US2632234A

US2632234A - Furnace roller and method of making it

Info

Publication number: US2632234A
Application number: US654181A
Authority: US
Inventors: Kenneth E Fitz
Original assignee: Babcock and Wilcox Co
Current assignee: Babcock and Wilcox Co
Priority date: 1946-03-13
Filing date: 1946-03-13
Publication date: 1953-03-24
Anticipated expiration: 1970-03-24

Description

March 24, 1953 z 2,632,234

FURNACE ROLLER AND METHOD OF MAKING IT I Filed March 13, 1946 Fig.3 Fig.4

INVENTOR Jzmetfi Z Fitz ATTORNEY Patented Mar. 24, 1953 FURNACE ROLLER AND METHOD OF MAKING IT Kenneth E. lFitz, Barberton, Ohio, assignor to The Eabcock & Wilcox Company, New York, N. Y., a corporation of New Jersey Application March 13, 1946, Serial No. 654,181

Claims.

The present invention relates, to abrasion and temperature resistant composite alloy steel members and more particularly to composite alloy steel rollers adapted for service within a heat treating furnace.

In the heat treatment of metal shapes or articles in process of manufacture, many modern furnaces for annealing, normalizing, hardening, and the like, utilize a plurality of rollers to support the metal articles in their passage through the furnace. Frequently, such rollers are formed with individual bearing supports and both the roller and its bearings are exposed to the ternperature and atmospheric conditions prevalent Within the furnace. Due to the furnace conditions, customary bearing lubrication is difficult or impossible to accomplish, and the wear between the roller and its bearings is especially severe and has heretofore resulted in short roller life. Although the usual abrasion between the metal articles under treatment within the furnace and the peripheral surface of the supporting roller is negligible, the work contacting surface of the roller must be cylindrical and rotate about a predetermined axis to avoid damage to the work.

While cast iron rollers have been successfully used in many furnaces wherein the temperatures have been relatively low, it has been necessary to resort to, alloy steels to withstand higher furnace temperatures and/or corrosive or oxidizing furnace atmospheric conditions. Alloy steels suitable for such service and having a high relative hardness for resistance to abrasion are well known in the art, but such alloys cannot be economically used in, rollers of the. type described unless they can also be readily machined. It is customary to consider metals having Brinell hardness numbers in excess of approximately 200 to300 as being non-machinable in that they cannot be machined by cutting tools, such as used in a lathe or planer, even though these metals can be finished by the use of grinding wheels. Moreover, it is well known in the art, that the cost of finishing metals by the use of grinding is many times that of machine turning with cutting tools. Consequently the alloys in use in furnace rollers have heretofore been softer than the more desirable abrasion resistant alloys available, and it has been found that the roller trunnions wear rapidly at their bearing supports and must be discarded long before other work contacting portions of the roller have shown any appreciable signs of wear. This results in an economic loss of alloy metals and undesirably high roller replacement costs.

It is therefore a principal object of the present invention to provide a composite alloy steel memto provide a composite alloy steel member highly resistant to high temperatures without deformation and having a non-machinable wear resistant surface and at least one other machinable surface. An, additional specific. object is to provide a composite alloy steel roller for use in a high temperature heat treating furnace characterized by a shaft portion that is non-machinable and highly resistant to wear and a roller portion which is machinable to provide a cylindrical outer surface that is coaxial with the shaft. A further object is to provide a simple low cost method of manufacturing a composite alloy steel roller of the character described. An additional object is to provide a high temperature resistant composite alloy steel member formed of alloys having substantially dissimilar abrasion resistant qualities while their other physical qualities are similar.

The various features of novelty which, characterize my invention are. pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of my invention.

Of the drawings:

Fig. l is, an elevation, partly in section, of a portion of a heat treating furnace with a 001m posits alloy steel, roller constructed in accordance with the. present inventionv installed therein;

Fig. 2 is an end view, partly in section, of the furnace and roller shown in Fig. 1;

Fig. 3 is a section, taken on the line 3-3 of Fig. 4, of a roller constructed in accordance with the present invention; and

Fig. 4 is an end view of the roller shown in Fig. 3.

The present invention is illustrated in the drawings in the form of a roller lli adapted to support a finished or semi-finished metallic article, such as a sheet H, in its passage through a heat treating furnace. In such a furnace, a plurality of rows of such rollers are installed in the furnace with their axes parallel and their top surfaces in a common plane to uniformly support the sheet in process of heat treatment.

