Screw Air Compressor Coolant Oil (Lubricant Oxidation)

  • Posted November 20, 2023
  • by admin
COOLANT OXIDATION

INTRODUCTION

In this report we will understand the screw air compressors and importance of lubricants used in Screw Air Compressors. Selection of screw air compressor lubricant and factors involve in oxidation (contamination) of lubricant that turns lubricant into sludge.

SCREW AIR COMPRESSORS

Screw air compressors also called rotary screw compressor. This type of air compressors uses two rotating screws (also known as rotors) to yield usable compressed air. Rotary screw air compressors are compact in design, quiet and more efficient than other compressor types. These machines are more trustworthy and dependable in when used continuously. Reliability of the screw air compressors is more efficient when they are looked after as per user manual and consumable parts are replaced on-time. Top of the list in consumable parts is lubricant which must be selected very carefully as low quality lubrication may cause reduced efficiency and machine break down in extreme cases. Other than lubricant Oil Filter, Air filter and Air/Oil Separator are consumables.

LUBRICANTS

Most of users of Screw Air Compressors use mineral oil for lubrication. Mineral oils are used widely in the world since more than 100 years. They are very efficient and low cost lubricants. Mineral oils are byproduct of crude oil. They directly come of ground after high level of processing and purification. Due to cheaper cost they are affordable when frequency of the oil change is high. Mineral oils use additives that may change their behavior and viscosity due to environmental variables. However mineral oil is time tested to use in screw air compressor. It is an inert and stable compound.

MINERAL OIL CHARACTERISTICS AND BEHAVIOR 

Unlike most other lubricated components, rotary screw air compressors face a unique triple threat to their life span: A constant influx of excessive heat, oxygen and water Any one of these three forces can degrade a lubricant and lead to equipment problems. In a rotary screw air compressor, all three are continuously present — increasing the challenge of proper lubrication and protection

www.iselinc.com

Oxidation in a lubricant can be caused by Heat, Water and Oxygen which leads to increase the possibility of poor lubrication leads to equipment failure.

 

ROOT CAUSES OF OXIDATION AND TAN FACTOR

It is an established fact that Heat, Water and Oxygen are common elements in a lubricant oxidation. In Screw Air Compressor working mechanism, Oxygen comes in through Air Inlet with Lubricant. Compressions of Air cause Heat and Moisture (Humidity from Atmosphere). Thanks to the modern research and development we have more advanced lubricant formulations which are proficient of resisting extreme temperature and deal with heat and water. But truth is no lubricant last forever and eventually oxidation will degrade the fluid and cause damage to equipment. TAN (Total Acid Number) is an oxidation tracking factor. It is the key factor to find the oxidation of lubricant. The rise of TAN is cause by the rise of oxidation [https://iselinc.com/].

When the increase in TAN level reaches above the acceptable range the following consequences are likely to happen [https://iselinc.com/].

  • Rust and Corrosion accelerate
  • Sludge and varnish formation
  • Consumable parts blockings

Above issues can result in compressor failure. This may lead to massive downtime and more costly repairs.

 

THERMAL EFFECT ON COMPRESSOR OIL

According to https://iselinc.com/ every 20 F° (11C°) increase in operational temperature beyond the lubricant recommended temperature cut the lubricant life to half.

For an example, a lubricant is rated 2000 operational hours and recommended operational temperature is 85 C°. This lubricant will last only 1000 hours in today’s common temperature of 96 C°. A further increase of every 1C° will cut down the life of lubricant significantly.

OVERCOMING THE PROBLEM

  1. It is not possible to eliminate the problem 100%. You can take multiple actions to reduce the chances of root cause, which ultimately leads to lubricant oxidation.

    In Screw Air Compressor triple threat (Heat, Water and Oxygen) can reduced by following

    • Checking oil condition on regular basis
    • Oil change-outs timely and regularly
    • Physical procedure in place to control of contamination

    In standard oil drain it is anticipated that up to 20% of old lubricants remain in the equipment. This will cause direct contamination. As a result new oil will oxidize more quickly and will considerably shorter service life.  To resolve this issue, equipment must be down for longer period of time to make sure maximum of the old lubricant is drained. All system components that contact lubricant must be cleaned thoroughly to drain the old lubricant as maximum as possible. Must keep all the equipments very clean, like pumps and pipes used to drain old lubricant before using them to add new oil. If possible separate equipment should be used to drain and add lubricant. Unused lubricant must kept in sealed containers to avoid physical contamination [https://iselinc.com/].  

    In high humidity environments, oxidation of the oil can be overcome by increasing the frequency of oil change.