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Efficiently measure large bearings

by:JNSN     2021-10-23

In order to be able to detect the size error of the roller bearing when receiving the goods, a carbon measuring instrument can now be used. This can prevent problems in the assembly process early and avoid production downtime.

In today's complex equipment manufacturing process, it is inevitable to purchase parts such as ball bearings and roller bearings from specialized suppliers. However, the manufacturer will be subject to the supplier’s product quality, defects or short life to a large extent, and the manufacturer will eventually bear it. At the same time, the accuracy requirements of machines and motors are getting higher and higher, but there are some problems in the detection of larger roller bearings, because electronic measuring devices are often more complicated and expensive.

An alternative to electronic measuring devices

As an alternative, some initial companies used carbon measuring instruments to measure the goods when they arrived at the factory. The material of this instrument is very light, so the operation of the measuring stick is very simple. At the same time, the carbon material is durable and has a low expansion coefficient, so it can ensure measurement accuracy and repeatability.

In terms of manufacturing accuracy requirements, taking wind turbine equipment manufacturing as an example, the speed of the blade tip can reach more than 300km/h, and even the upper part of the generator can reach 1100min-1. In addition, there are also factors such as irregular operation due to wind changes and partial side forces. The roller bearings on the rotor blades and drive components of wind power equipment (WEA) have to bear much larger loads than ordinary uniformly running equipment. Therefore, for large bearings with a diameter in the range of 0.6~2.5m, the machining tolerance is only allowed to be a few hundredths of a millimeter according to different diameter grades. If the part is too small, its larger gap will lead to earlier wear. If the bearing is too large, the friction will increase, the wear will also accelerate, or the initial matching is improper, and time-consuming and laborious rework is required, resulting in higher costs and production delays.

Equipment manufacturers often abandon the inspection of the bearings that come into the factory. The 3D measurement equipment (Figure 1) that detects the shape of the component through the measurement probe requires a sensitive and precise mechanical mechanism to fix the measuring rod and the scanning switch, which means a higher investment. Laser trackers are relatively inexpensive, but their accuracy is insufficient; and laser interferometers that determine the length through complex calculations of the phase shift of the reflected beam are relatively expensive and very complicated in operation.

Fig. 1 The 3D measuring device is a method to test the bearing, and the shape of the part is measured by the measuring probe. The probe transmits the value obtained by each contact to the highly sensitive switch, but this kind of precision mechanical device is expensive

Steel instruments are heavy and difficult to operate

Manual measuring instruments It is an alternative option, such as a measuring screw. However, it is also necessary to pay attention to the measurement accuracy and ease of operation: on the one hand, the instrument should be able to achieve accurate calibration; on the other hand, the adjustment value of the steel measuring instrument will be distorted due to the thermal expansion of the instrument material, which is more troublesome to correct. In addition, the steel equipment of the required size is very heavy, so it cannot be used by only one person. In view of this difficulty and out of cost considerations, many companies are more willing to trust the manufacturing quality of their component suppliers and take possible risks.

During this period, people have developed measuring instruments for large diameter parts in the high-precision field. Easy-Metric is composed of a carbon fiber rod. The fiber rod is equipped with two height and width adjustable Anodized aluminum styli (Figure 2). With this stylus, the required size can be accepted by the measuring workbench or Factory Master, which is also made of carbon and calibrated in advance, and applied to the inspection of the components.

Figure 2 An alternative that is not complicated and costly is a manual carbon measuring instrument, which is light in material and insensitive to temperature fluctuations, so the adjusted scale is stable and reliable.

The repeatable accuracy is within 5μm.

Because the expansion coefficient of carbon is only 0.4μm/moC, it does not respond to changes in heat. Calibration values u200bu200band many measurement processes are also acceptable. Stay stable for a long time. The verification of the adjustment value can be carried out on the Factory Master at any time and easily. Practice shows that the repeatable accuracy of the instrument can reach within 5μm. This obviously meets the requirements of equipment manufacturers for manufacturing accuracy. In addition, the carbon material used has the characteristics of good stability and corrosion resistance.

According to the different specifications of roller bearings, the measurement itself only lasts 2~5min. When measuring, the measuring instrument is placed on the workpiece, and the maximum diameter is measured with one end of the arc as the starting point, until the deviation on the dial indicator returns. When this point is found, the precise value of the deviation from the given diameter can be directly read on the dial gauge, so that it can be determined whether to treat the measured workpiece as a defective product.

The maximum measuring capacity of the Easy-Metric measuring instrument with a standard immersion depth of 300mm is 8m. According to user needs, longer styli can also be provided. The cost of this instrument is significantly lower than the cost of the electronic measurement system, so it can not only avoid subsequent costs due to unqualified components, but also reduce the initial investment level. Carbon measuring instruments can be used not only in WEA production, but also in various high-precision processing fields, such as aircraft manufacturing and automobile industry.

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