GB2228888A - Apparatus for applying a load to a workpiece - Google Patents

Abstract

Apparatus for applying a load to a workpiece, and particularly for clamping glued wooden fabrications, comprises a base frame 10, 11, 12, an abutment device 13 adjustably mounted on the base frame, and a load-applying assembly 19 also mounted on the base frame at a location spaced from the abutment device 13. The load-applying assembly 19 comprises a housing 20 fixed to the base frame and a piston bar 24 slideable within the housing and projecting from it. An inflatable bag 28 is sandwiched between the piston bar 24 and the interior of the housing 20, so that when the bag is inflated by air under pressure the piston bar is forced further out of the housing and applies pressure to a workpiece held between the piston bar and the abutment device 13. <IMAGE>

Description

"Apparatus for applying a load to a workpiece" The invention relates to apparatus for applying a load to a workpiece and particularly, but not exclusively, to apparatus for clamping and applying pressure to glued wooden fabrications while the glue sets.

It is common practice in the woodworking industry to apply mechanical pressure to glued fabrications while the glue sets, and many mechanical clamping devices are in common use, usually incorporating screw clamps. For example, material known as blockboard is assembled from a plurality of elongate wooden strips glued together side-by-side and overlaid with plywood facing sheets which are also glued in position. In assembling such blockboard panels it is necessary to apply clamping pressure to the sides of the panel to hold the strips firmly against one another while the glue sets, as well as applying pressure across the faces of the panel to keep it flat.

Wooden rails, for example for use as door stiles or other door frame members, may also be built up from a number of narrower wooden strips glued together side-by-side, and such rails also require to be clamped while the glue sets. Usually a plurality of glued rails will be clamped together side-by-side in a larger temporary assembly.

The mechanical screw clamps normally used for such clamping purposes are comparatively slow to operate and there may be a considerable time delay between releasing one complete assembly and clamping up the next. Also, in the case of large assemblies it may be difficult to operate the screw clamps to ensure even pressure over the whole length or area of the assembly.

An alternative method of applying clamping pressure to such wooden fabrications while they are glued is to use hydraulic or pneumatic rams, but such equipment is costly both to purchase and to operate.

The present invention sets out to provide apparatus which is comparatively simple and cheap to construct and operate and yet which allows clamping pressure to be applied and released very quickly and evenly.

According to the invention there is provided apparatus for applying a load to a workpiece comprising a base structure, an abutment member mounted on the base structure, and a load-applying assembly also mounted on the base structure at a location spaced from the abutment member, which assembly comprises two relatively movable parts between which is sandwiched at least one closed flexible inflatable bag having means for connecting it to a source of fluid under pressure whereby, in use of the apparatus, inflation of the container effects relative movement between said parts, means being provided for transferring the force exerted on one of said parts by the inflatable bag to a workpiece disposed between the aforesaid abutment member and the load-applying assembly.

Preferably the other of said relatively movable parts is fixed in relation to the base structure and is adjustably mounted thereon.

The fixed part of the load-applying assembly may provide guide means along which the movable part is slidable, the inflatable bag being disposed between facing opposed surfaces on the fixed part and movable part respectively. The movable part may have a piston portion which projects through, and is slidable in, an aperture provided in the fixed part.

Preferably resilient means are provided to oppose movement apart of the parts of the load-applying assembly, thereby to flatten the inflatable bag, by moving said parts together, upon release of the pressure within the bag.

The load-applying assembly may comprise a series of three or more relatively movable parts with an inflatable bag between each pair of adjacent movable parts, whereby the effect of inflation of the bags in moving the parts and applying forces thereto is cumulative.

In any of the above arrangements said abutment member is preferably fixed in relation to the base structure and is adjustably mounted thereon.

In a preferred embodiment of the invention one of said relatively movable parts of the load-applying assembly is moved towards the abutment member, upon inflation of the inflatable bag, whereby the assembly may apply a compression load to a workpiece disposed between the abutment member and said movable part.

