Membrane electrode hot press fixture with pre-pressing function

Abstract

The application belongs to the technical field of film electrode hot-pressing clamps, in particular to a film electrode hot-pressing clamp with pre-pressing function, which comprises an upper pressing plate cover, an upper pressing plate, a lower pressing plate, a lower pressing plate cover and a door-latch type quick clamp, and the upper pressing plate cover, the upper pressing plate, the lower pressing plate and the lower pressing plate cover are sequentially arranged from top to bottom, each guide rod sequentially passes through the whole body composed of the upper pressing plate cover, the upper pressing plate, the lower pressing plate and the lower pressing plate cover in the vertical direction, and the door-latch type quick clamp is connected with the outer circumferential surface of the upper pressing plate and the outer circumferential surface of the lower pressing plate respectively. The application can ensure the accuracy of the up-and-down movement of the upper pressing plate cover, the upper pressing plate, the lower pressing plate and the lower pressing plate cover, and make the film electrode be pre-pressed before formal hot pressing, so as to reduce the relative displacement risk between the main body of the catalytic layer and the diffusion layer of the film electrode before formal hot pressing, and further ensure the uniformity of the hot-pressing pressure distribution of the film electrode.

Description

Technical Field

[0001] This invention belongs to the field of hot pressing fixtures for membrane electrodes, specifically a hot pressing fixture for membrane electrodes with pre-pressing function. Background Technology

[0002] The fabrication process of PEM water electrolysis hydrogen production membrane electrode includes a hot pressing process, which is a necessary process to tightly compact the catalytic layer of the membrane electrode, reliably bond the diffusion layer, reduce the interfacial layer resistance, and form a reliable three-phase interface structure.

[0003] Currently, most membrane electrode hot pressing fixtures adopt simple flat plate designs or ordinary compression positioning fixtures. This can easily lead to the accumulation of errors in the parallelism of the upper and lower pressure plates of the press, the thickness deviation of the membrane electrode, and the parallelism deviation of the upper and lower pressure plates of the fixture, resulting in uneven distribution of the hot pressing pressure of the membrane electrode. Summary of the Invention

[0004] To address the above problems, the present invention aims to provide a membrane electrode hot pressing fixture with a pre-pressing function.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A membrane electrode hot pressing fixture with pre-compression function includes an upper pressure plate cover, an upper pressure plate, a lower pressure plate, a lower pressure plate cover, a latch-type quick clamp, and a guide rod;

[0007] The upper pressure plate cover, upper pressure plate, lower pressure plate and lower pressure plate cover are arranged in sequence from top to bottom. A membrane electrode receiving groove A for accommodating membrane electrodes is opened on the top surface of the lower pressure plate or the bottom surface of the upper pressure plate.

[0008] The guide rod is provided with at least two, and each guide rod passes through the whole consisting of the upper pressure plate cover, the upper pressure plate, the lower pressure plate and the lower pressure plate cover in a vertical direction. The outer circumferential surface of the upper pressure plate is respectively connected to the guide rod by a screw thread. Each screw bolt is used to abut against a corresponding guide rod.

[0009] The latch-type quick clamp is connected to the outer peripheral surface of the upper pressure plate and the outer peripheral surface of the lower pressure plate, respectively.

[0010] The upper pressure plate is equipped with a laser generator, which is used to determine the relative positional relationship of the membrane electrode on the top surface of the upper pressure plate.

[0011] When the membrane electrode receiving groove A is formed on the top surface of the lower pressure plate, a membrane electrode receiving groove B is formed on the bottom surface of the upper pressure plate at a position corresponding to the membrane electrode receiving groove A; when the membrane electrode receiving groove A is formed on the bottom surface of the upper pressure plate, a membrane electrode receiving groove B is formed on the top surface of the lower pressure plate at a position corresponding to the membrane electrode receiving groove A.

[0012] The shape of the membrane electrode receiving groove B matches the shape of the membrane electrode receiving groove A.

[0013] On the top surface of the lower pressure plate, and at a position outside the membrane electrode receiving groove A, there is a ring-shaped limiting protrusion group for limiting the position of the membrane electrode during hot pressing. The ring-shaped limiting protrusion group includes several limiting protrusions.

