US3667743A

US3667743A - Hearth scraping device

Info

Publication number: US3667743A
Application number: US113898A
Authority: US
Inventors: Edward J Kovalcik; Edward D Dowling
Original assignee: Pullman Inc
Current assignee: PULLMAN Inc A DE CORP; Davy McKee Equipment Corp
Priority date: 1971-02-09
Filing date: 1971-02-09
Publication date: 1972-06-06
Anticipated expiration: 1989-06-06

Abstract

THE SPECIFICATION DISCLOSES A HEARTH SCRAPING DEVICE, PARTICULARLY FOR ROTARY HEARTH FURNACES, TO LEVEL THE BED OF MILL SCALE INITIALLY PROVIDED ON THE HEARTH FOR BETTER SEATING OF THE WORK PRODUCT THEREIN AND TO REMOVE EXCESS SCALE DERIVED FROM THE WORK PRODUCT WHILE HOLDING THE FURNACE TEMPERATURE SUFFICIENTLY HIGH THAT THE MILL SCALE IS LOOSE AND MANAGEABLE. THE DEVICE COMPRISES A COUNTERBALANCED CANTILEVER TYPE BOOM, CARRYING A SERIES OF CANTED SCRAPER BLADES, INSERTED HORIZONTALLY THROUGH A CLEAN-OUT DOOR INTO THE FURNACE SUBSTANTIALLY ALONG A RADIAL LINE. WHEN IN INSTALLED POSITION, THE BOOM IS HINGEDLY SUPPORTED AT ITS OUTER END ON A PEDESTAL STRUCTURE AND RAISED AND LOWERED UNDER MANUAL CONTROL BY A JACK TO A POSITION FOR APPROPRIATE SCRAPING ACTION BY THE SCRAPER BLADES WHICH, IN COOPERATION WITH THE ROTATION OF THE HEARTH, CAUSES PROGRESSIVE MOVEMENT OF THE SCALE FROM BLADE TO BLADE RADIALLY OUTWARD THROUGH THE CLEAN-OUT DOOR. THE BOOM ASSEMBLY HAS SUITABLE PASSAGES PROVIDED THEREIN FOR WATER CIRCULATION AND CONSEQUENT COOLING TO WITHSTAND EXPOSURE TO HEAT.

Description

June 6, 1972 E. J. KOVALCIK EI'AL 3,667,743

HEARTH SCRAPING DEVICE Filed Feb. 9, 1971 2 Sheets-Sheet 1 mvsmons Edward J. Kovolcik a Edward D. Dowling June 6, 1972 J KQVALCIK ETAL 3,667,743

I-IEARTH SCRAPING DEVICE Filed Feb. 9, 1971 2 Sheets-Sheet 2 INVENTORS Edward J. Kovulcik 8 Edward D. Dowling United States Patent f) 3,667,743 HEARTH SCRAPING DEVICE Edward J. Kovalcik and Edward D. Dowling, Pittsburgh, Pa., assiguors to Pullman Incorporated, Pittsburgh, Pa. Filed Feb. 9, 1971, Ser. No. 113,898 Int. Cl. F27b 9/16 U.S. Cl. 263-7 15 Claims ABSTRACT OF THE DISCLOSURE The specification discloses a hearth scraping device, particularly for rotary hearth furnaces, to level the bed of mill scale initially provided on the hearth for better seating of the work product therein and to remove excess scale derived from the work product while holding the furnace temperature sufficiently high that the mill scale is loose and manageable. The device comprises a counterbalanced cantilever type boom, carrying a series of canted scraper blades, inserted horizontally through a clean-out door into the furnace substantially along a radial line. When in installed position, the boom is hingedly supported at its outer end on a pedestal structure and raised and lowered under manual control by a jack to a position for appropriate scraping action by the scraper blades which, in cooperation with the rotation of the hearth, causes progressive movement of the scale from blade to blade radially outward through the clean-out door. The boom assembly has suitable passages provided therein for water circulation and consequent cooling to withstand exposure to heat.

