The invention relates to a cover or lid for a hear chamber, and more particularly to such a cover having or. its inner side a lining of ceramic ibres. This lining iε made from individual lengths, modules or bodies of ceramic fibre, eg, blankets which are held to the underside of the cover. Covers including such linings are disclose.:, fcr example, in EP-A-170622. For convenience the word cover will b used tc describe covers, lids or the like.

It is known to locate such a cover on top of a soaking pit at a steelmill, to contain heat therein. Unfortunately, the ceramic fibre lining does not last, and it is rare for such a lining to last more than one month before it needs to be replaced by another ceramic fibre lining. It has been considered that at the high temperatures in the pit, the fibres undergo a chemical change and it is this which shortens their life.

We have studied the reasons for the short life of the lining and have discovered that there are two causes. The first is

is that in the pas. the assembly cf modules of the lining has been poor; once heat penetrates the thickness cf the lining it will deteriorate. To avoid this risk it is necessary to assemble the fibre bodies so that there are no gaps in between, both when the lining is first made and when it is first exposed to the heat and so undergoes shrinkage. Second, and more importantly, no-one has in the past taken any account of the fact that when the lining is crushed cr compressed, the lining is quickly destroyed. Our research suggests tha~ when the lining is crushed, the heat is able to quickly destroy it.

Accordingly, it is one object of this invention to provide a cover having a ceramic fibre lining and which will have a long life.

According to one aspect of the invention there is provided a method of heat insulating the opening of a heat chamber, the opening including a peripheral wall, the method comprising applying a cover to the opening, the cover having an inside lining of ceramic fibre arranged in use to contact the peripheral wall and including the step of maintaining the cover in contact with the opening under a load which is sufficient to form a seal with the wall but not sufficient to cause the lininσ to be crushed.

The invention may be applied tc a heat chamber having ar. opening in any wall. Typically, however, the opening will be in the top (as in the case of a soaking pit) and in this instance the cover is lowered on to the soaking pi- and the lining is engaged with the perimeter thereof, and a weight is applied to the cover so as to subject the lining to a predetermined pressure.

Preferably the mass cf the weigh- is selected relative tc the weight of the cover and the lining so that the pressure on the lining is substantially less than that which will cause the fibres tc be crushed, and is sufficient tc allow the cover to rise in the event of an excess of gas pressure within the chamber, and to return the cover back into contact with the perimeter when the excess pressure has been relieved.

In another aspect of the invention, there is provided apparatus for use in heat insulating the opening of a heat chamber, the opening including a peripheral wall, the apparatus comprising a cover dimensioned to overlie the opening, the cover having an inside lining of ceramic fibre arranged in use to contact the peripheral wall, and means arranged to apply the cover to the opening under a load which is selected so that the lininσ in contact w; - ^~ r. the

wall is subjected to a predetermined pressure sufficient t ^~ form a seal with the wall but no sufficient tc cause the lining to be crushed.

In yet another aspect of the invention there is provided a heat chamber including a cover.

The mass cf the weight can be calculated with reference t~ the pressure tc be applied tc the surface cf the fibre? resting on the perimeter surface cf the opening. If the weight balances the total weight of the cover and its lining then the fibres will not make an efficient heat seal, conversely if no such counter-weight is present the fibre modules will become crushed and the lining will be of littl? or no value. As far as we are aware, no-one has determined the resistance to crushing of the fibre modules in the direction of the load, and we have done this by applying dead loads to samples of fibre modules to determine how hig; a pressure can be borne before the module is crushed. We have then determined a load which will compress the fibres in the heat insulating direction, as will be indicated by the calculations below. It must be appreciated, however, that conditions in the pit (or other heat chamber) are not constant, for example, pressure will rise when heating up the air therein usinc burners and occasionallv explosions

occur. 3y selecting the load applied tc the cover lining, allowance can be made for this variable parameter sr that when such an event occurs the cover will lift off tc vent the excess gas and then will settle back. In this way, the invention provides a cover having a heat insulating seal having the heat insulating benefits of ceramic fibre but with the added benefit of pressure sensitivity.

The way in which the counterweight is applied tc t . ccver will depend on the structure of the soaking pit. If the cover travels on a carriage, then the weight (or weights may be suspended from the framework associated with the carriage, eg, using supplementary brackets. Where n: carriage is present and the cover is moved in or out cf service by means of a crane, an extra framework will be provided near the cover to receive the weight. It should be mentioned that the weight system used in this invention is not intended to raise or lower the cover during its installation or replacement but to adjust the load on the ceramic fibre lining when in contact with the perimeter of the soaking pit.

The heat chamber may be a soaking pit, furnace, oven, ladle, tundish or the like.

The lining is preferably secured tc the cover in the way described and claimed in patent application G3S6,18S52 dated August 1, 1986 (Agent's Ref 2365) because that lining is very well assembled.

In order that the invention may be well understood it will now be described by way of example with reference to the accompanying diagramatic drawings, in which

Figure 1 is a part sectional view cf one embodiment of the invention with the cover on the soaking pit -

Figure 2 is an enlarged view cf a detailed elevation of another cover.