[0014] A hot working fluid flow field A is formed in the middle of the top surface of the upper pressure plate, and a hot working fluid input interface A and a hot working fluid output interface A connected to the hot working fluid flow field A are respectively provided on the outer peripheral surface of the upper pressure plate; a hot working fluid flow field B is formed in the middle of the top surface of the lower pressure plate, and a hot working fluid input interface B and a hot working fluid output interface B connected to the hot working fluid flow field B are respectively provided on the outer peripheral surface of the lower pressure plate.

[0015] A sealing line groove A is formed on the top surface of the upper pressure plate at the outer periphery of the hot working fluid flow field A, and a sealing line A is embedded in the sealing line groove A; a sealing line groove B is formed on the bottom surface of the lower pressure plate at the outer periphery of the hot working fluid flow field B, and a sealing line B is embedded in the sealing line groove B.

[0016] The upper pressure plate cover is fixedly connected to the upper pressure plate by countersunk screws, and the lower pressure plate cover is fixedly connected to the lower pressure plate by countersunk screws.

[0017] Two latch-type quick-release calipers are provided, and the two latch-type quick-release calipers are located on both sides of the upper pressure plate and are symmetrical to each other.

[0018] Each of the guide rods is evenly arranged on the outer periphery of the whole formed by the upper pressure plate cover, the upper pressure plate, the lower pressure plate, and the lower pressure plate cover. Each of the upper pressure plate cover, the upper pressure plate, the lower pressure plate, and the lower pressure plate cover has a guide rod through hole that matches the shape of the cross-section of each guide rod.

[0019] All the guide rods described herein have the same cross-sectional shape and size.

[0020] The advantages and positive effects of this invention are as follows:

[0021] 1. This invention, through the coordinated arrangement of the upper pressure plate cover, upper pressure plate, lower pressure plate, lower pressure plate cover, latch-type quick clamp, and guide rod, can ensure the accuracy of the up-and-down movement of the upper pressure plate cover, upper pressure plate, lower pressure plate, and lower pressure plate cover, solving the problem of uneven hot-pressing pressure distribution of the membrane electrode caused by error accumulation. Furthermore, it allows the membrane electrode to be pre-pressed before the formal hot pressing, reducing the risk of relative displacement between the catalyst layer and diffusion layer of the membrane electrode before the formal hot pressing, and further ensuring the uniformity of the hot-pressing pressure distribution of the membrane electrode.

[0022] 2. By setting the hot working fluid flow field A on the upper platen and the hot working fluid flow field B on the lower platen, the present invention facilitates a more uniform temperature distribution on the upper and lower platens, ensuring uniform heating of the membrane electrode between the upper and lower platens, and making the temperature control of the hot pressing fixture more stable and precise.

[0023] 3. This invention can be combined with hot pressing during the fabrication process of membrane electrodes to control the uniformity of temperature and pressure under hot pressing conditions. It is easy to install, easy to mass-produce, and achieves consistency of hot pressing fixtures, thereby promoting the consistency of membrane electrode products. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of the present invention.

[0025] In the diagram: 1 is the upper pressure plate cover, 2 is the upper pressure plate, 201 is the thermal fluid flow field A, 202 is the sealing line groove A, 3 is the lower pressure plate, 301 is the membrane electrode receiving groove A, 302 is the limiting protrusion, 4 is the lower pressure plate cover, 5 is the latch-type quick clamp, 6 is the guide rod, 7 is the knob bolt, 8 is the laser generator, and 9 is the countersunk screw.

[0026] 001 is the membrane electrode. Detailed Implementation

[0027] The following is in conjunction with the appendix Figure 1 The present invention will be described in further detail below.

[0028] A membrane electrode hot pressing fixture with pre-compression function, such as Figure 1 As shown, this embodiment includes an upper pressure plate cover 1, an upper pressure plate 2, a lower pressure plate 3, a lower pressure plate cover 4, a latch-type quick clamp 5, and a guide rod 6.

[0029] In this embodiment, the upper pressure plate cover 1, upper pressure plate 2, lower pressure plate 3, and lower pressure plate cover 4 are arranged sequentially from top to bottom. A membrane electrode receiving groove A 301 for accommodating the membrane electrode 001 is formed in the center of the top surface of the lower pressure plate 3. Alternatively, the membrane electrode receiving groove A 301 can be formed separately in the center of the bottom surface of the upper pressure plate 2. The height of the cavity formed by the membrane electrode receiving groove A 301 after the upper pressure plate 2 and the lower pressure plate 3 are pressed together matches the compressed thickness of the membrane electrode 001.

