US2420119A - Method and apparatus for bending sheet material - Google Patents

Description

May 6, 1947, R. M. BOEHM ET AL 2,420,119

METHOD AND APPARATUS FOR BENDING' SHEET MATERI'AL 4 Smets-sheet 1 Filed Nov. 29, 1944 INVENTOR Fase-fr M 5v5/m4 ,4f/Pou 6l F100/v BY MATTO EY May 6, 1947- R. M. BOEHM ET Al.' 2,420,119

METHOD AND `AP.Pl-RIFUS FOR BENDING' SHEET MATERIAL I l Filed Nov. 29, 1944 4 sheets-sheep 2 .gsi

INVENTOR fPaaE/Pr M 50E/m4 675km/ A A4004/ y ATTORNEY May 6 1947-' R. M. BOEHM ET AL 2,420,119

METHOD AND APPARATUS FOR BENDING SHEET MATERIAL Filed Nov. 29, 1944 4 sheets-sheet s AT ORNEY May', 1947- R. M. BOEHM ET AL 2,420,119

METHOD AND APPARATUS FOR BENDING SHEET MATERIAL Filed Nov. 29, 1944 4 Sheets-Sheet 4 Patented May 6, 1947 ZAZMIQ METHOD AND APPARATUS FOR BENDING SHEET MATERIAL Robert M. Boehm, Laurel, Miss., and Aaron A. Ladon, Cleveland, Ohio, assignors to Masonite Corporation, Laurel, Miss., acorporation of Delaware Application November 29, 1944, Serial No. 565,768

11 Claims.

This invention relates to a method and apparatus for bending sheet material. It relates especially to a method and apparatus for bending hardboard sheet material into substantially U-shaped or trough-like articles which are substantially free from cracking or breaking. By use of the invention the sheet material is held under restraint by application of inwardly-directed pressure to its edges throughout the greater part of the bending operation, and is automatically released from such restraint when the bending operation is substantially completed.

While the method and apparatus of the present invention may be used to form permanent bends and deformations, substantially without breaking, in materials such as plywood, insulation board, hardboard and the like, the description below will be directed to forming elongated trough-like articles from plane sheets of lignocellulose liber hardboard. Such hardboard sheets are conveniently prepared by treatment of wood chips with steam followed by explosive disruption into fiber substantially as described in U. S. patent to Mason 1,824,221, and the resulting liber refined, and after its contents of water solubles have preferably been reduced as by washing, formed into porous sheets containing about 2% to 3% sizing material, and then pressed into hardboard sheets under heat and high pressure.

Hardboard sheet materials have heretofore been bent into various shapes, but such operations have generally been limited to bends having a relatively large radius of curvature- In cases where making bends of relatively small radius of curvature was atempted, difficulty was encountered in that the sheet would tend to crack or break.

With the use of the present method and apparatus, the sheet is held under edge restraint through substantially the greater part of the bending operation, that is, at least through the critical range of the bending operation wherein cracking and breaking might occur. In bending sheets While they are so restrained by suitable means applied to their side edges, the bending will progress by compression of the inner surface rather than by stretching of the outer surface of the sheet and thus cracking or breaking of the sheet will be avoided. Bends of relatively small radius may be obtained in this Way without breaking or surface cracking of the sheet material. When the bending has been completed, the edge restraint is automatically released, permitting the bent product to be removed.

An object of the present invention is the pro- 2 vision of a method and an apparatus for producing bends in sheet material, wherein the sheet is held in restraint throughout substantially the greater part of the bending operation by inward pressure applied to its edges and then automatically released from such restraint When the bend has been formed.

A further object is the provision of a method and apparatus for prcducing bends of relatively small curvature in sheet material without cracking or breaking the sheet.

Additional objects and advantages will be clear to those skilled in the art on consideration of the attached description and drawings.

The method of this invention may be performed with various types of apparatus, and such apparatus may be modied to bend hardboard sheets into many forms and shapes. The accompanying drawings illustrate one type of apparatus which is suitably designed to form troughlike articles from hardboard sheets in accordance with the method described herein.

In such drawings,

Fig 1 is an end view of the apparatus with portions broken away, and shows the sheet to be bent in restrained position prior to the bending thereof. f

Fig. 2 is a sectional plan View on line 2--2 with portions broken away of Fig. 1.

Fig. 3 is a sectional end vieW on line 3-3 with portions broken away of Fig, 1.

Figs. 4, 5, and 6 are diagrammatic views illustrating various positions of different parts of the bending apparatus in relation to the mold during the bending cycle; and

Fig. 7 is a diagrammatic View illustrating the method for determining the locus about which the restraining arm moves.

