GB1415176A - Heat gun - Google Patents

Abstract

1415176 Heat guns D S ZAGOROFF 9 Oct 1972 46529/72 Heading F4T In a hand-held heat gun for directing a flow of heated air against a work object, fuel gas from a jet 1 entrains and mixes with atmospheric air in a jet pump 3a, the fuel/air mixture passing into a pressure recovery passage 3d, constructed to convert the velocity head of said mixture into a pressure head, and thence via a bluff body flame holder 8a into a combustion chamber 5a having walls arranged to co-operate with said pressure head to convert combustion related expansion into velocity head of the combustion products, the outlet portion of the gun being constructed to produce a jet pump effect for mixing the combustion products with, and transferring heat to ambient air to produce a flow of heated gases at a desired temperature. An ignition recess 13 is provided in the chamber 5a out of the mainstream of gas flow therein but in communication therewith, a spark plug 15, activated by piezo-electric crystal 17, initially igniting the fuel/air mixture, and the flame holder producing combustion-stabilizing eddy effects which are insufficient to produce recirculation from the outlet of chamber 5a but sufficient to produce recirculation from the recess 13. The flame holder 8a comprises swirl blades which taper towards their trailing edges. To enhance the combustion products/air mixing, a cylindrical member 11a, which may have apertures 19 in its side wall, may surround the outlet of chamber 5a. An adjustable member may be provided at the outlet of the gun to prevent contact of the work object with the heated gases until they have cooled to a selected temperature. The flow cross-section of the downstream portion of chamber 5a decreases to an elongate outlet slit 5<SP>1</SP> 0 having a perimeter at least 25% longer than that of a circle of the same cross-section. The outlet of chamber 5a may alternatively be formed by an array of slits or multiple rounds. In a further embodiment the fuel/air mixture passes via respective flame holders (35), Fig. 4 (not shown), into a plurality of combustion chambers (30), one of which has the ignition recess 13 with ignition being transferred to the other chambers by interconnecting side passages (37).