Rotary double worktable exchange device for horizontal machining center of automobile parts

Abstract

The application discloses a rotating double-workbench exchange device of an automobile part horizontal machining center, relates to the technical field of workpiece machining equipment, and comprises a base, a main shaft for mounting a tool head is installed on the base, a supporting column is installed on the base, a reversing shaft is rotationally installed on the supporting column, a machining seat is fixedly connected to the reversing shaft, a normal machining surface and an auxiliary machining surface are arranged on the machining seat, the normal machining surface and the auxiliary machining surface are located on the front face and the back face of the machining seat respectively, the normal machining surface and the auxiliary machining surface can both be used for mounting a workpiece to be machined, a driving mechanism for driving the reversing shaft to rotate is arranged in the base, and a locking mechanism for limiting the reversing shaft is arranged in the supporting column. The application has the effect of improving the work efficiency of workpiece machining.

Description

Technical Field

[0001] This application relates to the field of workpiece processing equipment technology, and in particular to a rotary double-table exchange device for a horizontal machining center for automotive parts. Background Technology

[0002] Most automotive parts require workpieces (such as steel plates, alloys, etc.) to be placed on a worktable, where precision machining such as grinding, cutting, drilling, and chamfering is performed using cutters mounted on the worktable spindle. This reduces the difference between the actual size and the design size of the workpiece, improves the accuracy of the workpiece dimensions, and ensures that the workpiece can operate smoothly and stably after assembly and use.

[0003] In a typical workbench for machining workpieces, after the workpiece is finished, it needs to be removed from the workbench and then the next workpiece to be machined is installed on the workbench. This process is repeated continuously to complete the machining of the workpieces.

[0004] In the above structure, since the operator needs to remove the previous completed workpiece to free up the workpiece processing position so that the operator can install the next workpiece to be processed, the processing equipment is not in working condition (i.e., grinding or cutting, etc.) when the operator is installing the workpiece, which reduces the workpiece processing efficiency. Summary of the Invention

[0005] To improve the efficiency of workpiece processing, this application provides a rotary double-table exchange device for a horizontal machining center for automotive parts.

[0006] This application provides a rotary dual-table exchange device for a horizontal machining center for automotive parts, which adopts the following technical solution:

[0007] A rotary dual-table exchange device for a horizontal machining center for automotive parts includes a base, a spindle for mounting tool heads mounted on the base, a support column mounted on the base, a reversing shaft rotatably mounted on the support column, a machining seat fixedly connected to the reversing shaft, a front machining surface and a back machining surface provided on the machining seat, the front machining surface and the back machining surface being located on the front and back of the machining seat respectively, and workpieces to be processed can be mounted on both the front machining surface and the back machining surface. A drive mechanism for driving the reversing shaft to rotate is provided in the base, and a locking mechanism for limiting the reversing shaft is provided in the support column.

[0008] With the above technical solution, the operator can install the workpiece to be processed on the front machining surface and the secondary machining surface. After the workpiece to be processed is installed on both the front machining surface and the secondary machining surface, the reversing shaft is driven to rotate by the drive mechanism so that the workpiece on the front machining surface is aligned with the spindle on which the cutter head is installed. Then, the locking mechanism limits the ring shaft so that the cutter head can process the workpiece.

[0009] After the workpiece on the primary machining surface is finished, the locking mechanism is released and the reversing shaft is rotated by the drive mechanism, so that the secondary machining surface is aligned with the spindle, so that the cutting head on the spindle can machine the workpiece on the secondary machining surface. During the machining of the workpiece on the secondary machining surface, the operator can take out the workpiece that has been machined on the primary machining surface and install the next workpiece to be machined on the primary machining surface, so as to prepare for the machining of the workpiece on the next primary machining surface.

[0010] Therefore, when a workpiece is being processed on one of the processing surfaces, the operator can disassemble and install the workpiece on the other processing surface, which shortens the interval between processing two adjacent workpieces and thus improves the efficiency of workpiece processing.

[0011] In a preferred embodiment, the present application may be further configured such that: the drive mechanism includes a motor mounted in the base, a worm gear mounted on the output shaft of the motor, a transmission shaft rotatably mounted in the support column, one end of the transmission shaft extending into the base, a worm wheel mounted on the end of the transmission shaft extending into the base, the worm wheel and the worm gear meshing with each other, a first bevel gear mounted on the transmission shaft, a second bevel gear mounted on the reversing shaft, and the first bevel gear and the second bevel gear meshing with each other.

