In order to effectively detect the error influence of the two processes of push-boring rolling and scraping rolling on the deep hole processing technology of the hydraulic support forged cylinder, the single factor test analysis method was used to detect the size deviation and cylindricity of the two processes. The quantitative analysis was carried out in combination with the detection data curve. The results show that compared with the push-boring and rolling process, the standard deviation of the dimensional deviation of the scraping and rolling process is 142.8% of the push-boring and rolling process, the cylindricity is 153.8% of the push-boring and rolling process, and the degree of dispersion is greater, indicating that the push-boring and rolling process should be preferred when deep hole processing is carried out under the same conditions.
With the continuous popularization of intelligent working faces and the continuous extension of mine mining depth, the stress of coal seam surrounding rock is also increasing, which puts forward higher requirements for the bearing capacity and sensitivity of hydraulic support. The column is the main component of the hydraulic support to realize the support and bearing, and its processing technology directly determines the working performance of the whole support. However, in the process of use, there are often phenomena such as deformation and corrosion of the inner wall of the forged cylinder, thread damage, and forged cylinder expansion. It is necessary to perform deep hole processing and repair on the forged cylinder. Currently, the commonly used cylinder processing technology mainly includes push-boring and scraping rolling. Both processes will cause the size of the inner surface of the forged cylinder to change with time and cause the size to be out of tolerance, affecting the service life of the forged cylinder. Therefore, it is necessary to analyze the machining size error under the same conditions of the two processes to improve the machining accuracy of the forged cylinder.
1. Test scheme
The push-boring and rolling process is to perform overall reaming and rolling rounding of the forged cylinder by boring and rolling the extrusion tool so that a strengthening layer is formed on the inner surface of the forged cylinder to cause elastic-plastic deformation to achieve the purpose of repair and strengthening. The scraping and rolling process is to harden the inner surface of the cylinder by four processes rough boring, semi-fine boring, fine boring, and rolling through the scraper. This test uses six pieces of the same material, specifications of the cylinder, divided into two groups, pushed boring and rolling and scraping and rolling, and the cylinder’s internal surface size changes compared to the measurement.
1.1 Test principle
After the cylinder is pushed and rolled, due to the residual stress after the hardening of the cylinder itself, the inner surface size will change to a certain extent, and the overall size will become smaller → slowly larger → stable. The scraping and rolling can reduce the boring knife pattern, improve the cylinder’s surface hardness and shape accuracy, and the inner surface will not form a strengthening layer. Therefore, compared with the push-boring and rolling process, the size change should be small, and the overall trend is smaller → larger → smaller → stable.
1.2 Test method
In this test, six sets of hydraulic support column cylinders with the same conditions were used. The metal material was 30CrMnSi, and the specifications were Φ475mm × 45mm × 1245mm. The inner surface was Φ400mm, and the cylindricity was 0.057mm. Divided into two groups for testing. The first group of 3 sets adopts the push-boring rolling process, and the second group of 3 sets adopts the scraping rolling process. To ensure the accuracy of the data, the cylinder is subjected to stress relief annealing treatment before finishing, which effectively removes the residual stress existing in the processing.
1.3 Test route
The first group of push-boring rolling numbers are No.1, No.2, and No.3, and the second group of scraping rolling numbers are No.4, No.5, and No.6. The process route is shown in Table 1.
Table.1 Process route
|Group 1 push boring and rolling||No.1 to No.3||Rough machining, tempering, rough pushing, stress relieving annealing, chamfering, rolling, natural aging|
|Group 2 scraping and rolling||No.4-6||Rough machining, tempering, rough pushing, stress relieving annealing, chamfering, scraping and rolling, natural aging|
2. Experimental content
2.1 Stress relief process
To ensure the accuracy of the data, the cylinder is subjected to stress relief annealing before finishing. The annealing process is shown in Figure 1.
Fig.1 Temperature control curve of stress relief annealing
As shown in Fig.1, the cylinder is first heated to 550 °C and kept at this temperature for 6h, then slowly cooled to 350 °C, placed outside the furnace, and slowly cooled to a normal temperature at room temperature. Re-detect and record the change in the inner surface of the cylinder.
