US2444365A - Furnace roof or arch with self-adjusting mounting for thermal expansion - Google Patents

Description

June 29, 1948.

Filed April 16, 1945 J. E. PLUCK FURNACE ROOF OR ARCH WITH SELF-ADJUSTING MOUNTING FOR THERMAL EXPANSION 2 Sheets-Sheet 1 ATTOIPA/FVJ an an June 29, 1948. J PLUCK 2,444,365

FURNACE ROOF on ARCH WITH SELF-ADJUSTING MOUNTING FOR THERMAL EXPANSION Filed April 16, 1945 2 Sheets-Sheet 2 F/ G2. F G3. L a

Patented June 29, 1948 FURNACE ROOF OR ARCH WITH SELF-AD JUSTING MOUNTING FOR THERMAL Em PAN SION John Edward Pluck, Rotherham, England Application April 16, 1945, Serial No. 588,427 In Great Britain March 23, 1944 Section 1, Public Law 690, August 8, 1946 Patent expires March 23, 1964 8 Claims. 1

This invention relates to the roofs or arches of industrial furnaces for use at high temperatures and which are built up of bricks of refractory materials such as chrome magnesite, dolomite, and magnesite.

The main object of the invention is to provide improvements to the arched roofs of such furnaces whereby the roof life is considerably increased.

Refractories made of basic materials are most desirable for the building of all parts of furnaces working on the open hearth basic steel processes, because acid refractories cause undesirable re-actions with the vapours from the bath of metal. This invention is intended to overcome, or minimise such existing difficulties as spalling, iron oxide growth, and weakness under load at high temperatures. Magnesite, chromemagnesite and dolomite expand evenly in proportion to temperature increase, and contract in proportion to temperature decrease, whereas silica (the normal roof material) possesses the property of almost completing its expansion below 600 centigrade.

It has previously been proposed to accommodate a, small degree of outside expansion and a large degree of inside expansion by employing a roof buttress which is so pivoted on fixed axes carried by the lateral vertical furnace supports that all the necessary expansion can take place whilst at the same time any change of the roof radius is also accommodated.

In the case of the present invention, also, a pivoted roof supporting buttress is employed which accommodates small external and large internal expansions, but the invention has for its object to provide an improved construction or arrangement, which is characterised b several novel features. For example the load varies increasingly from cold to hot position so as to allow for variations in thrust due to changing radius of curvature. Further the buttresses at back and front on the furnace are coupled together, and weights are employed instead of springs to resist their movement, whilst the buttresses pivot about axes or slung fulcrums which are slidable along the lateral vertical furnace supports instead of being fixed in relation to said supports.

The invention also includes various important features of construction which may be summarised as follows:

At the back of the furnace each buttress is attached to a lever to which is connected a bellcrank lever rotatable about a, fixed pivot. From the free end of the bell-crank lever a weight bar is hung on which can be placed weights totalling the previously calculated amount necessary to balance the roof thrust loads, plus a small proportion as a safety factor.

The bell-crank lever is such that the leverage of the weight varies according to the position of the roof; thus, when the roof is cold and in its high position, the roof thrust is low, and when the roof is in its hot and lowest position the roof thrust is at its highest. Therefore, the variation of the weight leverage is to accommodate such difLrences of the roof thrust, plus a fixed slight proportion in excess for safety, all of which is applied automatically. This arrangement keeps the loads and the compressive stresses in the roof at the absolute minimum for stability. The possible weakness of chrome-magnesite bricks under compressive loads at high temperature is accordingly taken care of.

In order that the roof may be able to move in the above manner and yet be kept perfectly sta- 'ble, the front roof buttresses are made to move in exactly the same way as, but opposite to, the back by a system of levers and a tie-rod. Also through the same system of levers, the weights to balance the front roof thrusts are attached to the back weight bar, leaving only the smallest amount of gear at the front of the furnace. Even if a roof is built with different levels at back and front, the movements of front and back buttresses can be of equal amounts or can be fixed at an proportion of movement at any angle.

The general arrangement is such that the main furnace front stays and back stays are not cut and thereby weakened by supporting bolt holes, but all the gear is suspended by additional members, fixed across the top cross-ties. This system of support will allow any excessive upward expansion of the back and front walls to lift the whole roof, together with the operating gear, thereby eliminating nipping forces between wall tops and roof which are liable to cause damage when the roof is fixed.

At the maximum temperature the roof buttresses will have their outer faces touching the upright furnace stays. In the case of an explosion in the furnace causing a hole in the roof, or for any other reason, which in turn causes damage to any or all of the gear, then the remaining part of the roof, providing it is kept hot, will stay in position.

In order that the invention may be clearly 3 understood and readily carried intopraotioeitis illustrated, by way of example only. by the accomm drawings. in which:

Figure l is a front to back croassectional elevation of a construction of a furnace according to the invention.

Figure 2 is a front elevation of a section of the furnace showing two adjacent buttress ends.

Figure 8 is a rear elevation of a similar section of the furnace.