-It is common practice in the industry to provide a bed of mill scale of uniform thickness on the hearth of a rotary hearth furnace the better to seat the work product therein. It is also the practice to allow the mill scale from the work product to accumulate on the rotary hearth to the limit of tolerance, then to shut down the furnace and allow it to cool sufliciently to enable removal of the scale by manual labor. Unfortunately, as the mill scale cools, it solidifies into a hard sintered agglomerate that adheres to the hearth refractory. A pneumatic hammer is usually required to break up the cold mill scale to enable its removal from the furnace. This generally results in damage to the hearth, thus necessitating repair or patching of such damaged hearth area. The entire I,

clean-out operation is costly both from a labor standi In order to avoid use of pneumatic hammers by manual labor and the consequent usual damage to the hearth refractory, the charging mechanism for inserting the work product into the furnace through a charging door, or for removing it from the furnace through a discharge door, has been known to be employed or adapted so as to be employed, for scraping mil scale out through the charging door or discharge door of a rotary hearth furnace. This is, however, a slow tedious process requiring as it does progressive and repeated rotary positioning of different areas of the hearth on a radial line with the charging door or discharge door to enable the charging device to reciprocate back and forth, to level and scrape the bed of mill scale on the hearth at that point. This kind of operation is not only slow and tedious but it requires a crew of personnel to be in attendance.

In contrast to the foregoing methods, the hearth scraping device which we have devised and the method of its operation have decided advantages, some of which are as follows:

(a) The furnace does not have to be cold or, if heated,

ice

shut down to first cool sufficiently to enable the hearth leveling or clean-out operation to proceed. On the contrary, the furnace is first heated or allowed to continue in operation at a sufficient temperature level after discharging the work product therefrom, to maintain the mill scale in the hot condition essential to operation and performance by the scraping device constituting the invention. Thus, in the clean-out operation there is a great saving of time which was heretofore wasted in waiting for the furnace to cool. i

(b) The complete clean-out operation of the furnace can be accomplished in less time than heretofore, thus resulting in a further saving of clean-time and enabling utilization of the furnace for more productive hours.

'(c) Since the drive mechanism for normal operation of the furnace provides the motive power for the hearth scraping, additional power or drive means for scale removal purposes is not required. To this extent, the selling price of the scraping device to the user is reduced.

(d) The use of pneumatic hammers is avoided, thus eliminating the hard physical manual labor of scale removal as well as the damage to the hearth.

(e) The simplicity of the device enables a minimum of personnel attendance for this operation. Once installed in the furnace, adjustment of the height of the boom relative to the hearth bed is practically the only control required.

As will be made apparent more fully hereinafter, we provide a hearth scraping device for rotary hearth furnaces which is of simple low-cost construction and which minimizes the down-time of the furnace.

More particularly, we provide a device which comprises a cantilevered boom assembly hingedly supported at one end on a pedestal structure outside a clean-out door of a rotary hearth furnace, the boom having a series of parallel-arranged canted scraper blades and extending horizontally through the door into the furnace so as to be disposed above the hearth bed in a substantially radial position for the blades to scrape the excess accumulated scale from the hearth bed or for leveling it. The disposition of the scraper blades is such as to cause the quantities of scale scraped by the blades to move progressively from blade to blade in a radial direction from the inside diameter of the furnace toward the outside diameter of the furnace and thus to be automatically propelled out through the clean-out door to a suitable container. The position of the boom assembly is controlled manually and power-actuated to a desired position above the hearth bed to control the rate and degree of scale removal.

We further provide a boom assembly which is fabricated so as to provide for circulation of a liquid coolant, such as water, through that portion of the boom assembly which lies within and is subject to the heat of the furnace. Moreover, the boom assembly is so balanced, or counterbalanced, as to maintain it in a substantially horizontal position during installation in and removal from the furmace, and to at the same time provide for additional loading on the boom to resist upward displacement by an accumulation of scale scraped by the blades during the operation of the device.

In the foregoing discussion, various objects, features and advantages of the invention have been set forth. These and other objects, features and advantages of the invention together with structural details thereof will be elaborated upon during the forthcoming description of a presently preferred embodiment of the invention and a presently preferred method of practicing the same.

In the accompanying drawings:

FIG. 1 is a plan view, partially in section, showing the essentials of the hearth scraping device constituting the invention as installed in a furnace of the rotary hearth type;

FIG. 2 is an elevational view, taken along the line IIII of FIG. 1, showing further details of the boom assembly and of the pedestal structure to which the boom assembly is hinged;

FIG. 3 is a sectional view, taken along the line III-III of FIG. 2, showing additional details of the pedestal structure and method of anchoring it to the ground;

FIG. 4 is a plan view, on an enlarged scale to that of FIG. 1, showing additional details of the boom assembly and its supporting structure; and

FIG. 5 is an elevational view, on the same enlarged scale as FIG. 4, also showing further details of the boom assembly and its supporting structure.

