Biological stability evaluation method of metal cutting fluid 2
4 Dynamic test method (cycle test)
According to ASTM D3946-92, Standard Test Methods for Evaluating the Bacteria Resistance of Water - Dilutable Metalworking Fluid, the test method for evaluating the antimicrobial properties of water-based metal working fluids, established a test platform for the antimicrobial properties of water-based cutting fluids in the laboratory to evaluate the biological stability. This method is to evaluate the biological stability of water base cutting fluid by simulating the field conditions and conducting dynamic cycle test. By using this method, the experimental results of different water-based cutting fluids against microbial activity can be obtained. Compared with the bacteriostatic zone method, it can better explain the biological stability of water-based cutting fluid in field use and other problems that may occur. The disadvantage of this method is that the test time is longer. In this paper, the biological stability of water-based metal cutting fluid is studied by dynamic test method.
Main materials:
Gray cast iron filings (20~40 mesh);
Tap water (hardness of 100 ~ 150ppm);
Nutrients (corn starch, casein);
Bacteria (The spoilage water-based metal cutting fluid taken from the site, the total number of bacterial colonies after constant temperature culture >10 mL, true
The total number of bacterial colonies >10 mL);
SANI-CHECK tablet
Instruments used in the test:
PHS-3B precision acidity meter
E-201-C PH composite electrode
DHP781 thermostatic incubator
HHSY21-Ni type electric thermostatic water bath
CX-0088 type oxygen pump
OLYMPUS BX51 microscope
Specific test steps are as follows:
Add 900mL of water-based metal cutting fluid containing different fungicides with a concentration of 3% into a 1L beek, then add 100mL of cultured strains and 10g of nutrients required by microorganisms such as iron flakes, corn starch and casein, stir well, and take 100mL out for assessment of bacteria, fungi and pH value, respectively. The appearance of the test liquid was observed. The beaker is placed in a 30℃ constant temperature water bath, and air (200mL/min) is put in the test solution for seven days, each cycle is ventilated for 5 days, and the gas is stopped for 2 days, during which sterile water is added in time to supplement the loss caused by evaporation. The pH value of the test solution was determined every day, the appearance changes and odor emission were observed, and the number of bacteria and fungi were determined after 5 days of ventilation and 2 days of deaeration. Repeat until the water-based metal cutting fluid deteriorates. Due to the microbial reproduction process, cellular respiration releases CO2 and the organic acids produced in the degradation process will cause the pH value to drop. Therefore, the biological stability of water-based metal cutting fluid can be evaluated by the degree of pH reduction and the degree of microbial reproduction. As shown in the figure, the anti-microbial test platform for water-based cutting fluid.
