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Abstract: Affected by loading during operation and traditional cage structure, the crossed roller bearings used on main shaft of heavy machinery fail quickly. The rollers may be turned over and break away from raceway. With optimized design, the problem can be solved and users’ needs can be satisfied.
Key words: heavy machinery; crossed roller bearings; rolling elements; cage; optimized design
1. Preface
The rolling element of the cross roller bearing is a cylindrical roller, installed in a 1:1 cross arrangement, which can withstand both radial loads and axial loads and overturning moments. It has high support rigidity and high rotational accuracy. Due to its compact structure and excellent performance, it is widely used in various heavy equipment fields. The bearing cage usually adopts a split isolation block structure, which has the potential problem of difficult to ensure balanced clearance between rolling elements. When such bearings are installed vertically, such as the main shaft end of a free forging hydraulic press that serves as radial support and axial thrust, the force of gravity between the rolling element and the cage during operation can easily cause uneven clearance between the rolling elements, leading to poor lubrication of the rolling elements with small clearances, and even causing individual rolling elements to flip and detach from the raceway at large clearances, leading to premature bearing failure.
2. Optimization Plan
Based on analysis and calculation, combined with multiple experiments, the following optimization plan is proposed to address this issue.
2.1 Optimization Design of Rolling Element
Due to the common use of cross roller bearings in special applications, the overall dimensions are generally given by the user. As shown in Figure 1, after determining the dimensions of inner diameter d, outer diameter D, height B of shaft ring (part 4), height C of seat ring (part 1), diameter D1 and d1 of shaft ring and seat ring installation holes, considering the position of installation holes and the occupied space, the dimensions of bearing rotation center diameter Dpw, rolling element (part 3) diameter Dw, and length Lw can be determined based on the cross-section formed by bearing inner diameter, outer diameter, and height.
Dpw=0.5（D1＋d1） （1）
Dw=(0.40~0.55) (B or C) [integer value or accurate to 0.5] (2)
The value of Dw must meet the requirement that the minimum distance between the raceway and the installation hole wall is not less than (0.2~0.25) Dw.
The selection of the length Lw of the rolling element should avoid chord interference with the raceway and prevent it from affecting the installation of the rolling element and the performance of the bearing. After analysis and calculation, the optimization formula for the length of the rolling element is obtained:
[value to the nearest 0.1] (3)
Selection of the number of rolling elements
[even value] (4)
Figure 1 Bearing Structure
2.2 Optimization Design of Cage
As shown in Figure 2, the cage (part 2) is composed of several sections of carbon alloy thin steel plates welded together. Before welding, rectangular pocket holes are punched equidistant on each section of the steel plate, and then the steel plate is machined into an arc shape through mechanical stamping. After mechanical shaping, welding is carried out. After welding, secondary shaping, roundness testing, and surface phosphating are carried out. During the operation of the bearing, this integral retainer can effectively ensure the balance and stability of the clearance between the rolling elements, and prevent the rolling elements from flipping at places with large clearances.
After calculation and multiple experimental comparisons, the values of the pocket length JL, width Jb, and cage steel plate thickness Js are determined as follows:
[rounded to 0.5] (5)
Jb=(1.03-1.05) Dw [rounded to 0.5] (6)
Js=(0.1-0.15) Dw [integer value] (7)
Verify the width dimension of the cage beam based on the number of rolling elements Z τ， To ensure that τ≥ 0.14Dw。 If not, it can be obtained by adjusting the roller diameter Dw.
[rounded to 0.01] (8)
2.3 Optimization Design of Shaft Ring and Seat Ring Edge Diameter
The values for the diameter dp of the shaft ring edge guard and the diameter Dp of the seat ring shaft ring edge guard are as follows:
dp=Dpw－Js－ ε [Value to the nearest 0.1] (9)
Dp=Dpw＋Js ＋ ε [Value to the nearest 0.1] (10)
In the equation: ε= （0.005～0.010）·（Dpw－Js） （11）
3 Conclusion
The optimized integral cage effectively controls the imbalance of the rolling element gap and reduces the probability of rolling element flipping. At the same time, due to the good guidance of the rolling elements, there is sufficient space between them to store lubricating grease, thereby improving lubrication conditions and increasing the service life of the bearings. After being used by multiple domestic heavy equipment manufacturing enterprises, the improvement effect is obvious, not only ensuring the overall service life and working stability of the equipment, but also indirectly increasing its working speed, meeting the user's usage requirements.
More about KYOCM Cylindrical Roller Bearing:
KYOCM cylindrical roller bearings can meet the challenges of applications faced with heavy radial loads and high speeds. Accommodating axial displacement (except for bearings with flanges on both the inner and outer rings), they offer high stiffness, low friction and long service life. KYOCM cylindrical roller bearings include single row cylindrical roller bearings, double row cylindrical roller bearings and four row cylindrical roller bearings.
Cylindrical roller bearings are also available in sealed or split designs. In sealed bearings, the rollers are protected from contaminants, water and dust, while providing lubricant retention and contaminant exclusion. This provides lower friction and longer service life. Split bearings are intended primarily for bearing arrangements which are difficult to access, such as crank shafts, where they simplify maintenance and replacements.
2023-05-18