[0030] In this embodiment, four guide rods 6 are provided. Each guide rod 6 passes vertically through the entire structure consisting of the upper pressure plate cover 1, upper pressure plate 2, lower pressure plate 3, and lower pressure plate cover 4. A knob bolt 7 is threadedly connected to each guide rod 6 at a corresponding location on the outer circumference of the upper pressure plate 2. Each knob bolt 7 is used to abut against a corresponding guide rod 6. In this embodiment, the guide rods 6 are evenly distributed on the outer circumference of the entire structure consisting of the upper pressure plate cover 1, upper pressure plate 2, lower pressure plate 3, and lower pressure plate cover 4. Each of the upper pressure plate cover 1, upper pressure plate 2, lower pressure plate 3, and lower pressure plate cover 4 has a guide rod through hole that matches the cross-sectional shape of each guide rod 6. In this embodiment, all guide rods 6 have a circular cross-sectional shape and the same size; however, the cross-sectional shape of the guide rod 6 can also be other polygonal shapes. Rotating each knob bolt 7 can abut or loosen the corresponding guide rod 6.

[0031] The latch-type quick-release caliper 5 is connected to the outer peripheral surfaces of the upper pressure plate 2 and the lower pressure plate 3, respectively. In this embodiment, the latch-type quick-release caliper 5 is a commercially available product. The latch-type quick-release caliper 5 generally includes an upper fixed seat, a lower fixed seat, and a hinged linkage locking handle structure. The upper fixed seat of the latch-type quick-release caliper 5 is fixedly connected to the outer peripheral surface of the upper pressure plate 2, and the lower fixed seat of the latch-type quick-release caliper 5 is fixedly connected to the outer peripheral surface of the lower pressure plate 3. The hinged linkage locking handle structure of the latch-type quick-release caliper 5 is connected to the upper fixed seat and the lower fixed seat, respectively. Rotating the locking handle of the hinged linkage locking handle structure forward by a fixed angle allows the upper pressure plate 2 and the lower pressure plate 3 to approach and lock together; rotating the locking handle of the hinged linkage locking handle structure in the reverse direction allows the upper pressure plate 2 and the lower pressure plate 3 to separate. Each guide rod 6 ensures the accuracy of the up-and-down movement of the upper pressure plate cover 1, upper pressure plate 2, lower pressure plate 3, and lower pressure plate cover 4 as the upper pressure plate 2 and lower pressure plate 3 move closer and further apart. In this embodiment, two latch-type quick clamps 5 are provided, which are located on both sides of the upper pressure plate 2 and are symmetrical to each other, which can better ensure the uniform force on the membrane electrode 001 when it is pre-pressed by the hot pressing fixture.

[0032] Specifically, in this embodiment, a laser generator 8 is installed on the outer peripheral surface of the upper pressure plate 2. The laser generator 8 is used to determine the relative position of the membrane electrode 001 on the top surface of the upper pressure plate 2. The laser generator 8 emits a laser to determine the edge position of the membrane electrode 001. The laser shines on the top surface of the upper pressure plate 2, and the distance deviation between the edge of the membrane electrode 001 and the laser positioning is detected by the human eye, and the membrane electrode 001 is adjusted to a suitable position. In this embodiment, the laser generator 8 is a commercially available laser generator product, which is connected to an external controller. The laser generator 8 can also be embedded inside the upper pressure plate 2.

[0033] Specifically, in this embodiment, a membrane electrode receiving groove B is provided on the bottom surface of the upper pressure plate 2 at a position corresponding to the membrane electrode receiving groove A 301; when the membrane electrode receiving groove A 301 is provided in the middle of the bottom surface of the upper pressure plate 2, a membrane electrode receiving groove B is provided on the top surface of the lower pressure plate 3 at a position corresponding to the membrane electrode receiving groove A 301. The shape of the membrane electrode receiving groove B matches the shape of the membrane electrode receiving groove A 301. By replacing the upper pressure plate 2 or the lower pressure plate 3 with or without the membrane electrode receiving groove B, it can be applied to the hot pressing conditions of membrane electrodes 001 of different thicknesses, ensuring accurate positioning of the membrane electrode 001 when placed in the hot pressing fixture and good applicability. At this time, the height of the cavity formed by the membrane electrode receiving groove A 301 and the membrane electrode receiving groove B when the upper pressure plate 2 and the lower pressure plate 3 are pressed together matches the compression thickness of the membrane electrode 001.

