Birch, Raymond E.

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 The Knowledge Bank at The Ohio State University Ohio State Engineer   Title:  Manufacturing Building Bricks Creators:  Birch, Raymond E. Issue Date:  Nov-1924 Publisher:  Ohio State University, College of Engineering Citation:  Ohio State Engineer, vol. 8, no. 1 (November, 1924), 5-6. URI:  http://hdl.handle.net/1811/33646  Appears in Collections: Ohio State Engineer: Volume 8, no. 1 (November, 1924)   THE OHIO STATE ENGINEERMANUFACTURING BUILDING BRICKSBy RAYMOND E. BIRCH, '27.H ROM its many crude beginnings the manufactureof bricks has been carefully studied and devel-paj! oped until at the present time there are, amongIDSMB advanced peoples, three general methods of pro-ducing building bricks. The methods are, the soft-mudprocess, the dry press process, and the third, which is theonly one to be discussed here, is the stiff-mud process.Although there may be many relevant processes varyingwith the kind of clay used, these are usually associatedwith the stiff-mud process: (1) crushing, (2) pulver-izing, (3) tempering, (4) molding, (5) drying, andfinally (6) burning.Pugmill with teeth shown protruding above clay.(a) Waste clay returned by belt from brickmachine.The common form of crusher consists of a toothedroller which revolves at the bottom of a shallow bin.It takes care of the clay in its crudest state and dis-charges it in lumps hardly as large as one's fist.A bucket elevator carries the material to the dry pan,where two vertical wheels of great weight turn uponanother wheel placed in a horizontal position. Herethe clay is ground until is becomes fine enough to fallthrough the screen which surrounds the base wheel.Dry pans are recommended for shale, fire-clay, andother clay that can be ground without clogging thescreens.The screening process has been greatly improved byrecent developments. Leaving the dry pan the finelyground clay is conveyed to copper screens which arekept constantly vibrating by an electro-magnet equippedwith an interrupter.The clay in its pulverized form is ready for the pug-mill, where it is tempered with water to permit ofmoulding. The pugmill (see illustration) is a rotatingiron shaft with steel knives placed at regular intervals.After a thorough mixing the shaft forces the temperedclay from the rectangular frame (which incloses the pug-mill) into the brick machine. Much responsibility restsupon the "pugman," since he must always secure thecorrect mixture of water and clay. An overabundanceof water makes soft bricks which cannot be handledsuccessfully, while too stiff a mixture does not moldreadily.Although this country was slow in improving uponold world processes of brick making, at the present timeour's have no equal in any other nation. The first Amer-ican brick machine, although crude indeed, was in-vented in 1835, and the succeeding years have beheld anextensive development. Modern stiff mud machinesconsist of, with variations, an auger which rotateswithin a cylinder, forcing the clay out through a smallopening, thus giving it compactness. This mouthpieceor die through which the clay gains exit determines theshape of the product.As the bar of clay is forced from the auger machineit is cut by steel wires into "green" bricks of the propersize, and these are moved on by an endless belt. Greatcare is taken with the green brick to preserve the cor-ners and edges. The men who pick up the bricks fromthe belt to load them on steel drier cars are taught toeliminate pinching the soft bricks.Many mistakes made at the brick machine are re-vealed only in burning the product. One difficult prob-lem arises from the fact that stiff-mud bricks are aptto contain layers or laminations of varying densitieswhich will either cause cracking in burning or scalingafter the brick has been laid. This trouble has in agreat part been eliminated by improved lubrication ofthe bar of clay in the machine, thus preventing the clayfrom hanging back around the outside of the die.It is best to have the drier as near as possible to thebrick machine, for the bricks are ready to be sent di-rectly into the tunnel. We speak of tunnel becausethe drier which is most universal in its use consists of aseries of tunnels, each equipped with a track for thecars of bricks. The tunnels are heated by a system offlues passing under them, from furnaces at one end toa stack at the other. An outlet from each tunnel mustbe provided for the water vapor which is given off inthe process of drying.Cutter room. (a) Cutter with brick machine inbackground; (b) conveyor.Upon entering the receiving end of the drier tunnelthe green bricks are met by and enveloped in a vaporladen air, since the only exit for moisture is at that end.This humid condition is advantageous since it does notpermit the outside of the brick to dry prematurely, andthus resist the escape of moisture from the