During a meeting following a long period of consultation, the Purchasing Manager asked our Sales Representative, "Why should I use the synthetic lubricating grease you are offering me, which costs 50 times the one we are using now?" Our answer? "Thank you for your question!" Our Technical Sales Representative loves to be asked this, without irony. So, was the customer's question rhetorical or was it actually necessary to explain in detail what they were about to buy? The decision had already been technically approved but now it was necessary to summarise the results obtained and, above all, to quantify them economically. In this article, in addition to trying to resolve any lingering doubts, we will also look at:

Value for money of a mineral grease compared to a synthetic grease

We will do this with a crystalline example. We will compare the performance and the economic advantage that one of our customers has achieved by switching from the use of a lubricating grease composed of mineral oil costing €6 per kilogram, compared to a grease formulated with high-performance synthetic oil at €300  per kilogram.

We will tell the tale of a success story of a company specialising in the painting of frames for tractor cabs, belonging to a well-known industrial group. We will analyse the mechanical parts subject to high temperatures (180-190° C), to wear, friction and lubrication, comparing the results obtained with the lubricating grease in use and with the new solution proposed, tested, validated and adopted.

The frames of the cabs, following the cataphoresis process, are subjected to powder coating, which involves drying cycles in the oven at temperatures of 180-190° C. The frames are transported to the painting tunnel through drive chains and trolleys. The kinematics that require lubrication and which are subjected to the continuous working temperatures present in the furnace are:

• Axial sliding bearings (washers), consisting of a disc and counter disc in reciprocal rotation, facilitate the complete exposure of the frames during the painting process
• Ball bearings, located on the wheels of the frames and carriages
• Transport chain bearings, responsible for dragging the trolleys along the ground

The mechanical parts subject to friction are constantly found to operate in conditions of:

• High load
• Low reciprocal sliding speeds
• High temperature

The high temperature represents the most penalising aspect, as repeated and close cycles of lubrication must be foreseen due to the high evaporation rate of the lubricant in use, namely a lithium mineral grease. The evaporation rate, according to the Noack test, is shown below where the mass losses following exposure to 250° C for 1 hour of base oils having the same viscosity but of different chemical composition are highlighted.

Previously-used lubricant solution: lithium mineral grease

The customer uses a lubricating grease formulated from mineral oil and lithium soap with thermal stabiliser for high temperatures. The maintenance plan includes the below ordinary lubrication interventions, necessary to counteract the powerful thermal action to which the kinematic mechanisms are subjected, and to ensure they are not quickly deprived of the protective lubricating film:

• Every 15 days - re-lubrication of the wheel ball bearings
• Every 15 days - re-lubrication of the axial bearings supporting the cab frames
• Every 3 months - pyrolytic oven treatment of the carriage to remove excess carbonised grease between disc and counter disc

Despite the presence of thermal stabiliser, the high temperature produces a known series of phenomena in lubricating oils, which we report in this article in detail. The high evaporation loss that the temperature generates in the mineral oil constituting the lubricating grease in use, results in:

• Formation of vapours and fumes in hot areas (180-190° C)
• Condensation in cold areas (20-30° C)

The formation of oil vapours also renders the work environment unhealthy, with the consequent need to implement additional extraction systems and fume abatement.

Proposed solution: PTFE fluorinated grease

The new solution was proposed and tested directly in the most critical lubrication area, represented by the axial sliding bearings supporting the cab frames (per the image below). A uniform film of a high-temperature grease formulated with fluorinated synthetic oil was then applied, thickened with PTFE (Teflon®) and antioxidants. The tests carried out prior on just a few pieces have gradually been extended to the entire fleet of trolleys. The benefits achieved can be summarised as follows:

• 30% reduction of maintenance times
• 90% reduction in fumes generated by the evaporation of mineral oil
• 80% reduction in operation and greasing times 
• 50% reduction in pyrolytic treatments on trolleys
• 90% reduction in non-conformities on the frames (dodging)

Profit and Loss: mineral grease vs. synthetic grease

A breakdown of the individual annual costs are shown below, broken down into each phase of the maintenance process of the painting system. With a fleet of 16 trolleys, an overall annual saving of more than 30% - equal to over 2500 euro - has been achieved!

There are many instances in which a detailed economic analysis highlights various advantages to adopting a synthetic lubricating fluid compared with a mineral one. It is merely a question of opening one's eyes and evaluating the costs that have somehow been metabolised and no longer considered as optimised, due to becoming standard practice. For example:

• Replacement of mechanical parts subject to frequent damage
• Ordinary maintenance that should actually be extraordinary
• Number of non-conformities and returns

Lubricating mechanical devices is still dominated by solutions with little added value, namely oils and greases of mineral origin that work perfectly in standard conditions and which are often adopted in instances of normal working conditions - ambient temperature, low loads of average operation and speed ... But what if working conditions change and the mechanical device is required to operate beyond the traditional realm? Is it still possible to obtain a benefit in terms of efficiency simply by using a synthetic lubricating fluid? In our opinion, yes! And we can prove it.