Solutions to the Role and Importance of Screws and Large Nuts on Excavators

Solutions to the Role and Importance of Screws and Large Nuts on Excavators

The excavator is widely used as heavy construction machinery with a large digging force and loading capacity in various industries and fields. Its primary roles can be summarized as follows.

First, excavators are mainly used in earthwork construction, including excavation, filling, and site leveling. In constructing roads, bridges, tunnels, and buildings, excavators are widely used in earthmoving, rock drilling, drainage trenching, trench digging, and other operations, which can significantly improve the efficiency and quality of construction.

Secondly, excavators can be used in mining. In the mining industry, excavators are mainly used for mining ore, coal, metal ore, etc. It has a large digging force and loading capacity, which can efficiently carry out the mining and transportation of ores, providing strong technical support for developing the mining industry.

In addition, excavators are widely used in municipal engineering and environmental remediation. In urban construction, excavators can construct municipal infrastructure, including roads, bridges, electricity, water supply, drainage, etc. The excavator can also be used for environmental remediation, such as river dredging, lake management, reservoir dredging, and other work. It can quickly clean up sludge, sediment, and garbage, improve environmental water quality, and protect the environment.

In addition, excavators are also widely used in farmland water conservancy construction. The excavator can dig irrigation channels and dredge rivers and wells in farmland water conservation projects. It can quickly and efficiently carry out earth excavation and groundwater mining, which provides a strong guarantee for farmland irrigation and improves the yield and efficiency of farmland.

In addition, the excavator can also be used for all kinds of emergency rescue and disaster relief work. When a disaster occurs, the excavator can clean up road blockages, rush through communication and power lines, and quickly restore transportation and power supply. It can also be used to excavate debris, search and rescue buried people, rescue trapped animals, etc. Excavators play an essential role in disaster relief and rescue work.

Excavator working conditions are harsh, the Vibration is huge during operation, and the bolts at its working device, pin, block, supporting wheel, body attachments, etc., are easy to loosen. Therefore, the host factory's instruction manual requires that every period (such as 250h), check and fasten some critical parts of the bolt. However, this method can not eliminate the loosening of bolts, and there is a greater security risk in many essential parts of the bolts in the inspection and fastening cycle before the loosening.

The role of the lug nuts:The large lug nuts on an excavator are mainly used to connect the various components and parts of the excavator, including the joints, the boom, the bucket, and so on. These nuts combine and fix important parts, ensuring the safety and stability of the whole excavator. The size and material of the nuts are also significant and must be professionally designed and manufactured to ensure the strength and stability of the nuts; Excavator Track Plate Bolt High Strength Chain Plate Screws 22*65 with Square Nut. Hydraulic nuts or bolts are a new type of fastener. Ordinary nut locking is by turning the wrench to generate torque to lock, so more than 90% of the power is wasted in overcoming friction, and the preload force on the bolt is minimal, especially for large-diameter high-strength bolts, inhuman tools, and site and other factors, the preload force is simply in the locking can not meet the design requirements, quickly resulting in the loosening of the nut. Hydraulic nut locking and ordinary nuts are different; hydraulic nuts in the locking project rely on hydraulic pressure directly on the nut and produce ultra-high-pressure preload; even in the Vibration of the working conditions, the parts connected will not be loose.

Hydraulic nuts are especially suitable for tightening the connection of coal mining equipment, such as coal mining machines and stubborn feeders, in the narrow space of underground coal mines. They can also be used in metallurgy, chemical industry, and engineering machinery.

The importance of lug nuts:The large lug nuts on excavators are not just ordinary lug nuts; they are specially designed and manufactured from a high-strength alloy material, and their strength and stability play a crucial role throughout the excavator's work. Suppose the lug nuts are not strong enough or not adequately secured. In that case, they may cause parts to break or the excavator to become unstable, which will threaten the working environment and the safety of the workers and may even lead to accidents.

Overhaul of nuts:As the excavator often needs to work in harsh environments, the nut and other parts are also subjected to tremendous pressure and external impact. They may become loose, deformed, fall off, and other problems. Therefore, the Overhaul and nut replacement are also very important in the daily maintenance and repair of excavators. If the nut is loose or deformed, it must be replaced immediately and fixed by the specified torque standard.

The causes of bolt loosening are manifold and must be controlled from all aspects simultaneously. This paper combines the typical case of excavator bolt loosening, discusses the causes of bolt loosening from the elements of stiffness, Vibration, threaded anti-loosening structure, preloading force, materials, etc., and puts forward preventive measures.

Bolt stiffness:Including bolt (fastener) stiffness and frame (by fastener) stiffness, bolts in the axial variable load, in the fastening force under the same conditions, the smaller the stress change amplitude, the smaller the possibility of bolt fatigue fracture, the higher the reliability of the connection. When the working tension is unchanged, the stress change amplitude can be reduced by reducing the bolt stiffness.