[0012] With the above technical solution, when the operator needs to rotate the reversing shaft, the motor is started, the output shaft of the motor drives the worm to rotate, the worm drives the worm wheel to rotate, the worm wheel drives the first bevel gear to rotate through the transmission shaft, the first bevel gear drives the second bevel gear to rotate, and the second bevel gear drives the reversing shaft to rotate, thereby enabling the machining seat to rotate so that the cutting head on the spindle can process the workpiece on the machining seat.

[0013] In a preferred embodiment, this application may be further configured such that: both sides of the processing base are slidably provided with protective covers to prevent debris from splashing, and each of the two protective covers has a cavity for accommodating the processing base on the side that is close to each other.

[0014] With the above technical solution, since the machining seat can be accommodated in the cavity of the dust cover, during the workpiece machining process, the two protective covers are moved to the side closer to the machining seat so that the two protective covers abut against each other. At this time, the workpiece is then machined. Under the shielding effect of the protective covers, the possibility of debris splashing is reduced, which also reduces the labor intensity of the operator in cleaning up the debris later.

[0015] When the operator switches the machining surface, the two protective covers are moved away from the machining seat to facilitate the removal of debris from inside the protective covers.

[0016] In a preferred embodiment, this application can be further configured as follows: two support columns are provided on the base, the two support columns are respectively located on both sides of the processing seat, a reciprocating screw is rotatably mounted on each support column, the two reciprocating screws and the two protective covers are arranged one-to-one, the protective covers are threadedly connected to the corresponding reciprocating screws, a guide rod is installed on each support column, the two guide rods and the two protective covers are arranged one-to-one, and the protective covers are slidably mounted on the corresponding guide rods.

[0017] Through the above technical solution, the reciprocating screw can drive the corresponding protective cover to reciprocate, so that the two protective covers can move towards each other or away from each other, thereby realizing the contact and separation of the protective covers.

[0018] In a preferred embodiment, this application can be further configured such that: a first spur gear and a second spur gear are rotatably disposed inside the support column, the first spur gear and the second spur gear mesh with each other, the first spur gear is mounted on the reversing shaft, and the second spur gear is mounted on the reciprocating screw.

[0019] Through the above technical solution, during the rotation of the reversing shaft, on the one hand, the machining surface on the machining base can be switched to facilitate the machining of the next workpiece; on the other hand, the reversing shaft drives the first spur gear to rotate, the first spur gear drives the second spur gear to rotate, the second spur gear drives the reciprocating screw to rotate, and the reciprocating screw can drive the corresponding protective cover to move closer to or further away from the machining base, thereby simplifying the structure and operation steps of this equipment.

[0020] In a preferred embodiment, this application can be further configured such that: a sliding hole is provided on the support column, and the locking mechanism includes a fixing pin, which is slidably installed in the sliding hole and can be inserted between adjacent teeth on the spur gear.

[0021] With the above technical solution, after the operator aligns one of the machining faces with the cutter head on the spindle, the fixing pin is inserted between the teeth of the first spur gear. Under the obstruction of the fixing pin, the possibility of the first spur gear rotating is reduced, which also reduces the possibility of the reversing shaft rotating. This maintains the state of the machining face aligning with the cutter head, so that the cutter head can process the workpiece.

[0022] When the operator needs to switch the machining surface, he pulls the fixing pin outward to release the fixing pin's restriction on the first flat gear, so that the reversing shaft can drive the machining seat to rotate, thereby realizing the switching of the machining surface.

[0023] In a preferred embodiment, this application may be further configured such that: an annular groove is formed on the inner wall of the sliding hole, a baffle is slidably installed in the annular groove, the baffle is fixedly connected to the fixing pin, a spring is provided in the annular groove, one end of the spring is fixedly connected to the baffle, and the other end of the spring is fixedly connected to the inner wall of the annular groove.

[0024] With the above technical solution, the fixing pin can be pressed against the first spur gear under the elastic force of the spring, which reduces the possibility of the fixing pin disengaging from the first spur gear, and thus reduces the possibility of the reversing shaft rotating.

