US2298252A - Vibrator - Google Patents

Description

v. J. DAvls 2,298,252

VIBRATOR Filed Jan. 27, 1941 40j I 50 f A @152k I l "Q mllgl 47 im( 1 li j, 7.s|m\ i y INVENTOR AT RNEY Patented Oct. 6, 1942 UNETED STATES FFME VIBRATOR Vernon J. Davis, Buffalo, N. Y., assignor to American Radiator & Standard Sanitary Corporation, New York, N. Y., a corporation of Delaware 11 Claims.

rI'his invention relates to vibrating devices, and more particularly to vibrating devices of the general type used in foundries for various purposes; such, for example, as to shake the sand from flasks, castings, etc.

One object of this invention is to provide a vibrating device which is of improved construction and arrangement of parts.

Further objects are to provide a vibrator which is relatively simple and inexpensive in construction; one which is unusually compact and is of relatively few parts; one which can be readily assembled and disassembled in a minimum length of time; and one which is highly eilicient and effective in its operation.

The invention consists in the novel construction and combination of parts, to be more fully described hereinafter, and the novelty of which will be particularly pointed out and distinctly claimed.

In the accompanying drawing, to be taken as a part of this specication, I have fully and clearly illustrated a preferred embodiment of my invention, in which drawing- Fig. 1 is a vertical elevation showing one preferred embodiment of my improved vibrator;

Fig. 2 is an enlarged vertical section taken on the line 2 2 of Fig. 1;

Fig. 3 is an enlarged horizontal section taken on the broken line 3-3 of Fig. 1;

Fig. 4 is an enlarged fragmentary vertical elevation indicated by the line 4 4 of Fig. l; and

Fig. 5 is a perspective view illustrating a practical application of the preferred embodiment shown in Figs. 1 to 4, inclusive.

Referring now in detail to the construction illustrated, the reference numeral I indicates, in its entirety, one preferred embodiment of my improved vibrator. In general, the vibrator I0 comprises an open-ended cylinder II adapted to be supported in an upright position, as shown in Fig. upper and lower cylinder heads I2 and I3 closing, respectively, the upper and lower ends of said cylinder; a piston I4 mounted to reciprocate in said cylinder and operable to strike the upper head I2 on its 11p-stroke, and being prevented from striking the lower head I3 on its down-stroke; a first or supporting sling I5 having a lower end IB passing beneath and supportingly engaging the lower head I3 and extending upwardly therefrom and adapted to be hung by its upper end I1 from a suitable support; and a second or work-supporting sling I3 having an upper end I9 extending about and supported by the upper head I2 and hanging downward therefrom, and having a lower end 2S adapted to support the work.

In Fig. 5, I have shown one way in which my invention may be applied. In this View, two vibrators I0 and Ia are shown with their worksupporting slings I5 and I5a hung from the opposite ends of a supporting beam 25. The work-supporting slings I8 and Iiia support at their lower ends the work indicated diagrammatically at 21. As an example, the work 21 may be considered to be a foundry flask from which it is desired to shake the sand. The lower ends 20 and Za, of the slings I8 and Ita extend about trunnions 28 and 28a, respectively, projecting from opposite sides of the ask 21. It will be apparent that with the piston I4 of each vibrator lil and Illa. reciprocating in its cylinder II and striking the upper head I2 on each upstroke, the vibrations resulting therefrom will be transmited through the work-supporting slings I8 and |811 to the flask 21 and the sand will be jarred loose from the iiask in an eiective manner.

The cylinder II may be formed as a unitary casting and comprises a centrally disposed working bore 30, within which the piston Ill reciprocates. The upper and lower ends of the cylinder are formed with counterbores 3| and 32 which are of equal length and receive the upper and lower cylinder heads I2 and I3, respectively. The inner end of each counterbore provides an annular ledge or shoulder 33 which serves as a stop or abutment for the innermost end of its respective cylinder head.

Ihe cylinder II is provided at one side thereof with an enlargement 35 which extends lengthwise of the cylinder axis (see Figs. 2 and 3). The enlargement 35 is formed with a longitudinally extending passage 3S which, as will presently appear, serves as a supply passage or inlet manifold for the uid which motivates the piston i4. The outer end of the supply passage 33 may be closed by a suitable plug 39.

