Asbestos cement pipe & transite pipe product history, production & properties: this article describes the manufacturing process used for production of cement-asbestos pipe.
Asbestos-cement pipe was widely used world-wide for water supply piping, sewer piping, even some chimney applications as well as in various industrial processes. Built and installed more than 50 years ago, asbestos-cement pipes remain in use in some locations today.
A variety of manufacturing processes were used for making asbestos-cement pipe and are described here, including the Mazza process, the Magnani Process, the Dalmine Process, and the Hiamanit Process used for Making Asbestos-Cement Pipes. Some of these methods were used and may also still be used to produce reinforced concrete pipes that do not contain asbestos.
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Cement asbestos materials: this article series describes asbestos cement products & materials and the history of their production and use.
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This article includes text & data Adapted from Rosato (1959 out of print) on the production and use of asbestos-containing materials, adding photographs, inspection, repair and maintenance advice, and updates on asbestos hazards involved in the installation, repair, or demolition of asbestos cement products such as roofing and siding or asbestos millboard that remain in place on buildings.
Transite Asbestos pipes: a cement-asbestos product, were widely used for warm air heating ducts, especially embedded in floor slabs, also for gas fired heating appliance chimneys, and for water transport in some cities as well.
Asbestos-cement pipes have been used for many years. The comforts and conveniences of family dwellings and business establishments have required many thousands of miles of water pipes.
. Government and private
enterprises use asbestos-cement pipes for such applications
as fresh and sea water mains, gas mains, sewerage, mining
operations, agriculture, electrical cables, venting flues, etc. See Figure 3.4 (above left) and also
and TRANSITE PIPE AIR DUCTS for identifying photographs and advice
Figure 3.4. Asbestos-cement in transit.
(Courtesy Johns-Manville Corp.)
The experimental manufacture of asbestos-cement pres-sure pipes was started in Italy in 1913. Progress was rapid and by 1921, asbestos-cement pipes had been accepted in Europe.
At that time, the British Ministry of Health ap-proved the use of the pipe for water-mains. They provided for loans for these pipes, with a repayment period of 30 years; this period represented the same period allowed for cast iron pipes.
This type of pipe gradually superseded both metal and ceramic piping in a large number of applications because of the fact that they are resistant to corrosion, impervious to and free from electrolytic action when buried in the earth, light weight, elastic, strong, resistant to compression, eco-nomical to install, and unaffected by temperature changes.
They are unaffected by the ordinary corrosive agents en-countered in soils and waters which attack metal pipes and cause their destruction in a few years.
Tests have been conducted on pipes after 30 years in serv- ice with the conclusion that they had retained their original properties. These pipes have a smooth, glossy, cylindrical internal surface, and offer very low hydraulic frictional resistance to the flow of liquids.
The Italit Mazza asbestos-cement pipes manufactured by Eternit, Genoa, Italy, are still in operation throughout the world. Their experimental data show that the carrying capacity of pipe is on an aver-age of 25 per cent greater than that of new cast iron pipes and 30 to 60 per cent greater than that of old cast iron pipes, all being of the same internal diameter.*
Manufacturing Processes used for Making Asbestos-Cement Pipes.
There are three principal processes for making asbestos-cement pipes; i.e., the Magnani, Dalmine and Mazza Processes, with each process having been named for its originator. A more recent process is referred to as the Hiamanit. This process was developed by the Hiamanit HÃ¼ttenwerke A.G., Duisburg, Germany.
The initial steps in the process of making pipe and conduits are similar to those employed in the wet mechanical process. Engineering progress provided for the development of pipe after the sheets and shingles had been manufactured.
* "Asbestos-Cement Pressure Pipes and Low Pressure Pipes," London, Eng. Asbestos Cement Products Ltd. (Italit Mazza).
Asbestos-cement pressure pipes are generally manufactured on costly and complex machines which are automati-cally operated by means of hydraulic and electrical controls. The pipes are built up of a continuous, uniformly thin and highly compressed film of asbestos-cement. See Figure 3.5.
From mechanical stirrers located above the pipe manu-facturing equipment, a mixture of asbestos and cement of low viscosity flows through specially prepared conveyors which are endless felt blankets. See Figure 3.6.
Mazza Process used for Making Asbestos-Cement Pipes.
The Adolfo Mazza process is the most important commercial process used in the manufacture of pipes. High production equipment permits recirculation of cutoffs. The Mazza machine is similar to other machinery for wet processing. The basic difference is that the Mazza machines are wider.
The accumulator roll which is a feature of the oher machines is replaced by a mandrel. The diam-eter of r ndrels varies from 6 to 250 in.
Because of their weight, the larger diameter mandrels are more difficult to handle. These large mandrels are usually mounted in pairs; one attached to each side of the machine. The machine per-mits wrapping on one mandrel, as the previously wrapped pipe is withdrawn from the other mandrel.
