Abstract:
A thermoplastic board ( 20 ) comprising at least one smooth side edge ( 21 ) is produced by means of extrusion. The side edge of a synthetic web is heated at least to its melting temperature following calibration while the peripheral surface zones are kept at a temperature below the softening temperature by cooling. A smoothing device ( 10′ ) for a side edge of the thermoplastic board encompasses a guiding groove ( 14′ ) that is provided with at least one heating means ( 15′ ), located within the face ( 11′ ), and at least one respective cooling means ( 16′, 17′ ) located within the side surfaces ( 12′, 13′ ) that face each other. A cutting edge ( 21, 24 ) of a synthetic board ( 20 ) that can be guided inside the guiding groove ( 14′ ) rests against the face ( 11′ ) while the peripheral surface zones ( 22, 23 ) thereof lean against the side surfaces ( 12′, 13′ ).

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a method for producing a thermoplastic board comprising at least one smooth side edge. 
     Integral foam boards exhibiting a core of a foamed synthetic and sealed smooth surfaces are known. The surfaces can be manufactured pore-free and with a great luster by extrusion, for example, of hard PVC, and can be used in numerous applications. A particular advantage is the low density of the board, which is reduced due to the porous core. 
     However, the board widths vary during the extrusion process such that for applications, where plane edge surfaces and exact edge radii are important, the edges must be trimmed laterally to achieve the desired board width. Although it is possible to obtain a precise and straight side edge in this manner, the structure of the layers, and in particular the core with its coarse porosity, is visible, which may look objectionable in contrast to the shiny dense surfaces of the board. In addition, dirt and bacteria may be deposited in the coarse pores of the cut edges, which is a disadvantage for the preferred fields of application of integral foam boards, such as sanitary areas, medical technology and emergency vehicles. 
     In addition, with solid synthetic boards, the side edges are not always burr-free and smooth after trimming. 
     Often, the cut-out boards must be installed such that the cut edges are not visible, for example by framing the edges in profiles. 
     SUMMARY OF THE INVENTION 
     The principal objective of the invention is to improve the method for the extrusion of a thermoplastic board, in particular of an integral foam board, of the type described above such that the boards are sealed and/or smoothed on at least one side edge. 
     This objective is achieved in that, following calibration, the side edge of the web is heated to at least the melting temperature while the peripheral surface zones are kept at a temperature below the softening temperature by cooling of the same. 
     The particular advantage of the present invention is that a precise and homogenous side edge is achieved by the simultaneous cooling of the peripheral surface zones of the synthetic board during the fusion process at the face area. 
     The fusion process together with a small contact pressure of the smoothing device results in exact shaping of the side edge, which is determined by the contour of the smoothing device. Existing irregularities such as scores are removed. 
     Integrating the steps of the method subject to the invention into a typical extrusion process leads to pulling the molten side edge along at the feed rate at the face side of the smoothing device and thus to a smooth side edge. 
     Through cooling, the dimensional stability is retained in the peripheral zones of the board in spite of the melting of the side edge. This avoids warping, bending or other damage of the large plane board surfaces. 
     In addition, the invention relates to a smoothing device for a side edge of a thermoplastic board suitable for carrying out the method. 
     As a guiding groove, a configuration is defined that can be pressed against the side edge to be smoothed and in which, at the same time, the peripheral surface zones of the board are guided. This guiding groove can be molded into a metallic object. However, it may also be formed, for example, from three dies for the face area oriented at right angles to one another and the two side areas that are connected to one another in some other fashion. Important is only the U-shaped configuration of the three areas mentioned, within which the board is guided. 
     To avoid heat conduction within the smoothing device as much as possible, at least one thermal insulation layer may be provided between the respective means for heating and cooling or between the face area and the side area. 
     It is particularly advantageous if at least one insulation zone is provided between one cross-sectional zone where a heating means is located and one cross-sectional zone where a cooling means is located, where said insulation zone is formed by a guiding groove or a borehole that stretches across a major portion of the length of the smoothing device. 
     The air layer located in the guiding groove or the borehole blocks the heat transfer to a large extent, such that the heat loss in the heating zone is essentially defined by the strongly reduced heat streams that flow across the connecting webs between the heating and the cooling zones. Thus, less heating energy is required for the heating zones and less energy for maintaining the temperature of the cooling means in the cooling zones. In addition, the greater temperature gradient is created at the treated side edge of a synthetic board, such that the dimensional stability of the cooled peripheral surface zones is increased and, at the same time, melting is accelerated due to the increased heat transfer into the side edges. Due to the improved cooling of the adjacent zones, the molten synthetic at the side edge will solidify faster, such that deformations after the run through the smoothing device are avoided. 
