GB1587291A

GB1587291A - Coating surfaces of articles

Info

Publication number: GB1587291A
Application number: GB1984677A
Authority: GB
Original assignee: Lechler Chemie GmbH
Current assignee: Sika Holding GmbH
Priority date: 1976-05-11
Filing date: 1977-05-11
Publication date: 1981-04-01
Also published as: ATA332677A; AT354215B; FR2351346A1; IT1075548B

Description

(54) COATING SURFACES OF ARTICLES (71) We, LECHLER CHEMIE GmbH, a body corporate organised according to the laws of the Federal Republic of Germany, of Hohenstrasse 24, 7012 Fellbach bei Stuttgart, Federal Republic of Germany, 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 a process for applying compositions comprising cement to articles, and to forms of apparatus which may be used in such a process.

Linings based on hydraulic cement have been used for over 100 years in the United States of America and for about 20 years in Germany for the protection against corrosion of potable water pipes.

Various processes have been proposed for both the original and the subsequent application of these linings. These processes however suffer from a number of disadvantages, for example, their adhesion to the surfaces that were coated was relatively low, and they exhibited fissure formation due to shrinkage and formation of slime on the surface due to disproportionation.

None of the previously proposed processes could be used for the lining of shaped articles, bent pieces of pipe, etc. These parts are usually coated with compositions based on tar or bitumen or are protected by hot-tarring. If, in this case, the customer also requires a cement mortar lining, these parts can only be lined with mortar by hand at a high labour cost, and is therefore very inconvenient.

The invention provides a process for coating an internal surface of an article which comprises spraying a composition which comprises cement and one or more aggregates, the ratio of cement to aggregates being in the range of from 1:1.5 to 1:3.5 by weight, and includes from 2 to 25 percent by weight of an aqueous dispersion of one or more non-hydrolysable or sparingly hydrolysable polymers, calculated as solid matter and based on the weight of cement, and includes one or more despumating agents and/or liquefying agents, the composition having a water-cement value in the range of from 0.25 to 0.45, radially onto the internal surface to form a layer from 1 to 5 mm thick, preferably from 2 to 3 mm thick.

The term "water-cement value" used herein denotes the weight ratio of water to cement.

The composition for use in the process of the invention is one which comprises cement and one or more aggregates, the ratio of cement to aggregate being in the range of from 1:1.5to 1:3.5, preferably 1:1.5 to 1:2.0 by weight, and which includes from 2 to 25 percent, preferably from 3 to 25 percent, and especially from 5 to 10 percent, by weight of an aqueous dispersion of one or more non-hydrolysable or sparingly hydrolysable polymers, preferably an acrylic resin, the percentage being calculated on the solid matter of the dispersion and based on the weight of the cement, and also includes one or more despumating agents, for example silicone oils and/or tributyl phosphate, and/or one or more liquefying agents. The composition has a water-cement value in the range of from 0.25 to 0.45.

The composition may include pozzuolana and/or may contain reinforcing fibres or a fibrous material which may be organic or inorganic, for example asbestos, glass fibre, a synthetic plastics material, or mixtures thereof.

By the process of the invention, the known good properties of cement mortar linings e.g.

hygiene, protection against corrosion, avoidance of incrustations, are maintained and further improvements can be achieved. The composition may include usual Portland cements, iron Portland cements, blast furnace cements or trass cements, such as described in DIN 1164. In addition, oil shale cement or cements having a high sulphate resistance and/or low heat of hydration may be used. The aggregates may also comprise quartz sand having various ranges of particles size that are so composed as to form a low-cavity mixture (Fuller line). The particle composition should preferably fulfil the requirements described in the working sheet W 342 as follows: "The proportion of fine particles (passing through a sieve according to DIN 41 88 having a mesh width of 0.125 mm) must be at most 10 percent by weight." The proportion of particles having particles diameters of up to one-third of the average layer thickness of the lining is advantageously at least 50 percent. by weight, and the maximum particle diameter is preferably not greater than half the average layer thickness of the lining.

Water is preferably added in quantities such that the composition has a water-cement value of between 0.25 and 0.45, preferably less than 0.40. The total amount of water is made up of the water from the additives and the water added.

The invention also provides apparatus for spraying an internal surface of an article with a composition by means of a fluid, which comprises at least one discharge assembly comprising an outer tube having an inlet for fluid under pressure and a discharge outlet for said fluid, and an open-ended inner tube for supplying the composition positioned therein and parallel thereto to form a space between the inner and outer tubes, which space provides a channel for the fluid, and terminates at said discharge outlet, wherein the open end of the inner tube is in the vicinity of the fluid discharge outlet and each is directed toward a rotatable distribution member having a shape and configuration such that, in operation, when the composition is directed onto the distribution member, the composition is distributed radially outward therefrom by rotation of the distribution member, when used for spraying an internal surface of an article by a process of the invention.

