In recent years, national construction management departments have gradually recognized the many advantages of rotary drilling rigs. Through use and practice by construction departments across the country, the modern foundation construction equipment that integrates high efficiency, energy saving, and environmental protection—the rotary drilling rig—has been accepted by more and more users. Its construction coverage has gradually expanded from large-scale hydropower and culvert gate infrastructure projects to railways, highways, and civil facilities such as buildings, halls, museums, and institutes. With the steady improvement of domestic rig manufacturing quality, this type of equipment will surely benefit the Chinese land for generations.
　　In actual use of rotary drilling rigs, some rigs exhibit oil leakage at the cylinder head of the power head pressurized cylinder shortly after construction begins. As use time extends, the oil film on the piston rod gradually thickens and forms an oil flow, which then leads to serious leakage and shutdown for maintenance. A few years ago, a domestic rig working on the Qinghai-Tibet Railway even suffered serious damage to the front hinge point of the pressurized cylinder. The exposure of this fact has indeed sounded an alarm for many domestic rig manufacturers. If this defect is not thoroughly solved, it will directly affect the reliability and sales volume of domestic rigs, and the market for Chinese rotary drilling rigs will be handed over to foreign manufacturers.
　　Through observation, the assembly relationship among the power head, pressurized cylinder, and drill mast of the rotary drilling rig is as follows: the pressurized cylinder is fixed to the front end face of the drill mast (in the working state of the rotary drilling rig), the head of its cylinder barrel is hinged in the support lug of the front cover plate of the drill mast, the tail of the cylinder barrel is floatingly connected to another support lug of the front cover plate of the drill mast, the head of the cylinder piston rod is connected to the power head support lug via a pin shaft, and the slider brackets on both sides of the power head are fastened to the drill mast guide rails with sliders in between. During operation of the rotary drilling rig, the pressurized cylinder pushes the power head to move along the drill mast, and the sliders move up and down along the surface of the drill mast guide rails with the power head. During the entire movement, the front-back and left-right swing amount of the power head is mainly determined by the clearance between the sliders and the drill mast guide rails.
　　During operation, as long as the power head moves, friction between the sliders and the drill mast guide rails will occur. As the sliders wear, the swing amount of the power head will gradually increase. Within the allowable wear range of the sliders, the swing amount in the left-right direction (see Figure 2) is compensated by the clearance between the piston rod head mounting lug and the power head cylinder support lug, and the resulting lateral additional force is borne by the outer side surfaces of the guide rails on both sides of the drill mast. However, the swing amount caused by wear of the sliders in the up-down direction of the drill mast guide rails in Figure 2 has no place to be released. The additional force in the front-back direction (working state of the rig) generated by the power head can only be borne by the lower slider of the power head and the piston rod head lug of the pressurized cylinder. If the piston rod of the pressurized cylinder extends longer, due to deformation of the piston rod, the force is mainly borne by the upper and lower sliders of the power head and balanced with the force received by the drill mast guide rails.
　　As the sliders wear, during the process of the pressurized cylinder applying pressure to the drill rod, the piston rod will be subjected to an additional bending load perpendicular to its axis (mainly caused by the additional force in the front-back direction during the working state of the rig), and this effect will decrease as the extension length of the piston rod increases. When the pressurized cylinder is pressurized in the fully retracted state, the additional force acting on the cylinder guide sleeve and the front hinge point is maximum. The frequent occurrence of such working conditions can easily cause uneven loading and wear of the guide sleeve seal, thereby making it impossible to ensure the ideal service life of the seal of the pressurized cylinder guide sleeve, and may even cause scoring and gouging of the piston rod, further causing damage to the sealing elements. If the additional force exceeds the ultimate load that the front hinge point of the pressurized cylinder can withstand, damage to this hinge point is inevitable.
　　After the cause of premature oil leakage at the cylinder head of the pressurized cylinder was found, corresponding countermeasures were taken in the design of the new product RD12 rotary drilling rig. In order to compensate for the swing amount of the power head caused by wear of the sliders in the up-down direction of the guide rails, the cylinder support lug of the power head was designed from the original round hole into an elongated hole structure. The length of this hole is determined according to the allowable wear amount of the sliders, thereby completely eliminating the additional load on the guide sleeve, front hinge point, and piston rod of the pressurized cylinder caused by the swing in the front-back direction of the drill mast guide rails due to slider wear during rig operation.