US2876955A

US2876955A - Surface hardened annular grinding ring

Info

Publication number: US2876955A
Application number: US436104A
Authority: US
Inventors: Warren F Clements
Original assignee: Babcock and Wilcox Co
Current assignee: Babcock and Wilcox Co
Priority date: 1954-06-11
Filing date: 1954-06-11
Publication date: 1959-03-10
Anticipated expiration: 1976-03-10
Also published as: FR1125738A

Description

March 10, 1959 1 w. F. CLEMENTS' SURFACE HARDENED ANNULAR GRINDING RING F i ied .nine 11 1954 INVENTOR MP?! A u-wilvrs 01 K ATTORNEY United States Patent 2,876,955 SURFACE HARDENED ANNULAR GRINDING RING Warren F. Clements, Wadsworth, Ohio, assignor to The Babcock & Wilcox Company, New York, N. Y., a corporation of New Jersey Application June 11, 1954, Serial No. 436,104

4 Claims. (Cl. 241-129) that for grinding service full advantage of the improved wear service of the newer metals is sometimes not possible due to the tendency for the extremely hard metals to crack and break under service conditions.

usually also increases the brittleness of the metal so Many times the failure of a grinding element formed of the better wear metals is due to edge spalling of the element which leads to early failure of the part. Various expedients have been used as a compromise in an attempt to take advantage of the best wearing surfaces while also providing a tougher, less brittle edge to the grinding elements. For example, in certain grinding ring constructions the fiat surfaces of the wearing parts of the ring have been chilled while the edges of the same wearing surface have not been chilled. The object of this construction has been to provide a high-wearing surface centrally of the ring While the ring edges which are subjected to shock and spalling are formed of a softer but tougher material intended to be more resistant to breakage.

In accordance with my present invention I construct a grinding element with a raised or crowned central portion intended to contact the stationary or moving companion part of the grinding element while at the same time increasing the radius of curvature of the rounded edges of the element, and continuing the hard surfacing of the element around the edges beyond the direct wearing contact area of the grinding element. Unexpectedly the hardened metal of the edges resists spalling and breakage apparently due to the improved crystalline structure of the metal resulting from the hardening operation. The hardened edges cooperate with the raised or crowned central portion of the wearing surface to substantially eliminate edge spalling and breaking of the element.

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 the invention.

Of the drawings:

Fig. 1 is an elevation, partly in section, of a pulverizer illustrating a grinding ring constructed in accordance with the present invention.

Patented Mar. 10, 1959 Fig. 2 is an enlarged section view of a grinding ring shown in Fig. 1.

It will be understood that my invention is not limited to the construction of the grinding elements used in any particular type of pulverizer, and is not limited to any particular type or analysis of wear metal. In theillustrated embodiment of the invention a grinding ring constructed in accordance with my invention is installed in a pulverizer of the type disclosed in U. S. Patent 1,175,436.

As disclosed in the patent and shown in Fig. 1, the pulverizer 10 includes a base section 11 having an upturned annular flange 12 and an upper annular detachable section 13. The base section is covered by a housing 14 which encloses the grinding elements hereinafter described. A cylindrical superposed housing 15 is positioned on an annular cover plate 16 above the housing 14 to enclose the rotatable spider supporting the shafts 17 to which the rollers 18 are bolted. A vertical axle 20 is fixed by a pin 21 in a boss 22 positioned centrally of the base section 11 to provide a support for the rotating elements of the grinding machine. The upper end of the axle 20 is mounted in .a cap member 23 which is positioned by the arms of an A frame 24. Between the cap member 23 and the cover 25 of the housing 15 a belt driven pulley 26 is keyed to a feather shaft which is rotated thereby.

The construction and arrangement of the means for transmitting rotational movement of the roller mounting shaft 17 about the central axle 20 isdisclosed in detail in said patent. In the operation of the pulverizer described, raw material is introduced into the lower part of the housing 14 by spouts 27 which discharge the material into the path of the grinding elements. Rotating plows 28 agitate the material deposited in the base section 11 below the rollers, with the ground or pulverized material passing through a screen (notshown) and into a discharge passageway 30 opening to the outside of the pulverizer.

The rolls 18 are urged outwardly by centrifugal force by the rotation of the shaft 17 about the axle 20, with the roll surfaces contacting theinner surface of a horizontally disposed stationary grinding ring 31. The ring 31 is mounted and maintained in its operative position with the outer ring circumference bearing against the flange 12 and the detachable section 13. Thus the grinding action is accomplished by the rolling movement of the rollers 18 against the inner circumference of the ring 31, where the material grinding effect is attained by centrifugal force imposed by the rollers 18 moving circumferentially of the stationary ring 31.

