GB2064752A

GB2064752A - Hot gas generator

Info

Publication number: GB2064752A
Application number: GB8037642A
Authority: GB
Original assignee: Assi Can AB
Current assignee: Assi Can AB
Priority date: 1979-12-06
Filing date: 1980-11-24
Publication date: 1981-06-17
Also published as: BR8007979A; IT8026444A0; NL8006590A; DE3043165A1; FI803498L; NO803648L; PT72098A; DK518380A; BE886400A; PT72098B; IT1134592B; ES255275U; JPS5746834A; SE7910048L; ES255275Y; FR2470924A1

Abstract

A generator for applying a stream of hot gas to an area of a web consisting of a meltable plastics foil (32) or a plastics-coated web, comprises a supply chamber (1, 7) for receiving a combustible gas and separated from a combustion chamber by a wall (10) with a plurality of nozzle channels (13) which open into the combustion chamber. Arranged opposite the wall (10) is a heating shoe (15) having a plurality of outlet channels (16) for hot gases, these outlet channels (16) being in axial alignment with corresponding nozzle channels. <IMAGE>

Description

SPECIFICATION Hot gas generator The present invention relates to a hot gas generator and, in particular to a generator for generating and directing a stream of hot gas onto a predetermined area, for example, of a web of a meltable plastics material or to a plastics-coated web. Hot gas generators for this purpose are known which comprise a chamber for supplying a combustible gas, which flows into a combustion space or chamber through nozzle channels in a wall separating the combustion space and the supply chamber.

Generators of this kind have a wide application and can be used, for example, for heating a plastics coating on a fibre web which is to be joined, for example, to a plastics foil or another web. In this case, the combustion space is formed by the gap located between the openings or mouths of the nozzle channels, and the fibre web and plastics layer will thus be subjected to an open flame and caused to melt or become tacky when the fibre web passes the open flame.

In certain cases it is not possible to use an open flame to achieve the desired degree of tackiness. For example, if, when one plastics foil is to be joined to another plastics foil over the whole of its surface or along its edge portions, an open flame is used, the plastics foil will be either completely or partially destroyed by the flame, or at least deformed to such an extent as to render the foil unusable for the intended purpose. Another problem encountered when using an open flame is that it is not possible to melt a well-defined area.

Attempts have been made to heat to the desired extent, for example, an edge portion of a plastics foil which is to be bonded to an edge portion of the same foil, this latter edge portion being wound helically on a rotating mandrel with the aid of shoes which are heated electrically or in some other way and which lie closely adjacent said edge portion.

These attempts have been successful when the foils are extremely thin and when they do not comprise HD-polyethylene. If, however, such heated welding shoes are used on foils whose thickness is greater than 0,02-0,025 mm, however, the speed at which the plasticsfoil web can be moved past a welding shoe is much too low, said speed being of the order of magnitude of 10 cm/s. For example, a helically wound container tube can not be effectively produced at low costs at such low speeds. Modern machines for the manufacture of helically wound tubes, which are subsequently cut to form containers, require the webs which are taken from storage rollers and wound helically on a mandrel, whereat the edge portions of an inner foil web shall be welded together in a liquid-tight and air-tight fashion, to be moved at speeds of about 50 cm/s.Such a machine is described in Swedish patent specification no. 7811314-9.

Consequently, one object of the invention is to provide a hot gas generator which, despite having a very high heating effect, does not have the disadvantages of the open flame.

According to this invention we propose a hot gas generator comprising a supply chamber having an inlet for combustible gas and a combustion chamber separated from the supply chamber by a partition wall with nozzle channels communicating between the supply chamber and the combustion chamber which includes, opposite the partition wall a heating shoe having hot gas outlet channels each in axial alignment with one of the nozzle channels.

The combustion gas is ignited in the combustion chamber, which is open to atmosphere, and hot gases pass through the outlet channels of the heating shoe at high speeds, said gases being directed onto that area of a foil, e.g. a meltable plastics material or plastics coated web, which is to be brought to a tacky or molten state. At a distance of 5 mm from the foil, the outflowing gas has a temperature of 800-900 C after only some tenths of a second after ignition of the combustion gas. If the shoe is made of metal, the shoe will be heated to a red-hot state after only some minutes of operation, which contributes effectively to preventing cooling of the outflowing gases. This enables a foil having a thickness, e.g. of 0,07 mm and comprising a HD-polyolefine to be welded without difficulty at a speed of 50-80 cm/min.

The length of the nozzle channels and the outlet channels is of small importance and tests in which the lengths of the channels varied between 0,5 and 20 mm showed no appreciable difference with regard to the temperature of the hot gases, speed or direction.

The channels, which are preferably cylindrical, suitably have a diameter within the range of 0,1-2 mm, preferably a diameter of 1 mm.

The cross-sectional shape of the channels has no significance, although for practical reasons a circular cross-sectional shape is preferred.

