GB2291002A - Apparatus and method for producing blocks of foam - Google Patents

Abstract

The present invention provides an apparatus and method for producing foam blocks 100 particularly those made of polyurethane utilizing water in place of fluorinated hydrocarbon or other similarly hazardous materials, which are substantially square. The apparatus includes a mold assembly 10 having a slide 12, 14, 16, 18, a top 24 and a bottom 20 defining a mold cavity 22 and a means 70 for controlling the rate of expansion of foam 100 in cavity 22. The method comprises dispensing (e.g. using a drum 90) a given amount of liquid polyurethane into an open mold cavity 22, at least partially enclosing cavity 22 and expanding foam at a controlled rate, and removing foam block 100. Because the rate of expansion of foam is controlled, foam blocks are formed which are substantially square. A scissor link mechanism 70 operated by a hydraulic system 56 with hydraulic cylinder 58 may be used for lowering moveable bottom assembly 46 at a rate proportional to the expansion of the foam thereby controlling rate of expansion of the foam. Alternatively a raisable floating top may be used which may partially enclose cavity 22 or fully enclose it with inserts interposed between its edge and sidewall of assembly 10. <IMAGE>

Description

APPARATUS AND METHOD FOR PRODUCING BLOCKS OF FOAM The present invention relates generally to an apparatus and method for making blocks of foam, which blocks may be substantially square, i.e., flat and orthogonal, and more particularly to a mould assembly having a means for controlling the rate of expansion of foam in a mould cavity and a method of making a polyurethane foam block whereby the rate of expansion of the foam is controlled to yield a substantially square foam block.

In the manufacture of polyurethane, in particularly semi-rigid polyurethane foams such as those used for automotive headliners and other automotive interior trim parts, a liquid polyurethane formulation is typically poured into a mold and allowed to expand or free raise as it changes from its liquid to semi-rigid state. These types of polyurethane foams are generally produced by reacting alcohols with two or more reactive hydroxyl groups per molecule, such as diols or polyols, and isocyanates that have more than one reactive isocyanate group per molecule, such as disocyanates or piolyisocyanates. In addition, flexible foams including semi-rigid foams, are usually made by reacting a polyol with a disocyanate, water and amine and organotin catalyst in the presence of polymeric fillers.

While the prior art teaches the use of fluorinated hydrocarbon, such as Freon , in place of water in the above formulation and such substitution has shown some success in producing a square block of semi-rigid polyurethane foam, water Is presently preferred due to environmental and safety concerns.

A typical mold for this purpose consist of four walls and a bottom, with an opened top, i.e., no lid. When this type of mold is used, the resulting foam block or bun is similar in shape to a loaf of bread having a relatively flat bottom and sides but having a curved or rounded top. The length and width of the polyurethane foam bun will be determined by the size of the mold while the height of the polyurethane foam bun will be determined by the density of the polyurethane foam and its ability to rise when the polyurethane formulation is allowed to free rise.

Typically, the rounded top portion of the polyurethane foam bun must be removed and the bun squared up into a block having flat and orthogonal surfaces prior to slicing the block into blanks or sheets for further processing. There is, therefore, a substantial loss of material, in the range of about 35% to 40% of the total volume of the original foam bun, when the bun is squared up. Most of the loss is due to the removal of the four rounded corners on the top of the foam bun.

Attempts have been made to make foam buns having substantially square sides, top and bottom. For example, flat floating tops which fully enclose the mold cavity and include stops located at the upper mold surface have been utilized to this send. However, this approach has only been modestly successful and often requires the use of fluorinated hydrocarbon in the liquid polyurethane formulation. When the liquid polyurethane formulation includes water, as preferred, the corners of the bun, especially at the top of the bun, remain rounded, even with the use of a full floating top. Similar efforts to alleviate this problem have been attempted by increasing the initial quantity of polyurethane dispensed into the mold cavity, in an attempt to fill the voids between the foam and the floating top.However, with this approach, the top of the bun continues to be somewhat rounded and the resulting density of the foam block is heavier than the desirable density of about 25.62 kg/m3 (1.6 Ibsift3).

It would thus be desirable to provide an apparatus and method for producing a polyurethane foam block which has all sides substantially flat and/or orthogonal, i.e., square, and wherein the polyurethane formulation does not require fluorinated hydrocarbon but rather includes water.

