GB1579543A

GB1579543A - Method for mixing a particulate solid material with a liquid material and a nozzle for use in said method

Info

Publication number: GB1579543A
Application number: GB6575/77A
Authority: GB
Original assignee: Euroc Development AB
Current assignee: Euroc Development AB
Priority date: 1976-02-19
Filing date: 1977-02-16
Publication date: 1980-11-19
Also published as: FR2341354A1; SE397940B; SE7601915L; JPS52103065A; DE2706433A1

Description

(54) A METHOD FOR MIXING A PARTICULATE SOLID MATERIAL WITH LIQUID MATERIAL AND A NOZZLE FOR USE IN SAID METHOD (71) We, EUROC DEVELOPMENT AB, a Swedish Company, of Stormgatan 14, 211 20 Malmö, Sweden, 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 state ment :- The present invention is concerned with a method for mixing a particulate solid material with a liquid or fluid material by means of a spray nozzle.

It is known for reinforcing purposes to blow glass fibers into a jet of cement paste whereupon the mixture is deposited on the shaped surface of a substrate. Despite the low tendency of the cement paste towards wetting the glass fibers it has proved possible under certain circumstances to attain such an intimacy and such a uniform distribution of the glass fibers within the cement paste that, after shaping and setting the mixture obtained, the glass fibers increase the tensile strength and other mechanical properties of the cement product considerably.

It is thus known to blow glass fibers suspended in a stream of pressurized air into droplets of cement paste suspended in a stream of pressurized air under a certain angle, say 5--45". In order to attain a satisfactory, intimate and uniform mixture of the two materials it is in this connection very critical to determine at which point the two streams of material meet in front of the nozzle and the distance from this point to the shaped surface of the substrate. These distances can be determined by experimentation. If the mutual direction and position of the two streams deviate only slightly from what has proved to yield satisfactory mixing and spray results this will result in a nonuniform distribution of the fibers in the cement paste and dry fibers may appear locally on the shaped surface of the substrate.

In addition to the difficulty of adjusting the streams of glass fibers and cement paste under such mutual direction and position conditions that a satisfactory reinforced product is obtained this known technique suffers from the severe disadvantage that spraying cannot be changed from a mainly horizontal to a mainly vertical direction, or from a horizontal or vertical direction to any direction therebetween. Neither can the spray direction with respect to the shaped surface be varied without it being necessary to correct the mutual direction and position of the streams.

In order to avoid the above described disadvantages it is also known to blow glass fibers into a stream of pressurized air, said stream surrounding a cylindrical stream of cement paste droplets suspended in gaseous medium, in the form of a cylindrical shield.

Due to the fact that the stream of cement paste droplets suspended in a gaseous medium tends to force the glass fibers sidewards and due to the low tendency of said droplets towards wetting the dry glass fibers such attempts have been unsuccessful up to the present.

An object of the present invention is to provide a method by which the aforementioned can be overcome and by which an intimate and uniform mixture of a particulate solid and liquid material, such as glass fibers and cement paste, can be obtained by a spray process in a reproducible and readily controllable manner.

According to one aspect this invention consists in a method of applying a coating to the surface of a workpiece, comprising the steps of passing through a spray nozzle a stream of solid particulate material suspended in a gaseous medium, a stream of liquid material, and a stream of gaseous medium, said streams being concentric with one another; causing the stream of gaseous medium to be divided into two part streams; combining the stream of suspended particulate material with the stream of liquid material and with one of said part streams of gaseous medium at the exit orifice of the nozzle in a manner such as to form a conical stream of particulate material and fine liquid droplets suspended in said part stream of gaseous medium, and directing the other of said part streams in a manner to form a gaseous shield surrounding the point at which said streams are combined to retain said suspended material and said liquid droplets within the combination zone; and directing said conical stream onto a workpiece.

When the mixing and wetting process begins, the stream of particles of solid material passes through the cylindrical passage and the particles are then spread in the stream of the liquid material with continued mixing and wetting mainly in a conical zone towards the substrate and concentrically with respect to the stream of the liquid material.

