PAG-based synthetic lubricants bring benefits to gearboxes 

Marcos Thadeu Lobo

Mechanical Engineer Graduated from the State University of Campinas (Unicamp) in 1985. He joined Petrobras Distribuidora S/A in 1986 as a Product Technical Support professional. And currently holds the role of Senior Technical Consultant.

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Synthetic Lubricants for Heavy Duty

In many applications, given the high working temperatures and severe service loads to which the speed reducers are subjected, the use of mineral-based lubricating oils is not recommended, under penalty of low service intervals of the lubricating oil load caused by the term -oxidation and the acceleration of the wear rate of gears and bearings due to a lubricating film with insufficient thickness to separate the metallic surfaces in relative dynamic movement.

Figures 1/2 – Extreme conditions of temperature and efforts

Synthetic lubricating oils based on polyalkylene glycol (PAG) have a higher initial acquisition cost compared to those with a mineral base. However, the benefits in terms of reduced wear, improved reliability and availability of machinery outweigh the higher initial acquisition cost.

Benefits of PAG based synthetic lubricants

Among the benefits of using polyalkylene glycol (PAG) oils and synthetic lubricants we can mention:

1. High Viscosity Index: lower lubricating oil viscosity variations with temperature and, consequently, better lubrication of bearings and gears.
2. Greater resistance to thermo-oxidation: extends service periods up to 5 more than mineral-based lubricating oils.
3. Reduces wear on moving components (gears and rolling bearings): reduced maintenance expenses and unexpected equipment downtime.
4. Better lubricity: provides lower electrical energy consumption.
5. Reduces the equipment operating temperature by up to 5°C.

Figures 4/5 – PAG-based oils: better reliability and availability

Polyalkylene glycol (PAG) based oils for use in speed reducers generally meet performance standards:

1. DIN 51517 part 3: CPL PG
2. ISO 6743/ISO 12925-1 (CKC/CKD/CKE/CKS/CKT)
3. AGMA 9005-E02: EP
4. FZG (A/8.3/90) > 14; FZG (A/16.6/140) > 12: Gear protection tests)
5. FZG micropitting: Method GG-V378)
6. FAGFE8: Bearing wear protection test)

It is recommended to “flush” the gear reducer lubrication system in case of replacement of mineral-based or polyalphaolefin-based (PAO) lubricating oils by polyalkylene glycol (PAG) based products, considering that there may be incompatibility between said bases (mineral and PAO) with polyalkylene glycol (PAG).