Abrasive tool making process – material – or composition – With carbohydrate or reaction product thereof
Patent
1987-06-08
1989-08-08
Schmidt, Frederick R.
Abrasive tool making process, material, or composition
With carbohydrate or reaction product thereof
51436, 51438, B24C 700
Patent
active
048540900
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the feeding of abrasive material in a carrier liquid. Abrasive particles entrained in a liquid jet have been found useful for cutting through materials, particularly in an environment in which heat or flames cannot be tolerated.
The present invention is concerned with supplying abrasive material and carrier liquid at high pressure, that is at pressures of at least 10 bars (1 MegaPascal) and preferably above 15, 25, 35 or even 70 bars. The invention provides, according to one aspect, apparatus or a method of forming a high velocity cutting jet at a nozzle comprising (means for forming a mixture of abrasive material and carrier liquid which mixture is fed at said high pressure (as hereinbefore defined) to the nozzle. The abrasive material may be fed dry or in a slurry to a pressure vessel in which the abrasive material is then mixed with liquid at the high pressure of the liquid. The outlet of the pressure vessel may have added to it further supplies of water, for example to adjust the concentration of abrasive material, but these do not serve further to pressurize the material fed from the pressure vessel. After this optional addition, a single conduit leads to the nozzle, no mixing of the abrasive material and further supplying of water taking place at the nozzle. With only one conduit leading to the nozzle, it can be handled with greater ease than if two or more conduits were connected to it. Supplying a high pressure mixture of liquid and abrasive material to a nozzle is more efficient than entraining the abrasive mixture in a jet of carrier liquid (as described in U.S. Pat. No. 4,478,368), since the pressure of the carrier liquid drops when the jet is formed, so that the final mixture is then at a pressure lower than the original value to which the carrier liquid was raised. The inherent inefficiency of the momentum transfer process of the above U.S. specification is avoided by passing the high pressure abrasive slurry through a nozzle which effects an efficient conversion of the potential or `pressure` energy of the fluid mixture directly or kinetic or velocity energy. The resulting high velocity abrasive slurry stream can again be used for cutting a range of materials.
The flow through the pressure vessel is preferably arranged so that, at least at the central portion of the pressure vessel, the abrasive material settles out and is not in the form of a slurry. The slurry is created at the lower portion of the pressure vessel by the local flow pattern around the slurry outlet device. In the preferred embodiment, liquid, introduced at the top of the pressure vessel displaces liquid through the voids around the settled abrasive particles. A typical voidage fraction is about 50% for settled abrasive particles. The void flow area which is available to pass the liquid flow extends across the full cross sectional area of the vessel and so the average velocity of liquid flow is (a) downwards and (b) of relatively low magnitude tending to compact the settled abrasive particles rather than fluidize them. In the region of the entry to the abrasive slurry outlet, close to the base of the vessel, the liquid flow in the voids is deflected from its downwards direction and converges into a duct area. The convergence of the flow implies a reduction in available void area and hence an increase of local liquid velocity. The liquid therefore tends to fluidize the particles in the immediate vicintity of the duct and sweeps them into that duct. The volume of locally fluidized particles is a function of the liquid flow rate, whcih in turn leads to an approximately proportional relationship between the volume of abrasive material out of the vessel/unit time and the liquid flow rate. This relationship extends down to the low flow region, but the design of the outlet duct is such that a cessation of liquid flow into the pressure vessel results in a sharply defined cessation in abrasive feed from the vessel. This has advantages both operationally and in avoiding valve wear.
This method of metering give
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Fairhurst Robert M.
Heron Roger A.
Saunders David H.
Rachuba Maurina
Schmidt Frederick R.
The British Hydromechanics Research Association
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