The illustrated apparatus consists essentially of a heated, preferably hollow mold, means for holding a hardboard sheet on said heated mold,

restraining means pivoted at points so located that said means will hold the sheet in restraint by its edges during the principal part of the bending operation and automatically release the sheet during the latter part thereof, and means to apply a deforming force to the upper surfaces of the sheet to bend the sheet. One of the essential features of the invention consists in the prevention or minimizing of cracking and breakage caused by bending by the provision of restraining means operating as above described.

This novel feature of restraining the sheet while Y performing most or all of the bending operation and then automatically releasing the pressure on the sheet is accomplished by coaction between the edges of the sheet being bent with restraining means which are mounted on swinging arms pivoted to turn about a predetermined point on the apparatus, which point is generally below the horizontal plane of the sheet as originally inserted in place therein, preferably below the upper surface of the moldand adjacent to the curvature of the mold over which the sheet will be bent. A mode of determining the location of such points will be described below.

In the drawings, which disclose a suitable ap paratus to form bends in hardlooard sheets, ref'- erence numerals Ill indicate four upright framemembers rigidly secured in position by transverse cross members l2, I4, and I6 and longitudinally extending members i8, 20, 22.

At a convenient working-level height, a hollow metallic mold 24, which has a preferably flat upper surface and downwardly curved spaced side portions, is mounted onA bed plate 26 and supported by members i8, as shown in Fig. 1. Such a mold is suitable for bending sheet material into substantially U-shaped or trough-like articles. Suitable heating elements 28, such as electrical units, are mounted on the interior surface of mold 24 to supply necessary heat to the mold.

Near the upper surface of mold 24 and adjacent to mold curvature 3D about which the bend will be formed, a pair of swinging arms 32 are mounted at each side of the mold through pivotal connections 34 on supporting plates 36. A pair of adjustable sheet-restraining members 38, having angular recessed edges 39, are attached to arms 32 near the outer extremities thereof and extend in substantially parallel alignment with mold 24, there being one of the restraining members 38 along each side of mold 24. Members 38 serve to apply inwardly directed restraining pressure to the opposite edges of the sheetY material received in recesses 39 formed in said members 38. The members 38 may be adjusted to various positions on the arms 32 by means of adjusting nuts 40 and 4l, and by this adjustability thel machine is adapted for bending sheet materials of different widths. Suitable counterweights 42 are connected with restraining members 33 by means of flexible cables 43 which extend over pulleys 43a, and are anchored to eyes 43D on the restraining members' 38. The counterweight arrangement serves to substantially balance the weight of the arms 32 and restraining members 38 as shown in Fig.V l.

A hold-down plate 44, provided with an angular ange 46, is movably positioned above mold 24 and is adapted, when in the lowered position, to rmly clamp the sheet between it and the upper surface of mold 24. A series of movable linkages 48-50, 49--5I, and 52-54 are provided to link flange 46 of plate 44 to frame member 22 through a toggle-joint arrangement. A manually-operated lever 58, pivotally mounted on frame bracket 60, imparts movement to the toggle-joint arrangement through angular link 56 and a movable connection at 62, thereby moving hold-down plate 44 toward and away from the upper surface of mold 24. Linkages 48 and 50 are connected by cross link 64 to impart uniform movement to plate 44 at all times. Spring 66 fastened to link and frame bracket 68 serves to prevent excessive side movement of plate 44 when the toggle-joint arrangement is operated.

The pressure-applying means used for eiecting the bending consists of a pair of spaced rolls and 12 extending in substantially parallel alignment with mold 24 and movably positioned above the curved portions 30 of the mold. Rolls 1G and 12 are rotatably mounted at the lower extremities of bars 14 and 16 and spaced from each other by slotted connecting member 18. The sloted portion of member 18 permits relative lateral movement of rolls 10 and 12 during their downward movement in the bending operation. Springs 86 tend to pull rolls 10 and 12 toward each other at all times. The upper extremities of bars 14 and 16 are pivotally connected at 82 to channel member 84 which is vertically movablel and serves as a common supporting member for the pressure applying means. Racks 86, operating in guiding channels 83, positioned at each end of the machine, are connected to member 84. Drive pinions 93, mounted on shaft 92, which is supported by shaft bearings 93, intermesh with the teeth on racks 86, and, as pinons 90 are rotated, a substantially vertical movement of the mechanism attached to channel member 84 may be obtained. Rotative movement is transmitted to pinions 9e through pulley 94 mounted on shaft 92 and driven by any suitable driving means (not shown).

