Generally, cold heading forming oil with mineral oil as the carrier is used in cold heading of carbon steel. When circulating oil supply, a certain volume of air will be dissolved in the oil. The content of air in the oil is proportional to the pressure. When the pressure decreases, excess air will be separated from the oil. If the separated air is wrapped by oil and is not easy to crack and eliminate, it will form a "bubble", When multiple "bubbles" are gathered together, foam are formed. Two conditions must be met to produce a large amount of foam: 1. gas-liquid contact, that is, the gas is dispersed in the liquid; 2. The rate of foam production is greater than the rate of foam rupture.
The foam produced by pure liquid is unstable, but when there are other surfactants or components that can saponify each other in the oil, the foaming trend increases and the foam becomes stable.
The harm of foam
1. The oil pump has a lot of useless power. A large amount of foam causes the oil volume to increase, and the phenomenon of "half pipe oil" appears in the oil circuit;
2. The oil supply of the machined part is insufficient, increasing friction and wear;
3. Accelerated oxidation of oil products and increased oil change frequency;
4. Reduce oil cooling capacity;
5. The foam overflowed the oil pool, which caused the operation area to be wet and slippery, resulting in potential production safety hazards.
The foam aggregation process generated during processing is harmful, and the generated foam needs to be suppressed or eliminated to meet the actual production needs.
Category of foam
There are three kinds of positions in the oil tank or oil pool through foam; Oil bubble, oil bubble and mixed bubble.
1. Oil bubbles: floating on the oil surface, the diameter of oil bubbles is large, about 0.15-3mm or even larger, and there are many foam distributed on the whole liquid surface;
2. Under oil bubble: the foam suspended in the oil layer is called under oil bubble. Foam has small density and diameter, generally less than 1.5mm. In winter, oil products with higher viscosity or poor air release value are more likely to produce oil bubbles, which rise and disappear slowly.
3. Mixing bubble: when there are bubbles on the surface and the lower layer of the oil, it is called mixing bubble. The mixing bubble is distributed in the entire oil tank, and the density of foam is large, resulting in the decline of the transparency of the oil products and the decline of the oil pumping efficiency; In serious cases, foam overflows the oil tank.
Oil aging and overuse
Mixed use of oils from different manufacturers
Oil contaminated by soap powder on wire surface
Classification of Defoamers
Oily defoamers are divided into three categories: dimethyl silicone oil, non silicone polymer, and composite defoamers
1. Dimethyl silicone oil: chemical property -- inert, not easy to react with other distinctions in the oil formula, characterized by low surface tension, rapid spreading on the foam surface, and rapid defoaming; High flash point and low volatility; High temperature resistance and oxidation resistance. The disadvantage is that it is used for a long time, and the defoaming property is weakened.
2. Non silicon polymer: It has good dispersion performance in mineral oil, and its air release property is better than that of dimethyl silicone oil. The disadvantage is that some additives are selective.
3. Compound defoamer: When a single type of defoamer cannot meet the defoaming requirements of different working conditions or oil formulations, it is necessary to compound the defoamer.
Before and after the use of carbon steel cold heading oil, the acid value, saponification value, foam resistance and other data have changed greatly, and the content of various metal or non-metallic elements in the oil has also changed greatly. The oxidation of oil products in a short period of time is not the root cause of abnormal foam. Mixed use of oil products; The main reason for oil foaming is the saponification caused by the mixing of phosphatized skin, soap powder and wire drawing powder during processing.
Adding defoamers is the most common way to solve the foaming problem, but different types of oil-based defoamers have different solubility in the same oil-based foam system, and the defoamer molecules have different dispersion particle size, dispersion uniformity, and defoaming performance. Therefore, only by finding the direct cause of foam and applying the right medicine can the problem be fundamentally solved.
