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SKF Bearing Design Measurement and Bearing Standard

Writer: Eric Bearing Limited

 According to certain procedures, the content and requirements of the product manufacturing process are compiled and fixed in the form of documents and standards to form a process document.

The process documents can be divided into two types: one is a comprehensive process document, that is, all the requirements of a product are compiled in a single file, which is simple and clear, easy to query, and suitable for occasions with simple product structures and small production batches.

The second is the type of process documents, that is, the classification is based on the professional characteristics of product manufacturing technology, highlighting the professional characteristics, applicable to all types of products.  

Rolling bearings as a standardized mechanical parts and components, except for individual varieties, the production process of most varieties is basically similar. Therefore, the compilation of manufacturing process documents for SKF bearing parts is convenient for standardization and serialization.  

1. Types of process documents  

Bearing parts manufacturing process documents can generally be divided into three categories: dominant process documents, management process documents and production process documents. 

The dominant process is the foundation, the management process file is used to supply and manage the materials needed in the part manufacturing process, and the production process file is used to guide production.  

2. Basis for preparation of process documents  

Mainly include: product design drawings, national standards, enterprise standards, internal standards and regulations related to products, special requirements put forward by customers, process equipment, technology and management level possessed by the enterprise, production scale and production layout, etc.  

3. Features of the process documents  

(1) Mandatory process documents are important regulations to ensure product quality, ensure the orderly production and carry out enterprise management. Once issued, they must be resolutely implemented.  

(2) Basic process documents are the basis for the production organization, material supply, quality management and economic accounting of the enterprise, and are the basic documents for the work of each business department of the enterprise.  

(3)Operability The process document not only requires accuracy, completeness, uniformity and specification, but also requires easy-to-understand, simple and clear, suitable for ordinary operation. Therefore, it must have strong operability in actual work.  

(4) Corporate imagery The process document is formulated according to the actual situation of the enterprise. Its content concentrates the advantages of the enterprise in technology, management and process equipment, and reflects the strength and image of the enterprise from one aspect.

Standard for bearing size

1. Bearing measurement  

The measurement of the bearing hole can be measured after checking the reference size on the outer diameter micrometer using the inner diameter gauge, and the roundness and cylindricity of the bearing hole must also be measured. Burning out SKF bearings often reduces the diameter of the bearing hole at the opening and the roundness is extremely poor, which is extremely detrimental to the normal operation of the bearing.

If the positioning of the connecting surface of the connecting rod bolt is loose, the connecting rod bearing cover will be displaced and the roundness of the bearing hole will be excessive. The roundness error of the bearing hole should be controlled within the dimensional tolerance, and the cylindricity should be strictly controlled.  

2. Measurement of main dimensions of bearings  

(1) Bearing thickness: the fixed probe of the outer diameter micrometer is changed from a flat surface to a spherical surface, which can be used to measure the thickness of the bearing. The thickness of the bearing should generally be controlled in the range of 0.005 to 0.010 mm, otherwise the inner diameter of the SKF bearing will be out of tolerance. The bearing is slightly thinned near the opening, and care should be taken when measuring.  

(2) The tightness of the fit between the bearing and the bearing hole: the tightness of fit is guaranteed by the free spring-out of the bearing and the height of the residual surface. Under the method of measuring the height of the remaining surface: install the bearing according to the regulations, loosen one of the bolts after the bolts of the bearing cover are tightened to the specified torque, and use a feeler gauge to measure the gap at the interface of the bearing cover. The value should be in the range of 0.05~0.15 mm within.  

(3) Bearing inner diameter: Before measurement, the SKF bearing should be installed according to the regulations and the bearing cap bolts should be tightened according to the specified torque. After measuring the reference size on the outer diameter micrometer with the inner diameter gauge, the measurement should avoid the thinning area. The difference between the bearing inner diameter and the corresponding journal outer diameter is the fit clearance.  

(4) The coaxiality of the inner bore of the main bearing: The coaxiality error of the inner bore of the main bearing is mainly caused by the coaxiality error of its bearing bore, and the cause of the coaxiality error of the bearing bore is the deformation of the cylinder block.

When the radial runout of the main journal is within the specified tolerance, check the joint marks of the main journal and the bearings. If the positions of the joint marks of the main bearings are obviously inconsistent, it means that the coaxiality error is large. Scraping, boring bearings or Solve by replacing the cylinder block, etc., otherwise it is difficult to ensure the normal operation of the engine.

Why SKF bearings will crack

Do you suddenly break when using SKF bearings? Did you find that the mechanical equipment will suddenly produce abnormal sound during operation? Or do you find cracks on SKF bearings when overhauling bearings? Why do SKF bearings crack?

1. The martensite arrangement must be small, because the coarse martensite is brittle, and even there are many micro cracks, this arrangement is prone to grinding cracks;

2. Strictly control the carbide grade, because the carbide is a brittle phase, its cracking resistance is low, and its thermal conductivity is poor. Manipulating the carbide grade can greatly reduce the chance of wear and tear;

3. The remaining austenite should be less. The thermal conductivity of the remaining austenite is only half of the martensite. The more the remaining austenite, the greater the thermal stress during the grinding process, and the tendency to wear.

In this analysis, the surface metallographic arrangement of the SKF bearing inner ring contains large carbides and severe network carbides;

Improper grinding process (such as excessive grinding, poor cooling, etc.) during the grinding process will cause the outer surface of the bearing inner ring to be heated, resulting in secondary quenching or high temperature tempering burns; SKF 22228-2CS5K-VT143 bearings online , pls click here : 

These heating arrangements greatly reduce the cracking strength of the material surface, and the surface of the material cracks under the effect of grinding stress and arrangement stress.

SKF bearing machining accuracy profile

When positioning the workpiece, the degrees of freedom that affect the machining accuracy requirements of SKF bearings must be limited; the degrees of freedom that do not affect the machining accuracy requirements of SKF bearings may or may not be limited, depending on the specific circumstances. Determining the degree of freedom that the workpiece must be restricted according to the workpiece processing requirements is the primary problem to be solved in workpiece positioning.

Because the dimension A2 in the depth direction of the groove is required, it is required to limit the freedom of movement in the z direction; since the bottom surface of the groove is required to be parallel to the c surface, the rotational freedom X around the x axis and the rotational freedom y around the y axis are restricted;

Since the slot length A1 must be ensured, the freedom of movement X in the x direction should be limited; since the guide groove should be in the center of the pressure plate, consistent with the oblong hole, the freedom of movement y in the y direction and the freedom of rotation around the z axis limit. In this way, all six degrees of freedom should be limited when machining the guide groove. This type of positioning where all six degrees of freedom are restricted is called full positioning.

If grinding the plane on a plane grinder, it is required to ensure the thickness B, and the processing surface and the bottom surface should be parallel. At this time, according to the requirements of processing SKF bearings, only three degrees of freedom of Z, X, and Y are required.

This positioning method with less than 6 degrees of freedom based on the actual processing requirements of the part is called incomplete positioning. If the workpiece is processed in a certain process, the positioning method with unlimited degrees of freedom that should be restricted according to the processing requirements of the part is called under-positioning. Under-location is not allowed in parts processing.