**1. Introduction**

40 Heat Treatment – Conventional and Novel Applications

Cambridge, UK, 2001

[31] Bhadeshia H. K. D. H., *Bainite in steels*, 2nd edition, The University Press Cambridge,

[32] PN - 89/ H – 83157 Cast steels for elevated temperature applications. Grades.

Heat treatment of bearing rings implies the risk of deformations caused by internal tension. In order to eliminate internal tension, hardening is followed by tempering. In general, tempering will remove the tension. However, this tempering is not sufficient for the socalled thin-walled rings AX series bearing rings to eliminate the tension. This article discusses how to effectively eliminate occurrence of tensions in thin-walled bearing rings made from 100Cr6 by optimising their heat treatment. Results have been verified by experiments.

Manufacture of roller bearings (figure 1) is a challenging production process. Even though its specific manufacturing operations are widely known and established, some operations in bearing manufacture must be performed within narrow tolerances ranging from only a few micrometres to comply with requirements of tolerance analysis done before the parts are manufactured to ensure that clients receive a quality product that influences safety of plant operation, therefore safety of people. The manufacturing comprises a number of operations needed to produce rings, rolling elements and cages. It includes hammering of forgings at the beginning, turning, heat treatment, cutting, forming, grinding, washing of parts, their description, assembling bearing components and packaging. A number of preventive, intraoperational and final inspections and dimensional, chemical, metallurgic, endurance and other tests are carried out during the manufacturing process [ZVL & ZKL, 1996; ZVL, 2008]. Customers assemble these products in common applications with standard requirements on bearings, but sometimes they have special requirements either for the bearing as a whole, or for any of its parts. In this case it is not sufficient to implement only standard methods and working practices; they have to be modified or optimised. One of such requirements was a request from one of great important American and Deutschland company to produce bearings needed to place a rotor for an axial piston hydroelectric generating set with an inclined plate for one of its tractors. This application has its particulars. It was necessary to

© 2012 Panda et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Panda et al., licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### 42 Heat Treatment – Conventional and Novel Applications

modify the outer ring, inner ring and rolling elements. Mentioned company is considered to be a "Mercedes" in the field of production of tractors, harvesters and similar equipment. The demands on parts are therefore accordingly high. This article will not discuss all the modifications necessary to adjust the technological process of production in order to meet customer's requirements, although they are all interrelated, influence each other and represent a desired outcome of the targeted modification. We will deal only with the parameter that can be affected by heat treatment of the material in order to avoid unwanted deformations in the material and comply with a stricter requirement on ovality for inner rings.

Deformation Reduction of Bearing Rings by Modification of Heat Treating 43

Technologically, ovality results from non-symmetrical distribution of internal tensions before hardening and uneven heating and cooling. Ovality is a certain type of circularity

Since 1950s, devices using very accurate rotational tables or spindles are used in modern industry to measure circularity. The measuring base in this method is the axis of the component to be measured. The measuring device ensures very high accuracy, often better than 0.1 μm. However, it requires time-consuming preparations including centring and alignment of the component, therefore it is intended rather for laboratory measurements. These measuring devices are rarely used in production, also due to their low measuring

Ovality is checked at the output from the heat treatment line. A special diameter gauge (Figure 3) that included a dial deviation meter was used to measure ovality (table 1). Ovality was measured on three rings so that an ovality deviation was recorded after each rotation by 10°. The following procedure was applied. An bearing ring was inserted into the gauge. The ring was rotated manually in 10° increments. A value was read from the deviation meter after each rotation. If the deviation was higher than 0.2 mm, the ring being measured was discarded. It did not meet quality criteria and could not be passed on for subsequent hard

A high deviation in ovality may indicate uneven heating or cooling during heat treatment. Ovality measurement was made on three inner rings selected randomly from different batches. Ring No. 1 shows acceptable ovality up to 0.2 mm in maximum. Subsequent grinding operations can reduce or remove this deviation from circularity. Ring No. 2 shows ovality over 0.2 mm, so it is not suitable for further machining. It must be discarded. The lowest ovality value can be seen in ring No.3. For ring No. 2, it is necessary to identify the cause of such a significant deviation in cylindricality. The whole batch the ring No. 2 comes

Ring rotation (°) 0 10 20 30 40 50 60 70 80 90 100

110 120 130 140 150 160 170 180 190 200 210 220 230 0.18 0.17 0.17 0.16 0.13 0.09 0.04 0.02 0.03 0.04 0.09 0.13 0.16 0.04 0.09 0.13 0.16 0.17 0.18 0.19 0.21 0.2 0.19 0.18 0.17 0.17 0.13 0.14 0.15 0.15 0.14 0.13 0.12 0.11 0.1 0.09 0.05 0.02 0.04

Ring no. 1 0.02 0.04 0.09 0.13 0.16 0.17 0.17 0.18 0.19 0.2 0.19 Ring No. 2 0.21 0.2 0.19 0.18 0.17 0.16 0.13 0.09 0.04 0.03 0.03 Ring No. 3 0.09 0.05 0.02 0 0.02 0.04 0.08 0.09 0.1 0.11 0.12

**2. Ovality measuring on production plant** 

deviation.

capacity.

machining.

Ovality values measured for the rings

from should be checked.

**Table 1.** Measured values of ovality

**Table 2.** Measured values of ovality - continuation

Papers of authors [Jech, 1983; Panda et al., 2011; Vasilko, 1998] address processes of heat treatment of bearing components with related checks and tests (dimensional, chemical, metrological and endurance tests) and technological aspects of production of bearing rings are discussed in [ZVL & ZKL, 1996; ZVL, 2008].

The goal of the work was to modify the tempering process to eliminate or preclude undesirable deformations of the material and to ensure compliance with the stricter requirements for ovality of inner rings (figure 2).

**Figure 1.** Tapered roller bearing

**Figure 2.** Inner ring of Tapered roller bearing