[0034] In this embodiment, an annular limiting protrusion group for limiting the membrane electrode 001 is provided on the top surface of the lower pressure plate 3 and on the outer side of the membrane electrode receiving groove A 301. The annular limiting protrusion group includes several evenly arranged limiting protrusions 302, which can ensure the accurate positioning of the membrane electrode 001 in the hot pressing fixture, and abut against the bottom surface of the upper pressure plate 2 during the formal hot pressing operation to form a hard limiting structure, thereby controlling the hot pressing gap, ensuring the uniform and repeatable distribution of the hot pressing pressure surface of the membrane electrode 001, and preventing local over-pressure or insufficient pressure. A limiting shim can also be placed between the upper pressure plate 2 and the lower pressure plate 3 according to the pre-pressing thickness to limit the membrane electrode 001.

[0035] Specifically, in this embodiment, a hot working fluid flow field A201 is formed in the middle of the top surface of the upper pressure plate 2, and a hot working fluid input interface A and a hot working fluid output interface A connected to the hot working fluid flow field A201 are respectively formed on the outer peripheral surface of the upper pressure plate 2; a hot working fluid flow field B is formed in the middle of the top surface of the lower pressure plate 3, and a hot working fluid input interface B and a hot working fluid output interface B connected to the hot working fluid flow field B are respectively formed on the outer peripheral surface of the lower pressure plate 3. In this embodiment, a sealing line groove A202 is formed on the top surface of the upper pressure plate 2 at the outer peripheral position of the hot working fluid flow field A201, and a sealing line A is embedded in the sealing line groove A202; a sealing line groove B is formed on the bottom surface of the lower pressure plate 3 at the outer peripheral position of the hot working fluid flow field B, and a sealing line B is embedded in the sealing line groove B. In this embodiment, the processing and setting methods of the heat working fluid flow field A 201, heat working fluid input interface A, heat working fluid output interface A, and sealing line groove A202 of the upper pressure plate 2 are all existing technologies. The processing and setting methods of the heat working fluid flow field B, heat working fluid input interface B, heat working fluid output interface B, and sealing line groove B of the lower pressure plate 3 are also existing technologies and are basically the same as those of the upper pressure plate 2. For example, they can be processed by direct machining or additive manufacturing.

[0036] The heat transfer fluid input port A is connected via a pipeline to an external heat transfer fluid source A for inputting heat transfer fluid into the upper pressure plate 2. The heat transfer fluid output port A is connected via a pipeline to discharge the heat transfer fluid from the upper pressure plate 2. The heat transfer fluid from heat transfer fluid source A enters the heat transfer fluid flow field A 201 through the heat transfer fluid input port A and then flows out of the upper pressure plate 2 through the heat transfer fluid output port A. Similarly, the heat transfer fluid input port B is connected via a pipeline to an external heat transfer fluid source B for inputting heat transfer fluid into the lower pressure plate 3. The heat transfer fluid from heat transfer fluid source B enters the heat transfer fluid flow field B through the heat transfer fluid input port B and then flows out of the lower pressure plate 3 through the heat transfer fluid output port B. By inputting heat transfer fluid into the upper pressure plate 2 and the lower pressure plate 3 respectively, the temperature of the upper pressure plate 2 and the lower pressure plate 3 can be adjusted to suit the test conditions. In this embodiment, the external heat source A and heat source B are both existing technologies, allowing for independent control of the temperature, pressure, and flow rate of the output heat source fluid. The output heat source fluid can be water, ethylene glycol, heat transfer oil, or mixtures thereof. By allowing heat source A and heat source B to output heat source fluids at different temperatures, the temperature of the upper pressure plate 2 and lower pressure plate 3 can be controlled independently, which is beneficial for heat conduction and ensures uniform heat distribution on the surfaces of the upper pressure plate 2 and lower pressure plate 3. The sealing lines A and B ensure that the heat source fluid input to the upper pressure plate 2 and lower pressure plate 3 does not leak from the gaps between the upper pressure plate cover 1 and the upper pressure plate 2 or between the lower pressure plate cover 4 and the lower pressure plate 3.