An apparatus and method for producing substantially square foam blocks, in particular, foam blocks made of polyurethane utilizing water in place of fluorinated hydrocarbon or other similarly hazardous material, is provided. The apparatus and method of the present invention provides polyurethane foam blocks which are aubstantially square, i.e., all surfaces of the block are substantially flat and/or orthogonally. The apparatus generally comprises a mold assembly having a side wall, a top and a bottom plate which define a mold cavity and a means for controlling the rate of expansion of the foam in the mold cavity.The method generally comprises the steps of dispensing a given amount of liquid polyurethane into an open mold cavity, at least partially enclosing in the mold cavity, and expanding the foam at a controlled rate and removing the foam block prom the mold cavity.

Because the boundaries of the mold are at least partially constrained and the rate of expansion is controlled, foam blocks are formed which have substantially square, i.e. flat and orthogonal.

In a preferred embodiment of the present invention a mold assembly includes a mold having a side wall, a top and a base defining a mold cavity. A positionable bottom is located in the mold cavity such that the volume of the mold cavity can be varied. A hydraulicallyactuated lift table assembly is coupled to the bottom and enables the mold cavity volume to be varied so as to control the rate of expansion of the foam during the molding process.

In another preferred embodiment of the present invention, a mold assembly includes a mold having a side wall and a bottom defining an open mold cavity. A floating top having corner portions thereof removed is located in and partially encloses the mold cavity. The foam in the corners of the mold cavity are allowed to free rise while the floating top controls the expansion of the center portion of the foam block during the molding process.

In another preferred embodiment of the present invention, a mold assembly includes a mold having a side wall and a bottom defining an open mold cavity. A floating top is located in and encloses the mold cavity. Mold inserts are placed on the floating top and extend at least partially into the mold cavity along the inner walls thereof. As a result of the mold inserts, foam at the perimeter corners of the mold cavity is drawn upward to expand the foam at the edges of the mold cavity at substantially the same rate as the foam at the center portion of the foam block.

In order to appreciate the manner in which the advantages and objects of the invention are obtained, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings.

Understanding that these drawings depict only preferred embodiments of the invention and are not therefore to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: Figure 1 is a perspective of a mold assembly of the present invention having four side walls, a removable top which can be secured to the mold assembly, a base and a bottom which is positionable with the mold assembly for varying the volume of the mold cavity and controlling the expansion of the foam during this molding process; Figure 2 is a cross-section of the mold assembly shown in Figure 1 further detailing a lift table assembly coupled to the bottom plate for movably positioning the bottom within the mold cavity;; Figure 3 illustrates the step of dispensing and mixing the liquid foam formulation into a reduced volume of the mold cavity; Figure 4 illustrates the step of dispensing the liquid foam into the mold cavity; Figure 5 illustrates the step of sealing the mold cavity and controlling the expansion of the foam therein by movably positioning the bottom to vary the volume of the mold cavity; Figure 6 illustrates the step of raising the bottom and removing the foam block from the mold assembly; Figure 7 is a perspective of an alternate embodiment of the present invention which includes a mold assembly having four sides, a base and a floating top in which the corner portions of the floating top are removed to enable the corners of the foam block to expand in a free rise condition while the center portion of the foam block expands under the constraint of the floating top; and Figure 8 is a perspective of an alternate embodiment of the present invention which includes a mold assembly having four sides, a base and a floating top with mold inserts which extend at least partially into the mold cavity for controlling the expansion of the foam during the molding process.

The present invention provides an apparatus and method for making foam blocks, and in particular polyurethane foam blocks which are substantially square. The apparatus generally comprises a mold assembly having a side, a top wall and a bottom wall defining a mold cavity and at least of the walls being moveable to vary the volume of the mold cavity.

The term *substantially square" is meant to imply that the surfaces of the block including the top, bottom, and sides, are substantially flat and/or orthogonal. The substantially square polyurethane foam blocks of the present invention require little if any cutting of the foam prior to further processing of foam block (e.g. slicing the foam block into sheets or blanks). The apparatus and method of the present invention thus reduces the waste previously associated in the manufacture of polyurethane foam blocks for use in automotive applications.

