BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a method for making rigid foam-filled building panels, of the type commonly used in industry to make dwellings and other structures.

Description of the Related Art

Generally, in making foam filled building panels, a multiplicity of hollow panels are stacked on an hydraulic press. Foam precursor is injected into each panel, and the panels held in compression, together, until the foam expands and hardens. Such a ^■ batch-wise procedure for forming building panels is inefficient and time-consuming. Further, if one panel in the stack fails, the pressure is released and the other panels are spoiled.

Attempts have been made to make the manufacture of rigid building panels continuous. For instance, U.S. Patent 4,518,550 - Miettinen et al. shows a method of manufacturing rigid frame-building elements filled with hard foam plastic. That apparatus uses a series of rollers to apply pressure to the foam-injected building panels, and to move them along until the foam has substantially ceased expanding.

SUMMARY OF THE INVENTION

The present invention comprises an apparatus and method for forming building panels. The building panel comprises two flat planar faces of, for instance, gypsum board or plywood. These are applied to a frame, generally of lumber. Once the frame has been built, a

plywood sheet is secured to the frame. The gypsum board is heated with infrared radiation. Fiberglass insulation is placed in the interior corners and along one side of the frame and plywood. The gypsum board is then assembled to the plywood and frame, and the entire hollow panel is heated with microwave radiation.

Simultaneously, the foam precursor is heated with microwave radiation. The foam precursor is then injected into the hollow interior space of the panel. The panel is placed on a conveyor. The panel is situated between two sets of rollers, which apply pressure to the panel as the foam expands. Thus, pressure on the panel is maintained while the panel is conveyed through the apparatus, and the foam precursor foams to fill the panel, displacing the fiberglass insulation where necessary.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1 is a schematic view of the microwave foam precursor heater of the present invention.

Fig. 2 is a cross-sectional view of the panel heater of the present invention.

Fig. 3 is a cross-sectional view of the panel heater of the present invention.

Fig. 4 is cross-sectional view of an unfilled panel of the present invention.

Fig. 5 is an end view of the conveyor of the present invention.

Fig. 6 is a side view of the conveyor of the present invention.

Fig. 7 is a partial cross-sectional side view of the roller and roller frame of the present invention.

Fig. 8 is a partial cross-sectional side view of the roller and roller frame of the present invention.

Fig. 9 is a partial cross-sectional perspective view of the roller and roller frame of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The panels consist of dimensionally stable frames formed of wood, metal or other rigid materials. The frame is then covered with gypsum board (wallboard or sheet rock) , plywood or other planar materials. Thus, a hollow space is formed inside the building panel. Into this space is injected a urethane or isocyanate foam precursor consisting of two components, which are mixed

before injection. Once injected, the foam expands to fill the volume of the panel. During the foam expansion, the panel must be kept in compression to prevent the expanding foam precursor from deforming the planar faces of the panel and to force the foam into the corners of the panel.

The foaming of the isocyanate foam precursor is a delayed reaction. That is, a liquid is injected into the interior hollow space of the panel. The liquid reacts and foams once inside the panel. The amount of foaming action which occurs is temperature-sensitive. If the foam precursor components are too cold, the precursor will not foam properly and will not fill the interior space of the panel. If too much foam precursor is injected into the hollow space of the panel, or if the precursor components are warmer than thought, too much foam may be produced, and the panel may be damaged and spoiled by the foaming precursor. Therefore, temperature control of the precursor components is important, as is metering the amount of precursor injected into the building panel.

Not only is close control of the temperature of the foam precursor components important in forming foam- filled building panels, the temperature of the panel at the time of injection of the foam precursor is also important. If the panels are too cold, the foam

precursor will not foam properly, and the panel will be under filled. Worse than this is the uncertainty which this causes. Exactly how much the precursor will foam is difficult to predict, and, therefore, it is difficult to inject the proper amount of foam precursor.

Therefore, for best results, when making foam- filled building panels, it is important that the foam precursor be mixed at the correct temperature before injection into the building panel. A foam precursor useful with this invention is Isofoam, available from Dow Chemical. Isofoam has two precursor components, stock numbers R0379A and R0380B. One component may be at about 70°F, however, the other component should be at about 105 ^q F. Therefore, generally, at least one component should be heated before the building panel is formed. In some instances, one component may need to be cooled before the components are mixed.

