CA2165210A1 - Continuous plastics molding process and apparatus - Google Patents

Abstract

A continuous process and apparatus for forming products from thermoplastic materials between top and bottom mold carriages is disclosed. Each carriage has a frame including a backup plate coated with a low coefficient of friction material over which slides a continuously moving belt mold. The belt mold is comprised of a flexible silicone rubber mold adhered to a fiber belt.
The silicone rubber mold has a surface of desired shape for mating with an opposed mold surface to form a continuously moving mold channel into which is fed thermoplastic material at a moldable temperature. After molding the hot plastic material, localized surface heat of the belt molds is removed by cold air blown against the belt mold. The low coefficient of friction backup plates have numerous air-bearing holes for feeding high pressure air between the low coefficient of friction plates and the moving fiber belt to reduce friction and reduce wear. The fiber belts are guided and driven by a wide V-shaped central ridge or by twin-wide V-shaped ridges near their edges. The V-shaped ridges fit into and mesh with corresponding geared teeth in grooves of the sprocket drive rolls and operate to maintain alignment of the mold belts. An electric drive motor, with or without the assistance of a torque motor, drives both belt molds in unison to maintain their relative alignment. Electric screw jacks raise the top carriage, extend and retract the grooved exit rolls, and fine tune the alignment of the moving belt molds by adjusting the grooved exit rolls and move the machine to and from the extruder.

Description

2 1 6 52 ! O

Case No.: KEMCO-002A
Pat. Appln.

5CO~ NUOUS PLA8TICS MOLDING PROCESS AND APPARATUS

Field of the Invention The present invention relates generally to plastics molding and more particularly to a continuous process and apparatus for forming products from thermoplastic materials between top and bottom mold carriages. Each carriage has a frame including a backup plate coated with a low coefficient of friction material over which slides a continuously moving belt mold. The belt mold is comprised of a silicone rubber mold adhered to a fiber belt. The silicone rubber mold has a surface of desired shape for mating with an opposed mold surface to form a continuously moving mold channel into which is fed moldable thermoplastic material. After molding and cooling the hot plastic material, localized surface heat of the belt molds is removed as the belts return to the entry end of the machine through ducts of cold air moving in the opposite direction.

- 25Backqround of the Invention An apparatus and process for forming products from thermoplastic polymeric material having three-dimensional patterns and surface textures is disclosed in U.S. Patent Nos. 4,128,369 and 4,290,248 .

In the apparatus and process disclosed in said patents a thermoplastic material to be formed is heated above its glass transition temperature before introduction between travelling flexible belt molds, which revolve in opposed relationship. The flexible belt molds each include a thin, flexible sheet-metal belt of relative high thermal conductivity and form a traveling mold channel, at least one having a flexible three-dimensional pattern formed on its front face. Opposed nip rolls press the revolving belt molds against the entering thermoplastic material. At least one belt mold travels partially around the nip roll and impresses its three-dimensional pattern into the heated plastic material in a progressive localized rolling, squeezing action in the nip region. Thereafter, a series of backup rolls along the mold channel hold the traveling belt molds against the impressed material for maintaining the impression while being cooled by liquid coolant into the memory-retention state. A cooling liquid, mainly water at room temperature, is moved along the backup rolls and applied to the back surface (inside surface) of each thermal conductive steel belt for cooling each belt mold.
After the plastic material has been sufficiently cooled to retain three-dimensional patterns, the flexible belt molds are separated from it. Large area architectural panels can be produced. Belt molds are shown as including wide, thin, endless, flexible metal belts, at least two-feet wide, having a wide flexible mold formed of a heat-resistant material, such as rubber, bonded to the metal belt.
The prior disclosed apparatus utilizes thin steel belts which revolve upon large flat surface drive pulleys.
Steel belts suffer from the inherent problems of being susceptible to dents, crimped edges, and rust. They also require a weld seam. Steel belts present difficulties in the maintenance of alignment as they travel over flat surfaced metal pulleys.
Steel belts are susceptible to denting, crimping, rusting, and camber because they are extremely thin, being typically 0.025 to 0.075 of an inch thick. The use of such extremely thin steel belts in an industrial environment increases the probability of incurring damage thereto.
The use of a metal belt requires that the drive pulleys be comparatively large because the metal belt cannot be made to continuously travel over small-diameter pulleys. Small pulleys cause bend-yield-stress elongation of thin metal belts. Thus, the drive pulleys in the prior disclosed apparatus must be fabricated of a sufficient diameter to accommodate the metal belt and consequently the drive pulleys occupy a substantial amount of space within the disclosed machine. Thus, the space available for -cooling and other apparatus is strictly limited.
A weld seam is required in the formation of an endless-loop metal belt. An elongate planar sheet of metal is looped about itself and welded together to form the belt, thus forming a weld seam. The formation of such an endless-loop metal belt, without damaging it, is necessarily a time-consuming and somewhat difficult task.
The weld seam should be made to keep the belt edges parallel to each other and be ground flush to prevent distortion of the flexible rubber mold which is to be subsequently formed on the outer surface of the welded planar metal belt.
Further difficulties in the maintenance and alignment of the metal belt of the apparatus disclosed in said patents occur because the metal belt is installed upon flat pulleys which lack any self-aligning characteristics.
Sixty or more small-diameter rollers function to maintain the two travelling mold surfaces of the prior art apparatus in close contact. The small-diameter steel rollers rotate continuously and are continuously exposed to the liquid coolant, which is comprised mainly of water.

They are subject to frequent malfunction and require periodic maintenance. Also, the use of such numerous small-diameter rollers does not facilitate maximum intimate contact of the opposing travelling mold surfaces because of the many gaps inherently formed between such rollers. The 2165~1~