When the stiffness of the connected parts and the bolt stiffness are unchanged, the working tension can be increased by increasing the preload force, which can also reduce the stress change amplitude. Moderate increases in bolt length can reduce the bolt stiffness. For example, long bolts can reduce bolt stiffness in the slewing bearing, counterweight, track guard, cab protection net, etc.

Excavator frame stiffness:The frame (being fastened) stiffness can be improved by eliminating shims, using shims with higher stiffness, etc. If the travel pilot valve is connected to the travel pedal assembly by a transition block, the transition block can be bolted directly.

The smaller the frame's stiffness, the more likely the vibration source (engine) Vibration to the surrounding propagation process will be amplified, and the resulting stress amplitude will be more significant. On the contrary, the greater the stiffness of the frame, the better the machine's stability; the same conditions under the amplitude of the stress change are also more minor.

A small excavator machine from 5.5t level to 7t level, its engine, cab, and frame are used in the 5.5t level, its vibration isolation effect worsens, the machine vibration increases, and the bolt loosening phenomenon is aggravated. Through unilateral adjustment of the damper, the effect is not apparent. The problem was solved by strengthening the frame.

Vibration generated by the engine:Excavator bolts generally use ordinary threads with a thread rise angle less than the threaded pair's equivalent friction angle to meet the threaded pair's self-locking conditions. After the bolt is tightened, the friction between the head of the bolt and the support surface of the nut also has an anti-loosening effect. However, when the bolt is installed in the machine's Vibration, impact, and other variable loads, the friction between the threaded vice may be reduced or disappear instantly. The bolt will loosen after Vibration, shock, and many reciprocating actions. The vibration part of the excavator includes the Vibration generated by the engine and the Vibration caused by the excavator operation.

The Vibration transmitted from the engine to the whole machine, the arrangement of the engine suspension system, and the type of damper. For example, a 47t-class excavator is equipped with a Cummins QSM11 engine. The engine's original design adopted 3-point support, i.e., one support was set at the fan end, and two supports were placed at the flywheel end. In the 2000h excavation test, the machine bolt loosening is serious. After adjusting the axial stiffness of the damper, the axial acceleration and amplitude were improved, but lateral shock oscillation occurred, causing the fan shroud to be knocked off several times.

For this reason, the 3-point engine support was changed to 4-point backing, i.e., an adapter plate was set up at the fan end, which was connected to the engine's bracket in the middle and then connected to the frame through the damper at both ends. Tests were carried out after the improvement, and from the test data, the vibration isolation rate of the fan end was improved nearly one times compared with that of the 3-point support, and the vibration isolation rate of the flywheel end was also slightly improved.

The hardness of the engine damper rubber, the thickness of the frame plate, and the tightening torque will also affect the vibration isolation rate. Generally, the self-oscillation frequency can be reduced by lowering the axial stiffness of the damper to get a better vibration isolation effect. However, if the axial stiffness of the damper is reduced too much when the engine is impacted, there will be a gap between the damper and the frame plate, and the damper will be damaged due to friction. It will also affect the radial stiffness of the damper, causing the engine to oscillate.

Thread-locking structure:Commonly used methods of locking threaded connections include friction locking, mechanical locking, and destroying the spiral vice locking. Generally speaking, friction locking is simple and convenient but not reliable enough. The threaded connection of essential parts, especially the threaded connection inside the excavator, which is not easy to check, should adopt the mechanical anti-loosening method.

Friction locking: Friction locking includes double nuts and tightening, spring pads, self-locking nuts, and other methods. Double nuts and pull the anti-loosening method of simple structure, suitable for smooth, low speed, heavy load, and other fixed connection occasions. It can improve the pin of the excavator working device, the U-bolt, etc. Due to the uneven elasticity of the spring pad, the bolts are easy to bend, and the bent bolts quickly come loose under the action of shock and Vibration. A model of excavator early M8, M10, and M12 bolts are spring pads plus flat pads anti-loosening structure; its anti-loosening effect is poor, the whole machine works less than 500h, and many bolts loose after the change to homemade, increased shims to achieve a better anti-loosening effect. Increase the gasket surface should be smooth and there are no harmful cracks, scratches, burrs, and bending to avoid the assembly of bolts producing bending stress.

The self-locking nut is more reliable and will not reduce the anti-loosening performance after many disassembling and reassembling. This anti-loosening method can be used for smaller-sized threaded subs such as U-shaped handles of seat slides, radio antennas, and lighting lamps.

Mechanical locking (destroying the threaded vice to prevent loosening):Mechanical locking is generally used for engine damper bolts. The nut is welded to a bent piece of bracket, and the anti-loosening is achieved by restricting the bent side of the bracket.

