US3715840A

US3715840A - Apparatus and method for finishing workpieces

Info

Publication number: US3715840A
Application number: US00103266A
Authority: US
Inventors: R Davidson
Original assignee: Grav I Flo Corp
Current assignee: Grav I Flo Corp
Priority date: 1970-12-31
Filing date: 1970-12-31
Publication date: 1973-02-13
Anticipated expiration: 1990-02-13
Also published as: CA938449A; IT940937B; BE773768A; GB1323499A; DE2147476A1; FR2120669A5; NL7115007A

Abstract

A tumbling machine having an endless belt arranged so that the top run of the belt defines with a pair of side walls a V-shaped tumbling chamber in which the mixture of abrasive media and the workpieces are loaded so that at one side of the chamber the workpieces are caused to travel upwardly to a high point, then flow down towards the opposite side of the chamber where they are again conveyed by the belt around the apex of the V.

Description

United States Patent 1191 Davidson 1 1 -3, 71,4 1 1 Feb. 13, 197

[54] APPARATUS AND METHOD FOR FINISHING WORKPIECES [75] Inventor: Richard L. Davidson, Sturgis, Mich.

[73] Assignee: The Grav-l-Flo Corporation, St.

Joseph County, Mich.

221 Filed: Dec.31,1970

21 Appl. N01: 103,266

[52] US. Cl ..5l/163, 51/313 [51] Int. Cl. ..B24b 31/10 [58] Field of Search ..51/163,316, 313

[56] References Cited V UNITED STATES PATENTS 1,224,191 5/1917 Medgyes ..51/l63 2,538,242 1/1951 Hannon ..5l/163 2,523,304 9/1950 Johnson ..5l/163 X 3,161,997 12/1964 Balz .51/3 16 FOREIGN PATENTS OR APPLICATIONS 1,168,448 12/1958 France ..51/l63 559,869 3/1944 Great Britain ..5 H163 Primary Examiner-Harold D. Whitehead Attorney-Barnes, Kisselle, Raisch & Choate 5 7 ABSTRACT A tumbling machine having an endless belt arranged so that the top run of the belt defines with a pair of side walls a V-shaped tumbling chamber in which the mixture of abrasive media and the workpieces are loaded so that at one side of the chamber the workpieces are caused to travel upwardly to a high point, then flow down towards the opposite side of the chamber where they are again conveyed by the belt around the apex of the V.

17 Claims, 6 Drawing Figures PAIENTEDFEB 1 3 I975 sum 1 or 2 x i: x x x x x ATTORNEYS 3,715,840 sum 20F 2 PATENTED FEB 1 3 I973 5r F/ G. 5 wawa/ ATTORNEYS APPARATUS AND METHOD FOR FINISHING WORKPIECES This invention relates to an apparatus and method for surface finishing of metal workpieces.

Small workpieces are frequently deburred and/or polished on a production basis in tumbling barrels or vibratory finishing machines. Both of these types of machines have recognized shortcomings with respect to the rate of metal removal and the quality of the finish obtainable on the surface of the workpiece.

The object of the present invention resides in the provision of an apparatus and method for obtaining a high quality finish on workpieces in a minimum amount of time.

More specifically, the invention contemplates the finishing of workpieces by tumbling them with an abrasive or polishing media in a chamber having fixed side walls and a V-shaped bottom wall formed by the top run of an endless belt driven in one direction such that the mass of workpieces and finishing media are caused to travel in said chamber in a manner which promotes a high metal removal rate with a minimum of impingement and a maximum of rubbing or burnishing action.

The machine of the present invention is further characterized by the provision of simple and expedient means for discharging the workpieces and the finishing media from the machine by merely reversing the direction of belt travel and drawing the top run of the belt taut.

Other features and advantages of the present invention will become apparent from the accompanying disclosure and drawings, in which:

FIG. 1 is a side elevational view of a finishing machine according to the present invention.

FIG. 2 is a top view thereof.

FIG. 3 shows the machine as viewed from the discharge end thereof.

FIG. 4 is a fragmentary sectional view of a portion of the machine.

FIG. 5 is a diagrammatic view showing the manner in which the mass of media and workpieces are caused to travel in the machine of the present invention.