In any of the above arrangements the apparatus may comprise a plurality of load-applying assemblies spaced apart on the base structure, each assembly having an abutment member spaced therefrom. At least one loadapplying assembly and associated abutment member may be so mounted on the base structure as to apply to a workpiece a load in a direction at right angles to the load applied by at least one other load-applying assembly.

Said relatively movable parts of the loadapplying assembly may be elongate, and the inflatable bag may be in the form of an elongate tube, closed at its ends, extending longitudinally of said elongate parts and sandwiched between them.

The following is a more detailed description of embodiments of the invention, reference being made to the accompanying drawings in which: Figure 1 is a diagrammatic side elevation of apparatus for use in clamping a wooden fabrication, such as a staircase assembly, Figure 2 is a sectional view of the loadapplying assembly, taken along the line A-A of Figure 1, Figure 3 is a diagrammatic plan view of a typical inflatable bag for use in the apparatus of Figures 1 and 2, and other similar apparatus, Figure 4 is a diagrammatic side elevation of the bag shown in Figure 3, Figure 5 is a diagrammatic side elevation of apparatus for clamping panel-like assemblies, Figure 6 is a sectional view of the apparatus of Figure 5, Figure 7 is a horizontal section through the central load-applying assembly of the apparatus of Figures 5 and 6, Figure 8 is a vertical section through one of the lower load-applying assemblies of the apparatus of Figures 5 and 6, Figure 9 is a diagrammatic plan view of a general purpose clamping apparatus according to the invention, and Figure 10 is a cross section through one of the load-applying assemblies of the apparatus of Figure 9.

Figure 1 shows an apparatus suitable for clamping, while the glue sets, part of a wooden fabrication, such as a staircase. The apparatus comprises a base structure including two main longitudinal frame members 10 and 11 of box section steel, and a fixed box section steel cross member 12 connecting the longitudinal members at one end.

Adjacent the other end of the apparatus is a movable abutment device 13 which comprises two saddles 14 and 15 which are slideable along the longitudinal members 10 and 11 respectively and are connected by a cross member 16. The saddles 14 and 15 are formed with holes 17 any of which may be brought into registration with any of a series of holes 18 in the longitudinal members, pins then being inserted into the registering holes to locate the abutment device 13 in an appropriate position. The holes 17 and 18 are so spaced that the position of the abutment device 13 is adjustable by small increments, for example of 6mm.

Mounted on the cross beam 12 at the opposite end of the apparatus is a load-applying assembly 19, which is shown in greater detail, on an enlarged scale, in Figure 2.

The assembly, which may be fabricated from wood, comprises a fixed housing 20 which is fixedly clamped to the steel cross beam 12 by means of a pin 21, the ends of the pin projecting from the sides of the housing. Slideable within the chamber 22 within the housing 20 is a piston member 23 to which is connected a piston bar 24 having a steel capped end edge 25 which projects through a slot 26 formed in the end of the housing 20. The rear surface of the piston member 23 faces a parallel opposed surface of a base member 27 defining the end wall of the chamber 22 within the housing 20 opposite the slot 26. An inflatable bag 28, the construction of which is described below, is sandwiched between the base member 27 and the piston member 23.

A further pin 29 extends through the piston member 23 and through longitudinal elongate slots 30 (see Figure 1) in the side walls of the housing 20. The projecting ends of the pins 21 and 29, on each side of the housing 20, are connected together by elastic bands 31 looped around them.

Referring to Figure 3: the inflatable pressure bag 28 comprises a flattened tube of reinforced plastics or rubber which is closed at its ends by steel plates 32 which are bolted together with the tube sandwiched between them so that the tube is totally closed and airtight.

An inlet conduit 33 is connected to one end of the bag 28 and is connected via a control valve 34 to a source of air under pressure, indicated diagrammatically at 35. Operation of the valve 34 to place the interior of the bag in communication with the air pressure source 35 causes the bag to be inflated, as indicated in dotted lines at 36 in Figure 4. The valve 34 operates to switch the pipe 33 between a position where it is connected to the air pressure source 35 and a position where it is vented to atmosphere as indicated at 37.

