GB1592931A - Pipe manufacture - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO PIPE MANUFACTURE (71) We, TAC CONSTRUCTION MATERIALS LIMITED, a Company organised under the laws of Great Britain, of 20 St. Mary's Parsonage, Manchester M3 2NL (formerly of 77 Fountain Street, Manchester M2 2EA), do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to the manufacture of pipes by processes including the step of forming a layer on the surface of a rotary sieve from an aqueous slurry.

Such processes have hitherto been carried out using a slurry including asbestos fibre and cement, optionally with modifying agents, fillers and the like. In the most commonly used processes, e.g. the "Mazza" process, asbestos and cement are mixed and beaten with a large proportion of water to form a slurry, which is then stored while being agitated in a container known as a "stuff chest". This constitutes a reservoir from which supplies of a slurry are taken, diluted with water and fed to one or more vats in each of which a sieve cylinder is rotated. Each of these cylinders picks up the slurry as a continuous, thin wet layer, excess water draining through the meshes of the sieve, and the layer is applied to an endless conveyor belt by which it is carried to a rotating pipe formed or mandrel to which it is transferred and on which it is wound. The coating on the former builds up layer by layer until the required thickness is reached, whereupon the layer on the conveyor is washed off to stop build-up on the mandrel. The mandrel is removed and an empty one placed in position and then the build-up on the mandrel can be recommenced. The mandrel which has been removed, complete with green pipe, is then subjected to a warm humid atmosphere e.g. 600C to 700C and relative humidity about 80 /,, or more for 3 to 5 hours to cure the pipe to a stage where the mandrel can readily be removed without fear of distortion of the pipe.

Attempts to completely replace the asbestos fibre with vitreous fibre have been unsatisfactory in the processes because the physical characteristics of vitreous fibre are so very different from those of asbestos, making the formation of a coherent sheet on the rotary sieve extremely difficult, if not impossible.

Our UK Patent Application No. 23536/75 (specification 1521482) describes the manufacture of artefacts such as sheets and boards by a process similar to the above in which there is used an aqueous slurry containing an inorganic binder, from + to 20% by weight of vitreous fibres and a minor proportion of auxiliary-non- asbestos fibres having a Canadian Standard Freeness (C.S.F.) in the range 20 to 300 . The only auxiliary fibres specifically described in that specification are, however, natural fibres such as cellulosic fibres which are not suitable for use in pipes owing to their susceptibility to bacteriological attack, the main uses of asbestos-cement pipes being as water and sewage pipes.

According to the present invention, we provide a process for producing a pipe from an aqueous slurry by forming a layer on the surface of a rotary sieve, from which the layer is subsequently removed and wound on to a mandrel, the process including the step of forming the aqueous slurry from water, an inorganic binder and from + to 20% by weight (total dry solids) of vitreous fibres, together with a minor proportion of auxiliary synthetic polymeric fibre having a Canadian Standard Freeness in the range 20 to 3000.

Although "minor proportion" includes up to 49% by weight of total dry solids, other requirements may limit the proportion to a very much smaller figure, say to 10%.

The expression "Canadian Standard freeness" (C.S.F.) in the present context refers to the standard sheet forming test as commonly applied throughout the papermaking industry and wherein, for example, raw cellulose pulp exhibits a C.S.F. of 70-900" and a very highly opened papermaking cellulose pulp exhibits a C.S.F. of about 300O.

The vitreous fibre may be glass fibre, or mineral wool, or a mixture of these.

The term "mineral wool" includes both slag and rock wool. Where glass fibre is used, the staple length is preferably of the order of 2+ cm or less, 14 cm being especially preferred. The mineral wool may be pretreated to reduce its staple length, if necessary, for example by subjecting it to a milling treatment.

The amount of vitreous fibre may be varied according to the nature of the fibre or fibres used, its cost, and the degree of reinforcement required. It will generally be in the range 1% to 15 /" by weight of total dry solids, however, and when glass is used alone preferably not more than 8% by weight total dry solids is used.

The inorganic binder may be a hydraulic binder such as O.P. cement and in such a case it is preferred that the vitreous fibre be either alkali-resistant or at least treated to reduce its susceptibility to alkaline attack. The binder may also include a pulverised fuel ash.

