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.


图片1.png


Tags: Injection Mold | Injection Mold Supplier | Injection Mold Factory | Mold Factory | Mold Supplier | Injection Molding |
Related News about USM Injection Mold
  • Parting surface venting of runner system

    Parting 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...view
  • What is Called Draft Angle?

    What is Called Draft Angle?

    Dec 29, 2021The draft angle is also called demold angle and angle which is used for product removal from the mold and designed on the parting surface, the angle is called draft angle which shows in picture 1....view
  • Plastic cooling factors by injection parameter

    Plastic cooling factors by injection parameter

    Feb 10, 20221. Plastic parts design: mainly for the wall thickness of plastic products. The thicker thickness of the product, the longer the cooling time. Generally speaking, the cooling time is approximately...view
  • Slider of side core pulling mechanisum assembling

    Slider of side core pulling mechanisum assembling

    Jul 21, 2022The picture 1 shows a typical guide pin driven slider parting and core-pulling mechanism, we will talk about the composition and function of the lateral core-pulling mechanism. 1. Lateral forming...view
  • Venting of parting surface

    Venting of parting surface

    Mar 7, 2022The exhaust slot on the parting surface is easy to clean and processing, also not easy to be blocked, and has a good exhaust effect, it is the main area where the gas is exhausted, so the exhaust from...view
  • Slider designing tips 1

    Slider designing tips 1

    Aug 3, 20221. After the slider core pulls out, the length of staying in the guide pin slot should not be less than 2/3 of the total length of the slider, for special cases, the slider slot can be partially...view