Abstract:
A device for applying plastic onto a workpiece, consisting of a supply area to insert flowing plastic, a distribution area which follows the supply area in the flow direction of the plastic, and a nozzle area which follows the distribution area, wherein a circular opening in the device is surrounded by an annular outlet in the nozzle region, and a workpiece that is arranged within the opening is moveable in an axial direction with respect to the outlet and can be covered with plastic over its entire circumference. A device for the application of plastic is provided herein, which makes possible a uniform application over the entire circumference, even for large workpieces.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority of German patent application Nos. 10 2006 050 543.3 filed on Oct. 26, 2006 and 10 2007 007 139.8 filed on Feb. 9, 2007, the content of which is incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The invention concerns a device for applying plastic to a workpiece. Additionally, the invention concerns a method for producing a plastic corrugated pipe by means of the inventive device as well as the plastic pipe produced by this method. 
       BACKGROUND OF THE INVENTION 
       [0003]    EP 1 243 400 B1 describes a device for producing corrugated pipes which will allow the production of an indefinite number of plastic pipes with corrugated surfaces by means of an extruder device and a subsequent molding segment. Such corrugated surfaces provide good pipe ring stiffness for the least amount of material. It may be desirable to cover these or similar pipes with an additional outer coating of plastic, depending on the specific request. 
         [0004]    It is the invention&#39;s task to provide a device for the application of plastic to workpieces which makes possible a uniform application in the circumferential direction for large workpieces. 
       SUMMARY OF THE INVENTION 
       [0005]    This task is achieved by the inventive device with the features in Claim  1 . An especially uniform application of plastic in the circumferential direction of the workpiece is made possible by a distribution area with a ring-shaped outlet. 
         [0006]    In the preferred embodiment, the supply region includes a first, tubular supply line which branches into a number of secondary supply lines. In this way, the supply region can receive the first allocation of the plastic into at least two supply lines, and said plastic is ultimately to be applied as homogeneously as possible over the surface. It is preferred that at least one of the secondary supply lines branch into a number of tertiary supply lines, so that at least three and preferably four separate, evenly applied supply lines are present over the surface. The lines of the respective branching planes can then be reduced I cross-section, depending on the distribution of the flow of plastic. 
         [0007]    It is also advantageous if the supply region contains a number of distribution channels extending outwards from it in the circumferential direction of the circular opening. Thereby, the distribution channels are advantageously branched into at least one distribution plane. In this way, an additionally branching pre-allocation over the surface of the workpiece becomes possible even in the phase of the plastic supply. 
         [0008]    In the interests of achieving simple and effective production with easy maintenance access, the distribution plane contains a number of plate elements, where the distribution channels are molded to the plate elements. It is useful for the plate elements to be arranged on top of one another in the axial direction, so that the channels can be developed as grooves or bores in the circumferential direction. 
         [0009]    In a preferred embodiment, in order to guarantee sufficient pre-allocation of the plastic in the supply phase, particularly for workpieces with large diameters, the plastic flows from the supply region to the distribution region over at least 16, particularly at least 32, canals distributed in the circumferential direction of the opening. In a generally advantageous manner, the number of input points corresponds to a power, of 2. 
         [0010]    In a preferred embodiment of the invention, the distribution area has a ring-shaped cavity, so that the plastic flows into the cavity through a number of supply canals distributed in the circumferential direction and exits from the cavity through an annular gap. The circular cavity primarily brings about a homogenization of the plastic flow, so that the annular gap receives an even flow from the regularly highly viscous material. In an advantageous embodiment, the cavity has a decreasing cross-section in the radial direction from the outside inwards. In this way, the passage cross-section for the plastic flow decreases in the direction of the flow, which leads to the desired backlog. Particularly importantly, the cross-section takes the form of a triangle shrinking in the radial direction. The plastic has a main direction of flow in the distribution area cavity which runs radially from the outside inwards; a flow in the circumferential direction can be superimposed over this main direction of flow. It has been shown that this configuration allows good homogenization of the plastic to be achieved with a relatively small space available for the distribution area, especially for workpieces with large diameters. In addition, this solution is simple to produce and mechanically stable even at high pressure. 