multiplicity of these steel rolls causes the travelling flexible molds to experience considerable fluctuations in contact pressures as they successively travel over roller-gap-roller-gap-roller, etc.
In the prior disclosed apparatus, an offset is formed between the inside edge of the exit rollers and the path of the molded product to help strip the belt molds from the molded product. That is, the circumference of each exit roller is not tangential to the plane of one surface of the molded product path, but rather the bottom roll is downward and the upper roll is upward away from the molded product path, in order to help separate the belt molds from the molded product. This offset reduces the support provided to the molded product, thereby requiring that the molded product be sufficiently cooled and rigid to resist deformation prior to passing between the exit rollers.
The prior disclosed apparatus utilizes hydraulic actuators to tension the mold belts, provide a compressive force to maintain contact of the two opposing mold belts, and to lift the upper mold assembly off of the lower mold assembly to facilitate maintenance and the changing of mold belts.
As is well known in the art, hydraulic actuators require the use of a motor, pump, various hoses and valves, and actuator cylinders. The hydraulic system must be maintained in a leak-free condition in order to function 2 ! 652 1 0 properly and prevent contamination of the molded product.
Hydraulic systems constantly consume electrical energy when the apparatus is operative. That is, the hydraulic motor and pump must constantly be running in order to provide pressure to maintain and change position of the hydraulic actuators. The motor and hydraulic pump are inherently noisy and commonly located in close proximity to the apparatus. This makes the working environment of the apparatus extremely uncomfortable and contributes to an unsafe and unhealthy working environment.
The prior art discloses an apparatus and process that primarily removes the heat of the hot plastic by moving cold water along the small diameter backup rolls against the backside of the thin steel belts. This back-surface water cooling method proves inefficient because the heat of the plastic must first pass through the thick low thermal conductive silicone mold on at least one belt mold. The silicone mold material has a low thermal conductivity with a K factor of about 0.10 compared with the mild carbon steel which has a K factor of about 26Ø The K factor values for the materials are expressed in units of BTU per hour through a square foot per degree Fahrenheit of temperature difference per foot.
In addition to the difficulty of removing the heat of the plastic through the low thermal conductive silicone, this prior art back-surface method of cooling did not _, provide the means to control the temperature of the belt molds. It is desirable for good molding conditions to have the belt molds consistently at about the same temperature as the molds first contact the hot plastic each time they return to the entry end.
The back-side fluid cooling method also involves a water sump under the machine; a water cleaning system;
water chillers or water cooling tower; and a water recirculating system. This equipment needs constant maintenance, causes high humidity in the work place, and increases the cost of operating the machine.
Therefore, the prior disclosed apparatus and process has a variety of deficiencies which detract from its effectiveness, efficiency, and marketability. In view of the shortcomings of the prior disclosed apparatus, it is desirable to provide an apparatus and process which does not utilize thin steel belts and consequently is not susceptible to crimps and dents; does not have weld seams;
is not susceptible to rust and camber; and does not have difficulties in the maintenance of alignment as it travels over flat surfaced pulleys. It would be desirable to provide an apparatus with belt molds that can include a ridge and a gear or cog arrangement that will fit and mesh with a matching grooved drive roll sprocket as a means of maintaining mechanical alignment, both laterally and in the forward motion feeding direction. It would also be 2t65210 desirable to provide an apparatus which does not use a plurality of small-diameter rollers to maintain intimate contact of the upper and lower belt molds. These rolls require periodic maintenance as they are subject to the effects of wear due to friction and to exposure to the coolant water being applied to the steel belts.
Further, it would be desirable to provide an apparatus which uses small-diameter entrance and exit rollers to reduce the length of the mold belts required, increase the space available for cooling and other equipment, and reduce the size and cost of the machine as a whole.
Further, it would be desirable to provide an apparatus which does not require the use of hydraulic actuators and consequently would eliminate the need for a motor, pump, various hoses and valves, and actuator cylinders, as well as the requirements for maintaining these items in a leak-free state. It would also be desirable to provide an apparatus which operates quietly and does not constantly consume electrical energy.
Further, it would be desirable to provide an apparatus which does not utilize an offset between the exit rollers and the plane of the product path so that support is continuously provided to the molded product as it travels the length of the machine onto the product conveyors.
Further, it would be desirable to provide an improved means and apparatus to remove the heat from the surface of ~ ~ 21G52t~
~, the silicone molds. Extracting the heat through the silicone and the steel belt backing with cold water moving against the thin steel backing is an inefficient exchange of heat and limits production rates. Further, it improves the molding operation if the heat of the belt as it first contacts the hot plastic is controlled. This can be accomplished by controlling the cooling of the belt molds through a series of dampers in the cold air ducts that provide the means to vary the temperature of the molds by varying the amount of chilled air blowing on the belt molds as well as the ability to control when the belt molds will be cooled on their return to the entry end of the machine.

Summary of the Disclosure The following description and drawings disclose a new, improved process and apparatus for the continuous forming of products from thermoplastic polymeric material having three-dimensional patterns and surface textures.
The process and apparatus described in United States Patent Nos. 4,290,248 and 4,128,369 was disclosed eleven and thirteen years, respectively, prior to this application. Since then much has been learned, product design specifications have become more demanding, and new technology has become available. The apparatus and process embodying the present invention produce a molded plastic 21652~0 product having closer tolerances on a less-costly machine.
The machine is easier to maintain, uses less energy, is less expensive to operate, and is quieter in operation.
The present invention specifically addresses and alleviates the above-mentioned deficiencies associated in the prior art. More particularly, the present invention provides a continuous process and apparatus for forming products from thermoplastic materials between top and bottom mold carriages.
Each carriage has a frame including a backup plate coated with a low coefficient of friction material over which slides a continuously moving belt mold. The belt mold is comprised of a silicone rubber mold adhered to a multi-ply woven fabric belt made of non-metallic fibers.
The silicone rubber mold has a surface of desired shape for mating with an opposed mold surface to form a continuously moving mold channel into which is fed moldable thermoplastic material.
After molding the hot plastic material, surface heat localized in the surfaces of the belt molds is removed by cold air blowing from one or more air conditioning units directly onto the mold surfaces, preferably at temperatures about 35F to about 50F. The cold air is directed by a series of dampers in the air ducts to blow counter to the direction the belt molds are travelling and to cool the belt molds as desired in certain zones of their return to the entry end.
The low coefficient of friction backup plates have numerous air-bearing holes for feeding high-pressure air between the low coefficient of friction plates and the moving fiber belt to provide an air-bearing effect to reduce contact pressure and friction.
The fiber belts are guided and driven by a wide V-shaped central ridge or by twin V-shaped wide ridges near their edges. The V-shaped ridges fit into and mesh with corresponding grooves of the sprocket drive rolls and operate to drive the belts and to maintain alignment of the belt molds. An electric drive motor, with or without the assistance of a torque motor, drives both belt molds in unison to maintain their relative alignment. Electric screw jacks raise the top carriage, extend or retract the grooved exit rolls, and fine-tune the alignment of the moving belt molds by adjusting the grooved exit rolls.
The use of fabric belts eliminates weld seams, crimps, dents, and rust. The use of fabric belts also eliminates many of the alignment problems associated with the prior art steel belts. Additionally, the use of fabric belts permits the use of smaller diameter pulleys, thus providing more room for cooling and other equipment. The use of smaller diameter pulleys also reduces the required length of the mold belts.

21652~û

The use of a low coefficient of friction backup plate with air bearings eliminates the requirement for a plurality of small-diameter rollers. The backup plates stabilize the flexible travelling mold channel in height, configuration, and orientation, and provide belt contact pressure consistently as the flexible belt molds travel from the entry to the exit end of the machine. In addition, the associated problems of wear due to friction, the significant manufacturing costs, and the associated maintenance requirements are likewise eliminated.
The screw jacks used in the machine embodying the present invention operate quietly, consume power only when being used, and provide precision positioning of the moved parts. The screw jacks thus eliminate the problems associated with the prior art use of hydraulic actuators which require a motor, pump, various hoses and valves, and actuator cylinders; must be maintained in a leak-free state; operate loudly; and constantly use energy when running.
The use of small drive rolls, instead of the larger pulleys required by the use of steel belts in the prior art, makes it possible to construct a machine incorporating the present invention in a simpler and less expensive manner. The use of smaller diameter rolls makes maintenance and handling of the upper carriage substantially easier; provides room for cooling apparatus;

21 6~21 0 and reduces the required length of the mold belt.
In a machine embodying the present invention, the exit rolls are mounted in the same plane as the plane of the molded product and thus provide support to the molded product as it passes between the exit rolls to the product conveyor.
The exit rolls in a machine that embodies the present invention may also be crowned to aid in alignment of the fabric belt, thus simplifying maintenance and operation.
Air cooling is effective due to the use of counter-current-flow and a fabric belt. The use of counter-current-flow provides maximum heat exchange between the heated mold surface and the cooling air. The fabric base, has a low heat capacity and low thermal conductivity similar to the silicone molds. It therefore operates to keep the heat absorbed from the hot plastic near the surface of the belt mold where it may be readily extracted by cold air directly impinging against the mold surfaces.