The apparatus of the invention has the advantage that the composition can be applied in a thin layer and in an economical manner in tubes or shaped articles of any type.

The rotatable distribution member may be in the form of a circular plate having a rim directed toward the or each tube, i.e. toward the or each discharge assembly, the rim advantageously being outwardly inclined.

The invention further provides apparatus for spraying an internal surface of an article with a composition by means of a fluid, which comprises an open-ended tube for supplying the composition and a conduit for the fluid terminating in a plurality of jets which surround, and are directed across, the open end of the tube, each jet being oriented such that the projection of its axis, does not coincide with any radius of the tube, when used for spraying an internal surface of an article by a process of the invention.

Preferably the projection of the axis of each jet as viewed along the axis of the tube, subtends the same axis with the radius of the tube, for example 10 to 200, more especially about 15". Preferably the axis of each jet is inclined with respect to the longitudinal axis of the tube by an angle of from 30 to 60 more especially about 45".

Various forms of apparatus in accordance with the invention will now be described in detail, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an elevational view of one form of apparatus; Figure 2 is detailed view of part of the apparatus shown in Figure 1; Figure 3 is a side elevational view of another form of apparatus; Figure 4 is a front elevational view of the apparatus shown in Figure 3; Figure 5 is a side sectional view of another form of apparatus; Figure 6 is a side sectional view of part of the apparatus shown in Figure 5; Figure 7 is a front elevation of part of the apparatus shown in Figure 5; Figure 8 is a graphical representation showing the degree of shrinkage and swelling of composition used in the process of the invention and that of another composition when stored in air or in water; and Figure 9 is a graphical representation showing the degree of shrinkage and swelling of a composition used in the process of the invention and that of another composition when stored sequentially in air and in water.

Referring initially to Figures 1 and 2 of the accompanying drawings, there is shown an apparatus for applying a composition to an internal surface of an article by means of a fluid, which comprises a screw supply pump 1 which supplies the composition via a flexible tube 2 to a discharge assembly 3. The discharge assembly 3 comprises an inner tube 4 for the composition and an outer tube 5 positioned coaxially with the inner tube so as to form an annular space for supplying compressed air. The discharge assembly terminates at a discharge outlet which is directed toward a rotatable distribution member or centrifuging wheel 6 in the form of a plate with an inclined rim. The distribution member 6 is mounted on a shaft on which the discharge assembly is also mounted.

A modification of the apparatus is shown in Figure 3 or Figure 4. In this apparatus there are four discharge assemblies, 3~ a, b, c, and d, each directed toward the distribution member 6, and parallel to its axis. Thus, it is possible to direct the composition in the form of a jet simultaneously through four metering tubes. This form of apparatus has the advantage that considerably larger quantities of composition, e.g. cement mortar, can be processed per unit time. Thus, considerably higher speeds of supply are possible in coating tubes and shaped parts of large nominal width. By jetting the cement mortar from 4 metering tubes the layer-thickness tolerance at the periphery of the coated tube is reduced and also a better surface quality of the cement mortar applied is achieved.

In this apparatus, the inner and outer tubes may be connected to composition and compressed air supply means respectively via one or more connection pieces 7 and 8, the or each connection piece being cornmon to two inner or outer tubes. In the apparatus shown, the discharge assemblies 3a, and 3b are served by the same connection pieces, as are discharge assemblies 3b and 3c.

In a further modification of this apparatus, the distance of the discharge assemblies from the driving shaft is adjustable which enables distribution members of different sizes to be used.

Figures 5 to 7 show a form of apparatus that does not use a rotatable distribution member. In this apparatus compressed air issues from a tuyere ring 6a, which concentrically surrounds the tube for the cement mortar composition and has inclined air jets 9 in the form of a cone having a pronounced torque. The cement mortar is finely divided or atomised by the compressed air so introduced and thus distributed. This apparatus comprises a metering device 3 having an open-ended inner tube 4 for the composition and a compressed air conduit 5 leading to a tuyere system 6a, which is constructed in the form of a plurality of individual jets or tuyeres 9, which surround the outlet opening of the inner tube 4.

With this apparatus it is possible to coat with special advantage nominal widths of less than 1(30 mm to about 300 mm, because, with this spraying head, the rotatable distribution member is not needed, and as there is then no drive mechanism for the distribution member the construction of the apparatus can be kept small. This apparatus produces a somewhat coarser structure of the coating, so that it is expedient to smooth the surface subsequently by mechanical means or to improve it by subsequently rotating the tube.

By using the apparatus of the invention, it is possible to apply compositions to the internal surfaces of tubes and other shaped articles in a relatively uniform manner by spraying the compositions along flow paths which diverge, thereby giving a radial distribution and simultaneous deposition of the composition around the whole periphery of the tube or other shaped articles.

The process of the invention may be conducted by directing the composition in the form of a jet, preferably four jets from four discharge assemblies, by fluid under pressure and distributed on a rotating plate-like wheel and from there radially centrifuged.

