Drilling rig, mast assembly thereof and method for switching between multiple rig modes

Abstract

The application discloses a drilling machine, a mast assembly thereof and a mode switching method of a multi-method drilling machine. In the mast assembly, the mast comprises an upper mast, a first lengthening section, a middle mast and a lower mast which are sequentially connected from top to bottom; a first power head is slidably connected with the mast and is used for driving a first drill rod to rotate for construction; a first pulley is installed on the upper mast; a winch device is installed on the middle mast; a pressurizing pulley set is installed on the mast and is located below the winch device; one end of a lifting steel wire rope is connected with the winch device, and the other end of the lifting steel wire rope is connected with the first power head after winding around the first pulley; one end of a pressurizing steel wire rope is connected with the winch device, and the other end of the pressurizing steel wire rope is connected with the first power head after winding around the pressurizing pulley set. The winch device can be used to realize full-stroke free movement of the first power head along the length direction of the mast. Moreover, the first lengthening section is detachable, the height of the mast can be adjusted, and different requirements of different construction methods on the height of the mast can be met.

Description

Technical Field

[0001] This invention relates to the field of rotary drilling rig technology, and particularly to a drilling rig and its mast assembly, and also provides a method for switching between multiple drilling rig modes. Background Technology

[0002] Rotary drilling rigs, or simply drilling rigs, are widely used in mining, railways, highways, bridges, water conservancy and hydropower, tunnels, water wells, anchor bolts, small-diameter diamond core wireline drilling, civil engineering, engineering geological exploration, geothermal drilling, coalbed methane drilling, and anti-outburst drilling.

[0003] In existing drilling rigs, at least two winch mechanisms are often installed on the mast: one for lifting the drill rod and the other for lowering and pressurizing the drill rod. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a drilling rig and its mast assembly and a method for switching multiple drilling rig modes, which can realize the free movement of the first power head along the full stroke of the mast through a winch device; and through the detachable first extension section, the mast height can be adjusted, which is beneficial to meet the different requirements of different construction methods for mast height.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A mast assembly, comprising:

[0007] The mast includes an upper mast, a first extension section, a middle mast, and a lower mast connected in sequence from top to bottom. The two ends of the first extension section are detachably connected to the upper mast and the middle mast, respectively.

[0008] The first power head is slidably connected to the mast and is used to drive the first drill pipe to rotate for construction.

[0009] The first pulley is installed on the upper mast;

[0010] A winch device is installed on the central mast;

[0011] A pressure pulley block is installed on the mast and located below the winch device;

[0012] The lifting wire rope is connected at one end to the winch device and at the other end after passing over the first pulley to the first power head;

[0013] The pressure wire rope is connected at one end to the winch device and at the other end after passing over the pressure pulley block to the first power head.

[0014] Optionally, in the above-mentioned mast assembly, the pressure pulley block includes a second pulley, a third pulley, and a fourth pulley arranged sequentially from top to bottom;

[0015] The fourth pulley is installed at the lower part of the mast;

[0016] The pressurized steel wire rope passes sequentially around the second pulley, the third pulley, and the fourth pulley before connecting to the first power head.

[0017] Optionally, in the mast assembly described above, the side of the second pulley away from the central axis of the mast contacts the pressure wire rope;

[0018] The third pulley is in contact with the pressure wire rope on the side closest to the central axis of the mast;

[0019] The bottom of the fourth pulley is in contact with the pressure wire rope.

[0020] Optionally, in the above-mentioned mast assembly, the first power head is provided with a tensioning mechanism;

[0021] The pressurized steel wire rope is connected to the first power head through the tensioning mechanism.

[0022] Optionally, the mast assembly described above also includes a movable clamp and a fixed clamp, wherein:

[0023] The moving clamp is located below the first power head and connected to the mast. It is used to clamp the first casing unit sleeved outside the first drill pipe and can drive the first casing unit to rotate around the axis.