FIG; 6 is a fragmentary perspective view within the chamber of themachine showing the endless belt and the mass of finishing mediaand workpieces.

Referring to FIGS. 1 through 3, the base 10 of the machine comprises, a U-shaped stanchion having a pair of laterally spaced upright supports 12 (FIG. 3) on whichthe. spaced apart side walls 14 of the machine housing are mounted. As shown in FIG. 1, each side wall 14 has a downwardly sloping upper edge 16 and two generally converging side edges 18', 20. The machine housing includes a bottom wall 22 extending between the lower portions of side walls 14 and forming a drain trough at the lower end of the machine which slopes downwardly into a sump 24.

Two

drive pulleys

26,28 are journalled between side walls 14 at opposite ends of themachine and adjacent the upper edges of the side walls. An endless belt 30 is trained around

pulleys

26,28 and around a pair of idler pulleys 32. A belt tightener in the form of pivotally supported arm 34 carrying a roller 36 at its free end is also provided. The belt tightener is adapted to'be actuated by a hydraulic cylinder 38 between the two positions shown in FIG. 1.

On the inner surface of one side wall 14 there is fixedly secured a wear plate 42. A second wear plate 44 is mounted on the other side wall 14 for adjustment toward and away from wear plate 42 so that the two wear plates are engaged by the opposite side edges of endless belt 30 and wear plate 44 can be adjusted laterally to compensate for wear in the width dimension of belt 30. A generally V-shaped belt guide 46 which is narrower than belt 30 is secured to the two side walls 14 and extends between the two

wear plates

42,44. In FIG. 4 the two legs of the V-shap'ed belt guide are designated 48, 50 and the rounded apex of the V is designated 52. In FIG. 1 the upper edges of the

wear plates

42,44 are designed 51 and in FIG. 4 the opposite side edges of the wear plates are designated 53,55. At the rounded apex 52 the guide plate is provided with a plurality of drain openings 54. It will be observed that leg 48 of guide plate 46 extends along a line generally tangent to pulley 26 and leg 50 extends along a line generally tangent to pulley 28. Leg 48 is more steeply inclined than leg 50. In the embodiment illustrated leg 48 is inclined to the vertical at an angle of about 22 nd leg 50 is inclined to the vertical at an angle of about 4. As will be explained hereinafter, these angles can b varied within a limited range depending upon the speed at which the belt is driven.

Pulleys 26,28 are keyed to shafts each having a s rocket 56 on one end thereof. The output shaft of a s eed reducer unit 58 has a pair of sprockets 60 keyed t ereto. A pair of chains 62 are trained around both p ir of

sprockets

60 and 56 so as to rotate the two pulle s 26,28 at the same speed and in the same direction. B It 30 is driven by the frictional engagement of

pulleys

26,28 with the belt. Speed reducer unit 58 is preferably ad ustable so as to vary the speed of the belt as desired.

\ he diagrammatic showing in FIG. 5 illustrates the copfiguration of the top run 300 of belt 30 and the botto l run30b of the belt while the machine is in operation The locations of

drive pulleys

26,28 and idler pulley'sL32 are determined in relation to the length of belt 30 and the size of the load which the machine is designed to handle such that the upper run 30a of the belt assumes a configuration which generally parallels the shape of guide plate 46 and such that the upper run of the belt will be spaced slightly from guide plate 46 as indicated by the clearance space 64in FIG. 4. Thus, with'the machine operating in the manner, illustrated in FIG. 5 the upwardly travelling portion of'the top run 30a of the belt is inclined to the vertical at an angle of about 22 and the downwardly travelling portion of the top run 30a of the belt is inclined to the vertical at an angle of about 44. It will be appreciated however that FIG. 5 actually illustrates the dynamic, not the static, condition of the belt. Furthermore, it will be appreciated that the function of guide plate 46' is merely to prevent the top run 30a of the belt from swaying. Under ideal operating conditions guide plate 46 will be spaced throughout its extent from the underside of the top run 30a of the belt.

