OBSERVATION OF FURNACE INTERIORS

Abstract: This invention provides a method of observing the interior of a furnace by viewing, at a remote location, the image depicted by a pinhole camera sited in or within the furnace housing. The image may be real and viewed directly or via a reflective or fibre optic transmission system, or alternatively a video camera may be employed, in this instance the 'screen' of the camera may be constituted by light responsive elements, e.g. charge coupled devices. The camera may typically be sited in the furnace wall or roof and a pressurised blast of air or an inert gas, e.g. nitrogen or argon, may be employed for maintaining the integrity of the pinhole.

Description: This invention relates to the observation of furnace interiors, eg. iron and steelmaking (melting) or steel processing furnaces. Observation of the interior of a furnace is of inestimable value in determining process parameters and the condition of the charge within the furnace, and the furnace structure itself. However, the use of conventional cameras utilising a lens is virtually impossible by reason of the hostile environment encountered; it is an object of this invention therefore to provide an improved method and apparatus for such an observation. Cameras with small open apertures have been used, as for example in in patent specification US-A-4112763. From one aspect the invention provides a method of observing the interior of a furnace through a restricted opening in which the restricted opening is an optically active pinhole (pinhole camera) and the image created thereby is viewed remotely. The image may be viewed via a reflective or fibre optic transmission system or alternatively a camera responsive to defined frequency spectra such as a video camera may be employed and the screen of the camera may be constituted by light responsive elements such as charge-coupled devices. The invention also provides apparatus for observing the interior of a furnace by a pinhole camera sited in or within the furnace housing whose image is reproduced for viewing at a remote location. The camera may be sited in the furnace wall or roof, or blast furnace raceway etc. or alternatively it may be sited in a projectable boom or even in an interiorly disposed furnace component, e.g. a non-consumable electrode in an arc furnace. The whole apparatus may be water-cooled and a pressurised blast of air or an inert gas, e.g. nitrogen or argon, may be employed for maintaining the integrity of the pinhole. In order that the invention may be fully understood one embodiment therefore will now be described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a sectional side elevation through the pinhole camera/video camera housing and mounting; Figure 2 is a plan view of one component of the pinhole 'plate'; Figure 2A is a section on A - A in Figure 2; Figure 3 is a plan view of another component of the pinhole plate; Figure 3A is a section on B - B in Figure 3; and Figure 4 is a sectional side elevation of the composite plate. Referring now to the drawings the mounting 1 for the camera is sited in and extends through, say, the water-cooled or refractory lined roof of a furnace, e.g. a ladle furnace for treating molten steel. In particular, a cup-shaped housing 2 for an optical or video camera (not shown) having an acrylic window 3 is sealed and fastened within an upper part 4 of the mounting, the lower part 5 of which defines a baffled cavity 6 through which water is channelled via inlet port 7 and outlet port 8. This part 5 has a centrally disposed tapered cavity 9 and sited between the inner side of this part and the housing 2 is a composite plate 10 which has a central pinhole aperture 11 exposed to view by the cavity 9. The space defined between the housing 2 and the lower part 5, defines a passage for, e.g. filtered compressed air injected through an inlet port 12 and which exits through the pinhole aperture 11. The mounting 1 is itself sealed by a dust cover 13 to protect the video camera and the whole unit is enveloped by a radiation shield and protective cover 14 sited on the furnace roof. The pinhole plate 10 is shown in more detail in Figures 2 to 4. More particularly, this comprises two components. One, shown in Figure 2, embodies a circular-section recess 15 from which extends a wide tapered bore 16. A number of channels 17 extent into the recess 15 substantially tangentially thereof. The other component, shown in Figure 3, has a central tapered cavity 18 defining at its extremity the 'pinhole' 11 and a number of radially disposed channels 19 extend into the cavity 18. The diameter of the pinhole aperture may typically be between 0.15 mm and say 0.5 mm. The two components are assembled together as shown in Figure 4. In operation, the water cooling jacket ensures that the structure can withstand the elevated temperature of the furnace and the air flow through the pinhole aperture (downwardly through the space between the head of the plate 10 and the acrylic window 3) and the tangential flow through channels 17 and radial flow through channels 19 ensures that the pinhole aperture is maintained free from debris thrown up within the furnace which might otherwise obscure it. In the illustration shown the centre line of the pinhole aperture at the centre line of the video camera are offset from one another giving an effective viewing axis of about 10° away from the wall of the furnace - which in this example is considered to be on the right hand side of Figure 1 - to give a more informative view. It is understood that the embodiment shown in just one example of the invention and that various modifications may be made without departing form the scope of this invention. For example, as mentioned the provision of a video camera within the site of the pinhole housing itself is not essential, the image could be depicted on e.g. a ground glass screen at this side and viewed remotely. Further historical diagnosis may be effected by utilising a camera/recorder system. Image enhancement facilities may also be utilised and of course the camera may respond to wavelengths outside the visible spectrum, particularly infra red for thermal imaging. The design of the pinhole plate may also be different from that shown consistent with maintaining its integrity. Moreover, although air may be the favoured gaseous medium, should combustion or oxidation problems occur then, for example, argon or nitrogen may be used. The gas pressure may likewise vary depending upon the furnace activity; it will need to be higher in an aggressive environment such as a melting furnace than a more passive environment met in, say, a soaking pit. More than on camera may be sited in, or within, the furnace housing so that an observer may be presented with a more comprehensive series of pictures.

Claims: A method of observing through a restricted opening the interior of a furnace characterised in that the restricted opening is an optically active pinhole (pinhole camera) and the image created thereby is viewed remotely. A method according to claim 1, characterised in that the image is real and is viewed directly or via a reflective or fibre optic transmission system. A method according to claim 1 characterised in that the image energises elements in the camera responsive to defined frequency spectra, and the image is reproduced at said remote location through electrical signal transmission. Apparatus for observing the interior of a furnace characterised in that a pinhole camera is sited in or within the furnace housing whose image is reproduced for viewing at a remote location. Apparatus according to claim 4, characterised in that the said means incorporates elements in the camera responsive to defined frequency spectra and an electrical signal transmission system for reproducing said image at the remote location. Apparatus according to claim 5, characterised in that the camera comprises an inner housing having a sealed aperture aligned with an open aperture in an outer housing, and a plate disposed between said apertures in which the pinhole is defined and through which extend rays emanating from the furnace. Apparatus according to claim 6, characterised in that the plate embodies a number of channels through which in use gas jets are transmitted to describe flow paths conducive to a cleansing action such that the pinhole is cleansed by said gas jets. Apparatus according to claim 7 characterised in that the plate comprises two parts, one embodying a conical cavity terminating in the pinhole with channels extending radially from the cavity, and another embodying channels extending tangentially from the periphery of a circular-section recess coaxial with said cavity. Apparatus according to any one of claims 6 to 8, characterised in that the inner housing aperture is sealed by a transparent medium, the said rays lying in the visible spectrum and the said elements being light responsive.

Inventors: DAWSON, DAVID IAN
Applicants: BRITISH STEEL PLC
Application year: 1989
Main classification: C21C5
IPC codes: C21B7, G02B27, C21C5, G03B19, G02B23, F27D21