HEAT RETAINING MEANS

Abstract: The invention relates to screens for limiting heat losses from heated material, e.g. bars and slabs in rolling mills. Screens (20) are provided in the form of strings of heat insulating bodies composed of metal shells (32) containing insulating material (40). These screens may form curtains and/or covers (24) for the hot material. Containing chambers for the hot material may be provided with such strings of elements and the chambers may also comprise means for limiting heat conduction losses through the material sup­ ports therein. The screens may be collapsed over the hot material thereby completely surrounding and insulating the material from loss of heat. A displaceable chamber installa­ tion is also described for limiting heat loss when holding and transferring hot material between processing stages.

Description: This invention relates to the provision of means for and a method of reducing heat losses when handling hot material. It is particularly concerned with such means and methods of reducing heat loss from material continuous casting plant and in hot-rolling mills, e.g. from metal slabs and sections, continuous casting plant but is applicable to other installations and not only in metal processing industries. The use of heat-reflecting panels to reduce heat loss is known, but such panels have limitations, particularly in their use as upper and side boundaries of an enclosure. It is known that the efficiency of heat insulation falls as the space between the hot material and the enclosure walls increases, but in most practical applications a rolling mill is required to deal with a large range of sizes of material so that there is an inevitable loss of efficiency when handling sections smaller than the largest for which the installation is designed. Efficient heat-insulating panels, such as are described in GB-A-1 603 428, are relatively fragile and protective measures need to be taken if they are to be disposed close to the path of the material in a hot rolling mill. The additional cost and complication of these measures are only justified by the fact that damage to the hot faces of the panels can result in considerable financial loss having regard to the operating costs of modern hot-rolling mills. The known panels have been used to form tunnel-like enclosures along the material path through the rolling mill, the heat losses at the ends of the tunnel being unimportant if the path is occupied by moving material for most of the time. They would be less effective if they were to be used to limit heat losses from a static slab or billet near one or both ends of the enclosure, when losses through those ends will be significant. According to one aspect of the present invention, there is provided a heat-insulating screen for reducing the heat loss from a mass of hot material, such as a metal slab or bar, said screen comprising flexible strings of dependent elements, said elements comprising hollow, preferably metallic, bodies containing heat-insulating material, the screen being composed of a plurality of layers each comprising a series of strings of elements in laterally spaced relation, the strings of succeeding layers being placed in laterally staggered relation, to form a heat insulating curtain or covering for the material. Such screens have particular application to the insulation of partly worked metal products such as slabs or bars, but there are also useful applications outside the metal-working industry, eg. in glass and ceramics manufacture, for heat-insulating means of this form. A screen according to the invention may form part of a primary enclosure, eg. around a machine such as a forging press, or it may form a supplementary means of heat insulation within an enclosed chamber. According to another aspect of the invention, therefore, there is provided a heat insulating enclosure for a mass of hot material resting on support means, having above the support means in an arrangement extending both longitudinally and transversely over the support means, heat insulating means in the form of elements carried by a top cover of the enclosure and hanging at different levels below the cover to form a screen within the interior of the enclosure reducing the free space therein, said elements providing a covering for at least an upper surface of the hot material, the elements depending freely from said cover so as to permit relative displacement between the elements and the cover. While the use of a screen of said elements in an enclosure is able to reduce the problems described above, there may be other applications in which the elements can be utilized without being connected in strings, or where strings of elements can be used without a surrounding enclosure, and such possibilities are also within the scope of the present invention. To close off the end of an enclosure, a series of strings of elements can be hung from the upper edge of the end opening, the numbers of said elements in said strings and their dispositions being such that they at least substantially close off any direct heat radiation from the interior of the enclosure but are able to be freely swept aside by the material entering or leaving the enclosure, since they are freely suspended. For the connection of the elements into strings and their suspension, flexible means may be used in the form of temperature-resistant metal wires, cables or