RADIANT HEATING FURNACE

Abstract: A radiant heating furnace comprising a housing which is split into at least two parts which are movably mounted so that they can be brought together to enclose a specimen to be heated, each part including at least one substantially linearly extending radiant heat source, so that the sample can be heated uniformly, at least on two opposite sides.

Description: RADIANT HEATING FURNACE This invention relates to furnaces, and particularly to furnaces of the type adapted to focus a large amount of radiant energy over a small area, such as a narrow elongated specimen. It is known to utilise quartz halogen lamps, and particularly, linear quartz halogen lamps, in housings with suitably shaped reflectors, to provide an intense heating effect over a small area. Examples of heaters employing such techniques are the models 5215 and 5193 "line heaters" of Research Inc. of Minneapolis Minnesota 55424 USA. There are still a number of difficulties with devices of this kind, particularly because the known devices do not provide a uniform heating effect all around an elongate or linear object, and in particular, there is a need for furnaces capable of reaching very high temperatures, but concentrating the heat in the specimen itself rather than heating up the whole furnace, so that the furnace can be kept very compact. It is also desirable to be able to heat up samples very quickly, which also makes it desirable for the furnace to be kept compact. In particular, this is desirable in situations in which a specimen is being tested for its performance under extreme conditions, such as the heating conditions experienced by materials used in turbines. It is frequently required to be able to examine such specimens, at very close quarters, even whilst they are actually being subjected to heat treatment, so as to understand, (for example) how faults such as cracks will propagate in the sample under these circumstances. Consequently, it is necessary to keep the furnace as small as possible, and to avoid "leakage" of heat into the outside environment, so as to enable the sample to be inspected at close quarters, for example by means of a "telescope" arrangement, and also to facilitate a so-called "cold gripping" arrangement (i.e. allowing parts of the specimen to extend outside the furnace without further cooling) . Accordingly, a first aspect of the present invention provides a furnace comprising a body which is split into at least two parts which are movably mounted so that they can be brought together to enclose a specimen to be heated, each part including at least one substantially linear radiant heat source, so that the sample can be heated uniformly, at least on two opposite sides. It will be appreciated that by the expression "substantially linear radiant heat source", it is intended that the heat source comprises one or more radiant heating elements, which are so arranged in reflector housings as to provide an elongate region which is substantially uniformly heated. The uniform heating effect is preferably achieved by a combination of the configuration of the lamp itself, and the shape of the reflector in which it is mounted, and according to a first further aspect of the invention, the heat source comprises a heating element assembly including a plurality of lamps such as quartz halogen lamps, which are powered so as to emit a substantial part of their energy in the infra-red region, and which are arranged along the inside of a generally elongate, bowl shaped reflector, whose internal surface is shaped so as to compensate for the distribution of-the heat source elements. Alternatively, a single "linear" lamp may be used, in which case the elongate bowl shaped reflector is specially curved at each end, to compensate for the less even distribution of energy in that region of the lamp. However it is preferable to use a plurality of separate lamps since they can then be controlled in "zones" so that the distribution of energy can be changed as required. In a preferred embodiment of the invention, the furnace comprises two halves which are pivotally mounted on support means so that they can be pivoted into engagement to enclose an article to be heated, each half carrying a pair of adjustably mounted heating element assemblies which are directed towards the centre of the furnace, the heating element assemblies being so arranged, relative to one another, that when the furnace is enclosed around the article they substantially surround it. In this preferred arrangement, each heating element assembly preferably occupies one quadrant of a lateral cross section through the furnace, relative to the heating axis, and is provided with a slidable mounting which allows its position to be adjusted at least in a radial direction, and preferably also in a circumferential direction relative to the axis. Preferably, the heating element assemblies are so shaped and arranged that they cooperate to substantially enclose the article being heated when the furnace is closed, and concentrate the radiant heat output at an adjustable focus in the central region. In a preferred arrangement, in which a plurality of heat sources are arranged in a line along the reflector, the ends of the "bowl shape" are deeply curved in a "re¬ entrant" shape, so as to compensate for the "fall-off" in output at each end of the linear array of lamps, and so that the maximum concentration of heat occurs at or near the outer opening of the reflector. Preferably each heating element assembly comprises a metal body which is machined to form the required reflector shape and also to form internal channels for the circulation of fluid coolant. When the heating element assemblies are formed in