US2028095A

US2028095A - Air heating device

Info

Publication number: US2028095A
Application number: US725547A
Authority: US
Inventors: Thomas J Tully; Robert B Jackson
Original assignee: TULCRAN Inc
Current assignee: TULCRAN Inc
Priority date: 1934-05-14
Filing date: 1934-05-14
Publication date: 1936-01-14
Anticipated expiration: 1953-01-14

Description

Jan. 14, 1936; T. J. TULLY ET AL AIR HEATING DEVICE Filed May 14, 1934 INVENTORS Thomas J 7Z1/l Roberf B. Jacon y M ATTORNEW Patented Jan. 14, 1936 UNITED STATES PATENT OFFICE AIR HEATING DEVICE corporation of Ohio Application May 14, 1934, Serial No. 725,547

14 Claims.

()ur invention relates to air-heating devices. It has to do, more particularly,-with a portable air-heating device which may be readily handled and which is of the type commonly referred to as air-heating guns. This device which we have provided is particularly applicable to removing solidified or stiff oils and greases from crank cases, transmissions and differential cases or other gear boxes of automobiles or the like.

However, our device may be used for many other purposes.

There have been several types of air-heating devices of the general type indicated provided in the prior art. However, these prior art devices have not been entirely satisfactory. Probably the greatest disadvantage of these prior art devices resides in the fact that they are complicated in structure and are, therefore, difiicult and expensive to make, and are very diilicult to assemble which also adds materially to the cost of manufacture.

These prior art devices have, also, not been entirely satisfactory in operation. In the past, none of these devices have been provided with adequate means for insulating the outer casing and the handle, which are usually made of metal, from the heat developed in the gun, with the result that the said outer casing and the handle might become so hot as to burn the operator when he touches the gun. It has been proposed in the prior art to make the handle member of bakelite or some other material which would not conduct heat. However, when the handle is made of bakelite or the like, it will become cracked or broken readily since these guns are usually subjected to hard usage and may be dropped from time to time. Still another disadvantage of prior art devices resides in the fact that the heating elements of these devices are usually not adequately protected from shocks and jars. Also, these prior art devices are usually of such a nature as to be expensive to operate.

One of the objects of our invention is to provide a heating device of the type indicated which is very simple in structure and which is of such a that it may be readily assembled and, consequently, which can be manufactured and sold at a comparatively small cost.

Another object of our invention is to provide an air-heating device of the type indicated which will be very economical to operate and which will function in a very efficient and satisfactory manner.

Another object of our invention is to provide an air-heating device of the type indicated which can be made practically entirely of metal and will thereby be very sturdy and which will be provided with suitable insulating means so that there will be no danger of the operator being burned when handling the said device.

Another object of our invention is to provide an air-heating device of the type indicated which will be provided with a heating element so incorporated in the device that it will be protected from shocks and jars.

Another object of our invention is to provide a heating device of the type indicated which is provided with a safety device that will obviate any danger of the device becoming overheated or excessively heated.

In its preferred form, our invention contemplates the provision of a heating device for the purposes indicated which is provided with means for conducting air therethrough and with means for heating the air as it passes through the device. The air is caused to travel a comparatively great distance so that it will be adequately heated before leaving the device. The heating means is disposed in a housing which is made of metal and which has a suitable metal handle member connected therewith and the housing and handle member are insulated from the heating means at all points so that there will be no danger of the outer casing or handle member becoming so hot that it will be impossible for the operator to handle the device. A safety switch is provided so that the heating means will function only when air is being applied to the device and, consequently, there will be no danger of the device becoming over-heated.

Many other objects and advantages will appear from the following description.

The preferred embodiment of our invention is shown in the accompanying drawing wherein similar characters of reference designate corresponding parts and wherein:

Figure 1 is a longitudinal section of an airheating device made in accordance with our invention.

Figure 2 is a detail in section illustrating an air injector which we preferably incorporate in our device and, also, illustrating the automatically operative safety switch which controls operation of the heating element of our device.

Figure 3 is a perspective view of certain members of our device which are used in assembling the various parts thereof.

Figure 4 is a perspective view of a tube which is adapted to surround the heating element of our device.

