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What are the steps to follow in manufacturing hydraulic cylinders? As a hydraulic cylinder manufacturer with more than 20 years of experience, there is no better place than us to get the right answer. In order to produce high-quality hydraulic cylinders, there are 8 steps to follow and in this post, we are going to break them down in detail.
The hydraulic cylinders usually consist of a cylinder body, piston rod, and seal. All hydraulic components and sealing components have different requirements in terms of dimensional tolerances, surface roughness, shape and position tolerances, etc. During the manufacturing process, if the tolerance is too bad, such as the cylinder inner diameter, piston outer diameter, seal groove depth, width, and size of the seal ring hole, or out-of-roundness, burrs, or chrome plating due to processing problems In the case of falling off, the corresponding seal will be deformed, crushed, scratched, or not compacted. The seal function will be lost and the normal operation of the device cannot be guaranteed. In order to avoid such problems in the first place, when designing, ensure the geometric accuracy of each component and choose the correct seal; when manufacturing, ensure that the upper and lower tolerances of each component are matched. Starting from the factors affecting the leakage of the hydraulic system, comprehensive consideration should be taken to take effective measures to reduce the leakage.
2. Selecting The Right Steel Material
2.1 There is three common material used for hydraulic cylinders: # 20 steel; # 45 steel; Cr40 steel.
# 20 with the lowest hardness is normally used for low-pressure hydraulic cylinders used in places like excavators; # 45 steel and Cr40 are normally used in high-pressure hydraulic cylinders with a 10000 psi rated working pressure. The price of # 45 steel is normally less than half of the Cr40 price. The main role of Cr in heat treatment is to improve the hardenability of steel. due to the improved hardenability, mechanical properties such as strength, hardness, and impact toughness of 40Cr after quenching (or quenching and tempering ) treatment are also significantly higher than those of 45 steel. Normally products with lower quality use # 45 steel in the body and Cr40 in the piston and products with high-quality use of Cr40 in both parts, such as Enerpac, Simplex, Riverlake hydraulic cylinders, etc.
2.2 There are two types of raw materials: pipe material and solid steel rod material. You need to choose the proper one according to your application. If you need to manufacture long-stroke cylinders, the pipe material is used because it is really difficult to apply the machining process to the deeper part of the solid steel material, however, you need to purchase the pipe material that has gone through quenching and tempering treatment. The solid steel rod material is normally suitable for short-stroke hydraulic cylinder production. Some manufacturers will use pipe material that has not gone through the heat treatment to cheat the consumers, these cylinders will not be able to achieve 1.5 safety factory according to ISO10100:2001 standard.
3. Cutting & Drilling the material
Cutting with a sawing machine, the length is determined according to the design. Drilling the material according to the design.
4. Heat Treatment
quenching and tempering the materials to obtain comprehensive mechanical properties and ensure processing and application quality.
5. Machining Process
5.1 Turning: The chuck is used in conjunction with the center tip, one clamp, and one tip, and the cylinder is supported by the center frame to ensure the coaxiality of the cylinder and the machining allowance.
5.2 Boring: This is the main process of machining the cylinder body. In the manufacturing process, rough boring, semi-precision boring, floating boring and rolling processes are generally used. The boring process of the bore in the cylinder is to form a stable processing structure by the boring tool, the iron-bearing, and the bearing seat, and then use the boring tool to complete the processing. Before boring, place the cylinder in the holder of the boring machine and fix it. Use bolts to tighten and adjust the height of the boring tooltip so that it is consistent with the center of the cylinder body. ， Automatic centering; the boring feed rate is controlled by the adjustment of the boring tool. The roughing and finishing of the inner hole boring are completed separately. The floating boring process is the finishing stage of the cylinder body. For the horizontal position, select the appropriate cutting speed and feed amount. According to the process requirements, select the appropriate number of machining times and retain the machining allowance. Rolling: During the rolling process, the tightness of the ball should be adjusted to achieve the tolerance of the rolling head according to the cylinder tolerance requirements to meet the processing requirements. By using this method to process the cylinder, the tolerance of the holes in the cylinder can reach the required accuracy, and at the same time, the error repetition is reduced, and the roughness and tolerance of the cylinder can meet the design requirements.
5.3 Secondary turning: The center frame is used to adjust the thread and welding dimensions of the turning cylinder body according to the inner hole. Inspection: Finally, inspect all machined surfaces.
5.4 Problems easily encountered in the processing of hydraulic cylinders and control methods 5.4.1 Tooling Vibrating: The error in the boring process will affect the cylinder body, and the precision tolerance and position requirements of the hole position cannot be guaranteed. In the production process, in order to eliminate the influence of boring accuracy, generally choose to carry out a small boring volume many times in the boring and floating processing stages to accurately control the size accuracy of the bore in the cylinder. In the rolling stage, adjust the ball size, adjust rotation speed, and the cutting speed to ensure the smoothness of the holes in the cylinder. In addition, the coolant should be clean and free of impurities, and the flow rate should be sufficient to flush the iron chips out of the cutting edge of the floating boring cutter in time to prevent cutting tumors and scratches on the cylinder barrel surface, affecting the machining quality of the cylinder barrel inner surface.
