Document 70RzDDvBq7Ke0gx5MZGx0agqo

\J~- ylflc Asbestos cement pipes -- a manufacturing review ne OF THE LARGEST asbestos-cement pipe tonne pipes are produced by a remarkably-clever O manfacturing plants in operation is at Etemit- process involving rotating mats, different surface TAC's facility at Kapelle-op-den-Bos in Belgium. tension, and even an application of DC current at The plant currently has a turnover of BFr800- the right time. 900million. and forms a division of the larger As is described elsewhere in this issue of Pipes & Etemit company, whose turnover is over Pipelines International (see below), asbestos BFrSbillion annually. cement has an important role to play in the The organization is based on the use of asbestos manufacture of pipes for many applications. in building products of all types, pipe manufacture Etemit-TAC is certainly well aware of the uses of being one of several divisions. The pipe division, the material, and is (equally-importantly) aware of since absorption of the UK based TAC company in the possible problems with asbestos as a 1986. now produces about 60,000 tonnes per year of constituent The visitor to Kapelle-op-den-Bos AC pipe in Belgium in 4m and Sm lengths as cannot fail to note the precautions with which standard, for a wide range of industrial uses. asbestos is dealt from the carefully-controlled Although water supply and sewage disposal are unpacking of the raw materials to the continuous obvious applications, other current uses of AC pipe monitoring of production and waste management. include slurry transportation for the UK's CEGB We are pleased to publish below a detailed and waste oil transportation for French Railways. account by Etemit TAC's UK General Manager of Etemit-TAC's plant is undoubtedly impressive to pipe production at the company. As Dr Com mins the visitor, more so when it is revealed that the states (see page 11). the material has probably been complex process of manufacture (described below) more carefully examined from the safety point of is almost fully computer controlled. To the view of the end user than any other pipe material, uninitiated, the process seems difficult to but it is also true to say that asbestos cement has understand, but, as Geoff Vintin describes in his been equally carefully examined from the point of detailed article on the manufacturing process. 10- view of its manufacture. The manufacturing process of AC pipe by Geoff Vintin General Manager. Pipes Division. Etemit 1AC Ltd he strength and flexibility of asbestos fibres steel reinforcement used in ferro-concrete mixtures, T confer the toughness and tensile strength on but with the very important advantage that the fine the mixture known as asbestos cemenL The asbestos fibres are intimately mixed with the asbestos fibres are analogous in their action to the cement and have an affinity for the cement U PIPES & PIPELINES INTERNATIONAL S*Dttmb*r - Octobtr 19*8 CTD001271 pariulcv prmuling .1 homogeneous mass <>l uniform sirenglh throughout the bod\ ol llif material Asbestos is a naturally-occurring mineral, which is found as densely-compacted crystalline fibres aligned axially in voids in volcanic rock. The asbestos is separated from the general rock matrix at the mine head, but before the intrinsic qualities of the asbestos can be utilized, the denselycompacted fibres must be separated or "opened." The process of "opening" lakes place partially at the mine head, after which the now cotton wool-like material is pressure-packed and wrapped for shipment. The process of "opening" is continued at the Eternit factory - a blend of grades of fibre appropriate to the products in manufacture is fed via bag openers to one of five roller mills, together with approximately 10-15% water. The aim of the opening process is to separate the fibres without reducing their length. This is achieved by "crushing" the fibres under two axially-opposed, horizontally-running steel or granite rollers. The axle connecting the two rollers does not incorporate a differential gearbox and since the outside edges of the rollers have a greater horizontal circumference to travel than the inner edges, a constant "skid" is induced, which has the effect of mechanically tearing the fibres apart. The water introduced to the mill with the asbestos performs two functions: it helps to keep down dust within the mill and it assists in the "opening" process. Water is absorbed into the asbestos mass by capillary action between the unopened individual fibres, and as the weight of the rollers comes to bear, being incompressible, the water effectively explodes the fibres apart. Opened fibre is mixed with an excess of water and specially coarse ground Ordinary Portland cement or sulphate-resisting cement in the approximate ratio of 12 asbestos:88 cement. This slurry at roughly 65% solids is pumped to a holding