SANDWICH STRUCTURE
A sandwich structure employs a core sheet including alternating peaks and valleys therein. In another aspect, a sandwich structure includes at least one metallic core and at least one adhesively bonded outer face sheet. Yet another aspect of a sandwich structure has raised ridges bridging between adjacent peaks in a core sheet in one direction but not in a perpendicular direction, thereby achieving different properties in the different sheet directions.
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This application is a divisional application of U.S. patent application Ser. No. 14/105,989, filed on Dec. 13, 2013, now U.S. Pat. No. 9,925,736, issued on Mar. 27, 2018, which is incorporated by reference herein.
BACKGROUNDThe present invention relates generally to sandwich structures and more particularly to a sandwich structure including a core having alternating peaks and valleys.
Metallic sandwich structures having outer and core layers are known in the industry. For example, reference is made to the following U.S. Pat. No. 7,752,729 entitled “Method for Shaping a Metallic Flat Material, Method for the Manufacture of a Composite Material and Devices for Performing these Methods” which issued to Faehrrolfes et al. on Jul. 13, 2010; U.S. Pat. No. 7,648,058 entitled “Formed Metal Core Sandwich Structure and Method and System for Making Same” which issued to Straza on Jan. 19, 2010, and is commonly owned herewith; and U.S. Pat. No. 3,525,663 entitled “Anticlastic Cellular Core Structure having Biaxial Rectilinear Truss Patterns” which issued to Hale on Aug. 25, 1970; all of which are incorporated by reference herein. The Hale patent, however, teaches the use of vertically openable stamping dies to form nodes in a heated core sheet, with the objective of obtaining the same flexual and shear strength in all planes. A core stamped in this fashion is prone to tearing during node-forming and the node pattern is symmetrical. Furthermore, the Faehrrolfes patent disadvantageously requires a lubricant during its elongated wave shaping of the core to reducing tearing, which creates later problems with desired adhesive bonding of the outer sheets. It is also noteworthy that Faehrrolfes requires a complex mechanism in order to continuously adjust the forming roll positioning during shaping of each workpiece, which leads to tolerance accuracy concerns and rigidity inconsistencies within a single part as well as part-to-part. The Faehrrolfes wave pattern is also symmetrical in all directions.
SUMMARYIn accordance with the present invention, a sandwich structure employs a core sheet including alternating peaks and valleys therein. In another aspect, a sandwich structure includes at least one metallic core and at least one adhesively bonded outer face sheet. Yet another aspect of a sandwich structure has raised ridges bridging between adjacent peaks in a core sheet in one direction but not in a perpendicular direction, thereby achieving different properties in the different sheet directions. Another aspect employs at least three stacked cores. Moreover, arcuately curved and/or substantially perpendicularly folded exterior surfaces are achieved with a different aspect of the present core and outer sheet structure. Foam is located between a core sheet and an adjacent outer sheet in still another aspect. A further aspect includes a sandwich structure having a peripheral flange which may be hemmed or angularly offset. Additionally, another aspect provides a method of making a core structure including core sheet tensioning during forming, heating after adhesive application and/or pre-cut blank feeding through forming rollers.
The present sandwich structure and method are advantageous over prior constructions. For example, the present sandwich structure and method advantageously do not require a lubricant on the core material for forming of the peaks and valleys therein, thereby allowing an adhesive to be easily applied to the core without requiring removal of the undesired lubricant or an expensive adhesive formulation. Additionally, the present sandwich structure and method allow the peaks and valleys to be formed in the core in a very rapid, repeatable and low cost manner without the tearing concerns of the Hale and Faehrrolfes patents. Moreover, the present sandwich structure and method are advantageously strong and resistant to thickness compression, and also advantageously exhibit asymmetrical flexibility, shear stiffness, shear strength and length shrinkage factor properties, which enhance the sandwich structure product shaping and ease of manufacturing. Generally, perpendicular folding, arcuate curving and foam filling of the present sandwich provide additional strength and product formation benefits not readily achieved with prior devices. Additional advantages and features of the present invention can be ascertained from the following description and appended claims, as well as in the accompanying drawings.
