injection molding

[sisom]

i've been having a problem with our injection molding machine. the machine would run okay for about 20-30 parts then stop resulting in a hot motor. i'm really not an expert in hydraulics so any help is greatly appreciated. Thanks,
mike

 

[Barry1961]

What is getting hot, the hydraulic motor, electric motor or both?

If the pressure has been increased it could cause either to get hot if you have a variable displacement pump. The hydraulic fluid would get hot if the pressure was increased beyond the bypass setting.

Electric motors get hot when load beyond their capability. If you have increased pressure with same flow you are using more power. Is the incoming voltage to HPU correct and balanced?

Need to know more details. What type of pump do you have? What is history of machine before this problem?

Barry1961

 

[sisom]

thanks for helping me out a little barry. the electric motor gets hot. the control panel says thermocouple 2 or 1 faults and to check the thermocouple and ground strap whenever the machine stops. it's been about every 45min now. flow rate for the pump is 1.54gpm, pump motor is 2hp. i don't think it's a variable displacement by the schematic shown (only one arrow pointing up. that's what i got for now. thanks again.

 

[Barry1961]

I would have thought that the thermocouples would be used to monitor the temperature of the plastic at the hot end of the injection screw chamber. Most HPU’s that size just use a standard motor and motor starter with overload relay not thermocouples.

Thermocouples are used to measure temperature fairly accurately and are used to regulate the heat chamber commonly.

You can not tell from the symbol if the pump is variable displacement.

While thermocouples are fairly rugged mechanically they are very low voltage and very sensitive to bad connections and grounds. The output voltage will be somewhere in the mV range. The voltage can not be read accurately with a standard meter because the leads make a second dissimilar junction. They are also relatively cheap so it might be easier to just change them out. If you have to change the wiring make sure it is the same type of wire and do not butt splice in a patch.

If there really are two thermocouples on the HPU motor I would measure the amp draw on all the phases and if not high I would replace thermocouples.

Barry1961