` ` 2 1 6521 ~
--13a-According to one broad aspect the invention relates to a continuous molding apparatus having an input end and an output end, for molding heated thermoplastic material. The apparatus comprises a first flexible belt having a first mold formed upon the exterior surface thereof; a second flexible belt having a second mold formed upon the exterior surface thereof, the second flexible belt being disposable in l~ml n~r juxtaposition to the first flexible belt such that the first and second molds form a mold channel therebetween; a means for conveying the first and second flexible belts such that the mold channel moves from the input end to the output end of the continuous molding apparatus; and a means for air cooling the first and second molds by the application of air blown thereover.
According to a further broad aspect, the invention relates to a machine for continuous molding of thermoplastic material heated to a moldable temperature comprising: a bottom carriage; a top carriage positioned above and in alignment with the bottom carriage; the machine having an entry for continuously receiving heated thermoplastic material at moldable temperature and having an exit for continuously discharging molded thermoplastic material; the bottom carriage having a bottom drive roll rotatably mounted thereon and being positioned below the entry and having a bottom exit roll rotatably mounted thereon and being positioned below the exit. The top carriage has a top drive roll rotatably mounted thereon and is positioned above the entry and having a top exit roll rotatably mounted thereon and being positioned above the exit; a bottom flexible belt mold movable in a path around both -13b-the bottom drive roll and the bottom exit roll; a top flexible belt mold movable in a path around both the top drive roll and the top exit roll; molding surfaces of the top and bottom belt molds being adapted for engaging in mating relationship defining at least one mold channel between the bottom and top belt molds extending from said entry to the exit; means associated with the top and bottom drive rolls for enabling driving of the top and bottom drive rolls for driving said belt molds along the paths, for continuously moving the molding surfaces in the mating relationship, for continuously moving said mold channel from the entry to the exit, and for returning the top and bottom belt molds in separated relationship from the exit to said entry; and air cooling means for directing air against the molding surfaces as the top and bottom belt molds are returning from the exit to the entry for cooling said molding surfaces of the top and bottom belt molds as they are returning to said entry.
According to a further broad aspect, the invention relates to apparatus for continuous molding of thermoplastic material heated to a moldable temperature comprising: first and second flexible belt molds each including a flexible mold having a molding surface and each including a flexible backing on said mold; the molding surfaces of the first and second belt molds being matable for defining at least one molding channel extending along the belt molds between their mated molding surfaces; at least one ridge on the backing of the first belt mold; at least one ridge on the backing of the second belt mold; and the ridges extending along the respective belt molds.

--13c-srief Description of the Drawinqs Figure 1 is an elevational view of the new, improved apparatus for the continuous forming of products from thermoplastic polymeric material, with certain parts being - 21 b5210 shown in section;
Figure 2 is an enlarged partial elevational sectional view of the input or front end of the apparatus shown in Figure 1;
Figure 3 is a cross-sectional view taken along the line 3-3 in Figure 2;
Figure 4 is a partial cross-sectional view taken along the line 4-4 on Figure 1 showing one of the wide drive roll sprockets;
Figure 5 is a partial cross-sectional view taken along the line 5-5 on Figure 1 showing a crowned and grooved exit idler roll;
Figure 6 is a partial cross-sectional view similar to Figure 4 for showing a wide drive roll twin sprocket, which is an alternative to the drive roll sprocket shown in Figure 4;
Figure 7 is a cross-sectional view generally similar to Figure 3 for showing an alternative twin-ridged fiber belt supported on a twin-channeled guide plate. This twin-ridged fiber belt is also seen in Figure 6 being driven bythe twin-drive sprocket shown in Figure 6;
Figures 8A and 8B are cross-sectional views taken generally along the plane 8A-8A and 8B-8B through the apparatus of Figure 1. (For clarity of illustration, the mold belts have been removed in Figure 8A. The belt molds are shown in section in Figure 8B while components of the -frame and drive train are omitted from Figure 8B for clarity of illustration.);
Figure 9 is a partial cross-sectional view through a pair of opposed fiber belt molds which are properly aligned; and Figure 10 is a view similar to Figure 9 for showing how the product is deformed, when the fiber belt molds are not properly aligned.

Detailed Description of the Preferred Embodiment The new, improved process and apparatus for the continuous forming of products from thermoplastic polymeric material will now be described in detail with reference to the drawings. The same reference numbers are used in the various views to indicate the same components of the apparatus. Alternative embodiments of components of this apparatus are described and shown.

FRAME
Referring now to Figures 1-3, 7, 8A, and 8B, a metal frame 20 (Figures 1 and 8A) is comprised of steel side plates 21 (shown in Figure 8A), backup plates 22 (Figures 1, 2, 3, and 7), and cross-bracing members 23 lFigure 1).
The motors 48 and 48A, wide sprocket drive rolls 43, backup plates 22, grooved exit rolls 51, air conditioners 76, and other auxiliary equipment are mounted to this frame. The sides of the frame 20 may have lightening holes (not shown) to reduce their weight and provide easy access to wiring and miscellaneous mechanical and electrical equipment mounted inside the frame 20.
The frame 20 that forms the sides 21 of the bottom carriage 25 (Figures 1, 8A, and 8B) is joined at the top by the bottom backup plate 22B (Figures 2, 3, and 7) and cross-bracing members 23 (Figure `1). The bottom backup plate 22B and cross-bracing members 23 act as transverse stiffening webs which greatly stiffen the frame 20 of the bottom carriage 25. Similarly there is stiffening of the frame 20 of the top carriage 35, to be described later, so that their side plates 21 (Figure 8A) can be thinner than otherwise. One side of the bottom carriage 25 is joined to two (only one is seen in Figure 8A) vertical rectangular tubings 24 (Figures 8A and 8B) which are anchored onto a heavy metal floor base 26 (Figures 8A and 8B). The floor base 26 may be fitted longitudinally with inverted angle irons 27 (Figures 8A and 8B), V wheels, or similar means of sliding or rolling the machine 30 (Figure 1) away from the extruder 28 (Figure 1) to allow space to provide extruder or mixer maintenance and to change extruder dies 29 (Figures 1 and 2).
In operation, the machine position is adjusted as close as necessary to the extruder feeding die 29 (Figures 1 and 2) to provide the belt molds 34 and 36 with the melted plastic feed stock 77 (Figures 2 and 8B). The heated melted thermoplastic material is moldable. If the product is to contain foamed plastic, the foamed plastic being fed from the extruder feeding die 29 (Figures 1 and 2) is at an early stage of its foaming action to control finished product density and to produce a quality product.
The frame 20 (Figures 1 and 8A) that forms the sides of the top carriage 35 (Figures 1, 8A, and 8B) is stiffened by joining its sides 21 at the bottom by the top backup plate 22A (Figures 1 and 2) and cross-bracing members 23 (Figure 1). One side of the top carriage 35 has two (only one is seen) vertical slides 31 (Figure 8A) that are housed inside the two vertical rectangular tubings 24 (Figures 8A
and 8B). The top carriage can be raised by electrical screw jacks 32 (Figure 8A) up about eight inches from its lowest position in which the top carriage 35 (Figure 1) is resting against the bottom carriage 25 (Figure 1) or against set pins on the sides 21 of the bottom carriage 25.
It is necessary to raise the top carriage 35 to change the belt molds 34 and 36 as required to produce a product of a different design or pattern. The top carriage 35 is held in a raised, cantilevered position by the slides 31 (Figure 8A) held inside the two vertical tubings 24 anchored to the floor base 26. The top carriage 35 is lowered to bring the top and bottom belt molds 34 and 36 (Figures 1 and 8B) together to form the mold channel 33 (Figure 8B) in which the melted plastic is formed, cooled, and set.
The wide rectangular air-bearing chambers 63 (Figures 1, 2, 3, and 7), described later, which extend the length of the top and bottom carriages 35 and 25, respectively, as shown in Figure 1, act as strong, wide rectangular box beams which resist deflection and distortion of the mold carriages 35 and 25. The side plates 21 can be less massive than otherwise, because of the stiffening action of these air-bearing chambers 63.
On a machine embodying the present invention, as depicted in Figure 1, fiber belts 37 and 38 are cooled by removing surface heat from the mold surfaces 78 (Figure 8B) of the top 39 and bottom 40 molds with cold air while the surfaces of molds 39 and 40 are moving adjacent to chilled air in ducts 74. Such cold air 79 is being blown in a direction counter to the moving belt molds as the belt molds are returning from the exit end of the machine to the entry end, as will be explained in detail later.
Electrical screw jacks 56 provide positive and precise movement of the top carriage 35 and of the grooved exit rolls 51. Screw jacks are preferred to the prior art use of hydraulic jacks, since screw jacks only consume electrical power when they are being used to effect a change in position. Hydraulic jacks, on the other hand, constantly consume power merely to maintain position since 21 6521 0~

a hydraulic pump must constantly be driven by a constantly running electric motor.
The top carriage slide 31 provides a simple, perpendicular mating fit of the upper 34 and lower 36 belt molds and operates to open with a straight, vertical lift rather than in a clam shell fashion as occurs in the prior disclosed apparatus.
The molded product 52 is further cooled as necessary by passing through a water bath or spray, or by passing through downstream air-cooling ducts 84 (Figure 1). The cooled finished product "P" is cut to length as it continues to travel by a cutting means 85 (Figure 1), for example, a shearing, sawing, or similar device- moving at the same speed as the product.