In FIG. 6 the workpieces being processed are illustrated as dished-shaped discs 66 and the polishing media or chips are in the form of cones 68 molded from a mixture of a binder, such as a synthetic resin or a ceramic, and abrasive. The use of such preformed synthetic chips, as distinguished from natural stone chips, is very desirable because natural stone chips tend to splinter whereas the synthetic chips merely wear down in size and are therefore not apt to become wedged between the edges of belt 30 and wear

plates

42,44. For some types of finishing operations (polishing, for example, where chips are slippery) it is desirable to have angled cleats 70 on the belt to assist in elevating the mass by means of the upwardly travelling portion of the top run of the belt.

Nozzle 72 is illustrated in FIG. 1 and is located above and slightly inwardly of the upper end of the portion of the belt run travelling upwardly. The nozzle is utilized for.directing a spray of water or water containing a nonabrasive detergent over the mass of workpieces and abrasive media as it reaches the upper end of the upward travel. As indicated in FIG. 5 nozzle 72 is connected by a conduit 74 with the outlet of a pump 76 having its inlet connected to sump 24 above the bottom thereof. Thus, with this arrangement the water spray issuing from nozzle 72 cleans the parts and media and then drains into the sump through the drain holes 54 at the lower end of belt guide 50. The fine grindings off f the metal workpieces and the media preforms settles n sump 24 and the substantially uncontaminated water is recirculated back to nozzle 72. Flushing of the W kpieces and media is important in order to maintai a clean mass within the chamber of the machine. It ser es to accelerate the cutting action of the abrasive me la on the workpieces.

The spray nozzle 72 also clears the belt of abrasive chips and workpieces that might otherwise adhere to the belt and become discharged over pulley 26. i

In operation the machine is charged with a loa I of workpieces to be finished and an abrasive media, S i-ICII as the preformed chips 68. When pulleys 26,28 are driven in a counterclockwise direction as viewed in FIG. the mass assumes the configuration show in FIG. 5. Generally speaking, the moving mass be considered as divided into several areas or zones lhe most active zone, designated A, may be referred tip as the slide zone wherein the parts and media gra i ate from the vicinity of high point 78 to the vicinity of low point 80 adjacent the downwardly travelling portion of the belt. The downward slope of the slide area 80 depends upon the shape and surface characteristics of the media and parts. Generally speaking, the slide area inclines downwardly at a fixed angle of between 25 to 35. The second most active zone in the mass is designated B in FIG. 5 and comprises a layer of the mass adjacent the upper run of the belt. This portion of the mass is active not only because it is being positively driven by the belt, but also because the side walls of the chamber in which the mass is located, namely, wear

plates

42,44, remain stationary while the belt is carrying the mass, thus causing additional friction between the layer of the material at each of the sides of the chamber and the material in the center of the mass. The next most active zone is designated C in FIG. 5 and comprises the annular teardrop shape portion surrounding zones A and B. This activity, that is, the relative movement between the parts and the media, in this area is less than in areas A and B. The center area D may be referred to as the dead cone since there is considerably less activity in this zone than in the other zones. However, the parts do not remain stagnant in area D. workpieces and media continually work into and out of this area from and into the other areas represented in FIG. 5.

One of the features of the present invention resides in the fact that area D is relatively small in comparison to the size of the mass. This may be explained by the fact that substantial activity occurs in areas B and C as a result of the drag effect on the parts and media by the stationary wear plates while the mass is being positively driven by the belt.

The slope of the upwardly travelling portion of the belt and the speed of the belt are controlled so that as the parts approach the high end of the slide zone A they gently flow around the high point A and gravitate smoothly down toward the low point 80. If the slope of the upwardly travelling portion of the belt is too steep the workpieces roll out of the mass media too freely in the vicinity of high point 78 and simply roll down the slide area A over the mass of abrasive media. This produces relatively little work on the workpieces and prolongs the duration of the finishing cycle. On the other hand, if the slope of the upward travelling portion of the belt is not great enough, the parts tend to churn and remain too long in the high point area 78 where the work being performed on the parts is substantially less than in the slide area A. An inclination of about 22 for this portion of the belt is preferred but inclinations between 17 to 27 are possible.

