SUPPORTING BED FOR SHEET MATERIAL CUTTING MACHINE AND METHOD OF MANUFACTURE

Abstract: A supporting bed (20) for supporting a stack of sheet material (36) in a cutting machine (10) of the type retaining the material by means of a vacuum (40) applied from below the supporting bed is manufactured from a sheet of reticulated polyurethane foam material which has been compressed under heat and pressure so as to be permanently reduced to approximately 10-35% of its initial thickness. The degree of compression, the temperature and compression time, and the porosity of the reticulated polyurethane foam starting material are selected to provide particular airflow and firmness characteristics for the finished supporting bed. In a preferred embodiment of the invention, the starting material is a reticulated grafted polyether foam having a porosity of 30 pores per inch and a sheet thickness of 5 inches. The sheet of material is compressed to a thickness of one inch and retained under pressure for 10 minutes at a temperature of about 400 DEG F. In accordance with another embodiment, the supporting bed is manufactured from a composite structure of starting material including individual layers of reticulated foam material separate by layers of a hot melt adhesive web.

Description: SUPPORTING BED FOR SHEET MATERIAL CUTTING MACHINE AND METHOD OF MANUFACTURE Field of The Invention The present invention relates generally to pattern cuttin machines for sheet materials, and more particularly, concerns bed for supporting and retaining the sheet material during th cutting operation and a method for manufacturing the same. Background of The Invention Sheet material, such as fabric, is commonly cut int patterns on electronically guided machines comprising an elon gated table over which a cutting tool is moved in a desire pattern by means of an precision positional control mechanism Such tables are typically provided with a perforated top, belo which a vacuum is applied for the purpose of drawing a multipl ply stack of the sheet material against the tabletop, thereb retaining it in position while it is being cut. Should th multiple layers of sheet material be retained effectively, consistent relationship can be maintained between the cutti tool and the stack, enabling sheets with accurately cut pa terns to be obtained reliably. On the other hand, should t sheets within the stack move from their intended position, flawed pattern is cut into the sheets, resulting in excessi waste of material. The efficacy of the vacuum-operated she retention system therefore has a direct bearing on the econ mics of the entire cutting process. To assure that the lower layers of the stack are c properly, the cutting blade must be permitted to pass below t lowest layer. In order to avoid damage to the surface of t table, it is the common practice to provide a supporting bed between the tabletop and stack of material being cut. This supporting bed must have certain physical properties, in order to serve its purpose effectively. First of all, it must pro- vide a firm, relatively unyielding support beneath the stack of material being cut, to avoid undesirable stack movement beneath the blade and resultant pattern errors in or damage to the cut sheet material. Secondly, the supporting bed must not impede the vacuum which is applied beneath the tabletop. It must therefore be capable of having a substantial volume of airflow through it. Third, it should have a relatively high coeffi¬ cient of friction and should present the largest possible sur¬ face area to the bottom sheet of the stack, in order to avoid slipping of the stack relative to the tabletop. Finally, the supporting bed must have an upper surface which resists the gouging action of the cutting blade, in order to maintain the uniformity of its surface and to minimize the frequency of re¬ placement of the supporting bed. Various materials have been utilized for the supporting bed. Most commonly, it is made of a sheet of polyethylene foam which is approximately one inch thick. Polyethylene foam provides a rather firm support for the stack of sheet material. However, being a closed cell foam it is impervious to air. Accordingly, it is the common practice to punch or drill interspersed vertical holes through the poly¬ ethylene foam sheet, and a substantial number of such holes is required (per unit of sheet surface area) in order to provide the vacuum at the surface of the polyethylene sheet. Typical¬ ly, for a one inch thick sheet, the holes would be about 5/16 of an inch in diameter and would be at a center-to-center spacing of about 1.5 inches. However, such a density of holes substantially reduces the firmness and surface area of the supporting bed, and the expense involved in forming the holes substantially increases the cost of the supporting bed. In addition, such a perforated supporting bed holds the fabric effectively only at the holes. Between the holes, there may be wrinkling or bunching of the fabric, and the fabric above the holes may be stretched or frayed when the blade passes into the hole. Both of these effects result