Figure 1: DNB # 200 assembly site
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Regarding rotary drilling rigs, the structural designs of various countries and manufacturers are diverse. Regarding sliding motion related components, generally box type telescopic structures and truss structure masts do not have follower frames. Similarly, according to technical literature, the sliding frame motion pair of the power head uses rollers, polymer materials, and adjustable mechanisms such as elastic bodies and plastic machine sliders to reduce vibration and adjust clearances caused by wear. They come in various forms.
In order to pursue universality of the problem, this article generally refers to the sliding device of rotary drilling, and analyzes the friction pair between the sliding frame of the rotary drilling power head and the mast, which is typical and complex. Similarly, similar phenomena also exist in rotary drilling rigs, rock drills, drilling rigs, cranes, marine cranes, etc. The power head sliding frame and follower frame of the rotary drilling rig are supporting and guiding devices on the drill rod, which can slide up and down along the mast guide rail to fix and guide the drill rod. In an ideal state, the centerlines of the follower frame, drill rod, and power head should coincide to ensure the verticality of the borehole during drilling, lifting, and lowering.
Figure 1: DNB # 200 assembly site
Figure 1a: Power head part
Figure 1b: Enlarged Detail
The sliding frame of the rotary drilling power head belongs to the engineering machinery components, which have complex working conditions and variable failure causes. Due to different working conditions, it may be subjected to the combined effects of axial force, radial force, overturning moment, impact force, deformation stress, etc.
Several reasons for the failure of sliding frames:
1) Loose bolts.
2) Bracket issue: stress release deformation, insufficient flatness, insufficient rigidity
3) The coaxiality of the center lines of the follower frame, drill rod, and power head is poor, resulting in bending moments.
4) The impact caused by the movement pattern of the working conditions and the clearance between the friction pair structures may cause structural loosening or failure.
The following is an analysis of the morphological working conditions between the wear-resistant plate of the power head sliding frame and the mast guide rail:
Friction pair motion modes: Among the six recognized friction pair motion modes, the sliding frame occupies the three motion modes of sliding friction, relative impact, and vibration. Friction modes that have a significant impact on failure include micro motion friction, particle friction, and frictional vibration (stick slip).
Particle friction: Wear resistant plates are usually coated with high viscosity lithium based grease, which has an adsorption effect on particles and foreign objects in dusty environments. Causing particle friction between the wear-resistant plate and the mast, exacerbating wear. (For example, nylon board)
Easy to cause: linear scratches, biting, abnormal noise.
Friction vibration: here is a certain gap between the wear-resistant plate and the dual material in the design requirements. While ensuring the rigidity of each structural component, it cannot absorb impact energy, resulting in intermittent impacts during the motion of the friction pair.
Easy to cause: loosening of structural components, fatigue wear, fracture, stick slip phenomenon, and poor operation.
Micro friction: While the wear-resistant plate undergoes visible sliding motion, there is also micro friction present. Its movement direction is parallel to the sliding direction and intermittently moves.
Easy to cause: eccentric wear, pitting wear.
Local contact friction: caused by overturning force and other bending moments, even if the plane slides, the force will be uneven. In addition, the wear-resistant plate is fixed by bolts. During operation, the relative sliding speed between the wear-resistant plate and the guide rail is relatively high. When the two come into contact, a large radial force is generated on several of the fixed bolts, which can also cause uneven stress on the wear-resistant plate.
Easy to cause: eccentric wear, fatigue wear, plastic deformation.
At present, wear-resistant plates such as manganese steel wear-resistant plates, nylon plates, and porous self-lubricating wear-resistant plates are used for the connection part of the chute. Based on the phenomena that are prone to occur in wear-resistant plates and masts, the first requirement is to have relatively high added value for masts and minimize damage to them as much as possible. At the same time, solutions and improvements have been made to the above issues.
Manganese steel wear-resistant plate: widely used in parts that require wear resistance such as buckets, conveyor belts, and crushing equipment. At the same time, surface treatment (hardening, etc.) can be used to enhance performance. With physical and mechanical properties higher than carbon steel, its wear resistance is beyond doubt. In the hard hitting mode, the effects of vibration, particle wear, and dual material wear reduction need to be carefully considered.
Nylon and polymer wear-resistant plates: with different compositions, their properties vary greatly. Difficulty in obtaining special polymer materials. It usually has the characteristics of shock and vibration resistance, certain wear resistance, and good protection for the board. For particle wear (foreign object intrusion), the effect needs to be carefully considered.
Deno Solution:
Regarding particle friction (foreign object intrusion): DNB # 200 porous wear-resistant plate has porous properties, and small hard particles will be embedded inside the wear-resistant layer, reducing damage to the mast guide rail and playing a role in reducing wear.
Regarding frictional vibration: DNB # 200 material is a composite material of wear-resistant layer and carbon steel back, and the steel back plays a certain role in absorbing vibration and impact force. At the same time, the wear-resistant layer is uniformly distributed with solid lubricant, making it easier for various parts of the sliding surface to form static boundary lubrication, and the friction coefficient is stable. Reduce the occurrence of stick slip and poor operation. (In other technical literature, it is mentioned that plastic materials are added between the wear-resistant plate and the sliding frame structure to provide cushioning.)
Regarding micro motion friction: Similar to 2), the dispersion of solid lubricant through the wear-resistant layer is uniformly distributed to improve it.
Regarding local contact friction: The characteristics of the equipment cause local contact, allowing pressure to increase in the surface pressure value of some contact areas while reducing the contact area, which can easily lead to wear. DNB # 200 exhibits excellent wear resistance and anti wear effect on the dual material within the allowable maximum PV value range. Even in some contact areas, the long-term wear resistance extends the time interval for the occurrence of eccentric wear, which has an improvement effect. (Extreme projection contact areas that are too small or even line contacts are not within the scope of consideration.)
The above are some of our analysis and thoughts on the complex sliding device of rotary drilling.
Author: Mr. DERORE