How to properly handle the phenomenon of cutting fluid corrosion

Cutting fluid refers to a mixed lubricant used to lubricate and cool machining tools and components during metal cutting processes, commonly also known as metalworking fluid (oil). Reasonable use of cutting fluid during the cutting process can reduce friction between the tool and chips, as well as between the tool and the machined surface, lower cutting force and temperature, reduce tool wear, and improve the quality of the machined surface. In order to ensure the optimal function of Grinding fluid and truly implement its five major functions, it is necessary to pay attention to the phenomenon of corrosion of cutting fluid.

The main reason for replacing the working fluid

The deterioration of water-soluble cutting fluid is the result of rapid microbial growth under suitable conditions, leading to biochemical changes in the cutting fluid. The microorganisms that cause decay include fungi, actinomycetes, bacteria, and yeast. There are numerous genera of bacteria, widely distributed, and can be found in the atmosphere, soil, rivers, and natural objects.

01

The following representative fouling bacteria are often present in corrupt cutting fluids

A representative strain of copper green extremum for fish spoilage, and also one of the main bacterial genera for cutting fluid spoilage.

Another major strain of B sulfate reducing bacteria that produces foul odor in cutting fluid, reproduces under anaerobic conditions and exists under iron filings and scale. It can reduce sulfate ions, generate hydrogen sulfide, and emit a foul odor; Hydrogen sulfide corrodes iron to produce iron sulfide, causing the cutting fluid to turn gray brown and black. This is the main reason why cutting fluid needs to be regularly circulated, ventilated, oxygenated, and free of floating oil. When cleaning the fluid tank, rust and scale must be removed.

Yeast, Bacillus subtilis, and Fusarium graminearum produce strong enzymes in their bodies, causing the cutting fluid to become sticky, pH to decrease, and decay.

D. Penicillium is a representative bacterium that causes spoilage in food and industrial materials.

E. coli can corrode aluminum foil and various industrial materials.

02

The conditions for rapid microbial reproduction

A nutrient rich water-soluble cutting fluid provides sufficient organic matter (carbohydrates, mineral oil, fatty acids, fatty alcohols, etc.), minerals and trace elements, nitrogen-containing compounds (organic amine nitrates), and substances containing sulfur, phosphorus, and chlorine (extreme pressure agent EP) for microbial reproduction.

B Oxygen Itching Bacteria (Sulfur oxidizing Bacteria, Iron oxidizing Bacteria) - Light Odor

Itchy bacteria (sulfate reducing bacteria) - foul odor

Facultative anaerobic bacteria (sulfate reducing bacteria) - light odor

The temperature is relatively high. Bacteria are suitable for reproduction at 30-37 ℃; Fungi are suitable for reproduction at 20-30 ℃.

The pH value of D is not alkaline enough. Bacteria are suitable for reproduction at pH 6.0~8.5; Fungi are suitable for reproduction at pH 4.5-6.5. When the pH is greater than 9, the probability of bacterial and fungal reproduction is the lowest.

03

Phenomenon of corruption and deterioration of water-soluble cutting fluid

A) Produce a slight putrid odor, known as the 'Monday phenomenon';

B) The working fluid turns gray brown or red;

C) The pH value and rust resistance suddenly decrease sharply;

D) Producing gelatinous substances (bacterial skin) that clog the filter screen and pipeline, causing emulsion stratification;

E) Decreased processing performance;

F) Generate foul odor and pollute the environment.

04

Management of water-soluble cutting fluid

4.1 Raw material management

A) Avoid extreme cold, direct sunlight, and long-term storage.

B) Store above 5 degrees Celsius in winter.

C) Avoid direct sunlight in summer, preferably within three months of use.

D) The emulsion cannot be recovered after low-temperature demulsification.

4.2 Concentration Management of Working Fluid Preparation

The concentration of the working fluid is the basis for fully utilizing the functions of the cutting fluid. Low concentration can affect cutting function; Excessive concentration can also affect the normal functioning. From the perspective of anti-corruption, it is better to increase the concentration appropriately. For example, when the concentration of general microemulsion is 5% in the laboratory corruption experiment, it will begin to deteriorate after 6-7 months; When the concentration is 10%, it begins to deteriorate after 10-12 months.

II. Anti corrosion management

1. Choose clean water sources - tap water, groundwater, and if necessary, sterilize and adjust the water quality of the mixing water. The best hardness for mixing water is 80-120PPM.

2. When replacing the new fluid, thoroughly clean the fluid tank, pipeline, and machine tool processing area. If not cleaned or not thoroughly cleaned, especially if the cutting fluid has already decayed before the fluid change, it may decay within a few days after the fluid change.

3. Managing the use of cutting fluid

A) Maintain the specified concentration and replenish the cutting fluid promptly after consumption.

B) Keep clean and prevent foreign objects and dust from entering.

C) Timely remove floating oil and chips.

D) Drive and circulate cutting fluid for at least 1-2 hours daily, especially during holidays.

E) When the pH value is below 8.5, promptly replenish new solution and make adjustments.

When the pH value is greater than 9, the growth rate of bacteria and fungi is slow, so the international standard dilution solution pH=9 and the original solution pH=10 are the upper limit standards.

In summary, the reasonable use of cutting fluid can improve the service life of cutting tools and surface machining smoothness, ensure the treatment of waste liquid after use, meet environmental protection requirements, and use cutting fluid in normal production. If the above issues can be noted, unnecessary economic losses can be avoided and production efficiency can be effectively improved.