US1923773A - Furnace conveyer shaft - Google Patents

Description

Aug. 22, 1933. 0. K. CARPENTER FURNACE CONVEYER SHAFT Original Filed March 13, 1931 2 Sheets-Sheet 1 atbommqs Aug. 22, 1933- 0. K. CARPENTER FURNACE CONVEYER SHAFT Original Filed March 13, 1931 2 Sheets-Sheet 2 ouvn? A. CARPENTER Patented Aug. 22, 1933- UNITED STATES PATENT OFFICE FURNACE CONVEYER SHAFT Application March 13, 1931, Serial No. 522,499 Renewed October 15, 1932 11 Claims.

This invention relates to conveyer mechanism vfor continuous high temperature metallurgical furnaces and particularly to new and improved shaft construction for such conveyers. This invention relates further to a new and improved method of providing such shafts with a filling of heat insulating material. In high temperature furnaces, for example, metal heat treating furnaces in which the furnace temperatures may reach 2000 F., or more, the conveyer mechanism which transports the material being heat treated through the furnace is subjected to these \high temperatures and other severe service conditions which make it essential that the conveyer mechanism should be capable of withstanding all such conditions while hearing the load of the material being treated. In a common type of such furnaces theconveyer mechanism takes the form of rotating shafts in most cases provided with wheels or discs on which the material being treated is propelled through the furnace by rotation of the shafts.

Various attempts have been made heretofore to provide rotating shafts for such furnaces capable of withstanding the severe service conditions among which attempts has been the use of a shaft construction in which was used an axle surrounded by a sectional metallic wall which was spaced away from the axle to provide a heat insulating space. This space was filled initially with heat insulating materialsuch as asbestos and the like. The surrounding shell was composed of one or more members fitted together in a manner intended to prevent escape of heat insulating material. While such shaft constructions have been widely used, it has been found that the heat insulating material escaped from the space between the axle and surrounding shell, and that when this had occurred replacement of the heat insulating material or of the shaft was necessary.

For example, on a sectional outer sheath consisting of two or more parts such sections sur-.

rounding the central axle and joined together for common rotation by telescoping or dovetailing the following mechanical expansion and contraction of such a shaft assembly on lighting or shutting down the furnace causes the shell sections to pull apart more or less, thus allowing the insulation to leak out. This loss of in sulation in turn makes possible a distortion due to heat, of both the sheath or shell parts and supporting means which space the sheath parts from the central tubing or shaft. This distortion in turn causes irregular or flopping movement of the conveyer mechanism. This is accentuated because the work carrying discs are usually cast integral with the sheath parts. The resultant loss of insulation andmisalign-' ment of these conveyors causes enormous heat losses from the furnace by way of the cooling fluid in the shaft and prevents eflicient use of the conveying mechanism in the manner in- I tended. Thus, the material being treated re- 5 ceives not only ununiform heating but also can very easily be damaged by undue abrasion and distortion indirectly causedby the conveyer mechanism. I

Attempting to overcome the foregoing diiliculties, insulated shaft assemblies have been constructed consisting of one or more sheaths surrounding and spaced apart from the central .shaft, the ends of the sheaths terminating within the furnace walls and sometimes within'7 5 the furnace itself. Coaxial support and driving means for such assemblies must necessarily come within the heated area. In such -constructions, one end of the sheath or sectional sheaths is fixed to the shaft to provide a driv- 30 ing means between the shaft and sheath. The other end of the sheath is free to expand in a direction parallel to the axis of the shaft. The construction just described while eliminat- 1 ing a multiplicity of sheath parts, does not, however, reduce or eliminate the objectionable binding between the sheath and shaft which occurs when expansion takes place in the highly heated zone or areas. The possibility of distortion is increased in that the sliding contact in expansion is accumulatedat one end of the shaft assembly. If this one end where expansion accumulates is exposed to high temperatures as within the furnace walls or the furnace itself, it is necessary in order to prevent undue seizure, to provide or allow sufllcient clearance between the shaft and the sheath or end collar of the sheath to permit the expansion without this objectionable binding. Such clearance prevents the retension of heat insulating material. Accompanying the loss of insulation certain of the disadvantages and dimculties'above described becomecommon to these latter assemblies. Furthermore, internally extending spacing lugs or discs between the outer sheath and central tube for the concentric support of the sheath are more likely to collapse, break off or peen when insulation seeps out with resultant sagging of the outer sheath.