2.2 Size measurement
Firstly, the accuracy of the cylinder after stress relief is corrected, and then the position and size of the cylinder ring and joint are measured. Since the rings and joints belong to the post-weld accessories, the transverse shrinkage and longitudinal shrinkage caused by welding will have a certain error effect on the cylinder size and cylindricity. Therefore, in the actual measurement, the symmetrical positions of the lifting ring, the joint, and the bottom of the cylinder are measured respectively to calculate the cylindricity. The measurement position is shown in Fig.2.
Fig.2 Cylinder measuring position diagram
1-ring; 2-joint; a-from the cylinder mouth position 160mm; b-500mm from the cylinder mouth position; c-from the bottom of the cylinder position 160mm
As shown in Fig.2, the displacement deviations of cylinders A, B, and C are measured at every time point, and the measurement results are recorded in real-time. Time points were selected 4h, 8h, 12h, 24h, 36h, 120h, 168h, 216h.
3. Test conclusion
According to the measurement results, the deviation curve of the three points in the cylinder is drawn according to the time point of the horizontal axis and the deviation of the inner surface of the vertical axis, as shown in Figure 3, Figure 4, and Figure 5.
The cylindricity standard deviation and size deviation of 6 sets of cylinders are plotted according to the change of time point, as shown in Fig.6.
Combined with Fig.3, Fig.4, and Fig.5, after 160 h, the deviation degree of the two processes does not change, indicating that the time control is best at 160 h. The cylinder barrel processed by the push-boring and rolling process has the same change in the inner surface of the cylinder barrel and the scraping and rolling process. Both of them have experienced three sections: dramatic change section, moderate change section, and stable section. The violent change section refers to the U-shaped curve that the cylinder size decreases first and then increases with time from the beginning to about 36 h. The moderate change section refers to the slow increase of the inner surface size of the cylinder from 36 to 160h, and the increased range gradually becomes smaller. The stable section refers to 160-216h. At this time, the size of the inner surface of the cylinder does not change greatly, and it shows a stable trend. The period of cylindricity change is similar to inner surface deviation, but the change range is larger, indicating that cylindricity is more susceptible to deep-hole processing technology.
Fig. 3 The a-direction and b-direction size change curves of No.1-3 cylinder
Fig.4 The a-direction and b-direction size change curves of No.4-6 cylinder
Fig.5 Cylinder cylindricity variation curve of No.1-6 cylinder
Fig.6 Standard deviation of size deviation and cylindricity of No.1-6 cylinder
1-4-6 deviation standard deviation; no.2-4-6 cylindricity standard deviation; 3-1-3 deviation standard deviation; 4-1-3 cylindricity standard deviation
Combined with Fig.6, it can be seen that compared with the push-boring and rolling process, the standard deviation of the size deviation of the scraping and rolling process is 142.8% of the push-boring and rolling process. The dispersion degree of the deviation is greater, indicating that the scraping and rolling process has a greater impact on the inner surface size of the cylinder, which is more likely to cause larger machining errors. The cylindricity is 153.8% of the push-boring and rolling, which shows that the error effect of cylindricity is the same as the size deviation. Therefore, under the same conditions, the push-boring and rolling process should be preferred to process the inner surface of the cylinder, with smaller processing errors and higher precision.
By comparing the size deviation and cylindricity deviation of the two kinds of cylinder inner surface machining processes of push-boring rolling and scraping rolling, both experience three sections: dramatic change section, moderate change section, and stable section. The change range of cylindricity is larger than the size deviation, indicating that cylindricity is more susceptible to deep-hole machining. Compared with the push-boring and rolling process, the standard deviation of the size deviation of the scraping and rolling process is 142.8% of the push-boring and rolling process, and the cylindricity is 153.8% of the push-boring and rolling process. The degree of dispersion is greater, indicating that under the same conditions, the push-boring and rolling process should be preferred for the inner surface processing of the cylinder.
Author: Wang Hua