What are the key parameters that need to be matched for the selection of the disassembly nut when disassembling the heavy-duty disassembly sleeve?

What are the key parameters that need to be matched for the selection of the disassembly nut when disassembling the heavy-duty disassembly sleeve?

1、 Thread system parameters: matching of load-bearing and sealing foundations

When disassembling under heavy load, the thread parameters of the disassembly nut directly determine the load-bearing capacity and disassembly smoothness. It is necessary to match the thread specifications of the disassembly sleeve, including nominal diameter, pitch, and thread type. For small and medium-sized disassembly sleeves (nominal diameter ≤ 38mm), metric ordinary threads are commonly used, and the tolerance should comply with the 6g accuracy of ISO 965-3:1998 standard. The corresponding nut internal thread tolerance should be 5H to ensure uniform thread engagement clearance and avoid stress concentration during disassembly. For heavy-duty dismantling sleeves with a nominal diameter greater than 38mm, trapezoidal threads should be used, with tolerances following the 7e level of ISO 2903:1993 standard. The internal thread tolerance of the nut should be adapted to 7H. The tooth structure of trapezoidal threads can disperse axial loads, reduce shear stress at the root of the thread, and adapt to the high torque dismantling requirements in heavy-duty scenarios.

The depth of thread engagement is another key parameter, and sufficient number of engagement turns must be ensured under heavy load conditions. Generally, the ratio of engagement height to thread pitch diameter is not less than 2.0. For example, the pitch diameter of M60 trapezoidal thread is 57mm, and the engagement height of nut should not be less than 114mm. By increasing the contact area, the unit area pressure can be reduced to avoid plastic deformation or bite damage on the thread surface. At the same time, the threaded surface needs to be lubricated by using high-temperature grease containing molybdenum to reduce the friction coefficient during disassembly, reduce thread wear, and indirectly improve load-bearing stability.

2、 Load bearing capacity parameters: adapted to the mechanical requirements of heavy-duty disassembly

When disassembling the heavy-duty disassembly sleeve, the nut needs to withstand axial tension and torque far beyond the installation stage, so the matching of material and strength parameters is crucial. The material of the nut should preferably be high-strength alloy structural steel, such as 42CrMo quenched and tempered treatment or 35CrNiMo carburizing and quenching, with a tensile strength of not less than 1080 MPa and a yield strength of ≥ 930 MPa, to ensure that plastic deformation does not occur under the action of large disassembly axial force. For extreme heavy-duty scenarios (disassembly axial force>200kN), nuts can be made of wear-resistant alloy materials such as cast aluminum bronze ZCuAl10Fe3, with a permissible shear stress of up to 35MPa and a permissible bending stress of ≥ 50MPa, which can balance strength and wear resistance.

The rated bearing capacity of the nut needs to be calculated based on the specifications of the release sleeve and the type of bearing. For example, for the release sleeve matched with a φ 200mm self-aligning roller bearing, the axial force during disassembly is about 1.5 times the rated axial load of the bearing. The rated axial bearing capacity of the release nut needs to be 20% -30% higher than the calculated value, with a safety margin reserved. At the same time, it is necessary to verify the shear strength of the threaded tooth root, and calculate the thickness of the threaded tooth root through a formula (trapezoidal threads are usually 0.65 times the pitch) to ensure that the tooth root will not undergo shear fracture under high torque.

3、 Structure and adaptation parameters: ensuring the stability of disassembly operations

The special working conditions of heavy-duty disassembly require precise adaptation of nut structure, disassembly sleeve, and disassembly tools. The external structure of the nut needs to be matched with a specialized disassembly tool. For nuts with a nominal diameter<200mm, four equidistant grooves should be set on the outer diameter surface to facilitate the use of a special wrench to hook and apply force; For heavy-duty nuts with a nominal diameter greater than 220mm, it is necessary to increase the number of equidistant grooves to 8 and reserve installation holes for fastening bolts. The bolts can assist in applying force to avoid uneven load caused by tool slippage during disassembly.

The accuracy of the end face of the nut is equally critical. The flatness tolerance of the end face in contact with the disassembly sleeve should be ≤ 0.01mm, and the roughness Ra should be ≤ 0.8 μ m to ensure a tight fit and avoid the disassembly sleeve being skewed or stuck due to uneven force on the end face during disassembly. In addition, the height of the nut needs to be adapted to the thread length of the disassembly sleeve. Usually, the height of the nut should not exceed 1.2 times the thread length of the disassembly sleeve, which not only ensures sufficient screwing depth but also avoids interference with other components caused by the nut being too long during disassembly.

4、 Anti loosening and auxiliary parameters: reliability requirements for adapting to heavy load conditions

During the heavy-duty disassembly process, the nut needs to withstand frequent torque impacts, and the anti loosening performance parameters cannot be ignored. Prioritize the use of nut structures with locking washer slots, and achieve anti loosening through the elastic deformation of the locking washer. The washer material should match the nut, and 65Mn spring steel should be selected to ensure elastic recovery capability. For heavy-duty equipment with severe vibration, a double nut anti loosening structure can be used. The main nut and locking nut rotate in opposite directions, and the loosening risk caused by vibration is offset by the thread pre tightening force.

Environmental adaptability parameters also need to be taken into account. Under high temperature conditions (working temperature>120 ℃), the nut material should be made of high-temperature resistant alloys, such as Inconel alloy, to avoid a decrease in strength caused by high temperatures; In humid or corrosive environments, the surface of the nut needs to be galvanized, passivated or chrome plated to improve its corrosion resistance. At the same time, water-resistant lubricating grease should be selected to prevent moisture from entering the thread gap and causing rust, which affects the smoothness of disassembly.

5、 Core principles of selection matching

The selection of heavy-duty disassembly sleeve and disassembly nut should follow the principle of "mechanical adaptation first, precision matching as a supplement, and structural adaptation as a bottom line". Determine the thread specifications and material strength based on the disassembly sleeve specifications and disassembly axial force; Match tolerances and surface quality according to precision standards; Adapt tools and installation space through structural design. It is necessary to avoid blindly pursuing large-sized nuts. Parameter calculation should be carried out to ensure that each indicator matches the actual working conditions accurately, which not only guarantees the safety of the disassembly process, but also extends the service life of the disassembly sleeve and nut.