         [0011]    In an advantageous refinement, the cavity has a wall with a number of spiral grooves. The plastic mass is admitted into these grooves with a flow in the circumferential direction, where manipulation of the individual flow sections takes place depending on the construction of the grooves in order to assure good homogenization of the plastic. For this purpose, the wall preferably makes an angle with the radial plane, perpendicular to the axial direction, which is less than about 45°, particularly less than 30°, particularly between about 18° and 25°. 
         [0012]    A simple possibility for fine-tuning of the plastic flow in the distribution area is offered when at least a few, particularly all, of the supply canals have a throttle element for adjusting the cross-section of the canal. In a simple construction, each throttle element can have an adjusting screw protruding into the canal. The throttle elements are advantageously distributed around the periphery of the device and should be adjustable from the outside so that, in particular, adjustments of the throttle elements can be made while the device is in use. In this way, it is possible, even during application, to react to changes due to temperature or fouling in the areas where the plastic is flowing. 
         [0013]    In a simply constructed realization, the distribution area includes a ring-shaped distribution disk, where a wall of the cavity is molded to the distribution disk on the axial front side. The supply canals to the cavity are then configured as axial bores appropriately distributed over the distribution disk. If the supply canals are furnished with throttle elements, they can functionally include radial thread canals, through each of which an adjustment screw feeds into the supply canals. 
         [0014]    In an advantageous embodiment of the invention, the nozzle area has a rotationally symmetric annular gap in the axial direction, so that the plastic flows from the distribution area through the annular gap to the outlet. The annular gap does not have a stud in its path, so that the homogenization of the plastic flow in the circumferential direction is not affected. 
         [0015]    In the preferred embodiment, the annular gap has at least a first and a second segment, where the first section runs axially and the second at an angle to the axial direction. By thus dividing the annular gap into different sections, an additional optimization of the plastic flow can be achieved, particularly regarding changes in pressure and flow velocity. It is particularly preferred that at least one of the two segments has a decreasing cross-section throughout its path, to ensure the desired back-up of the plastic. 
         [0016]    In a particularly optimal embodiment, the first segment of the annular gap comes after the distribution area in the direction of flow and the second segment follows the first segment, and the second segment has conical walls with varying cone angles. 
         [0017]    In a more complete implementation, the annular gap also has a back-up ring area, where a local decrease in cross-section of the annular gap is configured through the back-up ring area. In this way, a targeted back-up of plastic is possible at an appropriate distance from the outlet. The cross-section decrease can, for example, be formed by an axially cylindrical gap of particularly small passage cross-section or as a ring-shaped projection which protrudes locally into the opening in order to decrease the cross-section. 
         [0018]    In a preferred implementation, the outlet opening is configured as the last segment of the annular gap, so that the outlet has a conical wall angled radially inwards in the direction of flow of the plastic. In an advantageous embodiment, the outlet opening has two conical walls with different cone angles, and the cross-section of the outlet narrows in the direction of flow of the plastic. Thus, in a simple way, the plastic flow is particular uniform and free of fluctuation. 
         [0019]    In order to make adjustments possible and in the general interest of simple production, the outlet opening is placed between the first ring element and the second ring element in the nozzle area. It is particularly preferred that the outlet be adjustable through mobility of at least one of the ring elements. 
         [0020]    In an advantageous implementation, the mobility is effected by the elastic malleability of the ring element by means of radial prestressing tendons. In a simply constructed realization, the tendons consist of a number of clamping bolts distributed radially around the periphery of the ring element, and the clamping bolts are adjustable, especially when the device is in use. Owing to this possibility of radially deforming at least one of the ring elements, the homogeneity of the material flow can be optimized in the circumferential direction, to compensate for changes during operation, for example pressure distribution or mechanical deformation due to pressure and temperature. 
         [0021]    Alternatively or complementarily, it is intended that the first ring element and the second element be adjustable relative to one another in the axial direction. In this way, this size of the outlet opening can be modified over the entire device. In a simple configuration, modifiable spacing elements are placed with one of the ring elements to adjust the distance between it and the second ring element. 
         [0022]    Alternatively or complementarily to the changeable spacing means, the first ring element can be adjusted to at least one thread relative to the second ring element. In this way, a simple and continuous adjustment is possible which, depending on the design, can also be carried out while the device is in use. 
