Determination of machining allowance after quenching of outer ring of carburized steel bearing
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**Determination of Machining Allowance After Quenching of the Outer Ring of a Carburized Steel Bearing**
Home > Bearing Knowledge > Determination of Machining Allowance After Quenching of the Outer Ring of a Carburized Steel Bearing
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**Source:** China Bearing Network | **Date:** February 3, 2013
After carburizing and quenching, the outer ring of a steel bearing often experiences a phenomenon known as "elastic retraction." This refers to the slight shortening that occurs when the part is removed from the mold. Elastic retraction is a critical factor in determining the final dimensions of the bearing and must be carefully accounted for during machining.
This article explores the calculation of elastic retraction for the outer ring of a carburized steel double-row tapered roller bearing. It also discusses how to determine the remaining machining allowance after turning, estimate the theoretical grinding amount post-quenching, and provides a practical example to illustrate these concepts.
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### 1. Calculation of Elastic Retraction
From production theory, it is understood that the amount of elastic retraction depends on the wall thickness and outer diameter of the workpiece. An empirical formula has been established:
$$ d = \frac{26B^4}{D^3} \quad (1) $$
Where:
- $ B $: Maximum wall thickness of the workpiece
- $ D $: Outer diameter of the bearing race
- 26: A constant derived from repeated theoretical analysis under rotary quenching conditions
This formula is applicable for workpieces with an outer diameter ranging from 200 mm to 300 mm.
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### 2. Determining the Remaining Machining Allowance After Turning
The machining allowance after turning is influenced by the elastic retraction. The greater the retraction, the larger the required roughing allowance. According to theoretical analysis and production experience, the allowance after turning ($ H - D_1 $) is proportional to the thickness-to-diameter ratio of the workpiece:
$$ H - D_1 = 0.042 \times \frac{D}{B} \quad (2) $$
Here, the coefficient 0.042 is based on repeated theoretical data.
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### 3. Theoretical Grinding Amount After Quenching
Once the machining allowance is determined, the theoretical grinding amount after quenching can be calculated. Since the elastic retraction remains relatively stable, the total grinding amount should include both the remaining allowance and the retraction:
$$ H - D_2 = H - D_1 + d \quad (3) $$
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### 4. Example Calculation
For a 197726 bearing, the following parameters are given:
- Maximum wall thickness $ B = 18.85 \, \text{mm} $
- Outer diameter $ D = 230.9 \, \text{mm} $
- Machining allowance after turning $ \Delta D_1 = 0.65 \, \text{mm} $
Using the formulas:
$$ d = \frac{26 \times (18.85)^4}{(230.9)^3} = 0.266 \, \text{mm} $$
$$ H - D_1 = 0.042 \times \frac{230.9}{18.85} = 0.514 \, \text{mm} $$
$$ H - D_2 = 0.514 + 0.266 = 0.78 \, \text{mm} $$
However, the original value of $ \Delta D_1 = 0.65 \, \text{mm} $ led to a measured grinding amount of 0.9 mm, which was higher than the calculated 0.78 mm. Adjusting $ \Delta D_1 $ to 0.5 mm resulted in a measured grinding amount of 0.76 mm, closely matching the calculated value, proving this adjustment more reasonable.
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It's important to ensure that the quenching die matches the turning diagram in size. Theory confirms that the elastic retraction during quenching is sufficient to achieve the desired shape.
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**Link:** [China Bearing Network](http://www.chinabearing.net)
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This article provides essential insights into optimizing machining processes for carburized steel bearings, ensuring precision and efficiency in manufacturing.