     A heat channel with a heated liquid such as oil, for example, flowing through it can be provided as a means of heating. The temperature of the liquid can be maintained exactly outside of the device, such that the heat transfer into the heating zone can be defined. 
     As an alternative, the heating means may be formed by at least one electrical heating cartridge. Its advantage over heating with a temperature-controlled liquid is a better and faster reacting temperature control. No direct heat losses of the heating means to the surroundings occur because the heating cartridge is integrated into the smoothing device using boreholes. 
     It has proven particularly advantageous if the heating means stretch across 0.4 to 0.6 times the length of the smoothing device. When heating only across about half of the length of the smoothing device, a zone of the smoothing device of about the same length remains which is cooled down but is no longer heated, enabling a cooling down of the thermoplastic material to below the softening temperature, while the side edges still run in the guiding groove of the smoothing device and are calibrated above it. 
     In particular, cooling channels with cooling liquids, especially water, flowing through them are provided as the means of cooling. 
     Preferably, the cooling channels are fed by a common cooling liquid lead line, such that a uniform temperature level can be achieved at the peripheral zones at the top and bottom sides of the synthetic board. For this reason, the cross-section of the smoothing device should be mirror-symmetrical, at least with regard to the cross-sectional areas for cooling. 
     To be able to re-machine existing board cuts, i.e., independent of the extrusion of continuous synthetic boards, an edge machining system with the features of Claim  15  or  16  is proposed additionally. 
     According to a first embodiment, the cut board is secured on a movable carriage of a guiding device and pulled through the stationary smoothing device. 
     According to a second embodiment, the synthetic board is secured stationary and is re-machined using a movable smoothing device, which is moved alongside the side edge. 
     Preferably, two smoothing devices are provided that are oriented symmetrical with regard to the direction of movement. In this manner, it is possible to finish two parallel edges at opposite sides simultaneously. This not only refers to rectangular cuts but also polygonal cuts with an even number of edges. 
     It is also advantageous if the carriage on which the board is secured, or the carriage that carries the at least one smoothing device, is provided with a rotating device. In this manner, it is possible to finish all edges in succession using only one smoothing device or one pair of symmetrical smoothing devices on opposite sides, without re-clamping the cut synthetic boards, even using automatic process controls. 
     To not only have the option of processing square cuts but also rectangular ones, preferably an adjustment device, acting perpendicular to the symmetry axis of the synthetic board, is provided for the at least one smoothing device. In this manner, the smoothing device can be moved and adapted automatically to the changed distance of one side edge after rotating the cut board. 
     For a full understanding of the present invention, reference should now be made to the following detailed description of the preferred embodiments of the invention as illustrated in the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view of a portion of a device for the manufacture of a synthetic board. 
         FIG. 2  shows a first embodiment of a smoothing device also in a perspective view. 
         FIG. 3  is a front view of a second embodiment of the smoothing device. 
         FIG. 4  is a top view of the smoothing device of  FIG. 3 . 
         FIGS. 5 and 6  are schematic top views of two embodiments of an edge machining system. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments of the present invention will now be described with reference to  FIGS. 1-6  of the drawings. Identical elements in the various figures are designated with the same reference numerals. 
       FIG. 1  shows a synthetic board  20  of a thermoplastic synthetic, for instance an integral foam web, which is produced continuously using an essentially known—not shown—extrusion device. 
     In the embodiment shown, the side edges  21  of the synthetic board  20  are cut in a straight line using suitable cutting devices  32 . At the side edges  21 , smoothing devices  10  that partially melt the surface zones located at the side edges are pressed onto both sides viewed in the drawing direction and, in so doing, homogenize and smooth the side edges  21 . 
     Where cutting of the side edge is not required, the untreated edge is guided to the smoothing device subject to the invention. 
     The peripheral zones  22 ,  23  at the side edges  21  are cooled when guided through the smoothing devices  10 , such that they remain dimensionally stable. In this manner, the particularly high-gloss surfaces of the synthetic board  20  retain their shape and surface structure in the peripheral zones  22 ,  23 . 
       FIG. 1  shows a smoothing device  10 ′ subject to the invention, which is formed of a metallic or otherwise heat-conducting object, which exhibits a guiding groove  14 ′. The guiding groove  14 ′ is defined by side areas  12 ′,  13 ′ and a face area  11 ′, with the side areas  12 ′,  13 ′ being primarily oriented plane-parallel to one another but in a zone towards the outside of the smoothing device  10 ′, are preferably slanted at a small angle to the center axis of the guiding groove toward the outside, such that an inlet slant is created. This transition avoids damage to the surface of the synthetic board  20  at the outer circumference of the smoothing device through scrape marks or the like. Here, the inlet slant refers to an expanding zone that may be formed by a plane area but also by a curved area. The latter offers the advantage that a continuous transition into the guiding groove, i.e., without an edge, is provided. 
