Q: What is the recommended grease replacement interval for rolling bearings?
A: Equipment using double-shielded or double-sealed bearings typically does not require grease replacement. This is a typical design that uses lubrication to extend life. On the other hand, all other open, single-shielded, or single-sealed bearings should have their grease replaced periodically to remove deteriorated, leaked, or contaminated grease. Generally, operating conditions determine the grease replacement interval.
All greases will deteriorate at certain speeds, even under moderate operating conditions. The main causes are oxidation, excessive oil seepage, and mechanical operation. At high temperatures, oil evaporation may also be a contributing factor. Oxidation eventually increases oil viscosity and causes soap hardening. A small amount of oil seepage is acceptable, but excessive seepage reduces the grease's ability to maintain an effective lubricating film. Mechanical operation or shearing can alter grease properties, such as stability, rendering the grease unsuitable for application requirements.
Excessive oil evaporation can lead to grease hardening. Deterioration usually ends in hardening, drying, and sludge formation, ultimately resulting in grease that neither lubricates the bearing nor prevents contaminants from entering.
Operating factors and other factors affecting grease replacement frequency include: temperature, continuity of use, grease injection volume, bearing size and speed, seal effectiveness, and the suitability of the grease for specific applications.
1. Higher grease temperatures accelerate oxidation; above 49°C, the oxidation rate increases by a factor of 1 for every 10°C increase. High temperatures also increase leakage and grease volatility. Furthermore, grease tends to soften with increasing temperature and may become fluid, leaking from the bearing housing. All other things being equal, high-temperature operation requires more frequent grease replacements or the use of high-temperature resistant grease.
2. Continuous use refers to the number of hours of use per day or other time unit. A grease that is continuously subjected to deterioration factors requires a higher replacement frequency compared to bearing grease that is used only occasionally.
3. A large amount of grease injected into a well-designed bearing housing will last longer than a small amount injected into a scaled-down bearing housing. A small amount of grease will operate more frequently than a fraction of a large amount and will not benefit from spare capacity (including more grease and additives). However, under moderate conditions, a small amount of grease in a factory-pre-filled lubricated seal or shielded bearing may last for a long time, even years.
4. A bearing Dn value (bore diameter [unit: mm] x rotational speed [unit: RPM]) is proportional to the linear speed of the rolling elements and can be used as a basis for determining the lubricant replacement frequency. In bearings operating in the Dn range of 150,000 to 200,000 or higher, the grease in the component channels is subjected to harsh operating conditions and high temperatures. These types of bearings require more frequent grease replacements, and even require the correct selection of grease that does not thin excessively. Some bearing manufacturers use Ndm (speed per minute x bearing pitch diameter in millimeters) instead of Dn. This method generates a higher reference value, but the effects of rolling element size and bearing cross-sectional diameter should be considered.
5. Vibration causes more grease to flow into the rolling element channels, where it is subjected to excessive running and heat. This reduces grease life, especially in high-speed bearings. The churning and shearing action within the bearing breaks down some of the grease, turning it into a fluid capable of causing excessive leakage. Any of these factors necessitates more frequent grease replacements.
6. If the grease is subjected to critical conditions for any of the following important characteristics—oxidation, leakage, pumpability, anti-wear and anti-corrosion properties, or mechanical stability—more frequent grease replacements are generally required.
About LJHB:
LuoYang JinShuo Precision Bearing Co., Ltd. is mainly committed to the R&D and sales of high-precision bearings and other special products, and provides bearings and transmission parts with high performance for customers' equipment. With quick response, from pre-sales technical communication to on-time production delivery, as well as perfect after-sales service, we win the recognition and trust of customers.
Our main products include cylindrical roller bearings, tapered roller bearings, slew bearings, gear drives, spindle bearings, crossed roller bearings, turret bearings, thin-wall bearings, tandem roller bearings, spherical roller bearings, etc. The bearing dimensions rang from 100mm to 6000mm, the accuracy reaches P5, P4 and P2 levels. The bearing are widely used in mining and metallurgy, industrial equipment, industrial gearboxes, petroleum equipment, cranes, medical equipment, robotic equipment, etc. Among them, cylindrical roller bearings with better performance and high-precision deep groove ball bearings have been explored for high-speed tubular strander rotating cable equipment, which have completely replaced imports, saving customers costs and time, and improving work efficiency. It has been recognized and widely praised by customers.
Contact LJHB:
Address: Yiyang Bearing Industry Zone, Luoyang City, China 47100
Tel/Wechat: +86-18037970383
Whatsapp: +86-18037970383
Fax: 0086-379-65199160
E-mail: lyjh@lyjhbearing.com
Website: www.chinajhbearing.com
