The injection rate, refers to the unit time injected into the volume of the melt in the cavity, which is equal to the product of sectional area of plunger or screw and its movement speed. In terms of a certain amount of injection molding machine, injection rate is determined by the injection speed injection speed and injection molding machine control is one of the important parameters of injection molding machine, have impact on many process factors.
  The injection rate will make the filling pressure increase, this is because of the rapid rate of melt filling can be maintained with higher temperature, the melt viscosity is reduced, flow resistance loss is reduced, thus, melt to enter the cavity with high pressure, the higher the cavity pressure. For the same reason, can make the flow length increased and the quality of plastic parts is uniform and dense. However, filling rate is too high will increase the pressure loss, flow instability will cause the melt and elastic turbulence, or due to the fluid velocity head impact, causing swell and melt overflow phenomenon. In addition, when injected at high speed, gas cavity were often not discharge, mixed in the melt and seriously affect the quality of plastic parts. Also, the mould wall thickness and the injection speed had significant effects on the melt solidification layer formed in the mold cavity thickness.
Injection rate had a great influence on the plastic parts, and the injection rate should be determined, according to the structure, shape and size of different injection products, properties of runner system and plastic, and the rheological data set. In general, the injection rate must ensure that the rheological data on the specified allowed material shear rate and shortest flow length, must ensure that the thermal effect produced by shear does more than allow the polymer thermo physical properties and shear strength level
  If the injection pressure, injection rate Q can be calculated from the following formula: Q=0.785VD*D type of V- theory in the injection volume, D- screw diameter