Ughill
The fire brick company Thomas Wragg & Sons owned a Pot Clay mine immediately to the south east of the hamlet. Pot Clay is the impure version of Ganister and was in demand in the Sheffield steel industry to make bricks for the lining of furnaces. In the early 1970s the mine was producing 15,000 tons of clay per year, with the company quoting, “The mine can be worked at the present rate for 100 years”. A refractory brick works stood at the entrance to the mine. However the Ughill mine had drainage problems and although powerful pumps had been installed in the 1950s to pump between 600 and 800 gallons per minute from the mine, the mine closed on 17 November 1977. It had become uneconomic to mine the clay due to water problems and the owners found it more profitable to bring in clay from the Midlands. The site of the mine has been landscaped and returned to agricultural use. J&J Dyson mined fireclay at their open cast quarry at Wheatshire between Ughill and Sugworth. The quarry is closed but can still be seen from the nearby road. Thos. Wragg had small firebrick works at Load Brook (closed 1957) and Brookside (Stopes Road, Stannington, closed 1960) the former previously owned by the Trickett family, the latter by the Drabble family and a major works (Old Wheel Brick Works) in the nearby Loxley Valley. Wraggs along with its local competitors, J&J Dyson of Griffs Works, Stannington and Thos. Marshall of Storrs Bridge Works, Loxley, mined the Stannington Pot Clay seam and manufactured fireclay-based casting pit holloware refractories for use in steel making worldwide. All three plants closed following a collapse in demand for casting pit refractories of the type made locally mainly because of the introduction of continuous casting of steel worldwide and the general demise of the British steel industry.
Sand casting
The choice of sand has a lot to do with the temperature at which the metal is poured. At the temperatures that copper and iron are poured, the clay gets inactivated by the heat, in that the montmorillonite is converted to illite, which is a non-expanding clay. Most foundries do not have the very expensive equipment to remove the burned out clay and substitute new clay, so instead, those that pour iron typically work with silica sand that is inexpensive compared to the other sands. As the clay is burned out, newly mixed sand is added and some of the old sand is discarded or recycled into other uses. Silica is the least desirable of the sands, since metamorphic grains of silica sand have a tendency to explode to form sub-micron sized particles when thermally shocked during pouring of the molds. These particles enter the air of the work area and can lead to silicosis in the workers. Iron foundries spend a considerable effort on aggressive dust collection to capture this fine silica. The sand also has the dimensional instability associated with the conversion of quartz from alpha quartz to beta quartz at 680 °C (1250 °F). Often, combustible additives such as wood flour are added to create spaces for the grains to expand without deforming the mold. Olivine, chromite, etc. are therefore used because they do not have a phase transition that causes rapid expansion of the grains, as well as offering greater density, which cools the metal faster, producing finer grain structures in the metal. Since they are not metamorphic minerals, they do not have the polycrystals found in silica, and subsequently do not form hazardous sub-micron sized particles.