The operation of the apparatus is as follows: Initially the load-applying assembly is in the condition shown in Figure 2 where the bag 28 is uninflated and is compressed under the action of the elastic bands 31 so that the piston bar 24 is substantially withdrawn into the housing 20. This allows the workpiece to be introduced between the cross bar 16 of the abutment device 13 and the projecting end 25 of the piston bar 24. The abutment device 13 is adjusted to the appropriate position in relation to the assembly 19, depending on the length of the workpiece. Once the workpiece is in position the valve 34 is operated to inflate the bag 28 and this forces the piston member 23 and piston bar 24 to the left, as viewed in Figures 1 and 2, engaging the workpiece and clamping it between the piston bar 24 and the cross member 16.The pressure applied may be controlled by reference to a pressure gauge (not shown) fitted into the air pressure circuit.

Where L is the length of the bag 28, W is its width and P is the air pressure in pounds per unit area, the load applied by pressurisation of the bag 28 (when it is still in a comparatively flat state) is: (L x W x P)/2240 tons.

When the glue has set, the pressure inside the bag 28 is simply vented to atmosphere by operation of the valve 34 and the elastic bands 31 then withdraw the piston bar 22, compressing the bag 28. Application of load to the workpiece, and subsequent release of the workpiece, are therefore effected extremely rapidly and the pressure exerted is also uniform over the length of the piston bar 25.

Figures 5-8 show an alternative form of apparatus which is particularly suitable for use in the manufacture of panel-like assemblies, such as blockboard panels, or temporary assemblies of laminated and glued wooden rails arranged side-by-side.

The apparatus comprises a base structure including four generally rectangular spaced parallel frame members 38 each having a central vertical post 39. The frame members are formed from box section steel. connecting the frame members at the upper end of the apparatus are two longitudinal box section steel beams 40, which also constitute the upper abutment members.

Vertical side abutment bars 41 are mounted on each vertical member 42 of each frame 38, the side bars 41 being adjustable towards and away from the central vertical post 39. Around the vertical post 39 of each frame is mounted a central double-sided load-applying assembly 43 which is shown in greater detail, in horizontal section, in Figure 7, which is an enlarged view.

Two further load-applying assemblies 44 extend horizontally along and within the lower ends of the frame 38, one on each side of the vertical posts 39.

Figure 8 is a vertical cross section, on an enlarged scale, through one of the lower load-applying assemblies. It will be seen that it is somewhat similar in construction to the load-applying assembly 19 of the Figure 1 arrangement and comprises a housing 45 defining a chamber 46 in which a piston member 47 is vertically slideable, a piston bar 48 being mounted on the piston member 47 and having a steel capped upper edge surface 49 which projects through a slot 50 in the housing 45.

An inflatable pressure bag 51, similar to the bag shown in Figures 3 and 4, is sandwiched between the underside of the piston member 47 and the lower wall 52 of the housing 45. The arrangement is such that inflation of the bag 51 under air pressure raises the piston member 47 and piston bar 48 so as to apply upward pressure to the lower edge of the panel, which is indicated diagrammatically in dotted lines at 53 in Figures 5 and 6.

Referring to Figure 7, the central doublesided load-applying assembly comprises a housing formed from two side walls 54 mounted on cross panels 55 secured to the central vertical post 39 of each frame 38. Slideable between the side walls 54 are vertical wooden piston bars 56, a pressure bag 57 being sandwiched between each piston bar 56 and the adjacent steel panel 55. A steel facing strip 58 is mounted on the outer face of each piston bar 56.

At intervals along its length each piston bar 56 has passing through it pins 59 which project through horizontal slots 60 in the side members 54. The projecting ends of each pair of pins 59 are pulled together by elastic bands 61 looped around them. Each piston bar 56 faces and is parallel to an associated vertical abutment member 41.

