EP0153942A1

EP0153942A1 - Concrete cutting apparatus

Info

Publication number: EP0153942A1
Application number: EP19840903189
Authority: EP
Inventors: Robert Mark Fairhurst; David Henry Saunders
Original assignee: British Hydromechanics Research Association
Current assignee: British Hydromechanics Research Association
Priority date: 1983-09-01
Filing date: 1984-08-31
Publication date: 1985-09-11
Also published as: WO1985001005A1; GB8323525D0

Abstract

De l'air amené au travers d'une première conduite (9) entraîne des premières particules (7) d'un matériau abrasif depuis un premier réservoir (1) entourant l'extrémité de sortie de la première conduite (9). La suspension des premières particules (7) dans l'air passe au travers d'une seconde conduite (11) s'étendant depuis le premier réservoir (1) et entraîne des secondes particules (8) qui sont plus grosses et plus lourdes que les premières particules (7). L'alimentation en secondes particules (8) se fait à partir d'un second réservoir (4) entourant l'extrémité de sortie de la seconde conduite (11) et on provoque le tourbillonnement de ces particules en les faisant passer par une chambre de tourbillonnement (14) formant la partie d'admission du second réservoir (4). La suspension des premières et des secondes particules (7 et 8) est dirigée sur le béton à couper au travers d'une troisième conduite (13) s'étendant depuis le second réservoir (4). Les premières particules (7) servent à éroder la matrice de ciment du béton et les secondes particules (8) servent à briser et déloger les particules d'aggloméré noyées dans la matrice.Air supplied through a first pipe (9) entrains first particles (7) of abrasive material from a first reservoir (1) surrounding the outlet end of the first pipe (9). The suspension of the first particles (7) in the air passes through a second pipe (11) extending from the first reservoir (1) and entails second particles (8) which are larger and heavier than the first particles (7). The second particles (8) are supplied from a second reservoir (4) surrounding the outlet end of the second pipe (11) and these particles are swirled by passing them through a swirl (14) forming the intake portion of the second tank (4). The suspension of the first and second particles (7 and 8) is directed to the concrete to be cut through a third pipe (13) extending from the second tank (4). The first particles (7) are used to erode the cement matrix of the concrete and the second particles (8) are used to break up and dislodge the agglomerated particles embedded in the matrix.

Description

Concrete Cutting Apparatus

Field of the Invention

The invention relates to fluid/abrasive βystems, including air/abrasive systems, for cutting concrete.

Background Art

Since concrete consists of larger particles (aggregate) bonded in a matrix of smaller particles (cement), known apparatus for cutting concrete comprises charging means for entraining particulate material in fluid and conduit means for directing fluid and the entrained particulate material on to a piece of concrete to be cut. Where the particulate material comprises small abrasive particules, it can easily erode the cement, but in general the apparatus has little effect on the aggregate unless the fluid medium is a liquid which can dislodge the larger particles of aggregate material. Thus, small abrasive particles entrained in high velocity water jets can produce good quality cuts in concrete. However, one disadvantage of this form of apparatus is the accumula¬tion of large quantities of liquid.

Disclosure of the Invention

This disadvantage can be ameliorated by providing charging means which are capable of entraining particulate material of at least two different sizes. including first particles of abrasive material and second particles which are larger and heavier than the first particles.

Thus, according to the invention, there is provided apparatus, for cutting concrete, comprising charging means for entraining, in fluid, particulate material of at least two different sizes , including first particles of abrasive material and second particles which are larger and heavier than the first particles, and conduit means for directing the fluid and the entrained particulate material onto concrete to be cut.

The invention also provides a method of cutting concrete comprising the steps of entraining, in fluid, particulate material of at least two different sizes, including first particles of abrasive material and second particles which are larger and heavier than the first particles, and directing the fluid and the entrained particulate material onto concrete to be cut.

The greater momentum of these second particles more effectively dislodges the larger particles of aggregate material which are exposed and loosened as a result of the erosion of the smaller cement particles by the first particles of abrasive material, even though these second particles can not effectively work on the matrix to achieve this state.

Although the first and second particles may be entrainedi n seperat e streams of fluid which are independently directed onto the concrete, it is preferred to entrain all of the particulate material in a single stream of fluid medium which is then directed onto the concrete to be cut.

One form of apparatus suitable for this purpose can be obtained by modifying the apparatus disclosed in British Patent Specification No. 1 569 736 in which a liquid jet is passed through a mixing chamber and particulate material is fed through one or more passages which each extend on an axis converging with the axis of the jet and open in to the mixing chamber at a position radially spaced from the liquid jet. For the purpose of providing apparatus for cutting concrete, in accordance with the present invention, the apparatus disclosed in British Patent Specification No. 1 569 736 may be modified by providing means for entraining the second particles in the liquid jet which is passed through the mixing chamber, the smaller first particles of abrasive material being fed through the or each convergent conduit. In this case, the smaller first particles of abrasive material could be fed either dry or in suspension with gas or liquid.

