WO1986004022A1

WO1986004022A1 - Acoustic panel, clear plastic sheet extensions and acoustic enclosures and walls made therefrom

Info

Publication number: WO1986004022A1
Application number: PCT/US1985/002099
Authority: WO
Inventors: Henry Swartz; Alan H. Miller
Original assignee: Anechoic Systems, Inc.
Priority date: 1985-01-04
Filing date: 1985-10-24
Publication date: 1986-07-17
Also published as: AU5015185A; CA1280571C; US4550798A; CA1253086A; EP0208698A1; EP0208698A4

Abstract

An acoustic enclosure (10) has interconnected sound reducing sheets forming a substantially rectangular structure which is configured to house a computer printer or other noise generating article. Each side (12, 14) sheet is a multiple strata sheet having an outer thin stratum (26), a multiple channel intermediate thermosplastic stratum (28) and an inner open celled acoustic material stratum (30). The rear and bottom sheets (16, 18) are multiple stratum sheets, having a multiple channel intermediate thermoplastic stratum (46) which is sandwiched between inner and outer polyurethane foam strata (44, 48). An adhesive material (42) is provided for bonding the outer stratum to the intermediate stratum and the intermediate stratum to the inner stratum for each of the sheets. An angle member (62) affixed to the intermediate stratum is provided for joining adjacent sheets of the enclosure. A rigid thermoplastic hinged sheet (22) having a uniform non-pinched bend (52) is provided as a window for the enclosure. Method and apparatus for producing such bends comprise use of sequentially initiated heating of the bottom (wide band continuous band heating to softening point) and then top of the sheet (narrow band focussed heating to a narrow bend) to make the sheet so bendable. The bent sheet serves as a supplemental panel extension to afford view zones of the enclosure. The various (side type, rear type) panels, with and without such sheet extensions, are also usable in the non-enclosing uses, including use as walls or room-dividers. Electrical wiring and fixtures and panel surface mounted heaters can be accommodated by the allowable constructions of the panels. The thin outer stratum can be replaced by an adhesive.

Description

ACOϋSTIC PANEL, CLEAR PLASTIC SHEET EXTENSIONS AND ACOUSTIC

-_NC___0SURES AMD WALLS MADE TBEREFFCH

BftCKGROCM) OF THE INVENTION

The present invention relates to panels and enclosures, and, more particularly, is directed toward acoustic enclosures and to laminated construction panels, and supplementary clear plastic sheet extensions or such panels, useful in constructing such enclo¬ sures and for other purposes including fixed room walls, free standing divider walls and the construction of such panel and sheet materials.

Modular acoustic sheets assemblies are well known for providing sound absorbing enclosures for noise making devices such as computer printers. Generally, manufacturers of such enclosures provide universal enclosures which have sound absorbing material on the interiors of their walls. The state of the art has not fully satisfied user needs for reliable, cost-effective construction of such sheets and enclosures.

It is an object of the present invention to provide acoustic panels and related non-acoustic, supplemental visual sheet portions, and enclosures using such panels and sheet portions which overcome^" the limitations and disadvantages of prior acoustic sheets and enclosures.

It is a further object of the present invention to provide acoustic panels which are effective in reducing noise, rigid in construction and aesthetically pleasing. Various members of such family of panels are usable in the acoustic enclosure's various applications and in other applications including office partitions, original and retrofit building, mobile home and ship construction, per se, or with heating and/or electrical conduit functionality added. It is a further object of the present invention to provide a modular acoustic enclosure having a series of interconnected sound reducing panels forming a substantially tetrahedral structure which is configured to house a noise generating device such as a computer printer. SUMMARY OF 3_BE INVΘΪTIDN

The objects of the invention are realized through a novel enclosure and component acoustic panels and supplemental sheet portions. The acoustic panels form most of each of top, side, and bottom sheets of a six face enclosure with one or more transparent supplemental sheet portions at useful locations. Each of the front and side panels comprises a multiple layered multiple stratum assembly having an outer polymeric stratum, a thermoplastic multi¬ ple channel intermediate stratum and an inner open celled acoustic material stratum. The rear and bottom panels are multiple stratum sheets, each sheet having a thermoplastic or metal multiple channel intermediate stratum which is sandwiched between inner and outer open celled acoustic material strata. The multiple channels comprise, in essence, side by side tubes of integral, shared wall form, with parallel axes, all essentially parallel to the planes of the inner and outer strata. The walls of the tubes are so thin as to avoid being significant sources of structure-borne noise, yet rigid enough to provide the needed structural integrity; typically - for a sound enclosure - .02 in. - 0.1in. thick of metal or simi¬ lar rigid thermoplastic, e.g., polycarbonate. An adhesive a- terial is provided to bond the outer stratum to the intermediate stratum and the intermediate stratum to the inner stratum for each of the panels. The outer, intermediate, and inner strata are superposed and held in fixed relationship to one another by the adhesive material. An angle member affixed to the intermediate stratum is provided for joining adjacent panels of the enclosure. The wall thickness of the inner and outer acoustic material strata and of tube components of the intermediate stratum are selected as a function of the level and frequency of the noise produced by the noise generating device housed within the enclosure.

Further, according to the present invention, outstanding acoustic and/or decorative effects can also be obtained with the acoustic panels and supplemental non-acoustic sheet portions of the invention. A decorative or acoustical material is disposed on one or both of the rigid outer sheets of the sheet so as to provide an aesthetically-pleasing exterior surface. The interior chambers (tubes) allow wiring to be run from a single receptacle thereby to eliminate unsightly wires from the office floor. Through the use of hollow chambers, the panel can be exceedingly lightweight but sufficiently rigid to support both the wiring and acoustical covering. The chambers can be in two series each angled, prefer- ably at right angles, to the other whereby wiring can be easily snaked to the desired locations of the receptacales that are to be fitted into it. Wires can be snaked almost anywhere in the panel without a significant amount of drilling or difficult fishing. Thus, in many situations, only one or two holes need be drilled to snake a wire to where the receptacle is to be placed. Moreover, since in such embodiment the chambers are disposed at right or other (substantial plus or minus 45° or more) angles to each other,^' the panel has increased rigidity stemming from the support that is given by the juxtaposed, spaced-apart, parallel strut members. The present invention affords the user the ability to dispose a decorative surface such as laminated paper products impregnated with phenolic resins and covered with a melamine skin (e.g., Formica brand veneer), or other thin laminates or non- laminates (e.g., pvc), in any case less than .05 inches thick, usually less than .01 inches thick —immediately upon one or both of the faces of rigid material. As is well-known, the laminated paper product has an extremely tough outer surface but is fairly brittle. If struck while it is unsupported, or is inadequately supported, the laminated product will break rather easily. Ade- quate support for the product requires some resiliency which is provided by the assembly, though it is rigid enough for strength purposes. Commonly, plywood or steel were used (with an overlying acoustic material, usually an open urethane foam) for a support surface for laminated paper products; but, the foam-covered ply¬ wood or steel are not fully acceptable for room separators because of their weight and flammability and their solid mass substrates which tend to expand sound waves (structure - borne noise). The open channel structure of the present invention's intermediate layer solves this problem. With the substrate of the present invention, even the corners and the edges of the sheet can receive screws because the chambers formed by the struts and sheets extend all the way to the edge of the laminated paper product.