FIBER-BACKED BELT MOLDS
Fiber belts 37 and 38 (Figures 3, 4, 6, 7, and 8B) for the belt molds 34 and 36 are each made of plies of woven fibers, such as nylon, polyester, or cotton, that are commercially bonded together. Both a four-ply woven cotton hot stock and water belt, Model 47, available from Beltservice Corporation of Sacramento, California, and a four-ply woven polyester belt available from Sparks Belting Company of Pomona, California, have proven to be satisfactory fiber backing for the endless belt molds 34 and 36. Fiber belts are preferred to prior art thin metal belts because fiber belts provide a belt mold backing with true parallel edges and have no weld or camber, and they have only about one-hundredth of the thermal conductivity (K
factor) as steel. Additionally, fiber belts will not dent, crimp, or rust, and are easier to store and handle.
The outer side of each of the top 37 and bottom 38 fiber belts (Figures 3, 4, 6, 7, and 8B) has a rough stipple or cloth surface to optimize the adherence of the respective top 39 and bottom 40 silicone rubber molds (Figures 3, 4, 6, 7, and 8B). The rubber silicone molds 39 and 40 may be comprised of General Electric RTV664 silicone rubber, manufactured by General Electric Company.
Another advantage of using a fiber belt instead of a thin steel belt is that the inner side of the fiber belt 37 and 38 can have a wide, flattened V-shaped ridge 41 (Figures 4 and 5) or other shaped ridge, or have a pair of spaced twin ridges 41 (Figures 6, 7, and 8B) that will fit a matching groove 42 (Figures 4 and 5) or grooves 42 (Figures 6, 7, and 8B) in the sprocket drive roll 43 (Figures 1, 2, 3, 4, 6, 8A, and 8B). The use of at least one-flattened V-shaped ridge 41 being received by matching groove 42 in the sprocket drive roll 43 provides mechanically positive transverse (tracking or side-to-side) alignment of the belt molds 34 and 36. Thus, the fiber belts 37 and 38 are mechanically held from drifting laterally. This positive mechanical transverse alignment is not accomplished with thin metal belts as shown traveling on flat-surfaced pulleys in U.S. Patent Nos.
4,128,369 and 4,290,248.
The V-shaped ridge 41 also has a gear or cog configuration 47A (Figures 4, 6, and 8B) that will fit a matching gear or cog configuration 47 in the groove 42 of a positive drive roll sprocket 43 (Figures 4, 6, and 8B).
Such a groove and gear or cog arrangement eliminates belt slippage and provides forward-motion, feeding-direction alignment of the patterns on the belt molds 34 and 36. A
timing chain or timing belt 44 (Figure 8A) connecting timing gears or timing pulleys 45 (Figure 8A) on the shafts 46 (Figures 8A and 8B) of the top and bottom drive roll sprockets 43 are used to maintain this forward motion alignment of the pattern 78 (Figure 9) of the top and bottom belt molds 34 and 36 such that the patterns 78 of the top and bottom belt molds 34 and 36 move in unison from the entrance 89 (Figure 1) to the exit 90 of the machine 30. In other words, the patterns on the two belt molds are caused to be moving forward at the same rate of travel with simultaneous, equal, synchronous forward motion.
Another advantage of using fiber belts is their ability to travel around a sprocket roll of small diameter compared to the larger diameter flat surfaced pulleys required to prevent bending-yield-stress elongation of thin metal belts. Because fiber belts may travel around a -diameter as small as 6 inches, small drive roll sprockets and grooved exit rolls of 6 inches to 16 inches in diameter are used to gain space for a compact-designed and efficient air-conditioning cooling system, especially in the limited space available for cooling equipment to cool the bottom belt mold 40. The facility and convenience for changing the belt molds 39 and 40 are also improved by utilizing the added available space obtained by using fiber belts 37 and 38 and small sprocket drive rolls 43.
A further advantage of using fiber belts 37 and 38 is their low thermal conductivity that approximately matches the low thermal conductivity of the silicone rubber molds 39 and 40. For example, bonded fibers have a K factor of about 0.27 and the K factor of silicone rubber is about 0.10. By comparison, 1 percent carbon steel has a K factor of about 26, or about one hundred times more than the fiber belts. The low thermal conductivity of the fiber belt and silicone rubber mold causes the heat of the hot plastics 77 (Figures 2 and 8B) to be retained on and near the mold surfaces 78 for faster removal by the more efficient method of using cold, dry, moving air to directly cool these molding surfaces 78 of the belt molds. The above K factor values for the materials involved are expressed in units of Btu per hour through a square foot per degree Fahrenheit of temperature difference per foot for steel and for rubber and per inch for bonded fibers.

SPROCKET DRIVE ROLLS
The small diameter sprocket drive rolls 43 (Figures 1, 2, 3, 4, 5, 8A, and 8B) are between 6 inches and 16 inches in diameter. The sprocket drive roll 43 has a single, central wide recess or groove 42 (Figure 4) or a pair of axially-spaced recesses or grooves 42 (Figures 6, 8A, and 8B), each such groove having gear or cog teeth 47 which engage with matching gear or cog teeth 47A on the ridge 41 of the fiber belt 37 or 38 resulting in a positive mechanical transverse and longitudinal alignment of the belt molds 34 and 36. The unison-forward-motion alignment, also called longitudinal alignment, is assured by connecting the shafts 46 (Figures 1, 2, 3, 4, 6, 8A, and 8B) of the top and bottom drive sprockets 43 with a timing chain or belt 44 (Figure 8A).
The small diameter sprocket drive roll 43 also allows more space for mold changing and for air-conditioning equipment positioned between the floor and the pass line of the extruded material, which is normally 39 to 44 inches from the floor.
The sprocket drive rolls 43, shown in Figures 8A and 8s and that shown in Figure 6, have twin-wide grooves 42 located near their opposite ends. Each of these wide grooves 42 have gear or cog teeth 47 which engage with matching gear or cog teeth 47A (Figure 6) on the twin-wide V-shaped ridges 41 located near opposite edges of the fiber -belts 37 or 38. As shown in Figures 6 and 8B, the twin ridges 41 are disposed near the edges of the fiber belts 37 and 38 beyond the edges of the silicone rubber molds 39 and 40. Those skilled in the art will recognize that other arrangements of the V-shaped ridges 41 are suitable. In Figure 6 the edge of the rubber molds 39 or 40 is shown spaced inward a distance of "Z" from the edge of the fiber belt 37 or 38, and this inward spacing "Z" is greater than the overall width of each V-shaped wide ridge 41.

SPROCKET DRIVE ROLL MOTORS
~ The top and bottom sprocket rolls 43 are driven by a D.C. motor 48 (Figure 8A) . Sometimes a torque motor 48A
and gear reducer 50A (Figure 8A) are used to assist the 15 drive motor. The torque motor helps to drive the load but does not override or fall behind the drive motor. This drive and torque motor arrangement 48 and 48A prevents the motors from forcing the belt molds 34 and 36 out of longitudinal alignment when two motors are used and maintains the integrity of the positive mechanical alignment between the sprocket drive rolls 43 and the geared belt molds 34 and 36. A sprocket gear 91 on the shaft of the motor 48 drives a chain 49 (Figure 8A) for driving the sprocket gear 92 of a gear reducer 50 (Figure 25 8A) connected to the shaft 46 of the bottom sprocket drive roll 43. If a torque motor 48A is used to assist the drive 2l6s~a :

motor, a gearbox 50A connected to the shaft 46 of the top drive roll sprocket 43 is connected to the torque motor 48A
by means of chain 49A.
This arrangement of drive 48 and torque 48A motors provides for usage of motors of less horsepower that are less expensive to purchase and operate when used with gear ratios, like 150:1, in the gear reducer 50 and 50A to achieve the necessary belt operating speeds using less energy.