in cutting errors or damage to the fabric. The use of a perforated poly¬ ethylene foam supporting bed therefore represents, at best, a compromise, which results in a serious limitation upon the height to which the sheet material may be stacked and, even then, a certain amount of undesirable movement of the stack and damage to the sheet material will occur during cutting. As a result, some portion of the sheets cut by the machine will be unacceptable and must be discarded. It has also been suggested that the supporting bed be made of upright bristles. Although such a construction pro¬ vides a substantial airflow, it hardly provides an adequately firm supporting surface, particularly when a relatively heavy sheet material is being cut. Furthermore, this relatively weak support deteriorates rapidly, as the bristles are damaged by the cutting blade, after repeated use, and the supporting sur¬ face they provide becomes uneven. Polyurethane foam has been suggested as a covering material for the surface of a supporting bed, because it ex- hibits the property of "healing* or recovering instantaneously from surface nicks inflicted by a sharp implement. Polyur¬ ethane foams may be either of the open or "tight* cell variety. In polyurethane foams, the individual cells are formed from a 3-dimensional skeletal structure comprising interconnected strands. Membranes or windows are attached to the strands and serve to divide or partition individual cells. In general the skeletal structure is substantially thicker than the windows or membranes. In so called "open cell" foams, a substantial num¬ ber of the windows or membranes are broken or ruptured (even though they are"still attached at their peripheral edges to the skeletal strands) . Some small percentage of the windows may not be attached to the strands at the edges, or may be missing altogether, and this permits a limited air flow through the foam mass. Tight cell urethane foams have essentially all of the cellular windows or membranes intact (unbroken) and at¬ tached to skeletal structure of the foam. The use of polyure¬ thane has been substantially limited, however, for essentially the same reasons as polyethylene. "Reticulated" materials are also known to the art. Such materials have the cell membranes or windows partially or totally destroyed. These reticulated materials are prepared from the cellular materials of the prior art. Reticulated foam materials generally permit the passage of substantially greater volumes of air, in comparison to open or tight foam materials. Such reticulated foams generally have higher porosity than com¬ parable "open* or "tight" cell foams. Thus, in these reticu¬ lated materials, the primary support is supplied by the skele- tal structure, since the cell membranes have been partially or totally eliminated. Examples of such reticulated materials extensively used by the prior art are the membrane destroyed or reticulated polyurethane foams which are employed in various filtering and detraining applications and as garment liners. Such reticulated foam materials and their process of manufac¬ ture are disclosed, for example, in U.S. patents No. 3,175,025 and No. 3,175,030 granted to Henry C. Geen on March 23,1965. Reticulated materials of the flexible polyurethane type, have been in use for some time, owing to their porosity and softness as compared to non-reticulated flexible polyure¬ thane cellular materials. However, attempts to use such mater¬ ials in the supporting bed of a cutting machine have proven unsuccessful, because such materials offer virtually no support to the stack of sheet material while it is being cut and be- cause the reticulated foam tends to collapse when the vacuum is applied. Broadly, it is an object of the present invention to provide a supporting bed for supporting a stack of sheet mater¬ ial in a cutting machine of the type retaining the material by means of a vacuum applied from below the supporting bed, which supporting bed overcomes the disadvantageous and shortcomings of prior devices of this type. It is specifically an object of the present invention to provide a supporting bed of the type described which is con- structed so as to permit relatively free airflow therethrough, so as not to impede the holding action of the applied vacuum. It is a further object of the present invention to provide a supporting bed of the type described which is con- structed so as to provide a relatively firm, unyielding slip- free and continuous support for a stack of sheet material being cut on a pattern cutting machine. It is yet another object of the present invention to provide a supporting bed of the type described which is sub¬ stantially resistant to surface gouging inflicted by a sharp instrument. It is yet another object of the present invention to provide a supporting bed of the type described which is relia- ble . and convenient in use, yet relatively inexpensive and simple in construction, and requires a minimum of preparation and maintenance. It is also an object of the present invention to provide a process for manufacturing a supporting bed