When glass fibre is used it is generally "chopped strand", i.e. staple fibre cut from dressed glass rovings in which case the staple fibre consists of bunches of individual glass filaments adhered together by the dressing. When using such raw materials in the present invention it is preferred that the staple fibres are subjected to conditions durlng their mixing into the slurry such that the individual glass filaments are separated. The basic requirement for these conditions is that the glass fibre is beaten in water for sufficient time for the adhesion of the dressing between filaments to be broken down. Increasing the temperature of the water is of assistance in this step, as is increasing the dilution of the aqueous slurry.

The auxiliary non-asbestos fibre is preferably a synthetic fibre pulp. The synthetic fibres are preferably of a polymeric material with a very high resistance to degradation by weathering processes and bacteria. Such materials include polyolefins, such as polyethlene and polypropylene, polyamides such as nylon 6, nylon 66 etc. and saturated linear polyesters such as polybutylene terephthalate.

Other polymers may also be used, also copolymers and graft copolymers such as those described in UK Patent No. 1,476,803.

It will be appreciated that in a conventional papermaking process C.S.F.

values of less than 300 are generally regarded as very low. In contrast, we find that the present process operates well with C.S.F. values of 1500 or even lower. We also find that the nature of material of the fibre used is relatively insignificant when compared to the requirement for the low C.S.F. value, although it is helpful if the fibre is hydrophilic, or treated to be so, as opposed to hydrophobic.

It is also possible to add free silica-containing materials for the specific purpose of reacting with substantially all of any free line released when the binder sets. This is particularly relevant to processes using hydraulic cement as the binder and where the binder is caused to set by autoclaving. Free lime would of course tend to degrade the vitreous fibres in the material of the pipe if no attempt to minimise its effects was made.

Material stripped from the rotary sieve is naturally in a wet condition and the process includes allowing the binder to set, for example, naturally on standing or on stoving, i.e. heating in an oven. Optionally, the wet pipes may be cut or trimmed prior to the binder setting. After setting the binder, the pipes may be removed from their formers. The pipes should then be cured either by air curing or by autoclaving or preferably by immersion in water for several days e.g. 7 days. After curing the pipes may be end turned or otherwise prepared for sale and/or use. The pipes may also be cut down into rings and internally machined for use as pipe joints in conjunction with rubber sealing rings.

The invention also includes pipes made by a process according to the invention.

The invention enables pipes to be made on the machine usually used to manufacture asbestos-cement pipes. The material of which the pipes are made is not only asbestos-free but also resistant to bacterial attack and weathering, so that the pipes are suitable for use as water and sewage pipes.

An example of a furnish which is particularly suitable for pipe manufacture is described below.

A slurry was made from the furnish tabulated below in Table I.

TABLE I % by weight Alkali resistant glass fibre (1.25 cm staple length) 3.0 Synthetic pulp (3000CSF) 4.0 Ordinary Portland Cement 89.0 China Clay 4.0 The furnish was mixed with water in a pilot plant scale Hollander beater 125 litres of water being needed for a 27 kg beater charge. The mixing time was of the order of 20 minutes, the temperature of the water was 40"C and the order of addition of the ingredients was pulp, glass fibres, and finally cement and china clay, the glass fibre being mixed for 15 mins.

The slurry was then run on a vat machine and processed into small boards for sample purposes. (It should be noted that the only major difference between pipe manufacture and board manufacture in this process is the type of cylindrical former used on the vat machine, it being more convenient to make board for testing of the properties of the material produced).

The sample boards were air matured for seven days and oven dried at 100"C for 24 hours.

The physical properties of the material were measured both in the wet state and in the dry state, and are given in the Table II below.

TABLE 11 wet dry MOR (N/mm2) 10.2 11.6 A/W ratio 0.97 0.98 RM Density (Kg/m3) 1141 1150 Dry Density (Kg/m3) 1374 1346 Charpy Impact Strength (KJ/m3) (across) 7.1 6.1 (with) 7.1 5.9 Drainage time of slurry (secs) 7.8 These results show that the synthetic pulp facilitates a reinforced cement of adequate strength to be produced.

The fibres in the synthetic pulp are made of polyethylene, so that the reinforced cement contains no material which is susceptible to bacteriological attack, and is therefore eminently suitable to be used in pipes.

WHAT WE CLAIM IS: 1. A process for producing a pipe from an aqueous slurry by forming a layer on the surface of a rotary sieve, from which the layer is subsequently removed and wound on to a mandrel, the process including the step of forming the aqueous slurry from water, an inorganic binder and from l to 20% by weight (total dry solids) of vitreous fibres, together with a minor proportion of auxiliary synthetic polymeric fibre having a Canadian Standard Freeness in the range 20 to 3000.