Therefore, the important but conflicting factors to be reconciled in making a highly satisfor supporting the sheath concentric with thecentral shaft or support and with the work carrying means.

My invention reconciles the above factors and provides a conveyer assembly which has proven highly satisfactory in extensive commercial use. Co'nveyer assemblies embodying the present invention in its preferred form include the following characteristics:

A monolithic one-piece sheath which permits the easy introduction of heat insulating media thereinto and retains such media therein; main supports of the sheath at points outside of area of excessive heat, and where the dissipation of heat is rapid; fixed contact between the sheath and shaft on one end only outside of area of excessive heat, thus providing positive coaxial and circumferential movement of sheath and shaft; a sliding fit between the opposite end of the sheath and shaft permitting free'accumulated expansion of the outer sheath relative to the shaft and sliding movement of the sheath on the shaft likewise outside of the excessive heat. area, thus eliminating undue binding of these two members; positive mechanical support between the outer sheath and the shaft at one or more points in the area of excessive heat, thus preventing possible sag or distortion of the outer sheath while permitting expansion of the sheath and shaft axially; ready and easy removal of wheels or discs detachably secured to the sheath; quick and easy disassembly of the parts of the assembly after long periods of use. In the drawings which accompany and form a part of this specification,

Fig. 1 is a fragmentary top plan view partially in section of a furnace equipped with one form 'of apparatus embodying the present invention;

Figure 2 is an enlarged plan view partly in section of the shaft construction shown in Figure 1;

Figure 3 is a transverse sectional view taken on line 3-3 of Figure 2;

Figure 4 is a transverse sectional view taken on line l4 of Figure 2;

Figure 5 is a transverse sectional view of a disc taken on line 5-5 of Figure 4; 4

Figure 6 is a fragmentary side elevation of Figure 2 showing the disc in section and means for removably mounting the discs on the sheath.

A description of one shaft assembly will suifice for all, since the assemblies are all alike in a given part of a furnace.

The central axle or shaft 1, preferably composed of steel tubing, is supported in bearings 2 outside of the furnace side walls 3. Each axle 1 extends entirely through the furnace as shown in Figures 1 and 2, and each axle has keyed at one end a sprocket 4 by which a chain driven by a motor or other source or power may rotate the axles.

A sheath 5, preferably constructed of a single, heat resistant, alloy casting is assembled on the axle 1, such sheath having its ends 6 tapered to a cylindrical seat '7 to rest loosely on the axle 1 outside .of the furnace walls 3 and adjacent to the journals 2. Collars 8 are threaded on each end of the sheath 5 and extend beyond the ends of the latter. Packing material 9 is disposed in side of the collars 8 and is pressed against the ends of the sheath 5 and the circumference of. the axle 1 by nuts 10, having screwed threaded engagement with the collars 8 and close-fitting contact with the axle l'. Preferably collars 8 and nuts 10 are composed of steel or any suitable material which will not seize on the shaft 1.

Rotary motion of sprocket wheel 4 is, in the illustrated embodiment of this invention, transmitted to the sheath 5 through primary and secondary driving means.

The primary driving means consists of a stud or a series of studs 11 rigidly secured in the walls of the sheath 5 and extending into suitable recess or recesses in axle 1. At the other end of the sheath, the secondary driving means is shown as consisting of a stud or series of studs 12 rigidly connected to the wall of the sheath 5 and extending-into a keyway or keyways 12a cut into the surface of the axle 1. It will be noted that the sheath 5 is anchored to the axle at one end only, that is by studs 11, the other end of the sheath being connected to the axle for circumferential motion, that is by studs 12, but it is free to slide lengthwise on the axle, thus taking care of the difference in lengthwise expansion between the tube 1 and the sheath 5. Both primary and secondary driving means between the axle and sheath are located at the cold ends of the shaft assembly at a point where practically minimum'expansion takes place and where cooling by radiation is rapid.