         [0023]    In a particularly preferred implementation, a second thread is included, so that the first and second threads have a different pitch. In this way, a differential thread is made possible, so that a differential thread can generally make fine adjustments in distance possible. In a simply constructed realization, a threaded ring that can be rotated for axial adjustment works together with the two threads. The first ring element and the second element are then controlled by an axial guide element so that they can move axially with respect to one another. In this way, a particularly precise compulsory control becomes possible, which limits the relative mobility precisely in the axial direction. The axial guide element can consist simply of guided bolts that move in bore holes by sliding and with as little free play as possible. 
         [0024]    It is generally preferable for the device to have a means of heating to heat the surface of the workpiece. In this manner, the surface of the workpiece can be heated to a specific temperature before the application of the plastic. This makes it possible to pre-melt the surface, especially of workpieces made from thermoplastic materials, so that the applied plastic can form a good adhesive, molecular binding with the surface. Appropriate means of heating include electrical resistance heating, especially ceramic heating, or radiant heating systems with light, lasers, infrared radiation, microwaves, or similar means. Hot air heating or other suitable heating systems are also possible. 
         [0025]    In a preferred implementation, the device has at least one elastic scraper positioned so that it can slide and is contiguous with the workpiece. The workpiece can be guided by such scrapers. In particular, this can result in a seal that is at least roughly airtight, creating a closed and pressurized cavity between workpiece, plastic flow, and device. In this way, it becomes possible to mold the soft plastic hose in the course of the task. This is particularly important when cavities and furrows are trapped in the workpiece by the applied plastic, as the gas pressure in these cavities can be adjusted in this way. 
         [0026]    In a particularly preferred detailed implementation, the workpiece is a corrugated pipe, where the applied plastic forms an essentially smooth exterior wall of the corrugated pipe. The corrugated pipe preferably has a smooth interior wall. Such corrugated pipes with smooth interior walls are well known and are in growing demand because they have many uses, for example as canalization pipes, and. Until now, the application of an additional smooth layer from the outside has been problematic, especially in the case of pipes with large diameters. 
         [0027]    The plastic preferably consists of a polyolefin or another plastic with good stability when heated. 
         [0028]    In a preferred implementation, the workpiece is a pipe with an outer diameter of at least 700 mm. It is particularly preferred that the outer diameter of the pipe should be greater than 1200 mm, especially around 1800 mm. It has been shown that a device of the inventive construction is particularly suited for the application of a layer of plastic to very large pipes, where the applied layer is very homogenous, especially in the circumferential direction. 
         [0029]    In another preferred embodiment of the invention, distribution area is intended to have a ring-shaped cavity, so that the plastic flows into the cavity through a number of supply canals distributed around the circumference and exits the cavity through a surrounding annular gap. In this way, the cavity preferably has an inner side wall shaped to an inner distribution part and, opposite it, an outer side wall shaped to an outer distribution part, so that each of the side walls essentially has the form of a conical section. Because of the conical-section form of the two walls, the cavity is angled as a whole with respect to the axial direction, which will typically be directed radially inward in the direction of flow of the plastic. This results in a particularly advantageous pressurized flow of the plastic in the cavity. The advantageous pressurized flow allows for a particularly flexible configuration of the nozzle area with an unchanged distribution area. 
         [0030]    At least one groove extending essentially in the circumferential direction is configured on at least one of the two side walls, particularly the inner side wall, to improve the distribution and homogenization of the plastic. 
         [0031]    In order to achieve an advantageous pressurized flow in the distribution area, there should be an angle between one of the side walls and the axial direction of 10 to 45 degrees, preferably between 20 and 30 degrees. In a particularly preferred implementation, the side walls shaped like conic sections have different cone angles from one another, so that the difference between the cone angles is not more than 5 degrees, preferably 3 degrees. In order to improve the pressurized flow, this angle between the two conic section side walls must be selected so that the radial distance between the side walls increases in the direction of flow of the plastic. 
         [0032]    In an appropriately constructed embodiment, the annular gap is at least partially placed between an inner ring element and an outer ring element, and the outer ring element is configured to be adjusted by a spacing element. In this way, a corresponding adjustment, preferably an adjustment even during the manufacturing phase, can be made to set a desired wall strength for the plastic webs exiting from the annular gap. In a simple realization, the spacing element consists of a radially working actuator that is supported against the outer spacing element. 
         [0033]    In an appropriate embodiment of the invention, an end area of the annular gap is bounded by another ring element. It is particularly preferable for the additional ring element to be adjustable by a spacing element, so that in particular in versions with relatively long nozzle areas, multi-position adjustability of the annular gap is possible in at least two areas. The spacing element of the additional ring element for this purpose has a radially working adjustment piece that is supported in particular against the outer ring element. 