The process may also be conducted on apparatus in which fluid issues from a tuyere ring with a torque in the form of a cone, which ring concentrically surrounds an opening from which the composition issues and the composition is finely divided by the fluid and distributed thereby.

-In particular, the process of the invention can be conducted with the forms of apparatus described above and in which the fluid used is a gas, preferably compressed air.

By means of the cement mortar composed in accordance with the invention it is now possible to apply economically by a spraying process, coats of uniform thickness that are smooth, non-disproportionating, free from fissures and of good adhesion without a disadvantageous layer of slime, at a thickness of lmm to 4mm. Cement mortars, which contained 1.5 to 3.5 parts by weight of aggregates per one part by weight of cement and had a water-cement value below 0.45, could also be supplied and sprayed as hitherto. Usually such cement mortars were applied in layer thicknesses of 8 to 15mm. The surfaces so obtained were extraordinarily rough, which had a disadvantageous effect on the speed of flow. For this reason such mortars were compressed by subsequent smoothing and levelling of the surface. The properties of such linings of cement mortar exhibit essentially the known disadvantages.

The cement mortars composed in accordance with the invention can be fed and sprayed unobjectionably at a water-cement value below 0.45. In this way it is possible to apply a cement mortar economically e.g. at a layer thickness of 1 mm to 4mm. The surface so obtained is closed and exhibits a slight "orange-peel" effect. The surface needs no subsequent treatment. The process enables a cement mortar so composed to be processed in an optimum manner.

The process carried out with material composed in accordance with the invention is distinguished by the fact that it is possible to coat economically with this process not only tubes, but also shaped parts. Hitherto it has not been possible to coat shaped parts by a spraying process with the usual cement mortars.

Cement mortar composed in accordance with the invention can be sprayed by this process onto nominal widths below 80 mm up to more than 1500 mm at a layer thickness for example of 1 mm to 4 mm, and preferably 2 mm. It ensures sufficient protection against corrosion and prevents incrustations. The process enables uniformly thick, smooth, non-disproportionating, fissure-free and good adhering coatings to be applied economically without a disadvantageous layer of slime. After-treatment by keeping moist or steam hardening is not necessary. Hydration of the cement mortar is effected only by high humidity of the air during storage or after installation by the following water. It can, of course, also be effected in special cases by treating the lining with water.

In the case of shaped parts there must be effected, in addition to sufficient internal protection, protection of the outer surface and sockets or sleeves. Usually, anti-corrision agents of bitumen or tar are applied by a dipping process. Previous processes did not permit internal cement mortar lining of the shaped parts, in contrast to straight pieces of tube. For hygiene reasons this is often not acceptable. However by the process of the present invention it is possibly to apply cement mortars also to such substrates. Tar and bitumen coatings can be covered with the usual cement mortar compositions only in a layer thickness of 10 to 15 mm, because these coatings support themselves and constitute, as it were, a tube within a tube. When cement mortars are applied in thin layers, such as are used for covering with cement mortars composed in accordance with the invention, that is to say 1 to 4 mm thick, coats of cement mortars of the usual composition would be torn away and fall off without resistance.

The following Example illustrates the invention and more especially the beneficial effect of the additive used according to the invention. This effect is shown when the additive is used with cement alone, as when it is used with cement and aggregate as specified in the process of the invention. Reference is made to Figures 8 and 9 of the accompanying drawings.

Example Cement mortar composed in accordance with the invention for lining tubes is prepared from: (a) Mineral constituents (including aggregates): 100 Parts by weight of Portland cement PZ 350 F 18 parts by weight of quartz sand F 36, average particle size 0.15 m 45 parts by weight of quartz sand F 33, average particle size 0.21 mm 87 parts by weight of quartz sand F 31, average particle size 0.32 mm Round sands produced by Quarzwerke Cologne are used. The sieve line of the sands is graded to have few cavities, and the particle range extends from 0.08 to 0.6 mm.

(b) Additive preparation: 0.7 Part by weight of a solution of 10% by weight strength of Calgon (Registered Trade Mark), 1.0 part weight of commercially available despumating agents, 0.2 parts by weight of cement liquefiers based on polyglycol ethers and 5.0 parts by weight of an aqueous solution of 20% by weight strength of a polycondensate of melamine and formaldehyde are stirred into 52 parts by weight of an acrylic resin aqueous dispersion of 47% by weight strength, and then 50 parts by weight of glass powder and 2.5 parts by weight of short-fibred asbestos are added in succesion.

Finally, 8 parts by weight of a methyl-cellulose solution of 2% by weight strength and also, as a preservative, 0.2 part by weight of formalin solution are stirred in.

40 Parts by weight of the additive preparation described under (b) and 24 parts by weight of water were added to all the mineral constituent preparation according to (a).

The advantages of the cement mortar lining used according to the invention are demonstated as follows.

The improvement in adhesion to bitumen lacquer is demonstrated in Table 1.