[0025] In a preferred embodiment, this application can be further configured as follows: a locking disc is fixedly connected to the reversing shaft, the fixing pin can slide along the outer wall of the locking disc, the locking disc has a locking groove for accommodating the first spur gear, and the locking disc has two through holes for the fixing pin to pass through, one of the through holes corresponding to the front machining surface and the other through hole corresponding to the secondary machining surface.

[0026] With the above technical solution, during the rotation of the reversing shaft driven by the motor, the fixing pin slides along the outer wall of the locking disc. When one of the machining surfaces aligns with the spindle, the corresponding through hole of the machining surface aligns with the fixing pin. At this time, under the elastic force of the spring, the fixing pin passes through the through hole and is inserted into the first spur gear, thereby completing the limiting of the fixing pin on the first spur gear.

[0027] In a preferred embodiment, this application may be further configured such that each of the protective covers has a through groove on its sidewall near the secondary machining surface, the through groove communicating with the corresponding cavity.

[0028] Through the above technical solution, operators can disassemble and install workpieces on the machining base through the through slot, reducing the interference caused by the protective cover to the installation and disassembly of workpieces.

[0029] In a preferred embodiment, the present application may be further configured such that: the bottom wall of the cavity is inclined downward on the side near the other protective cover, the top of the base is provided with an upward-curving edge, the upward-curving edge is provided around the top edge of the base, and both protective covers are located above the upward-curving edge.

[0030] With the above technical solution, since the bottom wall of the cavity is inclined downward on the side close to the other protective cover, when the two protective covers are separated, the debris trapped inside can slide down along the inclined bottom wall of the cavity and fall onto the top surface of the base. After falling onto the top surface of the base, the possibility of debris falling outside the base is reduced by the obstruction of the upward-curved edge.

[0031] In summary, this application includes the following beneficial technical effects:

[0032] 1. When a workpiece is being processed on one of the processing surfaces, the operator can disassemble and assemble the workpiece on the other processing surface, which shortens the interval between processing two adjacent workpieces and thus improves the work efficiency of workpiece processing.

[0033] 2. The protective cover reduces the possibility of debris splashing, thereby reducing the labor intensity of operators in cleaning up the debris later.

[0034] 3. The rotation of the reversing shaft not only enables the switching of the machining surface, but also enables the reciprocating movement of the protective cover, simplifying the structure and operation steps of this equipment. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the overall structure of an embodiment of this application, mainly illustrating the construction of the base and the mounting bracket.

[0036] Figure 2 This is a partial structural diagram of an embodiment of this application, mainly illustrating the structure of the protective cover, cavity, and upturned edge.

[0037] Figure 3 yes Figure 1 The cross-sectional view along the AA direction mainly illustrates the structure of the motor, worm gear, and worm.

[0038] Figure 4 yes Figure 3 The enlarged schematic diagram in section B mainly illustrates the structure of the drive shaft, bevel gear one, and bevel gear two.

[0039] Figure 5 yes Figure 2 The cross-sectional view along the CC direction mainly illustrates the structure of the fixing pin, the baffle, and the spring.

[0040] Figure 6 This is a partial structural diagram of an embodiment of this application, mainly illustrating the construction of the locking disc and the through hole.

[0041] Figure 7 yes Figure 1 The cross-sectional diagram along the DD direction mainly illustrates the structure of the first and second spur gears.

[0042] Explanation of reference numerals in the attached figures:

[0043] 1. Base; 11. Worm gear; 101. Spindle; 102. Upward-facing edging; 103. Mounting bracket; 2. Support column; 21. Reversing shaft; 211. Bevel gear II; 212. Flat gear I; 22. Machining seat; 221. Front machined surface; 222. Secondary machined surface; 23. Drive shaft; 231. Worm gear; 232. Bevel gear I; 24. Reciprocating lead screw; 241. Flat gear II; 25. Guide rod; 26. Sliding hole; 27. Annular groove; 271. Baffle; 272. Spring; 3. Drive mechanism; 31. Motor; 4. Locking mechanism; 41. Fixing pin; 5. Protective cover; 51. Cavity; 52. Through groove; 6. Locking disc; 61. Locking groove; 62. Through hole. Detailed Implementation

[0044] The following is in conjunction with the appendix Figure 1 -Appendix Figure 7 This application will be described in further detail.

