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Overheating Motor
Old automatic lathe's motor has overheating problems because it changes direction of rotation to unscrew.

An old automatic lathe that performs threading tasks on metal parts presents motor overheating problems because it changes direction of rotation to unscrew the part. the engine it has is a 2-speed Dahlander. This lathe was modified, apparently originally did not change direction of rotation or had other drive system.

In threading operations of the parts the lathe rotates at high speed. once finish the thread of the piece the machine has to stop and start to turn in the opposite direction in a period of 1 or 2 seconds to unscrew the piece. there is a large inertia that the engine has to overcome. the machine does not have a mechanical brake.

It is necessary to put a new engine and drive system. the best option
view was to install a three-phase motor (No Dahlander), a VFD
(Variable frequency drive), and PLC, but maybe the engine will continue to heat. The other option seen would be the installation of a servomotor.

I wanted to know what would be the best solution to avoid engine warming.


1 out of 1 members thought this post was helpful...

You are likely not a native English speaker, so just to let you know, "engine" does not apply to electric equipment, it's a "motor". Those terms are often interchanged in things like automobiles (which are technically engines, NOT motors, but it is done nonetheless), but that does not apply to electric equipment.

If your motor must stop and reverse too often, the heat that is created in the motor in stopping the load cannot radiate out of the windings and dissipate fast enough, so it can indeed do harm. But without details, we don't know how much heat you think is too much, or what you mean by "heating problems". Most people over estimate the heat they can feel as being too much. The amount of heat a motor is designed to take is very substantial. On the nameplate, there should be a code letter assigned to the insulation "class", which depicts the allowable heat it is designed to withstand. Of these, the LOWEST level, "class B", says that the motor is designed to operate in a 40C environment, the winding temperature can RISE and addition 80C and there can be an ADDITIONAL 10C "hot spot". So the point at which the motor becomes damaged is when the windings exceed 130C, far far above the point at which tour touch will react to something as "too hot". If the motor has Class H insulation, that number becomes 180C!

Bottom line, don't get excited about it until you know.

If it does turn out to be an issue, a VFD can be used with a feature called "Dynamic Braking" in which the energy that is required to stop the load is turned into electricity, then pulled out and dumped into an external braking resistor so that it does no harm to the motor.

JRaef2 thank you very much for your time and valuable information, the Dynamic Breaking seems to be the solution for this case, it will be studied and will surely be what is finally implemented

About how the motor heats, the owner says "it gets too hot and generates high current peaks", and really should be heated a lot that has decided to change motor and integrate a VFD

The machine has a duty cycle for each piece of 23 seconds approximately during which it has 4 stop and reverse, the reverse is currently done directly changing 2 phases by contactors, which causes the motor to overheatand overcurrent. This machine normally must work for several hours continuously and sometimes 24 hours a day

Sorry for poor English, thanks for the clarifications

Dynamic Braking has been the solution, the results have been good, the objectives have been met

A VFD, a braking resistor and a standard three-phase motor were installed. It was not necessary a PLC, the control is performed by the VFD. The lathe works 8 hours continuously machining around 2 pieces per minute, in each piece performs 2 threads (outer and inner), drilling and starting of chip. Motor and resistance does not heat

Many thanks once again for the valuable information.