vessel, which is used to convert the batch milling and mixing process to a continuous supply to the pipe making machines. From fibre bag opening to the holding vessel, all processes, plant and raw material input are constantly monitored by a computerized control system specially developed for the purpose. Slurry from the holding vessel is further diluted with water to approximately 4% solids and transferred to one of the two pipe-making machines, which between them can manufacture pipes ranging in internal diameter from 75mm to 2500mm. The large excess of water is used as a transportation medium and. as a factor in the control of the subsequent pipe-making process. Pipe making is carried out using the Mazza process developed by Comm. Mazza in Italy in Qanarel riaw of an o-e pipa manufacturing plant ahowring tha fait band wrtth tha lay** ol < alufry. 1913-16. which was itself a development of the Hatchek process used in the manufacture of asbestos-cement sheeting products. The process is essentially one of controlled filtration, dewatering and consolidation. The slurry, which by now has the appearance of dirty water, is fed simultaneously to two adjacent vats, in each of which is a cylindrical horizontally rotating sieve, approx. Im in diameter and 5m plus in length. The sieve cylinders sit in end seals, so that slurry fed into the vat on the outside of the cylinder is filtered through the sieve wire, depositing a layer of asbestos fibres and cement on the sieve surface. Filtrate water passes from the inside of the cylinder to return to the dilution system in a closed circuit. The Belgian factory has its own water treatment plant, which ensures that only the correct water quality is fed to the process and that no process water is allowed to go to waste. The thickness of the lamina built up on the outside of the sieve is a function of the speed of rotation of the sieve, the solids' content of the slurry fed to the vat. the hydrostatic head between the inside and outside of the sieve cylinder, slurry temperature, fineness of the cement and drainage characteristics of the blend of asbestos fibres being used. At this stage of the process the asbestos fibres OoMriip of tha felt tend dapoaiting a layer of o-c onto the eteal mandrel. A mallar-eaad mandrel can te aaan on the left eupporting a newhrmade pipe. PIPES & PIPELINES INTERNATIONAL September - October 1988 IS CTD001272 act as an additional till ration aid. continuously collecting ihc fine cement pa dielev from suspension ami preventing them passing through the comparatively-open sieve wire. Passing over the top of the vats is an endless. 5m plus wide polyester filtration blanket (fell) in contact with the tops of the two cylindrical sieves. The felt itself is the driven element which rotates the sieve cylinders in the vats by frictional forces alone. The lamina of asbestos fibres and cement deposited onto the sieve wire is constantly carried up to the point where the sieve and felt come into contact, at which point changes in surface tension cause the lamina to transfer from the sieve wire to the polyester felt and to be continuously carried away by it. The lamina produced in the second vat moves in an identical way. but is deposited on top of the lamina from the first vat. The combined laminae thickness on the felt is approximately 0.4* 0.5mm. The felt carries the laminae over a scries of suction boxes which progressively dewater the layer as it is moved towards the compression section of the Mazza machine. Pipe formation The compression section or head is that part of the machine where actual pipe formation takes place. The felt passes over a driven anvil ' roller: positioned over the roller on the felt is a steel mould or mandrel, which has vertical, downward pressure applied to it by a series of rubber-covered pressure rollers. The mandrel is a steel cylinder in excess of 5m in length, and is positioned across the width of the machine. It can been seen therefore that in asbestos cement pipe production, it is the width of the machine which fixes the length of the pipe which can be produced. The felt transports the layer to the point of contact with the steel mandrel where, again, differences in surface tension cause the layer to transfer from the felt to the surface of the rotating mandrel. The layer is then continuously wound around the mandrel until the total thickness of AC appropriate for the particular class of pipe under manufacture is achieved. Throughout the rollingup period a carefully controlled pressure profile is applied through the pressure rollers, which completes the dewatering process and consolidates the laminae. At this stage, the physical characteristics of the white asbestos fibre begin to make a bond between successive laminae as they come into contact At the end of the rolling-up process a DC current is briefly applied