Figure 4 is a horizontal section on the line IV-IV of Figure 1 at a buttress junction.

Figure 5 is a horizontal section on the line V-V of Figure 1 at a buttress junction.

Figure 6 is a horizontal section on the line VIVI of Figure 1 at a buttress junction, and

Figure 7 is a horizontal section on the line VII-VII of Figure 1 at a buttress junction.

Referring to the drawings the furnace brickwork 2 is supported by a steel bath receptacle 3 resting in bottom beams 4, and fitted with back stays I, front stays I and top tie members I. The roof bricks form an arch I extending across the; furnace and supported by buttresses H at front and back of the furnace. These buttresses H are at least long enough to support a section of the roof I between any two sets of stays, and are so designed as to allow the brick arch l to subtend any included angle of approximately 60, when hot. such an angle giving maximum stability under normal working conditions.

The buttresses II are bolted at II to the lower ends of leversi6 rocking on pivot shafts l3 journalied in bearings slidably mounted on adjacent pairs of back and front stays I, 8. Said shafts II also pass through the lower ends of links 20, whose upper ends are mounted on shafts I3, 38, parallel to but above the pivot shafts II, the upper shafts ll, 38, having their ends journalled in bearing brackets 31 slidably engaged with the aforesaid adjacent pairs of back and front stays so as to be capable of upward and downward movement due to excessive front and back wall expansion. Said bearing brackets 81 are suspended from top frame members 25 by rods 20 whose shanks are screw threaded and provided with washers II and nuts 24 so that by adjustment of the nuts 24 the bearing brackets I1 can be adjusted vertically. The central part of the upper shaft 33 at the front of the furnace carries a rocking lever 21 for each buttress lever IS, the lower end of which has a slot engaged with a pinor shaft 34 journalled in bearings bolted at H to the buttress lever It, whilst the other arm of the rocking lever is pivotally connected at 32 to one end of the part SI of a tie rod 29, Ill, 3!, extending across the arch to the back of the furnace, where the part I! of the tie rod is articulated at ll to the shortarm of a bell-crank lever II, which is mounted on a pivot pin or shaft 28 journalled in bearings fastened by bolts 11 on the buttress lever I. The bell-crank lever It takes the place of the rocking lever 21 at the front of the furnace, being mounted on the upper of the two shafts i. e. the shaft SI carried by the vertically sliding bearings 31, in a similar manner. The two parts 20, ll of the tie rod are connected together by a right and left handed screw coupling 30 to allow adjustment of its length to suit site irregularities.

Hung at 23 from the long arms of the bellcrank levers I! at the back of the furnace are suspension rods 2! for cheese type weights 22.

Since the buttresses II with levers It at the It rotate about different fixed pivots and have different radii of action, but are connected together by the shaft or pin II projecting from the side of the buttress lever It. the short arms of the bell-crank levers have a slot engagement with the projecting pin or shaft 2. to which the tie rod II is connected. When the furnace is cold the bell-crank levers I! are in a position in which their short arms are effectively longer and the long arms are effectively shorter than when the furnace is hot, since when the furnace is hot the short arms are vertical and the long arms are horizontal, and the lever has its maximum leverage.- Therefore the effective thrust on the buttresses will be varied and adjusted to suit the varied movement of the roof during temperature-changes.

The buttresses become fully supported by the back or front stays I and 0 when complete expansion has taken place, at which point further rotation is prevented by engagement of the outer surfaces of the buttresses with the back and front stays.

The proportions of the levers may be such that the necessary weights are very small in relation to the thrusts in the roof arches.

It should be understood that mechanism as described above is provided at each end of the buttresses I I, and the mechanisms for a pair of adjacent buttress ends are combined together. inasmuch as the upper shafts 33, SI, and the lower shaft l3 will be common, and the shafts or pins 28, N connecting the rocking and bell-crank levers with the tierod 28, II, which project from the side of the buttress levers I. will be common to the pair of adjacent buttress levers, the pair of rocking and bell-crank levers 21, ll, associated with a pair of adjacent buttress levers I, ll, being mounted side by side on the upper shaft II or 38 carried by the vertically adjustable bearing brackets 31.

In order to accommodate for increase in the radius of curvature of the roof arch 0 due to expansion when hot three beams ll are provided longitudinally above the arch, one at the centre and two half-way between the centre and the front and back. These beams are not attached to the roof arch but simply make contact therewith in its various positions. They are arranged to rise and fall with the movement of the roof, being moved through bell-crank levers 41, ll and 48 from the buttress levers II, the lever arms being so proportioned as to have the same ratio as that of the vertical movement of the roof to the longitudinal movement of tie rod 28, Ii.

The beams ll carry angle brackets II, II and M which are slung by links (I and pins 46 from the lower arms of the corresponding bell-crank levers ll, 40, 40 which are rotatably supported by brackets I0, ll, '2 fastened by bolts It to the main cross ties I. The upper arms of bell-crank lever 41 of the front beam ll are articulated to rods N, the other ends of which are articulated to the pins 32 at the ends of tie bars Ii.

