WO2000074875A1

WO2000074875A1 - Apparatus for compacting sand within a flask

Info

Publication number: WO2000074875A1
Application number: PCT/US2000/015375
Authority: WO
Original assignee: Vulcan Engineering Company, Inc.
Priority date: 1999-06-03
Filing date: 2000-06-02
Publication date: 2000-12-14
Also published as: AU5462500A

Abstract

An apparatus for use in lost-foam type foundry operations for compacting sand within a foundry flask (17) having a pattern secured therein prior to pouring molten material into the flask (17). The compacting apparatus utilizes a pair of horizontally displaced driven shafts (25, 26) having mechanically variable eccentric weights (28, 29) affixed thereon for generating a predetermined oscillating force upon rotation of the shafts (25, 26). The variable eccentric weights (28, 29) include a first disk shaped weight (28) rigidly affixed to a hub (40), which is in rotational engagement with the shaft (25, 26), and a second disk shaped weight (29) which is adjustably affixed to the first disk shaped weight (28) for rotation therewith. Rotation of the shafts (25, 26) generates a horizontal and a vertical component of compaction force, which is applied to the flask (17) having a pattern secured therein.

Description

APPARATUS FOR COMPACTING SAND WITHIN A FLASK

TECHNICAL FIELD

The present invention generally relates to an apparatus for producing an oscillating force. More particularly, the present invention relates to an apparatus for use in the foundry industry to efficiently compact sand within a foundry flask having a pattern therein, via application of an oscillating force to the flask prior to pouring the molten material into the flask. With further particularity, the present invention relates to a foundry sand compaction apparatus capable of generating and applying controllable horizontal and vertical oscillating forces. With even greater particularity, the present invention relates to a foundry sand compaction apparatus for generating controllable horizontal and vertical oscillating forces having a means for mechanically adjusting the force output of the apparatus without significant disassembly of the apparatus. With even further particularity, the present invention relates to a foundry sand compaction apparatus for applying an oscillating force to a foundry flask utilizing horizontally displaced rotating shafts having mechanically adjustable eccentric weights mounted thereon for generating controllable horizontal and vertical oscillating forces upon rotation of the shafts.

