What Is a Shaft Bearing?

Bearing (Bearing) is an important component in contemporary machinery and equipment. Its main function is to support the mechanical rotating body, reduce the friction coefficient during its movement, and ensure its accuracy of rotation.

According to the data of "China Bearing Manufacturing Industry Production and Sales Demand Forecast and Transformation and Upgrade Analysis Report", from 2009 to 2013, China's bearing manufacturing industry's total industrial output value has been increasing year by year. In 2013, the industry realized a total industrial output value of 249.363 billion yuan, a year-on-year increase of 12.92%.

An analysis of the data in the past five years found that from 2009 to 2013, the sales revenue of the Chinese bearing manufacturing industry also showed an increase year by year. In 2013, it realized sales income of 249.012 billion yuan, a year-on-year increase of 11.80%.

The rapid development of China's bearing industry, from small to many bearing types, product quality and technical level from low to high, industry scale from small to large, has formed a professional production system with basically complete product categories and a reasonable production layout.

Bearing installation and maintenance

Points to note

From the perspective of use, to ensure that the bearings can work reliably, pay attention to the following points:

1. Improve the quality of lubrication, control the pressure, temperature and flow of the oil, and strengthen the oil filtration.

2. Use fuel and lubricating oil that meet the requirements.

3. It is unfavorable to control the temperature state of the diesel generator set and work under the conditions of supercooling and overheating. On cold days, the diesel engine should be warmed up before starting, and the crankshaft should be turned by hand to allow the oil to enter the friction surface.

4. The surface quality and geometry of bearings and journals should be strictly guaranteed.

5. The bearing clearance should be appropriate. If the generator set is too large, it will cause an impact. If it is too small, it will cause poor lubrication and may burn the tiles.

How to ensure that bearings work reliably

Generally speaking, pay attention to the following points from the perspective of use:
1. The bearing clearance should be appropriate, if it is too large, it will cause impact, if it is too small, it will cause poor lubrication and may burn the bushes;
2. The surface quality and geometry of bearings and journals should be strictly guaranteed;
3 Improve lubrication quality, control oil pressure, temperature and flow, and strengthen oil filtration;
4 Use qualified fuel and lubricant.

In order to make full use of the bearing and maintain its proper performance for a long period of time, regular maintenance (regular inspection) must be properly done. Through proper periodic inspections, early detection of failures and prevention of accidents are important to improve productivity and economy.

installation

Whether the bearing is installed correctly affects the accuracy, life and performance. Therefore, the design and assembly department should fully study the installation of the bearing. It is expected to be installed in accordance with operating standards. The items of the operating standard are usually as follows:

(1) Cleaning bearings and bearing related parts

(2) Check the size and finishing of related parts

(3) Installation

(4) Inspection after bearing installation

(5) Supply lubricant

It is hoped that the bearing package will be unpacked just before the installation. Generally lubricated with grease, without cleaning, directly filled with grease. Lubricating with lubricating oil, it is not necessary to clean in general. However, bearings for instruments or high-speed use, etc., should be washed with clean oil to remove the rust inhibitor applied to the bearings. Bearings without rust inhibitor are susceptible to rust, so they cannot be left unattended. In addition, greased bearings are used without cleaning.

The method of installing bearings varies depending on the bearing structure, fit, and conditions. Generally, since the shaft is mostly rotated, the inner ring needs an interference fit. Cylindrical bore bearings are usually pressed in with a press or hot-loaded. In the case of a tapered hole, install it directly on the taper shaft, or install it with a sleeve.

When mounted to the housing, there is usually a large amount of clearance fit, and the outer ring has an interference amount. It is usually pressed in with a press, or there is a cold shrink fit method for installation after cooling. When dry ice is used as the coolant, when the shrink fit is installed, the moisture in the air will condense on the surface of the bearing. Therefore, appropriate rust prevention measures are required.

maintenance

Disassembly

The bearing is disassembled for regular maintenance and is carried out when the bearing is replaced. After disassembly, if you continue to use it, or if you need to check the condition of the bearing, the disassembly must be performed with the same care as during installation. Pay attention not to damage the various parts of the bearing, especially the disassembly of the interference fit bearing, which is difficult to operate.

