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Crompton help Hanson Aggregates keep to British Standards

Hanson Aggregates at Ashton, part of one of the largest construction materials businesses in the UK, choose Crompton Controls to improve product quality and reduce waste. The Ashton operation, headed up by Mr Howard Sant, provide materials for producing a wide variety of road surfaces. Different mixes are made up from any number of 14 independent cold storage bins containing aggregate. The aggregate ranges in sizes of 28mm or dust/sand.

The original plant was installed in 1988 and consisted of variable speed “tasc” drives controlled through a plc based operating system. Recipes for the various mixes are dialed up from the control room to feed the mixture from the cold storage bins to the waiting lorries and a fast and flexible supply is required.

However it became evident that the recipes were not being delivered correctly or consistently, for example when 100 or 150 Tonnes were requested only 90 and 130 Tonnes were being delivered etc..

Problems discovered included an inability to provide sufficient torque when the feed conveyors were started under load conditions and particularly in cold weather when ice can cause the aggregate to freeze. Then when running the old drives could not hold a constant speed and had major problems when at less than 25% nominal speed.

Finished aggregates are required to comply to a British Standard and to achieve this the old system had to be constantly adjusted to compensate for the anticipated shortfalls. This used up more material and in turn lead to a massive waste and rework problem.

Crompton Controls were called in to look at the problem and recommended the installation of a complete new drive system. The tasc drives were replaced with geared motors which would be accurately controlled from a customized panel designed and manufactured at Cromptons UK manufacturing plant in Wakefield.


At the heart of the system were 14 high performance frequency inverters designed for precise speed accuracy through direct control of torque and flux.

Crompton Controls successfully commissioned the control panel over the course of a weekend and Hansons were only really expecting marginal benefits but have been completely overwhelmed by the improvements the new system has given. “There is now little or no waste. The Crompton Controls panel with these excellent inverter drives has given us accurate and consistent results ensuring that every recipe is mixed to the exact standards we require without the waste and lost time previously experienced.”

Material produced by the new system at the Ashton plant has been used in the resurfacing of the Thelwall viaduct on the M6 motorway.