IL39980A - Burner and furnace which heat by radiation - Google Patents

Description

The present invention relates to a burner which heats by the effect of radiation and is more particularly adapted to heat rapidly parts or metallurgical products before a forging operation, a heat treatment or some other treatment.

Indeed, it is often of interest to effect before such a treatment a rapid heating of the product or part to be treated either because a localised heating is required or because the heating time is desired to be reduced so as to avoid overheating, excessive grain size or certain chemical or metallurgical transformations.

Now, for certain, part shapes the heating can only be effected by induction and a flame having a very high temperature is necessary. In this case there are employed burners in which the flame is put in contact with a refractory concrete which in turn heats by the effect of radiation so that a very rapid heating time results. The concrete, containing silica, aluminium or like product, has indeed a very high resistance to the high temperatures and a very high specific heat, that is to say, a considerable thermal inertia. Consequently, it maintains a relatively constant temperature which is very often a great advantage but constitutes a drawback when the furnace in which the burner is mounted is employed continuously for heating products which travel at a constant speed in front of the burner. In this case it is indeed necessary to regulate the temperature of the burner in accordance with the temperature of the parts to be burners employed at the present time are not bery suitable fpr this regulation. They are long to bring to the desired temperature and even longer to cool.

An object of the present invention is to overcom this drawback and provide a burner which permits a rapid heating and whose temperature may be easily modified.

The burner according to the invention comprises a body of a refractory fibre felt and a metal sleeve, which extends through the felt, is provided for supplying a fuel mixture and is a drive fit in the felt and may terminate in a flange for fixing the sleeve to the felt.

The felt employed for the body of the burner is highly insulating so that only the inner surface of the burner is brought to a high temperature. : The burner is consequently rapidly heated but,on the other hand, any modification in the supply of the fuel mixture results in a modification in the temperature of the burner.

Further, the fact that the sleeve is fitted in the felt and that a flange is fixed to the inner wall of the body of the burner results in an absolute fluid-tightriess of the assembly and precludes any penetration of fuel into the body of the assembly.

The present invention also encompasses a furnace of very simple construction in which the temperature may be easily regulated as desired and is distributed throughout the wall of the chamber, that is, throughout the outer surface of the parts.

Indeed, in known furnaces radiant elements, constituted by bricks of refractory material, are heated i. inside the furnace. When they are placed outside, the treating temperature is limited by the resistance of the metal alloys or other materials employed in the constructio of the furnace. When they are inside the furnace, they can be brought to a very high temperature but it is necessary to insulate them from the other parts of the furnace, so as to avoid an adverse effect on the supporting fixing or other elements. In order to allow heating to high temperatures, for example above 650°C, these furnaces are consequently composed of a plurality of separate parts: base, roof, walls, burners etc. made from different materials, each of which is adapted to the temperature to which it must be brought. The thermal expansions of the various parts of the furnace are not the same so that the construction of a chamber presents serious problems related to the rapid destruction of the parts which are brought to a high temperature. It is thus necessary to construct this chamber from numerous elements of small size which are juxtaposed so as to be replaceable and this renders the construction of the furnace complex. Moreover, the furnace is heavy and excessively large in size and yet does not afford a surface which is uniformly radiant at the same temperature.

For the purpose of overcoming these drawbacks, an object of the present inventio is to provide a radiant furnace for treating at high temperature, which comprises a case which is composed of a refractory fibre material having a very low thermal conductivity and defines a treating chamber, and at least one tube which extends supplying a combustible mixture and forms inside at least one burner for heating the whole of the inner wall of the treating chamber. .

In such a furnace, the wall of the treating chamber is constituted by a single material having a low thermal conductivity which constitutes both a refractory material affording a surface which heats by a continuous radiation and an insulator which precludes the transmissio of heat between its inner radiant surface and the exterior of the furnace. Thus a single material performs the function of all of the bricks of different materials employed in conventional furnaces. The overall size of the furnace is consequently considerably reduced and the furnace is considerably lighter. The furnace is thus particularly adapted to the treatment of parts of rather large size requiring a rapid/ regular and precise heating at a temperature of the order of 650-l400°C or more.

In some cases it may be advantageous to provide an outer reinforcement for mechanically protecting the material of refractory fibres. This reinforcement may also serve as a support for the combustible mixture supply pipes,' regulating or other means and even permit the fixing of the whole of the furnace.

The ensuing description of embodiments of the invention, given by way of examples to which the invention is not intended 'to be limited, and shown in the accompanyin drawings, will reveal the .features and advantages of the invention.

