Abstract: A method of manufacturing containers, the method comprising the steps of (a) extruding an elongate tube of plastics material, the tube having a rectangular outer cross-section and an elongate central cylindrical cavity; (b) cutting the tube transversely into a plurality of container body portions; (c) sealing a base to one end of each body portion; and (d) sealing a top to the other end of each body portion. The invention also provides apparatus for manufacturing containers, comprising an extrusion device for extruding an elongate tube of plastics material, the tube having a rectangular cross-section and an elongate central cylindrical cavity, a cutting device for cutting the tube transversely into a plurality of container body portions, a first sealing means for sealing a base to one end of each body portion and a second sealing means for sealing a top to the other end of each body portion.

Abstract: A plastic pipe with a hard outer shell lined with an inner shell of soft resilient plastic foam with a smooth central axial passageway adapted to be a conduit for liquid. A method of manufacturing this pipe which comprises simultaneously extruding the material for the outer shell and the foamable material for the inner shell into a pipe forming die.

Abstract: Plastic foam insulation panels are fabricated in a continuous elongated strip by an apparatus comprising upper and lower generally horizontally extending conveyors which form a support for the foam material during the expansion and solidification thereof. The thickness of the panel is determined by the vertical spacing between adjacent runs of the respective conveyors and the panel width is determined by spaced apart longitudinally extending sideplates which, together with the upper and lower conveyor runs define the cross-sectional dimensions of the insulation panel. The sideplates are mounted on laterally extending arms secured to spaced apart support stanchions and the position of the respective sideplates may be adjusted to vary the width of the panel.

Abstract: A method of forming foamed fibers which comprises the steps of forming a melt of a polymer of fiber-forming molecular weight in which is admixed a blowing agent, and a closed-cell-forming additive, extruding said melt through a spinnerette, quenching said melt downstream of said spinnerette under conditions at which bubbles form in said melt, and drawing said melt as it is quenched to produce a foamed fiber having fine bubbles contained therein is disclosed. The product fibers may contain substantially only closed-cells and/or substantially uniform cross sectional area cells.

Abstract: A foamed thermoplastic article having an integral outer unfoamed skin layer is formed from a mixture of thermoplastic resin containing a blowing agent by removing at least a portion of the blowing agent in the die of the extruder. The blowing agent is removed, e.g., by modifying the die so that it incorporates a porous section whcih allows the blowing agent to be removed from the mixture.

Abstract: A method and apparatus for the production of a foamed thermoplastic material. A cavity transfer mixer is provided between a screw extruder which melts, or fuses, the thermoplastic material, and a cooler. The cavity transfer mixer enables the formation of uniform and well mixed admixtures of a foaming agent and a thermoplastic material and, optionally, other desired additives.

Abstract: The process for the extrusion of an expandable plastic composition comprising extruding the composition to an at least partially expanded state through a cross section of die with an area essentially the same as that of the entrance to the cooling fixture which defines the shape and dimensions in the final profile to be produced and essentially having the shape of the latter, by leaving a space empty of material within the profile in the course of extrusion through said cross section and then confining the composition thus extruded immediately at the exit from said die cross section and essentially along the extension of the extrusion axis, within a cooled and elongated shaping space, open at both ends along said extrusion axis and having an exit cross section identical to that of the profile to be obtained, the improvement comprising separating said cooled and elongated shaping space into at least two parts separated from one another by a free space, with the first said part not exceeding a few centimeters i

Abstract: Porous shaped bodies are disclosed, and an apparatus and method of their production by extruding a homogeneous, single-phase liquid mixture of polymer and mixing partner liquid at the temperature of mixture preparation through a nozzle downwardly with a linear velocity v.sub.1 into a cooling liquid that dissolves the polymer insubstantially or not at all at the cooling temperature, the cooling liquid being provided from entry of the extruded mixture until at least the point of start of solidification thereof in a substantially vertically arranged tubular zone surrounded by a wall, velocity v.sub.2 of cooling liquid in this zone being less than v.sub.1. The cooling liquid is preferably contained in a U-shaped tube and its level is controllable by dosing at entry and/or exit points.

Abstract: Water instead of carbon dioxide is substituted for part of the volatile organic blowing agent, e.g., pentane, resulting in extruded foams having a smooth, lustrous drum side skin compared to foams containing only organic blowing agent or organic blowing agent plus carbon dioxide.