Further, according to the present invention, it is shown that the assembly mentioned above can be used to form a heating panel. The intermediate base can be used to support a radiant heater and provide radiant heat to the area around the sheet. To support the radiant heater, a resistance heating means is integral¬ ly associated with the intermediate structure and arranged to radiate heat outwardly therefrom. A decorative outer stratum is disposed on at least one side of the intermediate structure to provide an aesthetically pleasing appearance. Preferably, the resistance heating means is either laminated onto the intermediate structure by printing a conductive ink upon it or extruding conduc¬ tive resin upon it or applying pressure-sensitive conductive resin strips thereto. Although sometimes less desirable because of wiring costs, a series of resistance heating wires similar to those that are used for electric blankets can either be strung within the internal chambers of the channel structure or can be arranged on its outer surface to provide heat.

Non-acoustic plastic sheets of the type used herein, with longitudinally extending shapes and of thicknesses of at least 3/16 inch generally greater than about one-eighth inch and typical¬ ly 1/2 to one inches are readily bent in accordance with the inven¬ tion. Such sheets have previously been bent to fabricate various shapes and designs. Such bending, however, has frequently distor- ted the plastic at the bend and placed unusual stresses upon it (in contrast to the trouble-free regimen of bending 1/8 inch thick sheet). Bending plastic into decorative shapes requires utmost consideration for the appearance of the product and, in many cases, any distortions or thinning at the bend tends to reduce its attrac¬ tiveness and its strength. Most bending processes of the prior art merely heated the plastic sheet on one or both sides until it became sufficiently softened or plasticized to make the bend. The sheet was then bent to the desired angle and allowed to harden. While such processes usually provided adequate bends from a mechanical point of view, the plastic was thinner at the bend than on the other side, and this is unattractive. Further bending times of the state of the art are very slow (e.g., 1 - 2 hours for one inch thick acrylic sheets and 20 - 30 minutes for half inch thick). Also, stresses may be introduced into the sheet which may weaken it structually and make it less pleasing aesthetically. Frequently, such stresses can be seen as opalescence when the bent sheet is viewed in certain lighting angles. The present invention affords a resolution of such problems.

In the U.S. patent to Parmann, U.S. Patent No.4,097,573, a method of bending pipes is discussed in which a pipe is subjected to direct heat on the desired outer radius and cycled heat on the inner radius. While such direct and indirect heating may be suit¬ able for pipe, effective bends cannot be made with flat sheets unless sources of heat are applied to both sides. U.S. Patent No.3,767,752 to Karlyn disclosed a method of forming a map holder hinge from very thin plastic sheets. The sheet is heated with heat lamps that are disposed on both sides of the sheet. While there is some attempt to concentrate the heat, there is no attempt to provide a focussed heat band on one side of the sheet and a wide heat band on the obverse side.

Thick sheets of longitudinally extending, generally flat, rigid thermoplastic material, generally over one-eighth inch in thickness, can be bent without introducing stresses or thinning when using the process and equipment of the present invention at substantially faster speeds. The sheet must be heated on both sides — on a bottom and a top, the heaters being arranged so that two surface regions of softened plastic are formed on opposite sides of the sheet. One of the regions (on the bottom surface) is relatively wide and to form this region, sufficient low-intensity heat — below the melting point of the plastic used, but in its softening range — is applied so that at least between about 40 - 60% of the thickness of the sheet is plasticized. The width of the region is defined by the width of the softened portion of the sheet. The other region (on the top) is above the melting point of the plastic (thereby limiting allowable exposure time of the upper heat application) and is relatively narrow, or at least narrower than the wide region on the bottom and of a predetermined width. It is formed by focussing heat on the obverse side of the sheet during the time that it is being heated by the source which forms the wide band. It is important to note that the focussed heat should irradiate the center of the wider region. In this way, the focussed heater quickly softens the balance of the thickness of the sheet so that it can be bent without inducing stresses or thinning the plastic.

Because the high intensity, focussed heater will raise the temperature of. the sheet quite quickly, to achieve the desired bend according to the invention, initiation of the higher intensity focussed heat must be delayed at least until a substantial portion of the sheet is initially plasticized by the wide heat source so as to prevent deterioriation of the plastic due to prolonged heating at elevated temperatures.

A fuller understanding of the nature and objects of the present invention will become apparent upon consideration of the following detailed description taken in conjunction with the accom¬ panying figures of drawing, wherein: BREEF DE_X_R__P1Ϊ0N OF TBE ERASmG

FIG. 1 is a perspective view of an acoustic enclosure embodying the present invention;

FIG. 2 is a rear view of the acoustic enclosure of FIG. 1; FIG.3 is a perspective view, partly cut-away, of the side panel of the enclosure of FIG. 1;

FIG. 4 is a perspective view of the rear panel of the enclosure of FIG. 1;

FIG. 5 is a perspective view of the side panel of FIG.1 having an angle member attached thereto; and

FIG. 6 is a perspective, schematic view, partially broken away of a free standing panel that utilizes the principles of the present invention and illustrates schematically the disposition of various receptacles on the panel's surface.

FIG. 6A is a perspective, cross-sectional view of one embodiment of a panel according to the present invention in which a layer of laminated paper product is disposed on both sides of the panel.

FIG.6B is a schematic, cross-sectional view of another embodiment of the present invention in which one side of the panel is covered with a polyurethane or vinyl foam. FIG.6C is the same embodiment turned around and carrying an electrical fixture.