GROOVED EXIT ROLLS
The grooved exit rolls 51 (Figures 1 and 5) disposed at the output end of machine 30 are the same diameter and length as the drive rolls 43 disposed at the input end of the apparatus, but are not motor-driven nor geared to each other. The grooved exit rolls 51 on shafts 54 (Figure 5) are mounted to be aligned tangential to the slippery low coefficient of friction surface 59 (Figures 1 2, 3, and 7) covering the backup plates 22. By mounting each grooved exit roll 51 tangential to the slippery surface 59 of the backup plate 22, open space without support is reduced between the backup plates and a product conveyor 53 (Figure 1). The single or twin grooves 42 in the grooved exit roll 51 are smooth, without gear or cog teeth.
The grooved exit rolls 51 may or may not be crowned (dimension "Y" in Figure 5) and provide the means to fine tune the transverse (lateral) tracking alignment of the belt molds 34 and 36. For example, in the preferred embodiment such crowning "Y" is in the range from about 1/64 inch to about 3/16 inch per foot of axial length of the exit roll 51. One end of a shaft 54 of each of the top and bottom grooved exit rolls 51 is held stationary during operation at a desired position with a self-aligning bearing 55 (Figure 1). The desired position of this bearing 55 can be adjusted backwards and forwards, arrow 86 (Figure 1), by a first electric jack screw (not shown), but this bearing 55 is held stationary during running of the machine 30. The other end of the shaft 54 of each grooved exit roll 51 is in a self-aligning bearing 57 (Figure 1) that can be moved backwards and forwards by a second electric screw jack 56 (Figure 1) along slideways 58 (Figure 1) to increase or decrease the belt tension along one edge region, relative to the other edge region, thereby fine tuning the tracking of the belt molds as may be desired to keep the belt molds 34 and 36 aligned with each other within the tolerances required by the mold pattern.
Thus, the first electric screw jack (not shown) operates to set the overall tension on each exit roll 51 and the second jack screw operates to align the longitudinal axis of each specific exit roll 51 perpendicular to the direction of travel of the molded product 52.

-The product pattern is distorted (as seen by comparing Figures 9 and 10) if either the longitudinal alignment or transverse (lateral) alignment is not maintained.

Backup plates 22 (Figures 1, 2, 3, and 7) are comprised of steel up to l-inch thick and are coated with a layer 59 (Figures 1, 2, 3, and 7) of high or ultra-high molecular weight high-density polyethylene, Teflon, or other low coefficient of friction material having good lubricity and abrasion resistance.
The metal backup plate 22 coated with a material with excellent lubricity 59 provides an even, continuous level platen for supporting and guiding the belt molds 34 and 36 15(Figures 1, 2, 3, 4, 6, 7, 8, 9, and 10) to slide forward under a constant pressure thereby stabilizing the height, configuration, orientation, posture, and belt pressure being provided consistently along the travelling, flexible, mold channel 33.
20The backup plates 22 are shown drilled with a multitude of air-bearing holes 60 (Figures 2, 3, and 7), drilled at a 45-degree angle, aimed toward the advancing belt mold, as shown in Figure 2, and extending through the high-density slippery backup plate coating 59 (Figures 2, 3, and 7).

` 216521D

The air-bearing holes 60 (Figures 2, 3, and 7) are drilled to face forward to meet the underside of the advancing fiber belts at 45 degrees, creating a friction-reducing lifting action when preferably ambient temperature high pressure air 61 (Figures 1, 2, 3, and 7) is forced through the holes by a blower 62 (Figures 1 and 7). It is believed that forming the air-bearing holes 60 at an angle of 45 degrees to the surface of the backup plate and orienting the air-bearing holes 60 such that air blows in a direction opposite the direction of the belt's travel, maximizes the friction-reducing action of the air. There is also an analogous blower (not shown) for feeding an air chamber 63 (Figure 1) in the top carriage 35. Each blower feeds an air chamber 63 which runs the length and width of the backup plates 22 (Figures 1, 2, 3, and 7) in the top and bottom carriages 35 and 25.
This air-bearing system minimizes the belt mold sliding-contact pressure against the slippery coated backup plates 59 and reduces wearing of the belts and backup plate coating.

ELECTRIC SCREW JACKS
Electric screw jacks 56 (Figure 1) and 32 (Figure 8A) are used instead of the hydraulic equipment as is common in the art. This use of electric screw jacks saves the energy required to continuously operate a hydraulic pump and - motor. Electric screw jacks only operate (and only use energy) when activated. The electrical screw jacks 56 and 32 provide a more positive and accurate movement of the machine components than hydraulic cylinders and pistons.
Because of their precise positioning the movement of the machine components can be programmed to preset positions when using electric screw jacks. The need for maintenance of a hydraulic pump, hydraulic connecting hose and tubing, valves, and cylinders is eliminated. This prior art maintenance is particularly significant since these hydraulic items must be maintained in a leak-free condition to prevent contamination of the molded product. The continuous high decibel sound of a hydraulic pump is also eliminated by the use of electric screw jacks.
15The primary uses of the electrical screw jacks are:
1. Raise the top carriage 35 by jack 32 (Figure 8A) to disengage the top 34 and bottom 36 belt molds to facilitate changing the belt molds 34 and 36.
2. Lower the top carriage 35 by jack 32 (Figure 8A) 20to form the mold channel 33 (Figures 2 and 8B) for processing the resin feedstock.
3. Retract the grooved exit rolls 51 by jacks 56 (Figure 1) to let the belt molds 34 and 36 fall loose to facilitate changing the belt molds.
254. Extend the grooved exit rolls 51 to preset positions by jacks 56 (Figure 1) to put the belt ._ molds 34 and 36 in tension as required for the molding operation.
5. Add extra tension to one belt mold 34 or 36 or the other to compensate for small longitudinal mismatch of mold pattern, due to one belt being slightly longer than the other. This fine tuning is accomplished by adjusting the electronic controllers for the screw jacks 56 that set their stroke lengths.
6. Move the machine to and from the extruder as required to change extruder dies and to adjust the distance between the extruder die and the mold channel formed by the belt molds.

