Information on production of hand-made monastic and gothic bricks and their moulders

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Wypał w piecu hoffmana cegieł i kształtek pełnych licowych ręcznie formowanych
The production technology of ceramic products at “Trojanowscy” Brickyard, Plc. is a traditional technology based on natural processing of specific loess raw materials and entirely hand production. Owing to the traditional technology the products show specific physical-chemical features.

Description of technological process

The production line of hand-made ceramic building materials at “Trojanowscy” Brickyard, Plc. in Kraśnik may be divided into the following: extracting and processing raw materials, preparing the mass through moistening and processing in a vertical mixer, “sand” method manual forming of semi-finished products, drying semi-finished products in a yard, coal baking in a Hoffman round brick kiln.The technological process is based on extracting loess raw materials at a strip mine by means of bulldozers which pack raw materials into natural homogenizing reservoirs. The peculiarity of loess raw materials consists in considerable dust fraction contents, which results in the necessity of moistening and homogenization for at least 24 hrs. After this time loess clay becomes plastic owing to a big content of water, ca 24%. Mixing in a vertical mixer is aimed at homogenization in terms of moistness and composition. A mixer consists of a container made of a steel sheet or thick boards in a cylindric shape. In the middle of the cylinder there is a vertical steel shaft, to which clay mixing arms are adjusted at a certain angle so as to push the clay up and down while mixing. At the bottom part of the cylinder there is a hole supplied with a bolt to control the outcoming clay, which means that it also indirectly controls the amount of processing. The shaft turns around by means of an electric engine. The cylinder is usually half-dipped in the ground, and next to the outlet opening there is a pit dug out to receive the processed mass. Raw materials from the mine are put into the mixer from the top and after they have been processed, they are mixed with spadles and collected through the bottom hole. Should any need arise, the raw material is moistened with water in a mixer to obtain the proper moulding moistness. After the preparation, the mass is delivered to a semi-finished products moulding place, which is situated in a ”production” yard. There is also a horizontal double mixer used in case of products demanding the moulding mass to be more plastic and homogenous. It is equipped in batchmeteres to measure loose and liquid materials which are added to obtain better results in absorbability and durability of bricks and moulds.The process of natural and mechanical processing is therefore reduced to a minimum – is traditional. It means that the mass is neither precisely mixed nor homogenized in terms of moistness and composition – some part of the mass retains a layer structure. The mass is then directed to moulding stands where it is manually formed. A moulder throws a piece of the mass into a wooden mould with a considerable force – the mould, after having been moistened, is dusted with fine-grained sand. The sand is used to facilitate taking out a formed moulder from the mould. If the mass is thrown into a mould manually, it does not ensure either strong density or precise air release, which results in an air void texture, characteristic of hand-made products. Products moulded in such a way will show a low heat conduction coefficient, small volumetric mass, small compressive strength and high absorbability. These physical-chemical features make it a valued building material in the south of Poland, enabling putting up secured brickwork constructions and allowing high thermal comfort. The features of the wall made of “Trojanowscy” Brickyard hand-made brick are especially essential in reconstructing historical buildings with no ventilating ducts, and new building constructions with air-tight new generation windows and doors that reduce the gravitation ventilation of rooms. There appears a question of introducing steam through walls. Steam is to be found everywhere, in all inhabited spaces (2 litres/ a day generated by human beings, and 1.5/ a day as a result of living activities). Steam molecule concentration is levelled out by diffusion. Steam diffusion in brick walls is ensured by ceramic material microporosity, commonly defined as steam porosity. If moistness movements, which are difficult to control, are taken into consideration, diffusion resistance of used materials proves to be important. The construction of a loess material brick wall is characterized by a reduced diffusion resistance towards outside, which allows to carry off moistness from the inside. This feature ensures a good temperature and humidity microclimate in rooms whose walls are made of hand-moulded ceramic brick. These qualities are best proved by sacred buildings, palaces and castles where a specific microclimate forms – it is cool in summer and warm in winter.

