Detailed explanation of cutting oil quality inspection indicators
April 03, 2023
The main quality control indicators of cutting oil include viscosity, flash point, pour point, fat content, sulfur content, chlorine content, copper corrosion, moisture, mechanical impurities, and four ball test. For measurement methods, please refer to relevant test method standards, and only some items will be described here. Fat content Fat is an oily additive in cutting oils and an important indicator for classifying cutting oils. Fat in cutting oil can play a role in reducing friction coefficient and reducing tool wear (especially effective in preventing wear on the rear tool surface). Cutting oils with high fat content are particularly suitable for nonferrous metal processing and occasions where the cutting amount is small but the product accuracy and finish requirements are high (such as finishing threads). Generally, the saponification value can be used to roughly determine the fat content. High fat content in cutting oil or improper quality control can easily form sticky substances on the machine, causing inflexible movement of the parts, and in severe cases, it can become a paint film, known as "wearing a yellow robe".
Chlorine content The chlorine in cutting oil mainly comes from extreme pressure agents containing chlorine. Chlorine needs to be present at a high content (greater than 1%) to exhibit effective extreme pressure effects. If the chlorine content is less than 1%, it can be considered that it is not intended to improve lubricity. Generally, the chlorine content of extreme pressure cutting oils containing chlorine is above 4%, with a maximum of 30-40%. However, due to occupational health and environmental considerations, some countries have made regulations on increasing the content of chlorine in cutting oil, such as the JIS in Japan, which stipulates that the chlorine content should not exceed 15%. Chlorine is very effective in the processing of stainless steel as well as in the pull molding process. Its disadvantage is that it is not stable enough and can decompose to produce HCL when encountering water or excessive temperature, causing corrosion and rust. Sulfur content Sulfur in cutting oil comes from two sources. One is the added sulfur-containing extreme pressure agent, and the other is from other sulfur-containing compounds that have no extreme pressure effect, such as the original natural sulfides in the Base Oil, as well as rust inhibitors and antioxidants. Effective sulfur requires only a very low content (0.1%) to produce significant extreme pressure effects. Sulfur-containing extreme pressure agents are particularly effective in inhibiting chip buildup, but unfortunately, there is no simple method to detect sulfur with and without extreme pressure, respectively. Therefore, it is difficult to judge its extreme pressure based solely on its sulfur content (especially when the sulfur content is not high). However, most cutting fluid manufacturers now indicate the sulfur content of the extreme pressure agent added in their product manuals. Copper strip test The method of measurement is the copper strip method. The magnitude of corrosion activity is expressed in terms of progression, with levels 1 to 2 indicating low activity or non activity, and levels 3 to 4 indicating high activity. The greater the order, the stronger the corrosion activity. Steel is very sensitive to sulfur, and this method can be used to determine whether there are sulfur containing extreme pressure agents and the activity of extreme pressure agents in the cutting oil (Note: this method cannot determine the amount of sulfur containing agents). This item is also an important indicator for classifying cutting oils.
Four ball test
The maximum non seizure load can be measured. This method can be used to roughly determine the extreme pressure properties of cutting oils, especially when combined sulfur, chlorine content, and copper strip corrosion are comprehensively analyzed, which can provide a more comprehensive understanding of their lubricity. However, it should be emphasized that the extreme pressure property given by the four ball test is only an evaluation result under standard conditions, and there is no strict correspondence between this result and the cutting performance.