In the drawings : Fig. 1 is an axial sectional view of a radiant burner according to the invention; Fig. 2 is a side elevational view of a furnace according to the invention; Fig. 3 is a sectional view taken on line 2-2 of Fig. 1; Fig. 4 is a longitudinal sectional view of a modification of the furnace according to the invention, and Fig. 5 is a cross-sectional view of another embodiment of a furnace according to the invention.

The illustrated burner comprises a body 51 which has, for example, the shape of a portion of a cone the apex end of which is extended by a cylindrical portion 53.

According to the invention, the body comprises a felt of silica-base refractory fibres or like product..

For this purpose, the silica fibres are spun after heating in an electric furnace, pressed so as to form a felt and moulded to the desired shape. The body 51 is insulating, light and flexible. It is refractory at the temperatures of utilisation of the burner.

The cylindrical portion 53 of the body 51 has extending therethrough a metal sleeve 52 which is a force fit in the felt of the body and held in position, on the inner wall of the latter, by a flange 54 which penetrates the felt and, on the outside, by a ring 56' in contact with the cylindrical portion 53. The sleeve 51 is connected to a source of fuel (not shown) by any suitable means.

Preferably, there is placed inside the sleeve 52 heat conducting rod 58 which is coaxial with the sleeve performs the function of a diffuser for the fuel mixture. Thus the head 60 and the flange 54,heated.by the combustio in the burner, convey their heat through the rod 58 and the sleeve 52 to the combustible mixture or fuel which flows through the sleeve and the ignited combustible mixture is directed towards the inner wall of the body 51 by the effect of the head 60. The skin or surface layer of this inner wall is rapidly brought to a high temperatur and vitrified. However, owing. to the fact that the felt is highly insulating, this vitrification occurs to only a very small depth. The heated skin then contributes by radiation to the heating of the part or product..

This thin skin is easily brought to a high temperature and rapidly cooled so that a reduction in the amount of combustible mixture supplied by way of the sleeve 52 immediately lowers its temperature and consequen the temperature of the burner. Inversely, an increase in the amount of mixture supplied increases the temperature furnished by the burner practically without delay. The thermal inertia of the burner is therefore low.

In order to improve the pre-heating of the combustible mixture, radial fins 62 are fixed to the rod 58 of the diffuser inside the sleeve 52, as shown in Fig. 1, or to the sleeve 52.

It will be understood that the shape of the body 51 is determined by the utilization of the burner "and the design of the furnace. This body may have a parabolic or any other shape.

Further, the diffuser constituted by the rod 58 inside the sleeve 52 and affording a tangential supply.of combustible mixture at the outlet of the sleeve. Such a helical path may also be obtained by substituting helical fins for the fins 62.

In a modification of the burner according to the invention, a tangential supply of combustible mixture may be produced by disposing inside the sleeve 52 tangential combustible mixture supply orifices, the diffuser and the rod 58 being omitted.

Irrespective of the chosen arrangement, the ignited fuel mixture is directed towards the inner surface of the body 51 of the burner, which is maintained at a high temperature and affords a complementary heating by radiation .

Owing to the fact that the felt has great flexibility, expansions due to . the heat are easily absorbed in the body 51 with no adverse effect oh the strength of the burner.

Further, the felt is very light so that in most cases it is unnecessary to provide a special support for the burner and the latter may beyCarried solely by the fuel supply sleeve. Thus, for example, it is possible to construct furnaces having a very light roof constituted by felt burners arranged in adjoining relation and supported solely by the fuel supply sleeves. These burners may have bodies of parabolic, frustoconical or other shape defining a curved heating surface or bodies defining a plane heating surface. These bodies are then preferably united into a single unit so as to form a continuous surface in which Furnaces constructed in this manner are shown in Figs. 2 to 5 and will be described in more detail with reference to these figures.

The furnace shown in Fig. 2 and 3. comprises a case 4 of refractory material preferably constituted by a felt of refractory fibres having a low thermal conductiv- 2 ity for example lower than 0,18 k. cal/m /m/h/°C. This case defines a treating chamber 10. In the illustrated embodiment, the case is held in an outer metal reinforcement or framework 1 which has a circular cylindrical shape closed at both ends by walls 2 and 3.. At least one metal sleeve or tube 6 is fitted within the thickness of the case and secured, for example by welding, in an outer radial nozzle or spigot 8 of the reinforcement 1.