         [0034]    In an especially preferred implementation, the ring-shaped cavity has a diameter of more than 1700 mm, and in particular more than 1800 mm. The special characteristics of the inventive device thus allow a uniform and therefore high-quality application of a plastic coating over such large diameters. The annular gap preferably has a diameter of more than 1600 mm at the exit end, and in particular more than 1700 mm. In general the plastic piece that is created here should have a diameter that is only slightly less than that of the exit side cavity diameter. 
         [0035]    Another preferred embodiment of the invention encompasses a first set of ring elements, and at least a second set of ring elements, in which each of the sets of ring elements can be detachably secured to the distribution area, and the annular gap is shaped by the set of ring elements secured on each distribution area. In this way, at least in the given distribution area where the diameter has not been changed depending on the applied set of ring elements, plastic parts of various diameters can be coated. This appreciably raises the flexibility and the cost efficiency of the inventive device. In the preferred detailed embodiment, therefore, the first set of ring elements has a first diameter of the exit end of the annular gap, which is to be distinguished from a corresponding second diameter of the exit end of the annular gap of the second set of ring elements. 
         [0036]    Preferably, the first diameter is here larger than about 1600 mm, and especially larger than 1700 mm. It is further preferred that the second diameter be smaller than about 1200 mm, and in particular smaller than about 1000 mm. 
         [0037]    Thanks to these particular large differences in the diameter of ring element sets, economies in the costs of components can be expected, since the number of ring elements of the first set of ring elements is different from the number of ring elements of the second set of ring elements. In this way in general a ring element set with a large diameter of the annular gap includes fewer ring elements, since a shorter nozzle area is made possible because of the diameter similar to that of the distribution area. 
         [0038]    The invention also relates to a method for manufacturing a plastic corrugated pipe, including the steps for feeding a plastic corrugated pipe into a device according to claims  1  to  59 , and for applying a plastic coating on the fed-in corrugated pipe by means of the device. In particular corrugated pipes with an essentially smooth outer wall can be manufactured with such a process. 
         [0039]    The invention, in addition, relates to a plastic corrugated pipe manufactured in the method according to claim  60 . This detailed embodiment of the applied plastic coating forms an essentially smooth outer coating of the corrugated pipe. 
         [0040]    Other advantages and characteristics of the invention can be seen from the following description of the embodiment and from the associated claims. 
         [0041]    Hereafter several preferred embodiments of the inventive device are described and further discussed on with reference to the appended drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0042]      FIG. 1  shows a sectional view of a first embodiment of the inventive device along line A-A of  FIG. 3 . 
           [0043]      FIG. 2  shows a spatial presentation of the device from  FIG. 1 . 
           [0044]      FIG. 3  shows an overhead rear view of the device from  FIGS. 1 and 2 . 
           [0045]      FIG. 4  shows an overhead view of the distribution disk of the device from  FIG. 1 . 
           [0046]      FIG. 5  shows a sectional view of the distribution disk from  FIG. 4  along the line A-A. 
           [0047]      FIG. 6  shows a partial spatial presentation of the distribution disk from  FIG. 4 . 
           [0048]      FIG. 7  shows a detail enlargement of the device from  FIG. 1 . 
           [0049]      FIG. 8  shows a partial sectional presentation of a second embodiment of the inventive device. 
           [0050]      FIG. 9  shows a partial sectional view of a third embodiment of the inventive device. 
           [0051]      FIG. 10  shows a sectional view of another embodiment of the inventive device along line A-A of  FIG. 3 . 
           [0052]      FIG. 11  shows a variation of the device from  FIG. 10 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0053]    The inventive device according to the first embodiment from  FIG. 1  includes a primarily ring-shaped enclosing head  1 , which is held in a carrier frame  1   a . The enclosing head has a continuous circular central opening  2 , through which the workpiece  3  can be moved. The workpiece is predominantly a corrugated pipe  3  of plastic, in particular a polyolefin. The corrugated pipe  3  has a smooth inner layer  3   a  and a corrugated outer layer with corrugated peaks  3   b  and corrugated valleys  3   c . The corrugated pipe has an outer diameter d of about 1700 mm.  FIGS. 1 to 7  are each drawn to scale, so that the essential dimensions of the device can be deduced from the corresponding scaling. 