OPERATION AND FIBER BELT MOLD COOLING
In operation, as shown in Figures 1, 2, 8B, and 9, the continuously moving mold belts are mated and the top mold belt 34 is driven in an elongated oval path around the top carriage 35, as indicated by the arrows 87 (Figures 1 and 2). The bottom mold belt 36 is driven in a similar elongated oval path around the bottom carriage 25, as indicated by the arrows 88 (Figures 1 and 2). Thus, the mating molding surfaces 78 (Figure 2) define a continuously moving molding channel 33 or, in some instances, more than one molding channel that provides a changing profile as desired to produce a specific product configuration. The molding channel 33 is continuously moving forward from the entry 89 (Figures l and 2) of the machine 30 to the machine exit 90 (Figure 1).
The belt molds 34 and 36 are cooled by an air-cooling system in which conditioned, i.e. cold air (35-50 degrees Fahrenheit), is blown onto and along the molding surface 78 of the belt molds as the belts return from the exit end 90 to the entry end 89 of the machine 30 adjacent to the open side of the insulated air-conditioning ducts 74 (Figures 1, 8A, and 8B). The presently disclosed process and apparatus employ air cooling of the mold surfaces of the continuously moving flexible belt molds. Such dry cooling of the mold surfaces is more compatible with the heated thermoplastic materials being molded than is the use of cooling water on the reverse surfaces of thin metal belts as used in the prior art. The direction and the volume of cold air passing over the belt molds 34 and 36 are controlled by a series of hand adjustable dampers 75 (Figures 1, 8A, and 8B) which control the direction, angle, velocity, amount, and period during the return from the exit to the entry end of the machine 30. These dampers 75 have adjustment handles 75A (Figures 8A and 8B) which control the direction, angle, velocity, and amount of cold air during the return from the exit to the entry end of the machine 30. The cold air impinges the travelling hot belt molds.
The dampers control the direction and angle of the cold air to blow counter to the direction the molds are travelling and at the angle and velocity that optimizes the heat exchange. The amount of cold air and when the cold air contacts the travelling hot belt mold surfaces are also controlled by the dampers. The dampers also provide the means to cool the surfaces of the hot belt molds to a consistent temperature before the belt molds again contact the hot plastic, thereby optimizing the molding conditions.
In other words, it is desirable to have the temperature of the belt mold as it first encounters the hot plastic be uniform throughout a production run. The cold air~in the ducts 74 is supplied by air conditioners 76 (Figures 1, 8A, and 8B) of sufficient cooling capacity. The objective is ~ to remove all of the surface heat that the belt molds 34 and 36 retain from being in contact with the hot (100-600 degrees Fahrenheit) moldable plastic material before the belt molds return to the entry 89 to again contact the hot plastic.
When the hot plastic material 77 (Figures 2 and 8B) enters the mold channel 33 (Figures 2 and 8B), it is formed by the pressure of the moving top 34 and bottom 36 belt molds that are traveling around the entry drive rolls 43 Shortly after the hot plastic 77 has been formed, the cold mold surfaces 78 (35-100 degrees Fahrenheit) of the silicone rubber belt molds 39 and 40 chill the surface of the formed product in a similar manner as the mold surfaces ... ... .. . ...... ..

21652~0 of injection molds and extrusion dies chill the surface of the products formed by these processes. The cold rubber belt molds 39 and 40 chill the surface of the formed thermoplastic material 77 and such chilling then "sets" the 5 exterior regions of the molded plastic in its new, formed configuration. During the time the silicone rubber belt molds 39 and 40 are in contact with the hot plastic, these belt molds pick up heat, and the mold surface 78 (Figures 2 and 8B) of each of the silicone rubber molds 34 and 36 10 becomes hot.
Because the silicone rubber molds 34 and 36 and fiber belts 37 and 38 of these belt molds 39 and 40 are poor thermal conductors, the belt molds 39 and 40 do not transfer or absorb heat readily. As a practical matter, no 15 significant amount of the heat penetrates through the thickness of the silicone rubber during any one contact of the travelling belt molds with the hot plastic material 77.
The heat retained by the belt molds is surface heat localized near the mold surfaces 78. The concentration of 20 heat near the mold surface 78 permits the use of a more efficient cooling system of blowing cold air directly over the mold surface 78 of each belt mold to remove this surface heat and to return the mold surface 78 to a temperature of 35-100 degrees Fahrenheit before each 25 travelling mold surface 78 again contacts the hot plastic 77.

The cold air in the ducts 74 is generated and blown by one or more commercially available air conditioners 76 of sufficient capacity; e.g., one ton to ten ton, connected to insulated ducts 74 that are as wide as the belt molds 34 and 36. The open side of each duct 74 facing the hot mold surface 78 of the belt mold returning from the exit end to the entry end of the machine 30 is controlled with dampers 75 to direct the cold air against the hot mold surface 78 as required to remove the localized surface heat from the mold surface of the belt molds. The air-conditioning units 76 are mounted near the entry end of the machine above the returning top belt mold 34 and below the returning bottom belt mold 36 with the cold air traveling, as shown by the arrow 79 (Figures 1 and 8B) against and opposite to the direction of travel of the moving returning belts. Since the air-conditioner chilled, dry air is generally traveling in a direction 79 counter to the direction of travel 87 and 88 of the returning mold surface 78 from which heat is being extracted, we have provided a counter-current-flow heat exchange, which we believe to be an optimum flow relationship. An exhaust cold air flow 80 (Figure 1) from the cold air ducts 74 (Figure 1) is directed at the top and bottom surfaces of the molded product 52 (Figure 1) leaving the exit end of the machine 30.
As is well known, the amount of heat removed from a surface by the flow of a cooling fluid is dependent upon the velocity of the cooling fluid in relation to the heated surface. When the velocity of the flow of the cooling air 79 over the heated mold surface 78 is too low, the cooling air becomes saturated with heat and incapable of removing further heat from the heated surface prior to passing over the entire surface. When the velocity of the cooling air relative to the heated surface is too high, the air conditioners 76 and their blowers are operating at a rate which exceeds optimum efficiency because the cooling air does not remain in contact with the heated surface long enough to absorb the greatest amount of heat possible.
Therefore, a most efficient relative velocity exists wherein heat transfer from the mold surface 78 to the cooling air 79 is r~ir;zed. The counter-current-flow of the present invention attempts to maximize heat transfer efficiency from the belt molds 34 and 36 to the cooling air by providing an optimal relative velocity therebetween.
This optimal relative velocity is achieved by the means of adjustable dampers that cause the air to travel at a controlled velocity in a direction counter to the direction of travel of the mold surface 78.
The cooling system described is a dry cooling system which is preferred to a wet or water-cooling system in a hot plastics molding operation. The air-cooling system described here also eliminates the need for water chillers, pumps, a recirculating system, a water cleaning system, and 216521û

a sump under the machine.
If the molded product 52 requires further cooling, it travels through a water bath, water spray, or through air-conditioning ducts 84 (Figure 1). The cooled finished product "P" is cut at 85 to length, punched, slotted, painted, or has other finishing operations performed as it travels over the conveyor system 53 (Figure 1).
Electric screw jacks 81 (Figure 1) move the machine 30 away from the extruder 28, as shown by the arrow 82 in Figure 1, for service and maintenance and for changing the extruder die 29. Electric screw jacks 32 (Figure 8A) move the top carriage up and down to change belt molds, as shown by the arrow 83 (Figure 1).
Figure 9 is a cross-sectional view of the complementary silicone rubber top mold 39 and silicone rubber bottom mold 40, illustrating proper alignment thereof. The continuously moving mold channel 33 forms a shape which correctly corresponds to the desired product.
Figure 10 illustrates the effects of misalignment of the silicone rubber top mold 30 relative to the silicone rubber bottom mold 40, thus causing undesired distortion of the mold channel 33. This results in distortion of the final molded product.
It is a function of the wide V-shaped ridges 41 and the V-shaped grooves 42 as well as the crown on the grooved exit rolls to maintain proper alignment of the silicone 2~65~1~0 rubber top mold 39 relative to the silicone rubber bottom mold 40 and thereby prevent misalignment of the continuously moving mold channel 33.
The above-described process and apparatus has improved methods and components to continuously produce impression-molded thermoplastic products with closer tolerances on a less costly machine. The machine is easier to maintain, uses less energy, is less expensive to operate, and makes less noise.
It is understood that the exemplary continuous molding process and apparatus described herein and shown in the drawings represents only a presently preferred embodiment of the invention. Indeed, various modifications and additions may be made to such embodiment without departing from the spirit and scope of the invention. For example, the molds may be comprised of flexible, heat-resistant materials other than silicone rubber. Also, various arrangements of ducts providing cooling air to the mold surface are possible. Thus, these and other modifications and additions may be apparent to those skilled in the art and may be implemented to adapt the present invention for use in a variety of applications.

Claims (34)

1. A continuous molding apparatus having an input end and an output end, for molding heated thermoplastic material, the apparatus comprising:
(a) a first flexible belt having a first mold formed upon the exterior surface thereof;
(b) a second flexible belt having a second mold formed upon the exterior surface thereof, said second flexible belt being disposable in laminar juxtaposition to said first flexible belt such that said first and second molds form a mold channel therebetween;
(c) a means for conveying said first and second flexible belts such that the mold channel moves from the input end to the output end of the continuous molding apparatus;
(d) a means for air cooling said first and second molds by the application of air blown thereover.

