Patent Publication Number: US-8118370-B2

Title: Milling head and method for machining pile heads

Description:
The invention relates to a milling head and to a method for machining pile heads according to the introductory clause of claims  1  and  9 . 
     Milling heads for civil engineering are known for example from [1], “SPITZEN-TECHNOLOGIE, DIE WELTWEIT WEGE WEIST”, product catalogue of erkat-spezialmaschinen-service-gmbh, www.erkat.de, and from [2], DE 100 41 275 A1. 
     [1] discloses a device for machining pile heads which comprises a milling head (type erkat 300-2L) fixed to a hydraulic support unit such as an excavator. According to [1] the head of a pile can be machined with this device within 30 minutes. 
     Piles of this type to be machined which must typically be provided at unstable sites to support a structure are made of concrete which can be pressure loaded and reinforcing iron which can be tension loaded. The dimensions of the piles are selected according to the structure and the site and can vary within a wide range. Typically, piles are used which have a length of 5 to 50 meters and diameters of 0.4 to 2 meters. In order to manufacture the piles, holes are drilled for example in the ground, into which pipes are inserted. The reinforcing iron is inserted into the pipes and the concrete is filled in. Earth material at the bottom end of the pipe is thereby mostly displaced upwards and after completion of the pile is mostly in its head area, which is why the latter does not have the necessary strength. Furthermore, the pile or its head do not normally have the necessary dimensions. Coupling elements needed for the structure may also be absent. The pile head is therefore mostly machined and newly constructed with the required dimensions and the necessary quality. 
     For this, the pre-manufactured, normally cylindrical pile head, for example as shown in [1], is machined using a milling head typically over a length of 0.4 to 1 meter, in order to remove the defective concrete. The concrete must thereby be removed in such a way that the reinforcing iron typically arranged coaxially with the longitudinal axis of the pile is not damaged. By means of the milling head shown in [1] the pile core is milled out within the reinforcing iron as far as the edge of the reinforcing iron, whereby it depends upon the skill of the excavator driver whether the reinforcing iron is damaged or not. Then, the outer pile shaft adjacent to the iron reinforcement is removed, whereby this is even more difficult by means of the milling head according to [1]. If, on the other hand, the iron reinforcement is damaged, there are consequent strength problems or it is even necessary to refurbish the pile with considerable additional resources. The released original reinforcement must therefore fulfil certain requirements in order that the supplementary reinforcement can be assembled. 
     After the removal of the concrete and the release of the reinforcement the latter is normally extended by the supplementary reinforcement and provided with a casing which corresponds to the dimensions of the pile head to be newly created. The casing is then filled with concrete and removed once the concrete has set. 
     With the device described in [1] therefore the machining of the pile head is only possible using great time resources and skill, whereby there is always a considerable risk that the reinforcement will be damaged. 
     In order to accomplish more complex tasks, a complex system is disclosed in [2] with milling cutters that can be put together as desired, but which is not suitable for machining pile heads. 
     It is thus an object of the present invention to indicate a method and an improved milling head, by means of which a pile head can be machined more quickly and reliably, in particular without damage to the reinforcement integrated therein. 
     This object is accomplished with a method and a milling head which have the features indicated in claims  1  and  9 . Advantageous embodiments of the invention are indicated in further claims. 
     The milling head serves for the machining of the head of a pre-manufactured pile lowered into the ground which essentially comprises a cylindrical pile core, a hollow cylindrical pile shaft and a concreted-in metal reinforcement lying therebetween. The milling head provided with picks is connected by means of a coupling device to a drive shaft which can be moved by means of a lifting and drive unit, in particular being lifted and lowered, and can be rotated for the operation of the milling head. An excavator or a cableway with a corresponding driving device is preferably used as the lifting and driving unit. 
     According to the invention a central milling cutter provided with a plurality of central picks and an annular milling cutter provided with a plurality of annular picks are fixedly coupled with each other and arranged coaxially with the longitudinal axis of the drive shaft. The central picks are arranged within a central circular ring and the annular picks, separated from them by a middle circular ring, are arranged in an outer circular ring whereby the circular rings lie at least approximately perpendicular to and concentric with the longitudinal axis of the drive shaft. 
     It is possible with the method and the milling head according to the invention to remove segments of the pile core and the pile shaft simultaneously without the reinforcement of the pile lying in the region of the middle circular ring being damaged. The machining is realised with great precision so that the concrete itself can be removed at a small distance of a few centimeters from the reinforcement. The remaining thin concrete sleeve, in which the reinforcement is enclosed can then be quickly removed using a further tool. 
     It is particularly advantageous that the segments of the pile core and the pile shaft can be removed through linear lowering of the milling head. Complex movements of the milling head which had to be carried out by a skilled worker with a conventional tool are not necessary. The machining of the pile head is thus realised within a few minutes (previously, according to [1], 30 minutes). At the same time, the boring head is evenly loaded, so that more uniform and longer maintenance intervals result. 
     The central circular ring, within which the central picks of the central milling cutter are arranged is outwardly displaced preferably by 5 cm to 20 cm in relation to the outer circular ring, within which the annular picks are arranged, so that during the machining of a pile head the central milling cutter firstly penetrates linearly into the pile core and the annular milling cutter is subsequently guided correspondingly. As an alternative to this position displacement of the central picks, however, the central milling cutter is additionally preferably provided with a central boring unit arranged coaxially with the longitudinal axis of the drive shaft, which central boring unit projects over the picks and serves for more precise guiding of the milling head during the machining of the pile. 
     The central picks and the possibly provided central boring unit are arranged on the front side of a shaft preferably provided with a conveying spiral. The annular picks are preferably assembled on an outer assembly ring which is fixedly or detachably connected to an assembly cylinder. 
     The shaft of the central milling cutter and the assembly cylinder of the annular milling cutter which extend coaxially with the longitudinal axis of the drive shaft and thereby define an at least approximately hollow cylindrical empty volume are connected to the inner side of a coupling plate, on the outer side of which the coupling device which can be connected to the drive shaft is arranged. The coupling device preferably comprises an assembly sleeve with a multi-edged hollow profile, in which the inserted drive shaft can be locked for example using a pin. 
     The picks provided on the milling cutters which are preferably identical are subjected to a high load during operation and therefore preferably consist of a holder that can be welded or can be mounted in a shape locking way and also a pick element that can be inserted therein and can be routinely replaced. The holders are preferably connected by means of shape locking connections, e.g. dovetail joints, to the associated assembly elements or assembly rings. 
     In a preferred embodiment the central boring unit can be inserted in the front side of the shaft of the central milling cutter, on the front side end of which the central picks are fixed. The central boring unit can also therefore be easily replaced. 
     In a further preferred embodiment the central boring unit that can be inserted into the shaft is connected to an inner assembly ring, to which the central picks are fixed. The central picks and the central boring unit can thus be replaced with each other. 
     The inner and outer diameter of the inner assembly ring and of the outer assembly ring are preferably precisely adapted to the dimensions of the pile and the position of the reinforcement in the pile, so that a maximum removal of concrete is guaranteed and there is minimum risk of damage to the reinforcement. 
     Insofar as the inner assembly ring and/or the outer assembly ring can be exchanged, the fitting assembly rings can always be put in place to adapt the milling head to the pile to be machined. 
     In a further preferred embodiment a preferably manually actuated coupling element is provided for example on the coupling plate, in which coupling element the shaft of the central milling cutter can be inserted. It is thus possible to remove the whole central milling cutter from the milling head and to exchange it. 
     In order to ensure easy and quick exchange of the outer assembly ring, the latter can preferably be connected via flange elements in a shape locking way, preferably by means of a threaded or bayonet fastening, to the assembly cylinder. 
    
