A special case
September 1st 2004

Nigel Evenett of AEG looks at the arguments for using “special” electric motors outside of the IEC standards to incorporate application advantages.

For many years now, the IEC/BS standards have dictated what constitutes a ‘standard’ industrial electric motor. These cover the main areas of powers, dimensions and tolerances for both mechanical and electrical characteristics that allow for a large degree of inter-changeability between different manufacturers products.

The reasoning behind these standards is, at first glance, sensible and practical. For example, if an end-user wishes to replace a faulty 4kW, 4 pole, foot-mounted motor he knows that this should be available in a 112 frame (i.e. the height from the base of the feet to the centre of the shaft is 112mm).

Because the dimensions of the shaft and feet fixings are covered by the standards and, solong as the terminal box position is specified, a motor from any reputable source will fit the job.

The standard motor, however, is not ideal for every application. As a result, many OEM machine manufacturers choose to ‘tailor’ the primary driver for their equipment to gain a competitive edge in the market.

This may sound a bit like Fred-in-a-shed tinkering with his Ford Focus to earn his go-faster stripes but it is in fact being practiced, to good advantage, by all the major machine tool companies and many other primary industrial equipment suppliers on a large scale. The point is reinforced by the fact that of 500 000 motors produced at just one of AEG Electric Motors factories, some 60% are customised specials.

The reason an OEM opts for customised motors is to gain a competitive advantage in its market place. Benefits can be improved machine design or performance or even a combination of the two.

An illustration of enhanced machine design is an industrial blower from Air Control Industries of Chard. For this application, motor shafts are employed as the main impeller shaft saving the weight and space of a motor coupling while also simplifying assembly and eliminating potential maintenance demands. The fact that the motors can be supplied with multiple different shaft lengths (200mm, 350mm & 500mm) adds to flexibility of the ACI blower range.

Another example is a motor supplied with a specially engineered, squared-off, stator housing for grinding machines produced by Wadkin UltraCare of Leicester, a manufacturer of machines for the woodworking industry. This configuration permits a laterally moving arbor to travel along the length of the motor during the blade grinding process while offering a cutting capacity of up to 150mm length and 200 mm cutting circle diameter.

As well as being ideal for the task, the custom motor gives the OEM an edge in technology that provides him with an advantage that is less likely to be mimicked because of the investment required and the time delay in bringing copies to market.

If the special motor also offers the benefit of cutting the number of components required, such as couplings and belts, stock inventories will be reduced. Further, by incorporating a wide voltage range into the motor design, the need for the OEM to stock different motor types to meet different export markets is avoided.

Of course, in the initial stages of designing motor ‘specials’ a degree on investment is required to determine the exact motor characteristics to fulfil the OEM’s application needs. This is then followed by the cost of development on the part of the motor manufacturer. All these costs must then be set against the volumes involved.

Obviously the standard motor will cost significantly less, initially. However, as use overcomes the penalty of the original of tooling set-up time and the extra engineering costs the difference will shrink significantly. For example, the graph below demonstrates the pricing by volume for a typical 2.2kW motor which is customised.

It can be seen that the special motor becomes competitive when manufacturing volumes reach and exceed 3000 per year.

The use of special motors can give equipment manufacturers a real market edge. True, there are initial costs to be borne when resources are committed to the motors development but the rewards can include easier and faster machine building, superior machine performance, reduced inventories and the opportunity to create a market leading product that is technically more advanced that its competition.

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