Machine Made Clay Tiles
The machine made process begins with the crushing of the material which is performed by a set of high speed rollers. Then the clay is moved into a mixing unit where water is added to lift it to the correct moisture content. A mixing process follows where many tonnes of pressure allow the stored clay to distribute its water content equally.
To achieve the desired shape the clay is fed into an extruder or press where the air is removed by passing the material through a vacuum chamber. The de-aired plastic material is then forced through a shaped mouthpiece at high pressure, resulting in a formed ribbon of clay. Further forming takes place by cutter or die, producing the final product which is then stacked into setters or cassettes ready for drying or firing.
A few days are taken up by drying the newly formed clay products. The water in the clay body is slowly removed by gradually increasing the temperature in the drying chamber or tunnel. A lot of care has to be taken here in order not to crack or distort the clay ware. The tiles are then moved into the kiln for firing, at a top temperature of 1,100 degrees centigrade, which can take several days to complete. Slowly increasing and decreasing the kiln temperature and pressure allows the clay material to change to a hardened durable state suitable for the tiles to meet the requirements of BS EN 1304.
Machine Made Concrete Tiles
The process for producing concrete tiles begins with mixing a large batch of either raw or pigmented concrete in an industrial mixing vat. This concrete is then transported by conveyor belts to a production line. On the production line the concrete mix falls into an extruder which applies it at pressure onto a continuous row of metal pallets each formed to the shape of the underside of the tile. As the pallets move along the production line at high speed they pass underneath a profiled unit which forms the top shape of the tile.
Concrete tiles are cured at a much lower temperature than clay tiles as they do not require firing in a kiln. This process takes place in a curing chamber at a temperature of around 37 degrees centigrade; moisture is also added to the air to optimize the curing environment.
Once cured, depending on the tile surface finish, the tiles are either surface coated with paint or applied with coloured sand granules. The tiles are then moved to a drying cabinet which allows sufficient time for the surface coating to harden. Once the tiles are dry they are then moved to a packing area to be packed and stored prior to distribution.
The roofing process does not finish with the manufacturing of the tiles. As with all roofing products, a quality end product requires skilled craftsmanship when laying a clay or concrete tile roof. Construction Skills (CITB) and The National Federation of Roofing Contractors (NFRC) provide certification, qualifications and training courses for roofing contractors and their operatives in the form of the RoofCERT scheme and NVQs.