Referring to FIGS. 1, 2 and 3 of the drawings, the hearth scraping device constituting the invention is shown in its position as installed through the clean-out opening of a rotary hearth furnace. The hearth scraping device comprises a boom assembly 10, hereafter more fully described, hingedly supported at its outer end in a cantilever fashion, on a pedestal structure 11, anchored to the floor or ground. The boom assembly, in its installed position, extends through a clean-out opening 12 in the outer wall 13 of a rotary hearth furnace 14, in substantially radial relation. As apparent from the drawings, the rotary hearth element 15 of the furnace is in the form of an annulus horizontally rotatable between the outer wall 13 and the inner wall -16 with which it has sealed relation, as through water seals in well-known manner.

The boom assembly is shown, illustratively, as made up of a single I-beam 17 (FIGS. 4 and 5) the web of which is disposed horizontally and the flanges of which are positioned vertically. The outer ends of the flanges of beam 17 are cut out on a radius to provide a seating recess in which a hinge pin 18 horizontally seats. The pin 18 is secured to the flanges of the beam 17 as by Welding it thereto.

While the hinge pin 18 is shown as having a permanently fixed position relative to the I-beam 17, it will be apparent that the hinge pin may be adjustably secured to the I-beam to enable vertical adjustment of the hinge axis with respect to I-beam 17, thus providing for vertical adjustment of the hinge axis of I-beam 17 relative to the pedestal structure 11.

In order to provide for cooling of that portion of the boom assembly 10 which projects into the furnace, the space to either side of the web of the I-beam 17 is totally enclosed in a manner to sustain liquid pressure of from 45 to 50 pounds per square inch and communication between the sides provided by cutting out a section 19 of the web of the I-beam at its innermost end. To accomplish this enclosure, two similar plates 20 are Welded along the edges of the I-beam flanges, the inner end of the I-beam 17 is closed by an end plate 21 welded thereto, and two additional end plates 22, each with a central hole therein, are welded to the opposite ends of the plates 20, the Web and the flanges of the I-beam. All welds are such as to sustain a required liquid pressure of at least 45 to 50 pounds.

Secured in the holes in end plates 22, as by welding are suitable pipe couplings 23 to which respective lengths of pipe 24 and 25 are connected under control of valves such as globe valves 26 and 27. Pipes 24 and 25 are connected into a liquid coolant pressure system, such as an available water pressure system, for causing circulation of liquid coolant through the boom assembly in the direction indicated by the arrows. Thus liquid coolant under pressure is supplied from the system to pipe 24 by way of a flexible hose 28 (FIG. 2) having a quick-disconnect coupling 29 for connection to pipe 24. Similarly liquid coolant is returned to a sump, or to a cooling device if the coolant is to be recirculated via a flexible hose 30 connected to pipe 25 as by a quick-disconnect coupling 31.

As will be apparent from the drawings, particularly from FIGS. 4 and 5, the boom assembly further com- 4 prises a plurality, illustratively shown as seven in number, of so-called scraper blades 32 arranged in a substantially parallel uniformly spaced relation to each other and canted, that is disposed at an angle, with respect to the longitudinal axis of the boom assembly, and depending from the bottom surface of the boom assembly.

The particular angularity between the scraper blades and the longitudinal axis of the boom assembly is not critical but it is preferably in the range from 45 to 60. Scraper blades 32 are preferably made in two parts, one of which is an angle bracket 33 which is attached as by welding to the lower facing plate 20 of the I-beam 17, and the other of which is a replacement blade 34 attached as by bolts to the corresponding angle bracket. Preferably, blades 34 are made of special alloy steel for restricting deterioration due to contact with the hot metal scale in the bed of the hearth. v

To enable the boom assembly to be lifted and moved, as by an overhead crane or other similar device, a lifting bracket is provided consisting of a pair of substantially triangular plates 35 (FIGS. 4 and 5) attached, as by bolts, to the opposite flanges of the I-beam 17 and a cross-plate 36 extending therebetween and welded thereto. A hole 37 in the cross-plate 36 enables insertion of a hook on the lifting ropes of a crane. To provide some flexibility in the point of attachment of the lifting bracket for purposes of obtaining balance in the boom assembly, a series of holes may be provided in the flanges of the I-beam spaced uniformly longitudinally of the beam. Correspondingly spaced holes in the base of the triangular plates 35 may therefore be moved longitudinally into registry with different holes in the flanges of the I-beam to provide different longitudinal locations for attachment by bolts.