It is believed that a semi-rigid polyurethane formulation generates interior pressure on the order of .35 kg/cm2 (5 Ib/inl while expanding from the liquid to the finished semi-rigid state. The pressure exerted is multi-directional and generates significant frictional or drag forces on the foam at the interface between the expanding foam block and the wall surfaces of the mold cavity due to the large surface area of the sides of a traditional mold assembly.

It is further believed that this results in a non-uniform expansion of foam across the crosssection of the mold assembly. Thus, the foam in the center of the mold is able to rise more quickly since it does not experience this drag. Accordingly, the present invention is directed to providing a means to control the expansion of the foam across the cross-section of the mold, either by presenting additional surface area to the expanding block by increasing the volume of the mold cavity, or by allowing the foam in the corners to free rise while constraining the foam in the center portion of the mold, or by providing mold inserts which facilitate the expansion of the foam in the corners by reducing drag.

As shown in Figure 1, the apparatus of the present invention comprises a mold assembly 10 having four side walls 12, 14, 16 and 18, disposed on top of base 20 such that the side walls and base define a mold cavity 22. Top 24 is disposed on the side walls opposite base 20 for enclosing mold cavity 22. A horizontal hinge 26 connects side walls 12, 14 and 16 to base 20 such that side walls 12, 14 and 16 are pivotally attached about their lower edge to base 20. Vertical hinge 28 plvotally attaches side wall 18 to side wall 12 for providing access to mold cavity 22 from one end of mold assembly 10. Clamp 30 disposed on side wall 18 opposite vertical hinge 28 enables side wall 18 to be detachably secured to a complementary clamp 31 disposed on side wall 16.Side wall 18 further includes a transparent sighting window 19 disposed therein to enable the operator to monitor the interior of mold cavity during the molding process. While the dimension of the mold is dictated by the desired sized of foam block to be produced. the present invention may be employed to manufacture relatively large blocks of foam, on the order of two (2) meters long, one and one-half (1.5) meters wide and one (1) meter deep. One skilled in the art would readily recognize that the present invention may be adapted to produce varying sizes of foam blocks without deviating from the scope of the present invention.

In the preferred embodiment mold assembly 10 is constructed of aluminum plate which provides adequate strength for retaining the polyurethane foam during the molding process while providing a relatively light molding tool. Mold assembly 10 further includes a plurality of substantially identical support braces 32 interdisposed between side walls 12, 14 and 16 and base 20 to reinforce mold assembly 10 and prevent side walls 12, 14 and 16 from buckling. Support brace 32 includes rod 34 having an upper end attached to side wall 12 at upper attachment point 36 and a lower end attached to base 20 at lower attachment point 38. Upper attachment point 36 and lower attachment point 38 provide a pinned connection between rod 34 and side walls 12, 14, 16 or base 20.In the present embodiment rod 34 is approximately 1" in diameter and attached to side wall 12 at a point approximately 3/4 of the distance between base 20 and top 24 and at an angle of approximately 30 off vertical. While in the preferred embodiment mold assembly 10 presently includes three support braces along each side wall 12, 14 and 16, one skilled in the art would readily recognize that the size and number of support braces needed is determined by the internal loads generated during the molding process. Thus, greater or fewer braces may be incorporated as needed.

Top 24 includes support beams 40 axially along the top surface Or top 24 for providing additional rigidity thereto. In the present embodiment, top 24 is manufactured from 3/4" plywood and support beams 40 consist of a pair of 2 by 4's disposed axially thereon. Top 24 is releasably secured to mold assembly 10 by way of nylon straps 42 which extend over top 24 and engage eyebolts 44 disposed on base 20. Nylon straps 42 are of the type typically used for tieing down loads during transportation which can be adjustably tensioned and thus provide a means for releasably securing top 24 to mold assembly 10 in a rapid manner.One skilled in the art would readily recognize that the present invention may be adapted to provide alternative or additional means for securing top 24 to mold assembly 10, including automated closure systems pneumatically or hydraulically powered, without varying from the scope of the present invention.