The vibrator may be so constructed as to be operated by any suitable type of motivating uid, without departing from the present invention when considered in its broader aspects. In the construction shown, the motivating fluid is intended to be compressed air, which may be supplied to the passage 36 from any suitable source; such, for example, as the air storage tank of a conventional air compressor unit (not shown). A flexible air supply tube 31 is provided for connecting the vibrator to such a source. The tube 31 is c-onnected at its end to a passage 38 which extends transversely through the enlargement 35 and communicates at its inner end with the inlet passage or manifold 36.

Upper and lower annular inlet grooves 4I) and 4I may be cut in the inner wall or bore 35 of the cylinder I I and are connected, respectively, with the supply passage 35 by means of short connecting passages 42 and 43. In the construction shown, each of the grooves 40 and 4I lies in a plane approximately normal to the central axis of the bore 35. The inlet grooves 4I) and 4I are so spaced that their center lines lie approximately equal distances from the upper and lower ends, respectively, of the working bore 30. Theupper and lower connecting supply passages 42 and 43 may be suitably formed by drills entering, respectively, from the outside of the. enlargement 3.5, as

' indicated at 44 and 45. suitable plugs 4s and 41 serve to close the outer ends of the drilled passages 42, 44 and 43, 45, respectively.

For a purpose which will appear more fully hereinafter, the lower inlet passage 43 is preferably substantially larger in diameter than the diameter of the upper inlet passage 42. of example, the diameter of the lower passage 43, in the construction shown, is approximately ve (5) times the diameter of the upper passage 42. It is also noted that the lower inlet groove 4| is shown as having a width equal to the diameter of the passage 43 which is slightly larger than the width of the upper inlet groove 46.

The cylinder is also provided with upper and lower annular exhaust grooves 55 and 5| which are cut in the cylinder wall and are located between the inlet grooves 40 and 4I. The grooves 5i) and 5| also lie in planes approximately normal to the cylinder axis, and are so spaced that their center lines lie substantially equal distances from the Iupper and lower ends, respectively, of the bore 30. The grooves 5I] and 5| connect through upper and lower drilled exhaust passages 52 and 53, respectively, with an exhaust manifold 54, the latter being in open communication with the atmosphere, as shown. In order that the air may flow from the cylinder to the atmosphere with a minimum of restriction, I have provided four upper exhaust passages 52 and four lower exhaust passages 53. Fig. 3 shows the four connecting exhaust passages 53. It will be appreciated that the passages 52 are the same in dimension and arrangement as the passages 53. The exhaust manifold may be suitably formed as a separate cast plate and secured in position on the cylinder II by bolts 55.

The piston I4 is advantageously formed as a unitary forging from suitable material, such as a chrome-nickel steel. The surface of the piston is preferably hardened to withstand the shock of striking the upper cylinder head I2. The piston is formed with axially disposed upper and lower passages Si) and 6| which connect, respectively, the upper and lower ends of the piston and the cylinder with upper and lower sets of valve ports 62 and 65, extending horizontally through the walls of the piston, as shown. The upper set of valve ports G2 communicatively connects with the air` supply groove 4I! when the piston is at and near the upper end of its stroke and connects with the air exhaust groove 50 when the piston is at and near the lower end of its stroke. The lower set f valve ports 63 communicatively connects with the exhaust groove when the piston is at and near the upper end of its stroke and connects with the inlet groove 4I when the piston is at and near the lower end of its stroke.

By wayV In Fig. 2, the piston I4 is shown as being at the top of its up-stroke and in engagement with the cylinder head I2. The upper set of piston valve ports 62 is shown as being in full communication with the upper inlet groove 4U and the lower set of piston ports 63 is in full communication with the lower exhaust groove 5|. In this position, air under pressure is being admitted through the small connecting passage 42, groove 45, ports 62, and passage GEI, to the top of the cylinder, and the air in the lower part of the cylinder is at atmospheric pressure on account of the lower ports 63 being in communication with the outside atmosphere through the groove 5|, plurality of passages 53, and exhaust manifold 54. Air under pressure in the upper end of the cylinder forces the piston downward at a rate depending, of course, upon the weight of the piston and the value of the air pressure. As the piston is moved downward, the ports 62 and 63 move out of communication with the grooves 40 and 5I and move into communication with the grooves 55 and 4I, respectively. Air under pressure commences flowing into the lower end of the cylinder through the large connecting passage 43, inlet groove 4I, and lower piston ports 63. The air under pressure in the upper end of the cylinder will commence escaping to the atmosphere through the piston ports 62, exhaust groove 55, the plurality of connecting passages 52, and exhaust manifold 54.