Abstract: The present invention relates to a process and an apparatus for producing phenolic foam laminates with improved surface appearance. The process involves applying pressure on the foam forming mixture through one of its facings by a flexible member. The member is sufficiently flexible to allow continual rise of the foam but also smoothes out any uneven rise under the applied pressure thereby producing a laminate which has a surface immediately below the facing substantially free of any voids, craters or wrinkles.

Abstract: Pipelines for transporting sewage, water, slurries, liquid and gaseous hydrocarbons, and like materials are interlined with a composite tubular lining having an inner skin layer and a foamed layer contiguous with the inner skin layer. The foamed layer is either contiguous also, along its opposite surface, with the inner wall of the pipe or may be spaced therefrom by an outer skin layer of the composite lining. The lining may be applied either before the pipeline is placed into service or afterward, whether in situ or removed for maintenance or repair. For application in situ the lining is preferably more flexible than will suffice for insertion into new pipes.

Abstract: A system and method for the control of the density of extruded foam controls foaming based on the volume per unit time of extrudate being formed. A gear pump controls the flow of melt to the die. The pump speed provides an accurate measure of the volume per unit time of melt moving to the die. The speed and cross-sectional dimensions of the extrudate are measured to determine the volume per unit time of the extrudate. Since the unfoamed melt density times the volume per unit time of the unfoamed melt being delivered to the die is equal to the density of the foamed extrudate times its volume per unit time, a ratio of the density of foamed extrudate to unfoamed melt can be determined from the two volume per unit time calculations. Once the ratio for an appropriate foam density is determined empirically, density-affecting characteristics of the extruder can be controlled to bring the calculated ratio towards the desired ratio.

Abstract: Apparatus for making building panels includes means for positioning upper and lower rigid sheets of material, such as paper pulp, in spaced relation so that foamable material disposed between the sheets can move into gripping engagement with both sheets as it expands and solidifies.

Abstract: A support surface is formed into a trough, a liquid polymer which expands on reaction is dispensed onto the support surface, and the support surface is inclined to cause flow of the polymer to a region in which the polymer expands. The polymer is introduced onto a supporting liquid which supports the polymer in a zone which is substantially coextensive with at least a major portion of the expansion region. The supporting liquid has a specific gravity higher than that of the polymer, whereby the polymer floats on and advances across the supporting liquid in the form of an expanding mass having left and right sides, a flat bottom and a top which slopes upwardly in the direction of the advance. Conveyors support the expanding mass at the respective left and right sides thereof. The conveyors are submerged in the liquid at their upstream ends, and the direction of advance of their polymer-supporting active surfaces is substantially parallel to the sloping top of the polymeric bun as it expands.

Abstract: A liquid mixture containing a heat-expandable resin and a catalyst is cast onto a lower facing, which is heated from below to cause expansion of the mixture and hardening of its lower part. The upper surface of the expanding mixture is covered with an upper facing applied while that portion is still soft, and the composite formed thereby is introduced to a heated enclosure while the upper part remains soft. The thickness of the formed composite, and panels derived thereof, is calibrated or limited by opposed conveyors within said thermal enclosure, which limits the maximum expansion to a value less than the theoretical potential expansion of the foam, allowing hardening to be completed, and subsequent cutting of the composite into panels.

Abstract: A method for controlling a cellular foam cable coating extrusion process wherein the quench point or temperature of the foamed coating being extruded onto the core material, and the ratio of speed of extrusion to line speed of the extrusion process are simultaneously adjusted respectively in response to two error signals indicative of a variation in relative permittivity and annular area of extruded coating from required specified values. The method results in a faster process than possible heretofore while at the same time a tighter tolerance on deviation from required parameters is possible.

Abstract: A method and apparatus for making building panels includes means for positioning upper and lower rigid sheets of material, such as paper pulp, in spaced relation so that foamable material disposed between the sheets can move into gripping engagement with both sheets as it expands and solidifies.

