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
  • Water assisted injection molding introduction

    Water assisted injection molding introduction

    May 11, 2022Like the gas-assisted injection molding process, water-assisted injection molding injects a piece of plastic into the mold cavity and core firstly, and then injects water to squeeze the melt plastic...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
  • Temperature system of injection mold

    Temperature system of injection mold

    Feb 8, 2022Hi everyone,the mold cooling time is the longest during injection, so the design of mold temperature system controlling is very important, we will talk about mold cooling, heating system in following...view
  • The main design points of the design of the plastic mold pouring system

    The 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
  • Design Tips of Vacuum Venting Mold

    Design Tips of Vacuum Venting Mold

    Mar 30, 2022There are some regular venting way which are parting surface venting, insert venting, insert pin venting and well-ventilated steel, but there is a special way is vacumm venting, it will need vacumm...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