    
     
       The invention is described in greater detail below by reference to the drawings, in which: 
         FIG. 1  shows the lower side of a milling head  1  according to the invention which comprises a central milling cutter  11  used for machining the pile core  81  and an annular milling cutter  12  used for removing the pile shaft  82 ; 
         FIG. 2  shows a partial section through the milling head  1  with the milling elements of the annular milling cutter  12  and the milling and boring elements  111 ,  114  of the central milling cutter  11  arranged at a distance of h 3  below; 
         FIG. 3  shows the milling head  1  connected via a drive shaft  2  to a lifting and driving device, with the boring and milling elements  111 ,  114 ,  121  shown in  FIG. 2 ; 
         FIG. 4  shows the milling head  1  of  FIG. 3  in a three-dimensional illustration; 
         FIG. 5  shows the preferably designed milling head  1  of  FIG. 3  shown in sectional representation during machining of a pile  8 ; 
         FIG. 6  shows the shaft  112  of the central milling cutter  11  provided with a conveying spiral  113 , which is provided on the front side with a central boring unit  114  and central picks  111 ; 
         FIG. 7  shows the central boring unit  114  which can be connected to the shaft  112  of  FIG. 6  with an assembly plate  1140 , on which the central picks  111  are provided; 
         FIG. 8  shows the milling head  1 , seen from above, with a coupling device  13  which consists of a coupling sleeve  131  with a hexagonal hollow profile and a coupling pin  132 ; and 
         FIG. 9  shows a head  80  of a pile  8  lowered into the ground  6  that has been machined according to the invention and also the material removed in one work step with a vertical movement in the original form. 
     