BACKGROUND In order to manufacture a cast product in the foundry industry utilizing a lost-foam type process, first a pattern of the desired cast product must be produced. The pattern is manufactured of a material capable of melting and evaporating upon contact with a molten metal, when such a material is poured into the mold. The evaporative pattern is sprayed or coated with a refractor wash, and is then secured within a flask of sufficient size to completely contain the pattern. Subsequent to placing the pattern within the flask, the remaining volume of the flash suπounding the pattern is filled with a packing material, commonly fill sand, thereby forming a mold. An evaporative riser attached to the top portion of the pattern leads to the top of the sand, and is used to direct the molten metal into the mold upon pouring. High temperature molten material is thereafter poured into the flask, evaporating the pattern and riser and thereafter filling the volume previously occupied by the pattern and riser. Upon evaporation of the pattern, the molten material is contained or bound only by the shell formed by the refractor wash and the aforementioned fill sand in the shape of the pattern. Therefore, in order to maintain the desired structural shape and integrity of the cast product upon evaporation of the pattern within the fill sand, the fill sand must be sufficiently compacted around the pattern as to maintain the shape of the evaporative pattern upon the pouring of molten material into the flask. Presently, numerous systems exist in the foundry industry for compacting sand within a flask. Primarily, the current systems incorporate heavy weights mounted about substantially vertical parallel shafts, which are in releasable engagement with the foundry flask. Upon engagement of the flask and rotation of the substantially vertical shaft and weights, an oscillating force is exerted upon the flask, thereby compacting the sand around the mold. Cuπent industry practice teaches that in order for optimum compaction of the fill sand, the oscillating force produced by the shaft and weight arrangements should be substantially horizontal. The substantially vertical orientation of the shafts, along with a purely horizontal plane of rotation for the attached weights, inherently allows the present devices to theoretically generate the desired substantially horizontal oscillating force. However, it has been found that vertically orientated shaft designs are prone to imparting a swirling motion to the flask and sand within, which drastically reduces compaction characteristics and often causes physical damage to the pattern within the flask. Further, the present devices are generally extremely bulky in size, incorporate heavy weights necessitating increased power to start and stop operation of the compactor, and are extremely difficult to disassemble or maintain. Although the present devices generally provide sufficient horizontal oscillating forces to compact fill sand around a mold, the present devices are limited in that the orientation of the rotating shafts and weights does not allow for the production of a significant vertical component of oscillating force, which has recently been shown to significantly increase sand compaction characteristics. Further, any vertical component of force generated by the present devices is uncontrollable. Recent studies have concluded that the insertion of a controllable vertical component of force increases sand compaction characteristics, inasmuch as the insertion of the vertical component of force contributes to urging sand upward into previously unreachable portions of the pattern. Compaction of sand in these previously unreachable areas reduces the post pouring machining necessary to finish particular cast products. Further limiting the efficiency of the cuπent devices is the practice of using gear aπangements to synchronize and time the vertically oriented shafts. These gear aπangements, although capable of high shaft rotation speeds when accompanied by oil cooled bearings, nonetheless hinder the effectiveness and efficiency of the present compaction apparatuses, as significant time is expended in tear down, repair, maintenance, and adjustment processes due to the additional disassembly/assembly time required for the gear aπangements. Further, industry development has recently revealed that adequate sand compaction can be accomplished at lower shaft revolution speeds, thereby allowing for alternative drive systems having more efficient and cost effective characteristics than that which is accomplished through the gear and oil cooled bearing arrangements. Lowering the operating rotation speed of the compaction apparatuses increases bearing life and further allows for quicker startups and shut downs in the casting process, thus increasing efficiency and productivity. Additionally, some current devices utilize a second pinion gear assembly in conjunction with the vertical shaft to allow for counter-rotation of a pair of eccentric weights placed upon the single shaft. This particular gear assembly further limits the effectiveness of the present devices, as tear down times for maintenance, adjustment, and repairs are further extended. Finally, although the cuπent devices generally allow for a variation of the magnitude of the oscillating force by increasing or decreasing the shaft rotation speed, the variance in the oscillation force is limited to the range which can be provided by varying the rotation speed. Therefore, the foundry industry would greatly benefit from an improved sand compaction apparatus constructed from compact and significantly lighter weight materials than the previous apparatuses and having the ability to generate a mechanically adjustable oscillating force having a controllable horizontal and vertical components, which could be easily disassembled for repairs, maintenance, or adjustments. Such an apparatus would increase cast line capacity, minimize down time for repairs and maintenance, and reduce the post casting labor involved in finishing cast products.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved sand compaction apparatus capable of generating an oscillating force having a controllable horizontal and vertical components. It is a further object of the present invention to provide an improved sand compaction apparatus of reduced size and weight, which is capable of generating forces equal to larger and heavier prior art apparatuses and able to start and stop operation in a more time efficient manner, thereby increasing the efficiency of the compaction apparatus. It is a further object of the present invention to provide an improved sand compaction apparatus capable of adequately compacting sand at shaft rotation speeds within that which is accomplishable via general and economical belt and pulley drive assemblies utilizing simple grease type bearings. It is yet a further object of the present invention to provide an improved sand compaction apparatus utilizing horizontally orientated rotating shafts having mechanically adjustable eccentric weights mounted thereon for generating a mechanically adjustable horizontal and vertical components of force. It is yet a further object of the present invention to provide an improved sand compaction apparatus capable of efficiently compacting sand utilizing a light weight and easily assembled adjustable eccentric weight assembly rotatably mounted and driven via commonly known belt assemblies. DESCRIPTION OF THE DRAWINGS

A device/apparatus embodying the features of the present invention is depicted in the accompanying drawings, which form a portion of this disclosure, wherein:

FIG. 1 is a side elevational view of the present invention showing the sand compaction apparatus adjacent a flask used in lost-foam type foundry operations; FIG. 2 is a top plan view thereof;

FIG. 3 is a perspective view of the sand compaction apparatus; FIG. 4 is a front elevational view thereof; FIG. 5 is a side elevational view thereof; FIG. 6 is a sectional view taken generally along line 6-6 of Fig. 2;

FIG. 7 is a front elevational view of the hub portion of the mechanically adjustable eccentric weight assembly;

FIG. 8 is a front elevational view of the first disk-shaped weight portion of the mechanically adjustable eccentric weight assembly; FIG. 9 is a front elevational view of the second disk-shaped weight portion of the mechanically adjustable eccentric weight assembly;

FIG. 10 is an exploded perspective view of a shaft and a mechanically adjustable eccentric weight assembly;

FIG. 11a is a front elevational view of the mechanically adjustable eccentric weight assembly;

FIG. l ib is a front elevational view of the mechanically adjustable eccentric weight assembly;

FIG. 1 lc is a front elevational view of the mechanically adjustable eccentric weight assembly; and FIG. 12 is a sectional view of the flask engagement assembly.

