Improving plant performance with drives
01 May 2012
We select two recent case studies from ABB’s extensive portfolio of energy saving and plant automation success stories to demonstrate how a bit of investment up front will pay off quicker than you might think – and provide continuous savings thereafter.
The GKN Wheels plant at Telford produces a wide range of components for major vehicle producers around the world. Indeed, one of the production lines makes wheels for many of the leading manufacturers of agricultural and construction vehicles, including Caterpillar and JCB.
One part of the line involves a walking beam, which uses a system of reciprocating parallel bars to pass rolled and welded wheel rims from an oil dip to a flare press. As the beam reaches top dead centre, the larger wheel rims can cause the beam to over-speed and the momentum carries them too quickly towards the press. This can result in the system jamming.
According to production manager, Kevin Evans, this type of stoppage can take an average of two hours to remedy, resulting in lost production time and adding to operational costs. In order to maintain schedules the plant had to run overtime following such incidents, which, taking account of maintenance, materials, and lost production, totalled around £25,000 a year.
Systems integrator Estil and ABB were already on site investigating potential energy saving applications, when Mr Evans asked them if they could look at the walking beam and come up with a solution to the jamming problem. The system they came up with included a 1.5kW ABB standard drive, located externally to the press and appropriately housed in an IP54 enclosure.
At the beginning of the walking beam’s cycle, the drive is started and the internal timer runs it for one second at full speed. It then switches to two thirds speed and is gradually decelerated. The beam carrying the wheel rim is slowed gradually as it approaches the press, and when the press is reached, a limit switch triggers to stop the drive and complete the cycle.
Since installation, the plant has run without a single stoppage on this part of the process and GKN Wheels is now on target to save that annual £25,000 arising from the previous lost production.
A similar saving is being achieved by Milliken, a company that produces cloth for use in tennis balls and billiard tables. Eddy current drives were being used to power and control four carding engines, the speeds of which were varied via slipping clutch arrangements. This necessarily meant that the motors ran continuously, even when the machine was not in production, making them extremely inefficient. The motors were actually running in excess of 7,000 hours, though just 1,620 hours were taken up in production.
The original configuration comprised a 15kW motor, a 25kW motor and two 7.5kW ‘tandem motors’ to drive various sections of the machine. These motors where also driving the machine sections directly, shaft to shaft, meaning that the motors where continually running at full load current and sometimes overheating.
Tathams, a specialist in the control of textile machinery, was appointed to bring this control system up to date. The new arrangement uses four 11kW ac machinery drives with Direct Torque Control, which has enabled close synchronisation of the machine’s scribbler, carder and eccentrics sections. The motor ‘on time’ has now been reduced to just over 3,500 hours.
This, together with other benefits of the system, has achieved annual energy savings of 540,000 kWh for Milliken, reducing its energy bill by £27,000. Running the drives at 40Hz, enabled further energy savings to be achieved.
The installation paid for itself in just over 10 months.
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