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Method of Automatically Setting Bearing Clearance

by:JNSN     2022-03-12
In addition to presetting bearing assemblies, Timken has developed five commonly used methods of automatically setting bearing clearance (ie, SET-RIGHT, ACRO-SET, PROJECTA-SET, TORQUE-SET, and CLAMP-SET) as manual adjustment options. Refer to Table 1 for a comparison of tapered roller bearing setting methods to illustrate the various characteristics of these methods in tabular form. The first row of this table compares the ability of each method to reasonably control the bearing's mounting clearance range. These values u200bu200bare only used to illustrate the overall characteristics of each method in setting the clearance, regardless of the goal of setting the clearance as preload or axial clearance. For example, under the SET-RIGHT column, the expected (high probability interval or 6σ) variation in clearance, due to specific bearing and housing/shaft tolerance controls, may range from a typical minimum of 0.008 inches to 0.014 inches. The clearance range can be divided between axial play and preload to maximize bearing/application performance optimization. Refer to Figure 5 for the application of the automatic bearing clearance method. This figure illustrates the general application of the tapered roller bearing setting method using the design of a typical 4x4 agricultural tractor. We discuss in detail the specific definitions, theories and formal procedures for the application of each method in the following sections of this module. The SET-RIGHT method obtains the required clearance by controlling the tolerances of the bearing and the mounting system, eliminating the need for manual adjustment of TIMKEN tapered roller bearings. We use the laws of probability and statistics to predict the effect of these tolerances on bearing clearance. In general, the SET-RIGHT method requires tighter control over the machining tolerances of the shaft/housing, and at the same time (by means of the accuracy class and code) the critical tolerances of the bearing. This approach recognizes that each component in an assembly has critical tolerances that need to be controlled within a certain range. The laws of probability state that the probability that every part in an assembly is a combination of small tolerances or large tolerances is very small. And following the normal distribution of tolerances (Figure 6), according to statistical laws, the superposition of all part dimensions tends to fall in the middle of the possible range of tolerances. The goal of the SET-RIGHT method is to control only the most important tolerances that affect bearing clearance. These tolerances may be entirely internal to the bearing, or they may involve some mounting components (ie widths A and B in Figure 1 or Figure 7, and shaft OD and housing ID). The result is that, with a high probability, the bearing installation clearance will fall within an acceptable SET-RIGHT method. Figure 6. Normal distribution of frequency curve variables, x0.135%2.135%0.135%2.135%100% variable arithmetic Average value 13.6% 13.6% 6s68.26% sss s68.26% 95.46% 99.73% x Figure 5. Application frequency of automatic setting of bearing clearance Axial fan and water pump Input shaft Intermediate shaft Power take-off clutch Shaft pump drive main reducer Final input shaft Intermediate shaft Output shaft differential Planetary reduction gear (side view) Steering knuckle SET-RIGHT METHOD PROJECTA-SET TORQUE-SET CLAMP-SET METHOD , sometimes 99.994% or 8σ is required). No adjustment is required when using the SET-RIGHT method. All you have to do is assemble and clamp the machine parts. All dimensions that affect bearing clearance in an assembly, such as bearing tolerances, shaft outside diameter, shaft length, housing length, and housing bore diameter, are considered independent variables when calculating probability ranges. In the Figure 7 example, both the inner and outer rings are mounted using a conventional tight fit, and the end caps are simply clamped on one end of the shaft. s u003d (1316 x 10-6)1/2u003d 0.036 mm3s u003d 3 x 0.036u003d0.108mm (0.0043 in) 6s u003d 6 x 0.036u003d 0.216 mm (0.0085 in) 99.73% fit (probability range) possible interval u003d 0.654 mm (0.0257 inches) 100% of the assembly (for example) selects 0.108 mm (0.0043 inches) as the average clearance. For 99.73% of assemblies, the possible clearance range is zero to 0.216 mm (0.0085 in). †Two separate inner rings correspond to one separate shaft variable, so the axial factor is doubled. After calculating the probability range, the nominal length of the axial dimension needs to be determined to obtain the required bearing clearance. In this example, all dimensions are known except the length of the shaft. Let's take a look at how to calculate the nominal length of the shaft to get the proper bearing clearance. Shaft Length Calculation (Calculation of Nominal Dimensions): B u003d A + 2C + 2D + 2E + F[ [2 where: A u003d average width of housing between outer rings u003d 13.000 mm (0.5118 in) B u003d average of shaft Length (to be determined) C u003d Bearing average width before installation u003d 21.550 mm (0.8484 in) D u003d Bearing width increase due to average inner ring fit*u003d 0.050 mm (0.0020 in) E u003d Bearing width increase due to average outer ring fit* u003d 0.076 mm (0.0030 in.) F u003d (required) average bearing clearance u003d 0.108 mm (0.0043 in.) * Converted to equivalent axial tolerance. Refer to the Timken Tapered Roller Bearings Catalogue for practical guidelines on inner and outer ring fits.
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