In the asbestos-cement sheet machine, the accumulator roll is weighed against the breast roll below it; the woven felt passes between them.
The full density of the stock is obtained at this contact point. In the Mazza machine, there is a pair of press rolls above the mandrel which is hydrau-lically loaded. They apply a much heavier pressure on the pipe being formed than would be possible with the usual arrangement.
A second woven felt runs between these rolls and the mandrel in order to distribute the pressure and to provide a cushion to prevent damage of the pipe as it is formed. The result is that a higher density asbestos-cement product is obtained. Generally, a one or two cylinder vat is used in manufacturing pipes as compared to multi-vat arrangements for sheet producing equipment.
Figure 3.5. Front view of large asbestos-cement pipe machine.
Completed 13-ft. length of pipe is shown on mandrel at left of machine. Empty mandrel has just been swung into position against felt blanket. Cradle in foreground contains newly-made pipe.
(Courtesy Johns-Manville Corp.)
Magnani Process used for Making Asbestos-Cement Pipes.
In the Magnani process, a plastic paste mix rather than a slurry is used. It requires the lowest capital investment of the various methods.
It is necessary that the mixture flow slowly under gravity, but it must not be too thin in order to eliminate running.
The mixing of the cement and asbestos is performed by a number of different conven-tional procedures which includes those used in the wet mechanical process.
The stock is usually fed to the head box above the forming machine after it has been prepared.
Figure 3.6. Rear view of pipe machine. Slurry tank is in view.
(Courtesy Johns-Manville Corp.)
The machine consists of three separate units; the stock manufacturing unit, the compression operation unit, and the unit that is concerned with removal of the mandrel from the pipe. The first unit consists of a stock slightly wider than the length of the pipe.
The trough used is a shallow "17," with the side toward the mandrel almost horizontal. A steel backer roll is located below the lip of the trough, and moves horizontally in relationship to the mandrel. This procedure permits the increasing thickness of stock on the mandrel while maintaining pressure against it.
The mandrel serves the same function as the accumulator roll in the wet me-chanical process. It is a hollow steel or cast iron tube, perforated over its entire surface. Its ends are closed and fitted with vacuum tube connections. The trough is filled with the stock in the first operation. A mechanical or manual spreader is used to distribute the stock evenly.
The mandrel is wrapped with a strong filter cloth. After the vacuum has been drawn on the mandrel, the mandrel is rotated at a slow speed; the stock is hoed into the nip between the mandrel and the backer roll. Because of the suction, stock builds up on the mandrel, and it is partially dewatered. The backer roll smoothes the surface and compresses the stock as it is deposited. Buildup continues to a predetermined thickness.
A mandrel with its formed asbestos-cement pipe is then removed from the machine. It is placed in a compression unit which contains two rollers. One of the rollers is in a fixed position and the second roller is the pressure roll. Vacuum is applied to the mandrel during this operation.
A combination of pressure, rotation, and suction will compress the material and release more water from the stock. The rolling of the tube continues after the vacuum has been removed in order to permit the pipe to enlarge slightly. It is then transferred to the third unit and the mandrel is with-drawn. Wooden forms are usually inserted in the pipe in order to maintain its true shape until the cement has com-pletely set. The final product is smooth on its exterior, uni-form in wall thickness, and straight.
Dalmine Process used for Making Asbestos-Cement Pipes.
The Dalmine process is made up of one or more banks of parallel narrow wet mechanical machines each having a width of approximately 50 in. and operating simultaneously. This complex process permits manufacture of long pipe, independent of machine width.
In this process, the accumulator roll is replaced by a smooth tubular steel mandrel. It is angled to the axis of the small wet machine and it is removable. The roll moves across the machine as the pipe is built up. The stock is placed on the mandrel in a spiral form with each successive layer overlapping the pre-vious one. Presure is applied against the mandrel during this operation. After the desired thickness has been obtained, it is calendered and the mandrel is withdrawn.
Hiamanit Process used for Making Asbestos-Cement Pipes.
The Hiamanit process can be used for the manufacture of concrete and reinforced concrete pipes, as well as for asbestos-cement pipes. The equipment is such that any type of pipe can be made without modification. Its distinctive characteristic is the use of a rolling process which consists of a system of rollers. Lightweight-high burst pipes can be manufactured. A cloth belt is stretched over the roller. Te roller system is hydraulically actuated.
The pipe mandrel is perforated and covered with a thin fabric to prevent the cement mixture from entering the per-forations. The core is connected to a vacuum pump which is similar to the Magnani process. A quantity of the thick stock sufficient for the required length and thickness of the pipe is spread out on the belt in the form of a fiat sheet.
The pipe is formed immediately when the rolling opera-tion starts. It is compressed to the desired density by the hydraulically actuated pressure roller. Water is removed from the inside of the pipe by means of a vacuum and from the outside surface through the cloth belt. When the rolling is completed, the core is removed and an auxiliary core is inserted; it remains in the pipe until it sets.
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