[0024] The fixed clamp is located below the movable clamp and is connected to the mast. It is used to clamp the second casing unit that is sleeved outside the first drill pipe. The second casing unit is located below the first casing unit and is threadedly connected to it.

[0025] Optionally, the mast assembly described above also includes a second extension section, which is detachably connected to the bottom of the lower mast, and the fourth pulley is mounted to the bottom of the lower mast via the second extension section;

[0026] Optionally, the mast assembly described above also includes outrigger cylinders, which are detachably connected to the lower mast and can support the mast to the ground.

[0027] Optionally, the mast assembly described above further includes a second power head, wherein the output torque of the second power head is greater than the output torque of the first power head, wherein:

[0028] The second power head is slidably connected to the mast and can be used to drive the first drill pipe to rotate for construction.

[0029] A drilling rig, comprising:

[0030] The mast assembly described above;

[0031] In the anchor bolt mode, the first drill pipe is connected to one side of the mast via the first power head and is parallel to the mast;

[0032] The first casing unit is sleeved outside the first drill pipe, and the movable clamp holds the first casing unit and can drive the first casing unit to rotate around the axis.

[0033] The second casing unit is sleeved outside the first drill pipe, located below the first casing unit and threadedly connected to it, and the fixed clamp holds the second casing unit.

[0034] A method for switching modes of a multi-method drilling rig includes:

[0035] The hoisting device, the first extension section, the first power head, the moving clamp and the fixed clamp in the above drilling rig are removed, and the first drill rod is replaced with the second drill rod in the standard rotary drilling mode, so as to switch the drilling rig from the anchor bolt mode to the standard rotary drilling mode.

[0036] In the drilling rig of the standard rotary drilling mode:

[0037] The top of the middle mast is connected to the top mast;

[0038] A second power head and a pressure cylinder are provided on one side of the mast: the second power head is slidably connected to the mast and is used to drive the second drill pipe to rotate for construction; the piston rod of the pressure cylinder is connected to the second power head and is used to drive the second power head to move vertically along the mast.

[0039] A method for switching modes of a multi-method drilling rig includes:

[0040] Remove the first extension section from the drilling rig and connect the top of the middle mast to the top mast;

[0041] The mast and drill rod in the drilling rig are tilted relative to the ground at a preset angle.

[0042] As can be seen from the above technical solution, the present invention can control the lifting and pressurization of the first power head through the mast assembly, enabling the first power head to move freely along the entire length of the mast. Furthermore, since only one winch device is used in the mast assembly, it helps to save costs. In addition, since the two ends of the first extension section are detachably connected to the upper mast and the middle mast respectively, the mast height can be adjusted by assembling and disassembling the first extension section according to actual conditions, which helps to meet the different mast height requirements of different construction methods. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a schematic diagram of the rope winding principle of the mast assembly provided in an embodiment of the present invention;

[0045] Figure 2 A schematic diagram of a drilling rig in anchor bolt mode provided in an embodiment of the present invention;

[0046] Figure 3 for Figure 1 A schematic diagram of the connection structure of the first power head in the process;

[0047] Figure 4 A schematic diagram of a drilling rig in dual-power mode provided for an embodiment of the present invention (with a first extension section in the mast);

[0048] Figure 5 A schematic diagram of a drilling rig in dual-power mode provided for an embodiment of the present invention (with the first extension section in the mast removed);

[0049] Figure 6 A schematic diagram of a drilling rig in standard rotary drilling mode provided in an embodiment of the present invention;

[0050] Figure 7 This is a schematic diagram of a drilling rig in anchor cable mode, provided as an embodiment of the present invention.

[0051] in:

[0052] 1-Winding device, 2-Lifting wire rope, 3-First pulley, 4-First power head, 5-Pressure wire rope

[0053] 6-Second pulley, 7-Third pulley, 8-Fourth pulley, 9-Tensioning mechanism, 10-Mast,

[0054] 11-First extension section, 12-Upper mast, 13-Pulley frame, 14-Modible clamp, 15-Lower mast

[0055] 16-Second extension section, 17-Fixed clamp, 18-Outrigger cylinder, 19-Second power head,

[0056] 201 - First drill pipe, 202 - Second drill pipe. Detailed Implementation

[0057] This invention discloses a drilling rig and its mast assembly, as well as a method for switching between multiple drilling modes. It can achieve free movement of the first power head along the entire length of the mast through a winch device; and through a detachable first extension section, the mast height can be adjusted, which is beneficial to meet the different requirements of different construction methods for mast height.