Figure '5 is a diagram of the circuit for the electrical heating element.

Figure 6 is a perspective view, partly broken away, of our air-heating device.

Figure 7 is a diagrammatic view illustrating how our air-heating device may be used for cleaning a gear box or the like.

With reference to the drawing, we have illustrated our air-heating device as being in the form of a gun. Our device comprises a handle member l which is of the pistol type. This handle member is provided with a flange 2 at its forward end which is adapted to be bolted to a flange 3, formed on the rear end of the main casing d of the heating device, by means of screw bolts 5 passing through corresponding threaded openings in flanges 2 and 3.

The casing 4 is of substantially cylindrical form, as illustrated in the drawing, and its rear end is open as indicated. This casing is preferably made of metal and both its inner and outer surfaces are bright and polished. The forward end of the casing converges as indicated at 6 and has a substantially flat forward end I of annular form. This flat end I has a square opening 8 formed therein for a purpose which will be described subsequently.

The handle member I, as shown, is of such a type that it may be readily gripped in the hand. It is preferably made of metal although it might be made of other suitable material. The casing i is also preferably of metal. The handle member I has a passageway 9 formed therein which extends from the lower end thereof upwardly through the handle member and communicates at its upper end with the chamber formed within the casing 4. An electrical conduit I0 is adapted to be passed through this passageway 9 and is adapted to supply electrical current to a heating element which will be subsequently described.

The handle member I further has a vertically extending air passageway I l formed therein. The lower end of this passageway H has a coupling member 12 threaded thereinto which is adapted to be used for connecting a hose member (not shown) thereto. This hose member is adapted to be connected to a tank or the like containing asupply of compressed air. The coupling 52 has a screen member l3 on its upper edge which will prevent foreign matter which might be carried by the air stream from entering the passageway ll.

Adjacent the upper end of the passageway H, a forwardly extending air passageway 16 is provided, the rear end of which communicates with passageway II. This passageway extends entirely through the handle member and its forward end is open as indicated. The forward portion of this passageway M has a safety switch l5 mounted therein. This switch is mounted in a slightly enlarged portion 16 of the passageway id and is provided for automatically controlling the supply of electric current to the heating element of our device.

This safety switch 15 is of such a type that it is automatically operated by air pressure passing through passageway H and into passageway it. It will only complete the circuit to the heating element when air under pressure is in passageways l l and I4.

This safety switch i5 comprises a plunger which is composed of a body portion ll made of some suitable material which will not conduct electricity. This member ii is of less diameter than the enlarged portion I 6 of passageway 14. The rear end of this member ll has a metal bearing member l8 secured thereon by means of a bolt member [9 which is screwed into member ii. The bearing member I8 is of slightly less diameter than the enlarged portion it of passageway i i. A disc Zii of non-conducting material is held against the rear surface of the bearing member 'IS by means of the bolt I59 and a washer 2!. This disc 28 is of substantially the same diameter as member l8 and will contact with the shoulder 22, formed at the beginning of the enlarged portion it, when the plunger of the switch is in its rear position as indicated in Figure 2.

The member I! of the switch has a compression spring 23 disposed in surrounding relation thereto. 7 The rear end of this spring will abut the bearing member I8. The forward end of this spring will abut a collar member 24 disposed at the forward end of the passageway It. This collar member is secured in the position indicated in a suitable manner and is made of non-conducting material. It has an opening 25 extending therethrough. A contact member 26 made of metal is adapted to reciprocate in this opening. This contact member is preferably larger in diameter at its center portion than at its end portions as shown. It is mounted on the forward end of member I! by means of a bolt 27.

The forward side of the collar member 24 has a contact member 28 mounted at each side of the opening 25 formed therein. These contact members are resilient and extend over the limits of the openings 25. They extend forwardly and are directed towards each other as indicated in Figure 2. Each of these contact members is connected into the electrical circuit for the heating element as will be described later. As indicated in this figure, when the plunger of the switch is in its rearmost position, where it is normally held by spring 23, the contact member 26 will be disposed as indicated and there will be no electrical connection between the two contacts 28. However, if the plunger is moved forwardly, the contact member 26 will move between the two contacts 28, as indicated by the dotted lines, which will contact firmly therewith. Thus, electrical connection between the two contacts 28 will be established.

