Abstract:
The invention relates to an apparatus for cooling and calibrating extruded plastic profiles with a trough which is provided downstream of a dry calibrating device and has a water bath through which the profile is guided, with plates being arranged in the trough between the face walls in order to calibrate the profile under the influence of negative pressure. In order to achieve a high production speed with a low amount of expenditure it is proposed that a sleeve encompassing the profile is provided in a section of the trough, which sleeve guides at least in a zone of the main body of the profile and that the sleeve is provided with a distance to the face walls in the longitudinal direction.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an apparatus for the cooling and calibration of extruded plastic profiles with a trough which is provided downstream of a dry calibrating device and comprises a water bath through which the profile is guided, with apertures being arranged in the trough between the face walls for calibrating the profile. 
     An installation for the production of plastic profiles as are used for the production of windows or doors usually currently comprises the following arrangement: An extruder produces a profile of doughy consistency made of plastic granulate. One or several dry calibrating devices will cool the profile to a certain extent, so that a somewhat stable form is achieved. Dry calibration substantially consists of a steel block with an opening through which the profile is guided and with a plurality of vacuum slots in order to suck the profile under pressure against the walls of the opening. In this way the collapse of the still soft profile is prevented. Furthermore, several cooling ducts are provided. One or several wet calibrating apparatuses will ensure the final cooling and shaping of the profile. Wet calibrating apparatuses according to the so-called swirl bath principle have proven to be particularly beneficial in the past few years. In such apparatuses the trough is subdivided by calibration plates into several chambers and a turbulent flow of the cooling medium in the trough is caused by openings in the plates. A negative pressure present in the trough will press the profile against the calibration plates. This allows for a precise calibration and rapid cooling of the profile with a lower water consumption. A caterpillar pull-off will draw the profile through the upstream calibrating devices. 
     The technical progress of extruders and the recipes for profile extrusion has led to continuously rising demands placed on the work speed of extrusion lines. In order to meet these demands it is currently common practice to arrange several dry calibrations behind one another and, downstream of the same, to provide one or several water baths. Dry calibrations are very costly, however, so that for cost reasons a reduction in their number would be desirable. 
     Calibration systems can be used for slow working extrusion lines which make do with only one single dry calibration with the common length of approx. 300 mm. If in such a system the work speed is increased over a relatively moderate value, high-quality profiles can no longer be produced. 
     DESCRIPTION OF THE PRIOR ART 
     From DE 27 40 989 A, a calibration device for plastic profiles is known in which a profile is calibrated and cooled under vacuum in a water bath. A pipe element is attached to the entry-sided face wall of the calibrating trough in order to guide and calibrate the profile after the entry over a certain distance. However, there are unclear pressure situations in the interior of this pipe, so that a close fit of the profile on the tube is not ensured. In particular, the wetting with the cooling water in the space between the profile and the sleeve is not ensured. 
     Moreover, from DE 27 34 831 A, an extrusion apparatus for pipes is known in which a water bath is provided immediately downstream of a dry calibration apparatus, which water bath is arranged as in the aforementioned specification. It substantially also has the same disadvantages. 
     SUMMARY OF THE INVENTION 
     It is the object of the present invention to avoid such disadvantages and, on the one hand, to achieve high production speeds by achieving, on the other hand, a reduction of the required expenditure. In particular, the present invention is to allow making do with only one single dry calibration of the usual length. 
     These objects are achieved in accordance with the invention that at least one sleeve encompassing the profile is provided in a section of the trough, which sleeve guides at least one zone of the main body of the profile and, that a gap between the profile and the sleeve is in connection with the water bath on either side. Preferably, the sleeve is provided in the longitudinal direction with a distance to the face walls. 
     It was established that a main cause of the inadequate profile quality in the case of reducing the number of dry calibration apparatuses is that the profiles enter the water bath in a still very hot and therefore soft state. As a result of the negative pressure which prevails by the system in such a wet calibration, the profile is pulled apart in the zones between the calibration apertures, as a result of which inner bridges of the profiles are expanded in an uncontrolled manner. Although the outer contour of the profile is finally brought back again to the desired shape by the calibration apertures, the inner bridges of the profiles are beyond repair. Such profiles can no longer be used in practice. 
     In the present invention the profile is protected in a first section of the water bath from the attack of the vacuum by the sleeve. As the forces by the vacuum are proportional to the surface area on which they act, a guidance of the profile is mainly required in the zone of the main body. 
     The relevant aspect in the invention is that the sleeve is in connection with the cooling water at least at either end. This is achieved most easily in such a way that the sleeve is provided at its face sides with a distance to adjacent components such as the face wall of the trough. Apertures in the sleeve can also be provided which secure a continual wetting of the gap between profile and sleeve. 
