Method for automatically setting bearing clearance


In addition to preset clearance bearing components, Timken has developed five commonly used methods for automatically setting bearing clearance (ie SET-RIGHT, ACRO-SET, PROJECTA-SET, TORQUE-SET and CLAMP-SET) as manual Adjustment options. Refer to Table 1-”Comparison of tapered roller bearing set clearance methods” to illustrate the various characteristics of these methods in a table format. The first row of this table compares the ability of each method to reasonably control the “range” of bearing installation clearance. These values ​​are only used to illustrate the overall characteristics of each method in setting the clearance, regardless of whether the clearance is set to “preload” or “axial clearance”. For example, under the SET-RIGHT column, the expected (high probability interval or 6σ) clearance change, 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 the axial clearance and the preload to maximize the performance of the bearing/application. Refer to Figure 5-”Application of Automatic Method to Set Bearing Clearance”. This figure uses a typical four-wheel drive agricultural tractor design as an example to illustrate the general application of the tapered roller bearing setting clearance method.
We will discuss in detail the specific definitions, theories and formal processes of each method application in the following chapters of this module. The SET-RIGHT method obtains the required clearance by controlling the tolerance of the bearing and the installation system, without the need to manually adjust the TIMKEN tapered roller bearing. 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 of the machining tolerances of the shaft/bearing housing, while strictly controlling (with the aid of accuracy grades and codes) the critical tolerances of the bearings. This method believes that each component in the assembly has critical tolerances and needs to be controlled within a certain range. The law of probability shows that the probability of each component in the assembly being a small tolerance or a combination of large tolerances is very small. And follow the “normal distribution of tolerance” (Figure 6), according to statistical rules, the superposition of all parts sizes tend to fall in the middle of the possible range of tolerance. 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 may involve certain mounting components (ie, widths A and B in Figure 1 or Figure 7, as well as shaft outer diameter and bearing housing inner diameter). The result is that, with a high probability, the bearing installation clearance will fall within an acceptable SET-RIGHT method. Figure 6. Normally distributed frequency curve variable, 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 method Frequency of front wheel engine reduction gear Rear wheel power take-off Rear axle center articulated gearbox Axial fan and water pump input shaft intermediate shaft power take-off clutch shaft pump drive device main reduction main reduction differential input shaft intermediate shaft output shaft differential planetary reduction device (side view) knuckle steering mechanism tapered roller bearing clearance Setting method SET-RIGHT method PROJECTA-SET method TORQUE-SET method CLAMP-SET method CRO-SET method Preset clearance component range (usually the probability reliability is 99.73% or 6σ, but in production with higher output , Sometimes requires 99.994% or 8σ). No adjustment is required when using the SET-RIGHT method. All that needs to be done is to assemble and clamp the machine parts.
All dimensions that affect bearing clearance in an assembly, such as bearing tolerances, shaft outer diameter, shaft length, bearing housing length, and bearing housing inner diameter, are considered independent variables when calculating probability ranges. In the example in Figure 7, both the inner and outer rings are mounted using a conventional tight fit, and the end cap is simply clamped at one end of the shaft. s = (1316 x 10-6)1/2= 0.036 mm3s = 3 x 0.036=0.108mm (0.0043 in) 6s = 6 x 0.036= 0.216 mm (0.0085 inch) 99.73% of the assembly (probability range) possible interval = 0.654 For 100% of mm (0.0257 inch) assembly (for example), select 0.108 mm (0.0043 inch) as the average clearance. For 99.73% of the assembly, the possible clearance range is zero to 0.216 mm (0.0085 inch). †Two independent inner rings correspond to an independent axial variable, so the axial coefficient is twice. 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 except the length of the shaft are known. Let’s take a look at how to calculate the nominal length of the shaft to get the proper bearing clearance. Calculation of the length of the shaft (calculation of the nominal dimensions): B = A + 2C + 2D + 2E + F[ [2where: A = the average width of the housing between the outer rings = 13.000 mm (0.5118 inches) B = the average of the shaft Length (TBD) C = Average bearing width before installation = 21.550 mm (0.8484 inches) D = Increased bearing width due to average inner ring fit* = 0.050 mm (0.0020 inch) E = Increased bearing width due to average outer ring fit* = 0.076 mm (0.0030 inch) F = (required) average bearing clearance = 0.108 mm (0.0043 inch) * Converted to equivalent axial tolerance. Refer to the “Timken® Tapered Roller Bearing Product Catalog” chapter of the practice guide for inner and outer ring coordination.