The plunger of the switch will normally be held in the position indicated by the full lines in Figure 2 by the spring 23. However, if air under pressure is flowing through passageway II and passageway I4, the plunger of the switch will be moved forwardly as described and complete the circuit between the two contacts 28. However, if the air pressure in the passageways II and I4 falls below a predetermined degree or is eliminated, the plunger will be returned to its rearwardmost position and the electrical circuit will be broken. Thus, the only time that electrical current can be supplied to the heating element will be when there is a desired amount of air pressure in passageways H and i4.

We prefer to have our air-heating device connected to a supply of compressed air as indicated and which is obtainable at all gasoline filling stations or the like. However, in using our device, it is usually not necessary to have the air under pressure equal to that in the tank from which it is taken. Therefore, we have provided means for reducing the pressure of the air supplied through passageway II. We have also provided means for taking in air from the atmosphere in addition to that taken through passageway so that it will not be necessary to use an undesirable amount of air taken from the tank to which the passageway II will be connected. This means comprises an air injector which will now be described.

This air injector is formed in a passageway 29 formed in the upper portion of handle member and having its rear end communicating with passageway I I and its forward end communicating with the chamber formed within casing 4. The rear end of passageway 29 has a shoulder 30 formed therein as shown. Adjacent this shoulder 30 and forwardly thereof, the passageway 29 has a nozzle member 3| threaded thereinto. This shoulder limits rearward movement of member 3|. This nozzle member has an air discharge orifice 32 formed therein which is an approximate venturi. Atthe forward end of the passageway 29, a second nozzle member 33 is threaded thereinto. This nozzle member 33 is longer than the member 3| as shown and its rear end is spaced a considerable distance from the forward end of nozzle 3|. This nozzle member 33 also has a discharge orifice 34 extending entirely therethrough and which is in the form of an approximate venturi. It will be apparent that a chamber 35 is formed in passageway 29 between these two nozzle members.

This chamber 35 has an opening 36 formed in one wall thereof which opening communicates with the atmosphere. The forward end of nozzle member 3| extends slightly past the rear edge of opening 36. The

orifices

32 and 34 are substantially in alignment and the forward end of orifice 32 is of slightly less diameter than the rear end of orifice 34.

This injector will function in the usual manner. The air under pressure will flow through nozzle member 3| and will be directed into nozzle member 33 and will then be discharged therefrom into the chamber within casing 4. Air will also be drawn in through the opening 36 from the atmosphere in a well known manner and this induced air will be carried into the chamber within casing 4. The pressure of the air discharged into the chamber within casing 4 will be much less than the pressure of the air in the passageway being reduced by passing through the injector. Furthermore, since the air under pressure is supplemented by induced air from the atmosphere, it will not be necessary to use an undesirable amount of air taken from the tank to which passageway I may be connected.

The opening 36 not only serves as a means by which air may be drawn from the atmosphere but also serves as a safety valve which will prevent the building up of an undesirable degree of pressure in the chamber Within casing 4. The nozzle member 33 is so designed that when the pressure within casing 4 becomes too great the air will begin to back up through this nozzle member 33 and will pass to the atmosphere through the opening 36. In case it is desirable to ever build up a high pressure in the chamber within casing 4, the opening 35 may be closed, for example, by placing the finger thereover. This will cause the building up of a much greater pressure within the casing 4.

Centrally located within the cylindrical casing 4, is a heating element 31. This heating element may be of any suitable type but preferably comprises a porcelain core having heating coils wound therearound as indicated. The porcelain core has an opening extending longitudinally therethrough and a bolt member 38 passes therethrough. This bolt member is used to secure the heating element to a triangular member 39 which will be disposed at the rear of the chamber within casing 4 but will be spaced, as illustrated, from the forward end of the handle member This triangular member is made of some material which will not conduct heat and which is noncombustible. It will touch the casing 4 at three points as illustrated in Figure 6 but since it is composed of insulating material it will not conduct heat from the heating element to the outer casing. Also, due to its shape, air will be permitted to pass forwardly of this member 39. Further, this member 39 is made of material which is flexible so it will serve as a cushion which Will minimize shocks and jars on the heating element. The contact members 28 on the collar member 24 disposed adjacent the safety switch are connected into the electrical circuit for the heating element 3'! by means of wires 40. The circuit for the heating element is illustrated diagrammatically in Figure 5. The forward end of the heating element is provided with a plurality of outwardly projecting leg members 4| which are spaced apart to permit passage of air.