However, the effectiveness of using particulate material of at least two different sizes may be exploited even more where the particulate material is entrained in a gaseous medium instead of in a liquid medium or a mixed liquid/gas medium. Thus, by using a mixture of large and small particles, it is possible to achieve good quality cuts in concrete using standard portable air compressors and sub-sonic air velocities.

Because of the difference in particle sizes, it is difficult to accelerate all the particles effectively in a single stream of gaseous medium. The optimum conduit means required by the larger second particles will be too big to accelerate the smaller first particles to optimum velocity whereas smaller dispensing means would be blocked by the larger second particles. It is therefore preferred to entrain the second particles in a stream of gaseous medium in which the first particles have already been entrained. This permits the use of successive charging means which are designed to optimise the entrainment of progressively larger particles. Thus, in a preferred embodiment, the charging means comprise first and second reservoirs and the conduit means comprise first, second and third conduits; gaseous medium is supplied through the first conduit; the first particles of abrasive material are supplied through the first reservoir; the first conduit has an outlet, end and provides for the supply of gaseous medium; the first reservoir surrounds the outlet end of the first conduit and has a convergent portion extending beyond the outlet end of the first conduit for entrainment of the first particles of abrasive material; the second conduit has an outlet end and extends from the convergent portion of the first reservoir to form an extension of the first conduit; the second reservoir surrounds the outlet end of the second conduit and has a convergent portion extending beyond the outlet end of the second conduit; and the third conduit extends from the convergent portion of the second reservoir to form an extension of the second conduit.

When an abrasive particle removes material, the amount of material removed depends on the particle tip velocity. This tip velocity can be increased by inducing spin on the particle. If this spin velocity is significant then an increase in cutting performance can be realised.

In apparatus in which the particulate material is entrained in a stream of gaseous medium, it is thought worthwhile to induce spin in the larger second particles only. One way of doing this is by installing flutes on the inside of the second reservoir through which the larger second particles fall. The initial spin given to some of the second particles is amplified when they hit the stream of gaseous medium and smaller first particles of abrasive material.

Another method of producing particle spin is to use a vortex chamber at the inlet to the second reservoir. Once again the smaller first particles of abrasive material are entrained in the gaseous medium first, before the stream of gaseous medium is also used to accelerate the larger second particϊes. However, in this case, the larger particles enter through a tangential inlet creating a vortex which spirals downwards towards the convergent portion of the second reservoir. An air ejector may be used in this design to increase the swirl velocity at inlet to the vortex chamber while still maintaining suction at the inlet to the second reservoir.

Embodiments of the invention are hereinafter described, by way of example, with reference to the accompanying drawings.

Brief Description of the Drawings. Figure 1 is a sectional side elevation of a preferred concrete cutting apparatus in accordance with the invention;

Figure 2 is a schematic side elevation of a second embodiment, of the invention, comprising a modification of the apparatus shown in Figure 1;

Figure 3 is an enlarged view of part of Figure 1, showing a modification in accordance with a third embodiment, of the invention; and

Figure 4 is a schematic side elevation of a fourth embodiment of apparatus for cutting concrete, in accordance with the invention.

Modes for Carrying-out the Invention.

In the apparatus illustrated in Figure 1, first, second and third conduits 9, 11 and 13, of progressively greater diameter, are coaxially aligned with each other so that the second conduit 11 provides an extension of the first conduit 9 and the third conduit 13 provides an extension of the second conduit 11.

The outlet ends 10 and 12 of the first and second conduits 9 and 11 are surrounded by first and second reservoirs 1 and 4 respectively provided with inlet conduits 2 and 5 and convergent portions 3 and ( which respectively surround the outlet ends 10 and 12 of the first. and second conduits 9 and 11.

In operation, air blown through the first conduit 9 entrains first particles of abrasive material fed into the first reservoir 1 through the inlet conduit. 2 and this suspension entrains second, larger and heavier particles which are fed into the second reservoir Athrough inlet conduit 5 so that air containing a suspension of both first and second particles issues from the third conduit 13. The sizes of the first and second particles are chosen to suit the aggregate used in the concrete which is to be cut and this in turn determines the size of the components in the apparatus through which the particles are passed.

As an example, gravel and copper slag particles with maximum sizes, respectively, of 12mm and 2.0mm have been used to cut 50mm thick concrete with aggregate no larger than 25mm. These particles are passed through an apparatus in which the first, second and third conduits 9, 11 and 13 have internal diameters of 10 mm, 16 mm and 25 mm and in which the first and second reservoirs have internal diameters of 30 mm and 50 mm and convergent portions 3 and 6 in which the sides are inclined at 60 degrees to the horizontal.

At a traverse speed of 12.5 mm per minute, a stand off of 25 mm, air supply pressure of 4.6 bar and abrasive feed rate of 2.7 Kg per minute, the concrete was cut cleanly. The compressive strength of this concrete was 53 N/mm² and the abrasive was fed in proportions of 75% copper slag and 25% gravel, by weight.

