The number-one difference we find is that the operator on the hydraulic machine has the tendency to set the ejector positions beyond the mold eject mechanism travel capability.
  • The number-one difference we find is that the operator on the hydraulic machine has the tendency to set the ejector positions beyond the mold eject mechanism travel capability. With hydraulics, if the eject plate cannot travel to the set point, the oil ends up being bypassed over a relief valve back into the tank. In comparison, the electric machine motor drive design systems are set to increase the motor torque to achieve the position set point. If the set point is beyond the eject travel capability, then the drive system power will be increased to a point where eventually it will alarm out or mechanical damage can occur. In summary, the electric machine is less forgiving when it comes to setting the positions, but it has higher accuracy and repeatability.
     
  • Electric machine positions are set to 0.001” while hydraulic machines are typically only down to 0.01”.
     
  • Electric machine responses are faster, so to replicate the process from the hydraulic machine may require additional profile settings.
     
  • Most hydraulic machines set the injection pressure in terms of hydraulic pressure. The electric machines, since they have no hydraulic drive trains, measure injection pressure with melt pressure, usually via a load cell. The difference between hydraulic and melt pressures are typically represented by a difference in value of 10:1. Example: 23,000 psi melt pressure is similar to 2,300 hydraulic pressure. This can vary to 8 or 12:1, but 10:1 is a “rule of thumb".