The downward movement of the piston will continue until suiicient air has been admitted to the bottom of the cylinder to overcome the gravity and inertia forces of the moving piston; at which time, the downward movement of the piston will cease and the piston will then be moved upward on its 11p-stroke until it strikes the upper cylinder head, whence it commences again its down-stroke. At 51, I have indicated by a dot-and-dash line the approximate lowermost position of the piston which, as will be noted, is short of the lower cylinder head. If the piston I4 should strike the lower head I3, it

would place unnecessary strains on the sling |5 and support 25, and any resulting vibrational forces transmitted to the work would only be incidental. However, the striking of the upper cylinder head by the piston I4 results in the vibrational forces being transmitted directly to the work through the sling I3. This desirable operation is attained in the present construction because of the relative size of the passages 42 and 43 and the grooves 45 and 4I. It will be noted, however, that other means of obtaining this operation can be devised without departing from the broader aspects of the present invention.

In accordance with the present invention, the cylinder heads I2 and E5 close the outer ends of the cylinder and are each so connected to their respective cylinder ends that relative movement is permitted between the cylinder heads and cylinder ends in directions extending lengthwise of the cylinder. To this end, each cylinder head I2 and I3 is formed with a plug part "I0, slidably fitting its respective counterbore, 3| or 32, and engaging at its inner end the shoulder 33, and each head is also formed with a ange part 'II abutting the adjacent outer end of the cylinder. It will thus be seen that relative inward movement of the cylinder heads and their respective cylinder ends beyond xed points is prevented by the abutment means formed by the anges 'II and their respective cylinder ends and by the inner ends of the plugs 'I5 and their respective annular shoulders 33'. Relative outward movement of the lower cyhnder head I3 and the counterbore 32 is constantly opposed by the force created by the combined weight of the cylinder Il, the cylinder head I2, the work-supporting sling I8, and the work 21. Also, relative outward movement of the upper cylinder head I2 and the bore 3I is constantly opposed by the force created by the combined weight of the work-supporting sling I8 and the work 21. Thus, when the piston I4 is not operating., each cylinder head is maintained in engagement with its respective abutment means by the gravity forces, just explained.

The above described slidable connection between the cylinder heads and the cylinder possesses many advantages over the conventional rigid connection provided by tension bolts and the like. As the slidable connection eliminates the necessity for the tension bolts, or their equivalent, an unusually simple and inexpensive construction is provided which permits the assembly and disassembly of the vibrator in a minimum period of time. These advantages apply to the slidable connection between both the cylinder head I2 and the cylinder head I3 and their respective cylinder ends. The connection between the upper cylinder head I2 and the cylinder bore El provides the additional advantage of causing the transmission of the vibrational forces, set up by the piston .It striking the head IZ, directly to the Work 21 through the sling I8 and without the transmission of strains to the cylinder II such as would be the case if the head I2 were bolted to its respective cylinder end. In addition to the advantages of simplicity and relatively low cost, the slidable connection between the head I2 and the bore 3! provides a stronger and more durable construction, because there is no connection between the cylinder end and head I2 which is required to withstand strains set up by the vibrational forces and as there are no strains transmitted from the cylinder head I2 to the cylinder II.

In so far as the broader aspects of my invention are concerned, the cylinder heads I2 and I3 may be formed in any suitable manner and of any suitable material capable of withstanding the strains and shocks incident to the operation of the vibratorL heads are advantageously formed as steel castings and they are preferably identical in construction so as to minimize pattern costs. Each cylinder head is formed with a groove l5 in its eXtreme outer end, which groove is dened by parallel flanges I6 and ll, and the ilanges are spaced far enough apart to receive snugly an end of a sling. The groove 'I5 of head I2 receives the end I9 of sling I8, and the groove 'I5 of head I3 receives the end I 6 of sling I5. The grooves lie in planes extending parallel to the cylinder axis and the heads are so arranged in their respective cylinder ends that their grooves 'I5 lie in planes parallel to one another and at opposite sides of a longitudinal median plane extending through the cylinder axis.

