Alfred McAlpine Slate Limited is part of Alfred McAlpine plc which
has a turnover of 1000 MEURO and 3200 employees. They operate several
slate quarries in North Wales, with sales of 22 MEURO and 364 employees.
One of these quarries is the Cwt-y-Bugail (Welsh for "the shepherd's
hut") Quarry near Blaenau Ffestiniog, with sales of 3 MEURO and
60 employees. There has been quarrying at this site for some 150 years.
The company quarries slate, and processes this slate to produce roofing
slate tiles, decorative floor tiles, and tile products for specific
applications such as work surfaces, and ceremonial plaques (industry
sector Prodcom code 1413 - quarrying of slate). The company's main market
for its products is the building industry in the UK accounting for over
70% of sales.
The slate production process in common use throughout the industry
is reliant on several traditional manual or manually controlled processes.
The only significant process improvement achieved in the industry has
been through the use of power tools.
One major process involved in the production of roofing slate is the
sawing of the slate rocks into 300mm/450mm wide blocks for the subsequent
slate splitting and dressing operations. This process involves the use
of large circular saws fitted with diamond tipped blades to cut through
the irregularly shaped rocks. The process is currently manually controlled,
and this results in low process efficiency or frequent damage to the
saw blade as the tip of the blade hits the slate rock at too high a
The objective of this application experiment was to introduce a microcontroller
based block sawing control system to improve the process efficiency
and to increase the life of the diamond tipped blades.
The main functional features of the microcontroller based saw control
- Detecting the nearest point of the rock to the blade, so as to
maximise the rate of advance of the saw towards the rock until the
blade is about to reach the rock and thereafter to slow the advance
speed to a minimum to prevent blade damage.
- Controlling the rotational speed of the saw blade in relation to
rock thickness automatically.
- Detecting the point at which the rock has been sawn completely,
so as return the saw to the start position again quickly and minimise
the cycle time.
- This process efficiency gain will increase company profits through
reduced production costs, and assist in providing a more competitive
position in the UK slate market.
The duration of the application experiment was 10 months. The development
costs for the improved control system was 57 KEURO.
The company anticipates that the cost savings projected over the annual
production volume will give a payback of less than 9 months for the
application experiment costs of 57 KEURO. These cost efficiency savings
will be obtained each year. However, it is reasonable to assume that
the equipment will be replaced over a 10 year production period, and
the return on investment on the initial application experiment funding
will therefore, be 1,300%. The micro-electronic and management skills
acquired during the experiment will be applicable elsewhere in the business.