chains each of which has a number of said elements at spaced intervals along its length. A preferred form of heat insulating element, according to a further aspect of the invention, has a hollow body comprising a thin-walled metal shell provided with a heat-insulating filling and with at least one outwardly projecting fin, the element being arranged to be connectable with similar elements in a string of elements for use as a suspended heat insulating means. The invention will be described in more detail by way of example with reference to the accompanying diagrammatic drawings, in which: Fig. 1 is a transverse sectional view of a roll stand approach table provided with heat-insulating means in accordance with the invention, Figs. 2 to 8 illustrate examples of the construction of strings of heat-insulating elements according to the invention, Figs. 9 and 10 are side and end views respectively of a heat-insulating enclosure according to the invention, Fig. 11 illustrates a mode of operation of the enclosure of Figs. 9 and 10. Figs. 12 and 13 illustrate modifications of a heat-insulating enclosure within the scope of the invention, and Fig. 14 illustrates another form of heat-insulating enclosure according to the invention. Fig. 1 illustrates a roughing mill approach table in which a base structure 2 supports a roller table 4. The roller table is provided with heat-insulating panels 6 in the gaps between successive parallel rollers. Side insulating panels 8 are also present, with bumper bars 9 or the like protecting them from impact by material passing along the table, and there is an insulating hood or cover 10 which has sides 12 overlapping the side panels. The cover is mounted on side supports 14 through hydraulic jacks (not shown) that can move the cover between the raised position shown in full lines and the broken-line lowered position indicated by reference 10a. The table 4 may be required to hold hot steel billets of varying sizes (projected maximum and minimum cross-sections are indicated at Sg and Sm) for varying periods before they are passed through the roughing rolls. Suspended from the inner face of the cover and over an area somewhat larger than the plan area of the largest billet Sg, are strings 20 of elements 22 forming a heat-retaining screen 24 over the hot material. These elements are arranged so as not to impede the movement of the billet onto and off the table when the cover is raised, but surround the billet on the table closely when the cover is lowered. At the entry and exit ends (not shown) of the table the heat-insulating enclosures may be complemented by further rigid panels displaceable to give free passage for billets to and from the table, or the strings of elements in the entry and exit region may be extended to depend to the level of the table or below to form curtains in front of or behind the billet. It is, of course, possible to provide both these means of insulation at the ends of the table: in general the provision of a walled enclosure around the top, sides and ends of the hot material in addition to any strings of heat-insulating elements has the advantage that convection heat loss through the screen can be minimized. The heat-insulating elements 22 are made-up of thin-walled bodies filled with a high-grade insulation, e.g. of ceramic fibre. These bodies are threaded onto braided temperature-resistant metal cables or chains to form the strings and the groups of strings together make up the moveable or flexible screen or covering closely surrounding the hot material. Fig. 2 illustrates such bodies 30 formed from two hemispherical shells 32, joined alternatively by swaging 34, welded flanges 36 or spot-welded or riveted overlapping rims 38, filled with a pre-compressed ceramic fibre packing 40. The bodies have top and bottom apertures 42 for the suspension cable 44. The string of elements can be formed on a continuous length of cable 44a, with separating beads 46 between the bodies. Alternatively, the elements can be individually connected to each other, preferably releasably. In one example, the lower end of the cable is formed with a support spiral bend 48 and the upper end is formed with an eye 50 for attachment to the cable of the next element. In another example the lower end of the cable has a swaged portion 52 to hold a washer 54 on which the element rests and an eye 56 is formed below the swaged portion to attach the cable of the next element. The outer shells must be formed from a material with suitable resistance to high temperatures, but the upper surfaces of the bodies which are largely shielded from direct heat radiation from the hot material can be of a lower grade alloy. In the example of Fig. 4 the conical upper shell half 58 is made of a lower grade alloy than the hemispherical lower shell half 60. The lowermost one or more of a string of elements can contain a solid metal mass 61 which helps to keep the string 20 at its maximum possible extension and also acts as a thermal store. It is also possible to provide inner walls or membranes 62 within the external shell. Fig. 6 illustrates strings 20 composed of barrel-shaped elements 63, while Figs. 7 and 7a illustrate a particularly simple design of element with four-sided of tetrahedral bodies 64 that can be produced from a continuous length of tubing, connected together by rings 65. Figs. 8 and 8a illustrate a further modified configuration being