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We have continuously maintained our MIL-I-45208A quality assurance program for over 22 years. Combined with our in-house laboratory testing services, we can assure you that every aspect of both your internal requirements and other specification requirements are fully met for military projects.

Interference of the inner ring and shaft decreases when a radial load is applied to the bearing. The interference required for installation to solid shafts is expressed by formulae (7.1) and (7.2) for each load condition.General applications (Fr ≦ 0.3C0r)Δ dF = 0.08(d ∙ Fr / B)1/2 N ············ (7.1)Under heavy load conditions (Fr > 0.3 C0r)Δ dF = 0.02(Fr / B) N ············ (7.2)Where:Δ dF : Required effective interference according to radial load μmd : Bearing bore mmB : Inner ring width mmFr : Actual radial load, NC0r : Basic static load rating NFor solid shafts, please contact NTN Engineering.

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In some cases, an improper fit may lead to damage and shorten bearing life. Therefore it is necessary to carefully select the proper fit. Some possible bearing failures caused by an improper fit are listed below.

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Selection of a proper fit is dependent upon thorough analysis of bearing operating conditions, including consideration of:

Bearing fit is governed by the tolerances selected for bearing shaft diameters and housing bore diameters.Widely used fits for Class 0 tolerance bearings and various shaft and housing bore diameter tolerances are shown in Fig. 7.1.Generally-used, standard fits for most types of bearings and operating conditions are shown in Tables 7.2 to 7.7.

Interference between inner rings and steel shafts is reduced as a result of temperature increases (difference between bearing temperature and ambient temperature, Δ T) caused by bearing rotation. Calculation of the minimum required amount of interference in such cases is shown in formula (7.3).Δ dT = 0.0015 ∙ d ∙ Δ T ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙(7.3)Δ dT : Required effective interference for temperature difference μmΔ T : Difference between inner ring temperature and ambient temperature °Cd : Bearing bore mm

Decades of experience working with virtually every major U.S. military mean we understand the rigorous requirements of military shipbuilding projects—from exclusive military specifications to testing and certification requirements. That’s why the companies that work on U.S. military ships trust Tioga Military®.

To discuss your military project needs with a knowledgeable expert in the industry, contact Bennett Keiser at 215-831-0700.

(1) For bearing rings under rotating loads, a tight fit is necessary. (Refer to Table 7.1) “Raceways under rotating loads” refers to raceways receiving loads rotating relative to their radial direction. For bearing rings under static loads, on the other hand, a loose fit is sufficient.

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(2) For non-separable bearings, such as deep groove ball bearings, it is generally recommended that either the inner ring or outer ring be given a loose fit.

(3) Consideration must also be given to the fact that fit selection will effect internal bearing clearance selection. (refer to page A-88.)

For rolling bearings, it is necessary to fix inner and outer rings on the shaft or in the housing so that relative movement does not occur between fitting surfaces during operation or under load. This relative movement between the mating surfaces of the bearing and the shaft or housing can occur in a radial direction, an axial direction, or in the direction of rotation. Types of resultant fit include tight, transition and loose fits, which describe whether or not there is interference between the bearing and the shaft or housing.The most effective way to fix the mating surfaces between a bearing and shaft or housing is to apply a “tight fit.” The advantage of a tight fit for thin walled bearings is that it provides uniform load support over the entire ring circumference without any loss of load carrying capacity. However, with a tight fit, ease of installation and disassembly is lost; and when using a non-separable bearing as the floating-side bearing, axial displacement is not possible. For this reason, a tight fit cannot be recommended in all cases.

Interference decreases because the mating surface is smoothed by the resultant fit (surface roughness is reduced). The amount the interference decreases depends on the roughness of the mating surfaces. It is generally necessary to anticipate the following decrease in interference.For ground shafts: 1.0 to 2.5 μmFor machined shafts: 5.0 to 7.0 μmThe interference including this decrease amount is called effective interference.

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Table 7.2: Fits for radial bearingsTable 7.3: Fits for thrust bearingsTable 7.4: Fits for electric motor bearingsTable 7.6: Inch series tapered roller bearings Fits of (ANSI/ABMA CLASS 4)Table 7.7: Inch series tapered roller bearings Fits of (ANSI/ABMA CLASS 3, CLASS 0)Table 7.5 shows fits and their numerical values.

Tioga Military® offers one of the largest and most diverse inventories of military-spec critical materials in the world. Combined with the logistical advantages we gain through our close relationships with top mills, it’s no wonder you’ll find Tioga Military® materials onboard every U.S. Navy nuclear aircraft carrier and countless other U.S. military vessels across the world.

When bearing rings are installed with an interference fit, tensile or compressive stress may occur along their raceways. If interference is too great, this may cause damage to the rings and reduce bearing life. The maximum stress due to the resultant fit must not exceed approximately 127 MPa for safety. If the value is to be exceeded, consult NTN Engineering.See section “17.4 Resultant fit surface pressure” for the calculation method of maximum stress due to the resultant fit.

When materials other than steel are used for shafts and housings, the fits between the inner ring and the shaft and the outer ring and the housing change because of difference in the expansion coefficient of each material as the temperature rises during the rotation of the bearing. Therefore, it is necessary to set the resultant fit with expansion coefficients in consideration. The calculation formula of the change in interference is shown below.Δ dTE = (α1‒α2 )× d × Δ TΔ dTE : Change in interference caused by difference in the expansion coefficients mmα1 : Bearing expansion coefficient 1/°Cα2 : Shaft and housing expansion coefficient 1/°Cd : Reference dimension of resultant fit mmΔ T : Temperature increase by bearing rotation °C(Expansion coefficient: See Table 13.19 in “13. Bearing Materials.”)