In using the apparatus for bending sheet material, the pressure-applying mechanism and the clamp plate 44 are first raised to their respective uppermost positions. When the parts referred to are thus positioned, sufficient clearance is provided between tlie mold and the raised parts for easy positioning of sheet material 96 on top of mold 24. In positioning sheet 96, preparatory to the bending operation, the side portions of the sheet extend outwardly beyond the curved sides of the mold, and the edges of the extended portion are placed in the recesses 39 formed in restraining bars 38. The bars 38 are preferably so adjusted by nuts 4U, 4I that it will be necessary to slightly flex the sheet in order to insert the edges thereof in recesses 39 of the restraining bars 38 in a manner which will give a tight fit between the edges of the sheet and the restraining bars.

Such sheets are preferably treated with water before the bending operation for easier bending of the sheet, although such a step is not necessary in allrcases. In many cases sheet materials have a sufliciently high moisture content to make dampening with water unnecessary.

When sheet material S6 has been placed on the top surface of heated mold 24 as described,

hold-down clamp 44 is lowered into contact with the sheet, thus rmly holding the sheet between the upper surface of mold 24 and clamp 44. Rolls 10 and 12 are now lowered by means of racks 83. As the rolls 13 and 12 make contact with the sheet 96 and their downward movement continues, downward pressure is thereby applied in substantially vertical planes to the upper surface of the extended side portions of sheet 93. Thus the side portions of the sheet extending out beyond mold 24 will be forced inwardly toward the side-forming portions of mold 24. By bending in this way the sheet will be shaped to the curvature of the mold.

Upon the application of downward pressure to the surface of the sheet, restraining bars 38 are moved downward with and preferably by the extending side portions of the sheet to describe an arcuate path about pivot points 34 as the sheet material is gradually forced toward the sides of the mold. Near the end of the bending operation, restraining bars 38 automatically begin to release the edges of sheet 9S as shown inF'ig. 5, and such release will be complete when the bending rolls and restraining bars are positioned as shown in Fig. 6. This feature is illustrated in the schematic Figs. 4, 5, and 6 and will be further described in detail.

At the point of the bending operation shown in Fig. 6, the movement of racks 86 is reversed and rolls 70 and 'l2 are raised. Hold-down plate 44 is also raised by operating lever 58. Since the restraining bars 38 will have automatically released the edges of sheet 96 at or prior to the end of the bending operation, the bent sheet can be easily removed. Either before or after such removal restraining bars 38 are restored to the position shown in Fig. 1.

As has been stated above, the edges of sheet 96 are held in restraint by bars 38 during substantially the greater part of the bending cycle, and, when the bending is completed or substantially completed, the restraining bars 38 automatically release the edges of the sheet. This unique feature is accomplished by proper positioning of the pivoting points 34 about which arms 32 and restraining bars 38 are caused to turn. It has been found that, as sheet 96 is bent to conform to the curvature 30 of mold 24, the edge of the sheet describes a curve which corresponds to substantially the involute of a, part of the circle around which the sheet is bent. With this knowledge and by graphically plotting the curvature of mold 24 and the final curvature of sheet material 93, as illustrated in Fig. 7, point 34 may readily be so determined and located that the restraining bars 38 will hold sheet material in restraint by its edges during the critical portion of the bending operation and automatically release the edges at or shortly before the end of the bending operation.

Point 34 is located as follows: An arc 98 corresponding to the radius of curvature of the desired bend is drawn as shown in Fig. 7. This arc corresponds to curvature 30 of the mold. A second arc I 00 representing the nal bend in sheet 96 is drawn and is spaced from arc 98 by a distance equal to the thickness of the sheet to be bent. A third are |92 representing the center line of the sheet is also drawn. Arc 98 is then subdivided into relatively small segments, for example degree segments, by the radius lines |04, and such lines extended to intersect arc |02. From the points of intersection between arc |02 and radius lines |04, tangents |96 are projected. On succeeding projected tangents |06, points |08 are established by successively subtracting from distance A to B (distance from point where bending of sheet begins to edge of sheet) the length of the ,arc from A to the point of intersection between radius lines |04 and arc |02, and then plotting the difference on the corresponding tangent line. A series of points |08 are thus established on the projected tangents. By connecting points |08 a portion of the involute curve |09 described by the edge of board 96 when bent over the curvature of arc 98 is established.

This involute curve |09 is substantially arcuate for a considerable part of its length, after which it departs inwardly from the arcuate form. At any two suitable points, as X and Y, near the middle portion of the arcuate part of the involute curve, perpendiculars are drawn to this curve, and the point where the perpendiculars intersect represents the pivot point 34. In the bending apparatus, this pivot point 34 is generally below the horizontal plane of the sheet 96 as originally placed upon mold 24 and is in close proximity to the upper portion of the curvature 30 of the mold 24 over which the sheet is bent.

