US1686761A - Masonry arch for high-temperature use - Google Patents

Description

Oct. 9, 1928. 1,686,761

F. H. NORTON MASONRY ARCH FOR HIGH TEMPERATURE USE Filed Nov. 18, 1924 A TTORNE Y5 Patented Oct. 9, 19.28..

UNITED STATES PA T OFFICE.

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MASONRY-ARCH FOB, HIGH-TEMPERATURE USE,

Application filed November 18, 1924. Serial No, 750,538.

' In structures of various which are subjected to hi h temperature conditions,

considerable culty h s been experienced with masonry arches forming a part of, such structures. My invention is concerned with,

overcoming such diificulties andfor convenience will be described in connection with k11ns for burning high temperature refrac tories, but it is to be understood that it is applicable to industrial furnaces in general, in-

eluding boiler furnaces, metallurgical furnaces, etc. a v I In kilns as heretofore designed for high temperature work, considerable difficulty has.

- -.been expegienced with the roofs. In the case ving arched roofs which are unin of kilns h sulated, no great difliculties are experienced, since, due to radiation, the temperature at tained by such a roof is not high.- When high temperatures are sought, e. g., in the nei hborhoood of 3000 F. and above, the mo in common with the rest ofthe kiln must be well are used which have been insufliciently burned, and which, when subjected to the kiln temperature, undergo such shrinkage, as a result of internal changes in the material composing the bricks, that the final effect is a contraction rather than an expansion. However, it will be understood that in the usual case, a considerable increase in length of the arch must be provided for, and that furthermore, unless proper provision is made, parts of the brick, as, for example, the lower ends, will be subject to excessive pinching, .due to the relatively greater expansion of such lower ends over that of the upper..

' After considerable study and experimentation, I have discovered that the failure of arches. under high temperature conditions has been due. principally to the following causes:

(1). Excessive stresses due to eccentric loading, i. e., such that the lines of thrust make considerable deviation from the center line of the arch. 4 I l (2) Excessive stresses due to) change in length of are on heating.

V (3) Excessive stresses due to uneven expansion of the bricks occasioned by the fact that the lower ends of thebricks are heated to a higher temperature than the upper ends.

Accordingly, in constructing the arch of myinvention, I s shape the archas to enable the thrust through each brick or voussoir tocoincide substantlally with the geometric center thereof, or, what may be preferable, I may construct the arch so that the ,line of thrust will make a uniform, slight deviation from the centerof each voussoir' so as to allow for the fact that when the under part of a vous;

soir is heated to higher temperature than the upper, the yield point of the material at the hotter surface is less than that'of the cooler one.. Such an arch in either of the two, cases mentioned would, as is known, have the shape of an inverted catenary.

I have found that the excessive stresses,

due to the second and third causes mentioned,

maybe eliminated by providing means ale lowing a free expansion of the arch. In the form at present'preferred by' me, and which I have illustrated in the accompangin drawing, I hinge the arch at each skewac .and provide for movement of the two halves of the arch with respect to one another at the longitudinal mid-section. :This construction allows each section of the arch to expand .as a unit, and substantially eliminates pinching of theends of the bricks or voussoirs, due to unequal expansion of the lower and upper ends thereof.

It will be und'erstoodthat particularly when an articulated 'constructlon is employed at the mid-section, it is desirable to make the stress at this section as small as practicable. It will be found in the case of a catenary arch-that such stress willbe diminished as the heightof'the-arch is made greater. This is in contrast to an arch of circular shape for example, in which the stress per unitof cross section increases as the curvature (and consequently the height) 1 V is increased, so that slightly beyond say a 50 slope at the skew-backs, such an arch has a marked tendency towards instability. By

making the arch of inverted catenary shape,

however, they height of the arch may be increased to any desired amount without afl'ect- 'ing its stability. In practice, I have found an arch of catenary shape having a slope at the skew-backs of 55 to 70 to be desirable but refer to use the higher values.

