Honeycomb fabrication - Patent Review 5670001

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of making honeycomb product comprising the steps of:

advancing a plurality of substrate layers to be overlaid relative to each other;

applying to individual ones of said substrate layers a plurality of segment node strips of solid polymeric material having a softening temperature and a higher melting temperature, said solid node strips being placed spaced from and parallel to each other on each said substrate layer, and placed in alternating offset but parallel relationship to solid node strips on substrate layers thereabove and therebelow;

placing said substrate layers in stacked relationship to each other and applying pressure to said substrate layers and said solid node strips while elevating the temperature of said solid node strips to a value above said softening temperature but below said melting temperature, and maintaining said pressure and said temperature for a time sufficient to force softened portions of said solid node strips into full engagement with said substrate layers;

removing the pressure and cooling said layers and solid node strips and thereby bonding said solid node strips to said substrate layers to form a laminated structure; and

expanding said cooled laminated structure into a honeycomb core structure.

2. The method of making honeycomb product in claim 1 wherein said step of placing said substrate layers in stacked relationship to each other comprises applying pressure and elevating the temperature of said node strips only after a plurality of said substrate layers are so stacked.

3. The method of making honeycomb product in claim 1 wherein said step of placing said substrate layers in stacked relationship to each other comprises applying pressure and elevating the temperature of said node strips after each substrate layer is so stacked.

4. The method in claim 1 including the step of applying an uncured thermosetting resin to said expanded honeycomb core structure, and curing said thermosetting resin.

5. The method in claim 1 wherein said solid thermoplastic node strips comprise one or more materials selected from the group consisting of homogeneous thermoplastic strips, thermoplastic filaments, thermoplastic preimpregnated cloth, thermoplastic coated glass filaments, expanded thermoplastic film, and unexpanded thermoplastic film.

6. The method in claim 1 wherein said thermoplastic node strips comprise one or more of the group of thermoplastic materials selected from the group consisting of polypropylene, polyethylene, polycarbonate, polyetherimide, polyethersulfone, polyetheretherketone, and polyurethane.

7. The method in claim 1 including the steps of providing a continuous web of substrate material, and severing said web into said plurality of substrate layers.

8. The method in claim 1 including the steps of providing continuous strips of said polymeric node material, and severing said continuous strips into said segment node strips.

9. The method in claim 7 including the steps of providing continuous strips of said polymeric node material, and severing said continuous strips into said segment node strips.

10. The method in claim 1 wherein said strips are in the form of templates, each successive template of strips in said stacked relationship being laterally offset from any template therebelow and offset from any template thereabove.

11. The method in claim 1, wherein said solid node strips are advanced from at least one spool.

12. The method defined in claim 1 wherein the substrate layers that are advanced are made of a porous material.

13. A method of making honeycomb product comprising the steps of:

advancing a continuous web of substrate material;

advancing a plurality of continuous node strips of solid thermoplastic node material in the same direction as said advancing substrate material;

applying said node strips to a surface of said substrate material while said node strips are retained spaced from and parallel to each other;

heating said node strips above the softening temperature thereof and applying pressure to said softened strips against said substrate material to adhere said parallel node strips to said substrate material;

transversely cutting said continuous substrate material into substrate sheets and said adhered node strips into node segments;

stacking said substrate sheets and adhered node segments in layers, with said segment node strips on successive layers being laterally offset and parallel to node strips on layers thereabove and therebelow;

heating said segment node strips above the softening temperature thereof and pressing said layers together to bond said layers together with each other and with said node strips, along said node strips, to form a block;

cooling said block; and

expanding said block into a honeycomb structure.

14. The method in claim 13 wherein said plurality of node strips are extruded in situ while advanced.

15. The method in claim 13 wherein at least some of said node strips are each formed of a plurality of filaments.

16. The method in claim 13 wherein said filaments are multiple strands.

17. The method in claim 13 wherein said strips are formed from at least one continuous filament which is advanced across said web at spaced intervals.

18. The method in claim 17 wherein said filaments are advanced as doubled strands.

19. A method of making a honeycomb structure comprising the steps of:

advancing substrate material in a first direction;

advancing node strips of solid thermoplastic polymeric node material in a second direction transverse to said first direction across said substrate material at spaced intervals to provide spaced parallel node strips, for a combination of substrate and node strips;

effecting a stack of layers of said combination substrate and node strips while offsetting said node strips on each layer to be laterally offset midway relative to any node strips on a layer therebelow and any node strips on a layer thereabove;

pressing said stack of layers including said node strips while heating said node strips sufficiently to soften said node strips to bond to the layer therebelow and the layer thereabove, forming a block;

cooling said block; and

expanding said block into a honeycomb structure.

20. The method in claim 19 including the steps of providing said node strips in continuous form, and severing said advancing continuous node strips to a length substantially equal to the width of said substrate material.