The slope of the downwardly travelling portion of the top run of the belt is determined such that the slope of the slide zone intersects the plane of the belt at an included angle of less than 90. This has been found to be desirable to avoid impingement and build-up of the parts and media around the low point of the slide zone A. lmpingement should be avoided as much as possible in order to obtain the best quality finish. In the machine of this invention impingement is also avoided by reason of the fact that the downwardly travelling portion of the belt is at a fixed angle (as distinguished from a changing angle as in the case of a straight sided tumbling barrel) and the belt speed can be controlled so that the workpieces flow or fold smoothly into the portion of the mass being driven downwardly by the belt. While an inclination of about 44 to the vertical is preferred, inclinations of between about 40 to 50 are possible.

An extremely important feature of the present invention has to do with the length of a slide zone A in relation to the size of the mass and the size of the least active area D. Slide zone A in a machine of the present invention is substantially greater than the slide area of a tumbling barrel designed to accommodate the same size load and at the same time the size of the inactive area D in the machine of the present invention is substantially smaller than the size of the tumbling barrel designed to accommodate the same load. It follows, of course, that the slide area of a given tumbling barrel can be increased by increasing the diameter of the barrel but it must be remembered that as the diameter of the barrel increases the size of the inactive areain the barrel also increases.

In order to obtain values showing the relative rates of cut and the quality of finish obtainable with a machine of the present invention as compared with a vibratory finishing machine and a tumbling barrel, three identical loads of small door handles and preformed abrasive chips were run for a period of 4 hours in each of the three machines. The load consisted of I70 lbs. of 9/16 inch X 9/16 inch cone-shaped chips made ofpolyesther resin and silica abrasive along with 45 lbs. of zinc handles. A nonabrasive detergent compound was used at the rate of 1 ounce per gallon ofwater.

The tumbling machine had an actagon shaped cylinder I6 inches long and 30 inches across the flats, and, thus, had an optimum capacity of about 3.l cubic feet. The vibratory finishing machine also had a 3.1 cubic foot capacity. The tumbling barrel was rotated at 20 r.p.m. and the frequency of the vibratory finishing machine was 2,100 r.p.m. with an amplitude of oneeighth inch. The machine according to the present invention had a width of 8 inches and a radius of inches at the lower rounded end of the V-shaped belt. The two drive pulleys 26,28 had a diameter of 10 inches and were driven at 58 r.p.m. producing a lineal speed of the belt of about l,800 feet per minute. When the machine was operated with a load of 3.1 cubic feet of chips and handles, the mass assumed the configuration and relative proportions shown in FIG. 5. The

results of these tests are shown in Table I.

TABLE 1 Media Part Media loss loss loss per oz. of metal loss Tumbling Barrel 2 lbs. I A 02. 2L3 oz. Vibratory 6 lbs. Machine I0 02. 4 oz. 26.5 oz. Endless Belt 6 lbs. Machine 9 oz. l6.l oz.

. operating the machine with a mixture of workpieces and abrasive media. After the desired initial finish is obtained, a polishing compound can be added to the mass in order to obtain a smooth, high luster finish on the workpieces. The successive operations can be performed without removing the mass from the machine or without even stopping the operation of the machine. This feature of the present invention substantially reduces labor costs in comparison with the time and work required for obtaining a high luster, smooth finish on workpieces in a tumbling barrel.

Referring to FIG. I, it will be noted that when cylinder 38 is actuated, arm 34 is pivoted from its raised to the lowered position. Since roller 36 engages the inside face of the lower run of belt 30, the top run 300 of the belt la caused to gradually shorten in length to it finally taut condition shown at 02 In FIG. I. Thus, if the direction of rotation of the belt is reversed, that is, pulleys 26,28 rotated clockwise instead of counterclockwise, as the top run of the belt approaches its taut position the mass of workpieces and media is automatically discharged downwardly over pulley 28 onto a receiving conveyor or other collector and separating means guiding the belt around said rollers such that the 7 top run of the belt is slack and assumes a generally V- shaped configuration between the rollers which is nonsymmetrical about a vertical axis through the apex of the V, the side of the V adjacent the higher roller being moresteeply inclined than the other side of the V, a pair of fixed side plates disposed one adjacent each edge of the belt and cooperating with the top run of the belt to define a generally V-shaped chamber for containing a mass of workpieces and finishing media and means for driving the belt in one direction such that the mass of media and workpieces is caused to flow in said chamber in a path upwardly along said moresteeply inclined side of the V-shaped chamber in the direction of the upwardly travelling portion of the top run of the belt, then downwardly across the chamber in the direction toward the downwardly travelling portion of the upper run of the belt at the less steeply inclined side of the V and then downwardly along said last-mentioned side ofthe V and around the apex of the V to the upwardly travelling portion of the belt, the apex of said V being curved in an upwardly concave direction and the sides of said V being generally flat, the linear extent of said curved apex being small relative to the linear extent of the sides of said V.

