The motion form of sliding bearings is mainly characterized by the relative sliding of the journal and bearing pad. It is a type of bearing with sliding wear properties, and its structural forms are various. Liquid friction bearings are commonly used in production. According to the different principles of oil film formation on the two relative motion surfaces of sliding bearings, they can be divided into liquid dynamic pressure bearings and liquid static pressure bearings.
Liquid dynamic sliding bearings have the characteristics of smooth operation, simple structure, low noise, high stiffness, and anti overload ability. They are widely used in high-speed and heavy-duty situations; Hydrostatic sliding bearings have the advantages of high load-bearing capacity, good vibration resistance, low friction coefficient, long service life, high rotational accuracy, and the ability to work normally at high or very low speeds. They are widely used in high-precision, heavy-duty, low-speed, and other applications.
However, whether it is a static pressure bearing or a dynamic pressure bearing, after working for a certain period of time, there will be failures such as decreased rotational accuracy, vibration, bearing heating, and "holding the shaft" during operation. Due to the different working principles of the two types of bearings, their respective repair points are also different.
Key points for repairing dynamic sliding bearings
Due to the inability to form liquid friction between the journal and bearing during the startup and shutdown stages of dynamic pressure bearings, their mating surfaces gradually wear out, resulting in increased clearance, decreased geometric accuracy and surface roughness, reduced oil film pressure, and unreasonable distribution of oil film pressure. This initial stage of wear often leads to a decrease in spindle rotation accuracy and vibration. In the later stage of wear, the dynamic pressure effect is extremely unstable,
The direct friction between the journal and the bearing intensifies, and the working surface often wears out, or there are situations such as bearing alloy melting, peeling, or cracking. After long-term vibration, the back of the bearing pad also wears out and becomes loose.
Generally speaking, in response to this situation, methods such as repairing the journal, repairing or replacing bearings can be adopted to restore the reasonable clearance between the mating surfaces of the journal and bearings, and to restore the geometric shape accuracy and surface roughness that the journal and bearings should have. For bearings with multiple supports, the coaxiality and surface roughness of their supporting surfaces should be restored. The specific repair methods can be different depending on their structure.
Method of reducing the inner hole of the shaft sleeve
① When the integral sliding bearing is damaged, it is generally resolved by replacing it with a new component. For bearings of larger and more precious metals, spray plating can be used; Alternatively, an axial groove can be made on the shaft sleeve first, then closed to reduce the inner hole, and then the gap can be filled with copper welding, as shown in the figure. The outer diameter can be increased by metal spraying or embedding. Finally, the mechanical processing and scraping meet the requirements.
② The repair of inner and outer tapered sliding bearings should be carried out according to the damage situation. If the working surface is not severely scratched and only needs precision repair, the clearance can be adjusted through nuts. When there is serious damage to the working surface, the spindle should be disassembled, the bearing should be scraped and ground again to restore its fitting accuracy.
③ Repair of Split Sliding Bearing If the working surface of the split sliding bearing is slightly worn after use, its accuracy can be restored by re scraping and adjusting the gasket. For Babbitt alloy bearing shells, if the working surface is severely damaged, Babbitt alloy can be poured again and machined before scraping. When repairing, it should be noted that the distance between the bearing cover and the bearing seat should not be less than 0.75mm, otherwise it will affect the compression of the bearing shells.
Key points for repairing hydrostatic sliding bearings
Hydrostatic sliding bearings are mainly repaired to restore equal and stable pressure in the four oil chambers of the bearing. The unequal pressure in the four oil chambers can cause the journal to deflect, generate vibration, intensify friction between the journal and the bearing, and cause the bearing to heat up or even "hold the shaft".
However, the specific reasons for the unequal and unstable pressure in the four oil chambers of the bearing are also different. When repairing, specific fault causes should be addressed, including the following aspects.
① The bearing oil chamber leaks oil, and the pressure oil directly returns to the return oil chamber through the damaged part, causing the journal to lean towards the surface of the oil leakage chamber, causing deflection and intensifying friction. At this point, repair or replace the bearing by repairing it.
② The gap of the throttle is blocked, causing unequal pressure in the four oil chambers. The reason is that the impurities and particles mixed with the oil accumulate at the throttle port, causing the throttle gap to be blocked, causing the diaphragm to deform and the flatness to deteriorate, resulting in unequal gaps on both sides of the diaphragm and unequal pressure in the oil chamber. At this point, methods such as cleaning the throttle, replacing the diaphragm, and replacing the oil filter should be taken for repair.
③ The pressure in the oil chamber fluctuates, causing the spindle to vibrate. The main reason is that the spindle is deformed, bent, or the roundness of the bearings and journals deteriorates. When the spindle rotates, the gap between the bearing and journal undergoes periodic changes, causing fluctuations in oil chamber pressure and causing spindle vibration. Sometimes, due to the imbalance of the external load rotating parts of the main shaft, it can also cause pressure fluctuations in the oil chamber. Measures can be taken to balance the external load rotating parts and eliminate them.