21. The method in claim 17 including the steps of providing said substrate material in continuous web form, and severing said web form into sheets.

22. A method of making honeycomb blocks comprising the steps of:

providing a windup form having faces and being rotational about its center;

winding up onto said form at least one web of substrate material to form substrate layers thereof on said faces, while winding up a plurality of spaced parallel node strips of solid thermoplastic node material between the said layers of substrate material, said solid node material having a softening temperature and a higher melting temperature, and causing said spaced parallel solid node strips applied to successive substrate layers to be midway between the solid node strips applied to the previous substrate layer; and

heating and pressing said solid node strips and substrate layers to a temperature above said softening temperature, but below said melting temperature of said solid node strips to sufficiently soften said solid node strips and cause them to bond between adjacent layers of said substrate material.

23. The method in claim 22 wherein said step of heating and pressing is performed on said windup form, and then said bonded substrate layers and node strips are severed into honeycomb blocks.

24. The method in claim 22 including the step of separating said substrate layers and node strips wherein they are first separated from said windup form and then are heated and pressed sufficiently to elevate the temperature of said node strips above the softening temperature thereof to bond said substrate layers and node strips into honeycomb blocks.

25. The method in claim 22 wherein said strips are wound in the same direction as said substrate is wound.

26. The method in claim 25 wherein said strips are wound in a direction transverse to the direction that said substrate is wound.

27. The method in claim 22, wherein said solid node strips are advanced from at least one spool.

28. The method defined in claim 22 wherein the substrate layers that are wound up onto said rotational form are made of a porous material.

29. A method of making honeycomb precursor product, capable of expansion into a honeycomb product, from sheet stock, comprising the steps of:

providing a plurality of substrate layers;

corrugating said layers to result in parallel, spaced, offset crests and depressions in each layer;

placing on said crests node strips of solid thermoplastic node material having a softening temperature and a higher melting temperature, with said node strips being spaced from and parallel to each other;

stacking said substrate layers to cause said depressions in each layer to engage said node strips on the said crests of the layer therebelow, and thereby cause said node strips on said crests of each layer to engage the depressions of the layer thereabove;

applying pressure to said crests and depressions of successive said substrate layers while heating said node strips to a temperature above said softening temperature to bond said node strips to said substrate layers of said crests and depressions, and thereby bond said corrugated substrate layers together; and

cooling and removing said pressure from said substrate layers to result in a honeycomb structure.

30. A method for forming a precursor block expandable into a honeycomb structure, comprising the steps of:

providing and advancing substrate layers, and stacking said substrate layers;

providing and advancing successive sets of pluralities of solid polymeric node strips in parallel relationship, at equal spacings, onto said substrate layers before or while said substrate layers are stacked, one set for each layer, and each set laterally offset halfway relative to the strip spacing of the set therebelow; and

softening said solid node strips and pressing them into bonding relationship with said substrate layers to form a block, to thereby form an expandable block.

31. The method in claim 30, wherein said solid node strips are advanced from at least one spool.

32. The method defined in 30 wherein the substrate layers that are advanced are made of a porous material.

33. A method for forming a precursor block expandable into a honeycomb structure, comprising the steps of:

providing and advancing at least one web of substrate material to a stacking apparatus that stacks successive layers of said substrate material;

providing and advancing a plurality of spaced parallel node strips of solid thermoplastic node material toward said web of substrate material, said node material having a softening temperature and a higher melting temperature; and

heating said solid node strips to a temperature above said softening temperature, but below said melting temperature as said solid node strips are applied between adjacent layers of said substrate material to bond the adjacent layers of substrate material together as said solid node strips are allowed to cool.

34. The method in claim 33, wherein said solid node strips are advanced from at least one spool.

35. The method in claim 33, wherein said thermoplastic node strips are thermoplastic coated glass filaments.

36. The method defined in claim 33 wherein the substrate layers that are advanced are made of a porous material.

37. A method for forming a precursor block expandable into a honeycomb structure, comprising the steps of:

providing a windup form having faces and being rotational about its center;

winding up onto said windup form at least one web of substrate material to form substrate layers thereof on said faces;

advancing a plurality of spaced parallel node strips of solid thermoplastic node material toward said windup form, said node material having a softening temperature and a higher melting temperature; and

heating said solid node strips to a temperature above said softening temperature, but below said melting temperature as said solid node strips are wound upon said windup form between adjacent layers of said substrate material to bond the adjacent layers of substrate material together as said solid node strips are allowed to cool.

38. The method in claim 37 and further including the step of pressing said alternate layers of substrate material and node strips as said layers are wound onto said windup form.

39. The method in claim 38 and further including the step of severing the bonded substrate layers to form honeycomb blocks.