The point of attachment of the lifting bracket for the boom assembly is of necessity located nearer the outer end of the boom assembly because the major portion of the length of the boom assembly extends into the furnace. Consequently, in order to prevent downward tipping of the inner end of the boom assembly when the assembly is lifted, either for installation or removal, a counterweight .38 is attached to the I-beam 17 at a point adjacent the hinge pin 18. If desired, counterweight 38 may be a single steel block of appropriate weight extending between the flanges of the I-beam and welded thereto, or as shown, the counterweight 38 may be made up of a number of elements consisting of a main element and a plurality of additional smaller weight elements all welded together. In either case, a suitable plate 39 having a hole therein may be welded to the counterweight. Such member 39 functions as an auxiliary lifting bracket and also provides a means for a crewman to grasp to steady the outer end of the boom assembly when the assembly is being lifted. As will be evident, the counterweight 38 serves also to provide additional loading of the boom assembly against undesired lifting thereof from an intended horizontal position due to forces caused by an accumulation of metal scales under the scraper blades 34 during the scraping operation.

The pedestal structure 11, on which the boom assembly 10 is supported, is designed not only to support the weight of the boom assembly but also to withstand torsion forces exerted on the boom assembly due to the rotational drag of the rotary hearth thereon. Essentially structure 11 comprises (see FIGS. 4 and 5) two pairs of upright beams 40 illustratively shown as I-beams, disposed in rectangular spaced relation and having two longitudinally extending side beams 41 and two transversely extending end beams 42 connecting them to provide a rigid structure when welded together. The side beams 41 have their flanges cut back to allow the Web of the side beams to extend between the flanges of the upright beams 40 and their respective webs and flanges are welded together. The end beams 42 are welded directly to the flanges of the pairs of upright beams 40. The lower ends of the upright beams 40 are firmly attached in a concrete footer or foundation, as by being bolted to anchoring studs or bolts embedded in a concrete footer of foundation (see FIG. 3).

The location of the pedestal structure 11 with respect to the clean-out opening 12 in the outer wall 13 of the furnace 14 is preferably such that the longitudinal axis of the pedestal structure is oriented to be substantially radial to the rotary hearth of the furnace and to coincide with the center of the clean-out opening.

Structure 11 is not so shown in FIG. 1, but such variation as exists, was necessiated by the limitations of space outside the furnace wall in a particular installation of the device and is without special significance.

The hinge pin 18 of the boom assembly is adapted to seat in a saddle 43 attached to the outermost pair of upright beams 40. As shown, the saddle 43 comprises a pair of trough-shaped members 44 respectively supported by bracket plates on corresponding upright beams 40 in spaced horizontal alignment such that opposite ends of the hinge pin 18 seat respectively therein. In order to lock the hinge pin 18 in the saddle 43 against undesired or accidental dislodgment therefrom, a pair of C- shaped locking plates 45 are respectively attached, as by bolts, to the outboard side of the bracket plates supporting the saddle trough members 44 in such manner as to hold the hinge pin 18 in the trough member 44.

It should be noted from FIG. 4 that the I-beam 17 of the boom assembly is of somewhat lesser width than the space between the flanges at the upper ends of the pairs of upright beams 40 forming the pedestal structure, to allow ease of entry when the boom assembly is installed thereon. However, a plurality of screws 46 are provided in tapped holes in the flanges of the upright beams 40, which when screwed in against the boom assembly hold it firmly and rigidly in position against any torsion force resulting from the dragging effect on the scraper blades 34.

In order to enable the necessary vertical adjustment of the boom assembly while in the furnace, to obtain the desired height of the scraping edges of the scraper blades 34 with respect to the bed of scales on the furnace hearth for accomplishing leveling or removal of excess depth of scale, a jack 47, such as a hydraulic jack, is provided. As seen in FIGS. 3 and 5, the jack is interposed between the transverse end beam 42 at the end of the pedestal structure 11 closest to the furnace and the under surface of I-beam 17. A round rod 48 is preferably welded in a transverse position to a cross plate 49 welded to the bottom edge of the flanges of the I-beam for engagement by the head of the jack, to allow for some relative movement between the head of the jack and the I-beam occasioned by the up and down hinged movement of the boom assembly.