FIG. 6D is a schematic, cross-sectional view illustrating an embodiment in which the panel is clad with a layer of fiberglass for its acoustic properties and then a cloth for its decorative effect. FIG. 7 is a perspective, schematic view, partially broken- away of a free-standing heater panel that uses the principles of the present invention and illustrates schematically the disposition of the heater elements and the controls that can be placed on the heater elements and the controls that can be placed on the panel's surface.

FIG. 8 is a perspective, cross-sectional view of one embodiment of a heater panel according to the present invention in which a layer of laminated paper product is disposed on one side of the panel for its decorative effects and a layer of sound-absorbing material and open weave cloth are disposed on the outer side for the acoustical properties.

FIG. 9A is a cross-sectional view of a sheet of thermo¬ plastic material suitable for use in the present bending process and with the herein disclosed bending apparatus. FIG. 9B is a partial cross-sectional view illustrating the application of heat to a plastic sheet in accordance with the present invention.

FIGS. 10A and 10B are cross-sectional views illustrating a bent section of plastic sheet. FIG. 10A is illustrative of a type of deformity resulting from heating processes of the prior art. FIG.10B illustrates, in a 90 degree bend, the shape of the corner when the sheet is bent according to the present process.

FIGS.11Aand 11B illustrate a 180 degree bend in a plas¬ tic sheet. In FIG.11A (the prior art), the sheet is stressed and thinned out at the corner whereas no such thinning occurs in the sheet bent by the present process, and ullustrated in FIG. 11B.

FIG.12 is a schematic, perspective view; of one embodi¬ ment of apparatus suitable for bending the plastic sheets according to the present invention. DETAILED DESCRIPTION OF THE ERESEBKED EHHDIMENTS

Referring now to the drawings, particularly FIGS. 1 and 2, there is shown an acoustic enclosure 10 embodying the present invention. Enclosure 10 includes side panels 12, 14, a rear panel 16, a bottom panel 18, a front panel 20, and a cover 22. A noise generating device 24, for example a computer printer, is mounted within enclosure 10. The construction details of side panels 12 and 14 are shown in FIG.3, and the construction details of rear panel 16 and bottom panel 18 are shown in FIG. 4.

Referring now to FIG.3, it will be seen that each side panel 12 and 14 includes an outer polymeric stratum 26, a multiple channel thermoplastic intermediate stratum 28, and an open celled acoustic material inner stratum 30. Outer polymeric stratum 26 is composed of a rigid or flexible material that has aesthetically attractive finish on its outer or exposed face, for example a laminated plastic sheet such as that sold under the trademark FORMICA. Intermediate stratum 28 is composed of an extruded ther¬ moplastic of the rigid type, for example a polycarbonate, having an outer sheet 34, an inner sheet 36 and interior sidewalls 38 which form a plurality of linear internal chambers or channels 32. In the illustrated embodiment, outer sheet 34 and inner sheet 36 are in spaced parallel relationship to one another and chamber side¬ walls 38 are in perpendicular relationship to the outer and inner panels 34, 36, linear channels 32 having a substantially rectangu¬ lar profile in right cross section. The intermediate stratum, as a ^■ whole, is an integral extrusion piece. The longitudinal axis of each channel 32 is in spaced parallel relationship to one another and lie in a plane which is in spaced parallel relationship with the plane in which outer polymeric stratum 26 lies. In alternative embodiments, channels 32 are other than rectangular shaped chan¬ nels, for example, triangular or sine wave shape channels. As a still further series of alternatives side-by-side bonded tubes or 0 combinations of corrugated sheeting can be provided in various cross-sections in lieu of the preferred integral multi-channel, extruded piece. However, in any alternative embodiment, the longi¬ tudinal axis of each channel 32 lines in a plane which is parallel to the plane in which outer stratum 26 lies. The bending strength 5 of side sheet 12 resulting from the combination of polymeric outer stratum 26 and multiple channel intermediate stratum 28 is twice the bending strength of the intermediate sheet alone. In alterna¬ tive embodiments, the intermediate stratum is composed of a ma¬ terial other than a polycarbonate, for example, a high density 0 polyethylene, polystyrene, polypropylene, single or multi-walled corrugated paperboard or of metallic thin wall form, e.g., alumi¬ num, steel, nickel or super alloy (in corrosion resisting applica¬ tions). The outer side of intermediate stratum 28 and outer stra¬ tum 26 are affixed to one another by a suitable adhesive 40. Inner 5 stratum 30 is composed of an open celled acoustic material such as polyurethane foam or vinyl foam or of other light, highly porous material, e.g., fiberglass mats. Where a combination of metal intermediate stratum and fiberglass inner stratum is used, a fire proof construction is obtained (the relatively thin outer stratum 0 is far less critical). Where fiberglass is used it may be useful to encase it (to avoid fiber shedding in a very thin, sound transmitting, flexible sheath, e.g., matal foil or plastic film of less than .004 inches. Inner stratum 30 is attached to outer side of inner sheet 36 by a suitable adhesive 40. In the illustrated 5 embodiment, by way of example, the inner or exposed surface of inner stratum 30 is provided with a plurality of peaks and valleys which define a textured surface 42 with an enhanced surface area (at least 1.5 times the planar projection) for greater sound ab¬ sorption. In an alternative embodiment, the exposed surface of inner stratum 30 is generally smooth. Rear panel 16 and bottom panel 18, shown in FIG. 4, in¬ clude an outer open cell foam or lofted fiber mass stratum 44. an intermediate stratum 46 of a thermoplastic or metal multi-channel construction, and an inner stratum 48 similar to the outer stratum. Intermediate stratum 46 is sandwiched between inner and outer strata 44, 48 and fixed thereto by adhesive 40.

Front panel 20 is similar in construction to side panels 12 and 14. Cover 22 comprises in essence extensions of the top and front panels and is made, for example, of an optically clear rigid thermoplastic sheet, preferrably composed of an acrylic or polycar- bonate for example. It has one or more bends (just one shown in FIG. 1) and is hinged to a top shelf 50 which is attached to the rear of enclosure 10. Top shelf 50 is similar in construction to front panel 20. Cover 22 is provided with a bend 52 which is formed in a novel manner according to the steps shown in connection with the description (below) of FIGS. 9A - 12. Portions of the sheet which are not used for viewing (e.g., because they are covered with opaque reinforcing strips anyway) may be covered with acoustic foam on the inner face. The sheet may be of multi-piece construction instead of the one piece form shown to provide windows where needed with limited sacrifice of acoustic insulating benefits since major components of air-borne noise are suppressed by the side, bottom, rear, front and top laminate construction of the panels there.