DESCRIPTION OF THE BEST MODE Referring to the drawings for a better understanding of the principles of operation and structure of the invention, it will be seen that FIG. 1 generally shows a front view of the apparatus for compacting sand 15 rigidly mounted to a compaction table 16. Apparatus for compacting sand 15 delivers an oscillating force to flask 17 via compaction table 16 and flask engagement assembly 18, which is rigidly mounted to compaction table 16, as shown in FIG. 12. Flask engagement assembly 18 grips pads 50 (which are rigidly attached to horizontal ribs 19 of flask 17) through actuation of pneumatic or hydraulic cylinders 20. Horizontal ribs 19 are strategically positioned to maintain the combined center of gravity of flask 17, compaction table 16, and apparatus for compacting sand 15 between ribs 19 during the casting process, as maintaining the combined center of gravity between ribs 19 significantly increases compacting performance and efficiency. Therefore, the lowermost rib 19 must be placed at a position sufficiently low enough to be positioned below the combined center of gravity of the flask 17, table 16, and compacting apparatus 15, when the flask 17 is empty. The uppermost rib 19 must, therefore, be positioned above the combined center of gravity of the flask 17, table 16, and compacting apparatus 15 upon filling flask 17 with sand. Flask 17 is generally one of many flasks carried together for concomitant motion upon a rail system 21 in an assembly line type foundry operation, as shown in U.S. Patent No 4,736,787. Thus, prior to delivering an oscillating force to flask 17 for the purpose of compacting the sand within flask 17, flask 17 is frictionally engaged by flask engagement assembly 18. Thereafter, flask 17, in conjunction with compaction table 16 and compacting apparatus 15, is elevated slightly above rail system 21 by air bags 22 in order to isolate and contain the oscillating forces to be applied to flask 17. Compacting apparatus 15 is then urged to rotate for a predetermined period of time at predetermined rates of revolution, thereby generating and delivering an oscillating force to flask 17 and thoroughly compacting the fill sand around the pattern placed within flask 17.

A perspective view of compacting apparatus 15 separated from compaction table 16 is generally shown in FIG. 3. Frame member 24 rotatably supports vertically displaced upper main shaft 25 and lower main shaft 26 such that the longitudinal axis of shafts 25 and 26 is substantially horizontal in orientation. Shafts 25 and 26 are rotatably supported by general grease-type bearings 27, which are rigidly affixed to frame member 24. Shafts 25 and 26 each have a pair of mechanically adjustable eccentric weight assemblies 30 indirectly affixed thereto, as shown in FIG. 3 and FIG. 6, for concomitant rotation therewith. Although the present embodiment utilizes a pair of eccentric weight assemblies 30 mounted upon each shaft 25, 26, utilization of a single weight assembly 30, as well as multiple weight assemblies 30, is contemplated within the scope of the present invention. Rotation of shafts 25 and 26 is accomplished through a belt and pulley assembly driven by electric motor 23 (see FIG. 2). Motor 23 rotationally engages a distal end of lower main shaft 26 via motor belt 36 and motor belt shaft pulley 37, thereby rotating lower main shaft 26. Concomitant counter- rotation of upper main shaft 25 is accomplished by cogged drive belt 35, toothed upper shaft pulley 32, toothed lower shaft pulley 33, and toothed idler pulley assembly 34. Drive belt 35 fully engages idler pulley assembly 34 and lower shaft pulley 33, thus causing rotation of lower shaft pulley 33 and idler pulley assembly 34 in the same rotational direction. However, drive belt 35 engages upper shaft pulley 32, so as to impart counter-rotation of upper shaft pulley 32 with respect to lower shaft pulley 33. Counter-rotation of shafts 25 and 26 and eccentric weight assemblies 30 produces the required oscillating force to sufficiently compact the fill sand within flask 17. Although both upper main shaft 25 and lower main shaft 26 each have a pair of mechanically adjustable eccentric weight assemblies 30 indirectly attached thereto, only one of eccentric weight assemblies 30 will be detailed below, as the remaining weight assemblies are identically constructed. Weight assembly 30, as shown in FIGS. 8 and 9, includes a first disk shaped weight 28 having bore 39a eccentrically positioned therein for receiving shaft portion 41 of hub 40, and a second disk shaped weight 29 having a coπesponding bore 39b formed therein for cooperatively receiving shaft portion 41 of hub 40 with first disk shaped weight 28. First disk shaped weight 28 additionally includes a pair of smooth through bores 51 formed therein for securing a timing tab 38 thereto via threaded bolts having nuts rotatably secured thereto during assembly of apparatus 15. Installation of timing tab 38 during assembly of apparatus 15 insures that weights 28 and 29 are in the proper phase relative to each other for optimal performance of apparatus 15. However, timing tab 38 is removed from weights 28 and 29 prior to operation of apparatus 15. Shaft portion 41 of hub 40 is first received by first disk shaped weight 28 through bore 39a, and then cooperatively received by second disk shaped weight 29 also through bore 39b, as shown in FIG. 10. Second disk shaped weight 29 is adjustably secured to first disk shaped weight 28, which is rigidly secured to hub flange portion 49 via a common bolt arrangement, or other suitable means known in the art. Hub 40 is secured to main shaft 25 or 26 for rotation therewith by securing key 42 cooperatively placed within hub keyway 43 and shaft keyway 44. Additionally, hub 40 is longitudinally secured to main shaft 25 or 26 via a common set screw placed within bore 45. Although a general scheme for securing the elements of eccentric weight assemblies 30 together is disclosed herein, numerous commonly known methods for securing mechanical elements of various apparatuses are contemplated within the scope of the present invention.