A small hand-operated pump 50 (FIG. 1) connected to the jack 47 through a flexible hose 51 and located at a convenient point adjacent the pedestal structure serves to control operation of the jack by an operator stationed to observe the desired movement of the boom assembly through the clean-out opening of the furnace. A by-pass relief valve (not shown) may be provided to permit restoration of liquid to the sump of the pump to reduce or relieve the hydraulic pressure, thus causing the jack to lower and the boom assembly to correspondingly follow.

The manner or method of use of the hearth scraping device is largely self-evident. However, a brief explanation is thought to be of assistance in arriving at a full understanding thereof.

For initially preparing and leveling the bed of mill scale on the hearth, or for removing excess mill scale at the conclusion of the heat-run of furnace 14, the furnace is under heat suflicient to maintain the mill scale loose and manageable. Before attempting to install the boom assembly of the scraper device, the hose connections are first made to pipes 24 and 25 and valves 26 and 27 are are then opened so as to provide and insure circulation of the liquid coolant through the boom assembly before insertion of the boom assembly through the furnace cleanout opening 12 into the furnace. It will be apparent that the boom assembly must first be brought sufliciently close to the furnace to enable the hose connections to be made for establishing circulation of the coolant in the boom assembly.

Following establishment of the liquid coolant connections, as just mentioned, the boom assembly is then shifted horizontally, with the aid of the craneman and other crewmen, into the furnace through the clean-out opening, until such time as the hinge pin 18 is engaged in the saddle 43 and the boom assembly rests on the head of jack 47. An angle bracket 52 (FIGS. 4 and 5) Welded transversely to the bottom edges of the I-beam and projecting laterally therefrom serves as a stop, when engaged with the inside edge of the upright beams 40 nearest the furnace, to limit the movement of the boom assembly horizontally into the furnace. The locking plates 45 are then bolted in position over the ends of the hinge pin and the height of the boom assembly adjusted by the jack 47 to provide the desired depth of penetration of the scraping blades in the bed of mill scale on the hearth of the furnace. The movement of the rotary hearth is preferably interrupted sufficiently long to enable adjustment of the height of the boom assembly by operation of the jack 47.

As the hearth rotates in a clockwise direction, indicated by the arrow in FIG. 1, the bed of mill scale initially placed on the hearth or the accumulated scale from the work product which covers the bed of the rotary hearth begins to pile-up against the leading faces of the scraper blades 34. The canted arrangement of the blades is such that the leading and trailing edges of adjacent blades are on the same circumferential line, and in effect the blades form an uninterrupted dam across the bed of the hearth. However, as the scale piles-up against the faces of the blades, a portion spills off and is carried around, with rotation of the hearth, and picked up by the next scraper blade radially outward. This process is repeated until the scale reaches the longest scraper blade at the outer periphery of the hearth adjacent the clean-out opening. The motion of the hearth thus forces the scale radially outward off the last scraper blade and into chute 53 wherein it de scends by gravity and is collected in a metal container or box (not shown) for convenient removal.

The hearth rotates at a relatively slow rate, requiring abou 15 minutes for one complete revolution. It will be seen, therefore, that since repeated revolutions of the hearth are required to cause the scale to be shifted radially outward from scraper blade to scraper blade to the clean-out opening, the entire clean-out process may require as much as several hours. However, such time is negligible in contrast to the time heretofore required by the manual or other method.

While the operation of the hearth scraping device has been described above in connection with removal of excess or excessive scale, derived from the work product, it should be understood that the device may well be utilized also to initially level the bed of scale on the hearth before the start of a heat-run to prepare the bed for proper seating therein of billets or work product items of irregular shape.

Removal of the hearth scraping device from the furnace 1n'volves merely a reversal of sequence of the steps taken to install it. It is important that the liquid coolant connections be maintained until after the boom assembly of the device is completely out of the furnace, after which the supply of coolant may be shut off and connections broken. When not in use, the device may simply be stored in a conveniently removed location.

While a preferred embodiment of the invention has been described, it should be understood that variations thereof may be made within the scope of the following claims.

We claim:

1. A furnace hearth scraping device particularly adapted for use with furnaces of the rotary hearth type, and comprising a boom assembly having a plurality of scraper blades on a section thereof for scraping the furnace hearth to level the bed of mill scale thereon initially or to remove excess mill scale thereon derived from the work product, a support structure, means providing a separable hinged connection between one end of said boom assembly and said structure, and power means on said structure for supporting and pivotally moving said boom assembly to adjustably position the scraper blades with respect to the furnace hearth when said assembly is hingedly coupled to the support structure with said section thereof projecting into the furnace.