    
    
       FIG. 1  shows the lower side of a milling head  1  according to the invention which comprises a central milling cutter  11  used for machining the pile core  81  and an annular milling cutter  12  used for removing the pile shaft  82 . The central milling cutter  11  has, on its front side, a central boring unit  114  and six central picks  111  which surround the central boring unit  114  in a ring around an inner circular ring krl. The annular milling cutter  12  comprises, on its front side, an assembly ring  122 , on which six annular picks  121  are mounted in each of the four quadrants, whereby these are effective within an outer circular ring kr 3 . A middle circular ring kr 2  is kept free between the inner and the outer circular rings krl, kr 3 , in which middle circular ring kr 2  none of the central picks  111  or the annular picks  121  can engage. Upon lowering of the milling head  1  therefore the material to be taken away is removed in one work step, after which only a concrete sleeve  88  provided with the reinforcement  83  remains which corresponds to the middle circular ring kr 2 . 
       FIG. 2  shows a partial section through the milling head  1  with the milling elements of the annular milling cutter  12  and the milling and boring elements  111 ,  114  of the central milling cutter  11  lying at a distance h 3  below. Upon perpendicular lowering of the milling head  1  onto the head of the pile  8  (see  FIG. 5 ) therefore firstly the central boring unit  114  penetrates therein, whereby the milling head is guided precisely vertically upon further lowering and upon engagement of the picks  111 ,  121 . 
       FIG. 3  shows a milling head  1  according to the invention with the boring and milling elements  111 ,  114 ,  121  shown in  FIG. 2 . The assembly ring  122  with the annular picks  121  is connected to the lower side of a hollow assembly cylinder  123  (see also  FIG. 2 ), of which the upper side is connected to a coupling plate  133 . The assembly cylinder  123  is further provided with outlet openings  1231 , through which the removed material can leave the milling head  1 . 
     A coupling device  13  is fixed to the upper side of the coupling plate  133  (see also  FIG. 8 ) and consists of a coupling sleeve  131  and a coupling pin  132  which can be inserted therein. The coupling sleeve  131  secured by means of optionally provided reinforcement elements  134  comprises a hexagonal hollow profile, into which the correspondingly formed drive shaft  2  can be inserted and locked by means of the coupling pin  132 . After the coupling of the drive shaft  2 , represented by A in  FIG. 3 , the milling head  1  can thus be displaced and rotated by means of the lifting and driving device. For this purpose, the drive shaft  2  is connected to a correspondingly equipped excavator (see [1]) or crane. 
       FIG. 3   a  further shows one of the central picks  121  which consists of a holder  1111  and a pick element  1112 , shown enlarged. The pick element  1112  is retained in a force fit in the holder  1111  and can be knocked out and replaced after wear and tear becomes apparent, possibly being restored, as indicated by B. The holders can be welded or assembled preferably by means of shape locking joints, for example dovetail joints, and possibly be secured for example by means of a pin. Shape locking connection techniques are therefore particularly useful, because the milling head is always driven preferably in the same direction. Insofar as the holder is mounted in a shape locking way, it can be removed with a hand grip or using a hammer. The central picks  121  and the annular picks  121  are preferably designed to be identical depending upon the needs of the user. 
     The assembly cylinder  123  optionally further comprises a window  1232  which allows manual engagement in the milling head  1  in order to activate a coupling unit  14  optionally provided on the lower side of the coupling plate  133 , in which coupling unit  14  the shaft  112  of the central milling cutter  11  can be inserted. In this preferred embodiment of the milling head  1  therefore a fitting or a new central milling cutter  11  can be used as a replacement for a worn-out central milling cutter  11 , whereby this is represented by C. 
     D indicates an option that allows boring or milling elements  111 ,  114  of the central milling cutter  11  to be optionally assembled or dismantled. 
     E indicates an option that allows the assembly ring  122  provided with the annular picks  121  to be mounted on or dismantled from the assembly cylinder  123 . 