[0037] Specifically, in this embodiment, the upper pressure plate cover 1 and the upper pressure plate 2 are fixedly connected by countersunk screws 9, and the lower pressure plate cover 4 and the lower pressure plate 3 are fixedly connected by countersunk screws 9. This achieves pre-fixation between the upper pressure plate cover 1 and the upper pressure plate 2, and between the lower pressure plate cover 4 and the lower pressure plate 3, respectively, and ensures that the working fluid input into the upper pressure plate 2 and the lower pressure plate 3 does not leak. During hot pressing, the upper pressure plate cover 1 and the upper pressure plate 2 move together, and the lower pressure plate cover 4 and the lower pressure plate 3 move together.

[0038] Working principle:

[0039] During the assembly of the hot press fixture, first, each guide rod 6 passes through the upper pressure plate cover 1, upper pressure plate 2, lower pressure plate 3, and lower pressure plate cover 4 respectively. The upper pressure plate cover 1 and the upper pressure plate 2 are pre-fixed, and the lower pressure plate cover 4 and the lower pressure plate 3 are pre-fixed. The upper pressure plate 2 and the lower pressure plate 3 are connected using a latch-type quick clamp 5. Then, the axial position of each guide rod 6 is adjusted according to the environment of the hot press. The guide rod 6 is fixed to the whole structure consisting of the upper pressure plate cover 1, upper pressure plate 2, lower pressure plate 3, and lower pressure plate cover 4 by tightening each knob bolt 7.

[0040] During the hot pressing process, the catalyst layer and diffusion layer of the membrane electrode 001 to be pressed are placed sequentially in the membrane electrode receiving tank A 301 as required. The latch-type quick clamp 5 is operated to bring the upper pressure plate 2 and the lower pressure plate 3 close together and lock them, thereby realizing the function of pre-pressing the membrane electrode 001. Then, the hot pressing fixture is moved to the hot press machine, so that the upper pressure head of the hot press machine abuts against the top surface of the upper pressure plate cover 1 and the lower pressure head of the hot press machine abuts against the bottom surface of the lower pressure plate cover 4, and further presses the upper pressure plate cover 1 and the lower pressure plate cover 4 to realize the formal hot pressing. During the formal hot pressing process, the working fluid of the upper pressure plate 2 and the lower pressure plate 3 and the working fluid flow field B are continuously passed through to maintain a stable and uniform temperature distribution during hot pressing.

[0041] Meanwhile, the upper and lower pressure heads of the hot press are heated to keep the temperature of the upper pressure plate 2 and the lower pressure plate 3 constant, thus maintaining the temperature of the working fluid stable and allowing it to flow evenly through the working fluid flow field.

[0042] After the formal hot pressing is completed, the hot pressing fixture is removed from the hot press. By controlling the temperature of the hot working fluid, the membrane electrode 001 inside the hot pressing fixture can be cooled down rapidly.

[0043] After the internal temperature of the hot-pressing fixture drops to the pressure relief temperature required for the membrane electrode 001, the latch-type quick clamp 5 is operated to separate the upper pressure plate 2 and the lower pressure plate 3, thus obtaining the membrane electrode 001 after the hot-pressing process is completed. Each guide rod 6 ensures the accuracy of the up-and-down movement of the upper pressure plate cover 1, upper pressure plate 2, lower pressure plate 3, and lower pressure plate cover 4 as the upper pressure plate 2 and lower pressure plate 3 approach and move away, solving the problem of uneven hot-pressing pressure distribution of the membrane electrode 001 caused by error accumulation. Furthermore, the latch-type quick clamp 5 pre-presses the membrane electrode 001 before the formal hot-pressing, reducing the risk of relative displacement between the catalyst layer and diffusion layer of the membrane electrode 001 before formal hot-pressing, further ensuring the uniformity of the hot-pressing pressure distribution of the membrane electrode 001.