The channels of one and the same generator may have different diameters, although in order to be active, i.e. to allow hot gas to pass through, the outlet channels in the heating shoe, which is preferably of metal or a ceramic material, must be in register (alignment) with a corresponding nozzle channel. The number of nozzle channels may differ from the number of through-flow channels, although it is preferred that the number of channels is the same in both cases.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which Figure 1 is a side view, partly cut away, of a generator intended for heating a foil web which moves in one plane: Figure 2 illustrates the generator of Fig. 1 seen from one end thereof; Figure 3 illustrates the generator of Fig. 1 in plan view with the cover plate removed; Figure 4 illustrates the generator of Fig. 1 seen against the underside of the heating shoe; Figure 5 illustrates a generator having a curved shoe but otherwise is similar to the generator of Fig. 1; and Figure 6 illustrates the generator of Fig. 5 seen against the underside of the heating shoe.

The generator illustrated in Figs. 1-4 includes a cover plate 1 which is mounted on a burner body 3 in a substantially gas-tight fashion by means of screws 2. The cover plate 1 has a gas-supply pipe 4 connected to an opening 5 in the cover plate 1, said pipe 4 being sealingly connected to the opening 5 coaxially therewith by means of a weld 6.

Located beneath the cover plate 1 is an elongate recess 7, defined by parallel side walls 8 and 9 and a flat partition wall 10. The recess 7 and the cover plate 1 together form a chamber for receiving a supply of combustible gas through the pipe 4, the interior of which has screw threads 11 for screwing a connecting piece to a gas source. The wall 10 has a flat underside 1 2 and is formed with a plurality of nozzle channels 1 3 which, as is best seen from Fig. 3, are arranged in two parallel rows and equally spaced. A combustion space 14 is formed by an open ended rectangular groove in the body 3, and gas supplied to the chamber 8 flows though the channels 1 3 in the wall 10 into the combustion space 14.

The bottom of the combustion space 14 is defined by a heating shoe 1 5 through which outlet channels 16 pass, the number of outlet channels corresponding to the number of nozzle channels 1 3. In order for hot gas to flow out of the channels 16, these channels are coaxial with the channels 1 3. Any channel 1 6 which is not in exact register with a corresponding channel 1 3 will have no function whatsoever from the aspect of hot-gas outflow. The underside 1 7 of the heating shoe 1 5 is flat and is intended to co-act with a flat portion of a plastics layer or a plastics foil 32 to be melted or brought to a tacky state.To prevent the burning gas in the combustion chamber from forming an outwardly shooting flame there is provided, as seen to the right in Fig. 2, a protective plate 18 which is screwed to the body 3 by means of screws 19, 20.

Although in the above described embodiment the various channels 1 3 and 1 6 extend at right angles to the flat, mutually parallel surfaces 17, 21, 22, it will be understood that the channels may also extend obliquely to these surfaces. The only requirement is that the channels 1 3 and 1 6, which may have different cross-sectional areas, lie in axial alignment with one another. The area on a foil covered by the hot gas rapidly leaving the openings is extremely well defined and corresponds in the illustrated embodiment, to the peripheral edges of the shoe 1 7, i.e. edges 23, 24, 25, and 26.Outside this area the gas is cooled relatively quickly and, because of the distance between the surface 1 7 and the foil surface parallel therewith, will not melt the foil.

Figs. 5 and 6 illustrate in simplified form a modified generator in which the heating shoe 27 has an arcuate surface in which are formed three rows of outlet channels 28. The channels extend in the radial direction (of radius 29) and are in register with corresponding nozzle channels. In this embodiment, the combustion space has closed ends and an open arcuate side 30. The chamber (not shown) for distributing gas to the nozzle channels (not shown) is connected to a gas-supply pipe 3.

The heating shoe may be formed as a part of a helix when welding edges wound along a helix. Further the generator may, if desired and to advantage, be such as to enable a foil to be heated along the whole of its surface for joining said foil to another foil.

Claims

1. A hot gas generator comprising a supply chamber having an inlet for combustible gas and a combustion chamber separated from the supply chamber by a partition wall with nozzle channels communicating between the supply chamber and the combustion chamber which includes, opposite the partition wall a heating shoe having hot gas outlet channels each in axial alignment with one of the nozzle channels.

2. A generator according to claim 1, wherein the nozzle channels and the outlet channels are arranged in at least one row along the partition wall and the heating shoe respectively.

3. A generator according to claim 1 or claim 2, wherein the number of nozzle channels equals the number of outlet channels.

4. A generator according to any one of claims 1-3 wherein the heating shoe has a flat surface remote from the combustion space.

5. A generator according to any one of claims 1-3, wherein the heating shoe has a curved surface remote from the combustion space.

6. A generator according to claim 5, wherein the said surface forms part of a helix.

7. A hot gas generator constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.