[0045] This application discloses a rotary dual-table exchange device for a horizontal machining center for automotive parts.

[0046] See attached document Figure 1 As shown, a rotary dual-table exchange device for a horizontal machining center for automotive parts includes a horizontally arranged base 1, a vertically arranged mounting bracket 103 mounted on the top surface of the base 1, and a spindle 101 for mounting tool heads mounted on the mounting bracket 103.

[0047] See attached document Figure 1 and attached Figure 2 As shown, two vertically arranged support columns 2 are mounted on the top surface of the base 1. A machining seat 22 is rotatably mounted between the two support columns 2. Reversing shafts 21 are fixedly connected to both sides of the machining seat 22. The axes of the two reversing shafts 21 are collinear, and the two reversing shafts 21 and the two support columns 2 are arranged in a one-to-one correspondence. The end of the reversing shaft 21 away from the machining seat 22 is rotatably mounted inside the corresponding support column 2. The machining seat 22 is provided with a front machining surface 221 and a secondary machining surface 222, located on the front and back sides of the machining seat 22, respectively. Workpieces to be processed can be mounted on both the front machining surface 221 and the secondary machining surface 222.

[0048] When a workpiece is being machined on one of the machining surfaces (such as the primary machining surface 221), the operator can disassemble and install the workpiece on the other machining surface (the secondary primary machining surface 221), which shortens the time interval between the machining of two adjacent workpieces and thus improves the work efficiency of workpiece machining.

[0049] See attached document Figure 3As shown, a drive mechanism 3 for driving the reversing shaft 21 to rotate is provided in the base 1. The drive mechanism 3 includes a motor 31, which is installed in the base 1. The motor 31 is a double-headed motor 31. The two output shafts of the motor 31 correspond one-to-one with the two support columns 2. The following only describes one of the support columns 2 and its related structures. The other support column 2 will not be described in detail.

[0050] See attached document Figure 3 and attached Figure 4 As shown, a worm gear 11 is coaxially fixedly connected to the output shaft of motor 31. A vertically arranged transmission shaft 23 is rotatably mounted inside the support column 2. The bottom end of the transmission shaft 23 extends into the base 1, and a worm wheel 231 is coaxially fixedly connected to the bottom end of the transmission shaft 23. The worm wheel 231 and the worm gear 11 mesh with each other. A bevel gear 232 is coaxially fixedly connected to the top end of the transmission shaft 23. A bevel gear 211 is coaxially fixedly connected to the reversing shaft 21. The bevel gear 232 and the bevel gear 211 mesh with each other. When the operator starts motor 31, motor 31 drives machining base 22 to rotate through worm gear 11, worm wheel 231, transmission rod, bevel gear 232, bevel gear 211, and reversing shaft 21, thereby switching the machining surface so that the cutting head on spindle 101 can process workpieces on different machining surfaces.

[0051] See attached document Figure 5 and attached Figure 6 As shown, a spur gear 212 is rotatably mounted inside the support column 2, and is coaxially fixedly connected to the reversing shaft 21. A locking mechanism 4 for limiting the reversing shaft 21 is provided inside the support column 2. A sliding hole 26 is provided on the support column 2. The locking mechanism 4 includes a fixing pin 41 slidably mounted inside the sliding hole 26 along its length. The fixing pin 41 can be inserted between adjacent teeth on the spur gear 212. An annular groove 27 is provided on the inner wall of the sliding hole 26, and the axis of the annular groove 27 is collinear with the axis of the sliding hole 26. A baffle 271 is slidably mounted inside the annular groove 27 along its length and is fixedly connected to the fixing pin 41. A spring 272 is provided inside the annular groove 27, and is sleeved on the fixing pin 41. One end of the spring 272 is fixedly connected to the baffle 271, and the other end is fixedly connected to the inner wall of the annular groove 27.

[0052] See attached document Figure 5 and attached Figure 6As shown, a locking disc 6 is rotatably installed inside the support column 2. The locking disc 6 is coaxially fixedly connected to the reversing shaft 21. The fixing pin 41 can slide along the outer wall of the locking disc 6. The side wall of the locking disc 6 near the spur gear 212 is provided with a locking groove 61 for accommodating the spur gear 212. The locking disc 6 has two through holes 62 for the fixing pin 41 to pass through. One through hole 62 is corresponding to the positive machining surface 221, and the other through hole 62 is corresponding to the secondary machining surface 222. That is, the two machining surfaces are symmetrical about the axis of the locking disc 6.