The rates, amounts of material and ratios between the amounts of the liquid material and the particulate solid material and the cone angles of the two streams which can be used to attain satisfactory spray results, of course, depend on a plurality of factors such as the viscosity, density, and ability of the liquid material of wetting the particulate solid material, etc. It has, however, mainly been proved that the conditions of operation can be determined readily by experimentation so that before and at the latest at the same time as the mixed materials meet the substrate a satisfactroy homogeneous mixture of the sprayed materials and a good wetting of the particulate solid material with the liquid material has been attained.

The liquid material may be a binder. The stream of binder is propelled by a gaseous medium and is suitably produced by disintegrating, finely dividing and spreading a stream of the binder propelled by a pump or a pressure tank, for example, to the nozzle, the disintegration and spreading being effected by a concentric stream of gaseous medium such as pressurized air. The latter stream is in the form of a cylindrical shell surrounding the propelled mixture of binder when the mixing step begins. When an annular stream of finely divided, setting or curing binder is produced in this manner, the formation of any deposits of binder in the nozzle can be effectively counteracted and the nozzle maintained clean.

The binder may, for example, be a setting cement or gypsum mixture or a curing mixture of plastics such as a synthetic resin mass.

The particulate solid material may be glass fibers, but more generally is a reinforcing agent such as short mineral, vegetable, animal or synthetic resin fibers. The invention can be applied with advantage when the particulate solid material is a filler different from a reinforcing agent such as a pigment, dye stuff, curing agent, etc. or an aggregate such as perlite and sand.

According to another aspect, the invention also consists in a nozzle for carrying out the method. This nozzle comprises a first cylindrical passage for conveying a stream of solid particulate material suspended in a gaseous medium to a mixing zone; a second cylindrical passage extending around said first passage concentrically therewith for conveying a stream of liquid material through the nozzle to said mixing zone; and a third cylindrical passage extending around said second passage concentrically therewith for conveying gas under pressure to said mixing zone, the outlet orifice of said third cylindrical passage being arranged in a manner such that the gas under pressure is divided into two part streams such that the streams of particulate material and liquid material are combined with one partstream at said mixing zone, the other of said part streams forming a shield containing the mixed streams within said mixing zone.

According to a further embodiment of the invention, extending part way into the first cylindrical passage, at its end remote from the mixing zone, is a fourth cylindrical wall having a diameter which is smaller than the diameter of the first passage, the wall of said fourth passage defining together with part of the wall of the first cylindrical passage a narrow annular passage for supplying gaseous medium to serve as a suspending medium for the solid particulate material.

The invention will now be described in more detail with reference to the accompanying drawing which illustrates schematically and in an axial longitudinal section the function of a mixing nozzle according to the invention, said nozzle being used for spraying and mixing a particulate solid material with a liquid material according to the invention.

Rovings of glass fiber are cut in a glass fiber cutter 10 (only shown diagrammatically) to a suitable length (6-100 mm, preferably 10-35 mm). The fibers are collected by an ejector 11 (also shown diagrammatically) and passed by suction produced by the ejector through a cylindrical tube 1 and into a cylindrical tube 2 by a rapid stream of air from a source 12 of pressurized air through the thin annular passage between tubes 1 and 2. The fibers are blown into the tube 2 and out from the latter while leaving the opening of the nozzle. They are then spread in the form of a conical stream (the two dashed lines 32) and meet the shaped surface 40 of a substrate.

Liquid cement paste is pumped under a pressure of 200-300 kPa (kilopaseal) by a pump device 20 (shown diagrammatically), suitably a so-called Monopump (Registered Trade Mark), through a tube (not shown) into the annular passage between the tube 2 and a cylindrical tube 3 and is discharged at the nozzle opening. A rapid stream of air from a source 21 of pressurized air (shown diagrammatically) passes through the an nular passage between the tube 3 and a cylindrical tube 4, is discharged at the nozzle opening, and spread as indicated by the four continuous lines 30. During its passage, said rapid stream of air will disintegrate and finely divide the stream of cement paste thereby to spread it into a stream limited by the four dotted-dashed-lines 31.The fine droplets of uniformly dispersed cement paste meet and wet mainly all fiber pieces before or at the latest at the same time as the two streams of, respectively, cement paste droplets and fiber pieces meet the shaped surface of the substrate.