Each tube 6 is connected outside the furnace to combustible mixture supply pipes (not shown) . Inside the chamber 10, it terminates for example in a flange 12 and defines a burner orifice. A diffuser 14 is preferably mounted in alignment with this orifice and axially fixed in the tube 6.

The material from which the case 4 is made is capable of resisting high temperatures and in particular temperatures which are above 650°C and may attain 1500°C and more. This material, however, has a high heat insulating power so that the reinforcement 1 is protected from the heat given off by the burners. The inner surface of the case affords under _ the effect of this heat a continuous haating surface by the effect of radiation.

Thus the reinforcement may be of metal or be continuous and cover the whole of the surface area of the case as shown in Fig. 1 or be apertured and surround only certain parts of the case as desired.

The case 4 is constituted in the same way throughout the surface of the chamber 10. It may comprise a single layer of material or comprise, as shown in Fig. 2, several layers, for example two superimposed layers 4a and 4b having different refractory properties. These layers are, however, all constructed from a refractory fibre material having a low thermal conduct-, ivity and surrounding the whole of the treating chamber. It will be understood that the case may be constituted by a plurality of slabs or panels of the same material which are juxtaposed or fixed to each other so as to form a continuous surface.

In the embodiment shown in Figs. 2 and 3, the cylindrical case is truncated and has an externally plane lateral face 16 defining a slot 18 throughout the length of the furnace. The parts to be treated are introduced into, or fed along the chamber 10, through this slot.

They are subjected to th heat given off by the whole of the radiant surface 4 which thus acts on the whole of their outer surface irrespective of their position with respect to the burner. Indeed, the combustible mixture is supplied to the burners 6 in such manner as to bring the inner surface of the case 1 to a temperature at least equa to that of the treatment but, owing to the low thermal conductivity of the material, only a thin surface layer or skin of the latter is brought to a high temperature low. Means supervising the temperature of the treated part can easily control at each instant the regulatio of the combustible mixture supply in accordance with the desired temperature.

Such a furnace therefore permits the treatment by an extremely rapid heating of fixed or moving parts and the maintenance of the temperature at an even and precise value.

The number of tubes 6, and consequently the number of burners, depends on the shape and dimensions of the furnace. This number may be limited to a single burner 28, for example mounted opposite the slot 18 or two burners 6, such as those shown in Figs. 2 and 4. In the embodiment shown in Fig. 3, the furnace comprises a series of burners disposed in pairs at diametrally oppose points, but it is possible to employ in a furnace of this type only a single line of burners 28 which are evenly spaced apart along one of the generatrices of the furnace (Fig. 2) .

The furnace may also have several series of burners, for example simultaneously a series of burners 6 arranged in pairs in diametrally opposed relation and a line of burners 28 mounted between the burners 6 and placed either in the same plane as the two burners 6 or i an intermediate plane. The temperature of the burner or burners is in any case regulated in such manner that the inner surface of the case 4, namely the wall of the chamber 10, is fully heated and ensures an increase in the temperature of the part by the effect of a radiation of It will be understood that the chamber 10 may have either a cylindrical shape of circular cross-section as shown in Fig. 3 or a different section/ for example, a rectangular, square or other section, or any other shape. The furnace may be adapted to all types of treatments and to parts having widely varying shapes. The slot 18 may be replaced by two slots 20 and 22 formed in the centre part of each of the end walls 2 and- 3. A part to be treated 24 is then fed inside the furnace from one end to the other thereof and maintained constantly in the presence of the heating surface.

In other cases, the furnace may be closed and have in its centre means for supporting the part to be treated which is stationary throughout its stay in the furnace. The parts are then introduced in, and subsequentl withdrawn from, the furnace by shifting the furnace or shifting one of the walls 2 or 3 which acts as a door. A furnace of this type is shown in Fig. 4 and comprises a case 4 which defines a chamber having a prismatic shape and a rectangular cross-section protected by a reinforcement 1 and two combustible mixture supply tubes 6 placed in the centre. part of its large sides. A part 26 to be treated, which is flat in the presently-described embodiment, is located at an equal distance from two burners 12, but the whole of its surface receives the heat since the whole of the inner surface of the case 4 constitutes a radiant surface.

The case 4 may be in . a single piece but the furnace is preferably constructed from an assembly of unit cylindrical or prismatic case 40 and optionally a portion of reinforcement la and at least one combustible mixture supply tube 6. Similar unit elements are assembled to each other and to end elements so as to constitute a continuous furnace, by any appropriate means which are easily taken apart, such as screw and nut means. Each end element comprises a wall 2 or 3 which is integral with a ring 21 or 31 respectively for fixing it to the neighbouring unit element and is of a refractory material identical to that of the case 4 acid is adapted to extend the latter exactly, this wall being preferably maintained in position by a plate or other reinforcing element.