Abstract: Process for producing flexible PVC irrigation pipe by extruding a plasticized PVC composition containing a melt strength-enhancing aid and a chemical blowing agent and (a) the extruded melt being expanded by foaming thereof immediately on leaving the die into a substantially closed-cell extrudate of outer diameter greater than the die orifice with the extrudate surfaces being substantially unpunctured, (b) drawing down the extrudate in the atmosphere causing rupturing of the foam cell walls of the extrudate to form a substantially open-cell extrudate having punctured surfaces, and (c) when the extrudate has been drawn down to a degree which is prior to any cellular collapse which would lead to the formation of water-impervious pipe, cooling the extrudate by passing it through a cooling means in order to prevent said collapse. Preferably the extrudate passes through a tubular guide into a water bath in step (c).

Abstract: A method for continuously producing an insulation board comprising a rigid plastic foam core having two major surfaces and a facing material on one or both of the major surfaces, the method including conveying a facing material along a production line, depositing a partially expanded froth foam of a plastic mixture, which contains at least one frothing agent, on the facing material, and further expanding and curing the froth foam in contact wiht the facing material to form the insulation board. The board is particularly useful as roof insulation.

Abstract: A method of continuous production of foamed material, wherein foam forming materials are fed from below at a controlled rate and the foamed material is drawn away from above at a corresponding rate. Foaming takes place in a diverging expansion enclosure bounded by moving sheet material in the form of webs or in tubular form constrained to follow a diverging path and drawn away from above so as to travel with the foaming material at a rate corresponding to its rate of travel. The enclosure is defined above by foam already expanded, at the sides by the sheet material, and below by a feed zone sealed to contain the foam forming materials. The enclosure leads into an upwardly directed take off path for the foam. Appropriate machines for practicing the method utilize either webs of sheet material or sheet material in tubular form, which tubular form may itself be made by the machine from webs.

Abstract: Method and apparatus for making a continuous length of tubing having an annular wall formed of polyurethane, including a forming cylinder having a mandrel extending centrally therethrough. Two strips of paper material are pulled through the forming cylinder, one surrounding the mandrel and one being disposed at the interior surface of the cylinder, and a curable plastic mixture is injected into the annular space between the paper strips. A sensor is provided to determine the point at which curing of the plastic mixture begins in the annular spacing within the cylinder, and the speed of travel of the paper through the cylinder is regulated as a function thereof. The control system shuts the apparatus down if a break in the paper strips is detected, or if the paper supply approaches exhaustion, or if the point of full curing is within a predetermined minimum spacing from the inlet end of the cylinder.

Abstract: A molten polymer containing a blowing agent and, usually, a nucleating agent, is spun into fibers with screen packs or equivalent structures upstream of the spinning apertures. The use of screen packs enables the production of fibers with finer bubbles, which are therefore susceptable to greater melt-drawdown and postdrawing and can have better tensile properties. Foamed polyamide fibers are produced with average bubble diameters one-twentieth or less, compared to the effective fiber diameter.

Abstract: Disclosed is an apparatus for extruding thermoplastic compositions comprising an extruder, a die, and a cooling device positioned between the extruder and the die for cooling the heat plastified resinous composition exiting from the extruder to a uniform temperature desired for extrusion through the extrusion die. The cooling device includes at least one enclosed flow path for conveying the resinous composition from the inlet of the cooling device to the outlet of the cooling device, structure for circulating a cooling medium about the entire circumference of each of the resin flow paths, and flow control orifices at the inlet and the outlet of the cooling means across the entire cross-section of each of the resin flow paths.

Abstract: An apparatus for manufacturing continuous webs of polymer foam obtained from a mixture of liquid reagents, wherein the volume of a container is determined to form a zone of retention of the mixture of reagents in liquid phase and wherein the level of this mixture is maintained at a level slightly higher than the plane upon which the mixture in the liquid state flows, so that the primary phase of expansion of the mixture and its further expansion are produced outside the container on a moving surface of the conveyor, which surface is maintained in a substantially horizontal plane. The invention is particularly applicable to the production of webs of supple foam or of panels of rigid foam.

Abstract: A method for producing a crosslinked, uniformly expanded article of thermoplastic resin is provided.Thermoplastic resin containing a crosslinking agent and a foaming agent is extruded through a long-land die which is provided with a choking orifice at an end and/or an intermediate portion thereof; a lubricant is provided on the inner surface of the long-land die; the crosslinking agent is decomposed in the long-land die to lower the flow rate of the resin and the foaming agent is decomposed or heated to its boiling point in the long-land die to provide an expandable resin and the crosslinked, expandable resin is then released into an atmospheric or controlled pressure zone to produce the uniform, finely expanded article.

