GB2145353A

GB2145353A - Spraying fibre reinforced cement

Info

Publication number: GB2145353A
Application number: GB08421438A
Authority: GB
Inventors: Alastair Ian Stirling; Geoffrey Hugh Wainwright
Original assignee: CORROSION SYSTEMS Ltd
Current assignee: CORROSION SYSTEMS Ltd
Priority date: 1983-08-25
Filing date: 1984-08-23
Publication date: 1985-03-27
Also published as: GB8421438D0; GB8322812D0

Abstract

A cement applicator comprising a screw auger (5) and a nozzle assembly (8) defining an outlet passage to which a cement mixture is delivered by the screw auger. The nozzle outlet passage comprises a chamber (14) located adjacent the end of the auger screw, and an axial passageway (10) extends along the auger screw. Compressed air is delivered to the chamber (14) via the auger screw passageway (10). Air is also delivered to the nozzle outlet passage via a passageway (16) extending radially through the nozzle assembly. Chopped fibres are fed into the sprayed cement from a sprayer (9). <IMAGE>

Description

SPECIFICATION Cement applicator The present invention relates to a cement applicator.

It is known to reinforce cement to reduce cracking by mixing with it chopped fibres of for example glass. It is also known to apply fibre reinforced cement to a surface using a spray applicator. In one known spray applicator system a jet of cement is projected towards the surface to be coated and a chopped roving of glass fibre is introduced in an air stream into the centre of the spray as it emerges from the applicator. The air stream mixes the cement spray and fibres so that the reinforced cement deposited on the surface to be coated is reasonably homogeneous.

It is sometimes necessary to provide steel pipes as used in for example the petro-chemical industry with an anti-corrosion coating which can be applied to the pipes prior to their installation. The anti-corrosion coating is generally covered by a layer of fibre reinforced cement to protect it against damage, and attempts have been made to apply the cement to the pipe using a spray applicator. It has been found that the curvature of the pipe surface makes it difficult to spray apply the cement without considerable wastage of material, particularly in the case of pipes of relatively small diameter. To reduce the wastage applicators producing a fan-shaped spray have been provided, the applicators being positioned relative to the pipe such that the plane of the fan shaped spray is parallel to and extends through the pipe axis.

With the known fan-shaped spray applicators the fibre reinforcement has been incorporated in the cement mix prior to issue of the spray from the applicator. As a result the mix is stiff and difficult to spray, requiring powerful screw augers which rapidly wear out. The stiffness of the mix can be reduced by using high cement content mixes, but this increases material costs. The stiffness of the mix can also be reduced by using small particle size material but this adversely affects resistance to cracking. The stiffness of the mix can also be reduced by introducing the reinforcing fibres into the cement mix after the mix issues from the applicator, but if this is done in accordance with the known techniques referred to above the fan shape of the spray is disturbed so that the thickness of the spray in the direction perpendicular to the plane of the fan is increased.Such an increase in fan thickness increases the amount of waste material by a significant extent, particularly when spraying pipes of relatively small diameter, e.g. six inches.

The problems referred to above have proved to be so severe that it is conventional practice to apply cement to pipes using brush applicators. These comprise two contra-rotating brushes which pick up cement from a supply chamber and fling it in a fan shaped spray against the pipe. brush applicators of this type have proved difficult to use but are better than the available spray applicators.

It is an object of the present invention to provide a cement applicator which can deliver a well defined fan shaped spray of fibre reinforced cement.

According to the present invention, there is provided a cement applicator comprising a screw auger and a nozzle assembly defining an outlet passage to which in use a cement mixture is delivered by the screw auger, wherein the nozzle outlet passage comprises a chamber located adjacent the end of the auger screw, a passageway extends along the auger screw, means are provided for delivering compressed air to the nozzle outlet passage chamber via the auger screw passageway, at least one passageway extends radially through the nozzle assembly so as to communicate with the nozzle outlet passage downstream of the chamber, and means are provided for delivering compressed air to the nozzle outlet passage via the radially extending passageway.

The term "radially" is used herein to mean that the passageway extending through the nozzle assembly extends in a direction with a radial component. It is not intended to mean that a continuation of the passageway must cut through the outlet passage axis or be perpendicular thereto.

The invention also provides a method for spraying a cement mixture, wherein the mixture is delivered to the outlet passage of a nozzle assembly by a screw auger, compressed air is delivered to a chamber defined by the nozzle assembly adjacent the end of the auger screw via a passageway extending along the auger screw, and compressed air is delivered to the outlet passage downstream of the chamber via at least one passageway extending radially through the nozzle assembly.

The invention further provides a cement applicator comprising means for projecting a fan shaped spray, and means for blowing reinforcing fibres into one or both sides of the fan shaped spray.

Preferably, the nozzle assembly comprises an upstream member defining the chamber, a downstream member defining a downstream portion of the outlet passage, and an intermediate member defining an intermediate portion of the outlet passage, wherein the cross-section of the intermediate portion of the outlet passage is less than that of the downstream portion, and the radially extending passageway communicates with the downstream portion of the outlet passage.

The downstream and intermediate member may have mating frusto-conical surfaces at least one of which is grooved to define the or each radially extending passageway.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a plan view of a triple auger cement applicator embodying the invention; and Figure 2 is a cut-away view from the side of one auger of the applicator of Figure 1 which also shows a chopped fibre sprayer not shown in Figure 1.