Referring now to Figure 2, the apparatus of the present invention further comprises a movable bottom assembly 46 disposed within mold cavity 22 and positionable for varying the volume of mold cavity 22. Movable bottom assembly 46 includes floor 48 for providing a substantially flat surface at the bottom of mold cavity 22, subframe 50 disposed beneath floor 48 and providing strength and rigidity thereto and lift table assembly 54 interdisposed between subframe 50 and base 20. Lift table assembly 54 acts to control the position floor 48 within mold cavity 22. Moveable bottom assembly 46 further includes sealing box 52 disposed on the upper surface of floor 48 to prevent leakage of liquid polyurethane from mold cavity 22 during the molding process as will be described in further detail hereafter.

In the presently preferred embodiment, lift table assembiy 54 comprises a hydraulically-actuated scissor-type jack which utilizes hydraulic system 56 including hydraulic cylinder 58 coupled to scissor link mechanism 70 for raising and lowering moveable bottom assembly 46. Scissor link mechanism 70 includes upper rail 72 attached to subframe 50, lower rail 74 disposed on base 20, power link 76 coupled to hydraulic cylinder 58 and pivotally attached to upper rail 72, and follower link 82 pivotally attached to lower rail 74.

Power link 76 is a generally U-shaped member having a cross member and two arms extending therefrom. The cross member of power link 76 is attached to upper rail 72 at pivot 80. Power link 76 further includes roller 78 disposed at the end of each arm opposite pivot 80 for engaging base 20 to provide translational movement of roller 78 along lower rail 74.

Similarly, follower link 82 is a generally U-shaped member having a cross member attached to lower rail 74 at pivot 86 and roller 84 disposed at the end of each arm opposite pivot 86 for providing translational movement of roller 84 along upper rail 72. Power link 76 and follower link 82 are further plvotally coupled at scissor link pivot 88.

Hydraulic cylinder 58 is coupled to power link 76 such that extension and retraction of hydraulic cylinder 58 causes power link roller 78 to translate along lower rail 74. The geometry of scissor link mechanism 70 is such that translational movement of power link 76 causes follower link 82 to translate along upper rail 72 resulting in the vertical displacement of movable bottom assembly 46 in response to hydraulic actuation of hydraulic cylinder 58.

Hydraulic system 56 further includes a source of pressurized hydraulic fluid, such as a pump 64 schematically shown in Figure 1 which provides volumetric flow of hydraulic fluid at an adequate pressure for operating hydraulic system 56. Hydraulic system 56 also includes fluid supply line 60 for fluidly connecting pump 64 to hydraulic cylinder 58. Pressure gauge 66 and flow control valve 68 provide a means for monitoring and selectively controlling the actuation of hydraulic system 56, thereby enabling the controlled positioning of movable bottom assembly 46.

Scissor link mechanism 70 provides a compact and efficient means for movably positioning floor 48 in mold cavity 22 as previously described. While the presently preferred embodiment describes a lift table assembly 54 including scissor link mechanism 70 and hydraulic system 56 for variably positioning movable bottom assembly 46, one skilled in the art would readily recognize that other positioning means including pneumatically systems or conventional spring-damper systems could be incorporated herein without deviating from the scope of the present invention.

Turning now to Figures 3 through 6, a method of molding a substantially square block of foam according to the present invention will now be described. As shown in Figure 3, side wall 18 is swung into an open position to provide easier access to mold cavity 22. Movable bottom assembly 46 is raised within mold cavity 22 to a raised first position. Sealing box 52 is disposed on the upper surface of floor 48 and provides a means for preventing liquid polyurethane from leaking from mold cavity 22. The inner surfaces of side walls 12, 14 16 and 18 can be treated with a suitable wax or releasing agent to facilitate the removal of foam block 100 upon completion of the molding process.Drum 90, which dozes not have a top or bottom, is generally positioned in the center of sealing box 52 and provides a reduced volume wherein the individual components of the liquid polyurethane mixture may be mixed inside drum 90. After sealing box 52 and drum 90 have been loaded into mold cavity 22, side wall 18 is positioned to close mold cavity 22 and clamp 30, 31 (not shc.wn) are engaged to secure side wall 18 to side wall 16. The various reacting components of the polyurethane formulation is dispensed into drum 90 and adequately mixed therein.