Directly surrounding the heating element 37, is a tubular member 42 composed of suitable metal. The rear end of this member 42 is curled outwardly as indicated at 43 and when our device is assembled this curled portion 43 will project beneath a flange 44 formed on the inner periphcry of a ring 45. This ring 45 is fastened to the forward face of member 39 by means of screws 46.

It will be apparent that the legs 4| on the heating element will keep the forward end of the body portion thereof spaced from the tube 42. The tube 42 is provided with a plurality of small circumferentially spaced openings 4'! at its rear end. It will be apparent that a chamber 48 is formed within tube 42 and around heating element 37.

Disposed in surrounding relation to the tube 42 is a second tube 49 which will be spaced from the tube 42 and will form a chamber 50. This tube 49 is held in spaced relation to tube 42 by its inwardly curled ends. It has openings 52 similar to openings 4'! in its forward end. A third tube 53 is disposed in surrounding relation to tube 49 and is spaced therefrom in a similar manner to form a chamber 54. A chamber 56 is formed in surrounding relation to tube 53 by a tube 55 in a similar manner. Tube 53 is provided with openings 51 at its rear end and tube 55 is provided with similar openings 58 at its forward end. It will be apparent that the circumferential openings in each tube are at the end opposite to the end of the adjacent tube where the openings thereof are located. It will further be apparent that the only means which need be provided to maintain the tubes in spaced relation to form the various chambers are the inwardly curled ends of the tubular members. These tubular mem bers are preferably made of metal which has both its inner surface and outer surface polished for a purpose which will be brought out later.

When the air flows within the casing 4, it is adapted to pass forwardly along the outer tube 55, to flow through openings 58 into the outermost chamber 55, to flow rearwardly through this chamber to the rear end thereof and then through openings 51 into the next adjacent chamber 54. Then, the air will flow forwardly through this chamber until openings 52 in tube 49 are reached and will then flow therethrough into chamber 50. From chamber 50, it will flow through openings til into the chamber 48 surrounding the heating element. It will be apparent that the air will be caused to travel through a great distance before reaching the heating element. Thus, the air will be pre-heated before it reaches the heating element, since it will absorb heat from the various tubular members which are made of metal. Furthermore, since the surfaces of these tubular members are polished, they will serve as heat-reflecting surfaces and will much more readily give oii their heat to the air passing through the various chambers. Because the surfaces of the various tubes and the surfaces of easing 4 are polished, they will have a great insulating value. It will be apparent that the heat will not readily pass outwardly through these members but will be reflected from their inner surfaces back into the chambers. Further, since the outer surface of these members are polished, if the heat does pass into these members, it will not be given oiT readily. Also, since we have provided several chambers which will have air passing therethrough, the outer casing 4 will not be affected to any material degree by heat radiating from the heating element.

The rear ends of the various tubular members will contact with the metal ring 45 which is fastened to the triangular member 39. These various tubular members are held in place by a disc 59 of metal which is substantially of the same diameter as the outermost tube and which is held against the forward ends of the tubular members as shown in Figure 1. The disc will close the forward ends of any of the various chambers formed by the tubular members which are not otherwise closed.

