Impact of humidity on sfu ball screws
sfu ball screws, as high-precision transmission components, their core performance (transmission accuracy, service life, operational stability) is closely related to environmental humidity. Moisture in the air, through direct contact, infiltration or chemical reaction, has a multi-dimensional impact on the metal parts, lubrication system and sealing structure of the screw, which is summarized as follows.
First, the corrosion and damage to the metal core components
sfu ball screws of the screw shaft, nut substrate, ball and raceway are mostly made of high carbon steel (such as SUJ2) or alloy structural steel, the surface is quenched, ground and other processes in order to obtain high precision and abrasion resistance, but the chemical activity of the metal material makes it exceptionally sensitive to humidity.
Progressive destruction of electrochemical corrosion
In an environment with a relative humidity of more than 60%, moisture in the air will form a continuous film of water on the metal surface. If there are traces of salt in the air (e.g., in coastal areas) and industrial dust (containing sulfide and nitrogen compounds), the film of water will become an electrolyte solution, triggering electrochemical corrosion: a primary cell is formed on the metal surfaces of the screw shafts and nuts, and the anodic region The iron atoms in the anodic region lose electrons to form Fe²⁺, which combines with oxygen and hydroxide in the water to generate ferrous hydroxide, which oxidizes to reddish brown rust (Fe₂O₃・nH₂O).
Initial corrosion is only manifested as localized spots (diameter 0.1-0.5mm), but it will destroy the mirror precision of the raceway surface (Ra ≤ 0.4μm), resulting in tiny vibrations when the ball rolls, and the transmission noise rises from normal ≤ 55dB to more than 65dB.
Long-term high humidity (such as humidity > 80% for 1 month) will make the corrosion expansion to the entire raceway, the formation of corrosion grooves distributed along the helix, at this time the contact area of the ball and the raceway to reduce the 30% or more, the local stress increases, which may lead to the raceway spalling (fish scale debris), directly leading to the transmission accuracy of ± 0.01mm / 300mm from ±0.01mm/300mm to ± 0.1mm / 300mm or more, can not meet the needs of precision equipment. It is impossible to meet the demands of precision equipment.
Condensation damage in low temperature and high humidity environment
When the ambient temperature plummets (e.g., the temperature difference between day and night in the workshop is >15℃) and the humidity is >70%, the water vapor in the air will condense into dew on the surface of the screw and form a state of "liquid water directly immersed". This condensate not only accelerates corrosion, but also penetrates into the tiny gap between the ball and raceway (approx. 0.001-0.005mm), and at low temperatures (e.g. <10℃) may trigger localized icing, leading to "stalling" at the start-up of the Screw - Motor Drive Torque needs to be increased by 20%-30% to overcome the icing resistance, and in serious cases, it will cause the rigid impact of the ball and raceway, resulting in permanent deformation.
Second, the performance of the lubrication system attenuation effect
sfu ball screws rely on grease (such as lithium grease, polyurea grease) to form a film of oil, to achieve friction reduction between the ball and raceway, rust prevention and buffer. Humidity destabilizes the lubrication system through both physical dilution and chemical deterioration.
Emulsification and Failure of Grease
When humidity is >65%, water vapor will slowly penetrate into the grease through the gaps in the screw nut (e.g., the mating gap between the seal and the screw shaft). For ordinary lithium grease, when the moisture content exceeds 5%, emulsification will occur - the grease structure changes from a uniform colloidal state to an emulsion separating oil and water, and the film strength decreases from 0.05MPa to 0.02MPa or less. At this time, the probability of direct metal contact between ball and raceway increases, and the wear rate increases by 3-5 times, and there will be obvious "stuttering" when the screw is running, and even high-frequency vibration when it is running at high speed (e.g., the speed is >3000r/min), which affects the positioning accuracy.
Additive Consumption and Protection Failure
High-quality grease is usually added with rust inhibitors (e.g., calcium sulfonate) and antioxidants (e.g., phenolic compounds) to enhance protection. In high humidity environments, water vapor reacts preferentially with rust inhibitors to form soluble metal soap salts, causing the concentration of rust inhibitors to drop by more than 40% within 3 months. When a grease's rust protection is lost, the metal surface loses its protective layer, and even when humidity is reduced to 50%, the rate of rusting is still two times higher than normal. In addition, moisture will accelerate the decomposition of antioxidants, so that the oxidative stability of the grease (high temperature resistance, aging resistance) is reduced, and the service life of the grease is shortened from 12 months to less than 6 months.