After side wall 18 is closed and the polyurethane is thoroughly mixed in drum 90, drum 90 is lifted upwardly allowing liquid polyurethane to spill from the reduced volume of drum 90 into sealing box 52, as shown in Figure 4. In this manner, liquid polyurethane is allowed to quickly flow toward the perimeter of sealing box 52 and gravity acts to evenly distribute the liquid polyurethane therein. While the present invention contemplates dispensing liquid polyurethane into mold cavity 22 via drum 90, other conventional methods of dispensing liquid polyurethane into a mold cavity may be incorporated into the present invention without deviating from the scope thereof. For example, a mixing head disposed on the end of an overhead boom may be used to dispense liquid polyurethane in a serpentine manner along the outside perimeter of sealing box 52.

The viscosity of the liquid polyurethane foam may be varied such that a homogeneous liquid mixture is produced which readily flows into and distributes itself with the mold cavity.

In the present invention, a relatively high viscosity liquid formulation is utilized. The viscosity of the liquid formulation could be lowered with the addition of MDI or other similar constituents to thereby achieve better homogeneity or better distribution within the mold.

After the liquid polyurethane has been dispensed into sealing box 52, top 24 is located and secured over side walls 12, 14, 16 and 18 to enclose mold cavity 22, as shown in Figure 5, thereby preventing the displacement of top 24 during the expansio.1 of the polyurethane foam. As the liquid polyurethane foam expands into its semi-rigid state movable bottom assembly 46 is lowered at a rate proportional to the expansion of the foam, thereby controlling the rate of expansion of the foam. This is achieved by providing hydraulic fluid flows into hydraulic cylinder 58 causing scissor link mechanism 70 to retract downwardly thus lowering movable bottom assembly 46 within mold cavity 22. The hydraulic fluid flow can be monitored and controlled via gauge 66 and flow control valve 68 to maintain the desired rate of expansion of the foam.

In the presently preferred practice of the invention, the rate of travel of movable bottom assembly 46 is approximately equal to the rate of volumetric expansion of the polyurethane foam in mold cavity 22. In one embodiment of the present invention, a reasonably accurate rate of travel for movable bottom assembly 46 may be obtained by maintaining a constant hydraulic pressure in hydraulic cylinder 58 which reacts the internal forces generated in the mold cavity 22 by the expansion of the polyurethane foam. Alternately, a timed rate of travel may be incorporated into the present invention by computing a predicted rate of volumetric expansion of the polyurethane foam in mold cavity 22 and programming hydraulic system 56 to provide the appropriate rate of travel for movable bottom assembly 46. The rate of volumetric expansion is not necessarily linear with respect to time or with respect to the forces exerted in the mold cavity. Because the rate of expansion of the foam within mold cavity 22 is not necessarily linear with respect to time or internal forces1 one skilled in the art would readily recognize that control modes which provide non-linear control of the rate of translation of movable bottom assembly 46 may be incorporated into the present invention.

Once movable bottom assembly 46 has reached the end of its downward travel, mold cavity 22 is at its final volume. The polyurethane foam in mold cavity 22 is allowed to complete its expansion and conversion from a liquid state to a semi-rigid state. Polyurethane foam block 100 is then allowed to sufficiently cure so that it may be removed from mold assembly 10 without distorting the final shape.

Referring to Figure 6, the removal of foam block 100 is illustrated whereby movable bottom assembly 46 is raised upwardly to free polyurethane foam block 100 from mold assembly 10. At this point polyurethane foam block is substantially free from side walls 12, 14, 16 and 18. Clamp 30, 31 (not shown) are released and side wall 18 swung open to provide access into mold cavity 22. Polyurethane foam block is pushed out of mold cavity 22 through the opening created when side wall 18 is opened about vertical hinge 28 and removed from a mold assembly 10.

Referring now to Figures 7 and 8, an alternate embodiment of the present is shown in which mold assembly 110 incorporates a floating top 124 which is positionable within mold cavity 122 in place of movable bottom assembly 46 heretofore described in the first preferred embodiment and illustrated in Figures 1 through 6. Mold assembly 110 includes side walls 112,114,116and118andbase120. Sidewalls112,114and116areaLtachedtobase120 via horizontal hinge 126 while side wall 118 is attached to side wall 112 via vertical hinge 128.