The disc 5-9 is held in place and the entire unit formed by the various tubular members and heating element is held in spaced relation to the casing 4 by means of a nut and bolt structure 60 illustrated in detail in Figure 3. This structure comprises a reduced threaded portion 6! which extends through a central opening in disc 59 and which is threaded into a hub 52 on a spider member 83. This spider member will be disposed in the forward end of tube 52 and is held therein by an inwardly curled forward end 64 thereof. The disc 5% is held in place by a shoulder 64 formed by the enlarged portion 65 of the bolt structure. This enlarged portion 55 is threaded to receive a nut 65 which will be disposed within casing as shown in Figure 1. A pair of washers Ell will be disposed between nut 66 and the end of the casing l. These washers will be of material which will not readily conduct heat. The member 58 has a square member 68 integrally formed thereon which fits within the square opening 8 in the forward end of easing 4. This member it has a strip of heat-insulating material extending entirely around the edge thereof. The enlarged portion 55 will extend forwardly from the forward end of casing t as illustrated in Figure 1 and has a nut l6 threaded thereon. A washer ii of heat-insulating material is disposed between the nut it! and the end of the casing 4. The extreme forward end of member 66 is reduced as indicated at 72 and is threaded to receive a substantially L-shaped pipe or nozzle 73. The inher portion of this nozzle or pipe 13 is of cone shape as indicated at "M so that it will fit tightly in openings of various sizes.

The member 69 has an air passageway 15 extending entirely therethrough. The inner end of this passageway will communicate with the chamber where the heating element 3'1 is located.

The outer end thereof will communicate with a passageway I6 extending through the nozzle or pipe member 13.

In assembling our device, the casing 4, of course, will be separate from the handle member I. The unit embodying the heating element and the various tubular members will be'assembled first. This will be done by placing the inner tube member 42 in position with its rear end against member 39 and then positioning the ring member 45 as shown in Figure 1. positioned on the member 39, it will be apparent that the heating element will be mounted on this member 39 and the spider member 63 will be positioned in the forwardend of the tubular member 42. Then the various tubular members will be disposed in their proper positions, the disc 59 will be properly disposed and the rear end 6! of member 60 will be threaded into the spider member 63. This will cause the various tubular members to be tightly .held against disc 59 and ring 45 in an obvious manner.

The nut member 66 and washers 61 will then be mounted on the 'enlarged portion 65 of member 60. The entire unit so far formed and consisting of the various tubular members and the heating element together with member 60 will then be positioned in casing 4 with member 60 extending through the opening 8. Then the handle member 1 will be brought almost into cooperative relation with casing 4 and the wires 40 will be connected. Then, the handle member and the casing will be fastened together. The nut member 10 and washer H will then be-applied to the member 60 and adjusted into contact with the forward end of easing 4. 'Then', the pipe member 13 will be screwed into position on the member 60. It will be apparent that the square member 68 fitting within the square opening 8 will prevent turning of member 60 during application or removal of pipe 13. Thus, there will be no danger of turning the heating element so that the connecting wires thereof will be twisted loose and the electrical circuit broken. It will be apparent that this device may be easily assembled in a 'very satisfactory manner.

In the operation of this device, the L-shaped pipe or nozzle 13 is inserted in the opening of the gear case or other such member to which it is desired to apply the heated air. illustrate diagrammatically how this may be done. The pipe l3 will extend from the opening in the case aconsiderable distance and may be directed towards the bottom of the case so that all the hard or stifi grease or oil will be removed from the bottom thereof. Thecone-shaped member 14 on pipe 73 may be held in contact with the edge of the opening, regardless of its size, and pressure may be built up in the case if desired. If it is not desired to build up any appreciable amount of pressure in the case, the cone-shaped member may be held loosely in the opening.

When the air' under pressure flows into the passageway H and the passageway l4, it will move the plunger of the switch is forwardly and complete the circuit to the heating element 3? as previously described. The air will flow through the injector and will draw additional air into our device from the atmosphere. By passing through the injector, the air under pressure will be reduced in pressure and will then be discharged into the chamber within casing 4. Then it will flow forwardly until it passes through openings 58 in the'outer tubular member and will pass back and forth through the various .Before the member 42 is In Figure '7 we r chambers as indicated by the air arrows in Figure 1. During passage through these various chambers the air will be preheated and it will finally reach the chamber 48, surrounding the heating element 31. It enters this chamber at the rear end thereof and then flows forwardly along the heating element and will be heated considerably during its passage through this chamber. From the forward end of chamber 48, the air will flow through the passageway 15 in member 60 and then out through the passageway 16 in pipe 13. If air under pressure stops flowing into passageways II and M, the plunger of the switch l5 will be immediately returned by the spring to its rear position and will consequently break the electrical circuit to the heating element, thereby rendering the heating element inoperative.