A sandwich structure 31 can be observed in
The placement of ridges 45 and depressions 47 between the alternating peaks and valleys of core sheet 35 give the core sheet asymmetrical properties or characteristics after and during forming. For example, a length shrinkage factor fs, which is the initial core sheet length versus the formed end sheet length, is at least 1.08, and more preferably at least 1.10 in the roll direction L, as compared to a shrinkage factor fs of approximately 1.0 in the cross-roll/cross-feeding direction W. Furthermore, an out-of-plane shear stiffness of core sheet 35 is at least 1.3 times greater, and more preferably at least 1.4 times greater in the cross-roll/cross-feeding direction W, as compared to the roll/feeding direction L:
[L]−GWT/GLT≥1.3
Additionally, an out-of-plane shear strength of core sheet 35 is at least 1.05 times greater, and more preferably at least 1.1 times greater in the cross-roll/cross-feeding direction W, as compared to the roll/feeding direction L:
[L]−τWT/τLT≥1.05
These characteristics are believed to exhibit the data plots shown in the graph of
The compressive strength of the present sandwich structure 31, where the outer sheets are bonded to the core sheet, across the cross-sectional thickness (as viewed in
where tc is the initial sheet thickness of the core layer, C denotes the core layer height and fs is the shrinkage factor in the length direction L. Thus, the asymmetrical nature of the periodic array of peak and valley cells or dimples, as connected in one direction by raised ridges and separated in the other by steep depressions, advantageously provides for different directional forming and final product properties and characteristics.
A trailing set of tension pinch rotters 69 are provided downstream of embossing rollers 65. Alternately, “mud-flap-like” pressure arms 71 may flexibly extend from the machine housing 73 before and/or after embossing roller 65 in either of the combinations shown in
The shape of forming pins 81 can best be observed in
Returning to
Thereafter, coils of generally flat outer face sheets 33 and 37 are continuously fed in direction L and stacked above and below core sheet 35. A preheating oven 127 heats the sheet and more particularly, the adhesive, to a temperature generally between 200-300° F. and more desirably to about 250°. Preheating oven 127 uses top and bottom flames, electrically resistive elements or lights, and is positioned downstream of adhesive coating rollers 121.
A lower vinyl conveyor belt 128 thereafter moves the still continuously elongated but now pre-heated sandwich sheets in a laminating station which includes an upper endless vinyl belt 130 downward applying less than 20 pounds per square foot of pressure, and more preferably about five pounds per square foot of pressure along thickness T. The lamination station is within an insulated box or oven 131 containing at less 10, and more preferably 30, upper tubular bars 132 and the same quantity of lower tubular bars for radiating blown heat therefrom to heat up sheets to a temperature of 350-450° F., and more desirably about 400° F., for 30 seconds or less, and even more preferably 15 seconds or less. This causes very quick initial “green” curing of the bonded sandwich structure 31. Furthermore, belts 128 and 130 each have a feeding length L of at least 10 feet and more preferably at least 30 feet, thereby providing a generally uniform but gentle laminating pressure to one or more elongated sandwich structures therebetween. Subsequently, a fan blows air through liquid transporting chiller or refrigeration tubes in a cooling unit or station 133 downstream of the laminating belts, whereafter, cutting blades 135, water jet cutters, laser cutters or the like are employed to cut the finished and cooled sandwich structure 31 into the desired lengths, which are subsequently packaged and shipped to a customer.
Thereafter, the formed core sheet 35 is adhesively coated by coating rollers 121. Core sheet 35 is then manually or automatically stacked between the pre-cut outer layer sheets 33 and 37. The sandwiched sheets are subsequently fed into pre-heating oven 127, and the sandwich is then elevated in temperature while being laminated or compressed between laminating belts 128 and 130 to cause sufficient bonding therebetween, as discussed for
Another feature of the present sandwich structure 31 can be observed in
As can be observed in 14A and 14B, yet another variation of a sandwich 31 includes outer face sheets 33 and 37 sandwiching a formed core sheet 35 therebetween, bonded by adhesive 123 or the like. Adhesive 123, but not core sheet 35, is present at flanges 203 and 205. In this construction, peripheral flanges 203 and 205 of the face sheets are angularly offset and upturned. This creates a generally U-shaped and open hook-like configuration. Thus, a pair of oppositely oriented hook-like flanges 203 and 205 provide a tongue-and-groove interlocking joint 211 between mating sandwich structures 31. This advantageously allows for removability of adjacent panels which is ideally suited for use as a wall structure or partition 213 in an office, residential or industrial building 215 (see
Referring now to
Finally, a curved exterior shape can be created from sandwich structure 31, as is shown in
While various embodiments of the present invention have been disclosed, it should also be appreciated that other variations may be employed. For example, welding, spot welding or blind riveting may be used instead of adhesive bonding between the adjacent sheets, but many of the present weight, cost and quick assembly advantages may not be realized. Additionally, other dimensions and shapes may be provided for the core sheet, embossing pins and the like; however, many of the manufacturing advantages and property strengths will not be achieved. Variations are not to be regarded as a departure from the present disclosure, and all such modifications are intended to be included within the scope and spirit of the present invention.