of the type described. In accordance with the present invention, a supporting bed is manufactured from a sheet of reticulated foam material which has been compressed under heat and pressure so as to be permanently reduced to no greater than approximately 35% of its initial thickness. The degree of compression, the temperature and compression time, and the porosity of the reticulated foam starting material are selected to provide particular airflow and firmness characteristics for the finished supporting bed. Preferably, a 1-inch thick sheet of the material should permit an airflow of at least 1.5 cfm through an area four inches square, with a pressure drop between the surfaces of the sheet material corresponding to 1/2 inch of water, and it should be sufficiently firm so that compressing a 1-inch thick sheet by one quarter of its thickness requires a pressure in excess of 1.5 psi. In accordance with a preferred embodiment of the invention, the starting material is a reticulated polyurethane foam of the graft polyether type. The presently most preferred foam has a porosity of 30 pores per inch and a sheet thickness of 5 inches. The sheet of foam material is compressed to a thickness of one inch and retained under pressure for 10 mi¬ nutes at a temperature of about 400'F. Reticulated foam sheets of the type used in the present invention are manufactured from blocks or "buns" of foam material, from which each individual sheet is cut as a layer. Often, after all the sheets have been cut from the bun, the last remaining sheet will be too thin to use in the manufacture of a supporting bed according to the present invention. Until now, such thin sheets of reticulated foam have not been useful and have been treated as a waste material. As a result, there has been a substantial amount of waste, often in excess of 10%, in the manufacture of such supporting beds. It is a further object of the present invention to reduce substantially or eliminate this waste, thereby providing significant economies in the manufacture of supporting beds. In accordance with a further aspect of the present invention, the starting material for the supporting bed comprises a composite structure including a plurality of rela- tively thin reticulated foam layers which are stacked in superposed relationship, with at least one layer of a hot melt adhesive web being interposed between the reticulated foam layers. The thicknesses of the individual foam layers is selected to give a cumulative thickness which is the same as when a single sheet is used to manufacture a supporting bed, and similar pressure and heat are utilized to compress the starting material. In the process of forming the supporting bed, the adhesive webs melt and bond together the individual layers of the composite structure. The resulting supporting bed is comparable in strength, surface firmness and permeabi¬ lity to a supporting bed made from a single sheet of reticu¬ lated foam starting material. Brief Description of The Drawing The foregoing brief description, as well as further objects, features and advantages of the present invention will be more completely understood from the following detailed de¬ scription of presently preferred, but nonetheless illustrative, ■ embodiments of the present invention, with reference being had to the accompanying drawing, in which: Fig. 1 is an elevational view taken from the front end of the cutting machine, with portions being shown in section, to illustrate certain details of the table top; Pig. 2 is a sectional view taken along contour 2-2 in Fig.l and looking in the direction of the arrows; and Fig. 3 is a schematic representation of the Manufacture of a supporting bed in accordance with the present invention froa a starting aaterial including a plurality of layers of reticulated foaa. Detailed Description Turning now to the details of the drawing. Figs. 1 and 2 illustrate a cutting machine 10 for sheet aaterial, which incorporates a supporting bed 20 in accordance with the present invention. The cutting aachinβ includes a support table 30, which is provided with an air permeable top surface member 32 (shown dlagraanatically as a grating) . The supporting bed 20 rests upon the top 32 and is retained in position by aeans of an upright fraae 34. λ stack 36 of sheet aaterial to be cut is supported directly upon supporting bed 20. Below the table 30, there is provided a vacuua puap 40, which is appropriately coupled to a vacuua chamber 38 underneath the table top 32. λ cutting tool 50 is borne by a sub-carriage 52 which is, in turn, borne on a carriage assembly 54, which is aounted for precisely controlled movement along the length (i.e. per¬ pendicular to the plane of Fig. 1) of the table 30. The sub- carriage 52 is aounted for precisely controlled aovenent along the carriage 54 and therefore aoveβ across the table 30 (i.e. to the left and right in Fig. 1) . Appropriate aotorβ and con¬ trol mechanisms are provided to achieve the precisely control¬ led cutting action of cutting tool 50 through a pre-programmed cutting pattern. Zn operation, air flow produced by puap 