A turbine blade tenon grinding and clamping device

Abstract

The present invention discloses a turbine blade tenon grinding clamping device, comprising: a base, on which a clamping groove is provided, wherein two grooves are provided on a first side of the clamping groove, and a groove is provided on a second side, the first side has a first fixing point, the second side has two second fixing points, and an ejector pin is provided at the end of the clamping groove; a clamping block is provided above the clamping groove and is offset from the first fixing point and the second fixing point; a clamping assembly is provided below the base and is used to clamp the turbine blade to provide a buffer; the present invention can greatly improve the efficiency and accuracy of turbine blade tenon grinding while ensuring high precision and high stability, and is particularly suitable for the demand for precision machining of turbine blade tenons in the fields of aircraft engines and gas turbines, and has broad application prospects and significant industrial value.

Description

Technical Field

[0001] The invention relates to the technical field of turbine blades, and in particular to a turbine blade tenon grinding and clamping device. Background Art

[0002] Turbine blades are key components in high-performance power equipment such as gas turbines, and their blade tenons are crucial for blade fixation and optimization of airflow channels. Due to the complex geometry and high precision requirements of turbine blade tenons, traditional processing methods are difficult to meet the requirements of shape accuracy and dimensional accuracy at the same time, especially during the grinding process, how to ensure that the contour size of the tenon is accurate and stable has become a technical problem.

[0003] In the prior art, the grinding process of turbine blade tenons is often carried out manually or by traditional mechanical clamping methods. However, due to the complex shape of the turbine blades themselves and the high hardness of the materials, traditional clamping methods often cannot provide sufficient stability, resulting in deformation, dimensional deviation and poor surface quality during the processing. Summary of the invention

[0004] The main purpose of the present invention is to provide a turbine blade tenon grinding and clamping device, aiming to solve the existing technical problems.

[0005] To achieve the above-mentioned purpose, the present invention provides a turbine blade tenon grinding and clamping device, comprising:

[0006] A base, on which a clamping groove is formed, wherein two grooves are formed on a first side of the clamping groove, and a groove is formed on a second side, the first side has a first fixing point, the second side has two second fixing points, and an ejector pin is formed at an end of the clamping groove;

[0007] A pressing block is arranged above the clamping groove and is staggered with the first fixing point and the second fixing point;

[0008] The clamping assembly is arranged below the base and is used for clamping the turbine blades to provide buffering.

[0009] Furthermore, the clamping assembly includes a base, the base is moved by a cylinder, a symmetrical mounting groove is formed at the front end of the base, and open grooves are formed at both sides of the front end of the base;

[0010] A gripping unit, the gripping unit is arranged in the mounting groove, and the gripping unit comprises a support plate, a cylinder support rod is symmetrically arranged on the support plate, and a rectangular frame is arranged at the output end of the cylinder support rod;

[0011] The buffer unit is arranged on both sides of the base.

[0012] Furthermore, a movable clamping plate is provided on the rectangular frame, a linear slide mechanism is provided at the bottom end of the clamping plate, and the linear slide mechanism is symmetrically arranged on the rectangular frame.

[0013] Furthermore, a protective layer is provided on the surface of the splint, the protective layer is in a rectangular structure, and the thickness of the protective layer is one centimeter. The protective layer is composed of a panel with a rubber pad adhered to the surface, and the top of the protective layer passes over the top of the splint.

[0014] Furthermore, a rotating disk is provided on the top of the base, and the rotating disk is driven to rotate by a driver embedded in the inner cavity of the base. The rotating disk is arranged between the left and right clamping plates, and the position of the workpiece in the horizontal plane is adjusted by the rotating disk.

[0015] Furthermore, a rotatable flap plate is provided in the open slot, the flap plate is adapted to the size of the open slot, and the flap plate is driven to rotate by a stepping motor, and the rotation angle range of the flap plate is - degrees.

[0016] Furthermore, a rolling belt is provided on the surface of the flip plate, and the rolling belt is driven to rotate by a driving motor, and linear grooves are evenly opened on the surface of the rolling belt. By controlling the rolling belts on both sides to rotate in the same direction, the horizontal position of the workpiece is adjusted.