It is also important to design and make disassembly tools as needed. When disassembling, study the disassembly method, sequence, and investigate the matching conditions of the bearings according to the drawings to find the foolproof operation.
Disassembly of the outer ring The outer ring with interference fit is provided with several outer ring extrusion screw screws on the circumference of the casing in advance, and the screws are evenly tightened on one side while being disassembled. These screw holes are usually covered with separate bearings such as blind plugs, tapered roller bearings, etc. Several cutouts are set on the housing blocking shoulder, and they are disassembled with a press using a pad or lightly tapped.
Disassembly of the inner ring can be pulled out easily with a press. At this time, pay attention to the inner ring to withstand its pulling force. Moreover, the pull-out clamps shown are mostly used, and no matter what kind of clamps, they must be firmly clamped to the side of the inner ring. For this reason, it is necessary to consider the size of the shaft shoulder, or to study the groove on the shoulder so as to use the drawing clamp.
The inner ring of large bearings is disassembled by hydraulic method. Oil pressure is provided through the oil hole provided in the bearing to make it easy to pull. For bearings with large widths, the hydraulic method is used in combination with the pull-out clamp for disassembly.
The inner ring of a cylindrical roller bearing can be removed using induction heating. A method of heating the local part in a short time to expand the inner ring and then drawing. Where a large number of bearing inner rings need to be installed, induction heating is also used.

Clean

When removing the bearing for inspection, make a record of its appearance by photography or other methods. Also, check the amount of remaining lubricant and sample the lubricant before cleaning the bearing.

a, bearing cleaning is divided into coarse and fine washing, and can be placed on the bottom of the container with a metal grid.

b. For rough washing, remove grease or stickies with a brush in oil. If the bearing is turned in oil at this time, take care to prevent damage to the rolling surface due to foreign matter.

c. During fine washing, slowly rotate the bearing in oil, it must be done carefully.

Generally, the cleaning agent used is a neutral non-aqueous diesel oil or kerosene. If necessary, a mild alkaline solution may be used. No matter what kind of cleaning agent is used, always filter to keep it clean.

Immediately after cleaning, apply antirust oil or antirust grease to the bearings.

Inspection and judgment

In order to judge whether the removed bearing can be reused, it is important to check its dimensional accuracy, rotation accuracy, internal clearance, and mating surfaces, raceway surfaces, cages and seals. Because large bearings cannot be rotated by hand, pay attention to check the appearance of rolling elements, raceway surfaces, cages, ribs, etc., the higher the importance of the bearing, the more careful the inspection.

Causes of heating of rolling bearings and their elimination methods

• Low bearing accuracy: Use bearings with specified accuracy levels.

• Spindle bent or box hole not concentric: Repair the spindle or box.

• Poor lubrication: Use the specified grade of lubrication material and clean it properly.

• Low assembly quality: improve assembly quality.

• Bearing inner and outer ring: Replace the bearing and related wear parts.

• Axial force is too large: cleaning and adjusting the gap of the seal mouth ring should be between 0.2 and 0.3mm, correct the diameter of the impeller balance hole and verify the static balance value.

• Damaged bearing: Replace the bearing.

storage

The bearings are coated with an appropriate amount of rust-proof oil when they are shipped from the factory and packed with rust-proof paper. As long as the packaging is not damaged, the quality of the bearings will be guaranteed. However, for long-term storage, it is recommended to store it on a shelf 30cm above the ground under the condition that the humidity is less than 65% and the temperature is about 20 ° C. In addition, the storage place should avoid direct sunlight or contact with cold walls.

Bearing quality inspection

National standard

1. National Standard for Vibration Acceleration (commonly known as the Z standard)

This standard was established early to determine the quality level of the bearing by measuring the vibration acceleration value when the bearing rotates, and it is divided into three quality levels, Z1, Z2, and Z3, from low to high. At present, domestic bearing manufacturers are still using it. The vibration acceleration value is used to measure the pros and cons of the bearing, which simply reflects the fatigue life of the bearing.

2. Vibration speed standard (commonly known as V standard)

Since the original vibration acceleration standard has not been abolished, it appears as a standard issued by the Ministry of Machinery Industry. It is formulated with reference to European standards in combination with China s actual conditions and needs. standard). It is divided into five quality levels of V, V1, V2, V3, and V4. The quality grades of various ball bearings are V, V1, V2, V3, and V4 from low to high; the quality grades of roller bearings (cylindrical and tapered) are four quality grades of V, V1, V2, and V3.