40, is drawn through supporting bed 20 and table top 32 into vacuua chamber 38 (illustrated by curved arrows in Fig. 1). As a result, ambient air pressure forces the stack of sheet material down¬ wardly and retains it against the supporting bed 20. By de- sign, the supporting bed 20 is firm, yet provides uniform air permeability over its entire area. As a result, not only is the sheet aaterial held downwardly, but it is drawn into a very flat position, so as to avoid any wrinkling or bunching of the sheet material. Also, the firm support provided by supporting bed 20 assures that the fabric will not move downwardly as a result of the pressure provided by cutting blade 51, thereby assuring accurate cuts. As can be seen in Fig. 1, the cutting blade 51 must extend below the bottom sheet of stack 36, in order to assure that the sheet is completely cut. Consequently, blade 51 will also cut into the top surface of supporting bed.20. As a re¬ sult of its polyurethane foam composition, supporting bed 20 exhibits the property that the blade cuts " heal* or close up directly behind the blade. This avoids the need for frequent changes of the supporting bed and guarantees the continued durability and flatness of the bed. Foamed or cellular polyurethane products are made, in a manner well-known in the art, by reacting an organic isocyan- ate, such as an aromatic di-isocyanate (e.g. toluene di-isocya- nate) , with a polyether polyol or a polyester resin, along with various other ingredients (e.g. catalysts, blowing agents, stabilizers and the like) . λ gas or vapor is usually generated (along with heat) in situ while the reaction mixture remains in the plastic or fluid state. The generation of this gas results in the formation of bubbles, approximately spherical in form, in the plastic material. As these bubbles expand, cells are formed and the resulting structure of the cooled foam material is comprised of a skeletal structure and cell membranes. In accordance with the present invention, supporting bed 20 is manufactured from a reticulated foam material which has been compressed under heat and pressure in a conventional heated press so as to be permanently reduced to no greater than approximately 35% of its initial thickness, and preferably in the range of approximately 10-35%. The degree of compression, the temperature and compression time, and the porosity of the reticulated foam starting material are selected to provide particular airflow and firmness characteristics for the finished supporting bed. Preferably, a 1-inch thick sheet of the support bed should permit an airflow of at least 1.5 cfm through an area 4 inches square, with a pressure drop between the surfaces of the sheet material corresponding to 1/2 inch of water, and it should be sufficiently firm so that compressing a 1-inch thick sheet by one quarter,of its thickness requires a pressure in excess of 1.5 psi. With reticulated polyurethane foams, this is typically achieved by compressing the foam at 300-450*F for a time period between 8 minutes and 2 hours. The reticulated polyurethane foams which were used as the starting material in the examples below are all commer¬ cially available under the trademark Filtercrest from Crest- Foam Corp. of Moonachie, New Jersey. These foams were retic¬ ulated by the process described in U.S. Patent No. 3,175,025. This process involves providing a combustible mixture of an oxidizer material and an oxidizable material within and about a block of the foam material and igniting the mixture, so that the shock waves produced by the ignition destroy substantially all the windows within the block of material. However, this is merely illustrative of one type of starting material that may be used for the invention. Those skilled in the art will ap¬ preciate that materials reticulated by any other process will work equally well in the invention. Example 1 The starting material is selected as an 5 inch thick¬ ness of a reticulated grafted, polyether polyurethane foam sold under the trademark Filtercrest T-30 by the Crest-Foam Corp. of Moonachie, New Jersey. This material has a density of about 1.4 pounds per cubic foot, a porosity of about 30 pores per inch, and an airflow of about 18.5 cfm through an area four inches square, with a pressure difference corresponding to half an inch of water between its surfaces. The sheet was compres¬ sed to a thickness of 1 inch and maintained at a temperature of about 400*F for about 10 minutes. The resulting sheet material retained a thickness of 1 inch when the pressure was removed, but exhibited substantially improved firmness, while permitting substantial airflow: compressing the new sheet material by 1/4 of an inch required .67 psi and there was an airflow of 3.1 cfm through an area of four square inches with a pressure dif- ference across the surfaces of the sheet equivalent to 1/2 inch of water. E ample 2 Beginning with the same starting material as example 1, the material was pre-heated in a forced air oven at about 350- 400*F for about 15 minutes. An end product exhibiting the same firmness and air flow characteristics