Field of the Invention

The invention relates to fluid/abrasive βyεtems, 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 partirules, it can easily erode the cement, but in general the appara us 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 ent raining, in fluid, particulate material of at least two different εi-res, including first

OMPI

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 great.er 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 entrained n seperate 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 flui 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 Specifica ion No. 1 5*"* 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 5 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 lOfed 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 15_nedium 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 0difficult 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 5would 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 εecond 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 firεt reservoir; the first conduit has an outlet, end and provides for the supply of gaseous medium; the firεt reservoir surrounds the outlet end of the first conduit and has a convergent portion extending beyond the outlet end of the first conduit for entrain ent of the first particles of abrasive material; the second conduit has an outlet end and extends from the convergent portion of the first reservo 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

a plified when they hit the stream of gaseous medium and smaller firεt particleε of abrasive material.

Another method of producing particle εpin iε to uεe a vortex chamber at the inlet to the second reservoir. Once 5 again the smaller first particleε of abraεive material are entrained in the gaseous medium first, before the stream of gaseous medium is alεo uεed 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 , show¬ ing a modification in accordance with a third embodi¬ ment, 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-0u1 the Invention.

In "the apparatus illustrated in Figure 1, firεt, second and third conduits 9 _> 11 and J3, of progressivel greater diameter, arv coaxially aligned with each other εo that the second conduit ]] provides an extension of the first- conduit 0 an t-he tΛiird conduit 13 provides an extension of the second conduit ]].

The outlet ends 10 and 12 of the firs and second conduits and 11 are surrounded by firεt and second reservoirs 1 and 4 respectively provided with inlet conduits 2 and 5 and convergent portions and {» which respect vely surround the outlet ends JO and 12 of the firεt. and second conduits 9 an 11.

In operation, air blown through the first conduit 9 entrains firεt particles of abrasive material fed into the firεt reservoir 1 through the inlet conduit. 2 and this suspension entrains second, Jar-ter and heavier particles which are fed into the second reservoir A t-hrouph inlet conduit 5 εo that air containing a sus¬ pension of both firεt and second particleε issues from the third conduit 13- The sizes of the firεt and second particles are chosen to suit the aggregate used in t-he concrete which is to be cut and this in turn determines the si7.e of the components in the apparatus t-hrouph 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 conduitε 9, 11 and 13 have internal diameters of 10 mm, 16 mm and 25 mm and in which the firεt and second reservoirs have internal diameters of 30 mm and 5 mm and convergent portions 3 and 6 in 5 which the εideε are inclined at 60 degreeε to the horizontal .

At a traverse εpeed 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

10 cleanly. The compreεεive strength of this concrete was . 2 53 N/mm and the abrasive was fed in proportions of 75f copper slag and 25A gravel, by weight.

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

In the modified apparatus illustrated in Figure 2, first 0 particles 7 of abrasive material from a first reservoir 1 of a pressurised abrasive feed system lS, 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 5 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 0 of first and second particles 7 and 8 entrained in air.

OMPI_ ^" WIPO ^" ftNATlO^

In an alternative modif cation 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 aε to provide an inclined path for the second particleε 8 aε they paεs 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 effective¬ ness 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 particleε 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 in¬ jector 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•