     It is particularly favourable if the length of the sleeve is between 100 and 400 mm, preferably between 250 and 320 mm. Particularly in the case when the sleeve is provided with a thin-walled arrangement a further rapid cooling of the profile is achieved by the cooling medium flowing in the outer zone of the sleeve, so that downstream of the sleeve the shape has already stabilised to such an extent that there is no danger of any over-extension of the inner bridges of the profile. 
     In a particularly favourable embodiment of the invention, a guidance is provided in particular in the zones of the connection of the inner bridges with the outer shape of the profile. In this way the particularly critical parts of the profile are reliably protected. 
     Preferably, the sleeve is arranged in an upstream area of the trough. Several sleeves can also be provided behind one another. A particularly reliable cooling without endangering the shape of the profile can be achieved in this way with simple means. 
     It is particularly favourable if the sleeve is held by several plates and if the plates subdivide the trough into chambers in the axial direction of the profile, with apertures being provided in the zone of the sleeves to allow cooling medium to flow through. It can be provided in particular that at one end of the trough there is provided an inlet opening for a cooling medium and at the other end of the trough an outlet opening for a cooling medium, so that the trough is substantially flowed through by a cooling medium in the longitudinal direction. An outstanding cooling effect can be achieved by this solution with a low water consumption. 
     A particularly simple arrangement of the apparatus in accordance with the invention can be achieved that preferably the sleeve and/or the calibration plates are held movable in a limited manner in one direction transversally to the axial direction of the profile. A complex adjustment of the sleeve and the calibration plates transversally to the axial direction of the profile can thus be omitted. Tensions and a clamping effect, owing to an insufficient adjustment, can thus be securely prevented. 
     The present invention further relates to a system for the cooling and calibration of extruded plastic profiles with a dry calibration in which the extruded profile is cooled and calibrated by the application of vacuum. In this process one or several troughs are optionally used in which calibration plates are arranged in a water bath. 
     A particularly precise adjustability and fine-tuning capacity of the calibration is enabled in such a way that a trough equipped with at least one sleeve is provided downstream with a further trough with calibration plates in which there is a lower negative pressure than in the first trough. 
     It has been seen further that the vacuum in the dry calibration device can be maintained in a particularly favourable manner in that the trough is directly flanged onto the downstream face side of the dry calibrating device, so that the same is directly in contact with the cooling medium. As a result of this embodiment, the power demand of the vacuum pump for the dry calibration is kept low and a stability of the achieved vacuum is reached which has a positive effect on the profile quality. 
     As a result of the system in accordance with the invention, existing production lines with only one dry calibrating unit can be operated with substantially higher production speeds. 
     The achievement of the highest possible extrusion speeds is possible in high-performance systems. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is now explained in closer detail by reference to the embodiments represented in the drawings, wherein: 
     FIG. 1 schematically shows an extrusion line with an apparatus in accordance with the invention; 
     FIG. 2 shows an apparatus in accordance with the invention in a side view on an enlarged scale; 
     FIG. 3 shows a sectional view according to line III—III in FIG. 2 on an enlarged scale and FIGS. 4 to  6  show altered embodiments in sectional views according to that of FIG.  3 . 
    
    
     In the description of the figures, components with a principally similar function are designated in the individual embodiments with the same reference numerals, even if their shape is different. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The extrusion line of FIG. 1 consists of the following components which are arranged successively behind one another: an extruder  1 , a dry calibrating device  2 , a wet calibrating device  3  and a caterpillar pull-off  4 . The wet calibrating device  3  consists of a trough  5  which is flanged directly onto the face wall  6  of the dry calibrating device  2  and which is occluded towards the caterpillar pull-off by a downstream face wall  7 . In the upstream zone, cooling water is supplied through a cooling water connection  8 , whereas at the other end of the trough  5  the cooling water is discharged from the trough  5  by way of a further cooling water connection  9 . A negative pressure is produced in the interior of the trough  5  by way of a vacuum connection  10 . In the upstream region of trough  5  a sleeve  11  is arranged which is held by two fixing devices  12 ,  13 . Sleeve  11  is slightly distanced from face wall  6 . The length  1  of sleeve  11  is 300 mm, like that of the dry calibrating device  2 . Calibrating plates  14 ,  15 ,  16  are provided downstream of sleeve  11 , which plates calibrate the profile  17  in the known manner. Apertures  18  in the plates  14 ,  15 ,  16  are used for producing a turbulent flow of the cooling water, as is described in the European Patent No. 0 659 536. 
     FIG. 2 shows a slightly altered embodiment of the present invention on an enlarged scale. In the embodiment of FIG. 2 the trough  5  is occluded at the upstream end by an own face wall  6   a . Two sleeves  11   a ,  11   b  are arranged behind one another in trough  5 . The sleeves  11   a ,  11   b  are held by plates  12   a ,  13   a  and  12   b ,  13   b , respectively. The distances x between the face wall  6  and the first sleeve  11   a  or the distances y between the first sleeve  11   a  and the second sleeve  11   b  are sufficiently small with a few millimeters in order to prevent any deformation of the profile as a result of the negative pressure in trough  5 . 
