The invention relates to an apparatus for the heating of a bituminous roofing material, the apparatus comprising: air supply means; an elongated tubular combustion chamber with a first end and a second end having a wall surrounding a longitudinal axis of said chamber and including an exit for hot air at said second end and at least one air entrance near said first end for delivery of a primary air flow and a burner arrangement disposed essentially centrally within said combustion chamber near said first end, said burner arrangement comprising means for injection of fuel and means for ignition of said fuel.

Many heating devices for domestic and industrial use require a heat source. When applying a bituminous roofing material on a roof, torches are directed at the bitumen layer of the material in order to make this layer soft and sticky so that the material will adhere to the surface to be covered. It is well known that torches producing a flame or a hot air stream for welding or other purposes may be the cause of injuries to persons or fires if a person or structure is exposed to the flame for a period of time.

The provision of air chambers surrounding burner nozzles has been suggested to overcome this problem. For example, US patent nr. 3 883 290 discloses a burner where the generated stream of hot air is surrounded by an air current which insulates the wall of the guide pipe against heating.

This device has a substantial disadvantage. Extensive heat is still developed in the area proximate to the ignition and burner arrangement. Therefore the burner and ignition arrangement has to be constructed from materials which are able to withstand these temperatures. Furthermore, no known material will last indefinitely if heated, and the expensive ceramic materials used in prior art apparatus are subject to thermal shocks and will therefore deteriorate thereby limiting the longevity of the system.

The object of the invention is to solve the problem of high temperatures in the area proximate to the ignition and burner arrangement in a heating apparatus.

The object of the invention is achieved by a heating apparatus provided with a first end being essentially air-tight and said at least one air entrance being located in the wall of the combustion chamber near said first end, the air entrance comprising means to produce a helical current of air around said longitudinal axis of the combustion chamber. The supply of air leaves the centre axis of the combustion chamber more or less unaffected by the surrounding helical current of air. This entails a relatively calm and rich burning of fuel along the centre axis of the combustion chamber. The centrifugal forces caused by the incoming air affect the cooler air stream with a higher density to the effect that it is thrown against the wall of the combustion chamber and cools it, while the hotter gas stream, with a lower density, is gathering in the core zone.

According to a preferred embodiment, the at least one air entrance comprises an angled scoop, an angled hole or an angled tube.

According to a preferred embodiment, said burner arrangement comprises fuel injecting means adapted to inject the fuel in a direction essentially concentrically with said longitudinal axis (A) of the combustion chamber (10).

According to another preferred embodiment, the burner arrangement has wall means adapted to fit said apparatus to make said combustion chamber air-tight at said first end. Preferable the burner arrangement is releasably connected to the combustion chamber. This will facilitate access to the apparatus interior and thereby allow overall maintenance as well as easy renewal or replacement of worn parts.

According to another preferred embodiment, the location of the air entrance is at or downstream of the means for injection of fuel. This will make the initial gas air mixture richer in gas and therefore it facilitates the ignition.

The air entrance may preferably be at or downstream of both said means for injection of fuel and said means for ignition of said fuel.

A further object of this invention is to provide a heating apparatus with improved heating effects and a flame-free stream of hot air having a great uniformity in the temperature profile at the outlet.

This object of the invention is achieved by the apparatus further comprising means for introducing a secondary helical current of air, the secondary current of air having a direction of rotation opposite the direction of rotation for the primary air and being introduced further downstream the combustion chamber. The counter-flowing entering secondary air not only retards the helical motion and centrifugal effect, but it also slows down the formation of any excessive great axial velocity in the area of the core zone. The result is a flame-free stream of hot gases with a great uniformity in the diametric temperature profile at the outlet. The air entrance for said, at least one secondary airflow, can preferably be made as an angled scoop; angled hole or as an angled tube.

