Combustion – Flame holder having attached handle
Reexamination Certificate
1999-11-30
2001-05-08
Lazarus, Ira S. (Department: 3743)
Combustion
Flame holder having attached handle
C431S264000
Reexamination Certificate
active
06227846
ABSTRACT:
BACKGROUND OF THE INVENTION
The effectiveness of heat guns is predicated upon the ability of the combustion products to entrain and propel vast amounts of the surrounding air. Two factors have been found to enhance this process: 1) The speed of the combustion products to be as high as possible and 2) the combustor outlet to be in the shape of a slot in order to maximize the gas/air interface and create a fan shaped heat output pattern.
The speed of the combustion products is a function of the pressure recovery of the jet pump which is used to aspirate the combustion air by the expansion of the gaseous fuel. The performance of the jet pump is thus linked directly with the effectiveness of the heat gun.
One measure to improve the performance of prior art jet pumps has been to lengthen the diffusor to achieve maximum pressure recovery. One drawback of pushing the diffusor to its limits is the attendant tendency for flow separation and pressure fluctuation. The periodic flow separation occurs spontaneously, even in a perfectly draft-free room, but are exacerbated by any disturbance: by moving the heat gun about, by air drafts and even by sound. The result is an uneven flow, noisy combustion, bad emissions and performance fluctuations.
Another measure to improve the performance of prior art jet pumps has been to use multiple nozzles in place of a single nozzle. These efforts have aimed to arrange the nozzles to shorten the mixing process and minimize friction losses in the mixing duct of the jet pump.
The fan shaped pattern has the advantage of spreading the heat evenly over a wide area. The heated area is a long, narrow zone in line with the combustor slot which the operator sweeps over the object to cover the whole area.
The orientation of the slot relative to the handle of the heat gun is usually a matter of personal preference but in some instances also of practical significance. When shrinking a plastic bag over a pallet for instance, it is important to first shrink the bottom of the bag all around to prevent it from riding up. A horizontal orientation of the slot is most efficient for this operation. Subsequently, when shrinking the sides of the bag, a vertical orientation is more effective. Thus it is desirable to change the orientation of the slot easily and quickly.
One commercially available heat gun employs a screw with a wing head to fasten the cylindrical combustor inlet to the body of the heat gun so that the operator can adjust its orientation without tools. This arrangement however is awkward in practice since the mounting screw has to be loosened and tightened every time the slot orientation is changed. If the operator neglects to tighten the screw, he runs the risk of losing it.
Another need that arises in practice is to extend the length of the heat gun to heat objects which are out of reach. This situation occurs for instance when shrink wrapping tall pallet loads or big boats. In the past this has been accomplished by extension tubes. The extension tube ducts the combustible mixture from the jet pump to the combustor as well as providing an electrical lead and ground from the ignitor to the spark plug. The installation is particularly cumbersome. First the fasteners holding the combustor have to be removed, the spark plug lead disconnected and the combustor taken off. Then the process has to be repeated twice in the reverse order, once to attach the extension to the gun, and again to mount the combustor to the extension. Disassembly is an equally complicated process. An added problem arises in keeping the second set of fasteners from getting lost.
A serious ignition problem arises with the extension if the ignition lead is carried inside the extension tube. After operating the gun a few times the spark grows progressively weaker until it is unable to light off the gun. The only solution to this problem in the past has been to mount the ignition lead outside the extension tube. This arrangement is costly and makes the ignition lead vulnerable to damage in use.
SUMMARY OF THE INVENTION
The present invention is directed to a jet pump for a heat gun including an elongate hollow pump body lying along a longitudinal axis. The pump body has an inlet, a mixing section and an outlet. A nozzle unit is axially aligned with the inlet for directing pressurized fuel into the inlet of the pump body. Movement of the pressurized fuel into the inlet causes air to be drawn into the inlet to mix with the fuel within the pump body. A disk shaped air diverter is axially spaced away from the inlet of the pump body. The diverter has a length and a diameter. The diameter of the diverter is greater than the length of the diverter and larger than the inlet of the pump body. A housing is radially spaced from and surrounds the diverter forming a first annular gap therearound for air outside the housing to pass therethrough. The air moves around the diverter then changes direction between the diverter and the inlet of the pump body before entering the inlet.
In preferred embodiments, the nozzle unit is mounted to the diverter. The jet pump housing is radially spaced from and surrounds the pump body forming a second annular gap between the housing and the pump body. The housing includes an opening positioned radially relative to the pump body such that air outside the housing can enter through the opening and pass through the second annular gap to enter the pump body inlet. The diverter is preferably axially spaced from the pump body about 0.5 inches. The ratio of the diverter diameter to the inlet diameter is about 4 and the ratio of the diverter diameter to its length is about 2.
The nozzle unit preferably includes a series of elongate nozzle tubes arranged in a circle. The nozzle tubes extend into the inlet of the pump body and are angled radially outwardly for directing the pressurized fuel towards the walls of the pump body. The tip portions are preferably positioned along a circle having a diameter of about 0.28 inches and are at an 12° angle relative to each other. The nozzle tubes each have a stem portion with a first diameter and a first wall thickness. Each nozzle tube also has a tip portion with a second diameter and a second wall thickness. The second diameter at the tip portion is smaller than the first diameter of the stem portion with the ratio of the first diameter to the second diameter being about 1.6. The wall thickness at the tip portion is less than the wall thickness of the stem portion. The wall thickness at the tip portion is preferably about 0.003 inches and the wall thickness at the stem portion is preferably about 0.005 inches. The nozzle tubes are about 0.437 inches long with the tip portion being about 0.06 inches long.
The present invention further includes a combustor system including a first spring loaded button protruding radially from the pump body. A combustor attachment combusts an air/fuel mixture received from the outlet of the pump body. The combustor attachment is capable of being releasably coupled to the pump body and has an ignition device for igniting the air/fuel mixture. The combustor attachment has a first hole capable of engaging the first spring loaded button for locking the combustor attachment to the pump body in a first position. The combustor attachment also has a second hole capable of engaging the first spring loaded button for locking the combustor attachment to the pump body in a second position. The combustor system has a first electrical connector positioned in the pump body outlet for providing an electrical charge to the ignition device. The combustor system preferably includes a hollow extension piece having proximal and distal ends capable of being positioned between the pump body and the combustor attachment. The extension piece includes a second electrical connector at the proximal end for engaging the first electrical connector and a third electrical connector at the distal end for engaging the ignition device of the combustor attachment. The second and third electrical connectors are electrically connected together by an ele
Hamilton Brook Smith & Reynolds PC
Lazarus Ira S.
Lee David
Shrinkfast Corporation
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