Double Roller Crusher clay brick making

Clay bricks are used in a wide range of buildings from housing to factories, and in the construction of tunnels, waterways, bridges etc. Their properties vary according to the purpose for which they are intended, but clays have provided the basic material of construction for centuries. Brick is the oldest manufactured building material, and much of its history is lost in antiquity. The oldest burnt or fired bricks have been found on the sites of the ancient cities of Babylonia, some of which are estimated to be about 6000 years old. Brick is, after all, virtually indestructible. The industry developed on traditional lines, using hand-making processes for the most part. The first patent for a clay-working machine was granted in the year 1619.

Mechanisation, however, did not begin to take the place of manual methods until the middle of the nineteenth century. The moulded products were fired in relatively inefficient intermittent or static kilns until about 1858, when Hoffmann introduced a continuous kiln, which enabled all processes connected with the firing to be carried out concurrently and continuously. Since the introduction of clay working machinery and the Hoffmann Kiln, the Industry has made great progress, particularly since 1930, the output of bricks in Great Britain was doubled between 1930 and 1938.

What is clay?

In brick-making terms, clay covers a range of naturally occurring raw materials which are used to make a product. The clays vary considerably in physical properties, colour, hardness etc, and mineralogical content. They do, however, have certain properties in common. They have the ability to be crushed and mixed with water to form a plastic material which can be moulded into various shapes. This can then be fired to a high temperature during which process it attains a hard, weather resistant characteristic. The key, in geological terms, is the mineral content of the raw material. This is common to all clay types. Pure clay mineral is formed from the erosion and weathering of primary igneous rocks. The clay mineral is transported away by the action of water, wind, ice etc., and re-deposited elsewhere. In the process it picks up a number of impurities, Quartz, mica, Calcium Carbonate (lime), Iron Oxide etc, etc. The subsequent deposit becomes a sedimentary rock.

Due to variances in the age of the deposit, the conditions of its deposition and the impurities involved there will be variations between different clay types and even on occasions within the same deposit. These variations may affect the brick making process and the properties of the finished product.

Clay Winning

The choice of method of clay winning will depend on the depth, thickness, hardness and physical geology of the clay beds. The usual method for winning clay (extracting from the quarry) is once or twice a year by heavy plant machinery, whether it be excavators, back actors etc, to stockpile large amounts.The advantages of bulk winning are that it can take place during good weather, a large reserve close to the factory means that breakdown of quarry plant is not critical to the production schedule. The layering of the stockpile from large reserves helps to eliminate localised variations in the clay strata.

Laboratory testing of the clays from different parts of the quarry determine the likely characteristics of the layers and clay is mixed according to the required properties of the finished item. Particular attention is given to environmental factors both during the clay win and when restoring the landscape after excavations are complete.

Clay Preparation

Clay preparation methods may have to accommodate the physical characteristics of the raw material and special provision may have to be made to deal with certain impurities. Preparation consists of transforming the clay rock into plastic mouldable material by a process of grinding and mixing with water.

A typical factory might have a Primary crusher, these are used to break down large lumps of rock to manageable size, which can then be fed to a Secondary crusher, for example Pan mill, where the clay is reduced in size further. Water can be added here or if it is a dry pan the clay is reduced to dust and water added later.

Extrusion

The clay body is mixed to a fairly stiff texture and is then loaded into an extruder where a worm screw pushes it along a barrel into a vacuum chamber which compresses it through a taper and out through a die.

The die is machined to a precise size and shape larger than the finished size of the brick, calculating how much the clay will shrink during the drying and firing process. The clay emerges as a continuous brick shaped column. Initially this is smooth but it can be modified by removing a thin sliver from the top and sides using a taught wire to produce a ‘wiredrag’ effect or by placing textured rollers over the column to create a rusticated effect or even by blasting the column with sand.

The clay column is then cut into single bricks and palletised ready for the dryers or in some factories, are loaded directly onto kiln cars.

Extruded bricks are generally perforated and can be solid but cannot be frogged.

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