Claims
1. A method of making a vehicular trailer sandwich structure, the method comprising:
- (a) applying tension to a metallic core sheet;
- (b) forming alternating peaks and valleys in the core sheet during step (a);
- (c) forming raised ridges bridging between at least some of the peaks along a first direction but not along a perpendicular second direction during step (b);
- (d) the forming steps being done at ambient room temperature with embossing rollers which have rotational axes set at a fixed distance from each other during the forming steps;
- (e) applying an adhesive to substantially flat ends of the peaks after the forming steps;
- (f) pre-heating a metallic outer sheet and the core sheet after the application of the adhesive;
- (g) laminating the vehicular trailer sandwich structure under greater heat than in the pre-heating step, in an oven containing heaters to create at least an initial green curing of the bonded sandwich structure in 30 seconds or less;
- (h) cooling the laminated vehicular trailer sandwich structure in a cooling unit;
- (i) wherein out-of-plane shear strength of the core sheet is at least 1.05 times greater in a cross-feeding direction as compared to a manufacturing feed direction; and
- (j) wherein a length shrinkage factor of the core sheet, where a ratio of initial versus end formed length, is at least 1.08 along the manufacturing feed direction, which is greater than a shrinkage factor along the cross-feeding direction.
2. A method of making a sandwich structure, the method comprising:
- (a) applying tension to a core sheet while forming alternating peaks and valleys into the core sheet at ambient room temperature with embossing rollers;
- (b) applying an adhesive to outermost lands of the opposed peak and valley surfaces after forming the peaks and valleys in the core sheet between the embossing rollers;
- (c) pre-heating the outer sheets and core sheet after the application of the adhesive; and
- (d) laminating the assembled sheets under greater heat than in step (c) and under substantially uniform pressure.
3. The method of claim 2, wherein the laminating comprises laminating the outer facing sheets onto the lands of the core sheet at a pressure of at least 5 and less than 20 pounds per square foot.
4. The method of claim 2, further comprising cooling the laminated sheets with a cooling unit after the lamination.
5. The method of claim 2, further comprising:
- (a) creating an offset stepped peripheral flange between the outer face sheets without the core sheet located therebetween; and
- (b) hemming together the outer face sheets at the peripheral flange.
6. The method of claim 2, wherein the tension applied to the core sheet during the peak and valley forming is done with at least one pinch roller contacting the core sheet.
7. The method of claim 2, wherein the tension applied to the core sheet during the peak and valley forming is done with at least one biased pressure arm contacting the core sheet to create tension in only the feeding direction while the core sheet is being formed.
8. The method of claim 2, further comprising feeding individually cut blanks of the core sheet between the forming rollers which have rotational axes that are parallel and at a fixed positional spacing during the entire formation of the peaks and valleys within the core sheet.
9. The method of claim 2, wherein each embossing roller has a set of forming pins projecting at a free-standing height relative to a substantially cylindrical roller drum surface, the lateral diameter of each pin being no less than the free-standing height of the associated pin, and a radius located from the sidewall of each pin to the roller drum surface, and the forming of the peaks and valleys is free of a lubricant between the core sheet and the embossing rollers.
10. The method of claim 2, wherein the sheets are all aluminum, without foam therebetween.
11. The method of claim 2, wherein the sheets are all steel, without foam therebetween.
12. A method of making a sandwich structure, the method comprising applying tension to a core sheet while forming alternating peaks and valleys into the core sheet at ambient room temperature with forming rollers, and free of a lubricant between the core sheet and the forming rollers.
13. The method of claim 12, further comprising:
- (a) applying an adhesive to outermost lands of the opposed peak and valley surfaces after forming the peaks and valleys in the core sheet between the forming rollers; and
- (b) laminating outer facing sheets onto the lands of the core sheet at a pressure of less than 20 pounds per square foot.
14. The method of claim 13, further comprising:
- (a) pre-heating the stacked outer sheets and core sheet after the application of the adhesive; and
- (b) laminating the assembly under greater heat than in step (a) and under substantially uniform pressure; and
- (c) cooling the laminated sheets with a cooling unit after the lamination.
15. The method of claim 12, further comprising:
- (a) creating a peripheral flange between the outer face sheets without the core sheet located therebetween; and
- (b) hemming together the outer face sheets at the peripheral flange.