         [0054]    To apply a plastic layer, the workpiece  3  is moved through the opening  2  in an axial direction, and thus according to the presentation in  FIG. 1  from right to left. 
         [0055]    The enclosing head  1  has a supply area  4 , a distribution area  5 , and a nozzle area  6 , placed successively in the axial direction, and each of which can be passed through the heated and flowing plastic material. 
         [0056]    The supply area  4  comprises a primary main supply line  7 , through which a plastic material that arrives from an extruder (not shown in the illustration) is inserted into the device under pressure. In the supply area, this current of plastic material is divided into a total of 32 partial paths that are essentially of equal size. 
         [0057]    For this purpose, beginning from the main line  7 , the supply area  4  comprises a first distribution piece  8 , which divides the flow into two secondary supply lines  8   a ,  8   b . Each secondary supply line  8   a ,  8   b  flows to distribution pieces  9 , in which the flow is then divided into a total of four tertiary supply lines  9   a ,  9   b ,  9   c ,  9   d . In this way, a first distribution area is formed based on multiply branched discrete, pipe-like lines  8   a ,  8   b ,  9   a ,  9   b ,  9   c ,  9   c.    
         [0058]    The first distribution area is followed by a second distribution area, in which the flow of the plastic material is further divided up. The second distribution area consists of a number of plate elements  10  that extend in peripheral direction. Each of the four tertiary supply lines  9   a ,  9   b ,  9   c ,  9   d  flows into one of the four plate elements  10  of a first distribution plane of the second distribution area. Each of plate elements  10  comprises distribution channel that is branched symmetrically in relation to the site of the flow-in (not shown) in the form of a groove so that the number of the plastic material flows is again doubled. Each of the plate elements  10  of the first level is attached, flatly, to a plate element  11  of a second plane, and a corresponding arrangement of boreholes and groove-shaped supply channels of the plate elements  11  results in another doubling of the material flows. Each of the plate elements  11  of the second plate element plane is attached in turn to two of a total number of eight plate elements  12  of a third level, which analogously results in a last doubling of the number of the flow channels to a total of 32 channels. 
         [0059]    The last plane of plate elements  12  is screwed axially to a ring-shaped distribution disk  13 . A detailed illustration of the distribution disk  13  is shown in  FIGS. 4 to 6 . The distribution disk  13  comprises a number of boreholes and/or threaded blind holes  14  to assemble the plate elements  12  adjacent on one side and the ring elements adjacent at the other side (See subsequent description). 
         [0060]    In addition, the distribution disk  13  comprises 32 axial channels  15  configure as boreholes that are arranged in a peripheral circle at regular intervals and are connected to the 32 supply channels, designed as grooves, of the last plane of the plate elements  12 . A punched hole  15   a  with a thread coming in radial direction from outside leads into each of the axial channels  15 . These punched threaded holes  15   a  comprise setting screws (not shown) that extend in the corresponding radial direction and are accessible from outside. Depending on the adjustment of the setting screw, the free cross-section of each of the axial channels  15  can be modified so that the punched holes  15   a  together with setting screw function as a throttle element. 
         [0061]    An axial front surface of the distribution disk  13  is structured on the side of the distribution disk  13  that is opposite the plate elements  12 . The structure comprises a wall  16  that is inclined in the cross-section as shown in  FIG. 5 , namely a wall  16  in the shape of a conical segment, and this wall  16  comprises a number of spiral-shaped grooves  17 . Each of the grooves  17  extends over an angular segment of about 35-40 degree from the upper to the lower ends of the wall  16 . Over this course, the axial depth of the grooves levels off (see cross-section,  FIG. 5 ). The 32 channels  15  end in the upper or radially external end area of the wall  16 . The inclination of the wall in relation to the radial direction (or the plane of  FIG. 4 ) is about 22 degrees. In particular the values of the angular segments of the course of the grooves  17  indicated here and the inclination of the wall  16  are only indicative and can assume other values depending on the optimization of the device. 
         [0062]    The end face of the distribution disk  13  that is structured with the wall  16  is adjacent to an essentially planar side of the upper ring element  17  that is bolted to the distribution disk  13  by bolts  17   a  so that the wall  16  a the ring element  17  form a hollow space  18  (see the enlarged illustration in  FIG. 7 ), which in the cross-section has essentially the form of a radially inward-pointing acute triangle. 
