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How to determine the preload of a ball screw?
Excessively tight or loose preload of the ball screw
Beijing will implement vehicle gasoline and diesel Euro II standards from October 1.
Beijing, September 25 (Reporter Li Zhiyong) — In an effort to improve air quality and reduce pollution from vehicle emissions, Beijing will enforce new fuel standards starting October 1, 2004. All gasoline and diesel fuels sold for automotive use must now meet the European Union's Euro 2 emission standards. This move is part of a broader strategy to address environmental challenges in the city.
Li Kunsheng, an assistant researcher with the Atmospheric Environmental Management Department at the Beijing Municipal Environmental Protection Bureau, noted that while there have been improvements in Beijing’s environment, the overall situation remains serious. With the city’s bid to host the 2008 Olympic Games, the goal is to achieve Grade 2 or better air quality on 80% of days by 2008. However, current levels are only around 60%, highlighting the urgency of action.
According to Li, the primary source of air pollution in Beijing is particulate matter, which contributes to hazy skies and poor visibility. These fine particles can have severe health impacts, particularly on respiratory and cardiovascular systems. He pointed out that vehicle exhaust and dust from construction sites are the main contributors to this type of pollution.
Although nearly four years remain until the 2008 Olympics, the task of environmental improvement is still daunting. To support this initiative, Zhou Zhanzhu, director of the Important Commodity Management Subcommittee at the Beijing Municipal Administration for Industry and Commerce, emphasized the importance of enforcing the new fuel standards.
From mid-September to September 30, various industry branches were involved in promoting regulations and policies related to oil distribution. Starting October 1, the bureau began comprehensive supervision of all oil companies, ensuring that they sell fuels meeting the Euro 2 standard. A transition period was set from October 1 to October 20, during which existing stocks would be replaced. On October 20, inspections will be conducted, and any company failing to comply will face strict penalties.
It is also expected that by July 1, 2005, Beijing will implement even stricter Euro 3 fuel standards, further demonstrating the city’s commitment to cleaner air and sustainable development.
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Materials: Bearing steel and stainless steel are recommended.
Precision grade: C3/C5 (repeatable position accuracy is up to 8μm.)
Diameter: >16mm
Thread direction: Left-hand/Right-hand
Circulation method:Â Internal circulation
Determination of Ball Screw Preload
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Applying preload to the nut in a ball screw assembly can enhance the axial stiffness and positioning accuracy of the ball screw pair. Therefore, if only considering the stiffness and positioning accuracy of the ball screw pair, a larger preload is more beneficial, as it can better eliminate axial clearance caused by elastic deformation. Conversely, an excessively small preload, even if it eliminates axial clearance, does not necessarily improve stiffness.
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This is because the preload must be sufficient to eliminate the "low-stiffness zone" in the preloaded nut. Due to inherent errors (such as lead errors) between the ball screw shaft and nut components in the preloaded section of a double-nut assembly, some segments may exhibit higher contact stiffness after deformation (due to tighter contact), while others may show lower stiffness (due to looser contact). The latter is what is referred to as the "low-stiffness zone." To improve axial contact stiffness, the preload must be large enough to eliminate such low-stiffness zones, thereby truly achieving enhanced axial stiffness.
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However, an excessively large preload is also detrimental. It will increase the driving torque, reduce transmission efficiency, accelerate contact fatigue and wear between balls and raceways, and shorten the service life.
Causes of Backlash in Ball Screws
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1. Large manufacturing errors of the ball screw or axial movement
2. Excessively tight or loose pressure plate in the fit between the screw shaft and slide plate
3. Interference from other mechanical components
4. Loose taper sleeve of the screw shaft coupling
5. Excessively tight or loose preload of the ball screw support bearing
6. Excessively tight or loose wedge in the fit between the ball screw shaft and slide plate