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 Linear bearing

Linear bearing

Metal linear bearing is a linear motion system produced at low cost, used in conjunction with a cylindrical shaft with unlimited travel. It is widely used in sliding parts of industrial machinery such as precision machine tools, textile machinery, food packaging machinery, printing machinery and so on.

Introduction:
Linear bearing is a kind of linear motion system, used for linear stroke and cylindrical shaft. Because the load-bearing ball is in point contact with the bearing jacket, the steel ball rolls with the least frictional resistance. Therefore, the linear bearing has low friction, is relatively stable, does not change with the bearing speed, and can obtain smooth linear motion with high sensitivity and high accuracy. The consumption of linear bearings also has its limitations. The most important thing is that the impact load capacity of the bearing is poor, and the carrying capacity is also poor. Secondly, the linear bearing has greater vibration and noise during high-speed motion. Automatic selection of linear bearings is included. Linear bearings are widely used in sliding parts of precision machine tools, textile machinery, food packaging machinery, printing machinery and other industrial machinery.
Since the bearing ball is in point contact with the bearing, the load is small. The steel ball rotates with minimal frictional resistance, so as to obtain high-precision and smooth motion.
Plastic linear bearing is a kind of linear motion system with self-lubricating characteristics. The biggest difference from metal linear bearing is that metal linear bearing has rolling friction, and the bearing and cylindrical shaft are in point contact, so this is suitable for low load and high speed movement; Plastic linear bearings have sliding friction, and there is surface contact between the bearing and the cylindrical shaft, so this is suitable for high-load, low-speed movement.

 Linear bearing

Feature:
Linear bearings are used in conjunction with hardened linear drive shafts. A system for infinite linear motion. Because the load ball and the quenched drive shaft are in point contact, the allowable load is small, but when moving in a straight line, the friction resistance is minimal, the accuracy is high, and the movement is fast.
Plastic linear bearings have no special requirements for matching shafts; they can withstand greater loads than metal bearings, but because the movement between the bearing and the shaft is sliding friction, the speed of plastic linear bearings is limited to a certain extent; the movement resistance is higher than that of metal linear bearings. The bearing is larger; but its motion noise is lower than that of metal linear bearings, especially in the case of medium and high speeds, the influence of the noise of plastic linear bearings with speed is very small. Plastic linear bearings are allowed to be used in dusty occasions due to their internal chip groove design. The dust will automatically be brought out of the friction surface of the bearing body from the chip grooves during movement; plastic linear bearings are also allowed to be used For cleaning, the internal sliding film made of special materials can even be used for long-term operation in liquids.

 Linear bearing

classification:
(1) Standard type, clearance adjustment type linear bearings, open type linear bearings, extended linear bearings, general-purpose linear bearings
(2) Flanged linear bearings can be divided into: round flange type, method flange type, oval flange type, guided round flange type, guided method blue type, guided oval flange type, and extended round flange type.
According to specifications:
It is divided into two series, namely LM and LME series. Its code name LM series is used in Asia, Southeast Asian countries, Japan, Korea, China, etc. With the metric size as the standard, the outer diameter tolerance of the linear shaft is generally h7. LME series are mostly used in Europe, America, Germany, Italy and other regions. With inch size as the standard, there are also metric sizes. The outer diameter tolerance of the linear shaft is generally g6. The structural characteristics of the two series are roughly the same except for the different sizes and aperture tolerances.
According to the shape:
1: Straight cylinder type (shape like a cylinder, generally installed with a circlip, used for occasions with small installation size)
2: Flange type (the end or the middle has a mounting flange, which can be installed with screws. The flange is generally divided into three types: round, square and trimmed)
3: Open type (shape like a straight cylinder, with axial slits on the outside, used in occasions where gap adjustment is required, divided into two types: large opening and small opening)
According to performance points:
1: Ordinary type (used for general performance requirements)
2: Super type (for long life and high load performance requirements).

 Linear bearing

use:
Linear bearings are more and more widely used in precision equipment such as electronic equipment, food machinery, packaging machinery, medical machinery, printing machinery, textile machinery, machinery, instruments, robots, tool machinery, CNC machine tools, automobiles and digital three-dimensional coordinate measuring equipment Or in the special machinery industry.

Clearance:
The inner and outer diameters of adjustable linear bearings and open-ended bearings are measured before the cut, and there will be some elastic deformation after the cut, and the matching clearance should be measured in the bearing housing (similar to steel retainer bearings and KH bearings). The adjustment direction of the bearing seat with adjustable clearance should be perpendicular to the direction of the bearing cut to ensure uniform clearance. The structural characteristics of linear bearings cannot be rotated, and good guidance is required. Therefore, linear bearings generally use two shafts + four sets Bearings or two shafts + two sets of extended bearings are used in a combination, and the two shafts should be installed straight. After the entire assembly is assembled, the transmission mechanism must be flexibly pushed and pulled by hand without obstruction. The transmission power must be sufficient to overcome the bearing friction Resistance, linear bearing friction resistance is approximately one thousandth of the working load.