[0017] Furthermore, the buffer unit includes guide frames arranged on both sides of the base, and movable buffer blocks are arranged in the guide frames. The buffer blocks are fixedly connected to the sides of the base, and the buffer blocks can drive the base to slide on the guide frames, so that the base has a buffer stroke.

[0018] Furthermore, a telescopic support rod connected to the buffer block is disposed at the bottom end thereof, the bottom end of the telescopic support rod is movably inserted into the buffer tube, and a buffer spring is sleeved on the outside of the telescopic support rod.

[0019] Furthermore, an oil permeable plate is provided at the end of the telescopic support rod extending into the buffer cylinder, and oil guide holes are evenly opened on the oil permeable plate. The buffer cylinder is filled with oil at two-thirds of the liquid level.

[0020] The beneficial effects of the present invention are embodied in:

[0021] The present invention can greatly improve the efficiency and accuracy of turbine blade tenon grinding while ensuring high precision and high stability. It is particularly suitable for the demand for precision machining of turbine blade tenons in the fields of aircraft engines and gas turbines, and has broad application prospects and significant industrial value. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the structure of the present invention;

[0023] Figure 2For the present invention Figure 1 Schematic diagram of the structure from top view;

[0024] Figure 3 This is a schematic diagram of the connection structure between the clamping assembly and the base of the present invention;

[0025] Figure 4 This is a schematic diagram of the structure of the clamping assembly of the present invention;

[0026] Figure 5 This is a schematic diagram of the structure of the clamping unit of the present invention;

[0027] Figure 6 It is a schematic diagram of the structure of the present invention;

[0028] Figure 7 It is a schematic diagram of the structure of the buffer unit of the present invention.

[0029] Description of reference numerals:

[0030] A. Turbine blades;

[0031] 1. Base; 2. Clamping groove; 3. First fixing point; 4. Ejector pin; 5. Second fixing point; 6. Pressing block;

[0032] 100, base; 100a, mounting slot; 100b, open slot; 101, cylinder; 200, clamping unit; 201, support plate; 202, cylinder support rod; 203, rectangular frame; 204, clamping plate; 205, linear slide mechanism; 206, protective layer; 207, flip plate; 208, stepping motor; 209, rolling belt; 210, driving motor; 211, rotating disk; 300, buffer unit; 301, guide frame; 302, buffer block; 303, telescopic support rod; 304, oil-permeable disk; 305, buffer cylinder; 306, buffer spring. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. In the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0034] See also Figure 1-3 The present invention provides a turbine blade tenon grinding and clamping device, which is characterized by comprising:

[0035] A base 1 is provided with a clamping groove 2, two grooves are provided on a first side of the clamping groove 2, a groove is provided on a second side, a first fixing point 3 is provided on the first side, two second fixing points 5 are provided on the second side, and an ejector pin 4 is provided at an end of the clamping groove 2;

[0036] The pressing block 6 is arranged above the clamping groove 2 and is staggered with the first fixing point 3 and the second fixing point 5;

[0037] The clamping assembly is arranged below the base 1 and is used to clamp the turbine blade A to provide a buffer.

[0038] The present invention can greatly improve the efficiency and accuracy of turbine blade tenon grinding while ensuring high precision and high stability. It is particularly suitable for the demand for precision machining of turbine blade tenons in the fields of aircraft engines and gas turbines, and has broad application prospects and significant industrial value.

[0039] See also Figure 4 The clamping assembly includes a base 100, the base 100 is controlled to move by a cylinder 101, and a symmetrical mounting groove 100a is opened at the front end of the base 100, and open grooves 100b are opened on both sides of the front end of the base 100;

[0040] See also Figure 5 and Figure 6 , a clamping unit 200, the clamping unit 200 is arranged in the installation groove 100a, and the clamping unit 200 includes a support plate 201, a cylinder support rod 202 is symmetrically arranged on the support plate 201, and a rectangular frame 203 is arranged at the output end of the cylinder support rod 202; a buffer unit 300, the buffer unit 300 is arranged on both sides of the base 100.