     The face area  11 ′ is heated by hot oil, which flows through heating channels  15 ′, to a temperature of 130° C. to 250° C., in particular to about 185° C., such that a thermoplastic material such as hard PVC is melted in a localized area. 
     The length of the smoothing device is selected in relation to the drawing speed of the synthetic board  20  such that sufficient heat to reach melting temperature can be transferred during the contact of the side edge  21  with the face side  11 , without affecting too great a heat transfer into the core layers of the board that lie behind the side edge  21 . 
     To avoid too much of a heat transfer into the board, which could lead to a heating up of the peripheral zones  22 ,  23 , thereby exceeding the softening point with a resulting deformation, the side areas  12 ′,  13 ′ in the guiding groove  14 ′ are cooled using a cooling agent, in particular water, such that their temperature corresponds to about the surrounding temperature. 
       FIG. 3  shows a second embodiment of a smoothing device  10 , which, just like the first embodiment, is formed of a metallic or otherwise heat-conducting object exhibiting a guiding groove  14 . 
     The face area  11  is heated by a heating cartridge. 
     The heating cartridge  15  is extensively shielded from the surrounding zones through recesses  18 . 1 , . . . ,  18 . 5 , which stretch along the length of the smoothing device  10 , against the other material zones of the smoothing device, in particular the cooling channels  16 ,  17 . 
     The recesses  18 . 1 ,  18 . 3 ,  18 . 4 , which can be made by eroding, form an arch-shaped clasp in the shown exemplary embodiment, with the open side of said clasp being directed towards the face area  11  of the guiding groove  14  to be heated. 
     Only narrow webs  19 . 1  . . .  19 . 4  of solid material exist between the recesses  18 . 1 ,  18 . 3 ,  18 . 4  and the guiding groove  14 . These very narrow webs connect the heating cartridge  15  and the material zone surrounding it to the remaining cross-section of the smoothing device. However, the heat transfer across the narrow webs  19 . 1  . . .  19 . 4  is greatly restricted. 
     Additional recesses  18 . 2 ,  18 . 5  stretch parallel to the face area  11  and provide additional shielding of the heated cross-sectional zone of the smoothing device  10  located at the left in  FIG. 3  and the cooled cross-sectional zones above and below the guiding groove  14  located to the right of it. 
     As can be seen in particular in  FIG. 4  in a top view with covered lines to the smoothing device  10 , not only do the face areas jump at the peripheries towards the synthetic board to the outside, but also the guiding groove  14  at its beginning viewed with regard to the direction of movement  1 , exhibits an inlet slant  14 . 1 . Preferably, the transition from the inlet zone into the actual zone of the guiding groove is continuous, i.e., without an edge at the transition and thus without a sudden buckling of the molten side edge  21  of the synthetic board during re-machining. 
     In  FIG. 4 , it can also be noted that the heating cartridge  15  stretches across about half of the length of the smoothing device  10 . However, the section of the smoothing device that in  FIG. 4  is located above the heating cartridge  15  is also cooled above and below the guiding groove  14 , such that solidification of the molten material zone occurs with simultaneous guiding and calibration in the guiding groove  14 , before the molten zone of the side edge exits the smoothing device  10 . 
       FIG. 5  shows an edge machining system  100 , comprising a drive device consisting of a motor  32 , a guide  33  and a drive spindle  34 , as well as a carriage with means  35  for securing a synthetic board  20 . 
     The synthetic board  20  secured on the carriage can be moved in a direction of movement  2 , whereby the side edge  21  and the peripheral surface zone  22  are pulled through the smoothing device  10  and are re-machined there. 
     Two smoothing devices  10  positioned mirror-symmetric to the direction of movement  2  allow for simultaneous treatment of the side edges  21 ,  24  located on opposite sides in the guiding grooves  14 . 
     In addition, a rotating device may be provided with which the synthetic board  20  can be rotated relative to the carriage in the rotational direction designated with the number  3 . In this manner, the other side edges of the synthetic board  20  can be re-machined as well after a 90° rotation. 
       FIG. 6  shows an additional embodiment of an edge machining system  100 ′, where the synthetic board  20  can be stationary secured using a securing device  35 ′. The smoothing device  10  is guided in a movable fashion at a spindle  34 ′, which is driven by a motor  32 ′ and is guided with its guiding groove  14  along the side edge  21  or the peripheral zone  22  of the synthetic board  20 . 
     There has thus been shown and described a novel method for the production of a thermoplastic board comprising at least one smooth edge, device therefore, and edge machining system which fulfills all the objects and advantages sought therefor. Many changes, modifications, variations and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering this specification and the accompanying drawings which disclose the preferred embodiments thereof. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention, which is to be limited only by the claims which follow.