A simple requirement for two replacement drives? Not quite so found the Portland Dyeing Company of Leek, Staffordshire. Repeated overcurrent faults in a pair of frequency inverters used on a Montforts stenting machine were causing expensive loss of production. The situation was made more complex by the fact that the drives were set up with 87Hz technology and some of the machine manuals were lost. Lenze Systems Partner Cornfield Engineering Solutions stepped in and engineered up-to-date replacement drives which were up and running with only one day of downtime.
Portland Dyeing have a Montforts stenting machine which is used to stretch and set fabric. The stenting process uses heat to give stability to the fabric and prevent subsequent shrinking. It is commonly used for cotton-based materials. A web of cloth is connected on each side by hooks to a tractor conveyor. Each side of the conveyor has independent drives so that, although they normally run in synchronisation, they can be advanced and retarded. Also the two sides of the conveyor can be adjusted in width to tension the cloth web. The conveyor takes the cloth through an oven where even and continuous motion is required to prevent burning. The effect of a drive failure is potentially calamitous, as the surface of the cloth will burn in the oven resulting in scrappage.
Portland Dyeing called in Cornfield Engineering when the increasing overcurrent faults on the two Lenze 8608 inverters became a problem. Being 25 years old, it was no surprise that direct replacement drives were no longer available. Each inverter drives a 5.5kW planetary geared motor connected to the conveyor. The motors and drives were selected with a 87Hz setpoint, meaning that the nominal torque is achieved with a 4-pole motor speed of 2500r/min. This results in increased power from the motor, up from 5.5 to 9.4kW which in turn means the motor is compact and cost saving. The only special requirement for 87Hz operation is that the motor should have connections for 230V Delta. The inverter has to be sized appropriately for the increased power – in this case 11kW models were chosen.
Montforts have chosen the 87Hz technology as it increases the available speed range by 70 per cent. The motor nominal torque is generated at 2500r/min and the inverter can drive it down to 580r/min without cooling or down to 145r/min with a blower. The motor is effectively standard and runs with a small gain in efficiency at the higher speed. With a 132 frame motor giving the output of a 160 frame, there are further gains in size and purchase cost.
Chris Timbey, Director of Cornfield Engineering Solutions, investigated the application and selected up-to-date inverters from Lenze, the 8400 StateLine rated at 11kW. The inverters take in an analogue speed reference signal from a higher level control system. They are easily capable of the 87Hz settings and as a modern quality inverter they will give Portland Dyeing the reliability they need. It is not just the motor that is small – over 25 years the footprint from the old to the new inverter has reduced by 78 per cent.
Cornfield Engineering was able to support their customer from the initial assessment right through to installation and commissioning. In fact, their Director Chris Timbey is proud of how well the project went. He says: “We prepared well with new drawings and programs written with the Lenze L-force Engineer parameterisation software. The drives were changed and the machine was up and running again in less than one working day”.
Follow the link for more information about 8400 StateLine inverter drives from Lenze.