Third, the risk of blockage to the sealing and circulation system
SFU The sealing structure (e.g. dust ring, sealing ring) and the ball circulation channel (reverser, ball return groove) of the ballscrew are the key to guarantee the internal cleanliness, and the high humidity environment will reduce the system's sealing and smoothness in two ways, through the physical aging and the deposition of impurities.
Aging and Hardening of Seals
Seals commonly used in screws (e.g., polyurethane U-rings, nitrile butadiene rubber lip rings) in environments with humidity >70% will dissolve due to water absorption (volume increase of 5%-10%), while the crosslinked structure of the rubber molecular chain is disrupted by the water, resulting in a decrease in the modulus of elasticity of 20%-30%. Seals of the "lip" and the screw shaft of the adhesive force weakened, with the gap expanded from 0.01mm to 0.05mm or more, not only can not block the intrusion of water vapor, but also make the outside world of dust (such as metal shavings, fibers and impurities) with the airflow into the nut inside, and wet lubricating grease mixed with the formation of oil sludge, clogging back to the bead groove (diameter is usually <5mm), resulting in ball circulation. 5mm), resulting in poor ball circulation, triggering "stuck" failure.
Microbial growth in the circulation channel
In warm and high humidity environments (temperature 25-35°C, humidity >70%), the water vapor that seeps in combines with the organic components in the grease (e.g., hydrocarbons in the base oil) and may grow mold (e.g., Aspergillus, Penicillium). Mold mycelium will be entangled in the surface of the ball, forming a diameter of 0.1-0.3mm "film", resulting in uneven resistance to ball running; at the same time, mold metabolism of organic acids (such as citric acid) will further corrode the metal surface, the formation of "microbial-induced corrosion ", this corrosion and ordinary rust superposition, will make the service life of the screw shortened to the design value of 1 / 3.
Four, on the long-term storage and downtime state of the hidden damage when
SFU Ball Screws long-term downtime (such as equipment maintenance, seasonal shutdown) or storage, the impact of humidity is more insidious and more destructive. In an unprotected environment with >60% humidity, residual moisture on the surface of the screw will form an "occlusion cell" - a potential difference between the area covered by corrosion products (rust) and the bare metal, accelerating localized corrosion, which can form on the bottom of the raceway to a depth of 0.02-0.5mm within 3 months. Within 3 months, a corrosion crater with a depth of 0.02-0.05mm can be formed at the bottom of the raceway. These microscopic defects in the subsequent operation, will become a stress concentration point, in the alternating load (such as frequent forward and reverse rotation) triggered by fatigue cracks, resulting in the screw in the operation of 1,000 hours of sudden breakage, resulting in equipment downtime accidents.
In addition, humidity fluctuations in the storage environment (e.g. day and night humidity difference > 20%) will lead to repeated "hygroscopic - drying" of the metal parts of the screw, triggering thermal expansion and contraction stress, which, together with the volumetric expansion generated by corrosion, may result in the tightening of the nut and the screw shaft, or even the need for destructive dismantling to be able to separate them, which will directly lead to the scrapping of the parts.
Summarize and respond to the logic
The impact of humidity on sfu ball screws is the result of the synergistic effect of multiple links: from metal corrosion to lubrication failure, from sealing damage to circulation blockage, which ultimately leads to a decline in transmission accuracy, shorten the life of the drive and even sudden failure. For different humidity scenarios, need to take layered protection measures: low humidity (40% -60%) environment to regular lubrication and maintenance; high humidity (60% -80%) need to strengthen the seal (such as upgraded to double-lip seals) and the use of waterproof grease; high humidity (> 80%) or harsh environments need to be combined with stainless steel (such as 304 screw), active dehumidification equipment (such as rotor dehumidifier) and Regular antirust treatment can fundamentally curb the negative impact of humidity and guarantee the long-term stable operation of ball screws.
Contact Us
📞 Phone: +86-8613116375959
📧 Email: 741097243@qq.com
🌐 Official website: https://www.automation-js.com/