In a preferred embodiment, the apparatus comprises a mixing chamber arranged in extension of said combustion chamber at said second end in which chamber the mixing of the counter-flowing currents of primary and secondary airflows takes place. This improves a better mixing of primary and secondary airflows. In a further preferred embodiment, the mixing chamber arranged in extension of said combustion chamber and the apparatus are releasably connected. By arranging the mixing chamber in extension of said combustion chamber and the apparatus being releasably connected, it is possible both to remove said mixing chamber for maintenance purposes and to change between different mixing chamber units which are made such that they are suitable for particular tasks.

The apparatus may include a generally tubular housing surrounding said combustion chamber. This protects the operator against being charred or burned.

According to a preferred embodiment, the housing is arranged at least partially spaced from the combustion chamber thereby defining an air gap for delivering secondary air, whereby the housing is maintained relatively cool during the operation of the apparatus.

In a preferred embodiment the helical motion of the secondary air is accomplished by a helical spiral placed in the air gap bounded by the inside of the tubular housing and the outside of the combustion chamber. Preferably the air gap near said first end of the combustion chamber constitutes the initial air path for both primary and secondary airflows, said air path being subdivided into two separate air paths. This provides a more compact apparatus.

The invention in other aspect provides methods as recited in claim 16-17.

The methods facilitate the practical applications of generating flow of hot gases by way of providing both a relatively cool ignition area and a more efficient ignition inside the combustion chamber. The methods further facilitate the practical applications of generating flow of hot gases showing a great uniformity in temperature profile.

Further objects and advantages and features of the invention appear from the following description of the preferred embodiments given with reference to the drawings wherein:

Figure 1 shows a heating apparatus assembly in a side view;

Figure 2a shows the inner barrier with a fixed helical element;

Figure 2b is a drawing in perspective of the inner barrier, viewed from the entrance, with a fixed helical element;

Figure 2c is a drawing in perspective of the inner barrier, viewed from the exit, with fixed a helical element;

Figure 3a shows the inner barrier with a fixed helical element, the inlet ports having closed sides;

Figure 3b is a drawing in perspective of the inner barrier, viewed from the entrance, with a fixed helical element, the inlet ports having closed sides;

Figure 3c is a drawing in perspective of the inner barrier, viewed from the exit, with fixed a helical element, the inlet ports having closed sides; Figure 4a-4b is a detailed view of a preferred embodiment of the inlet ports and

Figure 5 shows, in perspective, a preferred embodiment of the inlet ports taken along line b-b in figure 1.

All figures are schematic and not necessarily to scale and show only items essential to the understanding of the invention, whereas other parts have been deleted for the sake of clarity. Throughout the figures the same references are used for identical or similar means.

The hand-held burner shown in figure 1 comprises like prior art apparatuses, a combustion chamber 10 with a burner arrangement disposed mainly centrally therein and connected with a fuel supply 83, an ignition arrangement 80 for the fuel and an air delivery system. The air delivery system delivers a helical spinning airflow. However, instead of using an axial blower disposed behind the burner to deliver a helical spinning airflow, the helical motion of air is accomplished by the provision of one or more air inlets 50 positioned in the wall 30 of the combustion chamber 10. These air inlets 50 preferably made as scoops, as best seen in figure 2-3, introduce into the combustion chamber 10 a primary airflow in a direction essentially tangentially to the wall 30 of the combustion chamber 10. The tangentially direction entails a flow of primary air through the combustion chamber 10 in a helically circulating motion around the combustion chamber's 10 longitudinal axis A. The circulating motion of primary air leaves the centre axis A of the combustion chamber 10 more or less unaffected and thereby it facilitates a rich current of fuel and gas along the axis.

As will be well known to those having operating experience with gas fired equipment, ignition is generally not possible in a lean mixture of gas and air. To ensure an easy and safe ignition of the heating apparatus, fuel is injected through the holes 88 in the burner arrangement. The injection of fuel gives rise to a relatively calm and rich current of fuel and air along the center axis of the burning chamber 10 and thus it facilitates an easy and safe ignition. The fuel is preferably injected in a direction parallel to and concentrically with the centre axis A of the combustion chamber 10.