2. A machine as called for in claim I wherein said belt driving means comprises both of said rollers.

3. A machine as called for in claim I wherein said belt driving means have a driving connection with said belt adjacent each of said rollers.

4. A machine as called for in claim I wherein said guide means includes means on the underside of the top run of the belt for maintaining the apex of the V- shaped top run of the belt in a generally fixed position between said rollers.

5. A machine as called for in claim 1 wherein said guide means are disposed on the underside of the top run of the belt and are arranged in generally V-shaped fashion with one of the legs of the V adjacent the upwardly travelling portion of the top run of the belt and and other adjacent the downwardly travelling portion ofthe top run of the belt.

6. A machine as called for in claim I wherein the upwardly travelling portion of the top run of the belt is inclined to the vertical at an angle of between about 17 and 27.

7. A machine as called for in claim 6 wherein the downwardly travelling portlon of the top run of the belt is inclined to the vertical at an angle of between about 40 to 50.

8; A machine as called for in claim 1 including belt tightening means for optionally removing said slack from the top run of the belt to cause said top run of the belt to extent substantially straight in a downwardly inclined angle between said upper and lower rollers.

9. A machine as called for in claim 8 including means for driving the belt such that said straight top run is travelling downwardly in the direction from said upper to said lower roller to discharge the contents of said chamber.

10. A method of finishing workpieces which comprises, charging a mixture of abrasive media and workpieces into a chamber having fixed side walls and a generally V-shaped bottom wall defined by the upper run of an endless belt causing the major portion of said upper run of the belt to assume an angle substantially more steeply inclined to the vertical at one side of the V than at the other side ofthe V and driving said belt in a direction such that the upper run thereof is travelling upwardly at the more steeply inclined side thereof and downwardly at the less steeply inclined side thereof thereby causing said mass to flow in said chamber in a path extending upwardly in a direction generally parallel to the more steeply inclined, upwardly travelling portion of said bottom wall, then downwardly across said chamber toward the less steeply inclined, downwardly travelling portion of the bottom wall, then downwardly in the direction of travel of the less steeply inclined, downwardly moving portion of the bottom wall and around the apex of the V to the upwardly travelling portion ofthe bottom wall.

11. The method called for in claim 10 wherein said mass is caused to travel in said upward and downward directions at generally fixed angles inclined relative to the vertical.

1 2. The method called for in claim 10 wherein at least the major portion of said mass is caused to travel in said upward direction at a generally fixed angle of between 17 and 27 to the vertical.

13. The method called for in claim 12 wherein at least the major portion of said mass is caused to travel in said downward direction toward the downwardly travelling portion of the bottom wall at a generally fixed angle to the horizontal of about 25 to 35.

14. The method called for in claim 13 wherein at least the major portion of said mass is caused to travel in said direction of said downwardly moving portion of the bottom wall at a generally fixed angle of about 40 to 50 to the vertical.

15. The method called for in claim 12 wherein the direction of travel of the mass in said downwardly direction toward the downwardly moving portion of the bottom wall and the direction of travel of the mass in the direction of the downwardly moving portion of the bottom wall intersect with an included angle of less than 16. A machine as called for in claim 1 including means disposed adjacent the upper roller and the upper run of the belt an operable to prevent the workpieces and media in the chamber from being carried upwardly over the top roller as the belt travels thereover and for assisting the workpieces and media to flow in said path downwardly across said chamber.