as the product of Example •1 was obtained by compressing the foam for only half the time specified in example 1. ' Example 3 The starting material was selected as an 7 inch thick¬ ness of a reticulated grafted, polyether polyurethane foam sold under the trademark Filtercrest T-15 by the Crest-Foam Corp. of Moonachie, New Jersey. This material has a density of about 1.4 pounds per cubic foot, a porosity of 15 pores per inch, and an airflow of about 22 cfm through a four square inch area, with a pressure difference corresponding to half an inch of water between its surfaces. The sheet was compressed to a thickness of 1 inch and maintained at a temperature of about 400*F for about 10 minutes. The resulting sheet material re- tained a thickness of 1 inch when the pressure was removed, but exhibited substantially improved firmness, while permitting substantial airflow: compressing the new sheet material by 1/4 of an inch required 6.63 psi and an airflow of 2.67 cfm through a four square inch area was obtained with a pressure difference across the surfaces of the sheet equivalent to 1/2 inch of water. Example 4 The starting material was selected as an 6 inch thick- ness of a reticulated polyester polyurethane foam sold under the trademark Filtercrest S-10 by the Crest-Foam Corp. of Moonachie, New Jersey. This material has a density of about 2.0 pounds per cubic foot, a porosity of 10 pores per inch, and an airflow of about 21 cfm through a four square inch area, with a pressure difference corresponding to half an inch of exhibited substantially improved firmness, while permitting substantial airflow: compressing the new sheet material by 1/4 of an inch required 7.43 psi and an airflow of 3.00 c.f.m. re¬ sulted through a four square inch area, with a pressure differ- ence corresponding to half an inch of water between its sur¬ faces. Example 5 The starting material was selected as an 7 inch thick- ness Of a reticulated polyester polyurethane foam sold under the trademark Filtercrest S-10 by the Crest-Foam Corp. of Moonachie, New Jersey. This material has a density of about 2.0 pounds per cubic foot and a porosity of 10 pores per inch, and an airflow of about 21 cfm through a four square inch area, with a pressure difference correspond ng to half an inch of water between its surfaces. The sheet was compressed to a thickness of 1 inch and maintained at a temperature of about 400*F for about 10 minutes. The resulting sheet material re¬ tained a thickness of 1 inch when the pressure was removed, but exhibited substantially improved firmness, while permitting substantial airflow: compressing the new sheet material by 1/4 of an inch required 12.44 psi and an airflow of 2.10 c.f.m. through* a four square inch area, with a pressure difference corresponding to half an inch of water between its surfaces. In accordance with a further aspect of the invention, as illustrated in Fig. 3, a supporting bed 20 in accordance with the present invention may be manufactured from a structure comprising a plurality of sheets or layers 60, 60 of reticu¬ lated foam material which are stacked in superimposed relation- ship. Between each pair of foam layers 60, 60, there is provided a hot melt adhesive web 62. A stack of such layers of foam material and adhesive webs is calculated to have the same total thickness as would be used if there were a single sheet of reticulated foam starting material. This composite struc- ture is then compressed under heat and pressure in a conven¬ tional heated press so as to be permanently reduced to less than about 35%, and preferably to approximately 10-35 percent of its initial thickness. The dwell time within the press is selected to be long enough so that the adhesive web 62 is totally melted, bonding the individual foam layers 60, 60 together. In addition, the degree of compression, the tempera¬ ture and compression time, and the porosity of the reticulated foam starting material are selected to provide particular air flow and firmness characteristics for the finished supporting bed. Preferably, a one-inch thick sheet of the supporting bed should permit an air flow of at least 1.5 cfa through an area 4 inches square, with a pressure drop between the surfaces of the sheet material corresponding to one-half inch of water, and it should be sufficiently firm so that compressing a one- inch thick sheet by one-quarter of its thickness requires a pressure in excess of 1.5 psi. As in the case of a single sheet of foam material, this is typically achieved by compress¬ ing the foam at a temperature of 300-450*F for a time period between 8 minutes and 2 hours. The supporting bed manufactured from the composite structure exhibits air flow and firmness characteristics comparable to those obtained with a supporting bed manufactured from a single sheet of reticulated foam material. In the examples described below, the reticulated polyester foam utilized as the starting material is commer¬ cially available under the trademark Filtercrest S-15M foam from Crestfoam Corp. of Moonachie, New Jersey. This material has a density of about 1.4 pounds per cubic