         [0063]    This hollow space  18  functionally forms the main part of the distribution area  5  of the device. The plastic material that is fed through boreholes 15 to 32 points of entry, which are evenly distributed in a circle, flows through the hollow space  18  essentially in radial direction from outside inwards, and, in addition, the spiral-shaped grooves  17  create a flow component in the peripheral direction. This allows proper homogenization of the flow of the plastic material, which was first discreetly distributed to 32 channels in the peripheral direction. 
         [0064]    The radially inside end of the hollow space  18  or the peak of the triangle leads into an angular gap  19  that extends uninterruptedly in peripheral direction and defines the nozzle area  6  of the plastic material flow. 
         [0065]    The walls of the angular gap  19  are formed by the surfaces of a total of three ring elements, namely the ring element  17  firmly bolted to the distribution disk  13 , an inner ring element  20  that is also attached to the distribution disk  13  with bolt  20   a  extending beyond the distribution disk  13 , and finally a front ring element  21  bolted to the upper ring element with a bolt  21   a . Because of corresponding shaping of the opposite surfaces of the ring elements  17 ,  20 ,  21  that are distanced so as to form the angular gap  19 , the gap forms a path that is optimal for the flow of the plastic material: 
         [0066]    The radially inner top of the hollow space  18  is adjacent to a first segment  19   a  that extends in the axial direction, that is, has the shape of a cylinder sleeve and has a constant flow cross-section. Then follows a second segment  19   b , which extends in the flow direction conically and in radial direction inwards, and the two conical wall sections of the involved ring elements  17 ,  20  have a different cone angle. Consequently the gap narrows down over its course so that its passage cross-section decreases with the flow path more rapidly than in a linear fashion. 
         [0067]    Adjacent to this double conical second segment  19   b , there is in turn a back-up area  19   c  in the form of an axial segment, which has a reduced cross-section area due to the distance between the walls. 
         [0068]    The gate ring area  19   c  is followed finally by an outlet  19   d , which narrows down similarly as the second segment  19   b  double conically and from which the plastic material exits. The outer conical wall of the outlet  19   d  is formed by the front ring element  21 . The distancing elements  21   b  in the form of inserted spacing disks or a single spacing ring are located between the front ring element  21  and the upper ring element  17 . This allows adjustment in the size of the outlet  19   d.    
         [0069]    Contiguous to the outlet  19   d  is an elastic scraper  22 , which slides on the undulated surface of the corrugated pipe  3 . In addition, on the other end of the device at the level of the supply area  4 , there are additional scrapers  22  so that a closed space is formed between the inner wall of the device and the outer wall of the workpiece  3 . Depending on the configuration, the space can also be closed off at one side by the exiting plastic material. The application of the plastic material can be influenced by targeted application of pressure using provided gas channels (not shown). For example, the gas pressure can be adjusted in the closed areas between the applied plastic material and the troughs of the corrugation ribs in order to achieve the desired concave, convex, or flat surface in the area of the ripple troughs after cooling off the plastic material. 
         [0070]    Moreover, a number of tensioning screws  23  that are distributed around its circumference and held in radial threaded boreholes of the upper ring exert force upon the front ring element  21 . In their entirety, the tensioning screws  23  provide a tensioning element, which allows an essentially radial deformation of the front ring element  20  so that the size of the outlet  19   d  can be changed in the direction of its circumference. This allows fine-tuning of the plastic material flow also during the operation in order to guarantee a defined thickness of the applied coat that is also constant over the entire layer. 
         [0071]    Furthermore, inside the opening  2  the device comprises a heating element  24 , which is positioned at a short distance from the surface of the workpiece  3 . The heating element  24  warms up the surface of the workpiece, primarily a corrugated pipe made of plastic material, and especially melts it down so that the applied plastic material creates a firm connection with the surface. For this purpose, the workpiece and the applied plastic material are ideally made of the same material or of suitable pairs of materials. 
         [0072]    A variant of the first embodiment is shown in  FIG. 8 . Functionally similar components are labeled with the same reference marks. A substantial difference consists in the fact that the size of the angular gap  19  can be continuously modified by means of a thread, especially during the actual operation. For this purpose, the upper ring element  17  is designed in two parts, and the stationary part  17 ′ is firmly attached to a differently formed distribution disk  13 ′ and the rest of the device. A movable part  17  is adjacent to the stationary part through an axial cylinder surface  24  and can be shifted in the axial direction. The front ring element  21  is in turn firmly connected to the movable ring element component  17  and, together with the part  17 , can thus be moved in axial direction in relation to the stationary part  17 ′ and a likewise firmly attached lower ring element  20 . This axial movement changes the size of the annular gap  19 . 
