CA3054896A1 - Joining method and composite - Google Patents

Abstract

The edges of two sheets of material are joined across their margins which margins have anchoring interstices and interdigitating scallops. The scallops and margins are flooded with a polymer powder that infiltrates the interstices where it is melt-fused and then cooled to a hard and anchored coating joining the sheets.

Description

JOINING METHOD AND COMPOSITE
FIELD OF THE INVENTION
The present invention is in the related fields of the joining of sheet material and composites thereof.
BACKGROUND OF THE INVENTION
Sheet materials such as metals, plastics, and textiles are often face-joined in various combinations to make a composite sheet. The large contact area between the sheets provides a strong joint. Edge-joining of sheets however requires welding because the line-wide contact area would not be strong.
However welding cannot be used for most dissimilar material edge joints.
Plus it is slow, requires high skill and is expensive.
The instant invention provides a novel method of joining edges of sheet material by providing anchoring interstices and scallops along the margins, and flooding the margins with a polymer powder that is melt-fused and cooled into a continuous anchored coating thereby joining the sheets.
The relatively wide scalloped zone creates a wide and therefore robust edge joint that spreads and dissipates bending stress and other loads and forces.
SUMMARY OF THE INVENTION

The method of the instant invention for joining the edges of sheet material whose edge margins have interstices, is as follows:
1. Scalloping into the margins;

2. Interdigitating the scallops;

3. Flooding polymer powder onto both margins;

4. Heating the sheets to fuse the powder;

5. Cooling the resulting composite sheet.
Variations contemplated include:
1. Scallop first and then create interstices on the scallops and margins;
2. Add fibres, grits, beads, etc, to/with the powdered polymer;
3. Interlay textile with the powder;
4. Shim a thinner sheet to achieve best placement.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a perspective of the anchor bearing faces of two sheet workpieces with interdigitated 'saw-tooth' scallops;
Figure 2 is a side cross-section view of a sheet with raised hook anchors that are submerged in powdered polymer such as a thermoplastic;
Figure 2a shows how the powder fuse-melts to a plastic coating embedding the anchors.

Figure 3 shows a cross-side view of a sheet with perforated anchors where each perforation necessarily has a projected hole rising from the upper face and a dimple recessed into the lower face. Also shown is how powdered polymer has passed through the hole to accumulate as a conical 'rivet head' in the dimple;
Figure 4 shows a top view of finger shaped scallops along the margins of two sheets to be joined by interdigitation. The upper sheet has the hook anchors of Fig 1 while the lower sheet is shown to have the perforation anchors of Fig 2. Powder has been applied to the entire upper sheet but only onto the margin of the lower sheet;
Figure 5 shows a top view of the plain (non-anchored) faces of two sheets each having saw-tooth scallops with a gap between, and where the 'tooth' tips are modified to allow powdered polymer from the anchored face to fill in the apex regions of the teeth and so to fuse as one with the surface layer of polymer;
Figure 6 shows a top view of two sheet with saw-tooth scallops and where the powdered polymer covers portions of the upper sheet and extends onto part of the the margin of the lower sheet. Four patches or pads of powder are also shown.
Any pattern of powder can be used;
Figure 7 shows scallops with different tip modifications to enable powder to flow into the scallop to increase bend resistance;
Figure 8 shows similar modifications for saw-tooth scallops with optional interstices;
Figure 9 shows a textile sheet above interdigitated with a solid sheet below;
Figure 10 shows square tooth scallops.