It has been customary to supply the ring 31 with a substantially flat, inner circumferential face with the top and bottom edges rounded to a radius of, for example, /2 inch. When alloy, chilled cast iron rings have been supplied it has also been found desirable to limit the chilled surface to only the central portion of the wearing surface. For example, when the ring is constructed of a size having a wearing surface width of approximately 8 inches, the chilled area width of the centrally located circumferential wearing strip will be from 4 to 6 inches. While edge spalling still occurs with this construction the spalling and breakage of the rings has been somewhat less than when the entire wear surface has been chilled to a high hardness. Under these same conditions the wear rate of the ring has been somewhat greater with the reduction in chilled wear surface, but the reduction in ring breakage has resulted in an increased average ring life.

In accordance with my invention the annular grinding ring 31 is constructed with a crowned inner wearing surportion of the inch on an 8 inch wide ring has a beneficial effect upon the wear life of the ring. This construction is shown in Fig. 2 where the high point of the ring in the crowned surface 32 thereof is positioned intermediate the upper and lower sides 33 and 34 respectively. Apparently this construction tends to prevent the normal edge thrust encountered in a flat surface ring where the edge thrust has heretofore contributed to the spalling of the ring edges.

I have also found it to be of advantage to increase the radius of curvature of the

edge portions

35 and 36 of the inner ring surface. This is likewise shown on Fig. 2 where the increased radius illustrated is of an inch.

When the wear surface of the ring: is crowned and rounded edges are employed, it has also been found beneficial to harden the entire surface of the ring. When the ring is cast of a wear resistant iron it is advisable to continue the chill surface entirely across the wearing surface of the ring, around the

edges

35 and 36 thereof and to a depth of as much as A of an inch along the top and bottom sides 33 and 34, respectively, of the ring. Chilling the edges of the ring is directly contrary to the experience of earlier ring constructions. As has hereinbefore been pointed out, chilling of the edges has heretofore apparently lead to ring spallage and cracking of the ring. However, when the ring is crowned in accord ance with the invention, as shown in Fig. 2, the improved grain structure of the edges definitely improves the wear resistance and useful life of the rings constructed in accordance with my invention. 1

By way of example, rings constructed in accordance with my disclosure can be expected to increase the useful wear life thereof from 50 to 100 percent, on the average, over rings made of the same alloy and constructed according to the specifications hereinbefore in almost universal use for this type of grinding mill service.

While in accordance with the provisions of the statutes 1 have illustrated and described herein a preferred embodiment of the invention, those skilled in the art will understand that changes may be made in the method of operation and form of the apparatus disclosed without departing from the spirit of the invention covered by my claims, and that certain features of the invention may sometimes be used to advantage without a corresponding use of other features.

What is claimed is:

1. A new article of manufacture comprising a cast annular grinding ring having its inner circumferential surface crowned, said ring having its circumferential edges rounded, and the inner circumference of said ring chill hardened in casting with the chilled wear surface thereof extending across the crown and around the rounded edges of the inner ring circumference.

2. In a pulverizing mill, the combination comprising at least one grinding roll and a stationary grinding ring, said roll being journaled upon a pivotal shaft for rotation of said shaft about the axis of said ring, rotation of the shaft and roll urging the roll into contact with said ring by centrifugal force, said ring being cast with a crowned surface in contact with said roll and a chilled surface extending across the wear surface thereof and around the circumferential edges thereof.

3. A new article of manufacture comprising an annular grinding ring having its inner circumferential surface crowned, said ring having its inner circumferential edges rounded, and the inner circumference of said ring hardened with the hardened wear surface thereof extending across the crown and around the rounded edges of the inner ring circumference. I r

4. In a pulverizing mill, the combination comprisin I at least one grinding roll and a stationary grinding'ring,

said roll being journaled upon a pivotal shaft for rotation of said shaft about the axis of said ring, rotation of the-shaft and roll urging the roll into contact with said ring by centrifugal force, said ring having its circumferential edges rounded and a crowned wear surface contacted bysaid roll, said crowned surface being hardened across the surface and around the adjoining circumferential edges thereof.

References Cited in the file of this patent UNITED STATES PATENTS 287,653 Fish Oct. 30, 1883 315,146 Koneman et al. Apr. 7, 1885 849,781 Fuller Apr. 9, 1907 1,145,629 Symons July 6, 1915 1,175,436 Griffin Mar. 14, 1916 1,358,739 Herbst Nov. 16, 1920 1,573,191 Raymond Feb. 16, 1926 1,777,605 Dimler Oct. 7, 1930 FGREIGN PATENTS 4,463 Great Britain of 1876 14,630 Great Britain of 1906