The cover C of Figure 1 comprises an outer metal frame 1 of I-section beams and dimensioned to overlie a soaking pit of the type installed at a steelworks or mill. The pit has side walls 2 which define at the upper side a perimeter P on which the cover C can rest to form a heat insulating seal. The frame 1 has hooks or the like 4 by which it may be connected to a raising or lowering means such as a crane or it may travel on an overhead carriage 5. The frame 1 supports a mesh plate 6 (Fig 2) below which is located a layer of heat insulating ceramic fibre F. The fibre may re alu inosilicate or the like.

The layer will typically be made cf modules cf blocks c ^* fibre F, and may be secured to the plate 6 in a variety cf ways. The layer is suspended below the plate 6 by a height of perhaps 30 cm. The cover is dimensioned so that its area is relatively oversized in area compared to that of the soaking pit, so that as shown in Figure 1, when lowered the fibre layer F of the cover C forms a seal with the perimeter ? cf the pit (as shown a gasket 3 is present i between ¹ . .- cable 7 extends from the too of the frame 1 across a ε r:: 3 to a weight 9 and is arranged so that when the cover C is lowered, the weight 9 resists a fast or overshoot lowering and in use prevents undue compression cf the fibres <~ f the layer F.

As shown in Figure 2, the modules, Ml, M2 , M3 etc hang down from rods 11 so that the free edges 12 thereof rest on the perimeter P of the soaking pit S . The modules are held together in side-by-side compressed relation so that the lining is tight and there are no heat conductive gaps into the lining. This is achieved by the presence of bars 13 having slots 14 spaced apart longitudinally of the bars by a distance to determine the extent of compression of the modules Ml, M2 , M3 etc. Preferably, each module is compressed by at least 20%, preferably about 33% of its thickness. The weight 9 determines the extent cf

compression applied tc the modules in the vertical direction as shown, so that a pressure sensitive seal is formed between the cover C and the soaking pit S.

The invention is illustrated by the following examples:

EXAMPLE 1_

A soaking pit measuring ^~ .2m long and 2.6m wide was provided with a cover of the invention. The cover comprised a metal steel fabricated frame having a steel mesh platform and I - section side walls and having a ceramic lining about 2Scm deep as shown in the drawings. Above the pit was a frame for a carriage to move the cover on to and off the pit. Brackets were welded alongside the carriage and weights were hung on cables passed over the brackets and connected to the cover. The mass of the weights was calculated according to the desired pressure to be applied to the lining and in the vertical direction as follows:

Assume that the lining is to lie on a 23cm wide strip around the perimeter of the pit. The available bearing area is thus the linear length of this strip x width = 19.5C x 0.23r. = 4.49m ² .

The weight of the cover and lining is 3855Kc, giving a

_ ~ pressure on the bearing surface of 8415Nm ~. This waε determined empirically to be too high because the lining will be crushed in use.

By applying a counterweight cf 3629Kg, the lead applied t-

_ *-_ the lining is 22141: and the pressure was 4921 ^" τ ^~ ~. Thι= c= be provided by two counterweights (one at each end cf the cover of 1814KQ . Similarlv

- a counterweight of 1509Kg gives a pressure

a counterweight of 2414Kg gives a pressure 3145NπT ² .

In this way, it is impossible to determine how large a counterweight to employ which will permit the formation of a heat insulating pressure sensitive ceramic fibre seal between the cover and the soaking pit. The fibres will forrr such a seal with the perimeter of the pit and will be compressed along the modules but only to the extent necessary to form the seal and not to the e :tent that under

extra pressure, eg, gas cr heat pressure they will be crushe .

A pit waε lined with such a cover and the lining was checked regularly. After six months the lining was intact. This was determined visually by the presence or absence cf weak points at the cold face of the lining which was visible at the upper side of the cover. A number of supplementary- benefits were determined by the steel mill and aε fcllcwε:

1. Less heat was required to heat ingots, slabs cr blooms in the pit.

2. Because of the efficient heat insulation the environment waε pollution free and more congenial.

3. Because of the efficient heat insulation adjacent parts were less prone to damage (where pits are arranged in a battery close together it has been observed that heat and flames escaping from one will damage the neighbouring one) . Less maintenance was accordingly required.

It will be appreciated that conditions within a heat chamber cannot be kept constant. In the case cf a soakinc pit

furnace for example, high pressure atmosphere conditions occur during a load heat up cycle, which may be d nr.g h gh fire or maximum fuel input. The high pressure affects the life of the ceramic fibre lining, because the hot face temperature will penetrate deeper into the lining when pressure is applied to the hot face. A cover cf the invention is better able to resist such pressure and keep i ^J away from the lining. In other words, a cover cf the invention provides a pressure resistant thermal seal t- the heat chamber. In the evaluation it was observed that ar. explosion occurred within a soaking pit because of a gas pocket- the cover lifted off the pit and gently returned t~ its lowered position without any visual damage whereas when an ordinary cover is used, the lining and the support structure can be damaαed.