Referring particularly to Figs. 1 and 2, the roller ill is constructed with a cylindrical roll portion 2 and a. shaft portion is which forms trunnions I Be and i319 projecting beyond opposite ends of the roll. The shaft is coaxial with the circumferenand 2| thereof extend outwardly and upwardly to a height greater than the trunnion diameter. Thus each crotch I! is open at the top for convenient placement and removal of the corresponding trunnion While the crotch sides 20 and 2| maintain the roller in a rotating position. Although the trunnion fits loosely in the crotch ll, it has been found that this construction is satisfactory to maintain proper roller alignment and to prevent binding in its bearings under the load and temperature conditions encountered in operation. Friction losses between the trunnion and the surface I8 of the bearing support may be reduced by proper design and high quality bearing finish, in which the materials used, unit bearing loads and speed of rotation are correlated for reasonable bearing life.

The supports 15 and it are usually cast or fabricated with a common base 22 and spaced to permit free rotation of the roller l0 when installed therebetween. The base 22 is secured to the floor 23 of the furnace by nut 25 engaging anchor bolts 25 which are embedded in the refractory bottom 26 of the furnace and project upwardly through corresponding openings in the base 22.

Since the trunnions and the surfaces I8 of the 7 supports I5 and H6 in contact therewith are subjected to abrasion under high temperature furnace conditions, they are preferably constructed of temperature and wear resistant alloys which will result in a minimum of wear. 7 Such alloys are hereinafter described in the construction of the shaft portion 53 of the roller l0 and, while the trunnion supports may also be constructed of the same alloy, it has been found desirable in some installations of the invention to cast. or fabricate the supports and their common base from a temperature resistant material and to deposit a hard wear-resistant metal alloy upon the surfaces I8, 20, and 2| by welding. Such surfaces may thereafter be finished to proper dimensions and a desirable high quality surface finish by grinding.

With the construction described, the roller in may be easily removed from its supports 15 and I6 and replaced by inserting a new roller, if desired.

of key projections 21 which are integral with the roll portion and extend into the grooves of the shaft thereby increasing the mechanical strength of the line or zone of juncture between the two metals. Thus when the composite roller casting is removed from the mold, the roll metal is effectively united with the shaft metal and the roller [0 may be placed in a lathe to machine the surface i l. While the metal of the shaft portion i3 is of a hardness impractical to machine in a lathe, the metal of the roll portion 12 is comparatively soft and may be machined with a cutting tool to provide a finished cylindrical roll surface HE coaxial with the shaft it. Thus the composite roller 10 will be finished to the desired dimensions and the cylindrical work supporting portion 12 will have the same axis of rotation as the trunnions [3a and lab.

In manufacture composite alloy steel members, such as the furnace roller described, I have found that the proper selection of the alloy steels used is vitally important to the successful casting of a unitary composite member. In addition to the ability of the metals selected to Withstan severe furnace temperature and atmosphere conditions without damage, and having the Wear characteristics previously described, the metals in general should be of a composition assuring high strength and ductility at the temperatures encountered in service, thereby avoiding any tendency to hot tearing due to shrinkage and expansion stresses. The composition of the alloys selected for the shaft and roll portions are further selected to be generally similar in certain physical properties, to avoid marked discontinuity at the junction line. Further, the alloys are selected so that the alloy of the roll portion may fuse into the shaft portion upon pouring without the necessity for high metal casting temperatures. Furthermore, it is desirable to select an alloy composition for the shaft portion of the composite roller that will maintain its hardness, and thus its wear resistant qualities following the rise in temperature resulting from pouring the roll metal therearound- I have also found that the differential between the coeflicients of expansion of the roll alloy and the shaft alloy throughout the temperature range of its service use is important in the selection of Likewise, the supports l5 and it are replaceable as a unit when necessary because of maintenance requirements or due to a change in the character or the shape of the articles being heat treated.

In manufacturing the roller l0, a wear resist- 1 ant alloy steel, the composition of which is hereinafter described, is cast and subsequently finished by centerless grinding to produce a finished elongated cylinder of the desired diameter which becomes the shaft portion [3 and trunnions l3a andl3b of the composite roller H3. The shaft is transversely grooved at longitudinally and angularly spaced points, such as shown in Figs. 3 and 4, placed in a mold and analloy steel, of a composition hereinafter described, is poured around the shaft to form the roll portion l2 of the composite roller. The poured roll alloy metal upon contacting the relatively cold metal shaft will, of course, heat the outer surface thereof and the roll portion and the shaft portion of the roller ID are fused together as a unitary member. addition, the poured molten metal will flow into the grooves, and uponsolidifying, form a series those alloys for the successful casting of the composite alloy roller.

With these general alloy specifications in mind, the following more specific alloy compositions for both the shaft and roller portions of the composite roller iii are tabulated by way of example.

For the shaft [3:

Alloy A Percent The balance in each example is substantially all iron having the usual traces of impurities.

For the roll: a

The. balance: in: each; caseis. substantially all ironhaving the usual traces of impurities.