a development of the spherical elements illustrated in Fig. 2. It had been found that for the most effective insulation against thermal radiation, the elements should collapse closely against each other when they hang freely and form a screen of several layers. By forming each element as an insulating body with projecting metal fins, this condition can be fulfilled and a given standard of thermal insulation can be obtained with the use of fewer elements. Also, rectangular metal blanks can be used, thereby reducing wastage to make better use of the metal from which the elements are formed. In the example of Figs. 8 and 8a, square sheet metal blanks have hemispheres pressed in them and each element 66 is formed by a pair of pressed blanks placed back to back, the hemispherical depressions providing a hollow sphere 67 that is filled with insulating material, as already described, and the two parts being secured together at their margins, e.g. by spot welding, which form rectangular fins 68. A ceramic fibre paper 40a may be sandwiched between the margins of the two parts forming the fins so that the fins themselves have heat-insulating properties; in this form, instead of spot welding the two parts are secured together and the ceramic fibre enclosed by bending the edges of the fins one over the other to form a clinched seal. Each element has holes drilled in diagonally opposite corners so that heat-resistant connecting rings 69 can connect adjacent elements to form the vertical strings. By forming a multiple layer screen in which the strings of succeeding layers are placed behind each other in laterally staggered relation, as is indicated in Figs. 8 and 8a, it is possible with as few as two layers to form a screen that substantially stops direct radiation loss from a workpiece. Additional layers can be provided to give the desired insulating properties. It is of course possible to provide such elements with other than spherical insulating portions, but generally parallelogramic sheet metal blanks will be preferred to get the maximum use from the material without wastage. It is to be understood, however, that individual features of the heat-insulating elements described can be adapted interchangeably, so that for example the tetrahedral bodies of Figs. 7 and 7a and the finned spherical bodies of Figs. 8 and 8a can be formed with the different upper and lower shell materials described with reference to Fig. 4. Figs. 9 and 10 illustrate an enclosure analogous to that already described with reference to Fig. 1 in that a cover or hood 70 with end walls 72 and heat-insulating strings 20 suspended from its internal top face is mounted over a roller table 4 to enclose a slab S of hot material on the rollers. The drawing shows the cover suspended from overhead rails 74 through a carrier 76, so that jacks 78 between the cover and the carrier can move the cover upwards when a hot slab is to enter or leave the roller table 4, and then lower it so that the elements on the strings completely surround and insulate the slab against heat loss. The cover and carrier can move as a unit on the rails 74 longitudinally of the roller table so that the material can be protected from heat loss as it moves along the roller table. Fig. 9 also shows a probe 80 fixed to the cover which contacts the slab to limit the downwards movement of the cover: it can be arranged that the frictional force between the probe and the slab is sufficient to ensure that the cover and slab move together along the roller table. If the hot material is to be held on the roller table for some minutes it is necessary to move it to and fro on the rollers. If the strings 20 are sufficiently long, it may be possible for them to be swayed to and fro by their contacts with the slab, as is indicated in Fig. 11, without increasing in any significant way the heat loss. Alternatively, the cover as already described with reference to Figs. 9 and 10 can be arranged to oscillate in synchronism with the slab, whether by entrainment through the probe 80 or by a positive drive as is exemplified in Fig. 12. Fig. 12 illustrates a drive chain or belt 82 from the roller table 4 to a clutch 84 which can transmit the drive to a rack and pinion mechanism 86 the rack of which is mounted on the cover. The clutch is disengaged while the roller table is operating in its normal through-pass mode but is engaged by an automatic interlock (not shown) when the table is in a hold mode so that the material and the cover will then oscillate together. The interlock with the roller table drive can also be used to ensure that the cover can only be lowered (as by the means shown in Fig. 10, for example) when the roller table hold mode has been selected. By way of further illustration of possible modifications, Fig. 12 shows a top cover or hood 88 that relies wholly on the screens formed by the strings of elements to enclose the edges of the hot material, and as there are no rigid heat-insulating entry and exit panels, the cover is mounted directly on the rails 76, being fixed in position other than for the oscillatory movement it can be given. The arrangement illustrated schematically in Fig. 13 is generally similar to that in Fig. 10 but there is shown one of a number of insulated beams 90 that can lift the hot material from the rollers and into the strings 20 of insulating elements. It wil be noted that this measure can be employed