Abstract: The necessity and working conditions of applying cen- tralized oil lubrication system in the bearings in the wire part of high speed paper machines were invesgated in this paper. Taken a felt roll as an example, the bearing assembly, or sealing devices, sealing principles and the centralized oil lubracation system in high speed paper machines were introduced.
Key words: felt roll bearing; no-touch seal; centralized oil lubrication
In the newly designed paper machines in China in recent years, most of the dryer bearings (including guide rollers) use centralized thin oil lubrication oil supply devices, but few of them are used in the wire section. This paper takes the guide roller of the paper machine with a paper width of 4800 m and a speed of 14000 m/min as an example to discuss the necessity of using thin oil lubrication in the web part, the mechanical guarantee, the waterproof sealing principle and the characteristics of thin oil lubrication system.
1 Necessity of centralized thin oil lubrication
1.1 Requirements for paper machine speed
Generally, grease lubrication is used at low speed; When the vehicle speed is high, use oil lubrication. Generally, d n=80000 is taken as the basis to roughly select the range of grease lubrication or oil lubrication. For this paper machine, the outer diameter of the guide roller is 710mm, the vehicle speed is 1400 m/min, 22322CKY-W33 spherical roller bearing is used, the outer diameter of the bearing is 240 mm, the inner diameter is 132mm, the average diameter is 186 mm, and the speed is n＝V/3.14D ＝ 627.97r/min, dn＝diameter × speed=116802, which is far greater than the allowable value of grease lubrication, so centralized thin oil lubrication must be adopted.
1.2 Requirements for paper machine structure
The height of the web part of the paper machine is 8860 mm. If grease lubrication is used, the service life is short. When manual oiling is used, the walking table cannot reach every bearing, which requires climbing. It is extremely inconvenient and unsafe. It is difficult to ensure that each bearing is in a good lubrication condition during normal operation. As long as the design of oil lubrication is reasonable, each bearing can be guaranteed to be in good working condition.
1.3 Requirements for paper machine operation performance
In a modern paper mill, the paper machine usually stops only once a month, and all potential problems must be solved at this time. Grease lubrication cannot meet this requirement.
1.4 Economic requirements
The one-time investment of thin oil lubrication is larger than that of grease lubrication, but the operation and maintenance are convenient. Compared with the continuous replacement of bearings, unnecessary waste of manpower and material resources, and economic losses caused by failure to ensure the operation rate, the cost is relatively low.
2 Working conditions of mesh bearing
2.1 Special requirements for working conditions of mesh bearing
The consistency of the pulp entering the wire section is about 0.2%, the moisture content is more than 99%, and the consistency of the pulp leaving the wire section is about 23%. Most of the free water in the pulp is removed from the mesh. Although a large number of dehydration elements are used, the bearings in this part are inevitably exposed to a large amount of water. The main requirement of thin oil lubricated mesh bearing device is to effectively avoid water immersion, namely, waterproof, moisture-proof and oil sealing.
2.2 Action mode of water on bearing
Water invades the bearing in various forms. Scour intrusion, such as water at the edge of high and low pressure spraying, chemical spraying, and the edge of the mesh. When starting and stopping, dilute the water used to wash the cloth with clean water and directly flush it on the housing of the bearing pedestal; Splash intrusion, streams of water, mist droplets splash onto the bearing pedestal; With the invasion of water vapor, the humidity of the mesh is high, the humidity is heavy, and the fog is large. Water is formed through the condensation of the bearing; High speed, water thrown out by rotating parts due to centrifugal force; Defects of mechanical devices, leakage or water soaked in the lubrication system; Failure of sealing elements, water in pipes entering the oil system, etc.
2.3 Corrosion of water on lubrication system
As the air and water in the oil are mixed, the oil will be emulsified, which will lead to the deterioration of the oil, increase the acid value of the oil, and accelerate the aging of the oil. Especially when metal particles such as iron and copper are contained, the oxygen in the water and air can rapidly oxidize the hydraulic oil, generate sludge, reduce the lubricating performance of the oil, cause corrosion and wear of the components, affect or shorten the service life of the bearing, and even the lubrication system can not work normally.
3 Mechanical structure
3.1 Selection of bearing sealing structure
Common felt sealing conditions: coarse felt Vc ＜ 3 m/s, fine felt, and polished shaft Vc ＜ 10 m/s, which can not meet the requirements of high-speed paper machine due to oil leakage, penetration, etc.
Because of the high speed, non-contact oil lubrication is selected. Only the lubricant in the sealing gap rubs, the equipment will not be worn, so it will be used for a long time and will not generate heat.
3.2 Sealing of guide roller bearing
3.2.1 Water retaining ring
Stainless steel material, split structure, connected with the bearing cover, can prevent most of the water from entering the bearing directly, that is, to prevent erosion, splash and intrusion. Its interior also serves as the blocking surface of the water splash plate.