[0058] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0059] Please see Figure 1 and Figure 2 This invention provides a drilling rig and its mast assembly, which includes a mast, a first power head 4, a first pulley 3, a winch device 1, a pressure pulley block, a lifting wire rope 2, and a pressure wire rope 5. Wherein:

[0060] The mast includes an upper mast 12, a first extension section 11, a middle mast 10, and a lower mast 15 connected sequentially from top to bottom. The two ends of the first extension section 11 are detachably connected to the upper mast 12 and the middle mast 10, respectively.

[0061] The first power head 4 is used to drive the first drill rod 201 to rotate for construction. The first power head 4 is slidably connected to the mast and can move the first drill rod 201 up and down along the length of the mast.

[0062] The first pulley 3 is installed on the upper mast 12, located at or near the top of the mast, which helps to maximize the movement space of the first power head 4 within a limited length.

[0063] The winch device 1 is installed on one side of the central mast 10 and can meet the requirements of the entry angle of the lifting wire rope 2 and the pressurizing wire rope 5;

[0064] The pressure pulley block is installed on the mast and located below the winch 1, which can guide and pre-tighten the pressure wire rope 5;

[0065] The lifting wire rope 2 is wound around the first area of ​​the winch device 1, with one end connected to the winch device 1 and the other end passing over the first pulley 3 and connected to the first power head 4.

[0066] The pressurized steel wire rope 5 is wound around the second area of ​​the winch device 1, with one end connected to the winch device 1 and the other end passing over the pressurized pulley block and connected to the first power head 4.

[0067] When the hoisting device 1 rotates in the forward direction, the lifting wire rope 2 is tensioned and the pressure wire rope 5 is relaxed, so that the first power head 4 can be lifted upward by the lifting wire rope 2.

[0068] When the hoisting device 1 rotates in the reverse direction, the lifting wire rope 2 loosens and the pressure wire rope 5 tightens, thereby controlling the first power head 4 to descend along the entire vertical stroke. Moreover, the pressure wire rope 5 can provide downward pressure to the first power head 4.

[0069] As can be seen, this mast assembly can control the lifting and pressurization of the first power head 4, enabling the first power head 4 to move freely along the entire length of the mast from the bottom to the top and from the top to the bottom. Furthermore, since this mast assembly uses only one winch device 1, it helps to save costs. In addition, since the two ends of the first extension section 11 are detachably connected to the upper mast 12 and the middle mast 10 respectively, the mast height can be adjusted by assembling and disassembling the first extension section 11 according to actual conditions, which helps to meet the different mast height requirements of different construction methods.

[0070] Preferably, the first extension section 11 includes multiple (e.g., two) extension sections that are detachably connected in sequence, thereby enabling more precise adjustment of the mast height as needed.

[0071] Specifically, please see Figure 1 and Figure 2 The aforementioned pressure pulley assembly includes a second pulley 6, a third pulley 7, and a fourth pulley 8 arranged sequentially from top to bottom, with the fourth pulley 8 installed at the lower part of the mast. Preferably, the second pulley 6 and the third pulley 7 are both installed on the middle mast 10, with the third pulley 7 located below the second pulley 6; the fourth pulley 8 is installed on the lower mast 15 and located below the third pulley 7, to maximize the movement space of the first power head 4 within the limited length of the mast. The pressure steel wire rope 5 from the winch device 1 passes sequentially around the second pulley 6, the third pulley 7, and the fourth pulley 8 before connecting to the first power head 4.

