1. What are the characteristics of oil-based cutting fluids compared with water-based ones?
In general, oil-based cutting fluids have better lubricity and water-based cutting fluids have better cooling properties. Oil-based cutting fluid is prone to smog and easy to catch fire at high temperature; water-based cutting fluid is prone to bacteria, short service life and easy to rust.
Second, what are the quality inspection products for cutting oil?
The main quality control indicators for cutting oil are viscosity, flash point, pour point, fat content, sulfur content, chlorine content, copper corrosion, moisture, mechanical impurities, and four-ball test. For the determination method, reference may be made to the relevant test method standards, and only some items are given a brief description here.
Fat content
Fat is an oily additive in cutting oil and an important indicator for classifying cutting oils. Fat in the cutting oil can reduce the friction coefficient and reduce the wear of the tool (especially to prevent the wear of the flank). Cutting oil with more fat is especially suitable for non-ferrous metal processing and where the amount of cutting is small but the product accuracy and finish are high (such as precision screw). The saponification value can generally be used to roughly determine its fat content. If the fat content in the cutting oil is too high or the quality is improperly controlled, it is easy to form a viscous substance on the machine, which makes the movement of the machine inflexible. When it is serious, it will become a paint film, which is called “wearing yellow robeâ€.
Chlorine content
The chlorine in the cutting oil is mainly derived from the extreme pressure agent containing chlorine. Chlorine needs to be at a higher content (greater than 1%) to exhibit an effective extreme pressure effect. If the chlorine content is less than 1%, it is considered not to improve lubricity. Generally, chlorine-containing extreme pressure cutting oil has a chlorine content of more than 4% and a maximum of 30% to 40%. However, due to occupational health and environmental considerations, some countries have already stipulated the maximum content of chlorine in cutting oil. For example, Japan's JIS regulations should not exceed 15% chlorine. Chlorine is very effective in the processing of stainless steel and in the drawing process. The disadvantage is that it is not stable enough. When it is exposed to water or the temperature is too high, it will decompose and produce HCl, causing corrosion and rust.
Sulfur content
Sulfur in cutting oil comes from two aspects. One is the added sulfur-containing extreme pressure agent, and the other is from other sulfur-containing compounds that do not have extreme pressure, such as the natural sulfur sulfides in the base oil, as well as rust inhibitors and antioxidants. Effective sulfur requires only a very low content (0.1%) to produce a significant extreme pressure effect. Sulfur-containing extreme pressure agents are particularly effective in inhibiting built-up edge, but unfortunately there is no simple way to separately measure extreme pressure sulfur and extreme pressure sulfur. Therefore, it is difficult to judge the extreme pressure based solely on its sulfur content (especially when the sulfur content is not high). However, most cutting fluid manufacturers now specify the sulfur content of the extreme pressure agent added in their product specifications.
Copper corrosion
The method of measurement is a copper sheet method. The magnitude of the corrosion activity is represented by a series, the grades 1 to 2 are low active or inactive, and the grades 3 to 4 are highly active. The greater the number of stages, the stronger the corrosion activity. Copper is very sensitive to sulfur. This method can be used to determine whether there is a sulfur-containing extreme pressure agent and an extreme pressure agent in the cutting oil (note: this method cannot judge the amount of sulfur-containing agent). This project is also an important indicator for the classification of cutting oils.
Four ball test
The maximum cardless bite load can be measured. This method can be used to roughly judge the extreme pressure of cutting oil, especially when combined with sulfur, chlorine content and corrosion of copper sheet, it can have a more comprehensive understanding of lubricity. However, it should be emphasized that the extreme pressure given by the four-ball test is only the evaluation result under standard conditions, and this result has no strict correspondence with the cutting performance.
3. What are the quality control projects for water-based cutting fluids?
Water-based cutting fluids are diluted with water when applied, and the test items can be divided into two parts: direct measurement and water addition. Directly determined items include storage stability, sulfur and chlorine content, and non-volatile components. The items measured after adding water have surface tension, pH value, foaming property, rust resistance, corrosion resistance, adaptability to paint, allowable amount of salt, and antibacterial property. Most of these projects are relatively clear in meaning. The following only describes some individual projects.
Storage stability
The concentrate of the water-based cutting fluid, although uniform in appearance, is mostly a colloidal system and contains a considerable amount of water. After long-term storage and temperature fluctuations, if the formula is improper, it is easy to cause precipitation, stratification, etc. and often cannot be recovered. So this is a very important test item.
Non-volatile component
The water-based cutting fluid concentrate contains moisture and this item is used to determine the effective component content.
Salt allowance
This test is used to understand whether the cutting fluid can allow the use of tap water with a higher chlorine content to prepare the working fluid.
Surface Tension
In most cases, a liquid with a small surface tension tends to spread on a solid surface, and thus a considerable number of people regard surface tension as a measure of the permeability of the cutting fluid. But strictly speaking, there is no direct correspondence between the two. Permeability is a relatively ambiguous concept that seems to be more closely related to wettability and fluidity (viscosity). The surface tension can be used as a criterion for determining whether or not a surfactant is added to the cutting fluid. Because of the small amount of surfactant, the surface tension of water can be greatly reduced. In addition, the surface tension is not as small as possible. Too small a surface tension can sometimes bring other negative effects.
Antibacterial test
Water-based liquids, especially emulsions, are probiotics, and their antibacterial ability is an important performance index. However, in the past, it has attracted attention in China and has not been used as a quality indicator for water-based liquids. There are some simple methods for measurement abroad, and qualified units should be applied as much as possible.
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