It reflects the quality of the bearing by detecting the vibration b speed of the bearing in different frequency bands (low frequency, intermediate frequency, and high frequency). It can be roughly analyzed whether the bearing has geometric problems (such as steel ring ellipse), the quality of the raceway / rolling body, the quality of the cage, which is a significant improvement over the quality of the bearing compared with the vibration acceleration. At present, domestic bearings exported to Europe, the Chinese military and the aerospace industry all carry out bearing quality testing according to this standard. At the same time, testing the quality of imported bearings in Europe and distinguishing counterfeit imported bearings provides a feasible means.

There are two standards of bearing quality inspection in parallel. However, bearings with a high "Z" quality grade may not have good quality performance when tested with "V". There is no corresponding relationship between the two. This should be paid special attention in the quality inspection of the bearing.

Quality discrimination

To identify the quality of equipment bearings, we usually proceed from the following aspects:

1. Is the packaging clear?

Double-row tapered roller bearings

Under normal circumstances, brands produced by regular manufacturers have their own dedicated designers to design external packaging, and arrange factories that pass the production conditions for production. Therefore, the packaging of the product should be very clear from lines to color blocks. unambiguous.

2. Is the steel printing clear?

Each bearing product is printed with its brand name, label, etc. on the bearing product body. Although the font is very small, the products produced by regular manufacturers use steel stamping technology and embossing before heat treatment. Therefore, although the font is small, it is deep and very clear. Under normal circumstances, the fonts of counterfeit products are not only vague. Because of the rough printing technology, the fonts float on the surface, and some can be easily erased by hand or the marks are severe.

3. Is there a noise

Hold the inner sleeve of the bearing with your left hand, and turn the jacket with a small amount of reciprocation in the right hand to make it rotate, and listen for any noise during the running of the bearing. Due to the backward production conditions of most counterfeit products and completely manual workshop operation, impurities such as dust and sand will inevitably be mixed into the bearing body during the production process, so when the bearing rotates, noise or unsmooth operation will occur. . This is the key to judging whether the product comes from a branded product of a regular manufacturer with strict production standards and machine operation.

4, surface

Whether there is turbid oil on the surface This requires us to pay special attention when purchasing imported bearings. Because there is still a certain gap between the domestic rust prevention technology and advanced foreign manufacturing countries, it is easy to leave thick oil marks when the bearing body is rust-proofed, and it feels sticky and thick when contacted by hand. Hardly any trace of anti-rust oil can be seen on the imported bearings. According to industry insiders, particularly careful people can smell a special taste on imported bearings, which is the smell of anti-rust oil.

5, whether the chamfer is uniform

The so-called chamfer of the bearing, that is, the junction of the horizontal and vertical surfaces, due to the limitation of production technology, counterfeit bearing products are not handled satisfactorily at these corners, which can be easily identified.

6. Packaging

Bearing packaging is divided into inner packaging and outer packaging

After the bearing is manufactured and qualified after inspection, it is cleaned and rust-proofed, and then placed in the inner packaging to achieve waterproof, moisture-proof, dust-proof, impact-proof, maintenance of the quality and accuracy of the bearing, and the convenience of use and sales .

The inner packaging of bearings is divided into three categories according to the rust prevention period:

Short rust-proof period packaging: The rust-proof period is 3 to 6 months, which is suitable for bearings that are delivered to the same subscriber in large quantities and put into use in a short time. Based on the agreement between the two parties, simple packaging is adopted based on the principle of convenience.

General rust-proof period packaging: The rust-proof period is one year, which is suitable for general purpose bearings.

Long anti-rust period packaging: Two-year anti-rust period, suitable for special and precision bearings.

The inner packaging materials of the bearing are polyethylene plastic tube (box), kraft paper, plain and wrinkled polyethylene composite paper, paper box, polyethylene or polyethylene plastic film, nylon fastening tape or plastic braided fastening tape, waterproof high-strength plastic tape , Burlap bags and so on. All the above materials need to ensure that the material's corrosion resistance test is qualified.