2. The combination according to claim 1, wherein the said scraper blades are canted with respect to the longitudinal axis of the boom assembly and disposed in uniformly spaced parallel relation along the section of the boom assembly which is adapted to extend into the furnace.

3. The combination according to claim 2, wherein the leading and trailing edges of adjacent ones of said scraper blades are adapted to lie substantially on the same circumferential radius with respect to the center of rotation of the rotary hearth, in the installed position of said device.

4. The combination according to claim 1, wherein said support structure is anchored in position outside the furnace and so oriented that said boom assembly when installed thereon extends through an opening in the furnace wall to a position above the furnace hearth.

5. The combination according to claim 4, wherein the said scraper blades are canted with respect to the longitudinal axis of the boom assembly and disposed in uniformly spaced parallel relation along the section of the boom assembly which extends into the furnace, the rotation of the hearth causing mill scale to be caught by the stationary blades and progressively shifted from blade to blade radially outward so as to be automatically propelled out of the furnace through the opening in the furnace wall.

6. The combination according to claim 1, wherein the portion of said boom assembly that is adapted to project into the furnace has two longitudinally extending passages therein that communicate with each other at the distal end of the boom assembly, with passages being adapted for connection in a liquid coolant pressure system for circulation of the liquid coolant in succession through said passages.

7. The combination according to claim 1, wherein said boom assembly is a fabricated structure having an Ibeam with the section of the assembly that is adapted to project into the furnace separated into two longitudinally extending totally enclosed passages at opposite sides of the web, a portion of the web at the distal end of the boom assembly being cut away to provide communication between the passags at the'opposite sides of the web, and wherein pipe means are connected respectively to said passages to provide means of supply and return of liquid coolant to and from said passages.

'8. The combnation according to claim 7, wherein flexible hoses with quick-disconnect couplings thereon for connection to said pipes provide the means whereby said pipes are connected into a liquid coolant pressure system.

9. The combination according to claim 1, wherein means are removably attached to said support structure to prevent separation of said hinged connection means.

10. The combination according to claim 1, wherein said boom assembly comprises an I-beam and wherein the means providing a separable hinged connection between one end of said boom assembly and said structure comprises a cylindrical rod attached horizontally to the outer end of the said I-beam and a pair of horizontally aligned and spaced trough members carried by said support structure in which said cylindrical rod seats.

11. The combination according to claim 10, wherein means removably attachable to said support structure is provided for preventing dislodgment of said cylindrical rod from its seat in said trough members.

12. The combination according to claim 1, wherein lifting bracket means is attached to said boom assembly at a point spaced from said hinged connection means, and counterweight means is attached to said assembly adjacent said hinged connection means whereby to maintain said assembly in a substantially balanced horizontal position as it is lifted and moved for installation into and removal from the furnace.

13. The combination according to claim 1, wherein counterweight means is carried on said boom assembly adjacent said hinged connection means to provide loading of said boom assembly to resist undesired elevation of said assembly due to interposition of mill scale under said scraper blades while said device is in operation.

14. The combination according to claim 1, wherein said power means comprises hydraulic pressure controlled jack means for pivotally elevating and lowering said boom assembly while hingedly coupled to said support structure.

15. The combination according to claim 14, wherein manually operated pump means is provided for controlling the liquid pressure delivered to said hydraulic jack means.

References Cited UNITED STATES PATENTS 2,676,006 4/1954 Martin 26 3-26 2,973,568 3/1961 Greger 2637 3,079,135 2/ 1963 Buckholdt 263-7 3,497,190 2/1970 Moore 263-26 JOHN .T. CtAMBY, Primary Examiner US. Cl. X.R. 26326 UNITED STATES PATENT OFFICE QERTHICATE CF CGRREQTION Patent No. 3,667,743 Dated June 6, 1212 Inventor(s) Edward J. Kovalcik et 8.1

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 57, "mil" should read mill Column 6, line 49, "abou" should read about Column 7, line 49, "with" should read said Column 8, line 5, "combnation" should read combination Signed and sealed this 31st day of October 1972.

(SEAL) Attest:

EDWARD MJLETCHERJR. ROBERT GO'ITSCHALK Attesting Officer Commissioner of Patents )RM po'mso noeg) uscoMM-oc 6O376-P69 U.S GOVERNMENT PRINTING OFFICE 1969 0-'366-!!4.