Tip of the Day 135: Screw Motor Pressure ≈ Torque => Good Data

Chris Whalen, one of our sales reps., responded to tip # 134 thus:

„…And, you get the added value of monitoring screw torque pressure over time on a machine, which can be a good indicator of screw wear, heater band issues, back pressure issues, etc.  Westland highly recommends monitoring this as an indicator to changes in the process associated with screw recovery and wear.“

Excellent point and it makes a lot of sense. Pressure applied to the motor should relate directly to torque except for losses due to inefficiency. And torque x RPM = power. Though we usually cannot get an RPM input to the eDART™, most machines can maintain a fairly constant screw motor speed. Thus the hydraulic pressure driving the screw relates directly to power.

Just watching the graph for shape changes is a human function, not an automated eDART one. But power x time = energy. Thus, to get a relative change in energy delivered through the screw, you can use the integral (area under the curve) of „Hydraulic Pressure / Screw Motor“ over the time that the screw motor is running. In the eDART this is the summary variable called „Recovery Integral / Screw Motor Pressure„. You could set a warning on this value to look for some of the problems that Chris mentions above.

Shane Vandekerkhof here at RJG also reminded me that there might be some residual pressure in the screw motor circuit after the screw has stopped. If this were so and you wanted to produce an accurate energy computation you could use the Raw Data Viewer’s „Details“ button on the „Hydraulic Pressure / Screw Motor“ line to zero the screw pressure while the offset is there.

Another concept is to use the eDART’s optional „Math Processing“ software tool to convert pressure to torque (from the screw motor specifications) and multiply by RPM to find the true power and energy delivered to the screw.

Note: If you wish to use these techniques please contact me, art.schubert@rjginc.com. We also have some advice in case you want to try this on an electric machine.