Polyurea greases are among the first organically synthesized, non-soap high-temperature greases, dating back to 1824, with the first patent granted in 1955. Their development represents an important milestone in lubricating grease technology, particularly in the period following the Second World War.

Japan played a major role in the technological development of polyurea greases, and they remain one of the most widely used specialty grease types in the country.

What Makes Polyurea Greases Different?

Polyurea greases are ashless, contain no metallic soap and are produced through a polymerization reaction. They are obtained by synthesizing various isocyanates and amines in mineral or synthetic base oils.

Polyurea greases produced in this way tend to offer strong high-temperature performance. Their natural antioxidative properties, high shear stability and thixotropic behaviour distinguish them from other high-temperature greases.

One of the most important characteristics that differentiates polyurea greases from other specialty greases is their long service life. For this reason, they are frequently preferred for lifetime lubrication applications.

Due to production difficulties, raw material storage requirements and the technical infrastructure involved, these greases can only be manufactured in specially designed facilities and laboratories. Many companies selling polyurea greases have their products manufactured in such specialized facilities.

In rolling bearings, polyurea greases can be used for extended periods at temperatures of up to 200°C.

Typical Applications of Polyurea Greases

• Central lubrication systems in the iron and steel industry, including rolling mill rolls, continuous casting line exit rolls, cooling line rolls, heating furnace conveyor rolls and walking-beam furnaces operating with high-temperature, low-speed rolling bearings
• Pellet presses
• Fan bearings
• Hot roll bearings in cardboard and paper machinery
• Systems operating under high-temperature conditions
• Cement rotary kilns
• Automotive constant velocity joints
• Glass, ceramics and bottling plants
• Agricultural machinery

Polyurea Greases in the Steel Industry

Unlike gold, silver, iron or copper, steel is not an element found in the periodic table. Producing steel requires human intervention. Steel is produced by modifying the carbon content of iron, and its molecular structure can then be adjusted according to its intended application to provide additional performance characteristics.

The thermal energy required for this process is approximately 1500°C. At this temperature, carbon atoms separate from iron atoms and liquid steel is formed. Approximately one billion tonnes of steel are produced worldwide each year.

In continuous casting, molten steel is transformed into intermediate products known as slabs, billets and blooms. The molten metal passes through a water-cooled, open-ended mould and changes into a solid phase. This mould, known as a continuous casting mould, consists of two nested jacket sections and is cooled with water.

When liquid steel is poured into the moulds, circulating water around the mould assists the forming process and helps produce a smooth surface. The resulting products are subsequently transferred to rolling mills for further processing.

These systems operate under high loads and temperatures, in the presence of water and at relatively low speeds. Such conditions make it difficult to maintain an effective lubricant film between bearing rollers and raceways.

Minimizing bearing failures is extremely important in the steel industry. A failed bearing can cause production downtime as well as significant financial and operational losses. The amount of cooling water applied during liquid steel casting can reach 3,750 litres per minute, creating conditions that challenge even highly effective bearing sealing systems.

What Is Expected from Greases Under These Severe Steel Industry Conditions?

• Minimizing friction and wear
• Preventing rust even in the presence of water
• Remaining non-reactive with passive, non-abrasive bearing materials and metals
• Continuing to lubricate without leaving the bearing even under pressurized water
• Maintaining chemical structure and original performance under production conditions involving temperatures of approximately 800–1000°C

Greases with high base-oil viscosity can be continuously exposed to cooling water and environmental contamination. Under these conditions, the grease must resist corrosion while remaining neutral toward elastomers and sealing components.

Polyurea greases provide strong operating performance with many types of elastomers and sealing elements, making them particularly suitable for bearing components where lifetime lubrication is required.

Pumpability, Sealing and Thixotropic Behaviour

In addition to these characteristics, polyurea greases offer excellent pumpability. Their ability to pump effectively even at low shear rates enables strong performance across long lines in centralized lubrication systems.

The thixotropic nature of polyurea greases also provides an effective sealing function, helping prevent water, abrasive substances and environmental contaminants from entering the bearing.

Their high dropping points and antioxidative properties contribute to extended high-temperature performance. By increasing operating time under elevated temperatures, these characteristics can also help extend bearing and housing service life.

Polyurea Greases in Agricultural Machinery

Another distinctive characteristic of polyurea greases is their tendency to thicken as temperature increases. This behaviour can help bearings operate for extended periods under elevated temperatures.

Because polyurea greases do not contain metals that can catalyse oxidation, they can provide longer grease life and contribute to longer and more reliable bearing service life.

For these reasons, polyurea greases have increasingly been used in agricultural machinery. JOHN DEERE has adopted polyurea grease as a first-fill lubricant in certain agricultural equipment.

These greases are particularly used for lubricating heavily loaded ball and roller bearings, steering boxes and bearings, universal joints, pins and bushings in cotton, wheat and corn harvesting machinery. They are also increasingly preferred in gear mechanisms.

One reason for this preference is that grease maintains its consistency and does not leak from gears as readily as liquid oil when the machine is not operating, allowing it to perform an additional sealing function.

Oxidation Resistance and Service Life

Metals can have a catalytic effect on oxidation, accelerating the degradation of lubricating greases. Since polyurea greases do not contain metal in their soap structure, they are highly resistant to oxidation and can provide longer operating life than metal-soap greases.

Polyurea greases also demonstrate strong high-temperature behaviour and service life. In high-temperature life analyses, they can provide up to 50% longer operating life compared with other types of high-temperature greases.

This characteristic contributes particularly to the service life of bearings operating under high-speed and high-temperature conditions and can help reduce maintenance costs.

Polyurea Greases in Automotive Applications

Automotive constant velocity joints are used to transfer energy from the transmission output shaft to the wheels smoothly. Significant quantities of grease are used to lubricate these systems.

The main purpose of using polyurea greases in these applications is to provide lubrication throughout the service life of the vehicle without requiring relubrication.

From a tribological perspective, these systems are highly complex. Under the most aggressive operating conditions, temperatures can reach 180°C. Polyurea greases are frequently preferred in such applications because of their high dropping point, oxidation resistance and non-carbonizing structure.

One of the strongest characteristics of polyurea greases in these systems is their thixotropic behaviour. Greases naturally tend to soften structurally after physical use. However, because polyurea greases have a strong thixotropic structure, when the vehicle stops and remains unused for a period of time, the grease can recover toward its original consistency and continue performing when operation resumes.

Tayfun Yılmaz

General Manager — Vario Grease