The upper arms of bell-crank levers ll of middle beam II are connected to short links I which are articulated to tie rod II, if at I. Similarly the upper ends of bell-crank levers ll, of rear beam II, are connected to rods I. which are also articulated to tie rod II, II at I.

Thus all three of the beams ll take movement from the tie rod 2:, SI and as will be seen. the bell-crank levers 41, ll, 40 have different included angles which are suited to the movement of the back of the furnace and their bell-crank levers 7s beam to which they pertain. The links ll are capable of slight side movement in order to accommodate any side movement of the bricks against which the beams ll may be pressing. The movements of the beams ll, as produced by their respective bell-crank-levers 41, 48, and 49, will be proportional to the movement due to expansion from the rotation of the main roof skew back buttresses II and also to the relative positions of the individual beams on the roof surface. In these circumstances there should be no stress or load between the beams 4i and the bricks of the roof arch.

Should any one section of the roof become heated more than the other sections, local excessive expansion and consequently alteration of roof curvature would tend to occur; flattening in a hot part, for example, would tend to cause bulging in a cooler part. By providing the beams 4|, however, which under normal conditions just touch the roof, should: local overheating occur, the cooler parts of the roof tending to bulge would be supported by beams ll so as to resist the bulging pressure, whilst in other parts tending to flatten the roof would move away from the beams ll. Change of shape of the roof is particularly liable to occur whenthe roof wears thin in parts, in which case the thicker and heavier portions tend to flatten and the thin parts to bulge.

Whatever maybe the cause tending to change the shape of the roof, the occurrence of an un-' desired change of shape will be prevented by the beams ll It should be clearly understood that the invention is not limited to the details of construction hereinbefore described and illustrated, which are capable of many modifications and variations within the scope of the invention as defined in the appended claims.

1. In a. furnace of the class described, the combination of a supporting structure, a roof arch associated therewith, supporting levers at opposite ends of said arch, buttresses for said arch received by one end of each of saidlevers, pivot means intermediate the ends of said levers, suspension means connected to said pivot means for supporting said levers and arch from said supporting structure, and connecting means connecting the ends of said supporting levers opp site the arch receiving ends for accommodating inward and outward movements of said arch ends with respect to each other due to expansion and contraction of the arch.

2. Arch supporting means as set forth in claim 1; wherein the suspension means is slidably connected to the supporting structure for vertical adjustments of the arch.

3. Arch supporting means as set forth in claim 1, combined with resistance means extending along the top of the arch for yieldably contacting the arch at spaced points therewith to resist buckling of the arch during expansion, supporting means for suspending said resistance means from the-supporting structure, and means for connecting said resistance means to the lever connecting means'to raise and lower the resistance means proportionately to arch expansion.

4. Afurnace arch supportofthe class described comprising in combination a supporting structure composed'of spaced uprights or stars and con- 6 mounted on said supporting structure at front and back of the arch,'an arch having buttresses at its front and back seated in the end of each suspension lever at one side of its pivot, connecting means intermediate the respective front and back suspension levers, including a rockable lever connected at one end to each front pivoted suspension lever aforesaid and at its other end to i one end of said connecting means, each said rockable lever being connected to one end of the associated pivoted suspension lever at the opposite side of the pivot from the arch buttress, whereby movement of a front pivoted suspension lever in one direction causes movement of the corresponding back suspension lever in the opposite direction.

5. A furnace arch support as set forth in claim 4, combined with means for resisting the movement of the pivoted suspension levers due-to arch expansion in a progressively increasing degree as the expansion increases.

6. A furnace arch support of the class described comprising, in combination, a supporting structure composed of spaced front and back uprights and connecting beams therefor, an arch arranged between the front and back uprights, supporting levers along the front and back of the arch in one end of which the buttresses of the arch are seated, pivot means for each of said supporting 11005118 beams b11381, YUM nupcmion IQVQII levers, adjustable suspension means connected to the said pivot means and to the supporting structure, a rocking lever connected to the free end of each front supporting lever and to the suspension means, tie rods connected to said rocking levers at one end and to the free ends of the back supporting levers, and weight supporting means connected to the back supporting levers and to the associated suspension means.

7. A furnace arch support as set forth in claim 6, wherein the weight supporting means comprisesa bell-crank lever having short and long lever arms, the short arm being connected to the associated back supporting lever and weights being suspended from the longer arm.

8. A furnace arch support as set forth in claim.

6, combined with spaced beams extending longitudinally above the roof arch, brackets depending from the beams connecting the front and ba k upri hts and bell-crank levers mounted on said brackets, one arm of each of which is connected to an associated longitudinal beam and the other arm of each of which is connected to an associated tie rod.

- JOHN EDWARD PLUCK.

REFERENCES 01'!!!) Thefollowingreferencesareofrecordinthe flleofthispatent:

Date m M III-.- M. 10 m

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