either with or without the raising and lowering of the cover 70. The provision of strings of insulating elements within an insulated enclosure can minimise a problem that occurs with particular sections of material, such as thick slabs. To explain this point further, whereas the heat loss from a thin bar will be mainly from the upper and lower surfaces, as the thickness increases the heat losses from the edges of the bar become more significant and they can produce undesirable temperature gradients. The strings of insulating elements act as a passive insulating system which is inexpensive to produce and install as compared with the known methods of using oxy-fuel burners or indication heaters to prevent a metal slab developing "cold" edges. The strings can be packed relatively densely and still be freely displaceable to allow a slab to pass through the screens of elements which simply reform when the slab has passed through them. The close proximity of the elements, which may or may not be in direct contact with the slabs results in the metal outer shells of the elements re-radiating heat as they quickly rise to a temperature close to that of the slab and the heat interchange between the adjacent surface of the slab and the elements is then substantially less than if the slab were allowed to radiate freely to the internal walls of the chamber. To perform their function for protecting the edges and ends of a slab, strings of elements would be confined to the peripheral regions of a chamber, forming a screen beyond the edges of the hot body and a covering for the marginal regions of the body adjacent to the edges. It has already been mentioned that it is also possible to deploy them as a complete covering (contacting or non-contacting) for the whole upper surface of a hot body. This function might be employed to reduce the heat loss for irregularly shaped bars or billets and it is not necessary for the material to be located in an enclosed chamber. The strings of elements may be arranged to be raised and lowered, as by the jacks 78 shown in Fig. 13, so that in the event of a stoppage they could rest on the material and form a contacting covering that conforms to its shape. Where the material is being held on a roller table it is preferably arranged that in the event of a prolonged delay the material can be lifted from the rollers by lifting means as already described. For such arrangements as these, an interlocked control system may be provided so that the insulating screen or covering cannot be lowered unless the rollers are stationary and the rollers cannot be restarted until the screen is lifted. Fig. 14 shows an insulating enclosure according to the invention on an existing roller table 190, of which side rails 192 are also shown. The enclosure comprises a top cover or hood 194 composed of heat-insulating panels 196, and sloping side shields 198 that project beyond the rails 192. Suspended from substantially the entire inner face of the top cover panels are strings 20 of heat-insulating elements, eg. of the form described with reference to Figs. 8 and 8a, to cover and curtain hot material S on the roller table. Lifting means (not shown) with insulating panels may be provided to lift the material from the roller table to the raised position S' indicated in broken lines. In the outer lateral regions of the screen, the strings of elements are attached at one end to the top cover to hang vertically when they are free of the table and the hot material. In the main central region the strings are supported from both ends to hang in catenaries 20a that extend laterally over this region. For clearer illustration only a few strings are shown but the elements are packed as closely as is permitted by the freedom of movement required of them, to completely curtain the ends of the enclosure as well as to cover the material within it, and if the elements are finned they will be suspended in such a way that the fins contribute to the screening effect. Fixed to the top cover 194 are suspension lugs 202 through which it is mounted from the series of cantilever beams 204 spaced along its length and supported on pillars 206 with counterweights 208 on their ends projecting past the pillars. Jacks 210 between the beams and the pillars can pivot the beams to a maximum lifted position illustrated by the phantom line 204a and so lift the top cover to the uppermost position 194a. A link arm 212 extends parallel to each beam and is pivoted at its ends to the corresponding lug 202 and pillar 206 at centres with the same spacing as the pivot centres of the beam. As the beams pivot upwards and downwards, therefore, the link arms 212 maintain the top cover horizontal. When the top cover is lowered, guide plates 214 mounted on the table side rails 192 guide the outermost strings of insulating elements 200 so that they are grouped closely around the edges of the material of the table. The figure shows the top cover in a normal lowered position in which the side shields 198 on the top cover have slightly overlapped the vertical extent of the guide plates 214. It is possible to lower the top cover further to a position in which the guide plates and side shields abut, as is shown in broken lines. It will be understood without further illustration that many of the individual features described can be employed interchangeably in other embodiments than those in which they are shown.