The furnace may thus have any desired dimension and can be constructed or modified in accordance with the treatment to be carried out.

The case of material containing refractory fibres, for example refractory fibre felt, is extremely light so that the furnace assembly comprising this material, means as simple as the exterior reinforcement and the burners, is light and may be easily fixed at any point and receive any desired orientation. The furnace may also be shifted if required with no considerable handling problems.

The properties of thermal insulation of the refractory material permits employing this material in relatively small thicknesses and obtaining a furnace which is small and easy to employ. Further, its low thermal inertia permits bringing, the furnace, to the required temperature and cooling the furnace extremely rapidly and permits a precise regulation of the temperature in the It will be understood that the chamber 10 may have a composite shape, for example a section which corresponds to that of the part to be treated, without . this requiring a great number of burners, the latter being easily disposed at suitable points to heat the whole of the inner surface of the case, namely the . whole of the wall of the treating chamber. 39980/2

Claims (14)

1. CLAIMS 1. A burner for heating by the effect of radiation, comprising a body of felt of refractory fibres defining a wall, a metal sleeve which extends through the body and is in interference fit in the felt for receiving a combustible mixture, an outlet orifice defined by the sleeve insid the body, a diffuser in alignment with said outlet for guiding the ignited combustible mixture in the direction of the wall of th body, and an inner surface layer on the felt wall which is vitrified by first high temperatur heating and constitutes a radiant non porous thin skin.

2. A burner as claimed in claim 1, wherein the sleeve terminates in a flange for fixing the sleeve to the body of the burner.

3. A burner as claimed i claim 1 or 2, wherei the diffuser comprises a head Integral with the end of a rod which is coaxial with the sleeve and is i contact with the combustible mixture inside the sleeve, the head and sleeve being heat conductive.

4. A burner as claimed in claim 3, comprising heat exchanging radial fins between the rod and the sleeve.

5. A burner as claimed in Claim 3, comprising helical fins mounted between the rod and the sleeve.

6. A burner as claime in claim 1 or 2, wherein the sleeve comprises an inner helical pipe for supplying the combustible mixture.

7. A burner as claimed in claim 1 or 2, wherein the sleeve comprises orifices for supplying the combustible mixture tangentially . Q.2f.

8. A burner, substantially as hereinbefore described with reference to and as shown in Fig. 1 of the accompanying drawings. 9. ίΓ.

9. A radiant furnace for treating parts at high temperature which comprises a case of a material containing a refractory fibre and having a very low thermal conductivity, and which defines a treating chamber, and at least one tube extending through the case and mixture connected outside the case to combustible/supply pipes and forming inside the chamber at least one burner 8 according to any one of the claims 1 to S5 for heating the inner surface of the treating chamber. 9^ jQt .

10. A furnace as claimed in claim Α-σ, wherein the combustible mixture supply tube or tubes fixed in the case are arranged on the wall of the treating chamber in such manner as to heat the whole of said wall. 9 10 jj .?.

11. A furnace as claimed in claim ] Γ or T, comprising an outer reinforcement for protecting the case of refractory fibres.

12. » >3". A furnace as claimed in claim W or wherein the case is closed and the part to be treated is fixed in position. 910 11

13. , Je4. A furnace . as claimed in claim {Γ, Jr or , comprising a longitudinal slot in the case for the passage of the parts to be treated. · 9 10 11

14. A furnace as claimed in claim W* , l-i^ or \Z, wherein the furnace has at each end a slot respectively for introducing and withdrawing the parts to be treated. 15· A furnace as claimed in any one of the 9 14 claims HT to l , comprising at least one unit element of a case of material containing refractory fibres through which extends at least one combustible mixture supply tube constituting a burner. 15 ^ge yf. A furnace as claimed in claim further comprising two end elements of the same material as the unit elements of the casing which define a treating chamber with the case. 17. β*. A radiant furnace, substantially as hereinbefore described with reference to and as shown in Figs. 2 and 3 of the accompanying drawings. 18. radiant furnace, substantially as hereinbefore described with reference to and as shown in Fig, 4 of the accompanying drawings. 19. -2"tf A radiant furnace, substantially as hereinbefore described with reference to and as shown in Fig. 5 of the accompanying drawings.