The pressure bags 57 of all four central double-sided load-applying assemblies, and the pressure bags 51 of the two lower load-applying assemblies 44, are connected to a common source of air under pressure and are controlled by valves in a control box 62 mounted at one end of the apparatus.

In operation, a panel-like assembly comprising a plurality of lengths of wood glued together side-byside is introduced into each side of the apparatus as indicated at 53 in Figures 5 and 6. The pressure bags 51 of the two lower assemblies 44 are then inflated to an appropriate pressure, forcing the piston bars 48 upwardly and applying upward pressure along the lower edge of each assembly 53 and clamping the lengths of wood firmly against one another. Subsequently, or simultaneously, the pressure bags 57 are inflated forcing the piston bars 56 outwardly away from one another and clamping each assembly between the piston bars 56 and the associated fixed abutments 41. The upward pressure exerted on the assembly, and the lateral pressure exerted on its faces, may be controlled by controlling the air pressure in the bags 51 and 57.

When the glue has set the pressure bags are vented to atmosphere. The piston bars 56 are then retracted by the elastic bands 61 and the piston bars 48 of the lower assemblies are retracted due to the weight of the assembly acting on them. The assembly is thus freed and may be readily removed from the apparatus.

Figures 9 and 10 illustrate a general purpose clamping frame in accordance with the invention, which may be suitable for clamping a wide variety of wooden fabricated articles. The apparatus comprises a generally rectangular steel frame 63 comprising side bars 64 and 65, a cross bar 66 at one end and a pair of spaced parallel cross bars 67 at the other end. All of the bars may be formed from box section steel.

The frame 63 also comprises two fixed longitudinal intermediate bars 68 on which are adjustably mounted fixed abutment members 69. Loadapplying assemblies 70 are mounted on the cross bars 67 so as to be slideable to various positions along the cross bars.

Slideable to various positions along the length of the frame 63 are three transverse assemblies 71. Each assembly 71 comprises a cross bar 72, an abutment member 73 adjustable to various positions on the cross bar 72 and a load-applying assembly 74 at the opposite end. Each transverse assembly 71 is slideable, with its associated abutment 73 and assembly 74, along the side bars 65 of the frame 63.

The load-applying assemblies 70 and 74 are similar and their construction is shown in Figure 10 which is a cross section through one of the loadapplying assemblies, on an enlarged scale.

As seen in Figure 10, each assembly comprises a wooden housing 75 defining a chamber 76 in which is slideable a piston member 77 carrying a piston bar 78 which projects through a slot 79 in one end of the housing and is provided with a steel capping strip 80.

In this case, two inflatable pressure bags are provided to permit the application of greater movement and pressure to the piston bar 78. The pressure bags are indicated at 81 and 82 and for transmitting the loads applied by the pressure bags when inflated a generally H-sectioned intermediate member 83 is positioned between the piston member 77 and an end block 84 within the housing 75. The intermediate member 83 is freely slideable within the housing 75. The pressure bag 81 is sandwiched between the piston member 77 and the intermediate member 83, and the pressure bag 82 is sandwiched between the intermediate member 83 and the end block 84.The operation is similar to the operation of the load-applying assemblies previously described, except that either one or both of the pressure bags and 82 may be inflated thus providing greater control over the pressure applied by the assembly as well as permitting a greater maximum pressure to be applied.

In operation the transverse assemblies 71 are slid to the required positions on the frame 63 and the load-applying assemblies 70 and the abutment members 69 and 73 are adjusted to the appropriate positions to contact parts of the workpiece which is laid on the frame. When this adjustment has been completed pressure bags 81 and/or 82 of the various assemblies are inflated to the required amount to apply the required pressure to the workpiece. The pressure bags of the various assemblies may be independently controlled to provide the maximum control over the pressure applied to different parts of the workpiece.

In any of the above arrangements, means may be provided for heating the wooden assembly, while it is clamped in the apparatus, to speed up the setting of the glue. For example, the apparatus may be covered by an enclosure, a heater and fan being provided to circulate hot air, for example at about 85"F, within the enclosure and around the wooden assembly.

