An innovative grease for all bearings

Lubrication of main, generator, blade pitch and yaw system bearings

To date, operators of wind power plants frequently have had to obtain different types of grease to suit the varying speeds, loads, sizes and functions of the individual bearings involved. Commonly wind parks contain units from different manufacturers and different models, so various lubricant recommendations have to be followed.
This entails extra expenses for logistics, warehousing and grease disposal, as well as a permanent risk of lubricant confusion. Since most turbines are relubricated manually, service technicians have to carry all these different lubricants with them when on maintenance visits. All required lubricants may also not be always available at certain locations worldwide.

Innovation from Klüber Lubrication: a single grease for all wind turbine bearings

Klüber Lubrication can now serve the differing requirements of all bearings in a wind turbine with a single lubricant consisting of a special base oil mixture and a carefully selected additive package: Klüberplex BEM 41-141 is a speciality lubricant for rolling and plain bearings operating under high loads. It has been developed for
– the wind turbine main bearing, which rotates slowly and is subject to high loads and vibration.
– the relubrication of generator bearings, which run at high speeds and have a high temperature. Initial lubrication takes place at the manufacturer, e.g. with Klüberplex BEM 41-132.
– blade pitch and yaw bearings, which also operate under high loads, vibration and oscillating motion.

Klüberplex BEM 41-141 meets and even exceeds, today’s requirements of bearing and wind turbine OEMs and operators. The lubricant’s wide service temperature range, its good pumpability and precise metering in centralised lubricating systems, as well as the good grease distribution and oil release, ensure a trouble-free operation of the wind power plant.
Good wear protection – even under vibration – extends the bearings’ service life. Klüberplex BEM 41-141 also helps to prevent the costly damage that tends to arise during standstill. The turbine may be stopped less often, which makes for a significant rise in productivity. The operator’s repair and spare parts costs decrease, as does the cost for used grease disposal. With Klüberplex BEM 41-141, the plant operator can restrict his lubricant range to a single grease! This means that lubricant confusion can be eliminated, and storage and logistics are simplified.

Why can Klüberplex BEM 41-141 be used for all bearings?

We have developed Klüberplex BEM 41-141 for the lubrication of bearings in wind turbines, taking into account all critical conditions under which the individual bearings operate. We attached particular importance to the lubricant’s performance during standstill and swaying with brakes engaged. These are extremely taxing operating conditions because friction is concentrated on the same point over an extended period of time. In Klüberplex BEM 41-141, the consistency and base oil viscosity were carefully tuned and combined with efficient oil release to enable the reliable build-up of a protective lubricant film and excellent grease distribution.

Klüberplex BEM 41-141 testing

In order to satisfy the numerous requirements of bearing manufacturers and plant operators, Klüber Lubrication always performs a variety of tests prior to releasing a grease for specific applications. Besides a large number of static tests, special dynamic rolling bearing tests were performed on Klüberplex BEM 41-141, e.g. the FAG FE8 rolling bearing wear test and the SKF ROF grease life test. All tests showed that this lubricant by far exceeds the requirements of the industry.

Results obtained in SNR-FEB2 rolling bearing grease test

The antiwear behaviour of lubricating greases in rolling bearings subject to small oscillating rolling and sliding motion is determined on the SNR FEB 2 rolling bearing grease tester. Since the wear pattern in this test resembles the indentation caused in the Brinell hardness test, the SNR FEB 2 test is also referred to as “false Brinell test”. An axial load of 8,000 N is applied, corresponding to a Hertzian pressure of 2,100 N/mm², with a frequency of 24 Hz and over an angle of oscillation of ±3°. The test duration is chosen based on the test temperature: 5 hours for the low temperature of –20°C and 50 hours for an ambient test temperature. For a better understanding, we test at –20°C and ambient temperature to see the performance of the greases over a wide range.

Klüberplex BEM 41-141 was tested at ambient temperature resulting in less than 5 mg of wear. The low-temperature performance at – 20 °C resulted in less than 10 mg of wear. Both results show the excellent False Brinelling behaviour of this grease for Wind Turbine applications.
Competitive lubricants available on the market do not reach the excellent results of Klüberplex BEM 41-141.

Klüber Lubrication also offers tailormade product solution for every application:

– Klüberplex BEM 41-301 is especially suited for main bearings where a higher base oil viscosity may be required
– Klüberplex BEM 34-131 N, one grease for two applications: generator bearings and blade pitch bearings;
it offers extreme corrosion protection
– Klüberbio LG 39-701 N, one grease for two applications: yaw open gear and bearing
– All products are miscible with most products for the wind industry on the market

An innovative grease for all bearings

Low-temperature characteristics of greases

In operation, wind power plants are often subject to huge temperature variations. The very low temperatures are especially tough for the operation of wind turbines. Electric components, plastic and other parts are not designed for temperatures below − 10 or − 15 °C, so turbines without a cold-climate package are normally switched off if temperatures drop below these values. Still, the rolling bearing grease has to resist changing under such temperatures, even while the turbine is standing still. As soon as the outside temperatures rise to acceptable levels, the wind power plant restarts. Starting at cold temperatures is often facilitated by a heating system. At the time of start-up, the rolling bearing grease still has to provide its full performance. To make sure the grease is capable of doing so, it has to undergo numerous tests before approval.

The lower service temperature of a grease is normally determined using the standardised flow pressure test or the low-temperature torque test (IP 186). Upper service temperatures are ascertained on the FE9 rolling bearing tester (DIN 51821) or in the SKF-ROF test. For Klüberplex BEM 41-141, the low-temperature torque test resulted in a lower service temperature of −40°C, and the SKF-ROF test in an upper service temperature of 150°C.

The lower service temperature is the lowest temperature at which the product passed the flow pressure test or the low-temperature torque test. A product’s lubricity, however, may not necessarily be sufficient at that temperature and it may not offer sufficient wear protection. This is why Klüber Lubrication has, also, conducted the SNR FEB 2 test to determine the wear characteristics at −20°C.

This test showed that both Klüberplex BEM 41-132 and Klüberplex BEM 41-141 retain their excellent lubricity at very low temperatures. It also demonstrates their outstanding antiwear characteristics. At this temperature, bearing wear of less than 20 mg was attained with both lubricants – an excellent result.

A special exposure test has shown that both greases Klüberplex BEM 41-132 and Klüberplex BEM 41-141 meet the temperature requirements of the wind energy sector without difficulties – even if they are considerably lower than the grease’s nominal lower service temperature. Even at a temperature far below zero, the lubricant does not change. And no changes means it offers full performance when the turbine is started again.

Furthermore, Klüberplex BEM 41-132 and Klüberplex BEM 41-141 offer very god adhesion even at extremely low temperatures, which also contributes to good lubrication in the cold. Klüber Lubrication has confirmed adhesion at low temperatures in an especially developed bent-strip test – conducted at temperature conditions considerably below the lower service temperature range