In both cases a cement mortar having a cement-sand ratio of 1 : 1.5 parts by weight was applied with and without the additives used according to the invention. The water-cement value was 0.4 in each case.

The composition of the usual cement mortar (comparison test) was as follows: 100 Parts by weight of Portland cement PZ 350 F 18 parts by weight of quartz sand F 36 45 parts by weight of quartz sand F 33 87 parts by weight of quartz sand F 31 40 parts by weight of water.

The preparation was carried out without the additives used according to the invention.

The adhesion of the cement mortar was determined after storage for 2 months in the air as pure tensile strength with the Herion testing appliance in accordance with DIN 53232: TABLE 1 Adhesive tensile strengths in kplcm2 on flat, cast iron plates after storage in the air for 2 months.

Condition of the cast Adhesive tensile strength iron surface (kp/cm2) Usual cement Cement mortar mortar. composition used (comparison test) according to the invention.

Sand-blasted. 1.5 34.3 Sand-blasted and immersed in 1 x bitumen lacquer. 2.3 25.0 Thus, tarring or bitumen lacquers can be used to achieve internal and external corrosion-protection and by the process of the present invention it is possible to apply thereto a fissure-free and hygienically-unobjectionable good adhering cement mortar lining in a thin layer.

The improvement in adhesion by the use of the additive used according to the invention to sand-blasted cast iron surfaces is confirmed by a further test. For this purpose also flat cast iron plates were coated in the manner described and, without after-treatment of the applied coating of cement mortar, subjected to storage under various conditions. The results of the adhesion tests in kp/cm can be seen from the Table.

Type of storage Usual cement Cement mortar composition mortar used according to the invention 2 Months in air 1.5 34.3 2 months in air and 1 month in water 15.6 45.6 2 months in air fall 1 month in water off 42.1 1 month in air at 0 It will be seen that by the use of the additives used according to the invention an increase in adhesion, as compared with the unimproved cement mortar, amounting to 23 times in the case of storage in air and amounting to three times in the case of air-water storage, is possible. When the coatings subjected to water were subsequently stored in air, the unimproved cement mortar, owing to the shrinking process, exhibited a decrease in the adhesion to 0, whereas the cement mortar composition of the invention showed practically no change in adhesion.

In addition to insufficient adhesion, the disadvantages most frequently observed in the case of tubes having linings of cement mortar relate to fissure formation and a layer of slime on the surface. By using the additives used according to the invention fissure formation is avoided.

The favourable influence of the additive used according to the invention on shrinkage behaviour is illustrated by the following test: (In this test the cement mortar contains less than the amount of aggregate specified according to the invention) The unimproved mortar is composed of: 1 part by weight of oil shale cement 1 part by weight of quartz sand 0 - lmm 0.35 part by weight of water.

The improved mortar contained: 0.20 part by weight of the additive described above and had a water-cement value of 0.32.

Prisms made therewith measuring 4 x 4 x 16 cm (DIN 1164) were stored for 30 days under water and for 30 days in the air, respectively.

The shrinkage or swelling taking place is shown in Figure 8. The shrinkage of the cement mortar stored in air for 30 days was O.70/oo and with the additive used according to the invention it was O.30/oo. By storage in water swelling occurred, as was expected; it amounted to O.60/oo in the case of the unimproved mortar, and 0.80/oo in the case of the improved mortar of the invention In a further series of tests the test bodies, after storage in air for 15 days, were stored under water (and vice versa, see Figure 9). It will be seen that the test bodies first stored in air swell in water, as expected, the unimproved cement mortar approaching the zero line; the improved cement mortar passing into the region of swelling.

Rings were made with the same cement mortars by means of a steel ring as core (L Hermit's test) and then kept moist. After one day the mortar rings were stored in air. In the case of the unimproved mortar a wide track due to shrinkage occurred after a short time, but not in the case of the mortar that contained the described additive.

In practice this has the effect that with the initial air-storage in the case of pure cement mortars cracks due to shrinkage occur, which favourably close again during subsequent storage in water. In the case of mortars containing the additive used according to the invention these cracks due to shrinkage do not occur during storage in air, and in subsequent storage in water a slight tension effect occurs, which in many cases, especially tube linings, is an advantage.

Cement mortar linings that have been applied by the centrifuging process exhibit disproportionation of the mortar constituents which is a critical disadvantage. As a consequence of these disproportionations there are formed on the surface of the cement lining the very disadvantageous layers of slime, which owing to their low strength cause an increased abrasion.

For testing the resistance to abrasion we used a testing apparatus which has been described by Heinrich Bauch, Wuppertal-Elberfeld (Title: "Kritische Betrachtungen und neuere Versuche Uber den Abrieb in Abwasserleitungen," appearing in the periodical GWF-Wasser-Abwasser, 109. Annual Number 16, 1968, pages 413-418).