rlhe supporting sling I5 comprises two side connecting elements 'i3 and '19, respectively, which extend in the same general direction as the cylinder axis and are connected at their opposite ends to the ends I E and I1. Likewise, the wom-supporting sling I8 comprises two side connecting elements S6 and 8i, respectively, which also extend in the same general direction as the cylinder axis and connect at their oppo- In the construction shown, the

site ends to the ends Iii and 26. In the construction shown, the element 'i3 lies adjacent the element 8i) at opposite sides of the aforementioned longitudinally extending median plane, and the element l lies adjacent the element 8i and also at opposite sides of such median plane. This arrangement of the slings is made possible by the aforementioned arrangement of the heads I2 and I3 in their respective cylinder ends, and it makes possible the eiective transmission of those forces through the slings to the heads I2 and I3, which forces act to urge the heads towards their respective abutment means, and the eiective transmission oi the vibrational forces from the head I2 through the sling I8 to the work 2l.

In order to maintain the slings I5 and I 8 in their proper relative position with respect to each other and with respect to the cylinder and cylinder heads, as just explained; a guide means is provided at each side ci each cylinder head and on one side of the cylinder. he guide means on each head is provided by aligned grooves SE and 84 located at opposite sides, respectively, of each head. The grooves and 8f3 are deiined at one side thereof by extensions 85 and d of the flange 'il and are defined at their other sides by ilanges and $8 arranged in spaced parallel relation with the two ilange extensions S5 and t, respectively. The guide means on the cylinder wall is in the form of a pair of spaced alignment bosses 39 and QSI extending outwardly from the cylinder and receiving therebetween adjacent side elements 'IB and @il of the two slings E5 and I6.

In accordance with the present invention, I also provide a resilient tension means $2 which connects each pair of adjacent side elements of the slings in such a manner that the end portions IS and I9 are constantly held in their respective grooves 'i5 with a force sufficient to constantly urge both cylinder heads against their respective abutment means. This permits the handling and shipping of the Vibrator as a unitl without danger of the heads coming out of their respective cylinder ends and also prevents the sling ends I5 and I Si from jumping out of their respective grooves during the operation of the vibrator.

A tension means is provided at each side of the cylinder and is here shown as comprising a loop S3 formed of a suitable resilient material, such as rubber, and connected at its opposite ends to spools 9d and 95 carried, respectively, by each of the two pairs of adjacent side elements of the slings. Each of the spools S43 and 95 is conveniently clamped. to its respective side element by U-bolts SS and the spools are so connected to their respective side element that the rubber loop S3 constantly pulls both the end I9 and the end I@ hard against its respective cylinder head.

What I claim and desire to secure by Letters Patent of the United States is:

1. A vibrator comprising a cylinder; a pair of heads closing opposite ends of said cylinder, respectively; a double-acting piston in said cylinder; means providing for the alternate admission of a motivating iluid into the opposite ends of said cylinder and for exhausting the iluid from said cylinder ends so as to eiect the reciprocation of said piston in said cylinder, said means comprising a source of motivating iiuid under pressure and a pair oi fluid inlet passages connecting, respectively, said source with opposite ends of said cylinder and one of said passages being of substantially greater cross-sectional area than the other so that the piston is prevented by the fluid under pressure from striking one cylinder head and is caused to strike sharply the other cylinder head each time the piston approaches said other head; and means for transmitting the vibrational forces from said other cylinder head to the work to be vibrated.

2. A vibrator comprising a cylinder; first and second heads closing the opposite ends of said cylinder and said first head being so connected to its cylinder end as to provide relative lengthwise movement therebetween; abutment means limiting relative movement of the cylinder and first head inwardly toward one another beyond a fixed point; a double-acting piston in said cylinder; means for supplying motivating iiuid to and conducting exhaust away from between both ends of the piston and the adjacent cylinder heads, respectively, so that the piston reciprocates in the cylinder and strikes said first head at the end of each stroke towards the latter and is prevented from striking said second head by a cushion of motivating uid at the end of each stroke toward said second head; and a worksupporting sling comprising an end portion extending about and engaging said iirst head, side elements extending therefrom along said cylinder, and another end portion adapted to support the work in such a manner that the weight of the work keeps the side elements taut and the first mentioned end portion in engagement with said rst head.