By varying the air pressure from the device 12 which produces the ejector stream, and from the device 21 which gives rise to the effect of spreading the cement paste, different angles of spread are imparted to the fiber stream and the stream of cement paste droplets. The spraying of materials over the shaped surface 40 can in this manner be readily controlled.

The air pressure giving rise to the ejector stream and the stream of glass fibers must not, however, be so high as to damage the fibers and/or render them such a speed out through the nozzle and through the stream of finely divided cement paste particles that they are only wetted slightly by the cement paste droplets before they are deposited on the shaped surface of the substrate together with said particles.

The concentration of glass fibers in the stream of pressurized air and in the product obtained by the spray process and the glass fiber length can be varied by varying the charging of the glass fibers and the cutting rate of the cutter 10. It is important to ensure that the amount of cut glass fibers per time unit for a given rate of air through the annular space between the tubes 1 and 2 should not be so high as to cause interruption in tube 1 or tube 2.

The nozzle described above can be easily hand-operated or attached to a spray robot (not shown). In the spray process, a satisfactory mixture having a uniform distribution between the cement paste and the fibers and a sprayed product with excellent strength properties can be obtained also when the distance between the nozzle and the shaped surface of the substrate and the angle between the spray direction and the shaped surface varies in the spraying, even if the angle and distance conditions are very unfavourable.

The described spray nozzle yields a sprayed surface which requires considerably less complementary work than conventional devices or no complementary work at all due to the initmate and homogeneous mixing between the glass fibers and the cement paste and the absence of dry glass fibers in the final product.

The cement paste particles are suitably only sprayed onto the shaped surface of the substrate for a short time, whereafter the glass fiber cutter 10 is started. The glass fiber spraying is then finished a short time before the spraying of cement paste is finished thereby to obtain particularly smooth glass fiber free surfaces of the sprayed and set product. Iu this embodiment of the invention, it is, however, necessary to use the two streams of air from the sources 12 and 21 of pressurized air in spraying the cement paste without addition of fibers to obtain the desired spread of the cement paste particles.

The glass fibers can be replaced by fine sand or mixed with fine sand which latter is blown through tubes 1 and 2 in which case the sprayed product will be, respectively, fine concrete and reinforced fine concrete. It is also possible to produce sprayed coarse concrete products by substituting coarse sand and gravel for the glass fibers, said sand or gravel being blown through tubes 1 and 2, which have to be constructed with a relatively large diameter. It is also possible in this manner to mix fibers of steel with cement paste droplets.

Since the new spray nozzle can be operated very easily, it will be particularly usable for spraying p]asters of different kinds with reinforcing agents and/or fillers, particularly when the substrate presents a complicated curvature and the spray result shall not be dependent upon the orientation of the receiving surface of the substrate.

The new spray nozzle is particularly useful for the manufacture of boat hulls. In this connection, the spray direction has to be constantly varied between the horizontal and vertical directions.

In order to illustrate the improvement of the quality of a product which has been sprayed according to the invention in comparison with a product which is produced by filling in a conventional manner test bodies were manufactured from each of (a) a curved plate produced by spraying a cement paste and 5 per cent of glass fibers with the above described spray nozzle towards a curved shaped surface of a substrate and (b) the same plate produced by filling or casting the same cement paste slowly and carefully on the same shaped surface, said paste having mixed therein 5 per cent of the same glass fibers.

The test body under (a) presented a bending strength about three times higher than that of body (b). It is probable that in case (b) the glass fibers have been partially broken and destroyed in the mixing process and in, respectively, the filling and casting.

When a cement paste and glass fibers are sprayed onto a vertical wall surface in a conventional manner a considerable amount of additional hand-work has to be spent, for example, in the form of rolling to eliminate irregularities in the surface and to press out air from the fibers to attain improved compacting, etc. In rolling and compacting the fibers, the latter will be damaged easily and the wall plaster obtains worse strength properties than it would have obtained by a process carried out under more, indulgent conditions. The new method according to the invention avoids any expensive complementary work thereby to obtain a rapid and perfect spray result provided that exceptionally long fibers and a great quantity of fibers per time unit are not sprayed. The fibers do not become damaged at all to the same extent as they are damaged in a conventional method.