It will be apparent that the member 60 is effectively heat-insulated from the outer casing 4. Also, since the member 39 at the rear ends of the tubular members and the heating element is composed of heat-insulating material, there will be no danger of heat passing to the outer casing 4 through this member. Thus, the inner unit embodying the various tubular members and the heating element will be effectively insulated from the outer casing land the handle member. Also, since the member 39 is flexible, it serves as a cushion which minimizes the effect of shocks and jars on the heating element.

It will be apparent from the preceding description that we have provided a device having many desirable features. This device is very simple in structure and can be readily assembled and, consequently, it can be manufactured and sold at a comparatively low cost. Furthermore, this device will function in a very eificient and satisfactory manner and will be very economical in operation. Also, our device may be made practically entirely of metal and will therefore be very sturdy, but since the inner unit is efiiciently heat-insulated from the outer casing and handle member, there will be no danger of either the outer casing or the handle member becoming so hot that the operator cannot handle the device. The heating element of our device is protected from shocks and jars. Also, we have provided a safety switch which is of such a character that it will render the heating element inoperative whenever there is no air under pressure flowing into our device or the pressure thereof falls below a predetermined degree. Consequently, there will be no danger of the heating element being operative while there is no air flowing through our device which would cause excessive heating of our device and serious injury thereto.

Having thus described our invention, what we claim is:

1. An air heating gun comprising a handle member, a main hollow casing secured to said handle member, said handle member having a passageway extending therethrough and cornmunicating with the interior of said main casing for conducing air under pressure thereinto, an air injector disposed in said passageway through which the air under pressure must pass before entering said casing, said injector being of such a type that it will take in additional air from the atmosphere and will reduce the pressure of the air under pressure as it passes therethrough, an electric heating element disposed within said casing, a plurality of metallic tubular members surrounding said heating element, said tubular and jars thereon, said tubular members being so arranged that the air entering said main casing must travel through all of said chambers before reaching said heating element, a tube leading from the chamber in which said heating element is disposed to a point outside of said main casing, a nozzle member mounted on the outer end of said tube, a switch for controlling said heating element, said switch being automatically operable by the air under pressure which flows through said passageway to cause the circuit to said heating element to be completed when air under pressure is supplied to the gun and to be broken when the pressure of the air supplied to the gun falls below a predetermined degree.

2. An air heating gun comprising a handle member, a main hollow casing secured to said handle member, means for conducting air under pressure into said main casing, an air injector through which the air under pressure must pass before entering said casing, said injector being of such a type that it will take in additional air from the atmosphere and will reduce the pressure of the air under pressure as it passes therethrough, an electric heating element disposed within said casing, a plurality of tubular members surrounding said heating element, said tubular members being of various diameters, means for maintaining the various tubular members in spaced relation so that a plurality of chambers surrounding said heating element are formed, each of said tubular members having openings adjacent one end thereof, the openings in one tubular member being formed therein adjacent the end opposite to that of. the adjacent tubular member in which the openings thereof are formed, said tubular members being so arranged that the air entering said main casing must travel through all of said chambers before reaching said heating element, means for conducting the air from the chamber in which said heating element is disposed to a point outside of the main casing, a switch for controlling said heating element, said switch being automatically operable by the air under pressure which flows to the main casing to cause the circuit to said heating element to be completed when air under pressure is supplied to the gun and to be broken when the pressure of the air supplied to the gun falls below a predetermined degree.

3. An air heating device comprising a main hollow casing, means for conducting air under pressure into said main casing, an air injector through which the air under pressure must pass before entering said casing, said injector being of such a type that it will take in additional air from the atmosphere and will reduce the pressure of the air under pressure as it passes therethrough, an electric heating element disposed within said casing, a plurality of tubular members surrounding said heating element and being of various diameters, means for maintaining the various tubular members in spaced relation so that a plurality of chambers surrounding said heating element are formed, each of said chambers being in communication with the adjacent chambers, said tubular members being so arranged that the air entering said main casing must travel through all of said chambers before reaching said heating element, a switch for controlling said heating element, said switch being automatically operable by the air under pressure which flows to the main casing to cause the circuit to said heating element to be completed when air under pressure is supplied to the device and to be broken when the pressure of air supplied to the device falls below a predetermined degree.