Fig. l shows an apparatus for heating one component of the foam precursor. A second, similar, apparatus may be added if the other component of the precursor must also be heated. Fig. 1 shows a bulk container 10, such as a storage tank, filled with the foam precursor component which requires heating. The component is taken from the storage tank via connecting pipe 12 through gate valve 14, and ball check valve 16.

The component then continues through a microwave impermeable mesh 18, and into oven 20.

Once inside oven 20, the precursor component flows through pipe 22 into heating, tank 24. While the component is inside the oven, it is irradiated by microwave units 30. A simple temperature feedback unit may be used to control the amount of microwave radiation which the liquid component receives. The number of microwave units installed in the oven may be greater than that needed to heat the liquid component, in order to provide sufficient radiation should one or more units fail. Thus, the need for emergency servicing of the microwave units and oven is removed. The component flows continuously through the oven and out to the building panels.

The heated precursor component is then removed via pipe 26, through a second microwave impermeable mesh 28, through valve 32 and pump 34. The heated component is then sent to be mixed withr the other component which may or may not have undergone a similar treatment. The mixed foam precursor is then injected into the hollow building panels. Any unused and unmixed precursor component may be recycled for reheating through pipe 36, valve 38, microwave impermeable mesh 40 and pipe 42 back into heating tank 24. Pipes 22, 26 and 42, as well as heating tank 24, must all be made of a material which

does not interfere with the transmission of microwave radiation, such as plastic, as must any other parts contained within oven 20.

Referring now to Figs. 2 and 3 , the panel should also be heated to the proper temperature before injection of the foam precursor. Figs. 2 and 3 show an apparatus for using microwave radiation to heat the panel before injection of foam precursor.

Panel 50 is delivered to oven 60 by way of conveyor 70. Conveyor 70 is comprised of individual rollers 72. Oven 60 is vertically movable by means of pneumatic device 52. Alternatively, a vertical movement of oven 60 may be produced by an hydraulic device. Oven 60 is then lowered over panel 50. The sides of oven 60 form a microwave barrier when the oven is in its lower position. Microwave units 54 are then used to irradiate the panel, to heat the panel- to the proper temperature for proper foaming of the foam precursor. If there is a delay between radiating the panel and injection of the foam precursor , ^" whereby the panel cools, the entire conveyor may be reversed, and the panel reheated in oven 60. The microwave units 54 receive power from controllers 56. Thus, only as many units as are needed must be activated.

Panels 50 are generally made from gypsum board on one side and plywood on the other. The gypsum board is not as susceptible to microwave heating as the plywood board. Therefore, when heating the panel with microwave radiation, the plywood will increase in temperature faster than the gypsum board. Since it is desirable to have both sides of the building panel 50 at the proper temperature, the gypsum board should be heated alone before assembly of panel 50 in order to achieve optimum foaming of the foam precursor.

Separate heating of the gypsum board may be accomplished with radiant heaters. The side of the board which is to face the inside of panel 50 should be heated by radiant heaters prior to assembly of the panel. It is generally unacceptable to heat the hollow panel with radiant heaters after assembly, because the radiant heat tends to delaminate the plywood. Further, heating the inside face of the gypsum board after assembly would be very difficult. Finally, heating by convection is similarly unacceptable. Heating by convection is inefficient, since it is the interior of the panel which requires heating. Further, convection heating is slow and requires a large amount of time and energy. This is undesirable in a continuous production process such as the one described herein.

Radiant heaters are arranged similarly in the radiant oven as microwave units 54 are arranged in microwave heating oven 60. In the radiant heating oven, only the gypsum board, and not the entire panel, passes beneath the radiant heaters. The oven used for the radiant heating need not form a seal since no harmful radiation is emitted by the radiant heaters. Both radiant and microwave heating have substantial advantages over convection heating, which make them particularly suited for continuous automated operation. Both radiant and microwave heaters may be programmed to operate automatically with feedback of the panel temperature. Both operate quickly, which is important in a continuous operation. Finally, both operate efficiently, with low energy loss, which is important in any operation, to lower costs as compared to conventional heating methods.

Despite close temperature control of both the foam precursor ingredients, and the building panels, over or under filling of panel 50 is still possible. Fig. 4 illustrates a solution to this problem. Fig. 4 shows a building panel 50 comprising a frame 58. The frame is generally made from 2 x 4 lumber, or some other dimensional wood. On top of frame 58 is plywood sheet 64, and on the other side of frame 58 is gypsum board 62.