[0053] During the rotation of the reversing shaft 21, the fixing pin 41 slides along the outer wall of the locking disc 6. When one of the machining surfaces is aligned with the spindle 101, the through hole 62 corresponding to the machining surface is aligned with the fixing pin 41. Under the elastic force of the spring 272, the fixing pin 41 passes through the through hole 62 and is inserted into the spur gear 212, thereby completing the limiting of the fixing pin 41 on the spur gear 212, which reduces the possibility of the reversing shaft 21 rotating, thus maintaining the state of the machining surface aligned with the cutting head, so that the cutting head can process the workpiece.

[0054] In addition, the operator can release the limiting position of the fixing pin 41 on the flat gear 212 by pulling the fixing pin 41 outward, so that the reversing shaft 21 can drive the machining seat 22 to rotate, thereby realizing the switching of the machining surface.

[0055] See attached document Figure 2 and attached Figure 3 As shown, a protective cover 5 is slidably mounted on both sides of the machining base 22 to prevent workpiece debris from splashing outwards. Two protective covers 5 and two reversing shafts 21 are arranged in a one-to-one correspondence, with the protective covers 5 located between the machining base 22 and the corresponding support column 2. The protective covers 5 have holes for the reversing shafts 21 to slide through, and each of the two protective covers 5 has a cavity 51 on its side closest to each other to accommodate the machining base 22. Each protective cover 5 has a through groove 52 on its side wall near the secondary machining surface 222, which connects to the corresponding cavity 51, facilitating the disassembly and installation of workpieces on the machining base 22 by the operator. The bottom wall of the cavity 51 is inclined downwards on the side closest to the other protective cover 5 to facilitate the downward sliding of debris. The top of the base 1 is provided with an upward-curved edge 102 to prevent debris from scattering outwards from the base 1. The upward-curved edge 102 is arranged around the top edge of the base 1, and both protective covers 5 are located above the upward-curved edge 102.

[0056] See attached document Figure 3 and attached Figure 7As shown, a reciprocating screw 24 is rotatably mounted on the support column 2, and the reciprocating screw 24 is threadedly connected to the corresponding protective cover 5. A guide rod 25 is fixedly connected to the support column 2. The guide rod 25, the reciprocating screw 24, and the reversing shaft 21 are aligned in the same length direction. The protective cover 5 is slidably mounted on the corresponding guide rod 25. A second spur gear 241 is coaxially fixedly connected to the end of the reciprocating screw 24 away from the protective cover 5. The second spur gear 241 meshes with the second spur gear 241.

[0057] During the rotation of the reversing shaft 21, not only can the processing surface on the processing seat 22 be switched to facilitate the processing of the next workpiece, but the reversing shaft 21 can also drive the reciprocating screw 24 to rotate through the first spur gear 212 and the second gear. The reciprocating screw 24 drives the corresponding protective cover 5 to move towards or away from the processing seat 22, so as to realize the contact and separation of the two protective covers 5, thereby simplifying the structure and operation steps of the equipment.

[0058] The implementation principle of this embodiment is as follows: the operator can install the workpiece to be processed on the front processing surface 221 and the secondary processing surface 222 of the processing base 22, and then start the motor 31. The motor 31 can indirectly drive the processing base 22 to rotate, so that one of the processing surfaces (such as the front processing surface 221) is aligned with the cutting head, so as to facilitate the processing of the workpiece.

[0059] After the workpiece on the previous machining surface (such as the positive machining surface 221) is finished, the reversing shaft 21 is rotated again to align the workpiece on the other machining surface (such as the secondary machining surface 222) with the cutting head, so as to continue machining the workpiece. At this time, the operator removes the workpiece that has been machined on the previous machining surface (positive machining surface 221) and loads the workpiece to be machined.

[0060] In summary, when a workpiece is being processed on one of the processing surfaces, the operator can disassemble and assemble the workpiece on the other processing surface, shortening the interval between processing two adjacent workpieces and thus improving the efficiency of workpiece processing.

