How to set the pressure value when disassembling and removing the hydraulic nut sleeve so as not to damage the cone surface?

How to set the pressure value when disassembling and removing the hydraulic nut sleeve so as not to damage the cone surface?

1、 The core logic of pressure setting is to balance the disassembly force and the cone bearing capacity. The core of hydraulic nut disassembly is to convert pressure into axial thrust, which creates a separation trend between the retraction sleeve and the cone surface of the shaft. The key principle is that the axial thrust should be greater than the frictional force of the mating surface and less than the jx load corresponding to the yield strength of the conical material. The essence of cone damage is plastic deformation or biting caused by excessive local pressure. Therefore, pressure setting should revolve around "uniform force" and "controllable load" to avoid instantaneous high pressure or local stress concentration. 2、 The scientific calculation method of pressure value is based on the basic pressure calculation formula. The pressure of the hydraulic nut is proportional to the axial thrust (F=P × S, where F is the axial thrust, P is the set pressure, and S is the effective area of the hydraulic cylinder). The pressure setting requires first calculating the required small axial thrust, and then deducing the pressure value. The formula for calculating the small axial thrust of z is: F_min=μ × F_n (μ is the coefficient of friction of the conical surface, and F_n is the normal pressure on the mating surface). Friction coefficient μ: take 0.15-0.20 when there is no lubrication, and take 0.08-0.12 after coating with special disassembly grease (the grease should be compatible with the conical surface material to avoid corrosion); The normal pressure on the mating surface, denoted as F_n, is approximately 1.2 times the rated radial load of the bearing. Referring to the interference fit during installation, the F_n of the heavy-duty relief sleeve (with an interference fit of 0.02-0.05mm) is approximately 1.2 times the rated radial load of the bearing. Example: A 180mm self-aligning roller bearing is equipped with a pull-out sleeve, with a rated radial load of 280kN. After grease coating, μ=0.10, and the effective area of the oil cylinder S=0.015m ². Therefore, F_min=0.10 × 1.2 × 280=33.6kN, and the set pressure P=33.6 ÷ 0.015 ≈ 2.24MPa. After reserving 20% safety margin, the set pressure is 2.7MPa. The verification of cone bearing capacity requires ensuring that the unit pressure of the cone corresponding to the set pressure does not exceed the allowable stress of the material. The unit pressure of the conical surface is σ=F/(π× d × L) (where d is the average diameter of the conical surface and L is the contact length of the conical surface). The allowable contact stress of the commonly used material (40Cr) for the disassembly sleeve is ≥ 250MPa. If the calculated σ exceeds this value, the pressure should be reduced and a step-by-step pressurization method should be used to avoid damage to the conical surface.  

3、 The pressure setting and control techniques at the practical level are divided into stages of pressurization: to avoid instantaneous impact, a four step process of "preloading, boosting, holding, and dismantling" is adopted: preloading stage: pressurize at 30% of the calculated pressure, hold for 5-10 seconds, observe whether there is initial displacement on the cone surface, and eliminate the jamming of the mating surface; Boosting stage: Increase by 0.3-0.5MPa each time, maintain pressure for 3 seconds at each stage, and monitor the axial displacement of the disassembly sleeve with a dial gauge. When the displacement reaches 0.01-0.02mm/MPa, it indicates that the cone surface is starting to separate and the boosting speed needs to be slowed down; Pressure holding stage: After reaching the target pressure, hold the pressure for 15-20 seconds to evenly release the stress on the cone surface and avoid scratches caused by stress rebound during disassembly. Pressure upper limit control: To prevent overload damage to hydraulic nuts, the working pressure must strictly follow the rated parameters of the tool (the rated pressure of conventional heavy-duty hydraulic nuts is ≤ 35MPa), and the actual set pressure must not exceed 1.5 times the calculated value. If the disassembly cannot be carried out even after reaching 1.5 times the pressure, the operation should be stopped and the conical surface should be checked for rust, biting, or foreign object jamming. Blindly increasing the pressure is strictly prohibited. The influence of the mating surface state on pressure: The conical surface has slight corrosion: it is necessary to first repeatedly apply low pressure (0.5-1.0MPa) and release pressure, use hydraulic thrust to loosen the rust layer, and then gradually increase the pressure to avoid high pressure causing rust particles to scratch the conical surface; Scratches on the conical surface: Reduce the set pressure by 10% -15% and increase the holding time to reduce stress concentration at the scratch site by uniformly applying force.  

4、 The auxiliary prevention and control measures for cone protection include pressure monitoring and feedback using a high-pressure oil pump with digital display to monitor pressure changes in real time. If the pressure suddenly rises (exceeding 0.5MPa/second), it is necessary to immediately relieve the pressure and check whether the cone is stuck or the tool is overloaded. At the same time, the hydraulic circuit needs to be vented in advance (according to the closed circuit venting specifications) to avoid pressure fluctuations caused by air and damage to the cone surface. The compatibility between the tool and the cone surface: The pressure bearing end face of the hydraulic nut should be completely in contact with the end face of the release sleeve, with a flatness tolerance of ≤ 0.01mm. Otherwise, it will cause axial thrust bias and cause local pressure on the cone surface to exceed the standard. If the fit is poor, an adjusting shim (thickness 0.1-0.3mm, made of copper or stainless steel) should be added to ensure even force distribution. After disassembling the cone surface, immediately clean the residual grease and impurities on the cone surface, and check for scratches, indentations, and other damages: minor scratches (depth ≤ 0.005mm): can continue to be used after polishing with a fine oilstone; Plastic deformation occurs (such as bulging or pulling on the cone surface): the removal sleeve needs to be replaced to avoid affecting the fitting accuracy during reinstallation. 5、 Common Misconceptions and Corrective Misconceptions: The higher the pressure, the faster the disassembly. Correction: Excessive pressure can cause local plastic deformation of the cone surface, especially when the contact length of the cone surface is short, which can easily cause bite damage. It is necessary to strictly control according to the calculated value. Misconception: Ignoring the influence of temperature on pressure. Correction: Under high temperature environment (>80 ℃), the strength of the material of the disassembly sleeve decreases, and the set pressure needs to be reduced by 15% -20%; At low temperatures (<-10 ℃), as the friction coefficient increases, the pressure can be appropriately increased, but not exceeding 1.3 times the calculated value.