Since the sheath 5 is spaced apart from the axle 1 except at the ends and is subjected to high temperatures and loads, as well as high local heat when the shafts are not turning, it is desirable to provide means to prevent excessive sagging of the sheath at the points intermediate its end supports '7. Accordingly, studs 13 are screwed through threaded holes in the sheath 5, the studs making touch contact with the surface of the axle as shown in Figure 3.

The sheath 5 may have various forms of exterior configuration, for example, the sheath may have a plain cylindrical outer surface between the furnace walls and the material to be conveyed, may rest directly thereon, or it may have cylindrical raised portions with plain surfaces on which the material may rest, or, as illustrated in the drawings, portions may be provided extending circumferentially of the sheath 5, in the form of segments 14, each segment 14 having a central circumferentially extending raised portion 15 and conveyer discs 16 may be secured thereon to support the material being conveyed through the furnace. Each disc 16 in turn is provided with a cylindrical material car'- ryingsurface 17 and an enlarged central opening with inwardly extending grooved projections 18, 135 shaped to fit on the segments 14 and raised portions 15. The axially extending grooves 19 of projections 18, together with the axial grooves 20 of the segments 14, form keyways for the locking keys 21 and the wedge keys 22. A packing gland 23, as shown in Figure 1, is attached to the furnace wall 3 and carries packing material, such as asbestos sheets 24 to prevent escape of heat from the furnace around the sheath, there being a packing gland for each end of each shaft.

- it will be noted-in Figures 1 and 2 that there are plugs 25 screw threaded into openings in the sheath 5. These openings are employed for fill ing the space 26 (Figure 2) between the axle 1 and. the sheath 5 with heat insulating material 27. I have found a heat insulating material which is satisfactory for long continued use in high temperature conveyer shafts and which, at the same time, can very readily be placed within the sheath, is composed of a mixture of dia-. tomaceous earth and Portland cement in a small. amount of water. Preferably, I employ about 9 parts of calcined celite, commonly known as C-3 in the trade at present, mix with it one part or more parts of Portland cement, and add just enough water to produce -a mixture which will flow readily, being careful not to use enough water to saturate the celite. The cement apparently keeps the water and celite from separating and thus produces a mixture with but very little water that will fiow lengthwise of the conveyer in space 26, when the shaft is rocked. The water so used is removed by drying the sheaths before they are subjected to high heat and then the plugs are screwed into place.

This mixture should be introduced into the sheath quickly after the addition of the water. The celite has the property of absorbing water rapidly but does not flow readily when it is saturated with water. Hence; the mixture should be poured into the sheath beforesuch absorption takes place and while the mixture is in flowing condition.

The manner of filling the space between the axle 1 and the sheath 5 with this mixture is to place the assembled sheath and axle in a hori: zontal position and pour the aforesaid mixture into one or both of the threaded openings in the sheath, meanwhile rocking the sheath to cause the mixture to fiow lengthwise of the sheath and fill completely the space, and to let some of the water escape through the threaded holes, the remaining water being absorbed by the celite with little or no increasein volume.

When the sheath is thus filled with this insulating material, the plugs 25 are screwed tightly into holes in the sheath. The celite and cement harden in a short time.

The assembled and insulated sheath then undergoes a drying-out process in which such water as has been absorbed is driven off in the form of steam, such steam escaping at ends of the sheath. Following this drying-out process,

the end screw plugs 10 are screwed into place as previously shown and described.

From the foregoing description, it will be obvious to those skilled in the art that I have provided a shaft for a high temperature furnace. which may be readily filled with heat insulating material and that the latter may be permanently vided as well as a new method of placing such mixture within shafts of the type shown herein. Having thus described my invention so that those skilled in the art maybe able to practice the same, what I desire to secure by Letters Patent is defined in what is claimed, it being understood that changes or alterations in the foregoing detailed disclosure may be made without departing from the scope of this invention. What I claim is: I 1. A conveyer assembly for a high temperature furnace comprising a rotatable shaft of a length to extend through a furnace and its walls and to ,be journaled outside of the latter, ,a sheath around the shaft and of a length to extend through. the furnace and its walls, the sheath for transmitting rotary motion frc the shaft to the sheath, a connection between the shaft and the other end of the sheath for permitting relative axial movement of the shaft and sheath while preventing relative rotational movement, heat insulating materialin the space between the sheath and shaft, packing means to prevent escape of insulation at the ends of the sheath, means to maintain the spacing of the sheath and shaft substantially constant and an article conveying surface on the exterior of the sheath.