A novel feature of the present invention as briefly noted above, is second disk shaped weight 29 being adjustably secured to first disk shaped weight 28. By adjustably secured, it is meant that second disk shaped weight 29 can be selectively secured to first disk shaped weight 28 in various eccentric angular positions, which varies the radial extension of the major portion of the disk and hence the moment, thereby increasing or decreasing the amplitude and range of force output of apparatus for compacting sand 15. This controllable increase or decrease in the amplitude of force output of the compaction apparatus 15 allows the user to mechanically select the magnitude of both the vertical and horizontal components of the force output of apparatus 15. In order to selectively secure second disk shaped weight 29 to first disk shaped weight 28 in various radial positions, second disk shaped weight 29 includes a plurality of smooth adjustment bores 48 formed therein for receiving a securing bolt 47 therethrough, which can be rotatably secured within securing bore 46 formed in first disk shaped weight 28, as shown in FIG. 10. Smooth adjustment bores 48 are formed on an arc concentric with the axis of rotation of the second disk shaped weight 29, thus the second disk shaped weight 29 may be simply angularly displaced and secured by bolt 47 to vary the force output of apparatus 15. Although the present embodiment utilizes a threaded bolt aπangement to selectively secure second disk shaped weight 29 in the desired position, alternative methods for securing known in the art are contemplated. In order to mechanically adjust the range of available force output of compaction apparatus 15, securing bolt 47 is removed and second disk shaped weight 29 is partially rotated relative to first disk shaped weight 28 to align an alternative adjustment bore 48 with securing bore 47 for cooperatively receiving securing bolt 47. Partial rotation of second disk shaped weight 29 relative to first disk shaped weight 28 varies the offset of the major portion of eccentric weights 28 and 29, thereby varying the force generated by rotation of such. When the major portion of eccentric weights 28 and 29 are 180° offset from each other, as shown in FIG. 11a, the force generated by rotation of weights 28 and 29 will be minimized. Alternatively, when the offset angle of the major portion of weights 28 and 29 is reduced, as shown in FIG. l ie, the force generated will be increased as the offset angle decreases. Positioning second disk shaped weight 29 in an intermediate position, as shown in FIG. l ib, generates an intermediate force upon rotation of shafts 25 and 26.

A second novel feature of the present invention is that the construction allows for rapid tear down and re-assembly of apparatus 15, thereby minimizing down time of the casting process. Disassembly of upper main shaft 25 requires removing drive belt 35, removing one of bearings 27, loosening hub 40, set screw 45, and sliding the shaft out of apparatus 15, while simultaneously slidably disengaging eccentric weight assemblies 30 from upper main shaft 25. Disassembly simply requires performing the assembly procedure in reverse; however, prior to installing drive belt 35, timing tab 38 must be secured to first disk shaped eccentric weight 28 of upper and lower eccentric weight assembly 30, as shown in FIG. 6. Timing tab 38 insures upper main shaft 25 and lower main shaft 26 are in the proper phase for optimal performance prior to installing drive belt 35. Upon completion of assembly of apparatus 15, and prior to operation, timing tab 38 is removed from weights 28 and 29. This simplicity in assembly and disassembly further allows the present invention to utilize multiple weight assemblies 30. In order to increase or decrease the range of force generated by compacting apparatus 15, weight assemblies 30 can be interchanged with heavier or lighter assemblies. The resultant range of force generated by compacting apparatus 15 will thereby be increased or decreased proportionally to the varied weight and/or mass offset of the alternative weight assemblies 30.

