Abstract:
A drilling apparatus  1  having a twin-impact system can work continuously with a shank end  5  is provided with a compensation ring  10  on the rotary impact side, which has a material with hardness that is lower than that of the material of the pipe and striker  8  and/or corresponding to the adjacent end portion  11  of the shank end  5  and has a shape and/or surfaces  21, 22  to compensate for the applied forces.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a drilling apparatus having spun-up outer pipes and spun-up inner pipes, which can be driven by a rotary drive and a rotary impact drive, the outer pipe being adapted for coupling at one of shank ends projecting on both sides of the rotary drive and being engageable with a striker that is mounted on the inner pipe for axial movement therewith. 
     Drilling apparatuses of this type are used in special underground construction, in mining and earth-moving operations and in the construction industry. They are used to form holes in rocks for insertion and fastening of anchors when various rocks are used as a foundation for construction. Such drilling apparatuses have an outer pipe string and an inner pipe string, each of the outer pipes and inner pipes having threads for making up the pipe strings. When flushing fluid is caused to pass through the interior of the inner pipes from the flushing head to the core drill bit, the flushing fluid filled with cuttings is removed to the ground surface through the space defined between the outer pipes and the inner pipes. Normally, the inner pipe is driven by a rotary impact drive, and the outer pipe is driven by a rotary drive only. This can be a problem, especially in dealing with hard rock. Accordingly, as described in DE-PS 35 03 893, the rotary impact drive for the inner string is also used to act upon the rear end of the outer string. For that purpose, the inner string has an annular shoulder for the impact engagement with the outer string. The impact mechanism can be pulled back axially with the ring shoulder, whereby the drilling apparatus can work with the outer pipes being driven for rotation only. To resolve this problem, the design according to DE-PS 35 03 893 involves gear teeth provided at the end face of the annular shoulder and at the end of the outer pipe to form a rotary coupling between the outer pipes and the inner pipes. This gearing causes another problem relating to strong wear of the annular shoulder and also of the end portions of the outer pipe, so such drilling apparatuses cannot be used for a long time. It should be also borne in mind that the annular shoulder that comes to engage the end portion of the outer pipe is also rotated together with the inner pipes. The two rotary systems are positively interconnected through the gearing. 
     The invention is based on the problem of providing a drilling apparatus having a design in which an outer pipe can have a rotary or a rotary percussion connected to, and driven by, the drilling apparatus. 
     SUMMARY OF THE INVENTION 
     This problem is resolved, according to the invention, by the fact that the shank end is provided with a compensation ring on the rotary impact side, which has the hardness that is lower than that of the material of the pipe and striker and/or corresponds to that of the end portion of the shank end and has a form and/or surfaces to compensate for the applied forces. 
     Using an annular shoulder for the striker to engage the end portion of the shank end is known from DE-PS 35 03 893. In this particular case, a compensation ring is provided between two engageable parts, namely the end portion of the shank end and the striker, and is used for compensation between the rotating impact part and the striking impact part to avoid premature overloading of, or damage to, both the striker and the end portion. With the proper construction and material for the compensation ring, even when the compensation ring is worn, the compensation ring is still capable of transmitting the applied forces and blows. This is ensured by a particular configuration and surface, as well as the general form of the compensation ring, that does not generally require any special material of treatment regardless of whether the drilling apparatus is used for a rotary or rotary impact drive of the outer pipe. Only when, for any reason, extreme stresses occur under an overload, is it required that the compensation ring be replaced when it shows signs of damage. 
     In a preferred embodiment of the invention, the compensation ring has, on one side, a surface corresponding to the adjacent end portion of the shank end, which is three-dimensionally curved. This ensures the alignment of the compensation ring on the one side and the shank end on the other side without any need for exact guidance of both parts. At the same time, such a compensation ring and an appropriately designed shank end ensure the central application of forces to the outer pipe in the case of the offset application of forces. This ensures reliable compensation by means of the compensation ring. 
     It is especially preferred, according to the invention, that the compensation ring have surfaces on both sides surface corresponding to the adjacent end portions of the shank ends, which are three-dimensionally curved, and it is understood that the shank end on the one side and the striker on the other side have surfaces that are respectively curved. The compensation ring has its curved surface or surfaces on the respectively curved shank end at the respectively curved striker. As will become clear from the description, in this manner the compensation ring will always remain in an optimum position without any additional adjustment or control devices being required. 
     The compensation ring should be preferably installed at the shank end in such a manner that the compensation ring made as a loose part remains at the shank end when the impact drive with the striker is pulled back. In order to rule out slip, tilt, and the like, it is provided, according to the invention, that the shank end has a casing supported by the rotary drive motor encloses the compensation ring. It is preferred for the sake of simplicity to provide the casing with projections that are designed to fix the compensation ring, with the striker having a respectively smaller diameter to be received within the casing in such a manner as to be in contact with the respective surface of the compensation ring during the rotary percussion operation. 