[0041] A movable clamping plate 204 is disposed on the rectangular frame 203 , and a linear slide mechanism 205 is disposed at the bottom end of the clamping plate 204 . The linear slide mechanism 205 is symmetrically disposed on the rectangular frame 203 .

[0042] A protective layer 206 is provided on the surface of the splint 204 to improve the protection performance of the workpiece. The protective layer 206 is in a rectangular structure and has a thickness of one centimeter. The protective layer 206 is composed of a panel with a rubber pad adhered to the surface, and the top of the protective layer 206 passes over the top of the splint 204.

[0043] A rotating disk 211 is provided on the top of the base 100. The rotating disk 211 is driven to rotate by a driver embedded in the inner cavity of the base 100, and the rotating disk 211 is provided between the left and right clamping plates 204. The position of the workpiece in the horizontal plane is adjusted by the rotating disk 211, and the workpiece is clamped by the clamping plates 204 on both sides. When necessary, the clamping plates 204 are retracted into the installation groove 100a, and the flip plates 207 on both sides are unfolded to make them in the same plane with the top surface of the base 100, and the position of the workpiece is fine-tuned in cooperation with the rotating disk 211 and the rolling belt 209.

[0044] A rotatable flip plate 207 is provided in the open slot 100b. The flip plate 207 is adapted to the size of the open slot 100b, and the flip plate 207 is driven to rotate by a stepper motor 208. The range of the rotation angle of the flip plate 207 is 0-90 degrees.

[0045] A rolling belt 209 is provided on the surface of the flip plate 207. The rolling belt 209 is driven to rotate by a driving motor 210, and linear grooves are evenly opened on the surface of the rolling belt 209. By controlling the rolling belts 209 on both sides to rotate in the same direction, the horizontal position of the workpiece is adjusted.

[0046] Example 2: Please refer to Figure 6 and Figure 7 The buffer unit 300 includes a guide frame 301 arranged on both sides of the base 100, and a movable buffer block 302 is arranged in the guide frame 301. The buffer block 302 is fixedly connected to the side of the base 100. The buffer block 302 can drive the base 100 to slide on the guide frame 301, so that the base 100 has a buffer stroke.

[0047] A telescopic support rod 303 is provided at the bottom end of the buffer block 302 and is connected thereto. The bottom end of the telescopic support rod 303 is movably inserted into the buffer cylinder 305. The oil in the buffer cylinder 305 passes through the oil permeable plate 304, thereby generating effective resistance to the oil permeable plate 304 and cooperating with the buffer spring 306 to reduce the impact force during the processing. A buffer spring 306 is provided on the outside of the telescopic support rod 303.

[0048] An oil permeable plate 304 is provided at the end of the telescopic support rod 303 extending into the buffer cylinder 305, and oil guide holes are evenly opened on the oil permeable plate 304. When the workpiece is processed, the vibration generated is transmitted to the base 100, driving the buffer block 302 to move along the guide frame 301, compressing the telescopic support rod 303, and the oil permeable plate 304 at the bottom end is arranged in the buffer cylinder 305. The oil in the buffer cylinder 305 passes through the oil permeable plate 304, and produces effective resistance to the oil permeable plate 304, and cooperates with the buffer spring 306 to reduce the impact force during the processing, thereby improving the stability of the workpiece during processing. The buffer cylinder 305 is filled with two-thirds of the liquid level of oil.

[0049] The rest of the structure is the same as that of the first embodiment.

[0050] The workpiece is clamped by the double-sided clamping plates 201, and when necessary, the clamping plates 201 are retracted into the installation groove 100a, and the flip plates 207 on both sides are unfolded to make them in the same plane with the top surface of the base 100, and the position of the workpiece is fine-tuned in conjunction with the rotating disk 211 and the rolling belt 209. When the workpiece is processed, the vibration generated is transmitted to the base 100, driving the buffer block 302 to move along the guide frame 301, compressing the telescopic support rod 303, and the oil-permeable plate 304 at the bottom end is arranged in the buffer cylinder 305. The oil in the buffer cylinder 305 passes through the oil-permeable plate 304, generating effective resistance to the oil-permeable plate 304, and cooperating with the buffer spring 306 to reduce the impact force during the processing, thereby improving the stability of the workpiece during processing.