     A further trough  5   a  is connected on the downstream end of the trough  5  in accordance with the invention, which further trough is arranged in the common manner as a water bath, as is described in the European Patent No. 0 659 536. Said further trough  5   a  is not subjected to such a high negative pressure as the first trough  5 . Depending on the properties of the profile and the other boundary conditions of the calibration, the first trough is set approximately to an absolute pressure of 0.4 to 0.7 bars, whereas a pressure of between 0.6 to 0.8 bars is set in the second trough  5   a . Here, the absolute pressure in the second trough  5   a  is approx. 0.1 to 0.2 bars higher than in the first trough  5 . 
     The embodiment of FIG. 2 is also distinguished from the embodiment of FIG. 1 in that the cooling water is sucked in by way of a first inlet opening  8   a . No pump is provided in the zone of said first inlet opening  8   a  and the negative pressure in trough  5  is used exclusively to cause the inflow. The cooling water stream can be set by way of a regulating apparatus which is not shown. At the downstream side at the end of the trough a second connection  10   a  is provided which is connected with a regenerative water pump which is not shown here. On the one hand, the required vacuum in trough  5  is produced by way of said connection  10   a  and, on the other hand, the cooling medium is drawn off. As a result of this design, a strong negative pressure can be produced in trough  5  with relatively simple means. In summary, it is possible by the present invention to achieve an improved profile quality by a stronger evacuation of trough  5  because the profile  17  is pressed more strongly against the sleeves  11   a,    11   b  and the calibration plates  14 ,  15 ,  16 . 
     In the embodiment of FIG. 3, the profile  17  is completely encompassed by sleeve  11 . Sleeve  11  consists of the individual components  21 ,  22 ,  23  and  24  which are screwed together. Sleeve  11  of FIG. 3 is held floatingly in plates, of which plate  13   a  is visible in FIG.  3 . As a result of this arrangement, the precise position of sleeve  11  is determined by the profile  17 , so that an arrangement with precise true alignment of all plates is not required in the production of the apparatus in accordance with the invention. As a result of the slight mobility of sleeve  11  in plate  13   a , any slight imprecisions can be compensated without causing any danger of unnecessary deformation of the profile  17  or any jamming. A plurality of recesses  25  is provided between the sleeve  11  which cause a turbulent flow of the cooling water directly on the outer side of the sleeve  11 . A particularly intensive cooling of the sleeve  11  is achieved in this way. 
     The embodiment of FIG. 4 corresponds substantially to the one of FIG. 3 with the difference that the plate is composed of four single parts  33   a ,  33   b ,  33   c  and  33   d  so as to allow an installation of the sleeve  11  from above. The sleeve  11  with its individual components  21 ,  22 ,  23  and  24  is not screwed together in this embodiment, but is held together by the plate  33   a  to  33   d . A floating mounting is naturally not possible in the vertical direction in this embodiment. Projections  31  in the plate element  33   a  and  32  in the plate element  33   d  hold the sleeve  11  in a vertically precisely defined position and press the individual parts  21  to  24  of sleeve  11 . 
     The individual parts  21  to  24  of sleeve  11  are also held together by the plate sections  33   a ,  33   b ,  33   c  and  33   d  in the embodiment of FIG.  5 . The difference in this embodiment is that the sleeve  11  does not completely encompass the profile  17 . A first profile projection  17   a  projects freely upwardly from the sleeve  11 . A second profile projection  17   b  is enclosed with a distance by sleeve  11 . Lining grooves  17   c ,  17   d  and  17   e  are placed freely in the inner zone and a free placement is also provided in a corner zone  17   f  of the profile  17 , i.e. a gap between sleeve  11  and profile  17 . In this way the friction between profile  17  and the sleeve  11  can be reduced without impairing the efficiency of the present invention. The relevant aspect is that the large-surface wall areas of profile  17  are securely supported by sleeve  11 . 
     FIG. 6 shows a particularly simple embodiment of the invention which is suitable for small profile cross sections. The inner profile of sleeve  11 , which is composed of two components  21  and  22 , is eroded into a cylindrical blank. The embodiment of FIG. 6 is arranged in such a way that sleeve  11  is rigidly connected with the lower plate section  33   a , with the two parts  11   a  and  11   b  of the sleeve  11  being tightly screwed together. It is obvious for the man skilled in the art that this cylindrical sleeve  11  can also be held floatingly. 
     The present invention allows the highest possible production speed at an extremely inexpensive arrangement of an extrusion line. Already existing tools can be retrofitted in a simple manner in order to achieve a considerably increased production output. As no slots or apertures are provided in the sleeves transversally to the direction of production, a high surface quality is achieved. 
     Furthermore, an extremely low friction is achieved by a water film between profile and sleeve, which ensures a very low shrinkage. All told, it is possible by the present invention to combine the function of a dry calibration with the simplicity of a swirl bath and to achieve with simple means the highest production output at good quality.