 Linear bearing

Maintenance:
Maintenance of metal linear bearings: lubrication and friction: anti-corrosion oil is injected into the linear bearing. If grease is used for lubrication, first use kerosene or organic solvent to remove the anti-corrosion oil, and then add grease after air drying. (It is recommended to use lithium soap grease with viscosity No. 0.2.) If lubricating with oil, it is not necessary to remove the anti-corrosion oil. According to the temperature change, the lubricating oil of ISO viscosity grade VG15-100 can be used. Shaft lubrication can be from the oil supply pipe Oil, or oil from the oil hole on the outer bearing housing. Since the sealing ring will scrape off the lubricating oil, oil lubrication is not suitable for non-porous bearings with sealing rings.
Maintenance of plastic linear bearings: Since the sliding film inside the plastic linear bearings is made of self-lubricating plastic, there is no need for additional oil supply and maintenance during use; and because the plastic linear bearings have chip grooves, even the bearing Or the shaft is packed with dust and there is no need to maintain it. The dust will automatically be taken out from the chip flute during the movement; only when the sliding film wears out, the internal sliding film can be replaced directly; maintenance is very convenient.
Disposal:
(1) The disassembly of each part of the linear motion bearing series may cause foreign matter to enter or adversely affect the assembly accuracy of each part, please do not disassemble.
(2) Please note that the linear bushing may be damaged if dropped or hit. When the product is impacted, even if the appearance is not damaged, the function can still be
It may be damaged, please pay attention.
lubricating:
(1) Please carefully wipe the anti-rust oil and seal in the lubricant before use.
(2) Please avoid mixing lubricants with different properties.

 Linear bearing

Linear guide bearings:
A groove or ridge made of metal or other materials that can bear, fix, guide moving devices or equipment and reduce friction.
The longitudinal grooves or ridges on the surface of the guide rail are used to guide and fix machine parts, special equipment, instruments, etc. The application of guide rails in our daily life is also very common. For example, the sliding grooves of sliding doors, the rails of trains, etc. are all specific applications of guide rails.

Linear bearing installation method:
1. Before installing the linear bearing, the burrs, dirt and surface scars on the mechanical installation surface must be removed. The linear bearing is coated with anti-rust oil. Please clean the reference surface with cleaning oil before installation. Usually, the reference surface is easy to rust after the anti-rust oil is removed. It is recommended to apply lubricating oil to the spindle with lower viscosity.
2. Gently place the linear bearing on the bed, and use lateral fixing screws or other fixing fixtures to lightly fit the linear guide with the lateral mounting surface. Before installation and use, confirm whether the screw holes are consistent. If the machining holes of the base do not match and forcibly tighten the bolts, it will greatly affect the combination accuracy and use quality.

 Linear bearing
3. Tighten the positioning screws of the linear bearing from the center to both sides in order to make the track fit the vertical mounting surface, and tighten from the center to both ends to obtain a more stable accuracy. After the vertical reference surface is slightly tightened, the locking force of the lateral reference surface is strengthened so that the linear bearing can fit the lateral reference surface reliably.
4. Use a torque wrench to tighten the torque one by one according to various materials, and slowly tighten the positioning screws of the linear bearing slide.
5. Use the same installation method to install the auxiliary rails, and install the sliding seat to the main rail and the auxiliary rail individually. Note that after the slide is installed on the linear slide, many subsequent accessories cannot be installed due to the limited installation space. The required accessories must be installed at this stage.
6. Gently place the mobile platform on the sliding seat of the linear bearing main rail and the secondary rail, and then tighten the lateral compression screws on the mobile platform. The installation can be completed after positioning.

Precautions for linear bearing installation:
1. When assembling the linear bearing in the bearing seat, do not directly hit the side end of the bearing housing, the snap ring and the sealing ring, please use special tools to evenly and slowly press in.
2. When assembling the linear bearing and the special shaft, pay attention to the axis of the shaft and the shaft of the bearing to be parallel. Do not install at an excessive angle. An excessive angle will easily affect the accuracy and service life of the bearing, and may even directly cause steel balls. Fall off.

 Linear bearing

working principle:
The hydrostatic bearing of the constant oil supply pressure system is the pressure oil supplied from the outside of the structure of the hydrostatic bearing and the bearing bush. After passing through the compensation element, the oil supply pressure drops to the oil chamber pressure, and then passes through the gap between the oil sealing surface and the journal From the oil chamber pressure to ambient pressure. In most bearings, when the shaft is not subjected to external force, the journal is concentric with the bearing hole, and the clearance, flow, and pressure of each oil cavity are equal. This is called the design state. When the shaft receives an external force, the journal is displaced, and the uniform clearance, flow, and pressure of each oil cavity change. At this time, the external force of the bearing is balanced with the vector sum of the oil film force of each oil cavity. The compensation element plays the role of automatically adjusting the oil chamber pressure and compensating flow, and its compensation performance will affect the bearing capacity and oil film stiffness. The compensating element in the system with constant oil supply pressure is called the throttle, and the common ones are capillary throttle, small hole throttle, slide valve throttle, thin film throttle and so on. Compensation components in the constant oil flow system include quantitative pumps and quantitative valve compensation components, and the bearing load-displacement performance is also different. Comparison of load-displacement performance of hydrostatic radial bearings with different compensation elements]) Due to the rotation of the shaft, hydrodynamic pressure is generated on the bearing seal oil surface, which is beneficial to improve the bearing capacity of the bearing. This phenomenon is called dynamic pressure effect. The higher the speed, the more obvious the dynamic pressure effect.

 Linear bearing

Date

27 October 2020

Tags

Linear bearing

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