Claims: A heat insulating screen for reducing the heat loss from a mass of hot material, such as a metal slab or bar, said screen comprising flexible strings (20) of dependent elements (22), characterised in that said elements comprise hollow bodies (30) containing heat insulating material (40), the screen being composed of a plurality of layers each comprising a series of strings of elements (67) in laterally spaced relation, the strings of succeeding layers being placed in laterally staggered relation, to form a heat insulating curtain or covering (24) for the material. A screen according to claim 1 wherein the strings comprise flexible means (44) in the form of temperature-resistant metal wires, cables or chains each of which carries a number of said elements (22) along its length. A screen according to claim 1 wherein the elements (30) of each string are releasably attached to each other in series. A screen according to any one of the preceding claims wherein at least one of the strings is suspended from both ends to hang in a catenary (20a). A screen according to claim 4 wherein strings in laterally outer regions depend vertically on each side of a central region of the screen comprising strings depending in catenaries A screen according to any one of the preceding claims wherein at least some of said elements are provided with at least one outwardly projecting fin. A screen according to claim 6 wherein said projecting fins are each composed of a heat insulating layer between outer metal walls. A screen according to any one of the preceding claims wherein the hollow bodies of at least some of the elements have a substantially tetrahedral form. A screen according to any one of the preceding claims wherein at least some of the hollow bodies are formed from generally parallelogramic sheet metal blanks. A screen according to any one of the preceding claims wherein there is at least one internal membrane (62) within at least some of the hollow bodies. A screen according to any one of the preceding claims wherein one or more of said strings of elements have the lowermost element supported by further elements of its string of elements and having a weighting mass (61) within its hollow body. A heat insulating enclosure for a mass of hot material resting on support means (4), having heat insulating means (10,20) above the support means in an arrangement extending both longitudinally and transversely over the support means, and characterised in that the heat insulating means comprise heat insulating elements (22) carried by a top cover (10 or 70) of the enclosure and hanging at different levels below the cover to form a screen (24) within the interior of the enclosure reducing the free space therein, and providing a covering for at least an upper surface of the hot material, the elements (22) depending freely from said cover so as to permit relative displacement between the elements and the cover. An enclosure according to claim 12 wherein said elements also form a curtain in the region of an end boundary or margin of the interior space of the enclosure. An enclosure according to claim 12 or claim 13 wherein the covering screen lies between opposite end curtaining screens that depend below the level of the covering screen. An enclosure according to claim 14 wherein said curtaining screens depend substantially to the level of a bottom wall or boundary of the enclosure. An enclosure according to claim 14 or claim 15 wherein said covering screen comprises a series of strings of elements depending from the cover in catenaries (20a) and said curtaining screens comprise a series of strings of elements depending vertically. An enclosure according to any one of claims 12 to 16 wherein the cover (10) is upwardly displaceable from a lowered or heat shielding position to facilitate the passage of the hot material past said screen or screens to and/or from the material support means. An enclosure according to claims 12 to 17 comprising means for moving said material relative to said support means (4) therefor and for moving the cover (70) synchronously with the material. An enclosure according to any one of claims 12 to 18 comprising a driven roller table (4) and control means (79) for raising and lowering the cover cooperating with the roller drive such that the roller drive cannot be engaged to pass the hot material along the table when the cover is being lowered. An enclosure according to any one of claims 12 to 19 wherein the cover (194) has a cantilever mounting (204, 206) for upward and downward displacement of the cover with its screen or screens. An enclosure according to claim 20 wherein the cantilever mounting comprises means (212) for maintaining the cover substantially horizontal in said displacement. An enclosure according to any one of claims 12 to 21 comprising side guides (214) that slope downwardly and inwardly to provide guide faces for heat insulating elements (22) in laterally outer regions of the enclosure.

Inventors: LAWS, WILLIAM R., REED, GEOFFREY R.
Applicants: ENCOMECH ENGINEERING SERVICES LIMITED
Application year: 1985
Main classification: B21B37
IPC codes: F16L59, C21D1, F27D3, F27D5, C21D9, B21B39, F27D1, B22D11, B21B45