The cement mortar of the invention mentioned above as an example (mortar 3) has been compared with an unimproved cement mortar (mortar 2) not having the additive used according to the invention, but otherwise of the same composition. In both cases the mortars were sprayed in accordance with the process of the invention into tube sections 11 cm long having a nominal width of 150 mm. The layer thickness averaged 2 mm.

For comparison, an ordinary commercial tube lined internally with cement mortar was also tested. The cement mortar lining had been applied by the centrifuging process (mortar 1).

The sample pieces were subsequently subjected to various storage conditions, and then filled with an abrading medium consisting of water, corundum and porcelain spheres, closed at both ends, and placed in a special rolling box and rotated. The circumferential speed was 0.52 metres per second. The mechanical abrasion was determined gravimetrically after 5450 revolutions and also after 54500 revolutions. The lower number of revolutions enabled a conclusion to be made in judging the upper layer and thus as to any layers of slime present. The subsequent further stress led to useful comparison values for assessing the resistance to abrasion of the core layer of mortar.

The amount of abrasion is given in milligrams, calculated on a square centimetre of the mortar surface at 10000 revolutions.

TABLE 2 Specific abrasion according to Bauch of the upper surface in mg/cm2 Type of Type of Mortar 1 Mortar 2 Mortar 3 Storage. after- (compari- (compari- (invention) treatment. son test) son test) Air- 1 Day moist. 12.5 64.7 3.7 storage. Air drying. - 148.0 4.6 lhr/65 C. - - 6.0 Air- 1 Day moist. 11.9 12.2 3.3 water- Air drying. - 22.9 4.9 storage. lhr/65 C. - - 4.4 Air- 1 Day moist. 12.2 9.0 4.9 water- Air drying. - 18.1 3.6 storage + lhr/65 C. - - 3.3 subsequent air-storage.

TABLE 3 Specific abrasion according to Bauch of the core layer in mglcm2.

Type of Type of Mortar 1 Mortar 2 Mortar 3 storage. after treatment.

Air 1 Day moist. 2.1 6.3 6.7 storage. Air drying. - 31.8 8.1 1 hr/65 C. - - 4.2 Air- 1 Day moist. 2.4 8.6 3.1 water- Air drying. - - 4.0 storage. 1 hr/65 C. - - 2.9 Air- 1 Day moist. 2.7 8.1 3.1 water- Air drying. - 7.7 3.0 storage + lhr/65 C. - - 2.0 subsequent air-storage.

The results clearly show that the cement mortar compositon used according to the invention (mortar 3), as compared with the cement mortars (mortar 1) applied in the centrifuging process, have a considerably better resistance to abrasion in the upper surface.

This improvement as compared with mortar 2 is more pronounced, especially in pure air-storage.

Comparison of the abrasion resistance of the core layers shows, surprisingly, that in the use of mortar 3 with the more unfavourable after-treatment (1 hour at 65"C.) a better abrasion resistance is achieved than with air-drying or keeping moist the applied mortar layer. The resistance to abrasion, in the case of the air-water-storage that is of interest in practice, approximates to the value for the mortar layer applied by the centrifuging process.

This is all the more surprising, when it is considered that a good abrasion resistance was achieved with mortar 3 having a water-cement value of 0.40, as compared with mortar 1, which has a water-cement value of below 0.35. The dependence of the abrasion resistance on the water-cement value is shown by mortar 2, which at a water-cement value of 0.40 exhibits a distinctly poorer abrasion resistance than does mortar 1. By the use of the additive used according to the invention in mortar 3 there is a surprising improvement.

Tables 2 and 3 also show that with the use of mortar 3 used according to the invention it is possible, without after-treatment of the applied cement mortar, to obtain good properties.

This is very satisfactory above all from the standpoint of economy. Moreover, it is shown that air-dried mortar 3, which has undergone practically only a very little hydration of the cement stone, after air-storage for more than two months, upon subsequent contact with water reacts with it, and the interrupted hydration of the cement stone continues. This also is very satisfactory from the standpoint of economy, because it is thereby possible to put the parts in storage without after-treatment and without technical expenditure, and without any harmful effects occurring, such as detachments or adhesion difficulties.

The interruption of hydration is contrary to the usual rules of practice, according to which it is absolutely necessary to keep a cement mortar sufficiently moist for a long period to develop its optimum properties. With the use of the additive used according to the invention it is even possible to line warm tubes or shaped parts, or, after lining, to subject them to a heat treatment, without the lining being harmed. Rather, the supply of heat is advantageous, because in this way the added synthetic resin can be better absorbed in the mineral components and thus contribute to improvement of the properties.

