Design of Positioning and Measuring Device for Joint Welding of Hydraulic Cylinder

1.Introduction

Whether it is mining machinery or construction machinery, hydraulic cylinders can be seen everywhere as a key executive power component. When the hydraulic cylinder is working, the working medium (water, emulsion, oil, air, etc.) is injected into the hydraulic cylinder cavity through the joint (or valve) through the pressure pump, so that the piston rod or cylinder body of the hydraulic cylinder reciprocates and drives it. The connected corresponding parts make the required motion trajectory, so as to convert the pressure energy into mechanical energy. The circulation of the working medium between the inside of the hydraulic cylinder and the hydraulic pump station is often realized through the joints on the hydraulic cylinder and the high-pressure hose. The connection between the joint and the cylinder block has welding type and screw thread, but the welding type is more used. As shown in Figure 1, only two representative joints are drawn here.

2. Problem description

According to the process of cylinder barrel processing, the joint is welded to the cylinder barrel first, then the inner hole of the cylinder barrel is processed, and finally the fluid hole on the cylinder barrel wall after the joint is welded with the cylinder barrel is drilled. Because the fluid hole on the cylinder wall is finished, the positioning of the joint on the cylinder barrel cannot be determined by the fluid hole of the cylinder barrel. It is necessary to measure the geometric size of the fluid hole on the joint that matches the cylinder, and then calculate the corresponding size. Take one of the joints as an example for illustration, as shown in Figure 2.

The positioning size of the joint required by the process is L, the size of the fluid hole on the joint is D2, and the positioning size is L4, and the joint size is L5. In order to facilitate the measurement in actual operation, the operator shall determine it according to the converted L7, that is, the conversion After L7=L-L6－D2/2.

After conversion, there is no problem if the shape of the joint is strictly in accordance with the size of the drawing. In fact, the joints usually only guarantee the shape and size of the inner hole. As for the overall size of the joint and the positioning size of the hole (especially the positioning size of the D2 liquid hole), the difference is large. After the cumulative conversion, the joint The final positioning size L will differ greatly. When the liquid passage hole deviates seriously inward, it will reach the sealing surface of the piston, which affects the sealing performance of the hydraulic cylinder; when the deviation is serious outward, the liquid passage hole will be blocked by the guide sleeve, and the liquid flow will not be smooth.

As shown in Figure 3, when the joint is shifted to the right, the liquid passing hole on the cylinder wall after being drilled will be blocked by the guide sleeve, and the flow is not smooth; the joint is shifted to the left, and the liquid passing on the cylinder wall after being drilled The hole will reach the position of the dynamic seal on the piston, causing liquid leakage.

1—Piston　2—Cylinder tube　3—Dynamic seal　4—Connector
5—Static seal　6—Guide sleeve　7—Piston rod

Once the above-mentioned deviation of the fluid hole occurs, the company often polishes the joint away, changes the position and re-drills it. If the joint position cannot be avoided, the only way to re-make the cylinder. Whether it’s breaking the joints and re-drilling, or making a new cylinder, it not only causes losses, but also affects the progress.

3. Solution

In order to solve the problem of the deviation of the positioning size of the fluid hole caused by the improper joint shape, we have come up with two solutions: one is to solve it fundamentally, that is, the joint is manufactured in full according to the size of the drawing, but each manufacturer The matching size of the inner hole is used as the inspection standard, and in terms of appearance, as long as it can be used, there will be no excessive requirements. Obviously this method cannot be realized. The second is to design a new measuring and positioning device to accurately position the joint’s positioning dimension L on the cylinder, that is, to make up for the defects of the joint itself in other ways, reducing the inaccurate positioning of the joints. Repair, in order to ensure the quality of processing. Figure 4 shows the designed joint positioning measurement device.

The device is mainly composed of a ruler body and a positioning rod (see Figure 5). The ruler body is L-shaped. Combining the actual situation of the company’s measurement and positioning when welding the joint, and combined with the measuring principle of the vernier caliper, the claw on the side of the reading is designed as a positioning rod. The cylindrical probe on the positioning rod matches the liquid inlet D2 of the joint. The center line of the head is at the absolute center position on the positioning rod, and a marking line is engraved on the center position. When measuring, the positioning rod is sleeved on the ruler, and the probe is placed in the liquid inlet hole of the joint; the front of the positioning rod is opened with an observation hole, which is convenient for reading the data on the ruler. The upper end is equipped with a set screw, which is convenient for fixing after adjusting the size. Prevent size deviation. Figure 6 is a schematic diagram of the use of the device.

4.Matters needing attention

1) The data scale on the ruler should be checked by a professional measurement and testing department to avoid excessive errors and affect the measurement effect.
2) The cylindrical probe of the positioning rod should be designed according to the liquid inlet of different joints. The positioning rod can be designed as an integral type (see Figure 5), or it can be designed as a split type with a replaceable probe. The size of the fluid hole of the joint can be replaced with a suitable probe; the height of the cylindrical probe should be higher than the height of the welded joint, which is convenient for the rotation, adjustment and spot welding of the joint during welding.

5.Concluding remarks

The device is simple in structure and convenient to measure, and no longer need to convert the size to measure. No matter the size of the joint or the deviation of the liquid hole, the measured size will not change with the changes of these objective conditions, only the process drawing requirements are required. The center size of the sensor, and directly read the size on the ruler, the positioning is accurate and reliable. After on-site practice, the effect is remarkable.