Abstract: A method of producing thermoplastic resin foams is disclosed. The method comprising extruding an expandable resin through a plurality of holes bored in a die in the inside of a frame fitted to the extrusion end surface of the die in an adjacent relation therewith and fusing together the thus-extruded materials while they are expanded and still softened, wherein the inner surfaces of the frame are inclined at an angle of inclination ranging between 5.degree. and 30.degree., so that the cross-sectional area of the frame is increased toward the outer end thereof, and the extruded materials are fused together while kept in contact with the inner surfaces of the frame.

Abstract: A method for preparing a multi-cellular foamed board of thermoplastic resin which comprises forming under pressure in a die a thermoplastic resin melt containing a foaming agent to give the resin melt a shape of a flat board having a broad width compared with a thickness thereof, extruding the resin melt from the die having the convex forward end with a middle portion in the width direction thereof protruding the greatest toward the extruding direction, introducing thus extruded resin melt immediately into a moulding passage having a concave end engaging with the said convex forward end of the die, allowing the resin melt to expand in the thickness direction at the portion adjacent to and extending along the concave end of the passage, and thereafter allowing the resin melt to expand in both the thickness and width directions of the board in the passage.

Abstract: Process and apparatus are disclosed for manufacturing foamed articles such as tubes used as pipe insulation, which tubes are of a high impermeability and flexibility and are formed of a polymer, such as polyethylene or polypropylene, containing up to about 25% of an elastomer.

Abstract: In the manufacture of skinned foam a technique for matching the viscosity of the skin as well as the foam so that both flow uniformly through the die includes the addition of blowing agent to all of the layers of the structure. To prevent foaming of the skin layers, nucleating agent is not added at those layers and the temperature is controlled so as to prevent nucleation without a nucleating agent. More specifically, the skins are kept above the boiling point of the blowing agent at atmospheric pressure and melt temperature, but below the temperature at which homogeneous nucleation occurs.

Abstract: Rigid plastic foam is flexibilized in an apparatus utilizing four sets of foam gripping belts. A first and second set of opposed belts traveling at a given speed forward the foam into the apparatus to a second and third set of opposed belts traveling at a slower speed than the first and second set of belts. The first and third and the second and fourth sets of belts are interdigitated in a region of foam crush.

Abstract: A method of continuous upwards production of foamed material by feeding foam forming materials from below and taking foamed material away from above, wherein foaming takes place in diverging expansion enclosure (1) the walls (13, 14) of which are provided with surfaces (15, 17) travelling with the foaming material, which enclosure (1) is defined above by foam already expanded, at the sides by said walls (13, 14) and below by a feed zone for the foam forming materials, and leads into an upwardly directed take off path for the foam.

Abstract: Disclosed is a process for increasing the density of thermoplastic resin foam waste material having apparent density as low as 5 kg/m.sup.3. The waste material in particle form is uniformly dispersed onto at least one vibrating plate of a furnace, and then heated to a temperature ranging between about 120.degree. C. and about 210.degree. C. The waste material is then compacted at the outlet end of the furnace and ground into particles of uniform size to be reused as thermoplastic resin material.

Abstract: A process for the continuous foaming of plastics, especially polyurethane, of the type in which the foaming space is delimited by flexible material bands which are fed together with the bun of foamed material being formed. As flexible material for these bands a composite web is used which comprises a support paper band and a thin impermeable band of plastics, preferably polyethylene having a thickness from 5 to 40 microns. The two bands of which the flexible is composed have a reduced adhesion to one another. The paper band is then detached from the bun of foamed material by disengaging it from the band of plastics which is left permanently adherent to the foamed material or is detached from this latter in an operation subsequent to the detachment of the paper band. In this way, losses of material are avoided, and the paper of the paper bands can be recovered.

Abstract: In the continuous production of block-foam from liquid reaction components, the danger of over-rolling exists in installations having low throughputs and in installations having high throughputs, which over-rolling results in faults in the finished block. These over-rolling phenomena are avoided by providing a conveyor belt in the mixture charging zone which belt transports on its conveying surface a foil which has trough-shaped indentations which can correspond to trough-shaped indentations in the conveying surface. The reaction mixture is portioned into the indentations of the foil. These portions are only spread out once the reaction mixture has reached the creamy phase.

