Analysis of the Causes and Countermeasures for Premature Oil Leakage of the Guide Sleeve of the Pressurized Oil Cylinder in Rotary Drilling RIGS

In recent years, the national construction management department has gradually recognized the numerous advantages of rotary drilling machines. After being used and practiced by construction departments across the country, the modern foundation construction equipment that integrates high efficiency, energy conservation and environmental protection - rotary drilling machines - have been accepted by an increasing number of users. Its construction coverage has gradually expanded from large-scale hydropower and culvert and sluice infrastructure projects to railway, highway and civil facilities such as buildings, halls, museums and institutions. With the steady improvement of the manufacturing quality of domestic drilling RIGS, this type of equipment is bound to bring benefits to the Chinese land for thousands of years.

In the actual operation of rotary drilling machines, some drilling RIGS have encountered the problem that oil leakage occurs at the head of the power head pressurized oil cylinder shortly after construction. And as the usage time extends, the oil film on the piston rod gradually thickens and forms an oil flow, which then leads to severe oil leakage and a shutdown for maintenance. Several years ago, a domestically produced drilling rig under construction on the Qinghai-Xizang Railway line even suffered a serious consequence of damage to the front hinge point of the pressurized oil cylinder. The exposure of this fact has indeed sounded an alarm for many domestic drilling rig manufacturers. If this defect is not thoroughly resolved, it will directly affect the reliability and sales volume of domestic drilling rig operations, and the market of Huaxia rotary drilling RIGS will also be handed over to foreign manufacturers.

After observation, the assembly relationship between the power head, pressurized cylinder and drill mast of the rotary drilling rig is as follows: The pressurized oil cylinder is fixed on the front end face of the drill mast (in the operation state of the rotary drilling rig), the head of its cylinder barrel is hinged to the support ear of the front cover plate of the drill mast, the tail of the cylinder barrel is floating connected to the other support ear of the front cover plate of the drill mast, the head of the oil cylinder piston rod is connected to the support ear of the power head through a pin shaft (see Figure 1), and the slider brackets on both sides of the power head are fastened to the guide rail of the drill mast There are sliders separating them (see Figure 2). When the rotary drilling rig is in operation, the pressurized oil cylinder drives the power head to move on the drill mast. The slider moves up and down along the surface of the drill mast guide rail with the power head. During the entire movement process, the swing amount of the power head forward and backward as well as left and right is mainly determined by the gap between the slider and the drill mast guide rail.

During operation, as long as the power head moves, friction will occur between the slider and the drill mast guide rail. As the slider wears out, the swing of the power head will gradually increase accordingly. Within the allowable wear range of the slider, the swing amount generated in the left and right directions (see Figure 2) is compensated by the gap between the installation lug of the piston rod head of the pressurizing cylinder and the support lug of the power head cylinder, and the lateral additional force generated is borne by the outer sides of the guide rails on both sides of the drill mast. However, in Figure 2, the swing force generated by the wear of the up and down direction sliders of the drill mast guide rail has nowhere to be released. The additional force generated by the power head in the forward and backward directions (during the operation of the drilling rig) can only be borne by the sliding block of the power head and the head ear of the piston rod of the pressurized oil cylinder. If the piston rod of the pressurized oil cylinder extends outward for a relatively long time, due to the deformation of the piston rod, its force is mainly borne by the power head and the sliding block, which is balanced with the force received by the drill mast guide rail.

As the slider wears out, during the process of applying pressure to the drill pipe by the pressurizing cylinder, the piston rod will be subjected to an additional bending load perpendicular to its axis (mainly caused by the additional action in the forward and backward directions when the drilling rig is in operation), and this action will decrease as the extension length of the piston rod increases. When the pressurizing cylinder is in the fully contracted state for pressurization, the additional force acting on the guide sleeve and the front hinge point of the cylinder is at its maximum. The frequent occurrence of such working conditions can easily cause uneven loading and wear of the guide sleeve seal, thus unable to ensure the ideal service life of the guide sleeve seal of the pressurizing cylinder. In severe cases, the piston rod may even be "scratched" and "chewed", further causing damage to the sealing elements. If the additional force exceeds the ultimate load value that the front hinge point of the pressurized oil cylinder can bear, the damage of this hinge point will be inevitable.

After the cause of premature oil leakage at the head of the pressurized oil cylinder was identified, corresponding countermeasures were adopted in the design process of the new product RD12 rotary drilling machine. To compensate for the swing caused by the wear of the slider on the power head in the up and down direction of the guide rail (see Figure 2), the support lug of the power head cylinder is designed from the original round hole to a long circular structure. The length of this hole is determined based on the allowable wear of the slider, thereby completely eliminating the swing of the drill mast guide rail in the front and back direction due to the wear of the slider during the operation of the drilling rig. Cause additional loads on the guide sleeve, front hinge point and piston rod of the pressurized oil cylinder.