Referring now to FIG. 5, there is shown a side panel which is provided with an angle member bracket 60, for example, a right angle bracket, for mounting adjacent panels. Angle bracket 60, which is composed of a material or synthetic material such as wood, aluminum or plastic, is affixed to intermediate strata 32 and 46. between the inner strata 30 and 42, respectively. In the preferred embodiment, angle bracket 60 is affixed to in the second or third chamber from the edge of intermediate strata 28 and 46 by rivets 62 or by a thermal/chemical bonding. As shown in FIG.1, outer strata 26 of selected ones of the panels extend beyond angle bracket 60 so that the angle bracket is not visible when the enclosure 10 is fabricated. The usage of the invention in several of its aspects is illustrated by the following non-limiting example.

EXAMPLE An experienced test laboratory measured and evaluated the noise reduction (attenuation) provided by a cabinet fabricated as described above in connection with FIGS. 1 - 5. Measurements were obtained in a 20,000 cubic foot semi-anechoic test chamber at the one-metal bystanders position with the printer and cabinet located at the center of a standard ISO test platform. Measurements ob- tained include average A-weighted sound levels, mean A-weighted impulse sound levels, and one-third octave band sound pressure levels during printer operation with and without the cabinet. Instrumentation and equipment used during this testing are listed in Table 1 below. The pertinent results of such measurements are summarized as follows:

1. The average operating sound level during continuous sheet operation of che impact printer was 65 to 67 dB(A). The printer noise was reduced by 20 dB(A) when installed inside the cabinet.

2. The impulse sound level during continuous sheet opera¬ tion of the impact printer was 67 to 69 dB(A). The impulse noise was also reduced by 20 dB(A) when installed inside the cabinet of the invention. 3. Such a cabinet was tested after the sound absorptive stratum (foam) of the laminated material had been removed. The sound level produced by the impact printer was reduced by 15 dB(A) when operated inside this cabinet of the invention.

4. The average operating sound level during continuous sheet operation of the dot-matrix printer was 70 to 71 dB(A). The printer noise was reduced by 23 dB(A) when installed inside the cabinet of the invention.

5. The impulse sound level during continuous sheet opera¬ tion of the dot-matrix printer was as high as 73 to 75 dB(a) . The impulse noise was reduced by 21 dB(A) when installed inside a cabinet of the invention.

6. Placing the dot-matrix printer inside a prior art cabinet reduced the noise level by 14 dB(A).

7. One-third octave band sound pressure levels were measured during printer operation with and without the cabinet of

10 the invention and yielded a substantial improvement of attenuation over a frequency range from 125 to 8000 Hertz center frequency of the 1/3 octave band (15 dB at 500 Hz, 25 at 1250 , 19 at 2500 - 5000 , 15 at 8000, 6 at 125) .

(end of example)

15 In order to maximize the sound absorbing characteristics of enclosure 10, selected thicknesses of the open celled acoustic material, for example polyurethane foam, or other foam, or lofted fiber mats, are provided on inner strata 30 of side sheets 12 and 14, front panel 20 and shelf 50, on inner stratum 44 of rear panel

20 16 , and on outer stratum 48 of bottom sheet 18, to minimize noise and vibration generated by computer printer 24. That is, the noise generated by computer printer 24 which is positioned within enclo¬ sure 10 and the enclosure is tuned for minimum noise generation by placing various thicknesses of the polyurethane foam at selected

25 places including (i) at paper feed openings, (ii) on cover por¬ tions, as noted above and (iii) over re-entrant fixtures (e.g., switches, fan openings, and the like). Sound measurements are taken at various locations about the enclosure 10 and additional thicknesses of polyurethane foam are added until the measured noise

30 level is below acceptable levels, for example 60 db. After this initial tuning of enclosure 10, complete sheets of polyurethane foam corresponding to the maximum thickness of the polyurethane foam positioned during the tuning process is then affixed to the side panels 12, 14, rear panel 16, bottom panel 18, front panel 20

35 and top shelf 50. The thicknesses of the intermediate strata 28 and 46 is in the range of 2mm to 40mm. As noted in FIGS. 1 and 2, enclosure 10 is provided with openings for air circulations, power cords, paper feed slots and the like.

There have been described so far two related forms of panels including the multi-channel intermediate stratum and an enclosure made from such sheets and supplemental transparent sheet extensions thereof with a clear bend. The panels and such sheet extensions are usable in other applications taking advantage of thermal insulation, as well as sound insulation, lightness, inter¬ nal geometry and strength properties thereof.

FIG.6 shows a combination of the material described above (a variant form) used as a free-standing panel 61 which is sup¬ ported upon legs 63 and 65. Preferably, legs 63 and 65 are made of hollow, extruded metal which are sufficiently rigid to support the sheet 61. A perimeter shield 67 encases the edges of the panel 61 and is preferably formed of either extruded channel aluminum (that is appropriately mitered at the corners) or channeled vinyls or other appropriate plastics. The panel 61 comprises a pair of face- to-face inner sheets 69 and 71 (sheets form outer parts of extruded channeling) that are adhesively bonded to one another. A pair of outer sheets 75 and 77 of the same rigid material are spaced from the respective inner sheets 69 and 71 by an array of regularly spaced-apart parallel wall members 81 (ribs) that extend longitudi¬ nally between each of the sets of the inner and outer sheets. In this way, two series of longitudinally-extending hollow chambers 79 and 80 are formed and are disposed between the respective sheets 60 and 71 and 75 and 77. This juxtaposed arrangement gives rigidity to the construction and provides for easy wiring irrespective of where a fixture or receptacle is to be dispoed on the sheet 61.

A covering, pref errably of open form such as open weave cloth and/or of micro-perforated thin metal or similarly perforated phenolic bonded paperboard laminate, is disposed over each of the outer sheets 69 and 77 for decorative and/or acoustical effects. In the embodiment shown in FIG. 6, a laminated paper product is disposed upon outer sheet 69 and a layer of porous form, e.g., polyurethane or vinyl foam 87 or of fiberglass, covered by a cloth layer 89. An electrical wire 88 is threaded through one of the vertically-extending hollow chambers 81 to a junction box 91 that is seated therein. The wiring is then run through the horizontal¬ ly-extending hollow chamber until it reaches a receptacle box 83. When the electric wire is snaked through to any point where a right-angle bend has to be made, the a hole is drilled through the panels at that point so that communication can be made between the vertically and horizontally-extending chambers. The wire is snaked through the vertically-extending interior chamber until it reaches the drilled hole. At that point it is fished to the horizontal chamber so that it can reach the desired terminal. In the drawing, cord 86 (that may be connected to a lighting fixture) is shown as the terminal and is disposed near the edge of the acoustic panel 61, adjacent its perimeter. Screws 85 are seated in the acoustic panel and firmly held therein even at the edge. The lighting fixture (or other electrical devices) is arranged from base plate 83. Since the wiring can be snaked either horizontally or verti¬ cally when using the sheet of the present invention, it can be threaded equally well to receptacles on both sides of the panel. Further receptacles are indicated at Rl and R2.