DETAILED DESCRIPTION OF THE INVENTION
For solid sheet material such as metal and plastic, surface interstices are formed by tooling that creates hooks and/or pierced holes and/or tabs, etc.
These can be formed on the entire sheet, portions of the sheet, or only along margins.
Textile sheets have innumerable natural surface interstices between fibres in fabrics, cloths, mats, weaves, naps, etc.
Such interstices allow distributed dry plastic powder to freely infiltrate the sheet's surface, flowing by gravity into, below, between, and about the interstices. Agitation by brush or vibration can enhance the infiltration, if needed additional powder can be added to build a layer of a desired thickness above.
Scallops formed into part of each sheet's margin allows the sheets to interdigitate or interlock. Scalloping involves forming a regular pattern of openings that are punched or cut.
Fig 1 shows two sheet workpieces 2 each with upper face surface (face) populated with interstices in the form of hooks 5, and each with margins 2a along respective edges. Margins do not have a defined width. Saw-tooth scallops 8 have been formed into each margin 2a and are interdigitated tightly or loosely as required. A
powdered thermoplastic polymer (not shown in Fig 1) such as polyethylene, PVC, Nylon, etc. will be spread along the margins (or over entire sheet) to flow freely and advantageously under and about the hooks and therebetween. On heating sheets 2, the powder 1 melts in place and fuses to a viscous liquid coating. The sheets are then cooled whereby a hard, continuous plastic layer is anchored to the two sheets 2 joining them as desired, into a single composite sheet 10.
Fig 2 shows a cross section of a row of interstice hooks 5 that have been raised by specialized tooling where toothed blades are repeatedly short-stroked across face/
margin of sheet 2 grooving the surface and raising hooks 5. Thermoplastic powder 1 which is essentially very fluid (low viscosity), is shown to have advantageously flowed fully and completely beneath hooks 5, which is more complicated and less successfully achieved with normal pre-melted thermoplastic processes due to its high viscosity.
Fig 2a shows the powder 1 having melted to a solid continuous plastic coating 1a which has fully entombed all hooks 5 and is therefore anchored to sheet 2 and will strongly resist de-lamination.
Fig 3 shows how pierced holes 3 (not punched, no ejected plug) provide anchors by allowing powder 1 to flow through and create a larger head 4 below to resist separation of the coating. Holes 3 would have a jagged rim of interstices (not shawm) naturally caused by piercing and which aid anchoring.
Fig 4 shows a top view of two sheets, the upper having its entire face populated with anchor hooks 5, while the lower sheet has anchor holes 3 only along the margin (2a in Fig 1). Finger scallops 9 are shown interdigitated. Powder 1 is shown to cover only a portion of margins 2a including the entirety of scallops 9. Loos fitting scallops 9 will allow powder 1 to fall between to add strength to the joint due to added thickness and the mechanics of such shaped inclusions.
Fig 5 is view of the un-anchored faces of sheets 2 where the loosely interdigitated scallop teeth have had the tips or apexes modified (see Fig 8) to allow additional intrusion of powder 1 for strength.
Fig 6 shows the anchored faces of interdigitated sheets 2 where powder 1 has been selectively applied including as pads or patches lb as may be useful to deal with thermal expansion issues such as when two different materials are joined.
Fig 7 is a perspective view of finger scallops 9 where tip 9a has been bevelled or chamfered to allow ingress of powder not top of the scallop. Tip 9b show the tip bend downward for the same purpose.
Fig 8 is a perspective of tooth scallops 8 modified for powder ingression where tip 8a has been truncated, tip 8b has been bevelled or chamfered, and tip 8c has been bent. Scallop 8 also shows how it can be provided with interstices 8f as roughness, tearing, abrasion, slitting etc.
In Fig 9 a textile sheet 2b with only horizontal fibre bundles into and between which powder can infiltrate, but, for clarity, has powder on the right half only while the left is left plain for clarity.
Fig 10 show a square scallop shape 10. Any convenient shape will work.

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Claims (3)

I CLAIM:
1. A method for joining the edges of sheet material whose edge margins have interstices, comprising:

1. Scalloping into the margins;
2. Interdigitating the scallops;
3. Flooding polymer powder onto the scallops and margins;
4. Fusing the powder;
5. Cooling the fused powder.

2. A composite sheet comprising at least two sheets, whose respective margins have interstices and scallops flooded with polymer powder fused to a solid.

3. The composite sheet of Claim 2 where substantially the entire face of at least one sheet has interstices.