Lubricating oil antifoam agent use effect is not good? These are the basics to understand

March 25, 2024

Lubricating oil antifoam agent use effect is not good? These are the basics to understand

Modern lubricating oil, whether it is engine lubricating oil, industrial lubricating oil or transmission lubricating oil contains a certain amount of additives, in the use of oil products due to the transport of oil or oil and machine parts of the severe vibration and other reasons, will make the oil has a tendency to foam, and the formation of stable foam will cause extremely adverse consequences, not only resulting in the waste of lubricating oil loss, It also reduces the performance of the oil and causes the wear and tear of the machine.

In order to prevent the formation of foam in lubricating oil or eliminate the foam as soon as possible, anti-foam additives are used in lubricating oil. In this paper, the action mechanism, types and selection of anti-foam additives used in lubricating oil are briefly introduced

Defoaming mechanism of antifoam agent

Oil foaming can be divided into two aspects, one is the surface foaming, usually can be controlled by Anti-foaming Agent; The other is the internal foam of the oil, the internal foam is not easy to be improved by the anti-foam agent, and the anti-foam agent that is effective for the surface foam may make the internal foam of the oil more stable. For oils that require excellent defoaming properties, base oils and additives need to be selected to be blended. The action mechanism of antifoam agent is more complicated, and the opinions are different, the representative views are to reduce part of the surface tension, expansion and penetration.

1. Reduce surface tension

This mechanism is achieved by reducing the surface tension, which is believed that the surface tension of the antifoaming agent is smaller than that of the foaming solution. When the antifoaming agent is in contact with the foam film, the surface tension of the foam film is locally reduced while the rest remains unchanged, and the stronger tension of the foam film pulls the weaker tension part, thus causing the foam to burst.

However, this mechanism is limited to local locations, because such substances are insoluble in water, so the diffusion power is poor, and the surrounding foam does not play much role. When the local tension on the surface of the foam is reduced, under the action of this force, it slowly spreads around and finally forms a rupture.

Step 2 Expand

In this view, the intrusion of antifoaming agent droplets into the membrane makes it a part of the membrane, and then expands on the membrane, which can effectively inhibit the diffusion of the active agent, making it difficult to exert its elastic ability, so as to eliminate the surface foam.

Step 3: Penetration

In this view, the function of antifoam agent is to increase the permeability of bubble wall to air, thus accelerating the combination of foam, reducing the strength and elasticity of the bubble wall, and achieving the purpose of bubble breaking.

Types of common antifoam agents

In the process of industrial production, many harmful foams will be produced, and anti-foaming agents need to be added. There are many kinds of anti-foam agents, organic siloxane, polyether, silicon and ether grafting, containing amine, imide and amide, with faster defoaming speed, longer defoaming time, a wider range of applicable media, and even harsh media environments such as high temperature, strong acid and strong base characteristics.

1. Silicon

The most commonly used is polydimethylsiloxane, also known as dimethylsilicone oil. Pure polydimethylsiloxane can not be used as antifoam agent without dispersion treatment. It has the characteristics of low surface energy and low surface tension, so it can effectively inhibit the generation of foam, reduce machine wear and extend the service life of oil products.

Silicone polymer antifoam agent is not dissolved in the oil, it is distributed in the oil through a highly dispersed and stable colloidal state, such as in acidic oil, with the extension of time, silicone type antifoam agent will be unstable and settling, resulting in the failure of antifoam performance. The action mechanism of silicone polymer anti-foam agent is to change the surface tension between liquid and air, so that it is not easy to form bubbles, so the oil containing silicone polymer anti-foam agent has poor air release. The addition of silicone type antifoam agent is usually 2-20ppm.

2. Non-silicone polymers

In acidic oils such as turbine oil and hydraulic oil, silicone polymers will lose their antifoam properties after long-term use, and non-silicon polymer antifoam agents can be used in this case. The most widely used non-silicone polymer anti-foaming agent for lubricating oil is the copolymer of acrylates and alkyl acrylates. They have good solubility in mineral oil, are not sensitive to blending technology, and the amount is very small 0.001% ~ 0.05% (mass fraction).

The anti-foam performance of this kind of anti-foam agent is greatly affected by the existing surface active substances in the system, and the effect of anti-foam agent depends on the entire oil system. Therefore, the same surfactant has the ability to reduce foam in one oil system, but may have no anti-foam performance at all in another case. In some cases, it not only has no anti-foam performance, but promotes the formation of oil foam. Special attention should be paid to the presence of detergents in the lubricating oil system. Compared with silicone antifoam agents, this kind of antifoam agent can effectively improve the air release property of oil products.

Because the action mechanism of this kind of non-silicone polymer anti-foam agent is to partially replace the surfactant in the original bubble film, thereby changing the intermolecular gravity of the film layer, reducing the film strength, or reducing the toughness and reducing the stability of the foam, so as to achieve the purpose of defoaming, the air in the oil containing this kind of non-silicone polymer anti-foam agent can be released in the form of bubbles. It has good air release.

3. Compound antifoam agent

Due to the advantages and shortcomings of the above two types of anti-foam agents, in some cases alone can not meet the performance requirements of oil products, so the development of composite anti-foam agents, through the combination to increase the anti-foam effect and improve the stability of anti-foam agents. Most of the composite antifoam agents are the combination of the above two types of antifoam agents, in order to play their respective advantages and meet the requirements of oil performance. In addition, there are also compounds between non-silicon antifoam agents.

Selection of antifoam agent

The principle of selecting the type of anti-foam agent depends on the composition of the lubricant and the use of the oil, the additives used in the lubricant are mostly surfactants, and a surfactant can have several effects, so the type of other functional additives used in the lubricant formula should be considered in reducing and inhibiting the formation of foam in the lubricant.

The interaction mechanism between surfactants in oil is complex, and many occasions can not rely on theoretical reasoning to solve the problem. In order to make the application of lubricant antifoaming agent play a good effect, it is necessary to carry out multiple tests of the actual oil system. In addition, research and use of multi-effect additives is the key to improve economic benefits and improve the quality of oil products.

Because the use of multi-effect additives can reduce the number of functional additives under the premise of meeting the function of the oil, which can reduce the complexity of the lubricating oil system containing a variety of surface active substances, reduce the influence of uncertain factors on the stability of the oil, the stability of the oil is the key to determine its quality.

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