In the FIG. 6 embodiment, the hollow leg 65 that supports the panel can provide both electrical service and other services such as telephone wires. The receptacles for both telephone and electric wires can also be installed with equal facility. While FIG. 6 shows receptacles, and especially telecommunications recep¬ tacles, can be disposed upon the outside of the panel.

The interior supports have been described above as being formed from inner and outer sheets supported by longitudinally- extending walls that form a plurality of longitudinally-extending hollow chambers. This entire construction is preferably an ex¬ truded rigid or semi-rigid plastic or extruded aluminum or other metal. Ωie longitudinally-extending hollow chambers are preferably extruded with the walls being disposed in a perpendicular relation¬ ship to the inner and outer .sheets 69 and 75 so that the longitudi- nally-extending chambers have a substantially rectangular profile in cross-section. In alternative embodiments, the channels may be defined in cross sectional shapes other than rectangular, for example, as triangular or sine wave shape chambers. However, in any such alternative embodiment the longitudinal axis of each internal chamber must be such that it lies in a plane which is parallel to the plane in which inner and outer sheets 69 and 75 lie.

Referring now to FIGS.6A - 6D embodiments are shown which use surface sheets 89 and 91 that are formed of a laminated paper product with an aesthetically attractive melamine finish. The surface sheets 89 are attached directly to an outer sheet 69 and 77 of the substrate by conventional adhesives commonly used for lami¬ nation of paper products. With such construction, an electrical receptacle 91 can easily be mounted in the body of the sheet and wiring 93 can be readily snaked through. Conventionally, such electrical receptacles require that the receptacle be screwed into the base that supports it, that is the laminated paper product layer 89 together with the outer sheet 69. The substrates provide adequate support for the screws.

Alternative embodiments are shown in FIGS. 6B, 6C and 6D. In FIG. 6A the laminated paper product 89 is on one side of the sheet and foam layer 95 and cloth 96 are disposed on the other, side. FIG.6C is 6B turned around to show accommodation of an electrical receptacle. In FIG. 6D fiberglass 95F and cloth 47 have been substituted for the foam and cloth covering shown in FIG. 6B. FIG. 7 shows a free-standing panel 101 disposed upon a pair of legs 103 and 105. Legs 103 and 105 can be of any conven¬ tional shape adequate to support the free-standing sheet 1 in the desired position. In a preferred embodiment, at least one of the legs 103 is hollow and adapted to receive wires 107 and 109 which connect to an electrical outlet 111 and a telephone communication jack 115. The wiring for the telecommunications cable 107 and the power cord 109 can be conveniently arranged to run through the hollow leg 103 into conventional junction boxed disposed internally within panel 101. A channel member 117 is disposed about the perimeter of panel 101 so as to give support to the structure and are secured to legs 103 and 105. Preferably, channel member 117 is for ed of a lightweight material such as aluminum or rigid, ex¬ truded thermplastic material. Conveniently, channel member 117 is mitered at the corners 19 to form a structurally sound product. Legs 103 and 105 can be attached to channel member 117 by any conventional mechanism utilized to join such elements together.

A thermostat can be disposed anywhere upon the surface of the panel 101 and can be arranged to allow the user of the panel to adjust the heat. Conventional thermostats, such as is commonly used with electric blankets or other similar types of resistance heating devices, can be used with the present sheet. In a prefer¬ red embodiment, an electrical receptacle 123 is shown disposed near the base of panel 101 so as to receive power cords from accessories such as typewriters, dictating machines and electric lighting fix¬ tures. A telephone jack 125 can also be disposed on the panel and is electrically connected to telecommunications cable so as to enable the user of the sheet to attach a telephone without a signi- ficant_*number of unsightly wires being disposed upon the floor. It is apparent that the location of the thermostat, the receptacle 123 and the telephone jack 125 can be anywhere upon the panel 101, as is required by the user so long as provision is made in the heating elements to accomodate the desired configuration.

In the broken-away section of FIG. 7, a pair of rigid sheets 125 and 127, formed of an extrusion of a rigid thermoplastic material or of aluminum, are shown disposed parallel to one another. A plurality of walls 129 are arranged parallel to one another and form a plurality of internal chambers 30 that lie on a plane which is spaced in a parallel relationship to the plane in which the sheets are disposed. While the internal chambers 130 that are shown have a generally rectangular cross-section, it is apparent that other cross-sections can be used in situations that dictate other shapes. For example, it is possible to use sinusoi¬ dal or triangular shapes in the internal chambers by realigning the walls 129 if the requirements of the sheet are such as to necessi¬ tate such shapes. Rectangular shapes, however, are highly prefer- red because of the ease of extrusion and also for the rigidity that a rectangular shape provides. The rigid channel structure formed by the sheets 125 and 127 and the internal chambers formed by the interior walls 129 provide an excellent location for wires that are to be disposed in the sheet.