As more clearly seen in figure 2a-3a, the inlet 50 could be made as angled scoops, and said scoops could be made with open sides as best seen in figure 2a-2c or with closed sides as best seen in figure 3a-3c. As an alternative to scoops, the inlet ports could be made as angled holes or angled tubes as seen, in cross sectional view, in figure 4a and 4 b. However, the helical current may be obtained in many other ways.

The ignition device comprises two electrical terminals 81 and 82 where the first terminal 81 is grounded, but any conventional ignition means could be used, e.g. a spark plug. After ignition of the fuel gas mixture, the initially still cold mixture of fuel and air travels through the combustion chamber 10 in a helical rotation about the combustion chamber's 10 longitudinal axis A. Due to the centrifugal caused thereby, the relatively cooler airstreams (with the highest density) are thrown against the wall 30 of the combustion chamber 10, while the hotter airstreams (with a lower density) are concentrating in the core zone along axis A. This entails a cool ignition area, and the bracket 85, which serves as a holder for the gas distributor 84 and the terminal 82 can therefore be made of materials which do not necessarily have to be able to withstand the high temperatures normally prevailing in the area proximate to the ignition. An especially inexpensive burner is achieved when the bracket 85 is made of an electrically non-conducting material such as plastic, but other electrically insulating materials could be used. Preferably the bracket 85 is adapted to make an air-tight fit against the wall of the combustion chamber 10 so as to seal the rear end of the combustion chamber 10. The bracket 85 is releasably fastened by a nut 87.

The hot air leaves the combustion chamber 10 in the form of a spinning current. Such a spinning current has a density which increases from the axis outward as a result of the centrifugal forces. In the area of the longitudinal axis A the density of air is very low and the temperature correspondingly high. Therefore the diametric temperature profile of the spinning current of hot air leaving the combustion chamber 10 does not show a great uniformity. To slow down the helical motion of the hot air leaving the combustion chamber and thereby improve the temperature profile of the leaving hot air, the apparatus comprises in a preferred embodiment means for introducing a secondary helical current of air. The secondary current of air is introduced with a direction of rotation opposite the direction of rotation of the primary air and is introduced further downstream the combustion chamber.

To maintain a cool exterior, the combustion chamber 10 is preferably mounted inside an outer housing 40 which is cooled by air delivered through the air gap 41 between the outer housing 40 and the combustion chamber 10. Advantageously the air gap 41 constitutes a part of the air path for both primary and secondary air supplied by a single air supply system through an initial channel 86. The inlets 50, which are positioned in the air gap 41 and just downstream of the electrical terminal 81 serve as entries for the primary air into the combustion chamber 10, and a helical spiral 60 positioned further downstream sets up a counter-flowing helical motion of the secondary air.

In some particular cases it is advantageous to modify the inclination or length of the helical spiral 60 to alter the overall air resistance of the secondary air supply. By changing for instance the inclination and/or length of the helical spiral 60 both the speed and/or angle of entry of the secondary air may be varied. But it is also possible to adjust and adapt the flow path of the primary and secondary air such that a single air supplier initially feeds all air through one single initial channel 86 which is downstream subdivided into two separate paths for primary and secondary air currents.

The majority or all of the mixing between the counter flowing primary and secondary air preferably takes place in a mixing chamber 20 arranged at a foremost 12 second end of the combustion chamber 30.

To facilitate maintenance of the apparatus, the combustion chamber 10 and the mixing chamber 20 are releasably connected by joints 22, e.g. snap-on mechanisms. By modifying the mixing chambers parameters, for instance the outlet profile 21 , the length of the mixing chamber, the diameter of the mixing chamber or the ratio between these parameters, it is possible to design special mixing chambers suitable for particular tasks, and the joints 22, make it possible to select and mount the mixing chamber most suited for the actual task.

Although specific embodiments have been described above it is emphasized that the invention may be exercised in several ways and that the explanation given above serves exclusively to clarify the invention and not to limit the scope of protection conferred, which is defined exclusively by the appended claims.

Although the invention has been discussed in relation to bituminous roofing material, the apparatus may be used for applying a bituminous web of any type of civil engineering structure.