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What is Hydraulic Oil Varnish?

What is Hydraulic Oil Varnish?


What is Hydraulic Oil Varnish?

Varnish is a fine deposit that is formed in a lubrication system, is difficult to wipe off and consists mostly of organic residues. Its chemical structure is quite diverse and is classified according to different degradation mechanisms. Although the terms "varnish" and "mud" are sometimes used interchangeably, they actually refer to different things.

While sludge is a sticky substance that is easy to wipe and usually contains moisture; The varnish has a more hardened, glossy structure and is difficult to clean. These definitions help users understand what type of debris they have in their system.

The varnish is formed as a result of a continuous oxidation process, which is accelerated by the action of temperature, metallic components and gas catalysts. Although initially oxidation was defined only as a reaction with oxygen, today it has been expanded to include all reactions in which electrons are transferred from a molecule. Oxidation is the main cause of deterioration of lubricant over time and loss of performance.

Pollutants also accelerate the oxidation process. There are three main types of contaminants in hydraulic oils:

  • Dirt (silt, wear metals)
  • Water
  • Air

Among the consequences of oxidation are the following:

  • Viscosity increase
  • Formation of varnish and sludge
  • Depletion of additives
  • Clogging of filters
  • Loss of foam durability
  • Increased acidity
  • Formation of rust and corrosion

These deposits form the direct link between oil degradation and machine performance.

Operational Effects of Varnish

Varnish leads to serious problems in lubrication systems. For example:

  • It accelerates wear by creating a "sandpaper" effect on surfaces.
  • It reduces the efficiency of heat exchangers by creating an insulating layer inside the tubes.
  • It disrupts the flow of oil and causes hunger problems.
  • It causes the filters to clog quickly.

Servo valves are the components most affected by varnish. When deposits form in these valves:

  • The valves are locked and a high level of friction occurs.
  • Cycle times are extended, production loses speed.
  • Sensitivity decreases, scrap rate increases.
  • Energy consumption increases and system efficiency decreases.

All this leads to increased maintenance costs and premature equipment replacements.

The Critical Role of Condition Monitoring

FMEA (Failure Mode and Effects Analysis), which has been used since the 1940s, was developed to evaluate failure modes, their causes, and effects. This method should form the basis of every oil analysis program. Because:

  • If you don't know the failure mode, you won't be able to do the right test.
  • If you know the main failure modes, your monitoring program should also be compatible with it.

Unfortunately, most hydraulic oil analysis programs do not have this sensitivity.

Case Study: "But My Oil Analysis Reports Look Good!"

A plastic injection molding plant was experiencing complaints of increased scrap rates and low productivity. The maintenance manager increased the frequency of oil analysis to show that oil was not the problem. For example, the oil analysis report from Machine 15 seemed perfectly acceptable.

However, during the physical checks, varnish accumulation was detected on the valves and in the hydraulic tank. As a result of in-depth analysis, the real problem was revealed:

  • Figure 1: The RULER (Voltammetry) test showed that there were almost no antioxidants left in the oil.
  • Figure 2: MPC test result of 61, which was above the critical range.

That is, standard analysis tests could not show the problem. The root of the problem was based on the oxidation of oil and the formation of varnish.

Identifying Problems in Advance with the Right Tests

The recommended tests to accurately detect oxidation and deposit formation in hydraulic oils are as follows:

  • Voltammetry (RULER Test - ASTM D6971): Measures the health of antioxidants.
  • FTIR (Fourier Transform Infrared Spectroscopy): Monitors oxidation products and additives at the molecular level.
  • Membrane Patch Colorimetry (ASTM D7843): Determines the tendency of varnish formation.
  • Ultracentrifugation: Physically separates spoilage products.
  • Air Release Test: Measures the ability of the liquid to expel air bubbles.

Innovative Approach to Deposit Challenge: Solvancer®

One of the most effective ways to remove deposits from hydraulic oils is to use a solubility enhancer. Here are the key features that solubility enhancers should carry:

  • It must be compatible with existing lubricant and system materials.
  • It should not have a corrosive effect on pollutants.
  • It must remain stable under oxidative stress.

Solvancer® Technology

Solvancer® technology, developed by Fluitec, is optimized to dissolve varnish and other deposits. The typical utilization rate is 3-5% and does not impair the performance characteristics of the oil. It begins to work quickly, both dissolves existing deposits and prevents the formation of new ones.

  • Figure 4: Results of accelerated oxidation testing with and without Solvancer.

Conclusion: Steps to More Reliable Hydraulic Systems

To improve reliability in hydraulic systems:

  • Upgrade your oil analysis package.
  • Run tests that monitor antioxidant health and buildup tendency.
  • If necessary, support the system with analyzer products such as Solvancer®.

These approaches are key to preventing system failures and extending oil life.