foot and a porosity of about 15 pores per inch, and an airflow of about 20 cfm through a four square inch area, with a pressure difference corresponding to half an inch of water between its surfaces. This foam was reticulated by the process described in U.S. Patent No. 3,175,025, referred to above. However, those skilled in the art will appreciate that materials reticulated by any other process, as well as other types of foams will work equally well in the invention. Example 6 The starting material was selected as a 7-inch thick¬ ness of reticulated S-15M, foam. The sheet was compressed to a thickness of one inch and maintained at a temperature of about 400* F for about 10 minutes. The resulting sheet material retained a thickness of one inch when pressure was removed, but exhibited substantially improved firmness, while permitting a substantial air flow: compressing the new sheet material by one-quarter of an inch required 6.3psi and an air flow of 2.9cfm through a 4 square inch area, the pressure difference corresponding to an half-inch of water between its surfaces. This supporting bed was then used as a control sample for comparing the characteristics of supporting beds made from stacks of superposed sheets of reticulated foam material. In each case, two sheets, each 3.5 inches thick, were stacked. However, any combination of thicknesses totalling 7 inches could have been used equally well. For the three different examples, the composite structures were provided, respectively, with 1, 2, and 3 layers of a hot melt adhesive web between pairs of foam sheets. The particular web utilized is commer¬ cially available from Sharnet Corporation of Ward Hill, Mas¬ sachusetts under the designation SHAR-NET SH151. In each case, the composite structure was compressed to a thickness of one- inch and maintained at a temperature of about 400'F for about 25 minutes. The resulting sheet material retained a thickness of one inch when the pressure was removed. Table I below indicates the characteristics of the controlled sample and the three examples. In all cases, the firmness was that pressure (in psi) required to compress the .one-inch supporting bed to a thickness of one-quarter of an inch. _________ No. Tear Layers Density Strength Air of Web π_b./Ft. 3 ϊ fLb./Inch Flow fcfw) Firmness 0 (control) 9.2 6.2 2.9 6.3 1 9.0 6.6 3.3 6.2 2 9.1 6.3 3 7.8 3 9.5 7.2 3.2 8.3 Although preferred embodiments of the invention hav been disclosed for illustrative purposes, those skilled in th art will appreciate that many additions, modifications and sub stitutions are possible, without departing from the scope an spirit of the invention as defined in the accompanying claims.

Claims: WHAT IS CLAIMED TS; 1. A supporting bed for supporting a stack of sheet material in a cutting machine of the type retaining the material by means of a vacuum applied from below the supporting bed, said supporting bed comprising a-sheet of reticulated foam starting material which has been compressed under heat and pressure so as to be permanently reduced to no greater than approximately 35% of its initial thickness. 2. A supporting bed in accordance with claim 1, wherein the starting material is a reticulated polyester foam sheet and is compressed for a period of time between 8 minutes and 2 hours at a temperature between 300*F and 450*F. 3. A supporting bed in accordance with claim 1 wherein said sheet of starting material comprises a composite structure including individual layers of reticulated foam material separated by at least one layer of a heat melt adhesive web. 4. A supporting bed in accordance with claim 3, wherein the starting material is a reticulated polyester foam sheet and is compressed for a period of time between 8 minutes and 2 hours at a temperature between 300*F and 450'F. 5. A supporting bed in accordance with claim 4 wherein the starting material has a plurality of layers haying a combined thickness of approximately seven inches, the foam material having a density of about 1.4 pounds per cubic foot and a porosity of about 15 pores per inch, the composite structure being compressed to a thickness of approximately one inch and maintained at a temperature of about 400*F for about 25 minutes. 6. A supporting bed in accordance with claim 1 wherein the starting material is a reticulated grafted polyether polyurethane foam. 1 7. A supporting bed in accordance with claim 6 wherein 2 the starting material is a sheet approximately five inches 3 thick with a density of about 1.4 pounds per cubic foot and a 4 porosity of about 30 pores per inch, the sheet being compressed 5 to a thickness of approximately one inch and maintained at a 6 temperature of about 400*F for about 10 minutes. 1 8. A supporting bed in accordance with claim 6 wherein 2 the starting material is a sheet approximately seven inches 3 thick with a density of about 1.4 pounds per cubic foot and a 4 porosity of about 15 pores per inch, the sheet being compressed 5 to a thickness of approximately one inch and maintained at a 6 temperature of about 400*F for about 10 minutes. 