Abstract: A process for producing a foamed synthetic resin body comprising continuously extruding a foamable thermoplastic resin extrudate composition from an extruder die into a reduced pressure zone, subjecting the extrudate to an expansion molding step, a cooling-hardening step and a cutting step while transporting the extrudate through the reduced pressure zone to obtain a foamed piece of predetermined length, shutting off a portion of the reduced pressure zone surrounding the foamed piece from the other portion thereof when the foamed piece has reached a specified position to restore the foamed piece surrounding portion to a normal pressure, subsequently discharging the foamed piece into the atmosphere, and thereafter bringing the surrounding portion into communication with the reduced pressure zone again upon reducing the pressure. Foamed resin bodies of desired expansion ratio and shape can be prepared continuously with high cooling efficiency. An apparatus for practicing the process is also disclosed.

Abstract: An insulation filled building plank having two spaced apart boards held together and separated by webs having dovetail connections with the boards and being at an angle to the longitudinal axis of the plank so that any transverse cut of the plank will cut a web is produced on apparatus which first cuts matching dovetail grooves on surfaces of the boards arranged face to face after which the boards are turned to have the dovetail surfaces facing each other and the apparatus pulls dovetails of webs into the grooves in the boards from a magazine and then the apparatus fills the spaces between the webs and boards with an in situ foamable insulation.

Abstract: Foam extrusion apparatus and methods employing a vacuum chamber at reduced pressure into which foamable material is continuously extruded, hardened and cut to length, means for inventorying a plurality of successively cut lengths in a second chamber then at such reduced pressure, and means for discharging the inventory from the second chamber to the outside after the second chamber has been brought to atmospheric pressure without affecting the reduced pressure in the vacuum chamber. Stacking devices are employed to inventory the cut lengths in either a vertical or horizontal stack for transfer as a stack into and/or out of the second chamber. Provision also is made for accumulating the boards in close but spaced facial relationship with substantially the entire surface areas of the cut lengths exposed to the reduced pressure prior to stacking and discharge to the atmosphere.

Abstract: A method of thermoforming comprising providing a continuous sheet of thermoplastic polymeric foam, transporting said sheet through an atmosphere of at least predominantly steam at a temperature of at least 215.degree. F. maintaining said sheet in said atmosphere for a time sufficient to cause a decrease in the density thereof; thereafter while under the influence of said temperature, deforming at least a portion of said sheet to a predetermined shape and while so deformed, cooling the same to cause retention of said shape and a system for carrying out said method.

Abstract: A process for preparing a poly(p-methylstyrene) polymer foam including extruding a poly(p-methylstyrene) foam structure from a melt at a temperature which will yield an open cell percentage less than that formed in general purpose polystyrene foamed under the same general conditions. It also includes performing the extrusion from a melt at a rate which will yield a foam structure at least comparable to that of general purpose polystyrene foam, wherein the extrusion rate is greater than the extrusion rate for said polystyrene foam.

Abstract: Disclosed is a process for extruding thermoplastic resinous compositions, comprising the steps of heat plastifying the resinous composition in an extruder; cooling the heat plastified resinous composition exiting from the extruder to a uniform temperature desired for extrusion through an extrusion die, including conveying the resinous composition through at least one enclosed flow path in a cooling device, circulating a cooling medium about the entire circumference of each of the resin flow paths and controlling by the means of orifices the flow of thermoplastic at the inlet and the outlet of the cooling device across substantially the entire cross-section of each of the resin flow paths; and, extruding the cooled thermoplastic resinous composition through an extrusion die downstream of the cooling device.

Abstract: A foam extrusion apparatus and method in which extrudate is extruded into a sealed chamber which may be subjected to pressure variation such as a vacuum with the controlled shaping of the plastic being obtained by power driven rolls within the chamber downstream of the die. Because of the harsh environmental conditions within the chamber it is desirable that the shaping or forming rolls be driven by an externally powered source which will therefore be not subject to the pressure, vacuum, or other deliterious conditions found within the chamber. Moreover, because of the external position of the drive with regard to the chamber, the entire system need not then be shut down in order to open the chamber and make the required adjustments or repairs. The chamber is preferably the upper end of a barometric leg into which the extrudate passes. The upper end of the chamber is closed by one or more bulkheads which are movable toward and away from the upper end of the chamber.