Clamp 130 is disposed along the edge of side wall 118 and engages a complementary clamp 131 on side wall 116 to securely close mold assembly 110 and thereby define mold cavity 122. Mold assembly 110 further includes floating top 124 which is sized to fit within mold cavity 122 and allowed to translate vertically therein. Cross member 123 is coupled to floating top 124 via a suspension member, such as chain 125, that cross member 123 can be disposed across side walls 112 and 116 to suspend floating top 124 in mold cavity 122.

While not illustrated in Figure 7 and 8, appropriate support bracing may be incorporated into mold assembly 110, as previously described, to provide adequate rigidity to the mold during the molding process. In addition, cardboard sidewalls (not shown) treated or covered with a suitable material such as "onion skin" may be disposed within mold cavity 122 along the inner surfaces of side wall 112,114,116 and 118 and along base 120 and floating top 124 to facilitate in the removal of foam block 100 once the molding process is completed.

As shown in Figure 7, floating top 124 has a removed portion or notch in its periphery 132 at each of the corners thereby defining opening 134 between the sidewalls and the top for allowing foam block 100 to free rise in the corners of mold cavity 122 while constraining the rate of expansion of the center portion of foam block 100 with floating top 124. In an exemplary embodiment, the opening at each corner is generally triangular in shape and having dimensions approximately 180 mm along each side of the mold. It is believed that the dimensions of the openings are governed by the particular polyurethane formulation being utilized and more specifically the surface tension generated by the foam as it expands. Thus, while these dimensions are typical for a given polyurethane formulation, they are not intended to limit this scope of the present invention.Furthermore, the invention as herein described includes a floating top having corner portions removed, one skilled in the art would readily recognize that the present invention contemplates other notches employed about the periphery of the floating top to allow free rise condition of the foam therealong.

At the start of the molding process, floating top 124 is removed from mold cavity 122 and liquid polyurethane is dispensed into mold cavity 122 as previously described. Floating top 124 is placed into mold cavity 122 and suspended from cross member 123 via chain 125.

As the polyurethane foam expands from its liquid state to Its semi-rigid s:ate, it engages the suspended floating top 124. The additional weight of floating top 124 acting on foam block 100 acts to control the rate of expansion of the foam at the center of foarn bun while allowing the corner portions to free rise resulting in a uniform expansion across he cross section of foam block 100. Upon completion of the expansion and curing of foam block 100, side wall 118 is opened and foam block 100 can be removed from mold cavity 122.

Referring now to Figure 8, an alternate embodiment of floating top 124 further includes a plurality of mold insert assemblies 140 disposed at the corners of floating top 124' and extending into mold cavity 122. In the present embodiment, treated or covered cardboard may be used to fabricate mold insert assembly 140. However, other suitable materials could be utilized without deviating from the scope of the present invention. Mold insert assembly 140 is generally in the shape of a right triangular prism and includes top portion 142 extending over and engaging a corner of floating top 124', first side wall portion 144 and second side wall portion 146 extending downward from top portion 142 and into mold cavity 122.First and second side wall portion 144, 146 are interdisposed between floating top 124 and a side wall of mold assembly 110 to provide a travelling corner mold surface within mold cavity 122 which translates therein in conjunction with floating top 124'.

In an exemplary embodiment, the first and second wall portions are rectangular, approximately 180 mm X 180 mm and extend approximately 180 mm inio the mold cavity.

The molding process of foam block 100 shown in Figure 8 is s:lbstantially similar to that described in the embodiment illustrated in Figure 7. Mold insert arSembly 140 acts to reduce the drag forces which occur at the corners of mold assembly 110 by providing a travelling mold surface in the mold cavity corner as floating top 124 is pushed upward.

While the invention as herein described includes mold inserts placed in the corner of the mold cavity, one skilled in the art would readily recognize that the mold insert could be adapted to extend into the mold cavity along any portion of the periphery of the mold cavity to encourage expansion of the foam therealong.

Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention which includes a mold assembly having a means for controlling the rate of expansion of foam in a mold cavity and a method for molding a foam block by controlling the rate of expansion of the foam which is particularly suited for manufacturing substantially square blocks of foam with a polyurethane formulation which includes water in place of fluorinated hydrocarbon. The present invention can be employed to fabricate foam blocks in a variety of forms. For example, the preceding detailed description has been described with particular reference to a generally cross-section. However, one skilled in the art would readily recognize that the present invention may be used to form a foam block having a circular, triangular or any other shaped cross-section by providing appropriately shaped side walls. Therefore, while this invention hat been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification and following claims.