It is to be understood that the form of the invention shown is a prefeπed embodiment thereof and that various changes and modifications may be made therein without departing from the spirit of the invention or scope as defined in the following claims.

Claims

1. An apparatus for optimally compacting a packing material around a foundry pattern contained within a mold flask (17) simultaneously with the filling of said mold flask (17) with said packing material by applying an oscillating force to said mold flask (17) as characterized by: at least two main shafts (25, 26) vertically displaced and rotatably mounted to a rigid frame member (24), said rigid frame member (24) having a means for engaging said mold flask (17), said main shafts (25, 26) positioned parallel to each other and having a substantially horizontal longitudinal axis; at least one mechanically adjustable eccentric weight assembly (30) fixably mounted to each of said main shafts (25, 26) for rotational motion therewith about said axis; and means for imparting counter-rotational motion to said main shafts (25, 26).

2. An apparatus as defined in claim 1, wherein said at least one mechanically adjustable eccentric weight assembly (30) is characterized by: a hub assembly (40), said hub assembly (40) having a bore formed therein for receiving one of said main shafts (25, 26) and means engaging one of said main shafts (25, 26); a first disk shaped weight (28) having a first eccentric smooth bore (39a) formed therein for receiving one of said main shafts (25, 26) cooperatively with said hub assembly (40), means for securing said first disk shaped weight (28) to said hub assembly (40), and a first threaded bore (46) formed therein for engaging a threaded connector (47); and a second disk shaped weight (29) having a second eccentric smooth bore (39b) formed therein for receiving one of said main shafts (25, 26) cooperatively with both said first disk shaped weight (28) and said hub assembly (40), and a second smooth bore (48) formed therein for cooperatively and slidably receiving therethrough said threaded connector (47) for selectively engaging said second disk shaped weight (29) to said first disk shaped weight (28) via engagement of said threaded connector (47) with said first threaded bore (46) on said first disk shaped weight (28).

3. An apparatus as defined in claim 2, wherein said mechanically adjustable weight assembly (30) is characterized by a plurality of smooth bores (48) formed in said second disk shaped weight (29) for slidably receiving said threaded connector (47) therethrough, said plurality of smooth bores (48) being radially and concentrically positioned about said second eccentric smooth bore (39b) for slidably engaging said threaded connector (47) cooperatively with said first threaded bore (46) of said first disk shaped weight (28).

4. An apparatus as defined in claim 1, wherein said means for imparting counter-rotational motion to said main shafts (25, 26) is characterized by: a drive belt (35); a first drive belt pulley (32) fixably attached to a first distal end of one of said first main shafts (25); a second drive belt pulley (33) fixably attached to a first distal end of one of said main shafts (26) and a first motor belt pulley (37) fixably attached to a second distal end of said main shaft (26); a drive belt idler pulley (34) fixably mounted to said rigid frame member (24), said drive belt (35) frictionally engaging said drive belt idler pulley (34) and said second drive belt pulley (33) for concomitant rotation, said drive belt (35) engaging said first drive belt pulley (32) for concomitant counter-rotation; and an electric motor (23) in rotational engagement with said first motor belt pulley (37) for rotating said second main shaft (26).

5. An apparatus as defined in claim 1, wherein said means for engaging said mold flask (17) is characterized by a compaction table (16) rigidly mounted to said apparatus for compacting and at least one pneumatic actuator (20) rigidly attached to said compaction table (16) for engaging said mold flask (17) and transferring an oscillating force thereto from said apparatus for compacting.

6. An apparatus for optimally compacting a packing material around a foundry pattern contained within a mold flask (17) simultaneously with the filling of said mold flask (17) with said packing material by applying an oscillating force to said mold flask (17), as characterized by: a first main shaft (25) rotatably mounted to a rigid frame member (24), said frame member (24) selectively in frictional engagement with said mold flask (17), said first main shaft (25) having a substantially horizontal longitudinal axis; a second main shaft (26) rotatably mounted to said rigid frame member (24) selectively in frictional engagement with said mold flask (17), said second main shaft (26) having a substantially horizontal longitudinal axis positioned substantially parallel to said first main shaft (25); at least one mechanically adjustable eccentric weight assembly (30) fixably mounted to said first main shaft (25) and said second main shaft (26); and belt driven means for imparting counter-rotational motion to said first main shaft (25) and said second main shaft (26).