WHAT WE CLAIM IS: 1. A method of applying a coating to the surface of a workpiece, comprising the steps of passing through a spray nozzle a stream of particulate solid material suspended in a gaseous medium, a stream of liquid material, and a stream of gaseous medium, said streams being concentric with one another; causing said stream of gaseous medium to be divided into two part streams; combining the stream of suspended particulate material with the stream of liquid material and with one of said part streams of gaseous medium at the exit orifice of the nozzle in a manner to form a conical stream of particulate material and fine liquid droplets suspended in the said part stream of gaseous medium; directing this conical stream onto a workpiece, and directing the other of said part streams of gaseous medium in a manner to form a gaseous shield surrounding the point at which said streams are combined to retain said particulate material and said liquid droplets within the combination zone.

2. A method as claimed in claim I, wherein the liquid is a binder.

3. A method as claimed in claim 2, wherein the binder is a cement, gypsum or synthetic resin mass.

4. A method as claimed in claims 1-3, wherein the particulate solid material is a reinforcing agent such as short mineral, vegetable, animal or synthetic resin fibers.

5. A method as claimed in claims 1--3, wherein the particulate solid material is a filler, pigment, dyestuff, curing agent or the like.

6. A nozzle for carrying out the method as claimed in any one of claims 1-5, said nozzle comprising a first cylindrical passage for conveying a stream of particulate material suspended in a gaseous medium through the nozzle to a mixing zone; a second cylindrical passage extending around said first passage concentrically therewith for conveying a stream of liquid material through the nozzle to said mixing zone; and a third cylindrical passage extending around said second passage concentrically therewith for conveying gas under pressure to said mixing zone, the outlet orifice of said third cylindrical passage being arranged in a manner such that the gas under pressure is divided into two part streams such that the streams of particulate material and liquid material are combined with one part stream at said mixing zone, and that the other of said part streams forms a shield containing the mixed streams within said mixing zone.

7. A nozzle, as claimed in claim 6, wherein extending part way into the cylindrical passage for particulate material, at the end thereof remote from the mixing zone is a fourth cylindrical passage which is concentric with the first mentioned passage and has a diameter which is smaller than the diameter of said passage, said fourth passage defining together with part of the first mentioned cylindrical passage a narrow annular passage for supplying gaseous medium to serve as a suspending medium for the particles of solid material.

8. A method of applying a coating to a workpiece, substantially as hereinbefore described with reference to the accompanying drawing.

9. A nozzle for applying a coating to a workpiece, substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawing.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. additional hand-work has to be spent, for example, in the form of rolling to eliminate irregularities in the surface and to press out air from the fibers to attain improved compacting, etc. In rolling and compacting the fibers, the latter will be damaged easily and the wall plaster obtains worse strength properties than it would have obtained by a process carried out under more, indulgent conditions. The new method according to the invention avoids any expensive complementary work thereby to obtain a rapid and perfect spray result provided that exceptionally long fibers and a great quantity of fibers per time unit are not sprayed. The fibers do not become damaged at all to the same extent as they are damaged in a conventional method. WHAT WE CLAIM IS:

1. A method of applying a coating to the surface of a workpiece, comprising the steps of passing through a spray nozzle a stream of particulate solid material suspended in a gaseous medium, a stream of liquid material, and a stream of gaseous medium, said streams being concentric with one another; causing said stream of gaseous medium to be divided into two part streams; combining the stream of suspended particulate material with the stream of liquid material and with one of said part streams of gaseous medium at the exit orifice of the nozzle in a manner to form a conical stream of particulate material and fine liquid droplets suspended in the said part stream of gaseous medium; directing this conical stream onto a workpiece, and directing the other of said part streams of gaseous medium in a manner to form a gaseous shield surrounding the point at which said streams are combined to retain said particulate material and said liquid droplets within the combination zone.

2. A method as claimed in claim I, wherein the liquid is a binder.