A varied assortment of commercially available resistance heating materials or elements can be utilized with the heating panel of the present invention. For example, as shown in FIG.8, conventional resistance heating wires such as are commonly used in electric blankets may be threaded through the internal channels in a manner well-known to the art. The only considerations are that the wires-must be in a location and position which will enable them to provide radiant heat to the subject and not be cut by the insertion of electrical receptacles. For example, it might be less than desirable to place the resistance heating wires within the chambers and then place acoustical material on either side of the wires which would essentially provide insulation and reduce the effectiveness of the heating. In such cases, it is more desirable to place a sheet of laminated paper product immediately upon the exterior of at least one side of the extruded base member and a layer of cloth may be disposed over the fiberglass for its decora- tive effects. Alternatively (not shown) one or both of the rigid sheets 125 and 127 may be printed with a conductive ink according to methods which are per se well known and commercially available so as to form an array of conductive stripes that may be connected to a busbar and further connected to a power supply cord. An electrical heating device that comprises a substrate with an elongated heater is used that extends longitudinally of the substrate with a semi-conductor pattern carried on the substrate and electrically connected to and extending from a pair of conduc¬ tors. Preferably, a sealing layer overlies the conductor. The conductors comprise a pair of metallic conducting elements that are arranged to be connected through an exposed surface to a power supply. Each of the members of the semiconductor pattern are somewhat removed from the perimeter of the substrate so as to form a freeboard portion which will allow for the disposition of sta- pies, blind rivets or adhesives so as to attach the heating device to rigid sheets. In the embodiment shown in the break-away portion of FIG. 7, layers of acoustical material 131 and 133 are disposed next adjacent to the rigid sheets 125 and 127 respectively. In the embodiment, the electrical heating devices 135 and 137 are disposed upon the acoustical material layers 131 and 133 respectively. Covers 139 and 141 which may be made (i) of open weave cloth or (ii) thin, perforated, solid sheets (e.g., metal or wood or lami¬ nate veneers) , to allow sound transmission, are disposed on the outside of the panel 101 to provide the decorative covering for the entire sheet. The channel member 117 caps the sheet for quite a while before bending.

As shown in FIG. 9, a sheet 44 of plastic, preferably one of the cobe conveniently provided through the hollow chamber 130. When desired, in the configuration shown in this drawing, two holes can be drilled through interior walls 129 (if the wiring is to be laid in a direction normal to the axis of the internal chambers) to receive the wiring for the receptacle 123. In those cases where two panels are used one of the sheets being at right angles to the other, such drilling along the length of the sheets may not be required.

Turning to FIG. 8, another embodiment of the present invention is shown in which a laminated paper layer 150 (which comprises Alpha type paper, 5 - 7 layers of kraft paper, a phenolic core and melamine surface with low binder, commonly sold, e.g., under the tradename Formica by the Formica Co.) is disposed upon a rigid multi-channel stratum is with single or multiple series of channels. One version of electrical heating (electrical resistance heating wires 148 such as described above) are disposed in chambers 147 and controlled by a thermostat (not shown) . Heat from the wires will flow through the rigid sheet IS and paper layer 150. As an alternative or in addition to resistance heating wires, a hea¬ ting element 137 (such as described above with reference to FIG. 7) may be disposed between a fiberglass layer 151 and a cloth (or perforated metal) cover 152. FIG. 8 also illustrates another embodiment of the inven¬ tion wherein an adhesive layer is provided to serve as layer 150 (or covering a paper layer 150) to enable wall mounting of the sheet as a whole or to enable mounting of the sheet from spaced studs. Alternatively bolts or screws can be passed through a sheet to mount it because the sheet construction as a whole limits stress propagation from holes therein and aesthetically also accommodates the same.

The (thermal/acoustic) insulation properties of strata 151 and adds to the effectiveness of the heater 137 in comfort of an area facing or surrounded by such sheets. In non-enclosure and enclosure applications, the sheets may be supplemented by flat, slightly curved or right angle bent transparent sheets. Such sheets also have many independent appli¬ cations.

Rigid or semi-rigid plastic sheets, e.g., for use as part 22 of FIG.1 above, of any width and length can be bent according to the present invention limited principally by the size of the heating and bending apparatus. A process and equipment therefor are now described in reference to FIGS. 9A - 12, and are most advantaneously used with sheets greater than about one-eighth inch thick. With sheets less than one-eighth inch they heat so quickly that the plastic softens too rapidly to provide any significant advantages through the use of the invention. Plastics which can bend according to such process include, among others, polystyrene, acrylics, high-density polyethylene, rigid polyproplyene and poly- carbonates. Individual softening temperatures of each of these materials are well-known to the art and the length of time neces¬ sary to achieve softening will vary depending upon the thickness of the sheet. For example, acrylic resins soften when the sheet reaches about 350 degrees F and polycarbonate resins soften when they reach a temperature of about 340 to 400 degrees F. Care, however, must be used with polycarbonates because they must be dried at elevated temperatures for quite a while before bending.

As shown in FIG.9, a sheet 44 of plastic, preferably one of the compositions mentioned above, is disposed upon a table or platform (not shown) and arranged so that it can be subjected to radiant heat approximately on a line where the bend will be made. As shown in FIG.9B, radiant heat 46 is applied by a heater 46R-1 in a band to a wide area 47 of one surface of sheet 44 and by heater 46R-2 in a band to a wide area 47 of one surface of sheet 44 and by heater 46R-2 to focussed band 55 on the obverse side. The heat source used to produce the upper band of focussed heat 46 is preferably a high intensity, commercially available quartz infrared lamp and a resistance strip is used for the other heater 46R-1. The heat paths are disposed in planes which are generally normal to the plane of the sheet 44. Heat source 46R-2 which is per se of a standard, commer¬ cially available construction, comprises a parabolic reflector 61 which concentrates the infrared light emitted from its internal lamp and focusses it upon the plastic sheet 44 so as to concentrate the heat in a band 45 which is narrower than the wide band 47. The width of the focussed band should be generally less than about twice the thickness of the sheet 44 and the width of the broad band should be greater than about four times the thickness of the sheet. The width of the wide band can be adjusted by a shutter disposed within a table or platform which is used to support the sheet or by varying the distance between the sheet or by shuttling the heater back and forth on a plane parallel to the plane_,of the sheet.

Changing the width of the focussed band is accomplished by moving heater 46R-2 on a plane normal to the plane upon which the sheet rests. In this way (within the focal limits of the heater) as the heater is moved nearer or further from the sheet, the width of the focussed band can be modified to accomodate various thick¬ nesses of sheets.

According to this process, the sheet is continuously heated on its bottom side in a wide band until between about 40 and 60% of its thickness is softened. The heat spreads upward from the lower surface and reduces in intensity (i.e., a non-linear decline of temperature) going out the width of the band from its centered position. As the wide band is softening, lamp 46R-2 is turned on to form the narrower, top side, focussed band so that the balance of the sheet is softened or plasticized. Lamp 46R-2 provides essentially instantaneous (1-5 seconds, preferrably 1 - 3) heat rise to a temperature above the melting point of the sheet. Generally, the programmed delay is such that the focussed heat is on for 25 to 50% of the time that heat source 46R-1 is on with (usually) a delay of between about 30 to 90 seconds between the start of the first heat source and the start of the second to form the focussed heat band. The difference in delay time depends upon the thickness of the sheet. A 30 second delay is generally used with one-eighth inch thick sheets and a 90 second delay can be used with one-half inch thick sheets. The total process time involved here for heating is less than three minutes for acrylic sheet (compared to 20 - 30 minutes for half-inch in prior art processes). For one inch thick sheets, the prior art involves 1- 2 hours; in the present invention an overall heat time of 30 minutes on the bottom is involved, the last 10 - 15 minutes of which involves top (high intensity, focussed) heating as well

Subsequent to heating the entire thickness of the sheet 54, the sheet is indexed to a location in a bending brake (not shown) where it can be bent to the desired angle. Preferably the bending brake is in the form of a floating platen in which the space between the underlying table and the brake is adjusted to that the plastic can easily slip beneath it.