40. The method in claim 37, wherein said node strips are wound onto said windup form in the same direction as the substrate is wound.

41. The method in claim 37, wherein said solid node strips are advanced from at least one spool.

42. The method in claim 37, wherein said thermoplastic node strips comprise one or more materials selected from the group consisting of homogeneous thermoplastic strips, thermoplastic filaments, thermoplastic preimpregnated cloth, thermoplastic coated glass filaments, expanded thermoplastic film, and unexpanded thermoplastic film.

43. The method in claim 37, wherein said thermoplastic node strips comprise one or more of the group of materials selected from the, group consisting of polypropylene, polyethylene, polycarbonate, polyetherimide, polyethersulfone, polyetheretherketone, and polyurethane.

44. The method in claim 37, wherein said thermoplastic node strips are thermoplastic coated glass filaments.

45. The method in claim 37 including providing continuous strips of solid node material and a continuous web of substrate material, and severing the layers of substrate material and strip nodes after the layers of substrate material are bonded together by said strip nodes.

46. The method defined in claim 37 wherein the substrate layers that are wound up onto said rotational form are made of a porous material.

47. A method for forming a honeycomb structure, comprising the steps of:

providing a windup form having faces and being rotational about its center;

winding up onto said windup form a first web of porous substrate material on said faces to form a plurality of layers of said first substrate web;

advancing a first set of spaced parallel node strips of solid thermoplastic node material toward said windup form for application onto said first substrate web, said node material having a softening temperature and a higher melting temperature;

winding up onto said windup form a second web of porous substrate material on said first set of spaced parallel node strips to form a plurality of layers of said second substrate web;

advancing a second set of spaced parallel node strips of said solid thermoplastic node material toward said windup form for application onto said second substrate web, said second set of node strips being applied to said second substrate web at spacings off-set halfway between the node strips of said first set;

heating said solid node strips of said first and second set to a temperature above said softening temperature, but below said melting temperature as said solid node strips are wound upon said windup form between adjacent layers of said first and second substrate layers to bond the adjacent substrate layers together as said solid node strips are allowed to cool, said node strips being applied as a softened solid material to prevent wicking of the node strips through the layers of said first and second webs of porous substrate material;

rotating said windup form until a multi-layered structure is formed that includes a plurality of alternating layers of said first and second substrate webs bonded together along nodes formed therebetween by said node strips;

cutting the multi-layered structure into flat precursor blocks; and

expanding a precursor block into a honeycomb structure.

48. The method defined in claim 47 and further including the steps of:

coating said honeycomb structure in a resin; and

curing said resin-coated honeycomb structure to form a rigid honeycomb structure.

BACKGROUND OF THE INVENTION

This invention relates to a method and apparatus for making honeycomb structure.

Honeycomb structure has been found useful for a wide variety of functions and purposes. As such, it is made from various materials including metal, e.g., aluminum, as well as paper, cloth and other materials. The primary techniques of forming honeycomb from layers, webs or sheets include expansion and corrugation. With the expansion technique, the sheets are adhered together at intervals and expanded. With the corrugation technique, layers or sheets are first formed into the corrugated configuration and then interconnected as by adhesive bonding, welding or otherwise.

In the known expansion process, the flat foil, fabric or film layers are typically joined together with thermosetting adhesive which is printed on the substrate sheet at discrete intervals to form bonding nodes. Adjacent sheets are printed at laterally offset intervals, see e.g. U.S. Pat. No. 4,957,577. The adhesive is suspended in a solvent typically amounting to around 80% of the composition. Multiple sheets and the applied thermosetting adhesive are cured under heat and pressure. If the substrate or layers are of a porous material, such as some fibrous materials, the liquid adhesive tends to penetrate completely through the layer so as to appear between the underlying and overlying layers, unless the sheets are specially pretreated. If this penetration happens, some or all of these layers may become bonded together in the heating and pressurizing stage into an unexpandable block. Consequently, preimpregnation pretreatment of the porous material sheets has normally been practiced as set forth, for example, in U.S. Pat. No. 3,519,510, to forestall penetration by the solvent adhesive clear through the layers. The solvent is evaporated from the adhesive and the layers and adhesive are carefully treated with heat and pressure applied to the plurality of sheets on which the adhesive has been printed. After cooling, the bonded structure is expanded, e.g., by connecting elements to the outer layers and pulling the structure into an expanded honeycomb.