The compositions of the shaft alloys A and B are such as to provide trunnion surfaces having a high hardness and desirable Wear resisting qualities. Although the high carbon cenmnt of these alloys will form iron carbides in the. matrix, tests of. the shaft will be" indicative of the hardness of that matrix and will have Brinell hardness numbers of the order of. 380 to 450. It is uneconomical to use lathe cutting or turning tools on such alloy steels and the shaft 13 is therefore. finished. by grindingv to form a properly dimensioned true cylinder as previously described.

The roll alloys C and D have Brinell hardness numbers in the range of 156 to 180 which is a hardness range that can be economically machined in a lathe with cutting tools available in. the ordinary machine shop. Thus the composite roller can be readily set up in a lathe and the roll portion i 2 turned to form a cylinder with its outer surface is coaxial with the shaft portion I3.

The ccefiicients of expansion of the described alloy steels constituting the composite roller of the present invention provide a reasonably small differential of' expansivity in the range of temperatures normally encountered. It is practically impossible to have the expansivity values of the alloys for both the shaft and roll exactly the same Alloys Temperature, F.

A B O D 200 8. X10 9.1)(' 8. 0X10 7. 4X10- 1,200 .u 9. 10. 4 9. 6 9. 2 1,500 l0. 8 10. 7 10. 0 9. 6

It will be noted in the described casting of the composite roller that the coefiicient of expansion of the shaft alloys are generally greater than those of the roll alloys. When the roll alloy is poured into the mold and comes in contact with the relatively cold shaft, the temperatures of the two metal masses will tend to assume a generally uniform temperature by heat exchange therebetween. However, the heat given up by the molten metal and absorbed by the solid shaft cannot reach stabilization prior to the solidification of at least that part of the molten metal adjacent the shaft, and a great part of the interchange of heat will occur during the time both metals are in their solid state. Since experience has proven that the roll metal and the shaft metal are fused together after the casting process described, it is apparent that the differences in the coefficient of expansion therebetween are not Suificient to cause breakage of the fused zone upon cooling following the casting process. However, it may be that the zone of fusion between the two metals does not have very great mechanical strength, particularly at lower temperatures. It

isfor this: reason that the keys, 21-, integral with the; rollmetal, are provided to; lock the: roll; pol";- ticn; H2. in nonrrotative relation with the shaft. I:3 particularly during its machining which naturally occurs at a relatively low ambient temperature. After the composite roller is finished to dimensions, installed and operated at the temperatures encountered in-a heat. treatingfurnace a greater ex-pansivity in the shaft portion will tend: to tighten the-shaft. within the roller portion, particularly when the roll portion thereof is ductile aspreviously described, so that such a composite roller will maintain" its unitary character under furnace operation conditions.

I claim:

1. The methodof manufacturing a work sup;- porting roller for service within a high temperature furnace which comprises casting a shaft of achrorne-nickel alloy steel having a selectedcm efficient of expansion a Brinell hardness: of approximately 350. to 450, grinding said shaft to form a true cylinder, casting a. chrome-nickel falioy steel roll portion with a Brinell hardness: of approximately 150 to 186 about a portion of said shaft, said roll alloy having a coefficient of'exs pans-ion less than that of said shaft andformunitary roller with said shaft by fusion therewith, and a machine cutting the surface of said roll coaxially with said shaft.

2. The method of manufacturing a composite alloy roller member for use, at high temperatures which comprises casting a core of high carbon chrome-nickel alloy steel having a vknown coefficient of expansion and a hardness above the range of machine cutting, centerless grinding said core to a true cylinder, grooving the outer surface of said core, and pouring a low carbon chromeenickel alloy steel sheath about the mid portion of said core. and into said grooves to fuse with said core to form av unitary composite member uponv solidification, said low. carbon alloy steel' sheath having a lower coefficient. of expansion than that. of said high carbonv alloy steel core .and having. a hardness within the range of machine cutting, and. machine cutting the surface of said sheath .coaxially with. said core.

3.. The method of: manufacturing. a roller for service within a heat treating furnace which comprises castingv an elongated: core of high carbon chrome-nickel heat and abrasion resistant alloy steel having a selected coefficient of ex pansion, grinding said core to form an accurately dimensioned cylindrical shaft, pouring a low carbon chrome-nickel heat and abrasion resistant alloy steel around the mid portion of said shaft, said low carbon alloy steel having a coefficient of expansion in the solid state substantially less than that of the high carbon alloy steel shaft and fusing therewith upon solidification to form a unitary roller, and machining the peripheral surface of said roller with a cutting tool to form a finished cylindrical surface coaxial with said shaft.