Contained inside of panel 50, and placed there while panel 50 is being constructed, is fiberglass

insulation 66. Insulation 66 is placed in the corners and along one wall of the interior of frame 58, within panel 50. The remainder of panel 50 is then assembled. Foam needed to fill panel 50 absent the fiberglass insulation is calculated, and slightly less than the amount of foam precursor required to form enough foam to fill 100% of the empty panel volume is injected into the panel space. As the foam expands, if it expands to 100% of its calculated volume, it will compress the fiberglass insulation against the panel frame 58. If, however, due to unforeseen circumstances, the foam precursor does not achieve 100% of its calculated volume (that is, nearly the volume of an empty panel) , the fiberglass insulation will fill the voids between the foam and frame 58, and the panel will not lose its superior insulating properties. Should the foam precursor expand to slightly more than calculated, the fiberglass will compress somewhat more than calculated, to avoid strain on the panel structure. In this way, a much larger margin of error is available when filling the panels with foam precursor.

Once the panel has been injected with foam, pressure must be applied to the panel faces (gypsum board 62 and plywood sheet 64) in order to prevent rupture of the panel by having the faces torn from frame 58 by the expanding foam. In a continuous operation, the panel may be passed through two sets of rollers, upper roller set

74 and lower roller set 76, comprising rollers 72, as may be seen in Figs. 5 and 6. The spacing between upper roller set 74 and lower roller set 76 may be adjusted by means of clamps 78. However, these adjustments are somewhat difficult. The press cannot compensate for small variations in panel thickness if rollers 72 are fixed on upper and lower set 74 and 76 respectively.

Therefore, in this invention, rollers 72 are not rigidly set, as may be seen in Figs. 7, 8, and 9. Upper roller set frame 80 is equipped with elongated slots 82 through which roller axle 84 extends. Axle 84 is then secured with eye bolt 86 in housing 88. Eye bolt 86 is secured by means of nut 92, which is pushed away from housing 88 by spring 90. Thus, spring 90 compresses rollers 72 against panel 50 by pressing eye bolt 86 downward, which in turn presses roller axle 84 and roller 72 downward. Housing 88 is, in turn, secured to roller set frame 80 by means of bolt 94. Since rollers 72 are not fixed in circular openings in set frame 80, the rollers may move up and down a short distance to account for variations in panel thickness across one panel or across several panels of slightly different size. Further, as the panel passes between rollers in roller sets 74 and 76, the immediate proportionate response to the compression spring tends to roll out any developing irregularities of the panel surface, and spread the expanding foam inside of panel 50.

Figures 7, 8, and 9 show one side of upper roller set frame 80. It should be noted that the attachment of rollers 72 to the other side of upper roller set frame 80 must also be made using eye bolts and springs to keep the rollers in upper roller set 74 parallel to the rollers in lower roller set 76. Further, although upper roller set 74 is shown with eye bolts and springs, lower roller set 76 can be equipped with springs instead of or in addition to upper roller set 74.

Due to the high compression needed for the panel, rollers 72 are generally made from an incompressible material such as steel. Therefore, friction between the smooth rollers and smooth panel 50 is small. Thus it can be difficult to move panel 50. This problem is solved with drive belt 68. Drive belt 68 contacts 100% of the panel surface, thus increasing the friction on panel 50 which helps the panels from becoming stuck in the apparatus. Belt 68 is preferably made from some high friction material. Rollers 72 are made from some relatively incompressible material, such as steel. Drive belt 68 thus increases the friction between rollers 72 and panel 50, which helps to prevent panels from being stuck in the apparatus. Further, a floating pressure on rollers 72, rather than a fixed pressure, allows the apparatus to operate with less friction on the drive train, thus, less energy is required to move the panels through the apparatus. Drive belt 68 drives panel 50

through the apparatus. Drive belt 68 is in turn driven by one or both of rotating drums 44. Drums 44 are powered conventionally by motor 46.

Rollers 72 are set so that very little pressure is initially applied to panel 50. A small amount of pressure is appropriate to keep panel 50 moving through the apparatus and to keep the panel flat. If panel 50 should begin to deform due to pressure from the expanding foam inside it, rollers 72 will be displaced by the panel, against springs 90. This will greatly increase the pressure on panel 50, to counteract the expanding foam. In this way, the pressure on panel 50 is kept to a minimum and the amount of energy required to move the panel is also minimized.

This invention has been described as an apparatus and method of manufacturing a building panel, and the product of such manufacture in the best mode known to the Applicant, however, it will be apparent that the invention may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the appended claims.