across the AC/steel mandrel interface, which electrolyses the water present at the interface into minute gas bubbles. Due to the continued rotation of the mandrel and AC pipe, these gas bubbles separate the AC from the steel vulficicntly to allow the mandrel to be withdrawn at a later stage. Ihc mandrels .ire manufactured to dimensions which take account of the separation gap and ensure the internal dimensions of the finished pipes are to specification. The pipe and mandrel are then lifted from the head and the next mandrel, which may be lor a completely different size of pipe, moved into position and the process repeals itself. Different sizes and classes of pipe require their own machine parameters, such as pressure profile at the compression head. etc. The individual parameters for all pipes are stored in a process control computer, which, when told the order of manufacturing, continuously monitors and controls all the appropriate parameters through the pipe-making process from dilution of slurry from the holding vessel onwards. The AC pipe, still on the mandrel, is traceability marked and then moves into a curing stove through which it passes for approximately eight hours under carefully-controlled conditions of temperature and humidity. Throughout this period slow rotation continues in order to prevent ovality developing due to the weight of AC on the mandrel and the separation gap. At the end of this time the mandrel is withdrawn from the AC pipe, which bynow has sufficient green strength due to the presence of the asbestos fibres to be self-supporting and remain cylindrical. The process of dewatering and consolidation produces an AC pipe which has insufficient final moisture content to fully hydrate the cement. The green pipes are therefore submerged in water maturing tanks for a period of 5-7 days. It is possible to steam-cure AC pipes but. although water maturing takes 10 times longer, the product is less susceptible to cracking, has a greater density and has a smoother bore. After maturing the pipes are machined on the ends to the correct spigot dimensions and accurate length, and hydrostatically tested to twice working pressure. If the materials are being supplied grey, uncoated, they are bundled and moved to stock. Alternatively they can have a range of coatings applied to them, depending upon the specific requirements of the application. Etemit Tac is able to supply pipes and fittings with a variety of surface finishes to suit a wide range of environmental conditions. In ascending order of protection, the finishes are as follows: -- natural grey OPC: -- natural grey sulphate-resisting cement; -- bitumen coating, internal, external or overall: -- epoxy-tar coating (bitumen/epoxy resin mixture); , -- pure epoxy. 300-micron coating (food-quality available): t PIPES it PIPELINES INTERNATIONAL September - October 1988 CTD001273 -- pure epoxy. 500-nticmn coating (food-quality available). The Widncs and Connie AC push-lit. drop-light joints are manufactured in the same way and from the same material as the AC pipes which they suit, and have the same pressure rating. The mandrels used are specifically sized for the purpose and the 'joint pipe' is rolled to a greater thickness to allow for subsequent machining. When removed from the water maturing tanks, instead of going for end turning, a `joint pipe' is sawn into slices which are then machined internally to the appropriate ring groove profile and tolerances for the particular joint. There is also a variety of other facilities for the production of specialist products. These include: -- the fitting of end caps if pipes are to be used as storage tanks: -- drilling of pipes for French'-drain type applications: -- conversion into single-piece manholes, incorporating all the customer-specified connections in the correct positions, baffles and hydraulic profiling (benching): -- sawing of pipes into oblique slices and subsequent rebonding to form fabricated bends: -- bonding of one pipe section into another to form angled junctions: -- fitting Of brackets and shelving into largediameter pipes for use as service galleries: -- extraction of the mandrel prior the curing stove for moulding of 5-m pipes into slow bends. Process control and operator responsibility, in conjunction with a high degree of automation and mechanical handling arc the basis of a strict quality assurance regime. Overseeing the factors disciplines, a company-wide quality-control department responsible to the Managing Director monitors all raw materials, production and finished product for compliance with both internal and external standards. The pipe factory already has compliance with several European Quality Assurance Standards, and has made application for compliance with BS 5750. PIPES & PIPELINES INTERNATIONAL September ->October 88 n CTD001274 P ip e M achine In fo rm a tio n