Although the invention has been particularly described in relation to the clamping of fabricated wooden assemblies, it will be appreciated that the invention is more widely applicable to any form of apparatus where a controlled load requires to be applied to a workpiece. Although in the arrangement described the load-applying assemblies are disposed to apply compressive loads to the workpiece, it will be appreciated that by suitable modification, and the provision of positive connections between the piston bars and the workpiece, it would be possible to apply tension loads to the workpiece, if required.

Claims (15)

1. Apparatus for applying a load to a workpiece comprising a base structure, an abutment member mounted on the base structure, and a load-applying assembly also mounted on the base structure at a location spaced from the abutment member, which assembly comprises two relatively movable parts between which is sandwiched at least one closed flexible inflatable bag having means for connecting it to a source of fluid under pressure whereby, in use of the apparatus, inflation of the container effects relative movement between said parts, means being provided for transferring the force exerted on one of said parts by the inflatable bag to a workpiece disposed between the aforesaid abutment member and the load-applying assembly.

2. Apparatus according to Claim 1, wherein the other of said relatively movable parts is fixed in relation to the base structure.

3. Apparatus according to Claim 2, wherein said part which is fixed in relation to the base structure is adjustably mounted thereon.

4. Apparatus according to Claim 2 or Claim 3, wherein the fixed part of the load-applying assembly provides guide means along which the movable part is slidable, the inflatable bag being disposed between facing opposed surfaces on the fixed part and movable part respectively.

5. Apparatus according to Claim 4, wherein the movable part has a piston portion which projects through, and is slidable in, an aperture provided in the fixed part.

6. Apparatus according to any of Claims 1 to 5, wherein resilient means are provided to oppose movement apart of the parts of the load-applying assembly, thereby to flatten the inflatable bag, by moving said parts together, upon release of the pressure within the bag.

7. Apparatus according to any of the preceding claims, wherein the load-applying assembly comprises a series of three or more relatively movable parts with an inflatable bag between each pair of adjacent movable parts, whereby the effect of inflation of the bags in moving the parts and applying forces thereto is cumulative.

8. Apparatus according to any of Claims 1 to 7, wherein said abutment member is fixed in relation to the base structure.

9. Apparatus according to Claim 8, wherein said fixed abutment member is adjustably mounted on the base structure.

10. Apparatus according to any of Claims 1 to 9, wherein one of said relatively movable parts of the load-applying assembly is moved towards the abutment member, upon inflation of the inflatable bag, whereby the assembly may apply a compression load to a workpiece disposed between the abutment member and said movable part.

11. Apparatus according to any of Claims 1 to 10, comprising a plurality of load-applying assemblies spaced apart on the base structure, each assembly having an abutment member spaced therefrom.

12. Apparatus according to Claim 11, including at least one load-applying assembly and associated abutment member so mounted on the base structure as to apply to a workpiece a load in a direction at right angles to the load applied by at least one other load-applying assembly.

13. Apparatus according to any of Claims 1 to 12, wherein said relatively movable parts -of the loadapplying assembly are elongate, and the inflatable bag is in the form of an elongate tube, closed at its ends, extending longitudinally of said elongate parts and sandwiched between them.

14. Apparatus according to Claim 13, and for clamping a wooden panel comprising a plurality of elongate beams extending longitudinally of the panel glued side-by-side, the apparatus comprising an elongate load-applying assembly spaced from an elongate abutment member so that, in use, the panel lies in the plane containing said assembly and abutment member and the assembly applies a load clamping the side-by-side beams together, and a plurality of further parallel elongate load-applying assemblies, each having an associated spaced abutment member, extending at right angles to the first said load-applying member and spaced apart along the length thereof so that, in use, said parallel loadapplying members apply clamping loads to the face of said panel and transversely of the elongate beams.

15. Apparatus for applying a load to a workpiece substantially as hereinbefore described with reference to Figures 1 to 4, Figures 5 to 8, or Figures 9 and 10 of the accompanying drawings.