Hand-moulding of full bricks

Mass that undergoes hand-moulding is homogenous and its dampness amounts to ca 24%. Hand-moulding of semi-finished products is done by means of “sand method” Semi-finished products are moulded on a proper table called ”strycharski”, which is to be very strong. However, it cannot be very heavy on account of the necessity of moving it around. The mass is delivered with a wheelbarrow over a board put askew, and thrown out on a flat part of the table. Single or double moulds are used to form bricks.Moulds are made of hard wood and their edges are covered with steel sheet to protect them from rubbing away. Mould sizes should be adjusted to a mass shrinkage factor so that baked bricks have required size. To scoop up an extra mass from moulds, “scoopers” are used. A moulder tears away a proper piece of mass and throws it energetically into a mould. After packing the mass, especially in the corners of a mould, a moulder scoops up an extra mass with a double movement of a “scooper” and smooths out the surface. Semi-finished products are laid on a square to dry.

Drying in a yard

Hand-made ceramic products are characterized by high moistness and should be dried before baking. Moulded moist ceramic material behaves typically when being dried.Semi-finished products are laid directly in a compact yard, covered with sharp-edged sand. First, bricks are dried ”flat” and ”on edges”, next they are arranged in a 8-10 layer structure, with a narrow side directed to the south-west. To protect the semi-finished product from strong sunshine and fall, they are covered or put into sheds. Drying time amounts to 15-30 days.

Baking in a ring brick kiln

The last stage of the process of technological production at “Trojanowscy” Brickyard is firing in a Hoffman ring brick kiln with hard coal, in result of which moulded and dried products acquire final qualities. Products firing consists of several stages, one stage turning into another. The speed of the firing process depends on the sizes of products, properties of materials, moistness of semi-finished products, and moreover on a brick kiln type and the type of heat exchange. Ring brick kilts are very old constructions and the principle of their functioning has not changed since they were invented. Maintaing their operating efficiency is connected with low reconstruction costs, their heat consumption factor is good (approx. 1254 kJ/kg of fired product), they are efficient and technically durable. The main disadvantage of this type of brick kiln is that it is difficult to achieve an equal temperature in the cross-section, and, apart from that, loading and unloading is carried out manually, and the work conditions are strenuous. All this results in baking differences and a various degree of products’ baking, i.e. different colour of bricks, from bright red to dark red-purple, and above all different physical-chemical properties, such as absorbability and compressive strength. The above described technology of the monastic brick production justifies the specific character of both the production method and physical-chemical properties of hand-made loess products of “Trojanowscy” Brickyard. On these grounds, as well as on the basis of the raports of Construction Laboratory-Alina Matuszak in Lublin, I state the following:
  • The production technology at “Trojanowscy” Brickyard in Kraśnik-Spławy II is based on the traditional production methods of loess raw material products without any admixtures, owing to which the products meet ecological and construction biology requirements.
  • Firing in the ring brick kiln does not allow to obtain homogenous products with respect to physical-chemical properties. Products in a batch will vary in terms of water absorbtion and mechanical strength.
  • The research on all types of hand-made building bricks conducted at the Construction Laboratory has shown that their absorbability comes to 18-20%.
  • High absorbability of products is condusive to the 2-3% increase of absorbability of products put to the “frost-dew” test. It is caused by mechanical activity of freezing water, which enlarges microstructure of product pores. The products therefore will not be frostproof. The products of different brick colour – some fired in higher temperature parts (purple), other in lower temperature parts (red) – will be frostproof in a different degree.
  • Results of the laboratory research on the products from a batch delivered to Stralsund (2005 production) confirm fulfilling frost resistance requirements according to PN-70/B-12016 (binding in 2005) and the requirements of PN-B-12050 Standard from 1996 “Ceramic building products. Building bricks”
  • Control tests of compressive strength, absorbability – water absorbtion and volumetric density, commissioned in March 2006, confirm the 2005 research results and explicitly classify the products as class 10 and 1.6 product range, i.e. to the class of products declared on sale.