1 9. A supporting bed in accordance with claim 1 wherein 2 the starting material is a reticulated polyester polyurethane 3 foam. 1- 10. A supporting bed in accordance with claim 9 is a 2 sheet approximately six inches thick with a density of about 3 2.0 pounds per cubic foot and a porosity of about 10 pores per 4 inch, the sheet being compressed to a thickness of approxi- 5 mately one inch and maintained at a temperature of about 400*F 6 for about 10 minutes. 1 11. A supporting bed in accordance with claim 9 is a 2 sheet approximately seven inches thick with a density of about 3 2.0 pounds per cubic foot and a porosity of about 10 pores per 4 inch, the sheet being compressed to a thickness of approxi- 5 mately one inch and maintained at a temperature of about 400*F 6 for about 10 minutes. 1 12. A supporting bed in accordance with any preceding 2. claim, wherein the degree of compression, the temperature, the 3 compression time, and the porosity of the reticulated foam 4 starting material are selected so that a 1-inch thick sheet of 5 the supporting bed permits an airflow of at least 1.5 cfm 6 through a four square inch area with a pressure drop between the surfaces of the sheet material corresponding to 1/2 inch of water, and so that compressing a 1-inch thick sheet by one quarter of an inch requires a pressure of at least 1.5 psi. 13. A method for manufacturing a supporting bed for supporting a stack of sheet material in a cutting machine of the type retaining the stack of material by means of a vacuum applied from below the supporting bed, said method comprising the steps of: compressing a sheet of reticulated foam starting material, and simultaneously applying heat thereto so as to permanently reduce said sheet to no greater than approximately 35% of its initial thickness. 14. The method of claim 13, wherein the starting material is a sheet of reticulated polyester foam and is compressed for a period of time between 8 minutes and 2 hours at a temperature between 300*F and 450*F. 15. The method in accordance with claim 13, wherein said starting material is first formed as a composite structure including individual layers of reticulated foam material separated by at least one layer of a heat melt adhesive web. 16. The method of claim 13, wherein the starting material is compressed for a period of time between 8 minutes and 2 hours at a temperature between 300*F and 450 * F. 17. The method of claim 15, wherein the starting material is made of a plurality of layers having a combined thickness of approximately seven inches, a density of about 1.4 pounds per cubic foot and a porosity of about 15 pores per inch, said method comprising compressing said sheet to a thick- ness of approximately one inch and maintaining it at a temper- ature of about 400*F for about 25 minutes. 18. The method of claim 13 wherein the starting material is a sheet of reticulated grafted polyether polyure- thane foam. 19. The method of claim 18 wherein the starting material is a sheet approximately five inches thick with a density of about 1.4 pounds per cubic foot and a porosity of about 30 pores per inch, said method comprising compressing said sheet to a thickness of approximately one inch and main- taining it at a temperature of about 400*F for about 10 minutes. " . 20. The method of claim 18 wherein the starting material is a sheet approximately seven inches thick with a density of about 1.4 pounds per cubic foot and a porosity of about 15 pores per inch, said method comprising compressing said sheet to a thickness of approximately one inch and main- taining it at a temperature of about 400 * F for about 10 minutes. 21. The method of claim 13 wherein the starting material is a sheet of reticulated polyester polyurethane foam. 22. The method of claim 21 wherein said sheet is approximately six inches thick with a density of about 2.0 pounds per cubic foot and a porosity of about 10 pores per inch, said method comprising compressing the sheet to a thick- ness of approximately one inch and maintaining it at a temper- ature of about 400*F for about 10 minutes. 23. The method of claim 21 wherein said sheet is approximately seven inches thick with a density of about 2.0 pounds per cubic foot and a porosity of about 10 pores per inch, said method comprising compressing said sheet to a thick- ness of approximately one inch and maintaining it at a temper- ature of about 400'F for about 10 minutes. 24. The method of any one of claims 13-23, wherein the degree of compression, the temperature, the compression time, and the porosity of the reticulated foam starting material are selected so that a 1-inch thick sheet of the completed support bed permits an airflow of at least 1.5 cfm through a four square inch area with a pressure drop between the surfaces of the sheet material corresponding to 1/2 inch of water, and %o that compressing a 1-inch thick supporting bed by one quarter of an inch requires a pressure of at least 1.5 psi.

Inventors: FISHER LEO, MOZIEKA MICHAEL, FISHER, LEO, MOZIEKA, MICHAEL
Applicants: CREST FOAM CORP, CREST-FOAM CORP.
Application year: 1987
Main classification: B26D7
IPC codes: B26D7