[0051] In addition, the specific clamping and control methods in the present application are as follows: Blade clamping: No. 1 and No. 2 correspond to two ejectors, No. 3, No. 4, and No. 5 correspond to the first fixed point and the second fixed point, and No. 6 and No. 7 correspond to two clamping blocks.

[0052] S1 Preparation work before inserting the blade into the fixture. All the clamping blocks are retracted to the bottom to prevent interference with the blade clamping. The blade basin is placed in the fixture upward, and the side ejector is pressed tightly. The tenon teeth are pressed until the blade does not shake up and down. The feeler gauge of 0.02mm at the positioning point is just right. The table is made according to the position shown in the figure. The corresponding movable block is adjusted to the position in contact with the blade, and the pre-clamping is completed.

[0053] S2 1.3 screws are tightened with a short-handled wrench to tighten the blades, then the 1st and 2nd screws are rotated synchronously to adjust the position of the blades in the fixture, and a 0.02mm feeler gauge is used to check that the two positioning points on the air inlet side of the blades are not too tight and then tightened;

[0054] S3 2.6, 7 screws are locked with a torque of about 4N to fix the blade. When tightening, make sure that the change range of the needle is within ±0.01mm;

[0055] S4 3. Tighten the screws on the side of the No. 4 and No. 5 screws to ensure that the needle is within the range of ±0.01mm. The tightening sequence is carried out in a pair-locking manner;

[0056] S5 checks the tightening status of each screw. The final result is that screws No. 3, No. 4, and No. 5 are tightened with long handles, and other screws are tightened with short handles. The anti-loosening nut is tightened, and the needle is within ±0.015mm. The clamping is completed; Online detection and feedback: During the grinding process, the tenon profile is detected in real time through the sensor, and the error between the actual profile size and the set target is measured and analyzed. The control system dynamically optimizes the processing path by adjusting the feed speed, cutting depth and other parameters of the grinding tool according to the error size.

[0057] Closed-loop control: A closed-loop control algorithm is used to write a blade grinding compensation program based on the probe detection system of the equipment. After each processing, the height size of the blade tenon is automatically detected. The difference between the actual profile and the preset profile is automatically adjusted to automatically adjust the working parameters of the grinding machine, and the tool position is corrected in real time to ensure accurate processing of the tenon profile.

[0058] The specific steps are as follows:

[0059] The S1 measuring device monitors the actual dimensions of the workpiece in real time;

[0060] S2 calculates the error by comparing the real-time measurement value with the set target value. Set the target size to L set , the actual size is measured to be L actual , the error is △L=L set -L actual The compensation amount is calculated using the PID controller. The PID controller dynamically adjusts the control amount based on the error proportion (P), the error change rate (D) and the error accumulation (I).

[0061] Compensation C = Kp*△L+Ki*∫△Ldt+Kd*d(△L) / dt

[0062] Among them, Kp, Ki, Kd are the proportional, integral, and calculus constants of the PID controller.

[0063] S3 controls the machine tool or processing equipment based on the calculated compensation amount. Specific adjustments may include: adjusting the position of the tool or the cutting depth, modifying cutting parameters (such as feed rate, cutting speed, etc.), and adjusting the processing path. During the adjusted processing, the size and state of the workpiece continue to be monitored in real time. If the error occurs again, the system will perform a new calculation and make adjustments again, thus forming a closed loop of continuous adjustment.

[0064] In the CNC machining of blades, closed-loop control algorithms are often used for tool wear compensation, thermal deformation compensation, feed rate control, etc. For example, when the tool is worn, the control system can compensate for the tool offset based on measured values ​​(such as cutting force or cutting position).