17. A machine as called for in claim 16 wherein said last-mentioned means comprises nozzle means for directing pressurized liquid streams against the top run of the belt in said chamber and adjacent the upper roller.

i i i i i

Claims

1. In a machine for finishing workpieces the combination comprising, a pair of rollers spaced apart on parallel axes, one of said rollers being located in a plane above the other roller, an endless belt trained around said rollers, said belt having a length substantially greater than twice the distance between the roller axes, means guiding the belt around said rollers such that the top run of the belt is slack and assumes a generally V-shaped configuration between the rollers which is nonsymmetrical about a vertical axis through the apex of the V, the side of the V adjacent the higher roller being more steeply inclined than the other side of the V, a pair of fixed side plates disposed one adjacent each edge of the belt and cooperating with the top run of the belt to define a generally V-shaped chamber for containing a mass of workpieces and finishing media and means for driving the belt in one direction such that the mass of media and workpieces is caused to flow in said chamber in a path upwardly along said more steeply inclined side of the V-shaped chamber in the direction of the upwardly travelling portion of the top run of the belt, then downwardly across the chamber in the direction toward the downwardly travelling portion of the upper run of the belt at the less steeply inclined side of the V and then downwardly along said last-mentioned side of the V and around the apex of the V to the upwardly travelling portion of the belt, the apex of said V being curved in an upwardly concave direction and the sides of said V being generAlly flat, the linear extent of said curved apex being small relative to the linear extent of the sides of said V.

2. A machine as called for in claim 1 wherein said belt driving means comprises both of said rollers.

3. A machine as called for in claim 1 wherein said belt driving means have a driving connection with said belt adjacent each of said rollers.

4. A machine as called for in claim 1 wherein said guide means includes means on the underside of the top run of the belt for maintaining the apex of the V-shaped top run of the belt in a generally fixed position between said rollers.

5. A machine as called for in claim 1 wherein said guide means are disposed on the underside of the top run of the belt and are arranged in generally V-shaped fashion with one of the legs of the V adjacent the upwardly travelling portion of the top run of the belt and and other adjacent the downwardly travelling portion of the top run of the belt.

6. A machine as called for in claim 1 wherein the upwardly travelling portion of the top run of the belt is inclined to the vertical at an angle of between about 17* and 27* .

7. A machine as called for in claim 6 wherein the downwardly travelling portion of the top run of the belt is inclined to the vertical at an angle of between about 40* to 50* .

8. A machine as called for in claim 1 including belt tightening means for optionally removing said slack from the top run of the belt to cause said top run of the belt to extent substantially straight in a downwardly inclined angle between said upper and lower rollers.

10. A method of finishing workpieces which comprises, charging a mixture of abrasive media and workpieces into a chamber having fixed side walls and a generally V-shaped bottom wall defined by the upper run of an endless belt causing the major portion of said upper run of the belt to assume an angle substantially more steeply inclined to the vertical at one side of the V than at the other side of the V and driving said belt in a direction such that the upper run thereof is travelling upwardly at the more steeply inclined side thereof and downwardly at the less steeply inclined side thereof thereby causing said mass to flow in said chamber in a path extending upwardly in a direction generally parallel to the more steeply inclined, upwardly travelling portion of said bottom wall, then downwardly across said chamber toward the less steeply inclined, downwardly travelling portion of the bottom wall, then downwardly in the direction of travel of the less steeply inclined, downwardly moving portion of the bottom wall and around the apex of the V to the upwardly travelling portion of the bottom wall.

12. The method called for in claim 10 wherein at least the major portion of said mass is caused to travel in said upward direction at a generally fixed angle of between 17* and 27* to the vertical.

13. The method called for in claim 12 wherein at least the major portion of said mass is caused to travel in said downward direction toward the downwardly travelling portion of the bottom wall at a generally fixed angle to the horizontal of about 25* to 35*.

14. The method called for in claim 13 wherein at least the major portion of said mass is caused to travel in said direction of said downwardly moving portion of the bottom wall at a generally fixed angle of about 40* to 50* to the vertical.

15. The method called for in claim 12 wherein the direction of travel of the mass in said downwardly diRection toward the downwardly moving portion of the bottom wall and the direction of travel of the mass in the direction of the downwardly moving portion of the bottom wall intersect with an included angle of less than 90*.

16. A machine as called for in claim 1 including means disposed adjacent the upper roller and the upper run of the belt an operable to prevent the workpieces and media in the chamber from being carried upwardly over the top roller as the belt travels thereover and for assisting the workpieces and media to flow in said path downwardly across said chamber.