Claims (16)

1. A mold assembly of the type where a metered amount of mixed foam formulation is dispensed into the mold assembly and allowed to expand and polymerize therein for molding a block of foam, the mold assembly comprising: a mold having a side wall, a top disposed at a first end of said side wall, and a base disposed at a second end of said side wall opposite said top, said side wall, base and top defining an mold cavity; and means for controlling the rate of expansion of at least a portion of the foam in said mold cavity such that a substantially constant rate of expansion of the foam occurs throughout said mold cavity during the polymerization thereof.

2. The mold assembly of Claim 1 wherein said means for controlling the rate of expansion comprises a movable bottom assembly having a bottom inlerdisposed between said top and said base within said mold cavity; and positioning means coupled to said bottom for adjustably positioning said bottom plate within said mold cavity and varying the volume of said mold cavity.

3. The mold assembly of Claim 2 wherein said positioning means comprises: a first link interdisposed between said base and said bottom plate and having a first end pivotally connected to said bottom plate and a second end engaging said base; a second link interdisposed between said base and said bottom plate and having a first end pivotally connected to said base and a second end engaging said bottom plate; said first and second link being coupled together for coordinated movement thereof to raise and lower said bottom; and driving means coupled to said positioning means for causing coordinated movement of said first and second link.

4. The mold assembly of Claim 3 wherein said driving means comprises a fluid actuated power cylinder.

5. The mold assembly of Claim 2 wherein said positioning means positions said bottom plate in a first position when the liquid foam formulation is dispensed into said mold cavity, and wherein said positioning means lowers said bottom plate to a second position at a rate of travel proportional to the rate of expansion of the foam formulation.

6. The mold assembly of Claim 2 wherein said mold assembly further comprises securing means for detachably securing said top plate to said side wall.

7. The mold assembly of Claim 1 wherein said top further comprises: a floating top having a peripheral edge and being disposed within and partially enclosing said mold cavity; suspension means for suspending said floating top above aid base within said mold cavity; and said controlling means comprise said peripheral edge and said side walls having an opening therebetween for allowing free expansion of the foam therethrough.

8. The mold assembly of Claim 1 wherein said top further comprises: a floating top having a peripheral edge and being disposed within and completely enclosing said mold cavity; suspension means for suspending said floating top above said base within said mold cavity; and said controlling means comprises a mold insert interdisposed between a portion of said peripheral edge and a portion of said side wall, said mold insert being at least partially disposed within said mold cavity.

9. The mold assembly of Claim 8, wherein said side wall forms a corner and said mold insert is disposed with said corner.

10. A method of molding a block of foam in a mold assembly having a mold cavity, the method comprising the steps of: dispensing a metered amount of liquid foam formulation into the mold cavity; enclosing the mold cavity; controlling the rate of expansion of the foam during the polymerization and expansion thereof such that a substantially constant rate of expansion of the foam occurs throughout said mold cavity; and removing the block of foam from the mold assembly after the block of foam is sufficiently polymerized to enable handling of the block of foam without distortion.

11. The method of molding a block of foam of Claim 10 wherein the step of controlling the rate of expansion of the foam comprises adjustably increasing the volume of the mold cavity proportional to the rate of expansion of the foam.

12. The method of molding a block of foam of Claim 10 wherein the step of controlling the rate of expansion of the foam comprises expanding a first portion of the foam in a free rise state, and constraining the expansion of a second portion of the foam, thereby equalizing the rate of expansion of said first and second portions of foam.

13. The method of molding a block of foam of Claim 10 wherein the step of controlling the rate of expansion of the foam comprises providing a travelling wall surface in the mold cavity.

14. The method of mold a block of foam of Claim 10 wherein the step of dispensing a metered amount of liquid foam formulation comprises: providing a mixing container In the mold cavity for mixing the liquid foam formulation therein; dispensing liquid foam components Into said mixing container and mixing said components into the liquid foam fiormulation; rapidly dispensing the liquid foam formulation from said mixing container into said mold cavity.

15. A mould assembly substantially as described herein with reference to the accompanying drawings.

16. A method of moulding a foam block, the method being substantially as described herein with reference to the accompanying drawings.