US3868212A

US3868212A - Radiant burner and furnace for treating at high temperature

Info

Publication number: US3868212A
Application number: US406849A
Authority: US
Inventors: Bernard J Lemaire
Original assignee: Ressorts du Nord SA
Current assignee: Ressorts du Nord SA
Priority date: 1971-08-03
Filing date: 1973-10-16
Publication date: 1975-02-25
Anticipated expiration: 1992-02-25

Abstract

Burner heating by the effect of radiation comprising a body of refractory fibre felt through which extends a metal sleeve for supplying a combustible mixture. A furnace is disclosed which comprises a case of a material containing refractory fibres having a very low thermal conductivity, the case having an inner surface defining a treating chamber. At least one tube extends through the material of the case and is connected to a source of combustible mixture outside the case and forms inside the chamber at least one burner which heats the inner surface defining the chamber.

Description

[ Feb. 25,1975

United States a Patent 1 Lem aire I RADIANT BURNER AND FURNACEFOR TREATING AT HIGH TEMPERATURE Henwood............................

Mm n e m e bf. he C Bk ir HK 0 7 9 Herzberg [75] Inventor: Bernard J. Lemaire, Faumont,

France [73] Assignee: Ressorts du Nord S.A., Paris, France Filed: Oct. 16, 1973 Primary Examiner-John J. Camby Appl, No; 406,849 Assistant Examiner-Henry C. Yuen Attorney, Agent, or Firm-Burns, Doanc, Swecker & Mathis Related US. Application Data Continuation of Ser. No. 275,293, July 26, l97 No. 3,801,080.

2. Pat.

ABSTRACT [30] Foreign Application Priority Data Aug. 3. 1971 Burner heating by the effect of radiation comprising a body of refractory fibre felt through which extends a metal sleeve for supplying a combustible mixture.

Apr. 4 1972 72.11736 A furnace is disclosed which comprises a case of'a material containing refractory fibres having a very low thermal conductivity, the case having an inner surface defining a treating chamber. At least one tube extends through the material of the case and is connected to a source of combustible mixture outside the case and 50 5 u mm BM H eme oo .0 4 5 W U ,R 3 n u l 2 l 4 7 9 /F n u woo 1 2 n4 i0 1 3 .l 4 mm] m mmoo H 7 u uh U N s u u 9 mmz m B L I. 3 d 5 m U IF a 00 5 55 forms inside the chamber at least one burner which heats the inner surface defining the chamber.

[56] References Cited UNITED STATES PATENTS 7 Claims, 9 Drawing Figures 2.071507 3/1954 Morck. Jr. 431/348 RADIANT BURNER AND FURNACE FOR TREATING AT HIGH TEMPERATURE This is a division of application Ser. No. 275,293, filed July 26, 1972, now U.S. Pat. No. 3,801,080.

The present invention relates to a burner which heats by the effect of radiation and is more particularly adapted to heat rapidly parts or metallurgicalproducts 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 inwhich 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 heated. Now, owing to the thermal inertia of the concrete burners employed at the present time are not bery suitable for this regulation. They are long to bring to the desired temperature and even longer to cool.

An object of the present invention is to overcome 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-tightness 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 by means of burners which may be placed either outside or 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 construction 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, bur'ners 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 ia uniformly radiant at the same temperature.

For the purpose of overcoming these drawbacks, an object of the present invention 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 through the chamber, is connected outside to supply pipes 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 transmission 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-l,400 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 accompanying 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. la is an axial, sectional view of a modification of the radiant burner shown in FIG. 1;

FIG. lb is an axial, sectional view of a second modification of the radiant burner shown in FIG. 1;

FIG. 1c is an axial, sectional view of a third modification of the radiant burner shown in FIG. 1;

FIG. 1d is a cross-sectional view of the sleeve 52 along the line 1d 1d in FIG.

FIG. 2 is a side elevational view of a furnace according to the invention;

FIG. 3 is a sectional view FIG. 4 is a longitudinal sectional view of a modification of the furnace according to the invention, and

Hg. 5 is a crosssectional 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, passed 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 extend-v ing 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 taken on line 3-3 of FIG.

cylindrical portion 53. The sleeve 52 is connected to a I source of fuel (not shown) by any suitable means.

Preferably, there is placed inside the sleeve 52 a heat conducting rod 58 which is coaxial with the sleeve 52 and terminates inside the burner 51 in a head 60 which performs the function of a diffuser for the fuel mixture. Thus the head 60 and the flange 54, heated by the combustion 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 temperature 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 consequently 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 and the head 60 may be replaced by a helical pipe formed inside the sleeve 52 and affording a tangential supply of combustible mixture at the outlet of the sleeve. This modified form of the burner is illustrated in FIG. lb. Such a helical path may also be obtained by substituting helical fins for the fins 62, as shown in FIG. la.

In a third modification of the burner according to the invention, a tangential supply of combustible mixture may be produced by disposing inside the sleeve 52 (FIG. 10) tangential combustible mixture supply orifices 64 (FIG. 1d), 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 on 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 be carried 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, frustconical 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 the sleeves are fitted at regular intervals.

Furnaces constructed in this manner are shown in FIGS. 2 to 5 and will be described in more detail with reference tothese figures.

The furnace shown in FIGS. 2 and 3 comprises a case 4 of refractory material preferably constituted by a felt of refractory fibres having a low thermal conductivity 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 and may attain l,500 C and more. This material, however, has a high heat insulating power so that the reinforcement l 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 heating surface by the effect of radiation.

Thus the reinforcement may be of metal or plastic material or any other suitable material. It may 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 alow thermal conductivity 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 the 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 equal 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 and the thermal inertia of the radiant material is very low. Means supervising the temperature of the treated part can easily control at each instant the regulation 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 ofthe 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 opposed 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 ofthe 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 in 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 heat to entire outer surface of the part.

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 subsequently 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-scction protected by a reinforcement l 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 presentlydescribed 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 may be in a single piece but the furnace is preferably constructed from an assembly of unit elements. Each of the elements comprises a portion of a 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 and 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 lightso 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 course of the treatment.

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.

Having now described my invention what I claim as new and desired to secure by Letters Patent is:

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 inside the body, a diffuser in alignment with said outlet for guiding the ignited combustible mixture in the direction of the wall of the body, and an inner surface layer on the felt wall which is vitrified by first high temperature heating and constitutes a radiant non porous thin skin.

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

6. A burner as claimed in claim 1, comprising a helical pipe inside the sleeve for supplying the combustible mixture.

-7. A burner as claimed in claim I, wherein the sleeve defines orifices for supplying the combustible mixture tangentially.

Claims

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

3. A burner as claimed in claim 1, wherein the diffuser comprises a rod which is coaxial with the sleeve and is arranged to be in contact with the combustible mixture inside the sleeve and a head integral with an end of the rod, the head and rod being heat conductive.

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

7. A burner as claimed in claim 1, wherein the sleeve defines orifices for supplying the combustible mixture tangentially.