2. A conveyer assembly for a high temperature furnace comprising a shaft of a length to extend through a furnace and its walls and to be journaled outside of the latter, a single piece sheath around the shaft and of a length to extend through the furnace and its walls, the sheath being spaced away from the shaft intermediate its ends and seated at its ends on the shaft out side the furnace walls, a positive connection between one end of the sheath and shaft to prevent relative axial and cincumferential movement of such ends of the sheath and shaft, heat insulating material in the space between the leakage of such material at the ends of the sheath, and an article conveying annular surface about the sheath.

3. A conveyer assembly for a high tempera sheath and shaft, packing means to prevent ture furnace comprising a cylindrical shaft of a length to extend through a furnace and its walls and to be journaled outside of the latter, a sheath around the shaft and of a length to extend through the furnace and its walls, the

sheath being substantiallycylindrical and spaced apart from the shaft intermediate its ends and the sheath having its end portions outside the furnace walls formed to seat on the shaft with close fitting engagement? the sheath having sealable apertures through which heat insulating material may be introduced to fill the space between the sheath and shaft, packing means to prevent escape of such material at the ends of the sheath, and means for transmitting rotary movement from the shaft to the sheath while permittingrelative axial movement at one end of the sheath.

4. A conveyer assembly for a high temperature furnace comprising a cylindrical shaft of a length to extend through a furnace and its walls and to be journaled outside of the latter, a sheath around the shaft and of a length 'to extend through the furnace and its walls, the

sheath being substantially cylindrical and spaced apart from the. shaft intermediate its ends, the sheath having frusto-conical portions to extend through the furnace walls, terminating in cylindrical ends seating on the shaft, collars on the ends of the sheath, packing glands adjustably secured to the collars, and packing means engaging the shaft and compressible between the sheath and the glands.

5. A conveyer assembly as set forth in claim 1 in which a plurality of annular discs having article engaging annular surfaces are secured to the sheathwithin the furnace.

6. The conveyer assembly set forth in claim 2 in which the article conveying surface is the peripheral surface of an annular disc secured to the sheath within the furnace.

7.'The conveyer assembly set forth in claim 3 in which a plurality of annular discs having article engaging annular surfaces are secured to the sheath within the furnace.

8. The conveyer assembly set forth in claim 4 in' which a plurality of annular discs having article engaging annular surfaces are secured to the sheath within the furnace.

9. A conveyer roll for heating furnaces comprising in combination a tubular axial shaft, an outer tubular sheath of heat-resisting alloy surrounding the shaft, the body of the sheath being spaced away from the shaft, forming an annular chamber, while the ends of the sheath are contracted to fit the shaft, a filling of heat-insulating material-for such annular chamber, and circular work-supporting discs of heat resisting material mounted in spaced relation on said shaft, the sheath being fixed at one end to the shaft while the other end of said sheath is mov able relative to the shaft to permit expansion and contraction of the sheath.

10. A conveyer roll for heating furnaces comprising an outer sheath of heat resistant alloy forming the perimetral surface of the roll, a centraltubular shaft having imperforate walls through-which air may bepassed and heat insulating material interposed between the sheath and the axial shaft, the ends of the sheath being contracted to fit the shaft, one end of said sheath being fixed to the shaft while the other end of the sheath is free to move longitudinally of said. shaft to permit'expansion and contracthe sheath, a connection between the shaft and the other end of the sheath for permitting relative axial movement of the shaft and sheath while preventing relative rotational movement, heat insulating material in the space between the sheath and shaft, means to prevent escape of insulation at the ends of the sheath, means to'maintain the spacing of the sheath and shaft substantially constant and an article conveying surface on the exterior of the sheath.

OLIVER K. CARPENTER.

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