16. The method of claim 12, wherein the tension applied to the core sheet during the peak and valley forming is done with at least one pinch roller contacting the core sheet.
17. The method of claim 12, wherein the tension applied to the core sheet during the peak and valley forming is done with at least one biased pressure arm contacting the core sheet to create tension in only a feeding direction while the core sheet is being formed.
18. The method of claim 12, further comprising feeding individually cut blanks of the core sheet between the forming rollers which have rotational axes that are parallel and at a fixed positional spacing during the entire formation of the peaks and valleys within the core sheet.
19. The method of claim 12, wherein each of the forming rollers has a set of forming pins projecting at a free-standing height relative to a substantially cylindrical roller drum surface, the lateral diameter of each pin being no less than the free-standing height of the associated pin, and a radius located from the sidewall of each pin to the roller drum surface.
20. The method of claim 12, wherein out-of-plane shear stiffness of the core sheet is at least 1.3 times greater in a cross-feeding direction as compared to a manufacturing feed direction.
21. The method of claim 12, wherein out-of-plane shear strength of the core sheet is at least 1.05 times greater in a cross-feeding direction as compared to a manufacturing feed direction.
22. The method of claim 12, wherein a length shrinkage factor of the core sheet, where a ratio of initial versus end formed length, is at least 1.08 along a manufacturing feed direction, which is greater than a shrinkage factor along a cross-feeding direction.
23. The method of claim 12, further comprising configuring the sandwich for attachment to a vehicle trailer.
24. A method of making a sandwich structure, the method comprising:
- (a) forming alternating peaks and valleys into a metallic core sheet at ambient room temperature with forming rollers which have axes stationarily set at a fixed distance from each other during the complete forming operation;
- (b) applying an adhesive to the peaks after the forming of the peaks and valleys;
- (c) pre-heating a metallic outer sheet and the core sheet after the application of the adhesive; and
- (d) laminating the assembly under greater heat than in step (c), in an oven containing heaters to create at least an initial green curing of the bonded sandwich structure in 30 seconds or less.
25. The method of claim 24, wherein the laminating includes using at least one elongated belt to compress against at least one of the sheets at a pressure of at least 5 and less than 20 pounds per square foot.
26. The method of claim 24, further comprising:
- (a) bonding a second outer face sheet to the core sheet;
- (b) creating a bent peripheral flange between the outer face sheets without the core sheet located therebetween; and
- (c) securing together the outer face sheets at the peripheral flange.
27. The method of claim 24, further comprising:
- (a) continuously feeding the core sheet to the forming rollers from a coil of sheet metal; and
- (b) cooling the laminated sheets with a chiller or refrigerator.
28. The method of claim 24, further comprising:
- (a) feeding individually cut blanks of the core sheet between the forming rollers; and
- (b) cooling the laminated sheets with a chiller or refrigerator.
29. The method of claim 24, further comprising applying tension to the core sheet during the peak and valley forming with at least one pinch roller contacting the core sheet.
30. The method of claim 24, further comprising applying tension to the core sheet during the peak and valley forming with at least one biased pressure arm contacting the core sheet to create tension in only the feeding direction while the core sheet is being formed.
31. The method of claim 24, wherein each of the forming rollers has a set of forming pins projecting at a free-standing height relative to a substantially cylindrical roller drum surface, the lateral diameter of each pin being no less than the free-standing height of the associated pin, and a radius located from the sidewall of each pin to the roller drum surface.
32. The method of claim 24, wherein out-of-plane shear strength of the core sheet is at least 1.05 times greater in a cross-feeding direction as compared to a manufacturing feed direction.
33. The method of claim 24, wherein a length shrinkage factor of the core sheet, where a ratio of initial versus end formed length, is at least 1.08 along a manufacturing feed direction, which is greater than a shrinkage factor along a cross-feeding direction.
34. The method of claim 24, wherein out-of-plane shear stiffness of the core sheet is at least 1.3 times greater in a cross-feeding direction as compared to a manufacturing feed direction.
35. The method of claim 24, further comprising folding the sandwich along a crease elongated in a direction substantially parallel to a cross-feeding direction.
36. The method of claim 24, further comprising configuring the sandwich for attachment to a vehicle trailer.
Type: Application
Filed: Mar 20, 2018
Publication Date: Jul 26, 2018
Applicant: CELLTECH METALS INC (Oceanside, CA)
Inventors: Douglas Cox (San Diego, CA), Fabien Ebnöther (Munich)
Application Number: 15/926,143