5.4.2Tooling Collapse: During the turning of the cylinder and piston rod, the alloy cutter is prone to chipping when turning the outer circle. For cemented carbide tips, the impact toughness of this kind of cylinder is not very high, and as the temperature rises, its hardness decreases significantly. When turning to the welding part of the cylinder body, the tool temperature is already high, but when the welding position is encountered, the hardness of the material suddenly changes, so it is easy to cause chipping. For this reason, it is necessary to make a reasonable selection of the cutter during the machining process, improve its machining performance, and improve safety. At the same time, we need to keep cooling down the temperature of the tooling with the cooling liquid used to protect the processing process, taking away excess heat and reducing the temperature of the cutting area; at the same time, it can also act as a lubricant to reduce the friction resistance between the turning tool and the workpiece and improve the surface quality.
6.Coating & Painting & Polishing
6.1Coating: Hard chrome coating on the piston or Blackening surface treatment
6.2Painting: Electrostatic spray on the outside surface of the cylinder body. after the coating, please use newspaper to cover the outside surface of the cylinder to prevent surface damage
6.3Polishing: When the electrostatic spray process finish, please polish the inner cylinder surface
And clean the whole space with the air compressor. Otherwise, the dirty things might stay inside and increase the friction between the sealing with the cylinder’s inner surface, damaging the cylinder and affecting the normal function of the hydraulic cylinder.
7. Assembly
Assemble the hydraulic cylinders( cylinder body,piston,sealing,saddle,stopping ring,dust wiper,Composite bearing,sealing ,relief valve,coupler).
8. Testing
8.1 Appearance inspection
According to the drawings, check whether the physical objects meet the requirements of the drawings, check whether the appearance of the hydraulic cylinder (such as paint color) is consistent with the requirements of the drawings, whether the paint surface is sprayed uniformly, whether there is paint loss, whether there is a color difference, whether there is sagging, Whether there is obvious dust and blistering; whether the surface without paint is rusty, whether the appearance is smooth and flat, whether there are marks such as indentations, pinch marks, scratches, scratches, etc., whether there is a smooth plating on the surface of the piston rod, whether Defects such as peeling, blistering and peeling
8.2 Dimensional inspection
Piston rod inspection: Use an outside diameter micrometer to check the seal groove and outer diameter dimensions on the piston rod to ensure that the dimensional tolerances are within the requirements of the drawing and check whether the plating thickness is acceptable (generally not more than 0.04mm). The bending limit of the piston rod is 1mm% 2Fm. During measurement, the two ends of the parallel portion of the piston rod are supported by V-shaped blocks, and the dial indicator is set in the middle of the two blocks. The piston rod is rotated to read the dial indicator. The difference between the maximum and minimum amplitudes.
The inspection of the cylinder body uses vernier calipers and micrometers to inspect the length and outer diameter of the cylinder. The inspection of the inner diameter requires an accurate inspection of the inner diameter gauge to confirm that the dimensional tolerances meet the requirements of the drawing and check whether the plating thickness is acceptable (generally no more than 0.04 mm).
If there is a very small longitudinal injury during the inspection of the oil cylinder, you can use the light stone to grind and trim it. If you feel that the nail is slippery after the dressing, electroplating again; if there are smooth pits, you need to grind the sharp edges around the stone with the oil stone. In some cases, if the longitudinal injury is too large or the pit is too deep, electroplating should be performed again. After re-plating, it must be ground, but the thickness of the coating can only be up to 0.07mm. When the plating layer disappears and the substrate is exposed during the dressing with an oil stone, it cannot be used, and it needs to be electroplated again.
8.3 Test method and project commissioning:
Adjust the system pressure, the hydraulic cylinder under test starts under no load, and reciprocates several times throughout, exhausting the air in the cylinder.
Starting pressure test: After the trial operation, under no-load conditions, adjust the overflow valve to gradually increase the pressure in the rodless cavity. When the hydraulic cylinder starts, record the starting pressure.
Pressure resistance test: Stop the tested hydraulic oil cylinder pistons at both ends of the cylinder, and input hydraulic oil 1.5 times the nominal pressure into the working chamber, and maintain the pressure for more than 2 minutes.
Endurance test: Under the rated pressure, the tested hydraulic cylinder is continuously operated at the highest speed required by the design, and continuously operated for more than 8 hours at a time. During the test, the parts of the tested cylinder cannot be adjusted.
Leak test: internal leakage, input hydraulic oil of nominal pressure in the working chamber of the tested hydraulic cylinder, and measure the leakage from the piston to the unpressurized cavity; external leakage, measure the leakage at the seal of the piston rod, and the joint surface must not be There is leakage. Buffer test: Release all buffer valves of the tested hydraulic cylinders, adjust the test pressure of the tested hydraulic cylinders to 50% of the nominal pressure25, run at the designed maximum speed, and check the buffer effect when the buffer valves are all closed.
Based on the comprehensive inspection situation, to determine whether the cylinder is qualified, if it is not qualified, it shall be handled according to the provisions of the processing procedure of the non-conforming product.
There are difficulties in the manufacture and inspection of hydraulic cylinders, this is a problem that manufacturers and users must face. In the processing of hydraulic cylinders, different parts have different processing requirements, and at the same time, higher requirements are imposed on quality control in production management. From the previous analysis, it is not difficult to see that in order to ensure the quality of the product, the necessary research and improvement of the technological measures should be carried out first, so that the technological measures can be adapted to the object of processing. In the inspection of hydraulic cylinders, check the dimensions and roughness of the components around the processing points to ensure that they are within the tolerance range; in the test phase, according to the test process, standardize the test operation, and be careful. In this way, the quality of the produced cylinder can be guaranteed.
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