3. A vibrator comprising a cylinder; first and second heads closing the opposite ends of said cylinder and said first head being so connected toits cylinder end as to provide relative lengthwise movement therebetween; abutment means limiting relative movement of cylinder and first head inwardly toward one another beyond a fixed point; a double-acting piston in said cylinder; means for supplying motivating fluid to and conducting exhaust away from between both ends of the piston and the adjacent cylinder heads, respectively, so that the piston reciprocates in the cylinder and strikes said first head at the end of each stroke towards the latter and is prevented from striking said second head by a cushion of motivating iiuid at the end of each stroke toward said second head; said means including a pair of fluid inlet passages connecting, respectively, a source of motivating fluid under pressure with opposite ends of the cylinder, the passage connected to the cylinder end adjacent said second head having a substantially larger ow capacity than the other of said passages; and a work-supporting sling comprising an end portion extending about and engaging said first head, side elements extending therefrom along said cylinder, and another end portion to support the work in such a manner that the weight of the work keeps the side elements taut and the first mentioned end portion in engagement with said first head.

4. A vibrator comprising a cylinder; first and second heads closing and connected to opposite ends of said cylinder, respectively, so as to provide relative movement of each head and its respective cylinder end in a lengthwise direction; abutment means preventing relative movement of each head with respect to its cylinder end inwardly of said cylinder beyond xed points; a piston reciprocating in said cylinder; a first sling having an end portion engaging about the outer surfaces of said first head, mid

portions extending therefrom lengthwise of said cylinder, and an outer end portion disposed beyond said second head; a second sling having an end portion engaging about outer surfaces of said second head, mid portions extending therefrom lengthwise of said cylinder and in a direction opposite to the mid portions of said first sling, and having an outer end portion disposed beyond said first head; and said vibrator being adapted to be suspended from the outer end of one of said slings and adapted to support the work from the outer end of the other sling whereby the weight of the work and the parts constantly forces the two heads toward their abutment means.

5. A vibrator comprising a cylinder; first and second head-s closing and connected to opposite ends of said cylinder, respectively, so as to provide relative movement of each head and its respective cylinder end in a lengthwise direction; abutment means preventing relative movement of each head with respect to its cylinder end inwardly of said cylinder beyond fixed points; a piston reciprocating in said cylinder; a first sling having an end portion engaging about the outer surfaces of said first head, mid portions extending therefrom lengthwise of said cylinder, and an outer end portion disposed beyond said second head; and a second sling having an end portion engaging about outer surfaces of said second head, mid portions extending therefrom lengthwise of said cylinder and in a direction opposite to the mid portions of said first sling, and having an outer end portion disposed beyond said first head; said vibrator being adapted to be suspended from the outer end of one of said slings and adapted to support the work from the outer end of the other sling whereby the weight of the work and the parts constantly forces the two heads toward their abutment means; and guide means for keeping the mid portions of both said slings in position alongside said cylinder.

6. A vibrator comprising a cylinder; first and second heads closing and connected to opposite ends of said cylinder, respectively, so as to provide relative movement of each head and its respective cylinder end in a lengthwise direction; abutment means preventing relative movement of each head with respect to its cylinder end inwardly of said cylinder beyond fixed points; a piston reciprocating in said cylinder; a first sling having an end portion engaging about the outer surfaces of said first head, mid portions extending therefrom lengthwise of said cylinder, and an outer end portion disposed beyond said second head; a second sling having an end portion engaging about outer surfaces of said second head, mid portions extending therefrom lengthwise of said cylinder and in a direction opposite to the mid portions of said first sling, and having an outer end portion disposed beyond said first head; said vibrator being adapted to be suspended from the outer end of one of said slings and adapted to support the work from the outer end of the other sling whereby the weight of the work and the parts constantly forces the two heads toward their abutment means; and resilient tension means connecting the mid portions of both slings so that the firstnamed end portion of each of said slings constantly forces its cylinder head inwardly towards the abutment means.