         [0073]    The movable part  17  can move in axial direction by means of guide elements in the form of pivots  25 . The ring element parts  17 ,  17 ′, which can move in relation to each other, comprise on their outer circumference a first outer thread  26  and a second outer thread  27 , and the two threads have a slightly different pitch. A ring nut  28  engages, with correspondingly opposite thread areas at the same time, in the corresponding threads  26 ,  27 . Thus, by turning the ring nut  28 , which spans the device on its circumference, one can make especially fine adjustments of the annular gap  19  in the manner of a differential thread. 
         [0074]    In the variant shown in  FIG. 8 , the hollow space  18 ′ of the distribution area extends essentially in the axial direction and not in the radial direction. However, a threaded adjustment element for the annular gap  19  can also be arranged in the first embodiment without any problem. For this purpose, the upper ring element  17  can be cut apart, for example, at the level of the end of the first segment  19  analogously to the cylinder surface  24  and thus separated into a stationary and a movable part. 
         [0075]    Another variant of the embodiment is shown in  FIG. 9 . Compared to the first embodiment, the only substantial change is the continuous adjustability of the outlet  19   d , which is designed in a manner similar to the aforementioned adjusting option of the second embodiment. 
         [0076]    Here, the front ring element  21 , which forms the radial outer wall of the outlet  19   d , is not firmly bolted to the upper ring element  17  as in the first embodiment, but can be moved in axial direction in relation to this upper ring element  17 . The movement is exerted by force over mutually overlapping cylindrical guide surfaces  29 , and, as in the second embodiment (there, the cylinder surface  24 ) the overlapping and contact of the cylinder surfaces  29  without any free play ensures the sealing of the annular gap  19 . 
         [0077]    A differential ring nut  30  is arranged between the ring element  17  and the front ring element  21 . The ring nut  30  comprises an outer thread  31  that extends in axial direction, and engages with a corresponding inner thread on a reduced section of the ring element  17 . An inner thread  32  of the threaded nut concentric with the outer thread  31  spans the front ring element  21  and engages with a corresponding thread on its outer surface. 
         [0078]    In a similar configuration as in the second embodiment, the two threads  31 ,  32  of the ring nut  30  comprise different pitches so that the turning of the ring nut by a certain angle induces an especially small and thus finely adjustable axial movement of the front ring element  21  in relation to the upper ring element  17  and thus of the lower or the inner ring element  22 . 
         [0079]    At least one axial groove with an inserted parallel spline  33  is provided between the upper ring element  17  and the front ring element  21 . This provides an axial guiding element, which prevents a simultaneous turning, for example, of the front ring element  21 , when the ring nut  30  is turned. 
         [0080]    Based on the construction of the differential ring nut  30  between the front and upper ring elements, the arrangement of the tensioning element or a number of radial tensioning screws  23  is changed. In the third embodiment, the tensioning screws  23  do not press directly on the front ring element  21 , but rather on the upper ring element  17 . The tensioning screws  23  are bolted together or counter-positioned in a distancing ring  34  that is separate from the upper ring element  17 . The distancing ring  34  and the upper ring element  17  together correspond approximately to the upper ring element  17  from  FIG. 7 , or to the first embodiment. On one of its sides, the distancing ring is firmly bolted to the distribution disk  13  and thus forms a wall of the hollow space  18 . On its other end, the spacer ring  34  is firmly bolted with bolts  34   a  to the upper ring element  17 . Because of a suitable configuration of these bolt connections, and because of the high pressing forces of the tensioning screws  23 , there exists a sufficient possibility of a radial deformation of the upper ring element  17  and, through the adjacent surface  29 , also of the front ring element  21  to allow a fine adjustment of the outlet in the peripheral direction. Just as in the first embodiment, here too, the tensioning screws are accessible also during the production so that the system can be fine-tuned during the production both by using the ring nut  30  and by means of the tensioning screws  23 . 