[0072] Preferably, the center of the third pulley 7 and the center of the second pulley 6 are on the same vertical line, satisfying the rope entry angle requirement. Furthermore, the side of the second pulley 6 furthest from the mast's central axis contacts the pressure wire rope 5, the side of the third pulley 7 closest to the mast's central axis contacts the pressure wire rope 5, and the bottom of the fourth pulley 8 contacts the pressure wire rope 5. The pressure wire rope 5 extends from top to bottom to the position of the fourth pulley 8, passes around the bottom of the fourth pulley 8, and then extends from bottom to top to the position of the first power head 4.

[0073] In practical implementation, since the mast is generally a vertically installed longitudinal pole, the section of the pressure wire rope 5 between the third pulley 7 and the fourth pulley 8 is a vertical line. That is, the extension direction of the section of the pressure wire rope 5 between the third pulley 7 and the fourth pulley 8 is parallel or collinear with the central axis of the mast. Moreover, preferably, the third pulley 7 and the second pulley 6 are located on the same side of the mast, and the fourth pulley 8 is closer to the first drill pipe 201 relative to the mast and the third pulley 7.

[0074] In practical implementation, to avoid interference between the wire rope and the mast, increase the mast's strength, and simultaneously place the wire rope as far outside the mast as possible to reduce the difficulty of threading it, it is required to maximize the distance between the second pulley 6 and the pressure winch 1. Furthermore, the shorter the distance between the second pulley 6 and the third pulley 7, the less interference there will be between the wire rope and the mast. Therefore, the second pulley 6 and the third pulley 7 should be placed as close as possible to or at the bottom of the middle mast 10.

[0075] In addition, in order to make the welding of the wire rope sheath easy and the rope threading convenient, the wire rope inside the mast should be arranged as straight as possible. In order to reduce the wire rope running through the mast, the distance between the third pulley 7 and the fourth pulley 8 should be shortened as much as possible.

[0076] Please see Figure 2 and Figure 3 In a preferred embodiment, the first power head 4 is slidably mounted on one side of the mast via a support, and a tensioning mechanism 9 is provided on the support. The pressure wire rope 5 is connected to the first power head 4 via the tensioning mechanism 9. Thus, the preload of the pressure wire rope 5 can be adjusted via the tensioning mechanism 9.

[0077] In specific implementation, the mast assembly also includes a movable clamp 14 and a fixed clamp 17 for loading and unloading the casing and correcting the drill pipe's verticality. Specifically: the movable clamp 14 is located below the first power head 4, slidably connected to the mast, and its lifting and lowering are controlled by the main winch. It is used to clamp the first casing unit fitted outside the first drill pipe 201 and can drive the first casing unit to rotate around its axis. The fixed clamp 17 is fixedly installed at the bottom of the lower mast 15, below the movable clamp 14, and is used to clamp the second casing unit fitted outside the first drill pipe 201. The second casing unit is located below the first casing unit and is threadedly connected to it. Through these two clamps, the casing fitted outside the first drill pipe 201 can be automatically disassembled.

[0078] In practice, the movable clamp 14 clamps the first protective tube unit located above, and the fixed clamp 17 clamps the second protective tube unit located below. When the movable clamp 14 rubs the tube (i.e. drives the first protective tube unit to rotate around the axis), the fixed clamp 17 and the second protective tube unit remain stationary, thereby causing the first protective tube unit to rotate relative to the second protective tube unit, thus separating from each other and achieving the purpose of loading and unloading the protective tube.

[0079] It should also be noted that the casing serves to correct the verticality of the drill pipe. When the drill pipe or borehole tilts, it will interfere with the casing, thus reminding workers to adjust the verticality of the drill pipe in a timely manner.

[0080] Specifically, a second extension section 16 is provided at the bottom of the lower mast 15. The second extension section 16 is fixedly installed at the bottom of the lower mast 15, and the fourth pulley 8 and the fixed clamp 17 are respectively installed at the bottom end of the lower mast 15 through the second extension section 16. It can be seen that the fourth pulley 8 is located at the bottom of the mast, and the first pulley 3 is located at the top of the mast. Thus, the full-stroke movement space of the first power head 4 can cover most of the mast, maximizing the movement space of the first power head 4 within the limited mast length.

