High bearing temperature in large double-suction horizontal circulating water pumps
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Routine maintenance is being carried out on the large double-suction circulation pumps in the plant; the drive end is equipped with NU series bearings, while the non-drive end features ball bearings at the junction of two 7-series bearings. These bearings are installed face to face and are lubricated with grease. A 0.3 mm shim is placed on the outer ring cover of the bearings on the non-drive end, and the radial bearing cover has an interference fit of 0.03 mm. After operation, the vibration on the non-driving side was about 7 mm/s too high. The bearings on the non-driving side were inspected again; the shims used to secure the outer rings of those bearings were removed, and the bearings were installed directly. There was a gap of approximately 0.1 mm between the outer rings of the two bearings. After 1 hour of trial operation, the temperature rose to 75°, so the bearing clearance was adjusted again. The radial gland clearance is 0.05 mm; an additional 1 mm shim is used for the axial gland. After operation, the vibration level is 5–5.5 mm/s, and the temperature remains below 50° (under normal conditions, the bearing temperature is at room temperature). Questions: 1. Why is the positioning bearing on the non-drive end installed in a face-to-face configuration rather than back-to-back? The manufacturer cannot explain this either 2 Is it necessary to tighten the outer ring retaining ring of the non-driving-end bearing? If there is a gap, how much should it be? 3 Is it reasonable for the rotor to move back and forth axially after there is a gap in the outer ring of the positioning bearing?
As a side note, first of all, this device was functioning normally before the maintenance, but problems arose after the maintenance. In fact, maintaining equipment means restoring its various parameters to the specified values required for normal operation. If it cannot be restored to its normal condition before maintenance, then it is a problem with the maintenance itself, and there is no necessary connection with anything else. During the process of further inspection and disassembly, it is necessary to proceed step by step, disassembling while checking, and recording everything. This allows identification of the vulnerable parts during use, which can serve as a reference for future maintenance plans. This type of maintenance is not difficult; simply restore it to its original state. As for the question you raised, it would be best to include an image or photo to facilitate discussion. It should also be noted that the data used for reinstallation should be based on the values specified in the equipment maintenance manual. It is recommended to check the tightness of the foundation bolts as well as the levelness of the rotor and the pump body. For reference.
:For this issue, it is recommended to first check the concentricity of the bearing seats on both sides; secondly, check the concentricity between the bearing seats and the sealing rings. If this pump model has been used successfully in other applications by the manufacturer, then an improper design of the bearing clearance can be ruled out
Reply 1: Angular Contact Ball Bearings can withstand both radial and axial loads. It can operate at higher speeds. The larger the contact angle, the higher the axial load-bearing capacity. The installation configurations of angular contact ball bearings include back-to-back, face-to-face, and in series. The outer ring of a angular contact ball bearing is thick on one side and thin on the other. The thicker side is called the \"back\", while the thinner side is called the \"face\". It should be noted that angular contact ball bearings are usually installed in pairs, and preloading is required. Proper installation can **improve** the operating accuracy of the host and the lifespan of the bearings ； Otherwise, not only will the accuracy fail to meet the requirements, but the lifespan will also be affected. 1. When installed back to back (with the wide end faces of the two bearings facing each other), the contact angle lines of the bearings extend in the direction of the rotation axis, which enhances the rigidity of their radial and axial support angles, resulting in the greatest resistance to deformation ； 2. When installed face-to-face (with the narrow end faces of the two bearings facing each other), the contact angle lines of the bearings converge toward the axis of rotation, resulting in relatively low angular stiffness. Since the inner ring of the bearing extends outside the outer ring, when the outer rings of the two bearings are pressed together, the original gap between the outer rings is eliminated, which allows for an increase in the preload on the bearing ； 3. When installed in a tandem arrangement (with the wide end faces of the two bearings in the same direction), the contact lines of the bearings are in the same direction and parallel to each other, allowing the two bearings to share the working load in that same direction. However, when using this type of installation, to ensure axial stability during installation, two pairs of bearings arranged in series must be installed opposite each other at both ends of the shaft
The last edit to this post was made by Xiuxi who fixes pumps on 2020-1-25 at 23:48. Reply 2: The outer ring retaining ring of the non-drive-end bearing does not need to be tightened; if there is a gap, it should be at least 20 threads on either side. This gap is known as the thermal expansion gap – as the bearing operates, its temperature rises, affecting both the inner and outer rings of the bearing. The balls and retainers expand; there is no gap between the cover and the outer ring of the bearing, which limits the expansion of the outer ring. As a result, the bearing clearance decreases and the bearing temperature rises. Conversely, when there is a gap, the bearing cover does not restrict the expansion of the outer ring. Before installing a combined angular contact ball bearing, it is necessary to adjust the bearing clearance; either an excessive or insufficient clearance can cause the bearing temperature to rise.
Reply 3: Once there is a gap in the outer ring of the bearing, the rotor will not move back and forth axially. The outer ring of the bearing is in interference fit with the bore of the bearing housing; if the bearing can move axially, it means that the fit between the outer ring and the inner bore of the bearing is not tight enough
The axial clearance of the non-drive-end bearing should be set to 0.2 mm – it shouldn’t be too large, as there is thermal expansion involved. The gland should be pressed with an interference fit of 0.02 mm; there must be no gap. Another thing is whether the bearing bodies at both ends are aligned
I’ve learned it.* One up on floor 4, like it.
We specialize in water pump dampers; we can discuss this together. Phone: 13773488901
Here, after the maintenance of the main circulation pump, the temperature of the bearing at the fixed end is 40 degrees. At the moving end in the horse area, the NU series bearings have a temperature of 62 degrees, which has reached the alarm threshold. Could some expert please help analyze this?