Heat gun

Claim 2

A hand held gun for providing a flow of heated air in the 250* F to 1,000* F range against a work object relying upon fuel alone without assistance of blowers or compressors, said gun comprising the combination of a gaseous fuel jet adapted for connection to a conventional fuel gas source such as propane having a stoichiometric burning temperature above 3,000* F, a jet pump activated by said gas jet and having an opening for drawing atmospheric air for combustion into a subatmospheric pressure region produced by said jet, said jet pump constructed to impart velocity to said combustion air by mixing, an enlarged pressure recovery passage into which the mixture of gaseous fuel and combustion air proceeds, said recovery passage constructed to convert velocity head of said gases to a pressure head exceeding atmospheric pressure, an internal combustion chamber, said chamber having an entry into which said pressure recovery passage discharges, a flame holding means at said entry and an outlet discharging combustion gases, the effective wetted perimeter of the flow cross-section of said outlet being at least 25 percent greater in length than the perimeter of a single circle of identical cross-sectional area, providing an extended interface between combustion gases discharging from said outlet and atmospheric air, and a temperature-limiting structure extending downstream of said outlet, said structure preventing direct access of the work object to said outlet and to the combustion gases emitting therefrom and defining an ambient air propelling and mixing zone through which said combustion gases flow preceding said work object, said temperature-limiting structure being open to admit atmospheric air freely, progressively to the stream of combustion gases as they proceed through said structure, the respective parts of said gun constructed to burn said fuel in substantially stoichiometric conditions and discharge said combustion gases through said outlet at a temperature exceeding 3,000* F and a velocity in excess of 4,000 feet per minute, said gun, through the cooperation of said extended combustion gas-air interface, effectively producing a flow comprised in major part of ambient air propelled and heated by said combustion gases, the effective length of said temperature-limiting structure downstream of said outlet determining the temperature of the resultant flow at the output end.

Claim 3

The gun of claim 1 having a multiplicity of elongated outlet aperture portions for combustion gases, and aperture portions arranged to discharge in the same general direction into different portions of said mixing and propelling zone.

Claim 4

The gun of claim 1 wherein said temperature limiting structure comprises a shield member extending about said outlet in a spaced relation defining an axial inlet for atmospheric air adjacent said outlet and having wall portions extending downstream providing a multiplicity of lateral atmospheric air openings along the length of said temperature-limiting structure through which air may freely enter said shield, there to be propelled and heated by said combustion gases.

Claim 5

The gun of claim 1 including means fixing the downstream end of said temperature-limiting device at a predetermined position from said outlet thereby for a given fuel flow, enabling the temperature at said downstream end to be set at a predetermined level.

Claim 6

A hand held gun for providing a flow of heated air in the 250* F to 1,000* F range against a work object relying upon fuel alone without assistance of blowers or compressors, said gun comprising the combination of a gaseous fuel jet adapted for connection to a conventional fuel gas source such as propane having a stoichiometric burning temperature above 3,000* F, a jet pump activated by said gas jet and having an opening for drawing atmospheric air for combustion into a subatMospheric pressure region produced by said jet, said jet pump constructed to impart velocity to said combustion air by mixing, an enlarged pressure recovery passage into which the mixture of gaseous fuel and combustion air proceeds, said recovery passage constructed to convert velocity head of said gases to a pressure head exceeding atmospheric pressure, an internal combustion chamber, said chamber having an entry into which said pressure recovery passage discharges, a flame holding means at said entry and an outlet discharging combustion gases, the effective wetted perimeter of the flow cross-section of said outlet being at least 25 percent greater in length than the perimeter of a single circle of identical cross-sectional area, providing an extended interface between combustion gases discharging from said outlet and atmospheric air, and a temperature-limiting structure extending downstream of said outlet, said structure preventing direct access of the work object to said outlet and to the combustion gases emitting therefrom and defining an ambient air propelling and mixing zone through which said combustion gases flow preceding said work object, said temperature -limiting structure comprising an elongated tube extending about said outlet in a spaced relation defining an axial inlet for induced flow of atmospheric air adjacent said outlet, said tube having a closed wall along its length and the flow cross-section and capacity of said air inlet and said tube being more than five times greater than the flow cross-section and flow capacity of said burner, the respective parts of said gun constructed to burn said fuel in substantially stoichiometric conditions and discharge said combustion gases through said outlet at a temperature exceeding 3,000* F and a velocity in excess of 4,000 feet per minute, said gun through the cooperation of said extended combustion gas-air interface effectively producing a flow comprised in major part of ambient air propelled and heated by said combustion gases, the effective flow capacity of said air inlet determining the temperature of the resultant flow at the output end.

Claim 7

A hand held gun for providing a flow of heated air in the 250* F to 1,000* F range against a work object relying upon fuel alone without assistance of blowers or compressors, said gun comprising the combination of a gaseous fuel jet adapted for connection to a conventional fuel gas source such as propane having a stoichiometric burning temperature above 3,000* F, a jet pump activated by said gas jet and having an opening for drawing atmospheric air for combustion into a subatMospheric pressure region produced by said jet, said jet pump constructed to impart velocity to said combustion air by mixing, an enlarged pressure recovery passage into which the mixture of gaseous fuel and combustion air proceeds, said recovery passage constructed to convert velocity head of said gases to a pressure head exceeding atmospheric pressure, an internal combustion chamber, said chamber having an entry into which said pressure recovery passage discharges, a flame holding means at said entry and an outlet discharging combustion gases, the effective wetted perimeter of the flow cross-section of said outlet being at least 25 percent greater in length than the perimeter of a single circle of identical cross-sectional area, providing an extended interface between combustion gases discharging from said outlet and atmospheric air, and a temperature-limiting structure extending downstream of said outlet, said structure preventing direct access of the work object to said outlet and to the combustion gases emitting therefrom and defining an ambient air propelling and mixing zone through which said combustion gases flow preceding said work object, said temperature -limiting structure comprising an elongated tube extending about said outlet in a spaced relation defining an axial inlet for induced flow of atmospheric air adjacent said outlet, said tube having a closed wall along its length and the flow cross-section and capacity of said air inlet and said tube being more than five times greater than the flow cross-section and flow capacity of said burner, the respective parts of said gun constructed to burn said fuel in substantially stoichiometric conditions and discharge said combustion gases through said outlet at a temperature exceeding 3,000* F and a velocity in excess of 4,000 feet per minute, said gun through the cooperation of said extended combustion gas-air interface effectively producing a flow comprised in major part of ambient air propelled and heated by said combustion gases, the effective flow capacity of said air inlet determining the temperature of the resultant flow at the output end.

Claim 8

The head gun of claim 1 wherein said burner has a constant or decreasing flow cross-section area leading to said outlet.

Claim 9

The head gun of claim 1 wherein said outlet comprises an elongated outlet aperture, said burner having walls diverging in the direction of elongation of said aperture.