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Clay Masonry Products Brick
1) Development Of Brick.
2) Steps In The Manufacturing Process.
3) Brick Today
4) Properties Of Brick
5) Characteristics And Shapes
1. Development Of Brick
Brick is one of the oldest manufactured building materials. Ancient records and excavations show that brick construction dates back more than 5000 years. Brick making was a highly respected skill in early civilizations. Many old masonry walls bore evidence of royal support for the craftsman who made the bricks. Royal seals and the names of kings were stamped in some of the bricks.
One of the earliest types of brick was adobe brick. These brick contained straw for greater strength, just as reinforcing wire is used in concrete to give it strength in modern construction. After the adobe brick were molded into shape, they were placed in the sun to dry. Adobe brick are still used in a few countries today.
After the sundried adobe brick had been in use for some time, it was discovered that a brick subjected to fire in a closed area such as a kiln, or oven, for a definite period of time became very hard and highly fire resistant. The fired brick resisted weather and the passage of time far better than unfired bricks. Some of the brick were coated with a thick enamel or glaze. The glazes were commonly red, yellow, green or a combination of these colors. When subjected to heat in the kiln, the color hardened and possessed a glass-like finish. Some of these glazed brick, recovered from old buildings, still retain their original color after 2000 years. Glazed brick are made today but have limited use since they are costly to manufacture.
In the past, the mason usually made the brick he was later to lay in the wall. Many of the brick made in ancient times had a recessed panel known as a frog. When mortar was forced into the frog, the brick had a stronger bond in the wall being constructed. The craftsman who made the brick also used the frog as a place to mold letters or inscriptions to identify himself or the job on which the brick was to be used.
The making of brick was regarded by many of the old world craftsmen as a secret process. Brick masons were one of the first groups of craftsmen to form an organization to keep these processes secret and confined to their own group. These specialized organizations were called guilds and were the forerunners of modern unions.
In 1666 a great fire changed London, England from a city of wooden buildings to a city of brick construction. The manufacture of brick attained a high degree of excellence and dominated the building field in this period of history.
Early records indicate that the first brick manufactured in the United States were made in Virginia in 1611 and in Massachusetts in 1629. The brick were made by hand using very simple methods and tools. Many of the brick used in construction in the early American settlements were brought from England as ballast in sailing ships. Some of these brick can still be found in the foundations and walls of the remaining original houses in the eastern part of the United States.
The invention of the steam engine in England in the year 1760, and the subsequent Industrial Revolution, brought a change from manual labor to the use of power-driven machinery to make brick. This change started the true development of the brick in dustry in America. The first brick-making machine was patented in 1800.
Technological developments during the last century have helped to make the manufacture of brick a very efficient and highly productive process. More complete knowledge of the characteristics of the raw material, improved kiln designs, controlled heat in the kilns, and extensive mechanization have all played an important part in modernizing brick manufacturing.
The modern brick plant meets the challenge of increasing production, while retaining a high quality for the final product, by using computerized manufacturing methods and highly skilled workers.Basically, brick are made by mixing water with finely ground clay or shale or a combination of both. The mixture is then formed into the desired shape, predried, and burned in a kiln for a predetermined time.
While the basic steps of brick manufacturing are standard throughout the industry, each brick-making plant has minor variations to these steps due to local conditions. For example, one brick plant may be near the source of the raw material, while another plant may have to truck or rail the material in from a distant source. These two plants will have different ways of obtaining and stocking their raw materials.
Manufacturing process diagram
2. Steps In The Manufacturing Process
The manufacturing process has eight maior steps taking the raw material from the ground, or winning; preparing the raw material for use; forming the material into brick units; predrying the units; burning the brick in the kiln under controlled heat; and drawing and storing the brick. All other operations of making brick stem from these eight major steps.
2.1. Taking the Material from the Ground. The removal of the raw material from the ground is called winning. Power equipment is used to mine surface clay and shale in open pits. Trucks or railways bring the material to the storage piles
Enough raw material is stored to assure plant operations for several days in the event that bad weather halts mining and/or shipping operations. Several storage areas are provided so that the clay and shale can be blended to yield material with a better composition. Blending produces more uniform raw material, helps control the color of the finished product, and permits some control over providing raw material suitable for manufacturing a given type of brick unit.
2.2. Preparing the Material. If the raw material is in large lumps, it may be crushed before it is placed on the storage pile. The crushing breaks up the large pieces and removes the stones. Following this, 4- to 8-ton grinding wheels revolving in a circular pan grind and mix the material. It then passes through an inclined vibrating screen which controls the particle sizes. The finely ground material is taken by a conveyor belt to the site where it is formed into single brick.
Raw material is stored to assure operations for several days.
2.3. Forming the Clay or Shale into a Brick Shape. Three methods of forming are us ed in the production of bricks: the stiff-mud process, the soft-mud process, and the dry-press process.
Stiff-Mud Process. The most frequently used process at present is the stiff-mud process. It produces a harder and denser brick than is obtainable from the other processes. A greater volume of brick can be manufactured by this method to meet the growing demands of the construction industry.
The first step in the stiff-mud process is to add water to the raw material to make a plastic, workable mass suitable for molding. The mixing is done in a machine called a pug mill. The pug mill has a mixing chamber which contains one or two revolving shafts which thoroughly mix the raw material and a measured amount of water.
The stiff mud process is done in a brick
machine which consists of a pug mill,
a de-airing chamber, and an auger extruder
After the mixing is completed, the pugged clay is forced through an opening called a die, a process much like toothpaste being forced from a tube. The long, formed ribbon of brick being extruded through the die is called the column. As the column moves away from the die, it is cut into lengths which are either the height (side cut) or length (end cut) of the brick. The cutting is done automatically by a large circular wire cutter which cuts each brick to the same size. These green brick (brick in their soft condition before they are burned in a kiln) are then placed on dryer cars.
Soft-Mud Process. This is the oldest way of making brick and was used before brick-making machines were developed. Automated machinery is now used in this process.
The soft-mud process is suited for clays which contain too much natural water for the stiff-mud process. The clay is mixed with twice as much water as in the stiff-mud process and is pressed into wooden molds. The molds are lubricated with sand or water so the clay does not stick to the mold. When sand is used to lubricate the molds, the bricks are sand-struck and have a sandy finish. When water is used, the bricks are water-struck and have a very smooth finish.
Dry-Press Process. In this process, the clay is mixed with a small amount of water as compared to stiff mud and is then forced into steel molds under very high pressure. This method is not in wide use now in the U.S.A., but some are produced in the Pacific Northwest. There is less demand for pressed brick because of its selected use and the high cost of manufacturing.
2.4. Predrying Brick Before Burning In the Kiln. Excess moisture must be removed from the brick before they are burned in the kiln. Years ago, brick were allowed to dry in the open air before they were placed in the kiln. The modern method is to predry the brick in the forward section of the kiln using the waste heat from the hot section of the kiln. The heat and humidity must be regulated carefully to prevent sudden changes in the temperature which will cause excessive cracking and deformation of the brick. The drying time in the kiln is greatly reduced from that of the open air process. In other words, with the brick being dried in the kiln, the weather is not a factor affecting the moisture content of the brick. The brick are placed in the drying chamber on special, rolling steel cars and are left there for a predetermined drying time before they move into the hot section of the kiln. The temperature in the drying area is 100 to 400 degrees in Fahrenheit.
The NW Masonry Guide Table of Contents
Masonry Institute of Washington
Washington State Conference of Mason Contractors