7. An apparatus as defined in claim 6, wherein said apparatus for compacting is rigidly attached to a compaction table (16), said compaction table (16) being selectively in engagement with said mold flask (17) via at least one pneumatic cylinder (20).

8. An apparatus as defined in claim 6, wherein said mechanically adjustable weight assembly (30) is characterized by: a hub (40) having a shaft portion (41) and a flange portion (49), said hub (40) having a longitudinal bore formed therein for selectively receiving and engaging said first main shaft (25) or said second main shaft (26); a first disk shaped weight (28) detachably secured to said flange portion (49) of said hub (40) having a first eccentric smooth bore (39) formed therein for receiving said shaft portion (41) of said hub (40) and a first threaded bore (46) formed therein for engaging a threaded connector (47); and a second disk shaped weight (29) having a second eccentric smooth bore (39b) formed therein for receiving said shaft portion (41) of said hub (40) cooperatively with said first disk shaped weight (28), and at least one second smooth bore (48) formed therein for cooperatively and slidably receiving therethrough said threaded connector (47) for selectively securing said second disk shaped weight (29) to said first disk shaped weight (28) via engagement of said threaded connector (47) with said first threaded bore (46) on said first disk shaped weight (28).

9. An apparatus as defined in claim 8, wherein said at least one second smooth bore (48) is characterized by a plurality of smooth bores (48) radially and concentrically positioned about said second eccentric smooth bore (39b) for cooperatively and slidably receiving therethrough said threaded connector (47).

10. An apparatus as defined in claim 6, wherein said belt driven means for imparting counter-rotational motion to said first main shaft (25) and said second main shaft (26) is characterized by: a first drive belt pulley (32) rigidly affixed to a first distal end of said first main shaft (25); a second drive belt pulley (33) rigidly affixed a first distal end of said second main shaft (26); a drive belt idler pulley (34) rigidly mounted to said rigid frame member (24); a drive belt (35) frictionally engaging said drive belt idler pulley (34) and said second drive belt pulley (33) for concomitant rotation, said drive belt (35) engaging said first drive belt pulley (32) for concomitant counter-rotation therewith; and a first motor belt pulley (37) rigidly attached to a second distal end of said second main shaft (26), said motor belt pulley (37) frictionally engaging a driven motor belt (36) for imparting rotational motion.

11. An apparatus for generating a mechanically adjustable oscillating force having vertical and horizontal components for optimally compacting sand within a foundry mold flask (17) as characterized by: a compaction table (16) selectively in frictional engagement with said mold flask (17); a rigid frame member (24) adjustably mounted to said compaction table (16); a first main shaft (25) having an elongated longitudinal axis rotatably mounted to said rigid frame member (24); a second main shaft (26) rotatably mounted to said rigid frame member (24), said second main shaft (26) having an elongated longitudinal axis positioned substantially parallel to said elongated longitudinal axis of said first main shaft (25); at least one mechanically adjustable eccentric weight assembly (30) fixably mounted to said first main shaft (25) and said second main shaft (26); and belt driven means for imparting counter-rotational motion to said first main shaft (25) and said second main shaft (26) thereby generating said mechanically adjustable oscillating force.

12. An apparatus as defined in claim 11, wherein said at least one mechanically adjustable eccentric weight assembly (30) is characterized by: a hub (40) having an elongated shaft portion (41) and a flange portion (49), said hub (40) having a longitudinal bore formed therein for selectively receiving and engaging said first main shaft (25) or said second main shaft (26); a first disk shaped weight (28) detachably secured to said flange portion (49) of said hub (40), said first disk shaped weight (28) having a first eccentric smooth bore (39) formed therein for receiving said elongated shaft portion (41) of said hub (40) and a first threaded bore (46) formed therein for engaging a threaded connector (47); and a second disk shaped weight (29) having a second eccentric smooth bore (39b) formed therein for cooperatively receiving said shaft portion (41) of said hub (40) with said first disk shaped weight

(28) and plurality of smooth adjustment bores (48) formed therein radially and concentrically positioned about said second eccentric smooth bore (39b) for cooperatively and slidably receiving therethrough said threaded connector (47) for selectively securing said second disk shaped weight (29) to said first disk shaped weight (28) via engagement of said threaded connector (47) with said first threaded bore of said first disk shaped weight (28).