[0061] The embodiments described in this specific implementation are all preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A rotary dual-table exchange device for a horizontal machining center for automotive parts, comprising a base (1), wherein a spindle (101) for mounting tool heads is mounted on the base (1), characterized in that: A support column (2) is installed on the base (1), and a reversing shaft (21) is rotatably installed on the support column (2). A processing seat (22) is fixedly connected to the reversing shaft (21). The processing seat (22) is provided with a front processing surface (221) and a secondary processing surface (222). The front processing surface (221) and the secondary processing surface (222) are located on the front and back sides of the processing seat (22), respectively. Workpieces to be processed can be installed on both the front processing surface (221) and the secondary processing surface (222). A driving mechanism (3) for driving the reversing shaft (21) to rotate is provided in the base (1). A locking mechanism (4) for limiting the reversing shaft (21) is provided in the support column (2). The drive mechanism (3) includes a motor (31) installed in the base (1), a worm (11) installed on the output shaft of the motor (31), a transmission shaft (23) rotatably installed in the support column (2), one end of the transmission shaft (23) extending into the base (1), a worm wheel (231) installed on the end of the transmission shaft (23) extending into the base (1), the worm wheel (231) and the worm (11) meshing with each other, a bevel gear one (232) installed on the transmission shaft (23), a bevel gear two (211) installed on the reversing shaft (21), the bevel gear one (232) and the bevel gear two (211) meshing with each other; Both sides of the processing base (22) are slidably provided with protective covers (5) to prevent debris from splashing. The two protective covers (5) are provided with cavities (51) to accommodate the processing base (22) on the side that is close to each other. Two support columns (2) are provided on the base (1). The two support columns (2) are located on both sides of the processing seat (22). A reciprocating screw (24) is rotatably installed on each support column (2). The two reciprocating screws (24) and the two protective covers (5) are arranged in a one-to-one correspondence. The protective cover (5) is threaded to the corresponding reciprocating screw (24). A guide rod (25) is installed on each support column (2). The two guide rods (25) and the two protective covers (5) are arranged in a one-to-one correspondence. The protective cover (5) is slidably installed on the corresponding guide rod (25). The support column (2) is rotatably equipped with a first spur gear (212) and a second spur gear (241). The first spur gear (212) and the second spur gear (241) mesh with each other. The first spur gear (212) is mounted on the reversing shaft (21), and the second spur gear (241) is mounted on the reciprocating screw (24).

2. The rotary double-table exchange device for a horizontal machining center for automotive parts according to claim 1, characterized in that: The support column (2) has a sliding hole (26), and the locking mechanism (4) includes a fixing pin (41). The fixing pin (41) is slidably installed in the sliding hole (26), and the fixing pin (41) can be inserted between adjacent teeth on the first spur gear (212).

3. The rotary double-table exchange device for a horizontal machining center for automotive parts according to claim 2, characterized in that: The inner wall of the sliding hole (26) is provided with an annular groove (27), and a baffle (271) is slidably installed in the annular groove (27). The baffle (271) is fixedly connected to the fixing pin (41). A spring (272) is provided in the annular groove (27). One end of the spring (272) is fixedly connected to the baffle (271), and the other end of the spring (272) is fixedly connected to the inner wall of the annular groove (27).

4. The rotary double-table exchange device for a horizontal machining center for automotive parts according to claim 3, characterized in that: A locking disc (6) is fixedly connected to the reversing shaft (21). The fixing pin (41) can slide along the outer wall of the locking disc (6). The locking disc (6) has a locking groove (61) for accommodating the first spur gear (212). The locking disc (6) has two through holes (62) for the fixing pin (41) to pass through. One of the through holes (62) is corresponding to the positive machining surface (221), and the other through hole (62) is corresponding to the secondary machining surface (222).

5. The rotary double-table exchange device for a horizontal machining center for automotive parts according to claim 1, characterized in that: Each of the protective covers (5) has a through groove (52) on its side wall near the secondary processing surface (222), and the through groove (52) is connected to the corresponding cavity (51).

6. The rotary double-table exchange device for a horizontal machining center for automotive parts according to claim 1, characterized in that: The bottom wall of the cavity (51) is inclined downward on the side near the other protective cover (5). The top of the base (1) is provided with an upturned edge (102). The upturned edge (102) is arranged around the top edge of the base (1). Both protective covers (5) are located above the upturned edge (102).

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