[0065] Refined control strategy: fine-tuning and step control strategies are adopted to optimize the grinding effect through refined feed and cutting speed control to avoid shape instability caused by over-cutting or under-cutting, especially in the small transition area of ​​the blade tenon.

[0066] Implementation method of fine-tuning control

[0067] Error detection and correction: During the machining process, the actual size of the workpiece is monitored in real time by sensors, and the error (i.e. the difference between the target size and the actual size) is calculated. Then, the control system corrects the parameters in the machining process (such as cutting depth, feed speed, etc.) through subtle adjustments based on the error information.

[0068] Small step adjustments: Fine-tuning control strategies usually use small step adjustments. For example, the system may only make small adjustments to parameters such as feed rate, tool position, cutting depth, etc. Each adjustment is usually a very small increment, which can reduce interference with the machining process and ensure the dimensional accuracy of the workpiece.

[0069] Control Algorithm: Fine-tuning control can be achieved through PID control, fuzzy control or model predictive control. For example, in a PID controller, the proportional (P) part may be used to adjust the error in a large amount, while the fine-tuning depends mainly on the derivative (D) part to make fine adjustments to the rate of change of the error.

[0070] Step control strategy

[0071] The stepper control strategy usually means that during the machining process, the control system gradually approaches the target size by gradually adjusting the machining parameters (such as cutting depth, feed speed, etc.) instead of making large adjustments at one time. The goal of stepper control is to gradually and accurately control the size of the workpiece through a limited number of steps. It is particularly suitable for systems that do not allow large changes, or when the error is large, stepper control can eliminate the error in a gradual manner.

[0072] Implementation method of step control

[0073] Step adjustment: The core idea of ​​step control is to adjust the machining process step by step by setting a predetermined number of steps. For example, the system only modifies a small part of the machining parameters in each step until the error is effectively corrected.

[0074] Periodic feedback and adjustment: Stepper control is usually adjusted based on periodic feedback. After each adjustment, the system will wait for feedback signals (such as real-time measurement of the workpiece size), and then adjust the control amount for the next step based on the feedback.

[0075] Step size: The step size of the step is usually set according to the size of the error. When the error is small, the step size is small; when the error is large, the step size can be relatively large to quickly approach the target.

[0076] Fine adjustment combined with step control

[0077] Fine-tuning and step control strategies can be used in combination to give full play to the advantages of both. In practical applications, it is usually adopted to first perform rough step control to quickly eliminate large errors, and then enter the fine-tuning stage to correct small errors with high precision.

[0078] Advantages of step control strategy

[0079] Smooth control: Step control avoids the impact of large parameter changes on the processing process through gradual adjustment, and can smoothly adjust the processing process.

[0080] Efficient correction: When the error is large, step control can quickly approach the target and reduce the total processing time.

[0081] Strong adaptability: Stepper control can adapt to a variety of processing environments, especially when conditions change greatly.

[0082] Multi-dimensional compensation technology: For complex tenon tooth shapes, multi-dimensional compensation technology is used to correct deviations that occur during the grinding process. This technology optimizes the processing path and combines tool wear compensation strategies to ensure the accuracy of every contour detail.

[0083] Temperature compensation: In some processing processes (such as high-precision machining), temperature changes can cause changes in the size of the machine tool or workpiece. By obtaining real-time temperature data through a temperature sensor and comparing it with the set temperature threshold, the processing process can be dynamically adjusted.

[0084] Tool wear compensation: During long-term processing, tool wear will affect the processing accuracy. By measuring the cutting force or cutting thickness, the control system can estimate the wear state of the tool and compensate by adjusting parameters such as feed speed and cutting depth.

[0085] Geometric error compensation: In multi-axis machining or complex surface machining, the geometric error of the machine tool (such as axial deviation, rotation error, etc.) may affect the final machining result. The closed-loop control system ensures the final workpiece accuracy through real-time error measurement and compensation.

[0086] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0087] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the meaning of "and / or" appearing in the full text includes three parallel schemes. Taking "A and / or B" as an example, it includes scheme A, or scheme B, or schemes that A and B meet at the same time. In addition, "multiple" refers to more than two. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist.