4. An air heating gun comprising a handle member, a main hollow casing secured to said handle member, said handle member having a passageway extending therethrough and communicating with interior of said main casing for conducting air under pressure thereinto, an air injector disposed in said passageway through which the air under pressure must pass before entering said casing, said injector being of such a type that it will take in additional air from the atmosphere and will reduce the pressure of the air under pressure as it passes therethrough, an electric heating element disposed within said casing, a plurality of metallic tubular members surrounding said heating element and being of various diameters, means for maintaining the various tubular members in spaced relation so that a plurality of chambers surrounding said heating element are formed, each of said tubular members having openings adjacent one end thereof, the openings in one tubular member being formed therein adjacent the end opposite to that of the adjacent tubular member in which the openings thereof are formed, all of said tubular members having polished surfaces so that they will readily reflect heat, said heating element having one of its ends supported on a flexible member in order to minimize shocks and jars thereon, said tubular members being so arranged that the air entering said main casing must travel through all of said chambers before reaching said heating element, a tube leading from the chamber in which said heating element is disposed, and a nozzle member mounted on the outer end of said tube.

5. An air heating gun comprising a handle member, a main hollow casing secured to said handle member, means for conducting air under pressure into said main casing, an air injector through which the air under pressure must pass before entering said casing, said injector being of such a type that it will take in additional air from the atmosphere and will reduce the pressure of the air under pressure as it passes therethrough, an electric heating element disposed Within said casing, a plurality of tubular members surrounding said heating element, said tubular members being of various diameters, means for maintaining the various tubular members in spaced relation so that a plurality of chambers surrounding said heating element are formed, each of said tubular members having openings adjacent one end thereof, the openings in one tubular member being formed therein adjacent the end opposite to that of the adjacent tubular member in which the openings thereof are formed, said tubular members being so arranged that the air entering said main casing must travel through all of said chambers before reaching said heating element, and means for conducting the air from the chamber in which said heating element is disposed to a point outside of the main casing.

6. An air heating device comprising a main hollow casing, means for conducting air under pressure into said main casing, an air injector through which the air under pressure must pass before entering said casing, said injector being of such a type that it will take in additional air from the atmosphere and will reduce the pressure of the air under pressure as it passes therethrough, an electric heating element disposed within said casing, a plurality of tubular members surrounding said heating element and being of various diameters, means for maintaining the various tubular members in spaced relation so that a plurality of chambers surrounding said heating element are formed, each of said chambers being in communication with the adjacent chambers, said tubular members being so arranged that the air entering said main casing must travel through all of said chambers before reaching said heating element.

7. An air heating gun comprising a handle member, a main hollow casing secured to said handle member, said handle member having a passageway extending therethrough and communicating with the interior of said main casing for conducting air under pressure thereinto, an electric heating element disposed within said casing, a plurality of metallic tubular members surrounding said heating element, said tubular members being of various diameters, means for maintaining the various tubular members in spaced relation so that a plurality of chambers sur rounding said heating element are formed, each of said tubular members having openings adjacent one end thereof, the openings in one tubular member being formed therein adjacent the end opposite to that of the adjacent tubular member in which the openings thereof are formed, all of said tubular members having polished surfaces so that they will readily reflect heat, said heating element having one of its ends supported on a flexible member in order to minimize shocks and jars thereon, said tubular members being so arranged that the air entering said main casing must travel through all of said chambers before reaching said heating element, a tube leading from the chamber in which said heating element is disposed to a point outside of said main casing, a nozzle member mounted on the outer end of said tube, a switch for controlling said heating element, said switch being automatically operable by the air under pressure which flows through said passageway to cause the circuit to said heating element to be completed when air under pressure is supplied to the gun and to be broken when the pressure of the air supplied to the gun falls below a predetermined degree.