. If desired, the use of cementing materials between the side faces of the voussoirs composing the arch may be dispensed with, as due to the improved. construction, such cement is not necessary for the stability of the arch. Thiselimination of the cementing material is of advantage, in that it allows the ready removal of a single voussoir, and,

furthermore, allows the voussoir to undergo some rearrangement durmg the heatingand cooling process.

My invention will best understood from the following detailed. description taken with the accompanying drawing, in which Fig. 1 is a view-more or less diagrammatic l taken in vertical cross section of a kiln of rectangular shape embodying a preferred form of my invention; Fig. 2 is an, enlarged view in vertical section through one skewback and shows the manner of supporting the qber 12, engaging the curved surface of an inclined stay 13, suitably secured in vertical supports 14;, which carry the weight of the arch. This hinged construction 'isprotected from the heat of the furnace by means of an extension of the inner walls 15, 15. -As

shown the arch is divided at the longitudinal mid-section in sections, A and B and conveniently, the hinge between them may be formed simply by giving aslightly convex curve to .the opposing voussoirs 10", 10. The amount p of curvature required is very slight, the ourvat'ure shown clearness.

, The side walls of the kiln are covered" with being exaggerated forsake of insulating material, as, for example, by a layer of refractory bricks 16, outside of which isplaced one or more layers 17 composed of a'br'ick having high insulating qualities such as those made of diatomaceous earth. The roof is preferably covered. With-a layer-ofinsplating .brick 18, beneath which may, if desired, be placed a monolithic layer of suitably refractory material .18.

, Vertical supports are fitted with extensions 20, opposite extensions 20 being joined by tie rods 21, by means of which the lateral thrust of the arch is opposed. F 1

If desired, I ma displace the locus of thrust throughout t e arch upwardly from" of the two sections at the mid point the same amount; In this manner the load on the voussoirs is distributed more in accordance with their ability to withstand it, since the portion of the voussoirs having the greater temperature will not have the same resistance to stress as the cooler parts thereof. Preferably, this displacement is just enough so as to produce uniform distortion of the voussoirs and may be easily .calculated, given the temperature gradient between the inner and outer surfaces of the arch when subjected to furnace temperatures and the yield points of the refractory material throughout the gradient; It is to be noted that only by the use of the inverted catenary shape for the arch,'is such a result possible, as in any other form, the locus of thrust is not coincident with or parallel to the center line of the arch. .The amount of displacement is small and as will be evident from the foregoing, is dependent upon the temperaturesof the inner and outer surfaces I have found a kiln roof embodying my improvements is exceedingly stable and that the temperature to which it may .be repeatedly heated is limited only by the refractoriness of the materialused. For example, anumber of kilns embodying my im rove ments have'been subjected to repeate heating at temperatures in excess of 3000 F., each of which-heatings lasted for several days, without the roofs of any of them showing the sli htest indications of failure.

arious changes within the spirit of m invention will occur to those skilled in the art, it being understood that the specific forms of my invention shown are by way of and the particular kind of refractory used.

; example only and that ,I do not intend to limit myself to such specific forms shown.

In theclaims Where the word furnace is used, it its to be understood that I intend to include not only furnaces but kilns where the roof or arch is-subjected to high temperatures due to hot products of combustion.

I claim: 1.-A furnace roof of refractory material for use under high temperature conditions, said roof being, composed of two sections, each of-which is cc to move as a unit when heated, and said roof being of substantially an inverted catenary shape and supported only at its edges. I

2. A furnace roof for use under high temperature conditions, said roof being com. posed of two sections, each of which has a hinged connection with the support on'which tially catenary shape.

3. A furnace roof for use under high tem-' 'verted catenary shape for use under high tem- 10 perature conditions, said roof being composed perature conditions supported so as to disof two sections, each of which has a hinged place the line of stress outwardly from the connection with the support on which it rests, center line of the roof by an amount sufficient 5 and a movable connection with said other secto give substantial uniform distortion of the ti0n,'said roof being of substantiall catenary voussoirs when the under side of the roof is 15 shape and having a slope at the s ew-backs heated to a given temperature. in excess-of 50. 7

' 4. A hinged voussoir furnace roof of in- FREDERICK HARWOOD NORTON.

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