4. As a new article of manufacture, a furnace roller comprising a central shaft portion of a heat resistant chrome-nickel ferrous alloy having a finished cylindrical surface and a Brinell hardness number in excess of 300 at room temperatures, and an outer roll portion cast integrally about an intermediate length of said shaft portion and having a finished cylindrical surface coaxial with respect to said shaft portion, said roll portion being composed of a heat resistant chrome-nickel ferrous alloy having a Brinell hardness number of the order of to 200 at room temperatures and having a small differential of expansivityrelative to said shaft portion throughout the operating temperature range of said roller.

5. As a new article of manufacture, a roller for heat treating furnaces comprising a central cylindrical finished shaft portion of a chromenickel ferrous alloy having a Brinell hardness in excess of 300 at room temperatures, and a material supporting roller portion cast integrally about said shaft portion, said roller portion being composed of a heat resistant chrome-nickel ferrous alloy generally similar to the alloy of the shaft portion and having a Brinell hardness of the order of 140 to 200 at room temperatures and finished with a cylindrical surface coaxial with said shaft portion, said roller portion having a small differential of expansivity relative to said shaft portion over the upper operating temperature range of the roller.

6. A furnace roller according to claim 4 wherein said alloy steel shaft portion comprises, carbon 1.00 to 1.50%, manganese .75 to 1.25%, silicon 1.00 to 2.00%, chromium 24.00 to 26.00%, nickel 10.00 to 12.00%, and the balance substantially all iron, and said alloy steel roller portion comprising carbon .45 to .55 manganese .75% maX., silicon 1.00 to 1.50%, chromium 15.00 to 17.00%, nickel 35.00 to 38.00%, and the balance substantially all iron.

7. A furnace roller according to claim 4, wherein said alloy steel shaft portion comprises, carbon 1.00 to 1.50%, manganesefl75 to 1.25%, silicon 1.00 to 2.00%, chromium 24.00 to 26.00%, nickel 10.00 to 12.00%, and the balance substantially all iron, and an alloy steel roller portion comprising carbon .25% max., manganese .70% max, silicon .70 to 1.50%, chromium 24.00 to 26.00%, nickel 19.00 to 21.00%, and the balance substantially all iron.

8. A furnace roller according to claim 4 wherein said alloy steel shaft portion comprises, carbon 1.50 to 1.60%, manganese .50 to 1.00%, silicon .50 to .80%, chromium 18.00 to 20.00%, nickel 6.00 to 7.00%, and the balance substantially all iron, and an alloy steel roller portion comprising carbon .45 to 55%, manganese .75% max., silicon 1.00 to 1.50%, chromium 15.00 to 17.00%, nickel 35.00 to 38.00%, and the balance substantially all non.

9. A furnace roller according to claim 4 wherein said alloy steel shaft portion comprises, carbon 1.50 to 1.60%, manganese .50 to 1.00%, sili- 'con .50 to chromium 18.00 to 20.00%,nickel 6.00 to 7.00%, and the balance substantially all iron, and said alloy steel roller portion comprising carbon.25% max., manganese max., silicon .70 to 1.50%, chromium 24.00 to 26.00% nickel 19.00 to 21.00%, and the balance substantially all iron.

10. In a heat treating furnace, a high temperature and abrasion resistant roller comprising a non-machinable chrome-nickel alloy steel shaft portion having a finished cylindrical surface, and a machinalole chrome-nickel alloy steel roll portion cast around an intermediate axial length of said shaft portion and fused therewith to form a unitary roller and having a finished cylindrical surface coaxial with said shaft portion, said alloy steel shaft portion having a coefficient of expansion similar to and higher than the alloy of said roll portion in the operating temperature range of said roller.

KENNETH E. FITZ.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 38,869 Reeves 1- June 9, 1863 1,273,909 OConnor July 30, 1918 1,455,307 Soulis et al. May 15, 1923 1 1,460,049 Baliantine June 26, 1923 1,724,299 Mitchell Aug. 13, 1929 1,864,590 Fifield June 28, 1932 1,904,253 Rydbeck Apr. 18, 1933 2,061,300 Daniels Nov. 17, 1936 2,097,709 Watters Nov. 2, 1937 2,155,610 Melaney Apr. 25, 1939 2,187,416 Daniels Jan. 16, 1940 2,195,256 Palmer Mar. 26, 1940 2,295,701 Wagner Sept. 15, 1942 2,295,702 Wissler Sept. 15, 1942 2,320,328 Meduna May 25, 1943 2,603,578 Ornitz 'July 15, 1952 FOREIGN PATENTS Number Country Date 464,901 Great Britain Apr. 27, 1937 OTHER REFERENCES Engineering Alloys, Woldman and Metzler (1945 revision), published by American Society for Metals, pages 775 to 780.