[0081] Specifically, the mast assembly is also equipped with a support leg cylinder 18, which is connected to the lower mast 15 and can be supported to the ground to provide support for the mast and even the drilling rig, ensuring the stability of the working machinery.

[0082] Furthermore, the second extension section 16 and the outrigger cylinder 18 are detachably connected to the lower mast 15, so as to facilitate disassembly and assembly according to actual needs and to facilitate the switching of working methods, such as switching the drilling rig from the anchor bolt mode to the standard rotary drilling mode.

[0083] In summary, all the above mast assemblies are single-power-head anchor bolt types (including deep well cases). For details, please refer to [link / reference needed]. Figure 1 and Figure 2Because the torque of the first power head 4 is relatively small in this mode, a single power head cannot complete the pressurized drilling operation when the soil is very hard.

[0084] Therefore, under certain operating conditions, a dual-power head mode can be used. For details, please refer to [link / reference]. Figure 3 The mast assembly described above includes not only a first power head 4 but also a second power head 19, whose output torque is greater than that of the first power head 4. The second power head 19 is slidably connected to the mast and is used to drive the first drill pipe 201 to rotate for drilling operations. For details on the drilling rig structure with dual power heads, please refer to [link to relevant documentation]. Figure 4 and Figure 5 At this point, you can choose whether to install the first extension section 11 based on your actual needs.

[0085] In summary, this invention also provides a drilling rig, which includes the mast assembly described above, a first drill rod 201 in anchor bolt mode, and a first casing unit and a second casing unit. Specifically: the first drill rod 201 is connected to one side of the mast via a first power head 4, a movable clamp 14, and a fixed clamp 17, and is parallel to the mast; the first casing unit is sleeved outside the first drill rod 201, the movable clamp 14 clamps the first casing unit and can drive the first casing unit to rotate around an axis; the second casing unit is sleeved outside the first drill rod 201, located below the first casing unit and threadedly connected to it, and the fixed clamp 17 clamps the second casing unit.

[0086] In practical implementation, due to the large torque of the second power head 19, it can be used not only in the anchor bolt dual-power head mode of the drilling rig but also in the standard rotary drilling mode. The switching process between the anchor bolt mode and the standard rotary drilling mode includes: removing the winch device 1, the part above the middle mast 10, the second extension section 16, the outrigger cylinder 18, the moving clamp 14, and the fixed clamp 17; then installing the upper mast 12, pulley frame 13, and pressure cylinder 21 of the standard machine onto the middle mast 10, and connecting the pressure cylinder 21 to the second power head 19. For details on the drilling rig structure in the standard rotary drilling mode, please refer to [link to relevant documentation]. Figure 6 .

[0087] Specifically, the pulley frame 13 includes a small pulley frame, and the wire rope of the auxiliary winch is connected to the steel cage through the pulleys on the small pulley frame to achieve the lifting and lowering of the steel cage.

[0088] Therefore, this embodiment of the invention also provides a method for switching modes of a multi-method drilling rig. The method includes: canceling the winch device 1, the first extension section 11, the first power head 4, the moving clamp 14, and the fixed clamp 17 in the above-mentioned drilling rig, and replacing the first drill rod 201 in the anchor bolt mode with the second drill rod 202 in the standard rotary drilling mode, so as to switch the drilling rig from the anchor bolt mode to the standard rotary drilling mode.

[0089] In this standard rotary drilling rig: the top of the middle mast 10 is connected to the upper mast 12; a second power head 19 and a pressure cylinder 22 are provided on one side of the middle mast 10: the second power head 19 is slidably connected to the mast and is used to drive the second drill rod 202 to rotate for construction; the piston rod of the pressure cylinder 22 is connected to the second power head 19 and is used to drive the second power head 19 to move vertically along the mast.