The arms 32 are mounted to pivot about points 34 so determined. In the turning movement of the restraining bars 38 their recessed parts 39 describe an arc ||0 as arms 32 are turned about the pivot points 34. This arc ||0 described about point 34 as the center and with the same radius as that of the arcuate portion of the involute curve |09 will closely follow the involute curve |09 through an arc of about 50 to 75 degrees, which approximately represents the critical sheet bending range. Consequently, within this range of travel of bars 38 the sheet 96 which is being bent will be restrained by its edges engaging in the recesses 39 in restraining bars 38. After following the arc ||0 through a considerable swing as above described, the involute curve |09 departs inwardly from the arc ||0, and at this point indicated by reference character |4 the sheet edges in departing from the arcuate path and following the involute curve |09 start to withdraw from the recesses 39 of bars 38, and such withdrawal is complete shortly thereafter. In this way the automatic release of the sheet from edge restraint is effected to take place at or preferably shortly before the completion of the bending operation.

Modications (and variations of the method and apparatus may be employed, and it is to be understood that the invention shall not be limited by the specific description given herein, but only by the scope of the appended claims.

We claim:

1. Apparatus for bending sheet material which comprises a heated rnold including an upper surface portion and downwardly curved spaced side forming portions, said upper surface portion adapted to support a sheet with its side portions extending outwardly beyond said curved side forming portions of the mold, arms at each end of the mold and pivoted at points in a plane below the upper surface of the mold and adjacent to the curvature of the side portions thereof, restraining bars having means for engaging the sheet by its edges said bars being adjustably secured to the outer ends of said arms and positioned in substantially parallel alignment to the sides of the mold, and rolls adapted to apply downward pressure to the outwardly-extending portions of the sheet to force these portions of the sheet and also the restraining bars toward the sides of the mold.

2. Apparatus as defined in claim 1, and also including clamping means for holding the sheet to the upper surface of the mold during the bending operation.

3. Apparatus for bending sheet material, which comprises a heated mold including an upper surface portion and a downwardly curved side portion, said upper surface portion adapted to support a sheet with its side portion extending outwardly beyond the curved side portion of the mold, clamping means for holding the sheet to the upper surface portion of the mold, an arm pivoted at each end of the mold, a restraining member having a recessed portion for engaging the sheet by its edge, said member being adjustably secured to the outer ends of said arms and positioned in substantially parallel alignment to the side of the mold, and movable means adapted to apply downward pressure to the outwardlyextending side portion of the sheet to force the side portion of the sheets and said restraining member toward the side of the mold.

4. Apparatus for bending sheet material which comprises a heated mold including an upper surface portion and downwardly curved side portions, said upper surface portion adapted to support a sheet with its side portions 'extending outwardly beyond said curved side portions of the mold, clamping means for holding the sheet to the upper surface portion of the mold, arms pivoted at each end of the mold, a pair of restraining members having recessed portions for engaging the sheet by its opposite edges, said members being adjustably secured to the outer ends of said arms and positioned in substantially parallel alignment to the side of the mold, and movable means adapted to apply downward pressure to the outwardly eX- tending side portions of the sheet to force the side portions of the sheet and said restraining members toward the side of the mold.

5. A method of bending sheet material which comprises bending a sheet into a curvedl formation such that in bending the sheet each of its edges describes substantially an involute curve, restraining the sheet while bending by application 'of inwardly-directed pressure to its opposite edges and carrying such application to each of the sheet edges through a substantial portion of a substantially arcuate path with which path said involute curve is substantially coincident in part and in part departs therefrom, and utilizing such departure to effect the release of the edges of the sheet from such pressure application.

6. A method according to claim 5, and in which the sheet is clamped at its middle portion during the bending operation.

7. A method according to claim 5, and in which the release defined in said claim is effected after at least the principal part of the bending has been completed.

8. A method according to claim 5, and in which the sheet is clamped at its middle portion during the bending operation and in which the arcuate path and the involute curve substantially coincide for at least 9. A- method of bending sheet material which comprises applying substantially vertical clamping .pressure along an area extending substantially parallel to the side edge of the sheet, bending the sheet into a curved formation such that 'in bending the sheet said side edge describes substantially an involute curve, restraining the sheet during bending thereof by application to the saidsfide edge inwardly-directed pressure at substantially right angles to said clamping pressure and carrying such application of inwardly-directed pressure through a substantial portion of a substantially arcuate path with which path said involute curve is substantially coincident in part land in part departs therefrom and utilizing such departure to effect the release of the sheet from such inwardly-directed pressure application.

v10. A method according to claim 9, and in which the release defined inY claim 9 is effected after the principal part of the bending has been completed.

1 1. A method according to claim 9, and in which the arcuate path and the involute curve substantially coincide for at least 50.

ROBERT M. BOEHNL AARON A LADON.

REFERENCES CITED The yfollowing references are of record in the file of this patent:

NITED STATES PATENTS

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