'7. A vibrator comprising a cylinder; first and second cylinder heads closing and connected to opposite ends of said cylinder, respectively, and

providing relative lengthwise movement between each head and its cylinder end; abutment means preventing relative movement oi each head and its cylinder end inwardly beyond a xed point; a reciprocating piston in said cylinder operable to strike said first head; a rst sling comprising two end portions and a pair of connecting side elements, and having one of its end portions extending about and engaging said second head, its side elements extending along opposite sides ol said cylinder and beyond said first head, and its other end portion being adapted to be hung from a support; and a second sling also comprising two end portions and a pair of connecting side elements, and having one of its -end portions extending about and engaging said first head, its sideelements extending along said cylinder and adjacent the rst-named side elements, respectively, and extending beyond said second head, and the other of its end portions being adapted to support the work therefrom so that the weight of the latter forces the iirst head toward its abutment means.

8. A vibrator comprising a cylinder; first and second cylinder heads closing and connected to opposite ends of said cylinder, respectively, and providing relative lengthwise movement between each head and its cylinder end; abutment means preventing relative movement of each head and its cylinder end inwardly beyond a xed point;

a reciprocating piston in said cylinder operable to strike said iirst head; a iirst sling comprising two end portions and a pair of connecting side elements and having one of its end portions extending about and engaging said second head, its side elements extending along opposite sides of Said cylinder and beyond said first head and its other end portion being adapted to be hung from a support; a second sling also comprising two end portions and a pair of connecting side elements, and having one of its end portions extending about and engaging said rst head, its side elements extending along said cylinder and adjacent the first-named side elements, respectively, and extending beyond said second head, and the other of its end portions being adapted to support the work therefrom so that the weight of the latter forces the first head toward its abutment means; and means for r'esiliently forcing each of said heads towards its abutment means.

9. A vibrator comprising a cylinder; Iirst and second cylinder heads closing and connected to opposite ends of said cylinder, respectively, and providing relative lengthwise movement between each head and its cylinder end; abutment means preventing relative movement of each head and its cylinder end inwardly beyond a fixed point; a reciprocating piston in said cylinder operable to strike said rst head; a iirst sling comprising two end portions and a pair of connecting side elements, and having one of its end portions extending about and engaging said second head, its side elements extending along opposite sides of said cylinder and beyond said iirst head, and its other end portion being adapted to be hung from a support; a secon-d sling also comprising two end portions and a pair of connecting side elements, and having one of its end portions extending about and engaging said rst head, its side elements extending along said cylinder and adjacent the first-named side elements, respectively, and extending beyond said second head, and the other of its end portions being adapted to support the work therefrom so that the weight of the latter forces the first head toward its abutment means; and resilient tension means connecting the adjacent side elements of the two slings so that the end portions of the slings which engage the heads, constantly force their respective heads inwardly toward the abutment means.

10. A vibrator comprising a cylinder adapted to be supported in an upright position; upper and lower cylinder heads closing the upper and lower Vendsof said cylinder, respectively, nand each of the heads being so connected to its respective cylinder ends as to provide relative sliding movement between each head and its cylinder end in directions extending lengthwise of said cylinder; abutment means limiting inward movement of each of said heads relative to the cylinder; a fluid-motivated reciprocating piston in said cylinder and operable to strike the upper cylinder head on the up-stroke; a first sling adapted to be supported at its upper end and extending downwardly along opposite sides of said cylinder and supportingly engaging said lower head; and a second or work-supporting sling engaging at its upper end said upper cylinder head and extending downwardly along opposite sides of said cylinder and adapted to support the work at its lower end.

1l. A vibrator comprising a cylinder; first and second cylinder heads closing, respectively, opposite ends of said cylinder and being s0 connected to said cylinder as to provide relative lengthwise movement between each head and its cylinder end; abutment means preventing relative movement of each head and its cylinder and inwardly beyond a fixed point; a double-acting piston in said cylinder; means for supplying motivating fluid to and conducting exhaust away from between both ends of the piston and the adjacent cylinder heads so that the piston reciprocates in the cylinder and strikes said rst head at the end of each stroke toward the latter and is prevented from striking said second head at the end of each stroke toward said second head; a first sling comprising two end portions and a pair of side elements connecting the end portions, and having one of its end portions extending about and engaging said second head, having its side elements extending along opposite sides of said cylinder and beyond said first head, and its other end portion being adapted to be hung from a support; and a second sling comprising two end portions and a pair of said elements connecting said end portions, and having one of its end portions extending about and engaging said rst head, having its side elements extending along opposite sides of said cylinder and beyond said second head, and the other of its end portions being adapted to support the work therefrom so that the weight of the work forces the rst head toward its abutment means.

VERNON J. DAVIS.

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