There is, of course, no reason why larger gravel particles or even a more angular gravel could not have worked even better. Also, concrete with, large aggregate pieces (50/75 mm) would require similarly sized second particles necessitating the apparatus dimensions to be increased accordingly.

In the modified apparatus illustrated in Figure 2, first particles 7 of abrasive material from a first reservoir 1 of a pressurised abrasive feed system 18, such as is commonly used for abrasive cleaning applications, are supplied with pressurised air through a flexible conduit 11 to a discharge nozzle 12 which is surrounded by a convergent portion 6 of a reservoir 4 containing second particles 8 which are larger and heavier than the first particles 7 of abrasive material. The second particles 8 are then entrained in the suspension of air and first particles 7 and issue from the conduit 13 as a mixture of first and second particles 7 and 8 entrained in air. In an alternative modification of the apparatus, shown in Figure 3, a helical band 17 of rigid sheet material is mounted inside the second reservoir 4, around the second conduit 11, so as to provide an inclined path for the second particles 8 as they pass through the second reservoir 4 towards the outlet end 12 of the second conduit 11. This causes second particles 8 to roll down the helical band 17 and at least some of these particles are flicked by the air and entrained first particles 7 issuing from the second conduit 11 so as to increase the rate at which these second particles spin and this spin increases the effectiveness of the second particles 8 in removing aggregate particles from the concrete to be cut. Figure 4 illustrates a different form of apparatus in which a spin is imparted to the second particles 8 to improve the effectiveness of these second particles 8 in removing aggregate particles of the concrete to be cut.

In this apparatus, a vortex chamber 14 is provided at the inlet end of the second reservoir 4 and the inlet conduit 5 extends tangentially of the vortex chamber 14 and is provided with a coaxially extending air injector 15 for the purpose of blowing second particles 8 from a hopper 16 into the vortex chamber 14 so that these second particles 8 follow a spiral path through the second reservoir 4 and into the third conduit 13.

Claims

1. Apparatus, for cutting concrete, comprising: charging means (1 to 6) for entraining particulate material (7 and 8) in fluid; conduit means (9 to 13) for directing fluid and the entrained particulate material (7 and 8) onto concrete to be cut; characterised in that: the charging means (1 to 6) are capable of entraining particulate material (7 and 8) of at least two different sizes, including first, particles (7) of abrasive material and second particles (8) which are larger and heavier than the first particles (7).

2. Apparatus, according to Claim 1, in which: the conduit means (9 to 13) are capable of directing a stream of gaseous medium onto the piece of concrete; and the charging means (1 to 6) include means (4 to 6) for entraining said second particles (8) in said stream of gaseous medium in which said first particles (7) are already entrained.

3. Apparatus, according to Claim 2, in which: the charging means (1 to 6) comprise first and second reservoi rs ( 1 and 4) and the conduit means (9 to 13) comprise first, second and third conduits (9, 11 and 13); the first conduit (9) has an outlet end (10) and provides for the supply of gaseous medium; the first reservoir (1) surrounds the outlet end (10) of the first conduit (9) for the supply of the first particles (7) of abrasive material and has a convergent portion (3) extending beyond the outlet end (10) of the first conduit (9) for entrainment of the first particles

(7) of abrasive material; the second conduit (11) has an outlet end (12) and extends from the convergent portion (3) of the first reservoir (1) to form an extension of the first conduit (9); the second reservoir (4) surrounds the outlet end (12) of the second conduit (11) for the supply of the second particles (6) and has a convergent portion (6) extending beyond the outlet end (12) of the second conduit. (11); and the third conduit (13) extends from the convergent portion (6) of the second reservoir (4) to form an extension of the second conduit (11).

4. Apparatus, according to Claim 3 , in which: the second reservoir (4) includes a vortex chamber (14) at the opposite end t'o the convergent portion (6); the inlet conduit (5) to the second reservoir (4) extends tangentially of the vortex chamber (14); and an air injector (15) projects coaxially into the inlet conduit. (5) for the purpose of blowing the second particles (8) into the vortex chamber (14).

5. A method of cutting concrete comprising the steps of entraining particulate material (7 and 8) in fluid and directing the fluid and the entrained particulate material onto concrete to be cut, characterised in that, the particulate material comprises first particles (7) of abrasive material and second particles

(8) which are larger and heavier than the First particles ( 7 ) .

6. A method, according to Claim 5, in which: the fluid medium is gaseous; the first particles (7) of abrasive material are entrained in the gaseous medium; the second particles (8) are entrained in the gaseous medium in which the first particles (7) have already been entrained.

7 . A method, according to Claim 5, in which spin isinduced in the second particles (6).

8. Apparatus, for cutting concrete, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

9. A method of cutting concrete, substantially as hereinbefore described with reference to the accompanying drawings.