2. The continuous molding apparatus as recited in Claim 1 further comprising:
(a) duct means associated with said air-cooling means for conveying air adjacent to the first and second molds; and (b) a plurality of adjustable dampers associated with said duct means for adjusting the directions of air onto said first and second molds.

3. The continuous molding apparatus as recited in Claim 2, wherein said dampers are approximately the same width as said first and second fabric belts.

4. The continuous molding apparatus as recited in Claim 3 wherein said dampers are disposed along the length of the horizontal portion of the returning belt mold.

5. A machine for continuous molding of thermoplastic material heated to a moldable temperature comprising:
(a) a bottom carriage;
(b) a top carriage positioned above and in alignment with said bottom carriage;
(c) said machine having an entry for continuously receiving heated thermoplastic material at moldable temperature and having an exit for continuously discharging molded thermoplastic material;
(d) said bottom carriage having a bottom drive roll rotatably mounted thereon and being positioned below said entry and having a bottom exit roll rotatably mounted thereon and being positioned below said exit;
(e) said top carriage having a top drive roll rotatably mounted thereon and being positioned above said entry and having a top exit roll rotatably mounted thereon and being positioned above said exit;
(f) a bottom flexible belt mold movable in a path around both said bottom drive roll and said bottom exit roll;
(g) a top flexible belt mold movable in a path around both said top drive roll and said top exit roll;
(h) molding surfaces of said top and bottom belt molds being adapted for engaging in mating relationship defining at least one mold channel between said bottom and top belt molds extending from said entry to said exit;
(i) means associated with said top and bottom drive rolls for enabling driving of said top and bottom drive rolls for driving said belt molds along said paths, for continuously moving said molding surfaces in said mating relationship, for continuously moving said mold channel from said entry to said exit, and for returning the top and bottom belt molds in separated relationship from said exit to said entry; and (j) air cooling means for directing air against said molding surfaces as said top and bottom belt molds are returning from said exit to said entry for cooling said molding surfaces of the top and bottom belt molds as they are returning to said entry.

6. The machine as recited in Claim 5, further comprising:
(a) bottom guide plate means extending from near said bottom drive roll to near said bottom exit roll;
(b) said bottom belt molding sliding along said bottom guide plate means in moving away from said entry and toward said exit;
(c) top guide plate means extending from near said top drive roll to near said top exit roll; and (d) said top belt mold sliding along said top guide plate means in moving away from said entry and toward said exit;
whereby both said top and bottom belt molds are substantially continuously guided between the respective drive roll sprocket and exit roll for stabilizing said molding channel in continuously moving away from said entry and toward said exit.

7. The machine as recited in Claim 6 further comprising:
(a) a low coefficient of friction coating on said bottom guide plate means along which slides said bottom belt mold; and (b) a low coefficient of friction coating on said top guide plate means along which slides said top belt mold.

8. The machine as recited in Claim 6, further comprising:
(a) said bottom guide plate means having multiple air passages extending therethrough in a direction toward said bottom belt mold;
(b) air blowing means and bottom air chamber means supplied by said air blowing means and being positioned below said bottom guide plate means and communicating with said multiple air passages for feeding air from said bottom air chamber means through said multiple air passages for introducing air between said bottom guide plate means and said bottom belt mold for providing an air-bearing effect therebetween;
(c) said top guide plate means having multiple air passages extending therethrough in a direction toward said top belt mold; and (d) top air chamber means supplied by said air blowing means and being positioned above said top guide plate means and communicating with said multiple air passages in said top guide plate means for feeding air from said top chamber means through said multiple air passages for introducing air between said top guide plate means and said top belt mold for providing an air-bearing effect therebetween.

9. The machine as recited in Claim 8, wherein:
(a) said multiple air passages extend through the respective top and bottom guide plate means at acute angles toward the respective top and bottom belt molds; and (b) said acute angles are aimed in a direction generally opposite to the direction in which said belt molds are moving from the exit to the entry.

10. The machine as recited in Claim 8, wherein:
(a) a low coefficient of friction coating is on said bottom guide place means and said bottom belt mold slides along said coating;
(b) said multiple air passages extending through said bottom plate means also extend through said coating on said bottom guide plate means for introducing air between said coating and said bottom belt mold;
(c) a low coefficient of friction coating is on said top guide plate means, and said top belt mold slides along said coating; and (d) said multiple air passages extending through said top guide plate means also extend through said coating on said top guide plate means for introducing air between said coating and said top belt mold.

11. The machine as recited in Claim 10, wherein:
(a) said multiple air passages extend through said bottom and top guide plate means and the respective coating thereon at acute angles toward the respective backing of the bottom and top belt mold; and (b) said acute angles are aimed generally opposite to the sliding direction of the respective backing along the coating.

12. The machine as recited in Claim 5, further comprising:
(a) said bottom belt mold having at least one flexible ridge thereon projecting inwardly from said bottom belt mold and extending longitudinally along said bottom belt mold;
(b) sprocket-engaging means of said bottom belt mold located on said ridge on said bottom belt mold;
(c) said bottom drive roll having at least one circumferential groove for receiving said ridge of said bottom belt mold;
(d) sprocket teeth on said bottom drive roll located in said circumferential groove, and said sprocket-engaging means on said ridge engaging in positive mechanical drive relationship with said sprocket teeth in said circumferential groove;
(e) said top belt mold having at least one flexible ridge thereon projecting inwardly from said top belt mold and extending longitudinally along said top belt mold;
(f) sprocket-engaging means of said top belt mold located on said ridge on said top belt mold;
(g) said top drive roll having at least one circumferential groove for receiving said ridge of said top belt mold;
(h) sprocket teeth on said top drive roll located in said circumferential groove, and said sprocket-engaging means on said ridge of said top belt mold engaging in positive mechanical drive relationship with said sprocket teeth in said circumferential groove;
(i) said bottom and top exit rolls each having at least one circumferential groove for receiving respective ridges of the bottom and top belt molds;
(j) said circumferential grooves of said bottom drive roll and bottom exit roll guiding said bottom belt mold in laterally aligned relationship relative to the top belt mold in defining the moving mold channel;
(k) said circumferential grooves of said top drive roll and top exit roll guiding said top belt mold in laterally aligned relationship relative to the bottom belt mold in defining the moving mold channel; and (l) said positive mechanical drive relationships of the respective bottom and top drive rolls with the respective bottom and top belt molds maintaining said bottom and top belt molds in longitudinally aligned forward-motion relationship in defining the moving mold channel.

13. The machine as recited in Claim 12 further comprising:
(a) bottom guide plate means extending from near said bottom drive roll to near said exit roll in linear juxtaposition to said bottom belt mold;
(b) said bottom guide plate means having at least one groove extending in a direction from said entry to said exit for receiving said ridge of said bottom belt mold;
(c) top guide plate means extending from near said top drive roll to near said exit roll in linear juxtaposition to said top belt mold; and (d) said top guide plate means having at least one groove extending in a direction from said entry to said exit for receiving said ridge of said top belt mold.

14. The machine as recited in Claim 5, further comprising:
(a) first and second side plates included in said bottom carriage;
(b) said bottom drive roll and bottom exit roll each being rotatably mounted on said first and second side plates and each being positioned intermediate said first and second side plates;
(c) third and fourth side plates included in said top carriage;
(d) said top drive roll and said top exit roll each being rotatably mounted on said third and fourth side plates and each being positioned intermediate said third and fourth side plates;
(e) bottom backup platen means extending from near said bottom drive roll to near said bottom exit roll in linear juxtaposed relation with said bottom belt mold for supporting said bottom belt mold in moving from said entry to said exit;
(f) said bottom backup platen means being connected to and extending between said first and second side plates for stiffening said first and second side plates in said bottom carriage;
(g) top backup platen means extending from near said top drive roll to near said top exit roll in linear juxtaposed relation with said top belt mold for holding said top belt mold down in moving from said entry to said exit in said mating relationship with said bottom belt mold; and (h) said top backup platen means being connected to and extending between said third and fourth side plates for stiffening said third and fourth side plates in said top carriage.