     It should be also noted that with the rotary percussion mode for the outer pipe described herein, the inner pipe and the striker of the rotary impact drive rotate simultaneously, because the rotary impact drive is connected to the inner pipe or is made integrally therewith. To avoid damage to the smooth surfaces, which can be in contact with the drilling fluid, according to the invention, the casing has lubrication holes opposite to the curved surfaces of the compensation ring. Grease or the like can be put into these lubrication holes at regular intervals, e.g., before starting operation or on an as-needed basis so as to ensure lubrication of both surfaces of the compensation ring and the mating faces of the shank end and the striker. 
     To remove the grease moving under pressure on both sides sliding over each other and, more specifically, to facilitate insertion of the inner pipe through the compensation ring during assembly, it is preferred that the compensation ring have a central hole of a diameter that is larger than the diameter of the inner pipe. It is preferred that this central hole have a chamfer to reduce damage caused by blows of the striker in this area. It is also preferred that the striker also have the chamfered edge in this area, and the opposite side of the central hole may also have a chamfer. 
     To ensure guidance for the compensation ring in the casing on the one hand and to allow the compensation ring to reciprocate over the full range over the surfaces of the shank end and the striker, the outer edges of the compensation ring are rounded. In this manner, the compensation ring has rounded edges all around to ensure good support for the compensation ring between the faces of the shank end and the striker. 
     The striker is mainly a part of the inner pipe; it is appropriately driven by the rotary impact mechanism and can transmit the impact energy to the outer pipe string. To facilitate make-and-break operations and to optimize installation, according to the invention, the striker is made as a striker sleeve that is loosely connected to the shank end of the rotary impact drive. This shank end has appropriate threads for replacement of the attached striker sleeve when required, for ensuring its intimate contact with the rotary impact drive and with the rotary drive when the outer pipe is only rotated. Quick make-and-break operations are thus made possible, especially when it is required to replace the striker sleeve for a larger or smaller striker sleeve or when a simple replacement is needed. 
     The compensation ring is engageable with the striker sleeve to assure the optimum transfer of appropriate forces if, according to the invention, the compensation ring has the outside diameter that corresponds to, and is preferably larger than, that of a head of the striker sleeve and of the shank end. The greater diameter of the compensation ring is advantageous in the case where the compensation ring is fixed in bosses or lugs of the casing. Otherwise, the compensation ring has the same diameter. 
     The rotary drive and the rotary impact drive are axially movable together so as to move or drive the interconnected outer and inner pipes with their respective strings into the hole. To allow for independent operation, according to the invention, the striker sleeve is axially movable together with the rotary impact drive independently of the rotary drive of the outer pipe. The rotary impact drive is thus retracted from the striker sleeve in such a manner that it can be only driven to rotate so that the outer pipe will only rotate, and the inner pipe will be driven by the rotary impact drive to assure hole formation. As the outer pipe is to be driven only through a relatively limited thickness of the ground shell, the rotary drive is used for a soft rock, and the striker sleeve can be retracted from the compensation ring and from the shank end to facilitate movement of the pipe strings. 
     To avoid injuries to the drilling crew, the striker sleeve is dogboned and has a funnel-shaped protective cover that is fixed at the end opposite to the compensation ring and covers the casing in a spaced relation thereto in the area of the compensation ring. This protective cover is preferably made of a flexible material, e.g., of hard rubber or plastic. It covers the striker area, i.e., the area in which the striker sleeve engages the compensation ring. If the striker sleeve is to be retracted from the compensation ring, the protective cover is made “shorter” and is preferably attached to the inner pipe, or more exactly, to the striker sleeve in order to move together therewith. The striker sleeve is in contact with the compensation ring, thus engaging the outer string and the shank end, and the protective cover is sealed against a respective projection of the casing, so that mishandling by the drilling crew cannot and does not damage the apparatus. If required, e.g., for inspection of the striker sleeve, the protective cover, which is secured by means of a retainer ring to the dogboned striker sleeve, may be removed. 
     It can be also noted that both the shape and the material of the compensation ring are such that the ring can perform its compensating function. The material is chosen in such a manner that, on the one hand, it can reliably transmit the impact of the striker sleeve to the shank end and then to the outer pipe and, on the other hand, the same shank end is protected and is not damaged by the blows. Both the form and the material are also chosen in such a manner that the blows that are transmitted in an imperfect alignment do not inflict damage upon respective parts, and the rotating striker sleeve is as if being centered by means of the compensation ring. The compensation ring can shift aside or tilt even inside of the surfaces of the compensation ring, and the shank end and striker sleeve are appropriately shaped. Generally speaking, according to the invention, if the compensation ring has hardness, as well as heat conductivity and other properties chosen so as to differ from the material of the shank end and striker sleeve, and its toughness is preferably higher, the compensation ring can perform its function. 
     It is preferred that this material be bronze and more specifically, forged bronze. Forged bronze ensures optimum properties for the compensation ring. It can take up the forces between the striker sleeve and the shank end both in terms of the hardness and toughness without causing damage to these parts. 
