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—rotary drilling rigs—integrating high efficiency, energy saving, and environmental protection, have been accepted by more and more users. Their 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 drilling rig manufacturing quality, such equipment will surely benefit the Chinese land for generations.

In actual use, some rotary drilling rigs have exhibited 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 to form oil flow, leading to severe 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. This fact has indeed sounded an alarm for many domestic rig manufacturers. If this defect is not thoroughly resolved, it will directly affect the reliability and sales volume of domestic rigs, and the Chinese rotary drilling rig market may be surrendered to foreign manufacturers.

Observation shows that the assembly relationship among the power head, pressurized cylinder, and drill mast of a rotary drilling rig is as follows: the pressurized cylinder is fixed to the front face of the drill mast (in working condition), the head of its cylinder barrel is hinged in the lug of the front cover plate of the drill mast, the tail of the cylinder barrel is floatingly connected to another lug of the front cover plate, and the head of the cylinder piston rod is connected to the power head lug via a pin (see Figure 1). The slider brackets on both sides of the power head are attached to the drill mast guide rails, separated by sliders (see Figure 2). During operation, 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. Throughout this movement, the fore-aft and left-right swing 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 occurs between the sliders and the drill mast guide rails. As the sliders wear, the swing of the power head gradually increases. Within the allowable wear range of the sliders, the resulting left-right swing (see Figure 2) is compensated by the clearance between the piston rod head mounting lug and the power head cylinder lug, and the resulting lateral additional force is borne by the outer sides of the guide rails on both sides of the drill mast. However, the swing caused by slider wear in the up-down direction of the drill mast guide rails in Figure 2 has no release. The additional force in the fore-aft direction (in working condition) 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 extends far, due to deformation of the piston rod, the force is mainly borne by the upper and lower sliders of the power head, balancing the force on the drill mast guide rails.

As the sliders wear, during the process of applying pressure to the drill rod by the pressurized cylinder, the piston rod is subjected to an additional bending load perpendicular to its axis (mainly caused by the fore-aft additional force in working condition). This effect decreases 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 front hinge point is maximum. Frequent occurrence of such working conditions can easily cause uneven loading and wear of the guide sleeve seal, making it impossible to ensure the ideal service life of the seal of the pressurized cylinder guide sleeve, and may even cause piston rod scoring and rod gnawing, further damaging the sealing elements. If the additional force exceeds the ultimate load that the front hinge point of the pressurized cylinder can withstand, damage to that hinge point is inevitable.

After identifying the cause of premature oil leakage at the cylinder head of the pressurized cylinder, corresponding countermeasures were taken in the design of the new RD12 rotary drilling rig. To compensate for the swing of the power head caused by slider wear in the up-down direction of the guide rails (see Figure 2), the power head cylinder lug was changed from a circular hole to an elongated hole structure, with the length of the hole determined by the allowable wear 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 fore-aft direction of the drill mast guide rails due to slider wear during operation. The improved structure is shown in Figure 3.