2. A process according to Claim I in which the proportion of auxiliary synthetic polymeric fibre in the slurry is no more than 10% by weight of total dry solids.

3. A process according to Claim 1 or 2 in which the vitreous fibres comprise glass fibres.

4. A process according to claim 3 in which the glass fibres introduced into the slurry have a staple length no more than 2.5 c.m.

5. A process according to Claim 3 or 4 in which the glass fibres are alkaliresistant glass fibres and are introduced into the slurry in the form of chopped etv S

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (14)

**WARNING** start of CLMS field may overlap end of DESC **. not only asbestos-free but also resistant to bacterial attack and weathering, so that the pipes are suitable for use as water and sewage pipes. An example of a furnish which is particularly suitable for pipe manufacture is described below. A slurry was made from the furnish tabulated below in Table I. TABLE I % by weight Alkali resistant glass fibre (1.25 cm staple length) 3.0 Synthetic pulp (3000CSF) 4.0 Ordinary Portland Cement 89.0 China Clay 4.0 The furnish was mixed with water in a pilot plant scale Hollander beater 125 litres of water being needed for a 27 kg beater charge. The mixing time was of the order of 20 minutes, the temperature of the water was 40"C and the order of addition of the ingredients was pulp, glass fibres, and finally cement and china clay, the glass fibre being mixed for 15 mins. The slurry was then run on a vat machine and processed into small boards for sample purposes. (It should be noted that the only major difference between pipe manufacture and board manufacture in this process is the type of cylindrical former used on the vat machine, it being more convenient to make board for testing of the properties of the material produced). The sample boards were air matured for seven days and oven dried at 100"C for 24 hours. The physical properties of the material were measured both in the wet state and in the dry state, and are given in the Table II below. TABLE 11 wet dry MOR (N/mm2) 10.2 11.6 A/W ratio 0.97 0.98 RM Density (Kg/m3) 1141 1150 Dry Density (Kg/m3) 1374 1346 Charpy Impact Strength (KJ/m3) (across) 7.1 6.1 (with) 7.1 5.9 Drainage time of slurry (secs) 7.8 These results show that the synthetic pulp facilitates a reinforced cement of adequate strength to be produced. The fibres in the synthetic pulp are made of polyethylene, so that the reinforced cement contains no material which is susceptible to bacteriological attack, and is therefore eminently suitable to be used in pipes. WHAT WE CLAIM IS:

1. A process for producing a pipe from an aqueous slurry by forming a layer on the surface of a rotary sieve, from which the layer is subsequently removed and wound on to a mandrel, the process including the step of forming the aqueous slurry from water, an inorganic binder and from l to 20% by weight (total dry solids) of vitreous fibres, together with a minor proportion of auxiliary synthetic polymeric fibre having a Canadian Standard Freeness in the range 20 to 3000.

2. A process according to Claim I in which the proportion of auxiliary synthetic polymeric fibre in the slurry is no more than 10% by weight of total dry solids.

3. A process according to Claim 1 or 2 in which the vitreous fibres comprise glass fibres.

4. A process according to claim 3 in which the glass fibres introduced into the slurry have a staple length no more than 2.5 c.m.

5. A process according to Claim 3 or 4 in which the glass fibres are alkaliresistant glass fibres and are introduced into the slurry in the form of chopped etv S

6. A process according to Claim 5 in which the glass fibre in the slurry is subjected to conditions such that the individual glass filaments in the chopped strands are substantially separated.

7. A process according to any one of the preceding claims in which the vitreous fibres include mineral wool.

8. A process according to any one of the preceding claims in which the auxiliary synthetic polymeric fibre is a polyolefin fibre.

9. A process according to any one of the preceding claims in which the inorganic binder comprises a hydraulic cement.

10. A process according to Claim 9 in which the binder is ordinary Portland Cement.

I 1. A process according to any one of the preceding claims in which the binder is at least partially set whilst the pipe is on said mandrel.

12. A process according to any one of the preceding claims in which the pipe is cut or trimmed before the binder is fully set.

13. A process for producing a pipe substantially as described herein with reference to the foregoing Example.

14. A pipe produced by a process as claimed in any one of the preceding claims.