The above-noted preimpregnation adds production steps and cost to the honeycomb forming process and product.. Moreover, preimpregnation must be performed just right to prevent the product from becoming scrap. As an example, glass cloth is normally preimpregnated with a thermosetting resin and partially cured. This is done so that the cloth may be printed on later without the adhesive bleeding through the fabric. In this procedure the resin content and degree of curing are critical areas. If the resin content is too high, the core will be very difficult to expand. If the resin content is not high enough, there will be holes through which the later applied adhesive will bleed. This may result in a bond in the area that must remain unbonded for the honeycomb to be expanded, resulting in an unexpandable block. Cure of the resin is also critical. If the impregnating resin is not cured enough, it will soften and bond to the adjacent layer of material during the subsequent press cycle. This also results in an unexpandable block. If the resin is overcured, the material becomes very hard and rigid, so that during the expansion process the node adhesion is insufficiently strong and will break, resulting in a partial or total failure of the block. After the fabric has been preimpregnated, lines of adhesive are printed on the surface. The adhesive must be partially cured by passing through an oven. However, this also advances the cure of the preimpregnated resin. Therefore, getting the preimpregnated polymer cured to the degree needed is difficult.

Typically, after the block is expanded it is dipped in thermosetting resin and cured. Dipping may occur as many times as necessary to achieve the desired density and strength for the honeycomb.

In the corrugation process, foil or film is first passed through configurated rolls to form individual corrugated sheets. Fabrics are impregnated and/or coated somewhat first, and then corrugated. These sheets are cut to length. After corrugation, adhesive is applied to the protruding flat surface areas of the corrugated sheets, the sheets are stacked and pressed together to bring the formed flat areas together, and the thermosetting adhesive is cured, usually by heat, to form the final honeycomb core. Alternatively, the corrugated sheet flat areas can be fused together by welding. Thus, a series of foils, films or fabric layers become bonded together at the contacting surfaces to form the honeycomb core. In the welding process described in prior patents such as U.S. Pat. Nos. 4,957,577, 5,139,596 and 5,039,567, unreinforced substrates are welded together by using "anvils" which can tend to cut rather than weld the substrate, when physical alignment is off and/or temperatures are too high. The node areas need to be compressed a great deal to achieve flow of the resin to cause welding, and sometimes cause cutting when the correct parameters do not exist.

SUMMARY OF THE INVENTION

The present development enables formation of honeycomb, even utilizing fibrous porous sheets or layers, yet without requiring preimpregnation of the layers and without the previous difficulty of the bonding material penetrating through the porous fibrous layers to undesirably bond to underlying and/or overlying layers and cause an unexpandable block. The curing problems of the prior preimpregnated resin are not involved. Also, the solvent evaporation problem of the prior technology is not present. The bonding material does not require a solvent. Also, cutting of substrates by anvils is avoided. Rather, the development involves laying down of sheets or webs of substrate material, preferably a fibrous base material, with intermediate, evenly spaced strips of solid, reinforced or unreinforced thermoplastic, node strips having a desired softening temperature distinctly different from and less than its melting temperature. The structure is bonded together by applying pressure and sufficient heat to elevate the temperature of the strips to a temperature above the softening temperature of the thermoplastic material, but preferably below the melting temperature thereof, for a sufficient time to cause some of the softened, pressed, node bonding material to penetrate around the surface fibers of the adjacent fibrous layers, or by fusion to the adjacent layer, and thereby bond to the layers. Subsequently, the pressure is removed and the structure cooled. When the expansion process is employed, the bonded layers are expanded into a honeycomb structure.

In creating the layered assembly, various novel forms of apparatus can be employed to apply and fuse the thermoplastic node strips to the substrate material. The resulting material can be coiled for further processing at a later date, and/or may be cut to length and stacked, immediately or later, for honeycomb formation. Alternatively, the solid thermoplastic node strips may be applied at the time of sheeting. That is, the fiber based substrate may be cut to length and laid down with alternating layers of node material. Each layer may be pressed and heat fused individually to the underlying layer, or a plurality of sheets may be stacked into multiple layers and all pressed and heated at the same time. As noted, the solid node material is pressed and heated sufficiently to cause the thermoplastic strips to soften, but not so much as to cause the strips to melt and flow in an uncontrolled fashion under pressure. This feature of the solid thermoplastic strips, the ability to soften without melting, because of a distinct difference between the softening and the melting temperatures, is highly preferred because it allows the node material to bond the layers of the substrate together without bleeding through layers and fibrous substrates and creating an unexpandable block. The pressed block of honeycomb is subsequently expandable by a conventional expansion technique. The expanded honeycomb may be subsequently heat set or dipped in resin, typically a thermosetting resin, and cured to retain its final shape. It may also be dipped in resin repeatedly in order to increase its density and strength to the point desired.

Various substrate materials can be employed, including woven or nonwoven, natural or man made materials. These include, but are not limited to, glass cloth, glass mat, aramid paper, wood pulp paper, cotton cloth, polyester cloth, and/or polyester, polypropylene or polyethylene spun bonded papers. These materials may be preimpregnated, if desired, but this is not necessary for this process. Each individual layer can also be a laminate of thermoplastic film bet