3 Types of Defoamers for Lubricant Blending

Foam can adversely affect lubricant production and product quality. Therefore, in lubricating oil, in order to eliminate (inhibit) bubbles or foam, it is often necessary to add a certain amount of additives. These chemicals that can inhibit or eliminate foam are called Antifoaming Agents or Defoamers

 

Causes of Lubricating Oil Foaming

 

When the lubricant works, the air is mixed and air bubbles are generated during the lubricant circulation.

The bubbles floating on the oil surface are called Foam, The property related to the foam is called Defoam

Those dispersed in the oil are called Dispersed Air Bubbles. The property related to the Dispersed Air Bubbles is called Air Release Value(ARV).

 

The foaming phenomenon of lubricating oil is generally expressed by Foam Tendency and Foam Stability. Foam tendency indicates how easy it is to generate foam.

Why the lubricating oil has a strong foam tendency? Because the oil contains not only air but also additives to improve the performance of lubricating oil. Most of these additives are surfactant substances, these surfactants enhance the foaming tendency of the lubricating oil.

Foam Stability is related to the viscosity, plasticity, and tenacity of the oil surface. The greater the surface viscosity, the better the plasticity and tenacity, the foam is more stable, and it is difficult for the foam to break.

 

In conclusion, the main reasons for oil foaming are:

 

• Lubricant additives, especially some surfactants enhance the foaming tendency.
• Oxidation and deterioration of the oil itself;
• Rapid air suction and circulation in the oil;
• Air is released as oil temperature rises and pressure drops;
• High-speed stirring of lubricant, mix with air;

The hazards of lubricating oil foaming

The generation of foam will bring many hazards to the equipment and the lubricating oil itself.

 

• It will cause dry friction of mechanical parts
• and may also cause air resistance to interrupt the oil supply of the oil pump, which will aggravate the wear and tear of mechanical parts until they are damaged.
• After the lubricating oil foams, the contact area with the air increases, which promotes the oxidation and deterioration of the lubricating oil and shortens the service life of the lubricating oil.
• Foaming will even cause the lubricating oil to overflow, causing oil shortage accidents.

 

Types of Antifoam Additives in Lubricant

 

The defoamer currently used in the market are mainly three types: Silicone Antifoam, Non-silicon Antifoam, and composite defoamer.

 

Type 1 - Silicone Antifoams

 

Silicone Antifoam Additive is polysiloxane (silicone oil), its main chain has a Si-O-Si junction, and the most use is polydimethylsiloxane, also known as dimethyl silicone oil, is a non-toxic Odorless, odorless organic liquid with low solubility in lubricating oil and water, can be used as an antifoam additive for lubricating oil and water-based lubricants.

 

Silicone Antifoam has the following characteristics:

(1) Low surface tension. The surface tension of polydimethylsiloxane is lower than that of water, surfactant aqueous solution, and general oil, so it is very suitable as an anti-foaming agent.

(2) Low solubility in water and general oils and high surface activity. Silicone oil has a special molecular structure. The main chain is a non-polar molecule with silicon-oxygen bonds. It is not compatible with polar solvents or water and has little affinity with general oil products.

(3) Low volatility and chemical inertness. polydimethylsiloxane has extremely low volatility and low surface tension, combined with it, it can defoam in a wide temperature range.

(4) Good thermal stability, low freezing point, good viscosity-temperature performance in a wide temperature range.

(5) Negative impact on lubricants. Although the anti-foaming performance of silicon oil is excellent, its poor oil solubility has a great influence on the air release property. Because for dispersed air bubbles, it reduces the surface tension and the diameter of the air bubbles generated becomes smaller and it is difficult to float up, resulting in poor Air Release.

(6) No physiological toxicity. Generally, the polydimethylsiloxane antifoam agent has a high degree of polymerization, while the polydimethylsiloxane from which oligomers have been removed is non-physiologically toxic.

(7) There are many varieties of polydimethylsiloxane antifoam agents, which can be used for a variety of foaming systems.

 

Type 2 - Non-silicone Antifoam Additives

Most of the non-silicon antifoam agents are polymers, and the homopolymers or copolymers of acrylate or methacrylate are mostly used. It is mainly a random copolymer of ethyl acrylate, 2-ethylhexyl acrylate, and vinyl n-butyl ether, in addition to polyethylene glycol ether, polybutylene glycol ether, fatty alcohol, alkyl phosphate, etc.

The effect of non-silicone deformer is not as good as that of silicone oil, and the dosage is larger than that of silicone oil - 0.001%~0.07% (by weight), but it has little effect on the air release value of lubricants, and it is not easy to separate out in lubricants. and the requirements for the blending process are not high.

The fine droplets of silicone oil dispersed in the oil are easily mistaken for particulate matter by optical calculators. Therefore, some OEMs (Original Equipment Manufacturers) stipulate that only non-silicone deformers are acceptable in hydraulic oil.

When non-silicone deformers are combined with certain additives, such as calcium alkyl salicylate (T109), polyvinyl n-butyl ether (T601), or barium dinonyl naphthalene sulfonate (T705), the antifoaming performance may decrease, so do pay attention to this. 

 

Type 3 - Composite Defoamer

 

Silicone oil and non-silicone antifoam have their own advantages and disadvantages, sometimes, it is difficult to increase the air release value and anti-foaming value of the oil by adding one single defoamer. In order to solve this problem, Compound Antifoams (Packages of Antifoam Additives) have been developed.

compound antifoam balances the advantages and disadvantages of Silicone oil and non-silicone antifoam, and consists of the two in an appropriate proportion.

Silicone oil has a good defoaming effect and a low dosage, but it is easy to make the air release value bad in the lubricant, and it is easy to precipitate in long-term storage due to its poor dispersibility.

The effect of non-silicone antifoam is not as good as that of silicone oil antifoam agents, and its dosage is high, but the side effect on air release value is small, and the antifoam durability is good. When the two types of defoamers are combined, the deforming performance is balanced and satisfied.

 

Performance Comparision of Silicone defoamer and non-silicone defoamer

 

Defoamer	Dimethyl Silicone Oil T901	Polyacrylic Ester Defoamer
Defoaming Performance	1. Reduce the amount of air bubbles generated in lubricant; 2. Improve the fluidity of the oil film on the surface of the foam, make the oil film of the bubble thinner, and accelerate bubbles rising to the oil surface and break; 3. make the air bubbles smaller. if the dosage more, Air Bubbles Release be slower in the oil	1. Reduce the amount of air bubbles generated in lubricant; 2. make the small air bubbles in the oil merge into large air bubbles, and quickly float up to the surface and break, thereby reducing the amount of small air bubbles in the oil and helping to improve the air release value.
Effect on Air Release Value	Serious adverse effects	Small adverse effect
Compatibility	1. Poor defoaming persistence in acidic medium; 2. good compatibility with various lubricant additives	1. Good defoaming persistence in acidic medium; 2. The effect becomes worse when combine with some additives