Patent GB-996281-A (GB)
Title: Method and apparatus for impacting a stream at high velocity against a surface to be treated
IPC: B24C5/00
Filed: 1961-06-26
Abstract: 996,281. Steam cleaning apparatus. J. A. BROWNING. June 26, 1961, No. 23042/61. Heading A4F. [Also in Divisions B3 and F1] A blasting stream containing suspended material is impacted at high velocity against a surface, e.g. for the removal of rust, paint, grease, oil or dirt by sandblasting or steam cleaning, by continuously introduce a fuel and an oxidant gas into a combustion chamber communicating with a restricted discharge nozzle, combusting the fuel with the oxidant gas within the chamber to produce thermal energy and a high velocity stream of products of combustion through the nozzle, introducing readily flowable material into the chamber during combustion of the fuel and discharging the resultant stream of products of combustion and flowable material suspended therein against a surface to be treated. In one form of apparatus, Figs. 1 and 3A, suitable for blasting with abrasive grit, air supplied through a hose to a passage 29 flows via a passage 70, a metering valve 75 and passages 72, 73 into an annular space 16; from there the air flows through the annular space 17 between outer and middle tubes 40, 42 and then through ports 18 into the annular space 19 between the middle tube 42 and a nozzle 27, so as to cool the latter. The air next flows through the annular space 24a between the middle tube 42 and the wall 24 of the combustion chamber, this wall having fins 28, and through radial ports 20 into an annular space 21 and then into the rear of the combustion chamber 22. Liquid fuel, such as fuel oil, is supplied through a metering valve to a passage 90 connected by a passage 91 to an injector port 92; atomising air flows from the passage 29 through passages 60, 61. Combustion is initiated by a spark from a plug 33. A small amount of air from the space 24a enters the plug through ports 36, serving to lengthen the arc path into the gases to be ignited and to cool the plug. Threads 37 are provided for the attachment of a shielded lead housing; the plug is connected through a shielded lead cable to a transformer. The combustion products travel through the reducer section 25 into the nozzle 27 from which expansion to atmospheric pressure produces a high velocity jet. Abrasive particles are conveyed by a small air flow through a hose to a passage 53 the outlet of which projects slightly beyond the annular space 21. The nozzle 27 which is replaceable may be of cast iron containing a high percentage of manganese or may be of titanium carbide. The wall 24 of the combustion chamber 22 has an internal coating of flame-applied aluminium oxide, and the middle tube 42 has a similar internal coating 43, these coatings reducing heat transfer from the combustion chamber 22 to the outer tube 40. In a modification, Fig. 6, suitable for steam cleaning or for other liquid injection into the hot gases, liquid is supplied through a metering valve and a hose to a tube 103 having a passage 105 leading to an injector port 106. The tube 103 extends well into the combustion chamber, so that the liquid jet 107 does not break into droplets 108 until a point well down the chamber is reached. Gaseous fuel, e.g. propane or natural gas, is supplied through a metering valve to a passage 102 leading into one of the radial ports 20. The liquid may be water containing detergent and a small quantity of abrasive, e.g. aluminium oxide, pumice or cement. The liquid may be a slurry comprising water and abrasive. In a modification, Fig. 5, water for dust suppression and nozzle cooling is supplied under pressure through a fitting 138 into the annular space 139 between the forward end of the outer tube 131 and the nozzle 135 which may be of tungsten carbide. The water passes through ports 142 into the exciting jet, and is stated to reduce the noise level of the jet. The heat of the water used in connection with blasting is stated to enhance the cleaning action as e.g. in removing paint, removing barnacles from ships' hulls &c. The abrasive flow may be stopped, using steam action alone to loosen the deposit, and the abrasive flow resumed to complete the cleaning. The jet may be used to cut concrete.