this way, they nay be arranged to substantially enclose the specimen being heated so that a separate cooling jacket is not required. Some embodiments of the invention will now be described by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic cross-section through a part of a furnace body in accordance with the invention, taken on the line A-A of Figure 2; Figure 2 is a diagrammatic front view of the furnace body of Figure 1; Figure 3a is an axial cross-section through a first type of reflector; Figure 3b shows a first type of lamp used as a heat source; Figure 3c shows an array of three lamps used as a heat source; Figure 3d illustrates a possible alternative arrangement of three lamps; Figure 4a is a diagrammatic side elevation of a second type of furnace according to the invention; Figure 4b is a side elevation of the furnace of Figure 4a; Figure 5a is a top plan view of a third type of furnace in accordance with the invention; Figure 5b is a side elevation of the furnace of Figure 5a; -Figure 6a is an end tiew of a reflector and lamp mounting assembly; Figure 6b is a side elevation of the assembly of Figure 6a; Figure 6c is a lateral cross-section through the lamp and reflector assembly of Figures 6a and 6b, taken on the line B-B of Figure 6d; Figure 6d is a top plan view of the lamp and reflector assembly of Figures 6a and 6b; and Figure 7 is a schematic view of a power circuit suitable for use with a furnace having lamp and reflector assemblies of the kind shown in Figure 6. Referring to Figures 1 and 2, the furnace illustrated comprises a body in two halves, which are substantially "mirror images" of one another, each half comprising a pair of lamp and reflector assemblies 2, 4, which fit together so that the reflectors 6 of each half face towards one another when the two halves are assembled together. Thus it will be appreciated from a consideration of Figure 1, that the operative "centre" of the furnace is in the region to the right of this figure, and it is surrounded by a square "water jacket" 8, through which water is pumped while the furnace is operational in order to prevent heat from escaping into the surroundings. Each reflector assembly is pivoted about a transverse axis 10, near its front end, so that the angle of incidence of the radiant heat on the article to be heated, can be adjusted. In addition, the reflector assembly is slidable along its axis, as indicated by the arrow X, so that the distance from the lamp to the heated article, can also be adjusted. Wing nuts 12, Figure 2, enable the reflector assemblies to be fixed in their adjusted positions. An air cooled window assembly 14 is also arranged between the two reflector assemblies 2, 4 with a viewing telescope 16 mounted between them, on an adjustable mounting, so that the article under test can be observed. As will be clear from the elevational view of Figure 2, when two substantially "mirror image" furnace halves as shown in Figures 1 and 2 are brought together, the article is substantially surrounded by the heater assemblies so that it can be evenly heated from all sides. It will of course be appreciated that the other half of the assembly, which is not shown in Figures l and 2 , will normally duplicate the water cooling shield 8 and possibly also the telescope assembly 16. Figure 3a illustrates a "elongate bowl shape" reflector profile, designed to produce a uniform heat output, and which may be used with a lamp of the linear "double ended" type as shown in Figure 3b, or, in slightly more refined configuration, with a multiple lamp array as illustrated in Figure 3c or Figure 3d. As can be seen from these drawings, it is possible, particularly with the use of a carefully shaped reflector, to arrange three or more lamps or light sources in various different relative orientations, to achieve a suitable spread of heat output relative to the front aperture of the reflector assembly. Figures 4a and 4b illustrate the arrangement of a furnace assembly particularly intended to utilise heat source arrangements of this kind. As shown in Figure 4a, the basic arrangement of the furnace body is similar to that of Figure 1, and includes two body "halves" 20, which can be brought together to enclose the article to be heated, each of which carries a pair of reflector assemblies 22, which are so mounted that the four reflector assemblies completely surround the article to be heated, each being arranged at 90° to the two adjacent assemblies. As illustrated in Figure 4b, each end of each reflector assembly is also pivo ally and slidably mounted in a radially extending slot so that the distance between each heating element and the article being heated, as well as the angle of the incident heating beam, can be adjusted, to suit objects of different shapes and sizes. Figures 5a and 5b illustrate an arrangement which is generally similar, but in which the reflector units are mounted vertically, when the article being heated needs to be arranged in a vertical orientation for testing purposes (e.g. to assess the "creep" characteristics of the material) . In this case, as illustrated in Figure 5a, the four reflector units 30 are mounted with their axes vertical (so that the ends are seen in Figure 5a, which is a plan view) , and mate closely together around the sample. However, as illustrated in Figure 5b, a slot 32 may be provided between the adjacent edges of two of the reflectors, to allow for making extensometry measurements. Figure 6a to 6d illustrate the arrangement of a preferred type of reflector unit constructed in accordance with the invention. The reflector unit shown has been milled from a rectangular block of aluminium (using a "CAOCAM" machine) so as to form a rather complex "boat shaped" cut out 36, whose axial plane of symmetry coincides with the diagonal plane 38 through the aluminium block. As will be seen from Figure 6b, the cut out has a "re-entrant" shape, so that the ends 40 of the opening 42 of the reflector, overhang the ends of the interior of the reflector. The external shape of the reflector body is such that it is particularly adapted to the type of arrangement indicated in Figure 4a or 5a in which the article being heated is substantially enclosed by the reflector bodies. As can be seen from Figure 6b and 6c in particular, a lamp base housing 44 connected to the back of the reflector body houses three "single ended" quartz halogen lamps 46, 48, and 50, and the curvature of the internal surface of the reflector is such that the distribution of radiation at the mouth of the reflector is substantially linear, between the two ends 40 of the opening. As can be seen from Figure 6c, water cooling channel 52 are drilled through the parts of the block forming the sides of the reflector, parallel to its longitudinal axis, and these channels are interconnected by manifolds 54 at each end of the body. In this way the necessity for a separate water cooling jacket may be avoided. A quartz window 100 may be provided to cover the front aperture of the reflector. Figure 7 illustrates a typical control circuit for the furnace apparatus. The interior of the furnace 60 is monitored by a temperature sensor 62 suitably positioned to detect the heat output of the three quartz halogen lamps 46, 48, 50. A water flow sensor 64 is arranged to detect the flow of water through the cooling channels 52 through the body of each reflector assembly. The output from the two sensors is supplied to a PID controller 66, which produces control signals on the line 68 for respective thyristors 70, 72 and 74 powering the three lamps at a suitable voltage to maximise their output in the IR region. A power supply 76 (which may be single or three- phase) supplies power via a line 78 to the controller and associated alarms, which are triggered if the temperature moves outside a specified range, or if the water supply is interrupted (for example) and also supplies power to the thyristors, via respective li iters 80, 82 and 84. It will of course be appreciated that more than three heating "zones" may be provided by incorporating more lamps and associated control circuitry.

Claims: CLAIMS (1) A radiant heating furnace comprising a housing which is split into at least two parts which are movably mounted so that they can be brought together to enclose a specimen to be heated, each part including at least one substantially linearly extending radiant heat source, so that the sample can be heated uniformly, at least on two opposite sides. (2) A furnace according to claim 1 in which the heat source comprises a heating element assembly including a plurality of lamps such as quartz halogen lamps, which are powered so as to emit a substantial part of their energy in the infra-red region, and which are arranged along the inside of a generally elongate, bowl shaped reflector, whose internal surface is shaped so as to compensate for the distribution of the heat source elements. (3) A furnace according to claim 2 further comprising control means for controlling the supply of energy to the lamps so as to vary the distribution of energy in different regions of the furnace. (4) A furnace according to claim 2 in which the lamps are arranged in a line along the reflector, and in which the ends of the "bowl shape" are deeply curved in a "re-entrant" shape, so as to compensate for the "fall-off" in output at each end of the linear array of lamps, and so that the maximum concentration of heat occurs at or near the front opening of the reflector. (5) A furnace according to claim 1 including a single "linear" lamp mounted in an elongate bowl shaped reflector which is suitably curved at each end, to compensate for the less even distribution of energy in that region of the lamp. (6) A furnace according to any preceding claim in which the housing comprises two halves which are pivotally mounted on support means so that they can be pivoted into engagement to enclose an article to be heated, each half carrying a pair of adjustably mounted heating element assemblies which are directed towards the centre of the furnace, the heating element assemblies being so arranged, relative to one another, that when the furnace is enclosed around the article they substantially surround it. (7) A furnace according to any of claims 1 to 5 in which the housing comprises four axially extending heating element assemblies each of which comprises one quadrant of a lateral cross section through the furnace, relative to the heating axis, and is provided with a slidable mounting which allows its position to be adjusted at least in a radial direction, and preferably also in a circumferential direction relative to the axis. (8) A furnace according to claim 6 or claim 7 in which the heating element assemblies are so shaped and arranged that they cooperate to substantially enclose the article being heated when the housing is closed, and concentrate the radiant heat output at an adjustable focus in the central region. (9) A furnace according to any of claims 6 to 8 in which each heating element assembly comprises a metal body which is machined to form the required reflector shape and also to form internal channels for the circulation of fluid coolant so that a separate cooling jacket is not required.

Inventors: BUSHBY ANDREW JOHN, BUSHBY, ANDREW, JOHN
Applicants: BUSHBY ANDREW JOHN, QUEEN MARY & WESTFIELD COLLEGE
Application year: 1993
Main classification: F27B17
IPC codes: C30B13, F26B23, F27B17, F27D11, H05B3