Claims

1. A membrane electrode hot pressing fixture with pre-compression function, characterized in that: Includes upper pressure plate cover (1), upper pressure plate (2), lower pressure plate (3), lower pressure plate cover (4), latch-type quick clamp (5), and guide rod (6); The upper pressure plate cover (1), upper pressure plate (2), lower pressure plate (3) and lower pressure plate cover (4) are arranged sequentially from top to bottom. A membrane electrode receiving groove A (301) for accommodating the membrane electrode is provided on the top surface of the lower pressure plate (3) or the bottom surface of the upper pressure plate (2). At least two guide rods (6) are provided. Each guide rod (6) passes through the entire structure consisting of the upper pressure plate cover (1), the upper pressure plate (2), the lower pressure plate (3), and the lower pressure plate cover (4) in a vertical direction. A knob bolt (7) is threadedly connected to the corresponding part of each guide rod (6) on the outer circumferential surface of the upper pressure plate (2). Each knob bolt (7) is used to abut against a corresponding guide rod (6). The latch-type quick clamp (5) is connected to the outer peripheral surface of the upper pressure plate (2) and the outer peripheral surface of the lower pressure plate (3), respectively; The upper pressure plate (2) has a heat working fluid flow field A (201) in the middle of its top surface. The outer circumference of the upper pressure plate (2) is provided with a heat working fluid input interface A and a heat working fluid output interface A connected to the heat working fluid flow field A (201). The lower pressure plate (3) has a heat working fluid flow field B in the middle of its top surface. The outer circumference of the lower pressure plate (3) is provided with a heat working fluid input interface B and a heat working fluid output interface B connected to the heat working fluid flow field B. A sealing line groove A (202) is provided on the top surface of the upper pressure plate (2) at the outer periphery of the hot working fluid flow field A (201), and a sealing line A is embedded in the sealing line groove A (202); a sealing line groove B is provided on the top surface of the lower pressure plate (3) at the outer periphery of the hot working fluid flow field B, and a sealing line B is embedded in the sealing line groove B.

2. The membrane electrode hot pressing fixture with pre-compression function according to claim 1, characterized in that: The upper pressure plate (2) is equipped with a laser generator (8), which is used to determine the relative positional relationship of the membrane electrode on the bottom surface of the upper pressure plate (2).

3. A membrane electrode hot pressing fixture with pre-compression function according to claim 1, characterized in that: When the membrane electrode receiving groove A (301) is opened on the top surface of the lower pressure plate (3), the membrane electrode receiving groove B is opened on the bottom surface of the upper pressure plate (2) at the position corresponding to the membrane electrode receiving groove A (301); when the membrane electrode receiving groove A (301) is opened on the bottom surface of the upper pressure plate (2), the membrane electrode receiving groove B is opened on the top surface of the lower pressure plate (3) at the position corresponding to the membrane electrode receiving groove A (301); The shape of the membrane electrode receiving groove B matches the shape of the membrane electrode receiving groove A (301).

4. A membrane electrode hot pressing fixture with pre-compression function according to claim 1, characterized in that: On the top surface of the lower pressure plate (3) and at the position outside the membrane electrode receiving groove A (301), there is a ring-shaped limiting protrusion group for limiting the membrane electrode during hot pressing. The ring-shaped limiting protrusion group includes a plurality of limiting protrusions (302).

5. A membrane electrode hot pressing fixture with pre-compression function according to claim 1, characterized in that: The upper pressure plate cover (1) and the upper pressure plate (2) are fixedly connected by countersunk screws (9), and the lower pressure plate cover (4) and the lower pressure plate (3) are fixedly connected by countersunk screws (9).

6. A membrane electrode hot pressing fixture with pre-compression function according to claim 1, characterized in that: Two latch-type quick clamps (5) are provided, and the two latch-type quick clamps (5) are located on both sides of the upper pressure plate (2) and are symmetrical to each other.

7. A membrane electrode hot pressing fixture with pre-compression function according to claim 1, characterized in that: Each of the guide rods (6) is evenly arranged on the outer periphery of the whole formed by the upper pressure plate cover (1), the upper pressure plate (2), the lower pressure plate (3), and the lower pressure plate cover (4). Each of the upper pressure plate cover (1), the upper pressure plate (2), the lower pressure plate (3), and the lower pressure plate cover (4) has a guide rod through hole that matches the shape of the cross section of each of the guide rods (6).

8. A membrane electrode hot pressing fixture with pre-compression function according to claim 1, characterized in that: All the guide rods (6) have the same cross-sectional shape and size.

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