The softened plastic is then arranged until the desired bend line for the sheet is exactly beneath the bending break. The break bar is then rotated to the desired bend angle so as to bend the sheet. The bent sheet is then held in this position until the plastic rehardens.

Turning to FIG.10A and 10B, two sheets of one-half inch plastic having right angle bends are shown. In the embodiment of the prior art, a prior art bend is shown. Dimension A-A of one- half inch is reduced by 20 to 40% at the bend 40, as indicated by dimension B-B. As can be readily understood, a thinned bend can be less pleasing aesthetically and also mechanically weaker because of strains that are introduced into the sheet during the bending process. In the embodiment shown in FIG. 10B, and fabricated according to the present invention, no significant thinning occurs at the bend 41. Dimension C-C is substantially the same as dimen¬ sion D-D and aesthetically, the sheet shows no significant distor¬ tions from thinning nor are stresses introduced from the bending process. Similarly with FIGS. 11A and 11B, in which 180 degree bends are shown, even in this extreme case and when using the principles of the present invention, dimension H-H at the bend is substantially the same as dimension G-G of the sheet. This sub¬ stantial identity in the sheet thickness at its flat surface and at its bend 42 is to contrasted to the sheet that was bent according to the prior art and shown in FIG.3B. In that latter case, the sheet is 25 to 50% thinner at the bend 41 (dimension F-F) than on its flat surface (dimension J-J).

FIG.12, as illustrative is shown of an apparatus suitable for bending the sheets according to the present invention. A fixture 201 is disposed over a table 203. A longitudinally exten¬ ding quartz incandescent lamp 205 is disposed within a reflector of that is arranged to reflect a focussed conical beam of infrared light upon a sheet 202 of plastic. The preferred focal point is selected within a range of depth below the upper surface of the plastic sheet to establish a narrow band of uniformly heated and softened plastic of the desired width (about twice the thickness of the sheet) on the upper surface. Meanwhile the lower band is non- uniformly heated to twice such width Fixture 201 is adjustable on a plane normal to the plane of table 203 by turning a handle and screw 209 disposed in upper carrier 204. A pair of guide pins 230 are attached to fixture 201 and slide within receiving holes 232 to insure alignments in a perpendicular plane. Carrier 204 can be moved on the horizontal plane and is supported on bearings 234 that move in tracks 235. Changes in positioning can be accomplished with motor 236 and pully 237. When fixture 201 is raised or lowered, the beam of conical radiant energy emitted by lamp 205 will be narrowed or widened to accommodate various thicknesses of plastic sheets. A longitudinally extending resistance heating element 215 is disposed beneath the table 203 at a distance sufficient for it to provide a wide band of heat on the lower side of plastic sheet 202. The width of the wide band of heat can be adjusted by shut¬ tling the resistance heater 215 along a plane parallel to the sheet 202 thereby forming a softened band of the desired width, the length of travel of the heater 15 determining the width of the softened band. The heater 215 is shuttled on a lower carrier 31 that travels on rollers 232 in track 233. Motor 236 can also be used to move lower carrier 231 by means of pulley 240. Heater 215 can be adjusted on the vertical plane by means of screw and handle 241. Timing of the heaters 205 and 215 is controlled by control box 242.

After the plastic sheet 202 has been softened, it is moved from between braces 243 and 244, which hold it in place during bending, to one of the conventional bending brakes 244a or 244b. In a specific example, a one quarter inch sheet of acrylic plastic was disposed on a table. A one-inch wide flat strip resis¬ tance heater.was disposed beneath the sheet and a quartz-incan- descant lamp housed in a reflector was disposed above it. The quartz lamp was arranged such that it could form a one-half inch band of softened plastic in the sheet. The flat heater, continu¬ ously on, heats 40 - 60% (preferably 50%) of the thickness of the sheet to soften. The surface temperature of the lower heater was 450 degrees F, but the temperature of the softened band of plastic on the sheet was only about 350 degrees F at a mid point of the band with a non-linear gradient duwn to about 300 F about two inches from said mid-point on either side, providing spreading waves of heat in the sheet which may be likened to ripples sprea¬ ding out from a pebble thrown into a pond. The temperatures therein are in the softening point range of the plastic. Following the softening of 50% of the thickness of the bottom side of the sheet, the quartz heater was turned on and the infrared light was focussed on the sheet to form a narrow band of softened plastic. The surface temperature of the narrow band was about 700 - 900 degrees F about two times the plastic's melting point but it was quickly done so as to avoid burning or melting through. The plas¬ tic sheet quickly softened throughout its thickness and it was then moved to the bending brake where it was bent into a ninety degree angle, upon cooling, a ninety degree bend was formed on the sheet. Neither stress lines nor thinning were noticed.

It will now be apparent to those skilled in the art that other embodiments, improvements, details, and uses can be made consistent with the letter and spirit of the foregoing disclosure and withing the scope of this patent, which is limited only by the following claims, construed in accordance with the patent law, including the doctrine of equivalents.

What is claimed is:

Claims

1. An acoustic sheet comprising:

(a) a planar, thin wall outer stratum;

(b) an intermediate stratum having inner and outer sheets disposed parallel to one another and a plurality of interior walls forming at least one repeating series of a plurality of internal elongated channels between said inner and outer sheets, the longi¬ tudinal axes of said internal chambers of a series being parallel to each other and lying in a plane which is in spaced parallel relationship to the plane in which the outer stratum lies; (c) a planar, inner stratum composed of a porous material which is thicker than the outer stratum; and

(d) said intermediate stratum being attached to said inner and outer strata.