         [0081]    In another preferred embodiment of the invention shown in  FIG. 10 , the distribution area  5  comprises a hollow space  118 , which has a different form from the hollow space of the first embodiment. This is essentially a ring space, which is delineated by an inner lateral wall  118   a  and an outer lateral wall  118   b , each of which has the form of the surface of a cone segment. The inner lateral wall  118   a  comprises a number of spiral-shaped grooves  118   c , which better distribute the plastic material that flows through the hollow space  118  analogously to the preceding embodiments of the invention. 
         [0082]    The conical walls of the hollow space  118  are inclined inward in the radial direction and in the direction of the flow. The cone angle of the two walls is of the same size, but not identical. The angle of the outer lateral wall  118   a  relatively to the axial direction is about 22 degrees and the angle of the outer wall is greater by about 2.5 degrees. Therefore, in the flow direction of the plastic material, the distance between the lateral walls  118   a ,  118   b  somewhat increases. 
         [0083]    Analogously to the first embodiment, the hollow space  118  is connected to the supply area  4  through a total of 32 supply channels  115 . The supply area  4  is configured exactly as in the first embodiment. The supply channels  115  are configured as boreholes in a ring-shaped inner distribution part  113 , which configures the inner lateral wall  118   a  of the hollow space  118 . Also analogously to the first embodiment, the punched holes  115   a  are oriented in radial direction from outside towards the channels  115  in order to allow adjustment of the flowing cross-section of the individual channels by means of inserted adjustment screws. 
         [0084]    The inner distribution part  113  is firmly bolted to an outer distribution part  117   a , which configures the outer lateral walls  118   b  of the hollow space  118 . 
         [0085]    The hollow space  118 , which mainly serves the purpose of homogenizing the flow of plastic material that is divided up among the 32 channels  115 , flows into a annular gap  119 . This gap is first configured between an outer ring element  117  and an inner ring element  112 . The ring element  117  can be adjusted in radial direction by means of adjusting elements configured as tensioning screws  117   b , and this is possible—depending on the requirements—by offsetting and/or by elastic deformation. In axial direction, the ring element  117  can be firmly bolted to the outer distribution part  117   a  using clamping screws  117   c , and these screws are somewhat loosened in order to adjust the outer ring element  117 . 
         [0086]    The inner ring element  120  is firmly connected to the inner distribution element  113  by means of axial screws  120   a  that penetrate the inner distribution element  113 . 
         [0087]    In the example shown in  FIG. 10 , the outer ring element  117  is followed by another ring element  121 , and the exit end  119   d  of the angular gap  119  is configured between the additional ring element  121  and the inner ring element  120 . The additional ring element  121  can be adjusted in radial direction by means of setting elements  123  in the form of tensioning screws  123 , and the tensioning screws  123  are retained or supported in the outer ring element  117  in a thread. This adds to the adjustability of the angular gaps  119  in its exit area  119   d.    
         [0088]    The corrugated pipe  103  shown in  FIG. 10  has an inner diameter of 762 mm (30 inches, diameter up to the inner wall  103  coated with corrugated web). The diameter of the angular gap  119  at its exit end is about 890 mm. The smallest diameter of the hollow space  118 , which must be measured at its exit end, is about 1,870 mm. This results in a relatively long course of the angular gap  119  so that the additional ring element is advantageous for adjustment. 
         [0089]    In their entirety, the inner ring element  120 , the outer ring element  117 , and the additional ring element  121  form a set of ring elements, which—with other components of the device left unchanged—can be exchanged in the manner of a module. 
         [0090]      FIG. 11  shows the same device as in  FIG. 10 , where, however, the illustrated first set of ring elements  117 ,  121 ,  121  has been replaced by a second set of ring elements  117 ′,  120 ′. The inner diameter of the outlet  119   d  is substantially greater, namely up to about 1,800 mm. The pipe  103 ′, accordingly, is a corrugated pipe with an inner diameter of 60 inches. Because of the proportionally shorter angular gap  119 ′, one of the ring elements and one adjusting option can be eliminated so that the nozzle area, or the angular gap  119 , is now formed only by one inner ring element  120 ′ and an outer ring element  117 ′. 
         [0091]    Depending on the set of ring elements arranged in the distribution area  104 , a part with a different diameter made of plastic material can be coated. In the present embodiment, as shown, the endeavor is to cover at least the area of about 30 inches up to about 60 inches inner diameter of the corrugated pipe, for which only the sets of ring elements need to be exchanged.