     The invention is characterized by the fact that it provides a drilling apparatus that can be used for driving the outer pipe string in both the rotary and rotary percussive mode. The rotary drive is used for driving the inner pipe string or inner pipe in the known manner, with the outer pipe being simultaneously driven by impacts. Between individual parts, namely between the striker sleeve on the one side and the end face of the shank end coupled with the outer pipe, there is provided a compensation ring that is used for compensation in every aspect, which also allows the impacts transmitted from the rotary impact drive to be transferred to the outer pipe when required. The compensation ring is also used to protect against heat, as well as excessive energy at the shank ends, especially at the end of the striker sleeve. The positive centering and the reliable transmission of forces are assured owing to a specific configuration of the compensation ring. In general, a drilling apparatus is provided that has prolonged life and that can work continuously when used for drilling in very hard rocks, with the outer pipes being driven in the rotary percussive mode continuously for a long time. 
     Other features and advantages of the present invention will become apparent from the following detailed description of its embodiments in conjunction with the accompanying drawings, in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a general view of a drilling apparatus having a twin impact clutch, in front elevation view; 
     FIG. 2 is a sectional view taken in the area of a compensation ring; 
     FIG. 3 is a sectional view of the compensation ring. 
    
    
     DETAILED DESCRIPTION 
     A drilling apparatus  1  for two pipe strings is shown in front elevation view in FIG.  1 . An outer pipe is shown at  2 , and an inner tube having a smaller diameter is shown at  3 . While the outer pipe  2  is engaged for rotation with a rotary drive  4 , which is not described in detail here, a rotary drive motor  6  is used for driving a rotary impact driven  7  with a striker device to drive the inner pipe  3  in the rotary percussive mode. 
     FIG. 1 shows a shank end  5  of the end of the outer pipe  2 , having twin threads  14 . 
     The rotary drive  4  and the rotary impact drive  7  are axially movable together on a slide, which is not referenced, so that the drilling pipe strings can be driven as a whole into the rock or into a building structure. The slide is divided into two parts. The parts are connected together by means of a hydraulic cylinder for retracting the rotary impact mechanism from the rotary drive. 
     The outer pipe  2  and the shank end  5  should be driven not only for rotation by the rotary drive  4 , but also simultaneously in the rotary percussive mode, which is required, e.g., in the case where the twin pipe string is to be driven through rock such as stone. When the rock or stone hardness requires that a striker  8  be activated in order to drive the outer pipe  2  not only for rotation by the rotary drive  4 , but also under the action of the striker  8  for percussive driving, the striker  8  is moved toward casing  9  by the hydraulic cylinder to a position in which it engages a compensation ring  10 . In this case the inner pipe string, more specifically, the inner pipe  3  will transmit the impact energy to the outer pipe  2 . This can be more clearly seen in FIG.  2 . 
     Similarly to the rotary drive  4 , the rotary impact drive  7  has a shank end  16  or a tail pipe that is in engagement with a rotary drive motor  6 ′ and a hammer member that is not shown. A force is transmitted directly from the shank end  16  to the inner pipe  3 . FIG. 1 also shows a flushing head  13  through which flushing fluid is supplied into an inner passage  20  of the inner pipe  3  and, more specifically, to the rotating inner pipe  3 . 
     FIG. 2 also shows the flushing head  13  that is mounted on the inner pipe  3 , and the striker  3  that is made as a striker sleeve  15 . The striker sleeve  15  acts through the compensation ring  10  upon the end portion  11  of the shank end  5  and, through it, upon the outer pipe  2 . The inner pipe  3  is connected to the striker sleeve  15  by means of threads that are not shown here. A head  17  of the striker sleeve  15  directly engages the compensation ring  10 , the rotary motion of the striker sleeve  15  is not restricted, and grease is pressed through lubrication holes  12  that are located in the area of the compensation ring  10 . 
     The drawing also shows the inner passages  20  through which the flushing fluid is supplied toward a core drill bit that is not shown. 
     The head  17  of the striker sleeve  15  and the end portion of a casing  19  with the appropriately positioned compensation ring  10  are enclosed in, and protected by, a protective cover  18  that is attached to the end  19  of the striker sleeve  15 , which is apart from the compensation ring  10 , for reciprocation with the striker sleeve  15  and for covering the compensation ring during operation in the impact mode. 
     FIG. 3 shows a sectional view of the compensation ring  10 , wherein surfaces  21  and  22  on both sides of the compensation ring  10  are shown as planar. Actually, as mentioned in the specification, these surfaces  21 ,  22  are three-dimensionally curved, among other things, to ensure self-alignment of the striker sleeve  15  in the percussive mode and to increase the surface area (contact area). 
     A central hole  23  is greater than the outside diameter of the inner pipe  3 , which can be clearly seen in FIG. 2, to facilitate insertion of the inner pipe without the inner pipe affecting the compensation ring  10 . 
     Outer edges  24 ,  25  are rounded as can be seen in FIG. 3, and inner edge  26  can also be rounded or chamfered. 
     The compensation ring  10  is made of the above-discussed tough material, and the surfaces  21 ,  2  should be sufficiently smooth to be able to eventually assure uniform movement of the rotating striker sleeve  15  even without a lubricant. It should be understood that the respective opposite surface of the striker sleeve  15  and the respective surface of the shank end  5  are also finished smoothly. 
     All the above-described features of the invention illustrated in the drawings can be used, according to the invention, singly or in combination.