The calcium hydroxide liberated during hydration of the cement is of special interest in view of a possible leaching of c

A cement mortar composition used according to the invention has, as compared with unimproved cement mortar, an increased flexural strength coupled with approximately constant compressive strength. The values given in Work Sheet W 342 for flexural strength and compressive strength are, for cement mortar having a water-cement value of 0.35, 60 kp/cm2 for the flexural strength and 500 kp/cm2 for the compressive strength. The usual unimproved mortar 2 described above attains after 28 days a flexural strength of 69 kp/cm2 and a compressive strength of 476 kp/cm2. Calculated therefrom the flexural strength/ compressive strength ratio is 1: 7 to 1: 10. By the use of the additive used according to the invention (mortar 3) the flexural strengths are increased by 100 - 150%. Owing to this, the flexural strength/compressive strength ratio is shifted into a more favourable range. In this case it is 1 : 3.

TABLE 5 Strengths in kpicm2 of prisms 4 x 4 x 16cm. (DIN 1164) Mortar 2 Mortar 3 (comparison (invention) test) Flexural strength 69 179 Compressive strength 476 550 Connected with the increase in flexural strength is lowering of the E-modulus. The lowering may amount to between 30 and 50%. This finally results in more elastic mortar layers, which in conjunction with a reduction in the thickness of the lining leads to considerably more flexible and impact-resisting cement mortar linings.

In order to test the impact resistance pieces of tube lined with mortar 3 were subjected to impact with a heavy falling hammer weighing 25 kg from a height of 4 metres. In spite of visible deformation of the cast iron jacket, the cement mortar composition of the invention showed merely a hair crack, with otherwise good adhesion. The adhesion of the mortar was also maintained when the piece of cast iron had previously been provided with a coating of bitumen lacquer.

In a further test sand-blasted metal sheets were coated at a thickness of about 0.5 mm with a mixture of Portland cement 350 F and water with and without the additive of the invention, and tested by the ball stream test according to DIN 53154. The water-cement value of both mixtures was 0.44. 1000 Steel balls having a diameter of 100 mm were allowed to fall from a height of 40 cm onto the coated sheet inclined at an angle of 30 . The number of balls just sufficient to damage the coating is a measure of the mechanical stress-resisting capacity of the coating. The results are given in Table 6: TABLE 6 Number of balls just sufficient to damage the coating (DIN 53154).

After 7 days After 1 day of air storage of air- 5 days of water storage storage 1 day of air storage Portland cement 350 F 1,000 20,000 Portland cement 350 F with 40% of additive 15,000 35,000 Accordingly, by the use of additives according to the invention the capacity of the cement coatings for being stressed is approximately doubled in the case of water-storage and in the case of air-storage, which generally corresponds to practice, it is increased to 15 times.

The water-cement value of mortar mixture 3 used according to the invention, described as suitable for lining tubes, is 0.40. However, it can be decreased by suitable known measures, such as a little thinning with sand and/or by the use of coarser sand and/or by the use of coarsely ground cement. The addition of coarsely ground cement having Blain numbers between 2000 and 4000 cm2/gm has especially a water-saving effect.

By these known measures it is possible to feed and unobjectionably spray mortar at water-cement values even below 0.30 by the process technique described above. By decreasing the water-cement value the properties of a cement mortar are further improved in known manner. In this way the density, strength, shrinkage behaviour and behaviour towards chemical attack are influenced very positively.

Cement mortar composed in accordance with the invention is also well suited in a thin layer for sealing water-permeable concrete. Especially in the case of tubes, which are made by the jolt-squeeze process, the centrifugal jolt-squeeze process or the centrifugal rolling process in a horizontal or vertical position, leakages cannot be excluded. The tubes must according to the standard requirement withstand a water pressure of 0.5 atmosphere gauge without penetration by water. It is possible to obtain an impervious tube by spraying on radially a layer of mortar composed in accordance with the invention having a thickness of 1.5 to 3 mm. At a layer thickness of about 3 mm, after air-storage, the cement mortar described fulfills the test for impermeability to water according to DIN 1048 up to a water pressure of 7 atmospheres gauge. In order to fulfil the water pressure test in the case of tubes, layer thicknesses of 1.5 to 2 mm suffice, because in this case only a water pressure of 0.5 atmosphere gauge is stipulated.

Further possibilities for improvement are offered by increasing the resistance to abrasion of such mortars. This can be effected in known manner by the use of corundum, silicon carbide or other naturally occurring or artificially produced hard stone additions. With such additions the additive described causes considerably improved adhesion and strengthening of the structure. This is illustrated by an example: Mortar of dry to stiff consistency composed of 300 gms of Portland cement 350 F, 750 gms of Cewilith slag (particle size 3 - 6 mm, supplier: Dampfkraftwerk Ensdorf/Saar) and 250 gms of Rhine sand of 0 - 4 mm, and having a water-cement value of 0.30, was compared with a mortar of the same composition having an addition of 15% of the additive used according to the invention (calculated on the cement portion).

