can be calculated.
The main cross-sectional shapes of the shunt: round, trapezoidal and rectangular, in order to reduce the pressure heat loss in the runner, the cross-sectional area of the runner should be maximized, and the internal surface area for heat dissipation should be the smallest.
The efficiency of the runner is expressed by the ratio of the cross-sectional area S of the runner to its cross-sectional circumference L.
Splitter efficiency (hydraulic radius) n=cross-sectional area/cross-sectional circumference=S/L
Hydraulic diameter=4n=4S/L
From the above information, we can see the flow efficiency of different cross-section runners, round and trapezoidal cross-sections are the preferred runners. The size of the runner is usually selected based on the diameter of the circular runner (equal to the hydraulic diameter); when other cross-section flow channels are used, the hydraulic diameter must be converted so that the flow efficiency can meet the calculation requirements (see the example below) ).
Example: It is calculated that a product needs a 8m hydraulic diameter runner, and a semicircular runner is now used; what size of semicircle is more reasonable?
Hydraulic diameter=4n=4S/L=(4*(πr²)/2)/(π*r+2r)=8
Radius r=8*(π+2)/(2π)=6.55
Diameter D=2*r=6.55*2=13.1
Answer: A semicircular runner with a diameter of about 13m is more suitable.
Key points of gas-assisted injection molding process
Apr 20, 2022Gas injection parameters The gas-assisted control part is a device that controls the gas pressure in each stage, the gas-assisted parameters have only two values: gas injection time (seconds) and gas...viewParting surface venting of runner system
Mar 10, 2022There are a large amount of gas in the main and sub channel, these gas are discharged through the pull rod (push rod) during injection processing, a part of gas come out from exhaust slot on parting...viewPlastic injection mold heating
Feb 16, 2022When the plastic injection molding process requires the mold temperature to be above 80°C, a temperature adjustment system with heating function must be provided in the mold. In addition,...viewReasons for making the exhaust system of the injection mold
Feb 28, 2022The gas in the injection mold includes not only the air in the cavity, but also the air in the gate and the decomposition gas generated by the plastic melt, and the steam which caused by plastic in...viewClassification of side parting and core pulling mechanism
Jul 17, 2022According to the structural characteristics of plastic moulding, the side core-pulling mechanisms are divided into the following six categories: 1. The side core-pulling mechanism of "slider + guide...viewThe main design points of the design of the plastic mold pouring system
Jan 11, 2022The main runner is the part where the molten plastic first passes when it is sprayed from the injection nozzle, and it is coaxial with the injection nozzle, because of repeated contact and collision...view