2. An acoustic sheet comprising: (a) a planar, outer stratum of a porous acoustic damping material stratum;

(b) an intermediate stratum comprising multiple elongated channels in at least one repeating series, the longitudinal axes of said channels of a series being parallel to each other and lying in a plane which is in spaced parallel relationship to the plane in which the outer stratum lies;

(c) a planar, inner stratum composed of a porous ma¬ terial; and

(d) said intermediate stratum being attached to said inner and outer strata.

3. The acoustic sheet of either of claims 1 or 2 wherein said intermediate stratum comprises an extruded thermoplastic mul¬ ti-elongated channel piece of integral form with longitudinal axes of the channels parallel to each other and to the planes of the inner and outer strata porous and said inner strata comprises a sound absorbing foam.

4. The acoustic panel of claim 3 wherein each said chan¬ nel of the intermediate member has a substantially rectangular profile in right cross section, with adjacent channels sharing a common wall.

5. The acoustic panel of claim 2 wherein said outer stratum is a thin, laminated sheet having a finished outer surface.

6. The acoustic panel of claims 1 or 2 wherein the ex¬ posed surface of said porous stratum is textured to provide an enhanced surface area per square foot relative to its planar pro- jection.

7. The acoustic panel of claims 1 or 2 wherein the inter¬ mediate stratum comprises adjacent tubes, sealed side by side.

8. An acoustic enclosure comprising a multiplicity of panels as recited in claims 1 or 2 and more particularly a tetra- hedial construction with:

(a) a pair of side panels;

(b) a rear such panel;

(c) a bottom such panel;

(d) said side sheets, said rear sheet and said bottom sheet attached to one another to form an enclosure having an opening at the top and front; and

(e) at least one transparent sheet forming a supplemental extension of at least one of said panels and constituting a cover hinged to said enclosure, said transparent sheet being moveable between an open position and a position closing up, said enclosure, said sheet including a bend therein.

9. The acoustic enclosure as claimed in claim 8 wherein said supplemental extension has a uniform cross-section thickness up to and through the bend, said bend being free of stress-induced optical distortion and having a thickness of at least 3/16 inch.

10. A sheet in accordance with claims 1 or 2 wherein superposed series of longitudinally-extending chambers are provided which are disposed at angles to each other.

11. The sheet according to claim 10 wherein said sheet includes an electrical connection means and wiring means operative- ly associated with said electrical connection means, said wiring means being disposed within said longitudinally-extending hollow chambers.

12. The sheet according to claim 11 wherein one of the series of longitudinally-extending chambers if disposed at right angles to the other of said series.

13. The sheet according to claim 1 further including means for supporting said panel at an edge thereof, said means being arranged to receive said wiring means whereby current can be conveyed from an outside receptacle to a receptacle disposed in said sheet.

14. The sheet according to claims 1 or 2 further compri¬ sing resistance heating means associated with said channel struc¬ ture and arranged to radiate heat from said channel structure; and a thin outer stratum disposed on at least one side of said rigid channel structure and exterior of said resistance heating means and wherein the resistance heating means is a series of resistance heating wires disposed within said parallel internal chambers.

15. The sheet according to claim 14 wherein the resis¬ tance heating means is a laminated structure containing an array of longitudinally extending spaced-apart conductive members disposed between a pair of conductors.

16. The sheet according to claim 14 wherein the resis¬ tance heating element comprises a conductive material of stripe form upon a panel surface and electrically connected to a power supply means whereby said resistance heating element can be heated.

17. The sheet according to claim 14 wherein the resis¬ tance heating means is disposed centrally of the exterior edges of said rigid channel structure whereby to leave a perimeter on which a thin outer stratum may be disposed directly upon the rigid chan- nel structure.

18. The panel according to claim 14 wherein the rigid sheet structure is formed of a lightweight thermoplastic material or aluminum.

19. The panel according to claim 14 wherein the rigid sheet structure is formed of metal.

20. The sheet according to claim 14 in which a stratum of an open-celled material is disposed upon the other side of said rigid channel structure.

21. The sheet according to claim 14 including a stratum of acoustical material disposed on at least one side of said rigid structure, a resistance heating means disposed upon said acoustical material, a decorative covering disposed over said resistance heating means, said lead-in wire means connecting said resistance heating means to a power supply, said lead-in wire means being threaded through said internal chambers to an exterior location.

22. The sheet according to claim 21 wherein a stratum of acoustical material is disposed on each side of said rigid struc¬ ture and a resistance heating means is disposed upon the outside of each of the resistance wires not being threaded through said inter¬ nal channels.

23. The panel according to claim 14 comprising means for vertical wall support thereof.

24. The panel according to claim 23 wherein said support means comprises an adhesive facing of said^"panel.

25. An acoustic enclosure comprising panels defining, at least in part, a substantially enclosed space, said panels compri¬ sing a structurally self-supporting array of side-by-side elongated channels, of thin wall form to limit structural noise transmission, in a series with parallel axes of the channels in such series.

26. An acoustic enclosure in accordance with claim 25 with said panels being lined toward the interior of the enclosed volume with acoustic absorbing, lightweight foam.

27. An acoustic enclosure in accordance with claim 25 with at least one of said panels having an exterior thin wall decorative facing overlying the multiple channel array thereof and bonded thereto.

28. An acoustic enclosure in accordance with claim 25 and further comprising at least 3/16 inch thick visually transparent plastic sheet extensions of the panels substantially completing the enclosure.

29. An acoustic enclosure in accordance with claim 28 with at least one such sheet having a visually clear bend therein.

30. An acoustic enclosure in accordance with claim 29 with such bent portion being at least 1/4 inch thick and loosely linked to a panel to form a displaceable cover for ease of inser- tion of items, and removal of them from, the enclosure.

31. An acoustic enclosure in accordance with claim 30 wherein said bent portion is hinged to a panel.

32. A method of bending thick sheets, 3/16 inch and lar¬ ger, of plastic materials with resultant bends which are substan¬ tially stress free and of substantially the same structural and visual properties as adjacent unbent portions comprising the steps of:

(a) arranging such sheet substantially horizontally;

(b) heating a relatively wide region along the sheet bottom with heat application which effects a non-linear gradient spreading of the heat externally applied or internally generated therein to soften 40 - 60% of the sheet thickness upwards of said bottom surface to plasticity;

(c) the heating an overlying top surface region of the sheet with intense heat limited to a narrower zone aligned with a critical part of the lower heated zong while maintaining the lower heat until the upper heated zone melts in part;

(d) then bending the sheet.

33. A bent, plastic sheet as produced by the process of claim 32.