Composition of the slag: 54% of SiO2 10% of CaO, MgO, K2O, 17% of Awl203 Na2O, MnO, TiO2 9% of FeO 10% of HCl-insolubles Prisms measuring 4 x 4 x 16 cm were scoured for one day and, after air-storage for 28 days, their strength was tested: TABLE 7 Without additive. With 15% of additive, calculated on Portland cement.

kp/cm2 kp/cm2 % increase Flexural strength 20.3 62.6 209 Compressive strength 130 414 219 The Table shows that by incorporation of the additive used according to the invention an increase of more than 200% in the flexural and compressive strengths is possible. Breaking up of the edges is prevented to a great extent by incorporation of the additive used according to the invention.

By the use of cement mortar composed in accordance with the invention it is also possible to obtain, in addition to an improvement in the resistance to abrasion, a visually better internal surface of the tubes. In this case also it absolutely essential that such mortars should exhibit no disproportionation. This is the case with cement mortar composed in accordance with the invention. In this way it is also possible to make waste goods flawless and marketable again. As a further variant such cement mortar linings can be coloured by the addition of pigments resistant to cement.

WHAT WE CLAIM IS: 1. A process for coating an internal surface of an article which comprises spraying a composition which comprises cement and one or more aggregates, the ratio of cement to aggregates being in the range of from 1:1.5 to 1:3.5 by weight, and includes from 2 to 25 percent by weight of an aqueous dispersion of one or more non-hydrolysable or sparingly hydrolysable polymers, calculated as solid matter and based on the weight of cement, and includes one or more despumating agents and/or liquefying agents, the composition having a water-cement value as hereinbefore defined in the range of from 0.25 to 0.45, radially onto the internal surface to form a layer from 1 to 5 mm thick.

2. A process as claimed in claim 1, wherein the composition includes an acrylic polymer.

3. A process as claimed in claim 1 or claim 2, wherein the composition includes a melamine-formaldehyde polycondensate.

4. A process as claimed in any one of claims 1 to 3, wherein the proportion of the sparingly hydrolysable polymers in the composition is in the range of from 3 to 25 percent by weight.

5. A process as claimed in claim 4, wherein the porportion of the sparingly hydrolysable polymer in the composition is in the range of from 5 to 10 percent by weight.

6. A process as claimed in any one of claims 1 to 5, wherein the composition includes pozzuolana.

7. A process as claimed in any one of claims 1 to 6, wherein the composition is reinforced by a fibrous material.

8. A process as claimed in claim 7, wherein the fibrous material comprises one or more of asbestos, glass fibre and a plastics material.

9. A process as claimed in any one of claims 1 to 8, wherein the water-cement value is less than 0.40.

10. A process as claimed in any one of claims 1 to 9, wherein the cement comprises Portland cement, iron Portland cement, a blast furnace cement or a trass cement.

11. A process as claimed in any one of claims 1 to 10, wherein the composition includes oil shale cement or a cement having a high sulphate resistance and/or a low heat of hydration.

12. A process as claimed in any one of claims 1 to 11, wherein the composition includes quartz sand.

13. A process as claimed in any one of claims 1 to 12, wherein the aggregate comprises not more than 10 percent by weight of particles which will pass through a sieve having a mesh width of 0.125 mm.

14. A process as claimed in any one of claims 1 to 13, wherein the composition includes a despumating agent comprising a silicone oil or tributyl phosphate.

15. A process for coating an internal surface of an article which comprises spraying a cement mortar composition which has (a) a ratio of cement to aggregate of 1 part by weight of cement to 1.5 to 3.5 parts by weight of aggregate, and which contains (b) aqueous dispersions of resins that are non-hydrolysable or difficult to hydrolyse, the synthetic resin dispersion being used in quantities of 3.0 to 25 percent by weight, calculated as solid matter, calculated on the cement, and which contains (c) the usual despumating and/or liquefying additives, and which optionally contains (d) pozzuolana and/or reinforcing inorganic and/or organic fibres or fibrous materials, and in which (e) the water-cement value as hereinbefore defined is between 0.25 and 0.45, radially onto the internal surface to form a layer from 1 to 5 mm thick.

16. A process as claimed in claim 1, wherein the composition is substantially as hereinbefore described in the Example.

17. A process as claimed in any one of claims 1 to 16, wherein the thickness of the layer is in the range of from 2 to 3 mm.

18. A process as claimed in claim 1, conducted substantially as hereinbefore described in the Example.

19. A process as claimed in any one of claims 1 to 18, wherein the composition is directed in the form of a jet by fluid under pressure and distributed on a rotating plate-like wheel and from there radially centrifuged.

20. A process as claimed in any one of claims 1 to 18, conducted on apparatus in which fluid issues from a tuyere ring with a torque in the form of a cone, which ring concentrically surrounds an opening from which the composition issues, and the composition is finely divided by the fluid and distributed thereby.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. marketable again. As a further variant such cement mortar linings can be coloured by the addition of pigments resistant to cement. WHAT WE CLAIM IS:

1. A process for coating an internal surface of an article which comprises spraying a composition which comprises cement and one or more aggregates, the ratio of cement to aggregates being in the range of from 1:1.5 to 1:3.5 by weight, and includes from 2 to 25 percent by weight of an aqueous dispersion of one or more non-hydrolysable or sparingly hydrolysable polymers, calculated as solid matter and based on the weight of cement, and includes one or more despumating agents and/or liquefying agents, the composition having a water-cement value as hereinbefore defined in the range of from 0.25 to 0.45, radially onto the internal surface to form a layer from 1 to 5 mm thick.