[0088] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A turbine blade tenon grinding and clamping device, characterized in that ,include: A base (1) is provided with a clamping groove (2), wherein the first side of the clamping groove (2) is provided with two grooves, and the second side is provided with a groove, the first side has a first fixing point (3), and the second side has two second fixing points (5), and an ejector pin (4) is provided at the end of the clamping groove (2); A pressing block (6) is arranged above the clamping groove (2) and is offset from the first fixing point (3) and the second fixing point (5); A clamping assembly is arranged below the base (1) and is used to clamp the turbine blades to provide a buffer.

2. A turbine blade tenon grinding and clamping device according to claim 1, characterized in that: The clamping assembly comprises a base (100), the base (100) is controlled to move by a cylinder (101), a front end of the base (100) is provided with symmetrical mounting grooves (100a), and two sides of the front end of the base (100) are provided with open grooves (100b); A gripping unit (200), the gripping unit (200) being arranged in the mounting groove (100a), and the gripping unit (200) comprising a support plate (201), a cylinder support rod (202) being symmetrically arranged on the support plate (201), and a rectangular frame (203) being arranged at the output end of the cylinder support rod (202); A buffer unit (300) is provided on both sides of the base (100).

3. The multifunctional clamp for metal forging according to claim 2, characterized in that: A movable clamping plate (204) is provided on the rectangular frame (203), a linear slide rail mechanism (205) is provided at the bottom end of the clamping plate (204), and the linear slide rail mechanism (205) is symmetrically arranged on the rectangular frame (203).

4. The multifunctional clamp for metal forging according to claim 3, characterized in that: The surface of the splint (204) is provided with a protective layer (206), the protective layer (206) is in a rectangular structure, and the thickness of the protective layer (206) is one centimeter. The protective layer (206) is a panel with a rubber pad adhered to the surface, and the top of the protective layer (206) exceeds the top of the splint (204).

5. The multifunctional clamp for metal forging according to claim 4, characterized in that: A rotating disk (211) is provided on the top of the base (100). The rotating disk (211) is driven to rotate by a driver embedded in the inner cavity of the base (100). The rotating disk (211) is provided between the left and right clamping plates (204). The position of the workpiece in the horizontal plane is adjusted by the rotating disk (211).

6. The multifunctional clamp for metal forging according to claim 5, characterized in that: A rotatable flip plate (207) is provided in the open slot (100b), the flip plate (207) is adapted to the size of the open slot (100b), and the flip plate (207) is driven to rotate by a stepping motor (208), and the range of the rotation angle of the flip plate (207) is 0-90 degrees.

7. The multifunctional clamp for metal forging according to claim 6, characterized in that: A rolling belt (209) is provided on the surface of the flip plate (207), and the rolling belt (209) is driven to rotate by a driving motor (210). Linear grooves are evenly provided on the surface of the rolling belt (209). By controlling the rolling belts (209) on both sides to rotate in the same direction, the horizontal position of the workpiece is adjusted.

8. The multifunctional clamp for metal forging according to claim 7, characterized in that: The buffer unit (300) comprises a guide frame (301) arranged on both sides of the base (100), a movable buffer block (302) is arranged in the guide frame (301), and the buffer block (302) is fixedly connected to the side of the base (100). The buffer block (302) can drive the base (100) to slide on the guide frame (301), so that the base (100) has a buffer stroke.

9. The multifunctional clamp for metal forging according to claim 8, characterized in that: The bottom end of the buffer block (302) is provided with a telescopic support rod (303) connected thereto, the bottom end of the telescopic support rod (303) is movably inserted into the buffer tube (305), and a buffer spring (306) is sleeved on the outside of the telescopic support rod (303).

10. The multifunctional clamp for metal forging according to claim 9, characterized in that: An oil permeable plate (304) is provided at the end of the telescopic support rod (303) extending into the buffer cylinder (305). The oil permeable plate (304) is evenly provided with oil guide holes. The buffer cylinder (305) is filled with oil at a two-thirds liquid level.

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