3.2.2 Water flinging ring
The stainless steel material is connected with the end face of the roll body with bolts, which is consistent with the shaft head. It is provided with a boss and a long groove. The front of the boss has a gradient to move the water to the boss side, which is used to prevent water from entering the groove. When there is more water, the water in front of the boss and the water entering the groove are thrown to the inner cavity of the water retaining ring under the centrifugal force of the high-speed rotating shaft, and then under the action of gravity, it is gathered at the bottom of the water retaining plate, flows out through the drain port, and prevents water from entering the bearing. The stainless steel material can prevent the corrosion of the roller body shaft head. Both are mechanical waterproof devices.
3.2.3 Bearing end cover (oil deflector) and W-shaped oil groove
The centrifugal force and small clearance are used to realize the oil seal of the bearing. The sealing principle is: when a small amount of lubricating oil leaks out from the small clearance between the shaft and the oil deflector ring, it will be collected into the W-shaped oil groove on the shaft, and the flow will be blocked on the shaft for many times, resulting in a large energy loss. At the same time, the oil attached to the high-speed rotating shaft will be thrown towards the inner cavity of the oil deflector ring under the centrifugal force, and the oil pressure thrown out will have a certain gradient. The oil pressure near the bearing is high and the flow is large; The oil pressure near the outside of the bearing is low, and the flow is small until there is no flow. The face opposite to the shaft on the oil deflector ring is also provided with a W-shaped groove, which is staggered from the W-shaped groove on the shaft. Its length is shorter than that on the shaft and deviates inward. The oil thrown into its inner cavity moves towards the inner surface of the bearing and continues to lubricate or flow to the bottom; Part of the oil moves towards the W-shaped groove and collides with the oil thrown towards the inner cavity of the oil groove. After many times of flow resistance, a large energy loss is generated, and the pressure head drops greatly. Then, it is gathered at the bottom of the oil retaining ring under the action of gravity and flows back to the thin oil station through the bearing shell. In this way, the oil can be prevented from escaping and difficult to leak to achieve the purpose of sealing. For oil groove seal, the smaller the clearance between shaft and housing, the better the sealing effect. Fig. 1 The radial clearance between the central shaft and the oil deflector ring is 1.5m. The oil groove is semicircular with a radius of 3mm. The number of oil grooves is 3-5 and the spacing is 8mm.
3.2.4 The role of intersections
It can be seen from Figure 1 that the long waterproof groove of the water slinger is on the outside of the bearing end cap (oil deflector ring), and the end faces are overlapped. Excess water flows into its own lower channel along the outside of the oil deflector ring and out of the bearing seat through the further blocking effect of the bend. At the same time, the oil will not flow out of the W-shaped area, so that water and oil can be separated, and the actual effect is very good.
3.3 Structure of other rolls in the wire section
The breast roll and couch roll of the mesh section also adopt similar structures, but because of their complex internal structures, they are equipped with special V-shaped sealing rings. In the press section, the pulp concentration is relatively high, and the water flow is small. Instead of using a water splash plate, add an oil splash ring seal. For higher speed paper machine, reverse spiral shaft head seal can also be used.
4 Thin oil lubrication system
4.1 Oil selection
According to the diameter and speed, No. 150 lubricating oil can be selected, and it is better to select lubricating oil with anti emulsification additives, such as Esso No. 150.
4.2 Water removal device
Use oil purifier to drain the water entering the oil. In addition to meeting the flow and pressure requirements, the standard thin oil lubrication station for the network is generally equipped with filters, electric heaters, cooling devices, etc., and it is better to be equipped with a water removal device. If not, portable oil purifier can be used, but it is time-consuming. For example, the 1500L thin oil station adopts the structure described in the text, and the water removal amount can reach 20~30ml, taking about 20h.
4.3
Since non-contact oil lubrication is adopted, certain centrifugal force, that is, a certain speed, is required, otherwise oil leakage will occur, which is one of the reasons why the creep speed of high-speed paper machine reaches 300~500m/min.
Fig. 1 Sealing of guide roller bearing
1 - Water retaining ring 2 - Water throwing ring 3 - Bearing seat end cover (oil retaining ring) 4 - W-shaped oil groove 5 - Roller body end cover
More about Marginal Self - Lubricating Bearings:
As a specialized manufacturer of self-lubricating bearings & bushings, Marginal Bearing is devoted to researching and producing new self-lubricating bearing materials.
Self-lubricating bearings, as the name suggests, provide their own lubrication during operation without requiring application of grease or oil lubricants. Due to this, self-lubricating bearings are also referred to as maintenance-free or greaseless bearings as they require no relubrication or grease.
An important distinction to make is that self-lubricating bearings are not bearings that come pre-applied with grease or oil lubricant – these bearings are instead referred to as prelubricated bearings. Prelubricated bearings will require relubrication at some point in their service life.
Self-lubricating bearings work by having lubricant impregnated within the sliding layer of the bearing. This lubricant can either be liquid (oil) or solid (graphite, MoS2, lead) based on the requirements of the application (such as operating temperature). As the bearing operates, the lubricant is released through pores in the sliding layer, lubricating the bearing surface. The lubricant is uniformly dispersed throughout the sliding layer and thus there is no reduction in low friction bearing performance, even if the sliding layer becomes worn. A “running-in” surface is also usually included at the top of the sliding layer to provide low friction bearing performance at start up before the impregnated lubricant reaches the bearing surface.