21. Apparatus when used for spraying an internal surface of an article by a process as

claimed in any one of claims 1 to 18 by means of a fluid, which comprises at least one discharge assembly comprising an outer tube having an inlet for fluid under pressure and a discharge outlet for said fluid, and an open-ended inner tube for supplying the composition, the inner tube being positioned in the outer tube and parallel thereto to form a space between the inner and outer tubes, which space provides a channel for the fluid, and terminates at said discharge outlet, wherein the open end of the inner tube is in the vicinity of the fluid discharge outlet and each is directed toward a rotable distribution member having a shape and configuration such that, in operation, when the compositions is directed onto the distribution member, the composition is distributed radially outward therefrom by rotation of the distribution member.

22. Apparatus as claimed in claim 21, wherein the rotable distribution member is in the form of a circular plate having a rim directed toward the or each tube.

23. Apparatus as claimed in claim 22, wherein the rim is outwardly inclined.

24. Apparatus as claimed in any one of claims 21 to 23, wherein in the or each discharge assembly, the inner and outer tubes are concentric.

25. Apparatus as claimed in any one of claims 21 to 24, wherein each tube is substantially parallel to the axis of the distribution member.

26. Apparatus as claimed in any one of claims 21 to 25 which comprises a plurality of discharge assemblies.

27. Apparatus as claimed in claim 26, which comprises four discharge assemblies.

28. Apparatus as claimed in claim 26 or claim 27, wherein the inner and outer tubes are connected to composition and fluid supply means respectively via one or more connection pieces, the or each connection pieces being common to two inner or outer tubes.

29. Apparatus as claimed in any one of claims 21 to 28, which includes a drive shaft for the rotable distribution member upon which shaft the or each outer tube is mounted.

30. Apparatus as claimed in claim 29, wherein the distance between the or each outer tube and the drive shaft may be varied.

31. Apparatus when used for the process of producing anti-corrosion coatings on the inner surfaces of tubes and tubular shaped parts and fittings by a process as claimed in any one of claims 1 to 18 comprising a screw supply pump which feeds the coating material via a flexible tube to a metering tube, which consists of two tubes arranged concentrically one within the other, the inner tube being provided for the material and the annular space between the outer tube and the inner tube being provided for compressed air, and a rotatable plate-like centrifuging wheel, which is mounted by means of a shaft in front of the outlet opening of the inner tube so that it can receive, distribute and centrifuge the material supplied by the inner tube.

32. Apparatus as claimed in claim 21, substantially as hereinbefore described, with reference to, and as shown in, Figures 1 and 2 of the accompanying drawings.

33. Apparatus as claimed in claim 21, substantially as hereinbefore described, with reference to, and as shown in Figures 3 and 4 of the accompanying drawings.

34. Apparatus when used for spraying an internal surface of an article by a process as claimed in any one of claim 1 to 18 by means of a fluid, which comprises an open-ended tube for supplying the composition and a conduit for the fluid terminating in a plurality of jets which surround, and are directed across, the open end of the tube, each jet being oriented such that the projection of its axis, does not coincide with any radius of the tube.

35. Apparatus as claimed in claim 34, wherein the projection of the axis of each jet, as viewed along the axis of the tube, subtends the same angle with the radius of the tube.

36. Apparatus as claimed in claim 35, wherein the said angle is in the range of from 10 to 200.

37. Apparatus as claimed in claim 36, wherein the said angle is about 15".

38. Apparatus as claimed in claim 37, wherein axis of each jet is inclined with respect to the longitudinal axis of the tube by an angle in the range of from 30 to 600.

39. Apparatus as claimed in claim 38, wherein the angle of inclination of each jet is about 45".

40. Apparatus as claimed in any one of claims 33 to 39, wherein the jets are oriented such that the envelope of their axes define a hyperboloid.

41. Apparatus as claimed in claim 33, substantially as shown in figures 5 to 7 of the accompanying drawings.

42. A process as claimed in claim 19, conducted with apparatus as claimed in any one of claims 21 to 33.

43. A process as claimed in any one of claims 1 to 18, conducted with apparatus as claimed in any one of claims 34 to 41.

44. A process as claimed in any one of claims 19, 20, 42 and 43, wherein the fluid is a

45. A process as claimed in claim 44, wherein the fluid is compressed air.

46. An article having an internal surface which has been coated by a process as claimed in any one of claims 1 to 20 and 42 to 45.

47. An article as claimed in claim 46, which is a tube.