center of thebricks. As the car progresses through the tunnel andtoward the source of heat, the temperature graduallyraises, meeting changing needs of the clay.Following the drying, which requires from two to four5THE OHIO STATE ENGINEERdays, the bricks are transferred on the drier car directlyto the kilns where they are unloaded and set.Before an explanation of burning is attempted it isnecessary to recall the various types of brick kilns.Although the general shape of the kiln may vary fromcircular to rectangular, the fundamental principles arenearly identical. Kilns for burning brick thoroughlyare usually provided with flues arranged beneath a per-forated floor and leading to the main chimney. Firechambers designed for any fuel are placed along thesides of the kiln and the fire enters the kiln from behindwalls of brick so as not to touch the bricks directly.Various continuous kilns are now in use, and the lat-est kiln to be perfected is the railway tunnel kiln. Bythe latter process of burning, the ware loaded on cars ismoved through a tunnel in which the fires remain sta-tionary, and the waste heat is used for preheating thebricks.Since all kilns are not equipped with pyrometers, theburner must acquire considerable ability in judgingis burned it changes form and, resists the outward move-ment of waste from the center of the brick.The temperature of the kiln is gradually raised so thatthe heat will have an opportunity to permeate the bricks.A heat of 1,500° F. to 1,700° F. should be maintainedduring about half the burning period. If a kiln shouldbe taken on and rapidly raised to a high degree of heat,the head bricks would probably be drawn into the bag-walls, which are the walls extending in front of the fuelinlets. Bricks are also known to have run togetherwhen these intermediate temperatures were not utilized.After this carbon burning period is past, the bricks canbe heated to their maximum burning temperature. Thistemperature is different for all clays, but seldom variesmore than a few hundred degrees either above or below2,000° F. This temperature is maintained until thecones melt, and until the desired settle is obtained. Thefiring now ceases and the kiln is allowed to begin cooling.Cooling also is accomplished gradually in order toprevent "checking" or cracking of the ware. When thekiln is finally open several days are required with theaid of mechanical methods of cooling, in order that theshaders can begin sorting the bricks.It is the burner's clream to secure an even burn fromthe top of the kiln to the bottom, but such a wish is yetto be realized. The head and top bricks are most oftenburned hard while among the lowermost bricks thereare usually some "soft" ones. Bricks having been ex-posed to excessive heat are apt to be swollen and havecurled edges.Between the hard head bricks and the soft bottomones there are many intermediate shades and grades.The present trend in brick buildings is toward the utili-zation of many of these shades on the same wall. Ar-fchitects and building contractors, realizing the pitifulbleakness of mono-color walls, are urging the uje ofblended shades, for here beauty of construction falls inline with economy.Chiefly because of their longevity and cheapness ofupkeep, builders are now using more brick—the buildingmaterial that is stronger than granite blocks.Shrinkage and settle. (a) Green brick;(b) dried brick; (c) burnt brick.heats. He knows that a certain color of heat in thekiln is necessary for the carbon burning period, andhe realizes the maximum degree of whiteness that thebrick can stand—the heat beyond which there is dangerof the bricks becoming swollen.The two infallible aids in brick burning are pyro-metric cones and shrinkage. Segar pyrometric cones areformulated so that a certain definite heat will cause themto wilt over or curl. They are placed near the bottomof the kiln where they can readily be seen through apeep-hole. All bricks shrink or "settle" in burning, andthis settle is fairly uniform for any given clay. Thepercentage being known, the settle for a kiln may beeasily calculated. A small hole through the crown ofthe kiln permits the burner to measure the height of thebricks by means of an iron rod and a stationary marker.Even though the drying has been thorough, an ex-tended period of water-smoking is necessary, duringwhich the temperature of the kiln is usually maintainedbetween 200° F. and 400° F. Before the burning isbegun in earnest the white steam will have disappearedfrom the chimney.Experimentation from the crude beginning of brickburning to the present day has developed with finalitythe basic idea that in burning brick the method mustbe, center first, surface last. The moment the exterior6

Manufacturing Building Bricks

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Manufacturing Building Bricks

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