Applying thread-locking adhesive to the threads before the threaded pair is screwed together is considered to be destroying the threaded pair to prevent loosening. After using thread-tightening adhesive on the threads and tightening the threaded sub, the thread adhesive hardens and solidifies, and then the threaded sub can be prevented from loosening. Thread fastening adhesive is used for bolts in essential parts, such as supporting wheel, sprocket, engine support, engine vibration damper, cab floor frame, cab vibration damper, counterweight, slewing motor, traveling motor, and slewing bearing bolts.

Preloading force:

1. The bonding surface should meet the requirements: the accuracy of the threaded hole is generally at the 6H level, the size of the preload and the effect of fastening by the fastener, and the fastener bonding surface of the friction coefficient. Damage or corrosion of the thread, before fastening, should be tapped or plate teeth repaired (commonly known as "back to the wire"), and then use the cleaning agent will be inside the screw hole, the bolt surface as well, as the combined surface of the residual paint and stains cleaned.

2. Pre-tensioning force should be appropriate: Increasing the pre-tensioning force can reduce the amplitude of stress change. However, the preload should not be too large and must be controlled in the specified range. Too much preload will cause the bolt strength to reach the yield point. When using a torque wrench to tighten the bolt, the bolt stress (preload) is generally 75% of the yield strength of the bolt. For example, if 10.9-grade bolts have a tensile strength of 1000MPa and a yield of 900MPa, then the preload force is 675MPa. When using a torque wrench, the theoretical tightening torque T and preload force F have the following relationship:

T ≈ 0.2Fd

where d is the nominal diameter of the thread.

In addition, the tightening torque is also related to the precision of the fastening tool.

When using socket wrenches and ordinary wrenches, the tightening torque should be slightly smaller than when using torque wrenches.

3. Disposition after tightening: When the bolt is tightened as required, color markings need to be applied to the head of the bolt (or nut) and the surface of the fastener. Once the bolt is loosened, it can be gradually tightened in the direction of fastening until the head of the bolt (or nut) and the markings on the surface of the fastened parts coincide again.

Various fastener materials:

1. The fastener: bolt screwed into the fastener, the fastener material is different; fastening bolts screwed into the depth is distinguishable by the fastener is steel, cast iron, light alloy order, and the depth of the bolt screwed into the depth should gradually increase. The depth of the bolt screwed into the steel should be slightly more significant than the nominal diameter of the thread, but when the nominal diameter of the bolt is less than 12mm and screwed into the occasions for the battery terminal, pipe clamps, wire clamps, radiator dust net, the bottom of the sealing plate, the depth of its screwed into the nominal diameter can be equal to. Cast iron casting after the formation of graphite in the base body has an expansion effect, can reduce the casting volume contraction, and can reduce internal stress; the vibration transmission can also weaken the role of Vibration, and vibration-absorbing performance is excellent. For example, when walking the pilot valve on the transition block, engine bracket, and compressor bracket made of cast iron, the fastening bolts of the anti-loosening effect are better.

2. Threaded seat: threaded seat material selection is essential. When the yield strength of the threaded seat is too small, it may cause deformation of the bolt screwed in, causing early fatigue failure; the bolt is also easy to loosen. Part of the material's yield strength and the plate's thickness, such as Q235 steel, the thicker the plate, the smaller the yield strength, the selection of materials should be noted. If the tensile strength of the threaded seat is too small, when using a torque wrench to tighten, it will directly damage the thread. Therefore, the critical position of the threaded seat steel is generally Q345B and the general position of the threaded seat steel is generally Q235B.

3. Homemade large gasket: tighten the bolt to increase the gasket. It is not a standard part; strict technical requirements exist, so it is only homemade. Homemade increased gasket material is generally No. 45 steel, hardness of HRC39, heat treatment for quenching, and medium temperature tempering. If the hardness of homemade gaskets after heat treatment is insufficient, it may lead to deformation. When the hardness of the homemade gasket reaches HRC38 or more, if you want to electrochemical galvanize, you must go through a six h low-temperature (200 ℃) drying treatment to prevent hydrogen embrittlement and then slow cooling in the furnace. The above anti-loosening measures are comprehensively applied in the machine design and assembly process; users reflect that the machine bolt loosening problems were significantly reduced, and good results and economic benefits were achieved.

Although the big nuts and screws on the excavator seem to be very common, they are indispensable and essential parts of the excavator, which must be professionally designed and manufactured and reasonably overhauled and replaced in daily maintenance. Only by ensuring the strength and stability of the nuts and screws can we ensure the everyday work of the excavator and improve the working efficiency and safety.

Please get in touch with us if you want high-quality nuts fasteners or technical support for structural design. Thanks.Email:adelajonly@gmail.com

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