     Options C, D and E which can be provided individually or in combination result in considerable advantages for the production, operation and maintenance of the milling head  1 . On account of the exchangeability of the boring and milling tools, the most varied requirements can be met with a basic structure of the milling head  1 . Through the choice of the boring and milling tools in the desired dimensions, the milling head  1  can be adapted with few hand grips to the respective structure and the dimensions of the pile  8  to be machined. Through the corresponding choice of the outer diameter rd 2  the assembly ring  122  can be adapted to the outer diameter d of the pile  8  (see  FIG. 5 ). Through corresponding choice of the inner diameter rd 1  the assembly ring  122  can be adapted to the position of the reinforcement  83  within the pile  8 . For adaptation to the core  81  of the pile  8 , a fitting central milling cutter  11  is used or a fitting milling ring  1140 ,  111  (see  FIG. 7 , diameter zd of the assembly plate  1140 ) is placed on the shaft  112  of the central milling cutter  11 . The milling head  1  can therefore be adapted with few hand grips and without dismantling from the drive unit to the pile  8  to be machined in each case. 
     It is particularly important to be able to remove the inner and/or outer assembly plate  122  or  1140 , also having regard to maintenance and/or down times of the milling head  1 . The exchange of the inner and/or outer assembly plate  122 / 1140 , of which the picks are worn out, can be realised within a few minutes so that there are no significant down times. In addition the picks can be more easily repaired or exchanged. Return to the workshop is possible as the milling and boring units can be mounted and stored in a small space. 
       FIG. 4  shows the milling head  1  of  FIG. 3  in a three-dimensional illustration and without a window  1232 . In this arrangement the shaft  112  of the central milling cutter is therefore fixedly mounted or screwed in. On the other hand the above-described options D and/or E can be advantageously used. 
       FIG. 5  shows the preferably designed milling head of  FIG. 3  shown in sectional representation during the machining of a pile  8  which is shown in a cut open view. The material of the pile head  80  has already been extensively taken out and removed through the outlet openings  1231 . The annular milling cutter  12  has removed a segment of the pile shaft  82  and the central milling cutter  11  has removed a somewhat longer segment of the pile core  81 . A concrete sleeve  88  remains with the iron reinforcement  83  remaining undamaged in it. The remaining concrete sleeve  88  can subsequently be dealt with using a further tool, such as manually used milling cutters and clamps. It can be seen from  FIG. 5  that the pile head  80  has been machined very carefully, which is why the concrete has not quite been removed as far as the reinforcement  83 . Through the use of a suitable inner and outer assembly ring (see  FIG. 2  and  FIG. 7 ) it is possible on the other hand to additionally remove concrete so that only a thin concrete sleeve  88  remains. It is further shown in  FIG. 5  that the outer assembly ring  122  is connected by means of a threaded flange to the assembly cylinder  123  and can thus be easily released (the assembly ring  122  is locked for this purpose and the assembly cylinder  123  is turned by the driving device in the other direction). The central boring unit  114  and/or the central milling ring  1140 ,  111  is/are preferably constructed and can likewise be dismantled according to  FIGS. 6 and 7 . 
       FIG. 6  shows the shaft  112  of the central milling cutter  11 , provided with a conveying spiral  113 , which has a recess opening  1120  in the front side, into which the connecting pin  1142  of the central boring unit  114  provided on the front side with hard metal blades  1141  can be inserted. Furthermore, the shaft  112  can be connected on the front side to central picks  111 . For example their holders  1111  are welded to the shaft  112 . 
       FIG. 7  shows the central boring unit  114  that can be connected to the shaft  112  of  FIG. 6 , with an assembly plate  1140 , on which the central picks  111  forming a milling ring are assembled. 
     The central boring unit  114  of  FIG. 6  or the central boring unit  114  of  FIG. 6  provided with the milling ring can therefore be optionally connected to the shaft  112  and removed again. 
       FIG. 8  shows the milling head  1 , seen from above, with the coupling element  13  described above. 
       FIG. 9  shows a head  80 , machined according to the invention, of a pile  8  lowered into the ground  6  and also the material removed in one work step with a vertical movement in the original form, consisting of the removed core segment  91  and the removed shaft segment  92 . 
     LITERATURE 
     
         
         [1] “SPITZEN-TECHNOLOGIE, DIE WELTWEIT WEGE WEIST”, Product catalogue of erkat spezialmaschinen-service-gmbh, www.erkat.de 
         [2] DE 100 41 275 A1