Is Preloading Deep Groove Ball Bearings Necessary for High-Speed Performance

1. Working Principle and Internal Clearance of Deep Groove Ball Bearings

Standard State of Deep Groove Ball Bearings Deep Groove Ball Bearings are designed primarily to withstand radial loads, consisting of an inner ring, an outer ring, steel balls, and a cage. In their original factory state, these bearings typically have Internal Clearance, meaning there is a tiny physical gap between the balls and the raceways. This design compensates for interference fits during installation and metal thermal expansion during operation, preventing the bearing from seizing. Difference Between Clearance and Preload

• Clearance State: When the bearing is unloaded or lightly loaded, there is physical space between the balls and raceways. Friction torque is minimized, but rotational accuracy and rigidity are relatively low.
• Preload State: A permanent axial or radial force is applied through physical means to bring the balls and raceways into tight contact. Once the Deep Groove Ball Bearing enters a preloaded state, internal clearance is eliminated, and the rolling elements are under compression, enhancing system stability.

Internal Clearance vs. Preload Parameter Comparison Table

Technical Point: Deep Groove Ball Bearings typically use C3 (Large), CN (Standard), or C2 (Small) clearance grades. In applications requiring preload, standard or small clearance models are usually selected to achieve the ideal working state through axial displacement adjustment.

2. Determination Criteria for Preloading Deep Groove Ball Bearings

In mechanical system design, Deep Groove Ball Bearings do not always require preloading. Whether to apply a preload force depends primarily on the specific requirements for precision, speed, and stability of the application.

Non-Mandatory Preload Scenarios

In the following common scenarios, Deep Groove Ball Bearings typically operate with positive clearance and do not require preloading:

• Standard Industrial Motors: Allows for slight axial movement, prioritizing the reduction of friction loss.
• Household Appliances: Such as fans or washing machines, focusing on low cost and low heat generation.
• Low-Speed Transmissions: When the speed is significantly lower than the limiting speed, the impact of clearance on service life is minimal.

Special Scenarios Requiring Preload

When application requirements exceed basic load-bearing capabilities, a preload must be applied to Deep Groove Ball Bearings:

• High-Precision Rotation: To eliminate radial and axial runout, ensuring absolute trajectory accuracy of the shaft center.
• Suppression of "High-Speed Skidding": Under extremely high speeds and light loads, balls may slide rather than roll due to inertia. Preload provides the necessary minimum load to prevent raceway smearing.
• Enhanced Rigidity: When subjected to alternating loads or cantilever loads, preload reduces shaft deflection.
• Noise Reduction Requirements: To eliminate the impact noise of balls entering the load zone, making operation smoother.

Operating Parameter Comparison: Preload vs. Clearance

3. Primary Methods for Achieving Preload in Deep Groove Ball Bearings

In the application of Deep Groove Ball Bearings, preloading techniques are mainly divided into Axial Preload and Radial Preload.

Spring Preload

This is the most common preloading method for Deep Groove Ball Bearings. A wave spring or helical spring is typically placed against the side of either the outer or inner ring.

• Principle: The spring provides a constant axial pressure, pushing the balls against one side of the raceway.
• Advantages: The preload force remains basically constant even if component dimensions change slightly due to thermal expansion; excellent for suppressing vibration at high speeds.
• Disadvantages: System rigidity is lower compared to fixed preloading.

Fixed Preload (Positioning Preload)

The relative position of the bearings is forced into adjustment using mechanical components such as locknuts, spacers, or precision end covers.

• Principle: Relative displacement is generated between a pair of Deep Groove Ball Bearings by tightening a nut or grinding spacer thickness to eliminate internal clearance.
• Advantages: Provides extremely high system rigidity and can withstand large tilting moments.
• Disadvantages: Highly sensitive to thermal expansion; if the shaft expands, the preload force can increase sharply.

Parameter Comparison: Spring Preload vs. Fixed Preload

Radial Preload

Achieved through Interference Fit.

• Method: Selecting bearings with small clearance (e.g., C2 group) and increasing the interference between the shaft/inner ring or housing/outer ring to expand the inner ring or contract the outer ring.
• Note: This method requires extremely tight machining tolerances.

4. Effects of Preload on Deep Groove Ball Bearing Performance

Positive Effects of Preload

• Optimized Load Distribution: Once preload is applied, all balls contact the raceway, distributing the load more evenly across a larger number of rolling elements.
• Reduced Uncontrolled Movement: Preload eliminates axial endplay and radial play, ensuring high synchronization and low jitter.
• Noise Suppression: By eliminating gaps for component collisions, high-frequency vibration and metallic clatter are reduced.

Risks of Negative Effects

• Rapid Temperature Rise: Preload increases the frictional torque. Increased friction directly leads to higher heat generation.
• Shortened Service Life: If the preload force exceeds the design limit, internal stress increases sharply, causing premature fatigue flaking.

Performance Parameter Trends Under Different Preload Levels

5. FAQ for Deep Groove Ball Bearings

Q1: Can Deep Groove Ball Bearings handle high preload like Angular Contact Ball Bearings?

A: No. The initial contact angle of a Deep Groove Ball Bearing is 0 degrees. Applying excessive axial preload forces the balls against the raceway edges, creating edge stresses that lead to overheating and early failure.

Q2: How can I determine if the preload on a Deep Groove Ball Bearing is appropriate?

A: This can be determined by "Friction Torque" and "Operating Temperature Rise."

• Starting Torque Test: Rotation should be smooth; starting torque should be slightly higher than the non-preloaded state but without noticeable resistance.
• Temperature Observation: Temperature should stabilize after 30-60 minutes. If it continues to climb, the preload is excessive.

Q3: How do I choose the amount of preload force when using a spring?

A: It is generally estimated based on the Basic Static Load Rating (C0) of the bearing:

• Light Preload: 0.005 x C0 to 0.01 x C0
• Medium Preload: 0.01 x C0 to 0.02 x C0

Q4: How does ambient temperature affect the preload of Deep Groove Ball Bearings?

A: It has a huge impact on Fixed Preload. Thermal expansion of the shaft can significantly increase the preload force. In contrast, Spring Preload is insensitive to temperature changes, with force fluctuations typically under 5%.

Q5: Why do some Deep Groove Ball Bearings become noisier after preloading?

A: This is usually due to "Over-Preloading" causing raceway deformation or lubricant film breakdown. When contact pressure exceeds the lubricant's load-carrying capacity, metal-to-metal contact occurs, resulting in humming or high-frequency grinding sounds.