15. The machine as recited in Claim 14, further comprising:
(a) said bottom backup platen means having multiple air passages extending therethrough in a direction toward said bottom belt mold;
(b) air blowing means and bottom air chamber means supplied by said air blowing means;
(c) said bottom air chamber means being positioned below said bottom backup platen means and being connected to said bottom backup platen means forming therewith a bottom box beam for torsionally stiffening said bottom carriage;
(d) said bottom air chamber means communicating with said multiple air passage for feeding air from said bottom air chamber means through said multiple air passages and between said bottom backup platen means and said bottom belt mold for providing an air-bearing effect therebetween;
(e) said top backup platen means having multiple air passages extending therethrough in a direction toward said top belt mold;
(f) top air chamber means supplied by air blowing means;
(g) said top air chamber means being positioned above said top backup platen means and being connected to said top backup platen means forming therewith a top box beam for torsionally stiffening said top carriage; and (h) said top chamber means communicating with said multiple air passages in said top backup platen means for feeding air from said top chamber means through said multiple air passages and between said top backup platen means and said top belt mold for providing an air-bearing effect therebetween.

16. The machine as recited in Claim 15, wherein:
(a) said air blowing means supplying said bottom air chamber means includes a bottom air blower;
(b) said air blowing means supplying said top air chamber means includes a top air blower separate from said bottom air blower;
(c) said top carriage being mounted in said machine for enabling vertical raising of said top carriage upwardly relative to said bottom carriage; and (d) electric screw jack means associated with said top carriage for raising said top carriage upwardly relative to said bottom carriage.

17. The machine as recited in Claim 5, further comprising:
(a) said bottom and top exit rolls being movably mounted on said bottom and top carriages for adjusting movements toward and away from said bottom and top sprocket drive rolls, respectively;
and (b) bottom and top electric screw jacks associated with said bottom and top exit rolls for producing said adjusting movements of the bottom and top exit rolls for adjusting the tension in the bottom and top belt molds, respective.

18. The machine as recited in Claim 5, wherein said cold air is at a temperature below room temperature.

19. The machine as recited in Claim 6, wherein:
(a) said bottom exit roll is tangent to the plane of said bottom guide plate means; and (b) said top exit roll is tangent to the plane of said top guide plate means;
thereby providing substantially continuous guidance to said belt molds extending substantially continuously to said bottom and top exit rolls for holding the molded material firmly within said mold channel until the molded material has reached said exit.

20. Apparatus for continuous molding of thermoplastic material heated to a moldable temperature comprising:
(a) first and second flexible belt molds each including a flexible mold having a molding surface and each including a flexible backing on said mold;
(b) said molding surfaces of said first and second belt molds being matable for defining at least one molding channel extending along the belt molds between their mated molding surfaces;
(c) at least one ridge on said backing of said first belt mold;
(d) at least one ridge on said backing of said second belt mold; and (e) said ridges extending along the respective belt molds.

21. Apparatus as recited in Claim 20, wherein each of said ridges includes sprocket-engaging means positioned along the ridge for driving said first and second flexible belt molds, respectively, with a positive mechanical drive relationship for each of said belt molds.

22. Apparatus as recited in Claim 20, wherein said flexible backing on each of said first and second belt molds comprises a plurality of plies of fabric laminated together.

23. Apparatus as recited in Claim 22, wherein each of said plurality of plies of fabric laminated together has a thermal conductivity less than one-half the thermal conductivity of a comparable thickness of mild steel, said thermal conductivity being measured in BTU per hour, per square foot, per degree Fahrenheit per foot.

24. Apparatus as recited in Claim 22, wherein said plurality of plies of fabric laminated together is comprised predominantly of polyester fabric.

25. Apparatus as recited in Claim 24, wherein each of said plurality of plies of fabric laminated together as a thermal conductivity less than one-half the thermal conductivity of a comparable thickness of mild steel.

26. A continuous molding apparatus for molding heated thermoplastic material, the apparatus comprising:
(a) first and second flexible belt molds each having a molding surface;
(b) said molding surfaces of the first and second belt molds being matable for defining at least one molding channel extending along the belt molds between their mated molding surfaces;
(c) a plurality of first rollers for supporting said first flexible belt mold;
(d) a plurality of second rollers for supporting said second flexible belt mold;

(e) one of said first rollers and one of said second rollers being positioned at an input end of the continuous molding apparatus and another of said first rollers and another of said second rollers being positioned at an output end of the continuous molding apparatus for supporting said first and second belt molds with their mated molding surfaces extending from said input end of the continuous molding apparatus to said output end for defining said molding channel extending from said input end to said output end;
(f) one of said first rollers being a first drive roller and one of said second rollers being a second drive roller;
(g) means associated with said first and second drive rollers for enabling said first and second drive rollers to be driven with rotary motion for causing the mated molding surfaces of said first and second belt molds to move in unison in a forward direction from said input end toward said output end with said mold channel defined therebetween and for causing said belt molds to return separately from said output end to said input end; and (i) air cooling means for blowing cold air against said first and second belt molds for removing heat from them.

27. The continuous molding apparatus as recited in Claim 26, further comprising:
(a) at least one first flexible ridge formed on said first flexible belt mold and extending along said first flexible belt mold;
(b) first sprocket-engageable means being located along said first ridge;

(c) at least one second flexible ridge formed on said second flexible belt mold and extending along said second flexible belt mold;
(d) second sprocket-engageable means being located along said second ridge;
(e) said first drive roller including at least one first circumferential groove for receiving said first ridge in said first groove;
(f) said second drive roller including at least one second circumferential groove for receiving said second ridge in said second groove;
and (g) first and second sprocket means adjacent to said first and second circumferential grooves, respectively, for mechanically engaging said first and second sprocket-engageable means in regions where said first and second ridges are being received in said first and second grooves, respectively.

28. The continuous molding apparatus as recited in Claim 26, wherein said air cooling means blows air against said molding surfaces of said first and second belt molds during return of the belt molds from the output end to the input end of the continuous molding apparatus.

29. The continuous molding apparatus as recited in Claim 28, wherein air is directed against molded thermoplastic material issuing from the output end of the continuous molding apparatus.

30. The continuous molding apparatus as recited in Claim 28, wherein said air is at a temperature below room temperature.

31. A continuous molding apparatus having an input end and an output end for molding heated thermoplastic material, the apparatus comprising:
(a) a first flexible belt having a first mold formed upon the exterior surface thereof;
(b) a second flexible belt having a second mold formed upon the exterior surface thereof, said second flexible belt being disposable in laminar juxtaposition to said first flexible belt such that said first and second molds form a mold channel therebetween;
(c) a means for conveying said first and second flexible belts such that the mold channel moves from the input end to the output end of the continuous molding apparatus;
(d) at least one first means formed on the interior surface of said first and said second flexible belts for maintaining alignment thereof;
and (e) a corresponding number of second means formed on said conveying means for cooperating with said first means to maintain alignment of said first and second flexible belts; and (f) wherein said first means and said second means have complimentary surfaces which limit relative lateral motion therebetween when the complimentary surfaces are mated.

32. The continuous molding apparatus as recited in Claim 31 wherein:
(a) said first means is a ridge; and (b) said second means is a groove.

33. The continuous molding apparatus as recited in Claim 32 wherein said ridge and said groove are generally V-shaped.

34. The continuous molding apparatus as recited in Claim 33 further comprising:

(a) first teeth formed upon said first means; and (b) complimentary second teeth formed upon said second means such that said first and second teeth cooperate to communicate motion from said first means to said second means to drive said flexible belts such that the mold channel moves from the input end to the output end of the continuous molding apparatus.