8. An air heating gun comprising a handle member, a main hollow casing secured to said handle member, means for conducting air under pressure into said main casing, an electric heating element disposed Within said casing, a plurality of tubular members surrounding said heating element, said tubular members being of various diameters, means for maintaining the various tubular members in spaced relation so that a plurality of chambers surrounding said heating element are formed, each of said tubular members having openings adjacent one end thereof, the openings in one tubular member being formed therein adjacent the end opposite to that of the adjacent tubular member in which the openings thereof are formed, said tubular members being so arranged that the air entering said main casing must travel through all of said chambers before reaching said heating element, means for conducting the air from the chamber in which said heating element is disposed to a point outside of the main casing, a switch for controlling said heating element, said switch being automatically operable by the air under pressure which flows to the main casing to cause the circuit to said heating element to be completed when air under pressure is supplied to the gun and to be broken when the pressure of the air supplied to the gun falls below a predetermined degree,

9. An air heating device comprising a main hollow casing, means for conducting air under pressure into said main casing, an electric heating element disposed within said casing, a plurality of tubular members surrounding said heating element and being of various dimeters, means for maintaining the various tubular members in spaced relation so that a plurality of chambers surrounding said heating element are formed, each of said chambers being in communication with the adjacent chamber, said tubular members being so arranged that the air entering said main casing must travel through all of said chambers before reaching said heating element, a switch for controlling said heating element, said switch being automatically operable by the air under pressure which flows to the main casing to cause the circuit to said heating element to be completed when air under pressure is supplied to the device and to be broken when the pressure of air supplied to the device falls below a predetermined degree.

19. An air heating gun comprising a handle member, a main hollow casing secured to said handle member, means for conducting air under pressure into said main hollow casing, an electric heating element disposed within said casing, a plurality of tubular members surrounding said heating element, said tubular members being of various diameters, means for maintaining the various tubular members in spaced relation so that a plurality of chambers surrounding said heating element are formed, each of said chambers being in communication with the adjacent chamber, said tubular members being so arranged that the air entering said main casing must travel through all of such chambers before reaching said heating element, said heating element having one of its ends supported on a flexible member in order to minimize shocks and jars thereon, a tube leading from the chamber in which said heating element is disposed to a point outside of said main casing, and a nozzle member on the outer end of said tube.

11. An air heating device comprising a main hollow casing, means for conducting air under pressure into said main casing, an electric heating element disposed within said casing, a plurality of wall members surrounding said heating element and being disposed in spaced relation so that a plurality of chambers surrounding said heating element are formed, each of said chambers being in communication with the adjacent chamber and being so arranged that the air entering said main casing must travel through all of said chambers before reaching said heating element, a switch for controlling said heating element, said switch being automatically operable by the air under pressure which flows through the main casing to cause the circuit to said heating element to be completed when air under pressure is supplied to the device and to be broken when the pressure of air supplied to the device falls below a predetermined degree.

12. An air heating device comprising a main hollow casing, means for conducting air under pressure into said main casing, an air injector through which the air under pressure must pass before entering said casing, said injector being of such a type that it will take in additional air from the atmosphere, an electric heating element disposed within said casing, a plurality of wall members surrounding said heating element and being disposed in spaced relation so that a plurality of chamberssurrounding said heating element are formed, each of said chambers being in communication with the adjacent chamber and being so arranged that the air entering said main casing must travel through all of said chambers before reaching said heating element.

13. An air heating device comprising a main hollow casing, means for conducting air under pressure into said main casing, an air injector through which the air under pressure must pass before entering said casing, said injector being of such a type that it will take in additional air from the atmosphere, an electric heating element disposed within said casing, means for permitting the heated air to flow from said casing, and a switch for controlling said heating element, said switch being automatically operable by the air under pressure which flows through the main casing to cause the circuit to said heating element to be completed when air under pressure is supplied to the device and to be broken when the pressure of the air supplied to the device falls below a predetermined degree.

14. An air heating gun comprising a main,

from place to place with the hands, means for U conducting air under pressure into said main casing, an air injector through which the air under pressure must pass before entering said casing, said injector being of such a type that it will take in additional air from the atmosphere and will reduce the pressure of the air under pressure as it passes therethrough, an electric heating element disposed within said casing, said casing being provided with a passageway of much smaller cross-sectional area than the main casing for permitting the heated air to flow from said casing, and means for operating said heating element.

THOMAS J. TULLY.

ROBERT B. JACKSON.