Abstract: There are provided methods for making heat-resistant, foamed, crystalline plastic materials. For example, polyethylene terephthalate may be foamed with a polycarbonate, extruded into a foamed sheet and this foamed sheet may be thermoformed by being subjected to crystallization annealing. The thermoformed, foamed, crystalline plastic sheets prepared by this process are particularly useful for forming light weight, ovenable food containers.

Abstract: A process and system for the formation of a polymer foam sheet of comparatively uniform biaxially orientation and comparatively uniform dimensions prepared by extruding polymer foam so that it rides on a fluid bearing film between the point of extrusion and a point of diameter expansion of the extruding tube.

Abstract: A shrink-fit article is made by extruding a silane-grafted polymer which foams, at least at its surface, and cross-links. Upon completion of foaming and cross-linking, the article is expanded while (still) warm and cooled in the expanded state.

Abstract: A method and apparatus for producing a foamed polymeric sheet having comparatively high density skin layers. Molten polymer containing a foaming agent is extruded from a die into a post-extrusion region defined by the die and a spaced pair of rotating chill rolls which are spaced from the die. The post-extrusion region is maintained at a pressure sufficient to at least inhibit expansion of the foamable molten polymer through the use of cooled sealing elements which occupy a substantial portion of the space between the die and the chill rolls, and are spaced from the chill rolls. The rolls and the sealing elements are cooled so that foamable molten polymer in the space between the sealing elements and the rolls becomes solidified, completing the seal. The chill rolls are maintained at a temperature below the temperature of the molten polymer to aid the skin formation on the surfaces of the polymer. If desired, the polymer can pass directly from the chill rolls into a water bath.

Abstract: A method and apparatus for preparing a substantially uniform thermoplastic foam extruded from an extruder, the molten thermoplastic resin having uniformly distributed therein a foaming agent. A cooling-mixer continuously receives the extruded mass of resin and foaming agent from the extruder and intimately mixes and substantially cools the mass. A substantially adiabatic zigzag mixer is connected to the cooling-mixer and divides the mass into a plurality of separate streams which are at least partially separated and recombined. A die is connected to the zigzag mixer and extrudes the uniformly cooled mass into a lower pressure zone to produce a substantially uniform thermoplastic foam.

Abstract: An apparatus adapted to be positioned downstream of a foam extrusion die in an environmental control or vacuum chamber for remote monitoring of the thickness and profile of foam boards, planks and like extrudates soon after the extrudate exits the die and takes its final shape, is characterized by opposed, relatively narrow shoes on opposite sides of the extrudate path and respective carriages therefor which together are movable transversely with respect to the extrudate path by respective worms and translating nuts and a common worm drive. One shoe is operative to support the bottom surface of the extrudate in a predetermined position while the other shoe rides on the extrudate and is position monitored by a transducer operative then to provide an output signal representative of the spacing between the shoes, and thus the thickness of the extrudate passing between the shoes, to remote monitoring circuitry located outside of the vacuum chamber.

Abstract: A system and a method for the production of thermoformable plastic foam material from a mix of plastic foam selvage and a foamable virgin plastic resin. Accordingly, the present invention provides for a selvage formed during the production of thermoformed foam material articles from a plastic foam sheet stock is recycled and admixed with the virgin foamable plastic resin, in that the material components are admixed in a feed hopper and then conducted from the feed hopper into a twin-screw compressor which will impart a positive forward feed to the compressible plastic materials conveyed therethrough.

Abstract: A foam extrusion die and monitoring apparatus, including a pair of adjustable die lip members having opposed, rigid die lips defining therebetween an elongated arcuate die orifice, is characterized by position sensors located along the arc of the die lips to monitor the die opening at such locations. The position sensors include sensing styli mounted for movement with the lip members at respective sensing locations such as at the arc ends and arc centers of the die lips, and provision is made for connecting the sensing styli as by precision push-pull, flexible cables to respective linear variable displacement transformers which provide electrical output signals representative of sensed positions to remotely located monitoring circuitry. The apparatus has particular application in a vacuum extrusion line wherein the extrusion die is located inside a vacuum chamber and thus is inaccessible during extrusion.

Abstract: A method and an apparatus for measuring and controlling foam sheet blow-up in a thermoformer oven. Control of the oven operation is achieved through monitoring the measured blow-up of a material which being heated in the thermoformer oven in order to regulate the thickness of the plastic material prior to its conveyance into a molding or forming station.