Referring to the drawings, the illustrated applicator comprises three identical augers 1, 2 and 3 to which a cement slurry incorporating cement, sand and appropriate additives such as polymer is supplied via an inlet chute 4. Each auger comprises a helical screw 5, and a motor 6 and gear train 7 drive the three screws so as to feed slurry from the chute to a nozzle assembly 8. The nozzle assembly 8 of each auger produces a narrow-cone-shaped spray, the sprays from each auger being aligned so that a fan shaped spray results in the same plane as the augers.

Chopped fibre may be mixed with the cement supplied to the hopper 4. However, as shown in Figure 2, a chopperlsprayer 9 may be positioned above the augers so that its nozzle is directed towards the fan shaped slurry spray. Fibre glass roving is fed to the chopper/sprayer 9, cut into short lengths, and blown from the nozzle into the slurry spray. A homogeneous fibre reinforced fan shaped cement spray results which can be directed against a pipe.

Figure 2 shows details of the structure of one of the nozzle assemblies 8 and of the auger screw 5.

The auger screw 5 is provided with an axial bore 10 which defines a passageway communicating at the end of the screw remote from the nozzle assembly 8 with a compressed air line 11 via a sliding connector 12. The tip of the auger screw supports a nozzle 13 which opens into a frustoconical chamber 14 defined by an upstream nozzle member through which slurry is forced by the auger to an intermediate nozzle member 15. The nozzle member 15 has a grooved frustoconical face 16, the grooves (not shown) defining passageways with a mating frustoconical face of a downstream nozzle member 17. Jets of air are delivered via the grooves from a compressed air line 18. Each groove may define a target to a circle centred on the axis of the outlet passage defined by the nozzle assembly. The pressure of the air supplied to the lines 11 and 18 is typically 30 and 20 pounds per square inch.The cross section of the outlet passage defined by member 15 is less than that defined by member 17.

The ease with which cement can be sprayed is a function of cement content (the higher the proportion of cement the easier it is to spray), the particle size (the higher the particle size the harder it is to spray), and the fibre content (the higher the fibre content the harder it is to spray). Experience with the illustrated applicator has shown that supplying air to an upstream portion of the nozzle assembly via the auger screw 5 in combination with supplying air to a downstream portion of the nozzle assembly via the grooves in the nozzle member 15 makes spraying considerably easier. This means that either the spray quality can be enhanced thereby reducing wastage, or a less easily sprayed slurry can be used, thereby saving in cement costs by reducing the cement content or increasing the particle size and/or fibre content to improve crack resistance in the finished product.

It will be appreciated that the shape of the projected spray will not be that of a perfect fan with parallel upper and lower surfaces as the spray will spread somewhat in the direction perpendicular to the plane of the spray. However, with the arrangement described the spray is sufficiently well defined to be directed against a pipe so that most of the projected material sticks to the pipe with the result that there is little wastage.

Figure 2 shows a single chopper/sprayer 9, but it is preferred to use at least two chopper/sprayers to give a good coverage of the whole of the fan of cement slurry.

Adjustment of the pressures in the air lines 11 and 18 changes the shape of the fan of cement slurry. Thus by adjustment of these pressures it is possible to modify the shape of the fan substantially so as to achieve the optimum fan shape and hence to minimise waste.

Claims

1. A cement applicator comprising a screw auger and a nozzle assembly defining an outlet passage to which in use a cement mixture is delivered by the screw auger, wherein the nozzle outlet passage comprises a chamber located adjacent the end of the auger screw, a passageway extends along the auger screw, means are provided for delivering compressed air to the nozzle outlet passage chamber via the auger screw passageway, at least one passageway extends radially through the nozzle assembly so as to communicate with the nozzle outlet passage downstream of the chamber, and means are provided for delivering compressed air to the nozzle outlet passage via the radially extending passageway.

2. A cement applicator according to claim 1, wherein the nozzle assembly comprises an upstream member defining the chamber, a downstream member defining a downstream portion of the outlet passage, and an intermediate member defining an intermediate portion of the outlet passage, wherein the cross-section of the intermediate portion of the outlet passage is less than that of the downstream portion, and the radially extending passageway communicates with the downstream portion of the outlet passage.

3. A cement applicator according to claim 2, wherein the downstream and intermediate members have mating frusto-conical surfaces at least one of which is grooved to define the or each radially extending passageway.

4. A cement applicator according to claim 3, wherein the or each groove defined a tangent to a circle centres on the axis of the outlet passage.

5. A cement applicator according to any preceding claim, comprising means for blowing reinforcing fibres into the side of a spray of cement issuing from the nozzle assembly.

6. A method for spraying a cement mixture, wherein the mixture is delivered to the outlet passage of a nozzle assembly by a screw auger, compressed air is delivered to a chamber defined by the nozzle assembly adjacent the end of the auger screw via a passageway extending along the auger screw, and compressed air is delivered to the outlet passage downstream of the chamber via at least one passageway extending radially through the nozzle assembly.

7. A cement applicator comprising means for projecting a fan shaped spray, and means for blowing reinforcing fibres into one or both sides of the fan shaped spray.

8. A cement applicator substantially as hereinbefore described with reference to the accompanying drawings.

9. A method for spraying a cement mixture substantially as hereinbefore described with reference to the accompanying drawings.