[0090] In practice, the drilling rig in the above-mentioned anchor bolt mode can also be switched to anchor cable mode. During anchor cable mode construction, the drill rod is at a certain angle to the ground. The drilling rig uses the same pulley block for full-stroke pressure in both anchor bolt and anchor cable modes.

[0091] During the switching between the bolt and cable anchoring methods: Because the drill rod is at a certain angle to the ground surface during cable anchoring, ensuring overall machine stability requires removing the two upper mast sections 11, directly connecting the upper mast 12 and the middle mast 10. See details in [link to documentation]. Figure 7 .

[0092] Therefore, this embodiment of the invention also provides a method for switching modes of a multi-method drilling rig, the method comprising: canceling the first extension section 11 in the above-mentioned drilling rig, connecting the top of the middle mast 10 to the upper mast 12; and controlling the mast and the first drill rod 201 in the drilling rig to tilt at a preset angle relative to the ground.

[0093] In summary, the drilling rig provided in this embodiment of the invention can switch to any one of three working methods—anchor bolt mode (including deep wells), rotary drilling mode, and anchor cable mode—according to actual working conditions.

[0094] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0095] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0096] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A mast assembly characterized by, Comprise: Mast, comprising upper mast (12), first lengthening section (11), middle mast (10), lower mast (15) connected in turn from top to bottom, both ends of the first lengthening section (11) are respectively detachably connected with the upper mast (12) and the middle mast (10); First power head (4), slidingly connected with the mast, used for driving the first drill rod (201) to rotate construction; First pulley (3) is installed on the upper mast (12); Winch device (1) is installed on the middle mast (10); Pressurized pulley block is installed on the mast and is located below the winch device (1); Lifting steel wire rope (2), one end of which is connected with the winch device (1), and the other end is connected with the first power head (4) after passing through the first pulley (3); Pressurized steel wire rope (5), one end of which is connected with the winch device (1), and the other end is connected with the first power head (4) after passing through the pressurized pulley block; Movable clamp (14), the movable clamp (14) is located below the first power head (4), is slidingly connected with the mast, is controlled to rise and fall through the main winch, is used for clamping the first casing unit sleeved outside the first drill rod (201), and can drive the first casing unit to rotate around the shaft; Fixed clamp (17), the fixed clamp (17) is located below the movable clamp (14) and is connected with the mast, used for clamping the second casing unit sleeved outside the first drill rod (201), the second casing unit is located below the first casing unit and is threadedly connected with it; The pressurized pulley block comprises second pulley (6), third pulley (7) and fourth pulley (8) arranged in turn from top to bottom, and the fourth pulley (8) is installed on the lower part of the mast; the pressurized steel wire rope (5) passes through the second pulley (6), the third pulley (7) and the fourth pulley (8) in turn and is connected with the first power head (4); The first power head (4) is provided with a tensioning mechanism (9), and the pressurized steel wire rope (5) is connected with the first power head (4) through the tensioning mechanism (9).

2. The mast assembly of claim 1, wherein, It also includes a second lengthening section (16), which is detachably connected with the bottom of the lower mast (15).

3. The mast assembly of claim 1, wherein, It also includes a support leg oil cylinder (18), which is detachably connected with the lower mast (15) and can support to the ground.

4. The mast assembly of claim 1, wherein, It also includes a second power head (19), the output torque of which is greater than that of the first power head (4), wherein: The second power head (19) is slidingly connected with the mast and can be used to drive the first drill rod (201) to rotate construction.

5. A rig characterized in that, Comprise: The mast assembly of any one of claims 1 to 4; The first drill rod (201) in anchor rod mode is connected to one side of the mast through the first power head (4) and is parallel to the mast; The first casing unit is sleeved outside the first drill rod (201), the movable clamp (14) clamps the first casing unit and can drive the first casing unit to rotate around the shaft; A second casing unit is sleeved outside the first drill pipe (201), is located below the first casing unit, and is threadedly connected with the first casing unit. A gripper (17) clamps the second casing unit.

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