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Corrosion problems and detection of metal processing fluids

January 03, 2015

Processing oil & liquid Is often used in metal processing and treatment processing, how to prevent metals from corrosion, rust, metal working oil is an important performance index.

For easy description, the technical engineers tips: hereinafter referred to in the metal processing oil contains both used in metal processing oil and metal treatment processing oil. Corrosion, as mentioned here, contains both steel and iron rust, also contains "rust" of other metals.

Machine rust problem:

Corrosion is the chemical reaction of partially or all of the metal surface, dissolving or softening. "Rust" only refers to the corrosion of iron and steel. "Corrosion" includes not only iron, but also other nonferrous metals. Therefore, this article discusses not only the corrosion of iron and steel.

Metal processing oil, to solve the corrosion problem of two aspects: prevent corrosion processed metal objects, prevent the machine parts, metal parts processing task) corrosion. Four types of metals are most common in industry, steel, aluminum, magnesium and titanium. Let's discuss each of these.

What factors will causes metal rust and corrosion?

Factors affecting corrosion in addition to the composition of metal processing, and moisture/humidity, temperature, air quality, and whether the oil contamination (acid, salt, and other liquids such as chemical liquid and other oils, etc.), concentration of bacteria liquid, water quality, processing, or processing liquid concentration is uneven, lead to the concentration of the metal surface in contact with the different regions of disequilibrium, the metal surface has cracks, gaps, or between the galvanic corrosion of dissimilar metals.

Steel:

Steel is the most common kind of metal, low price and high strength, which is easy to corrode (rust). In the laboratory, ASTM D4627 is tested for rust resistance. Rust inhibitors commonly used in metal processing oil include amines, which are critical for preventing rust, and check for amine content. In practice, the factors that affect the performance are poor water quality, high bacteria content, high humidity, and acid in the air.

Aluminum:

Aluminum is lighter than steel, only about a third of the density of steel. The advantage of it is not susceptible to corrosion. However, in some cases, the aluminum is corroded, such as exposure to certain metal salts (such as chloride), which are too high and have an electric dielectric corrosion in contact with other metals.

How can metal processing oil corrode aluminum metal? Method is as follows:

Take a piece of aluminum, use a beaker take some metal processing liquid, then dip half part of the aluminum into the liquid and observe the corrosion of the aluminum sheet next day. Another more complex Method is ASTM F1110 Corrosion Test (Standard Test Method for Sandwich Corrosion Test), also called Boeing interlining test (Boeing Sandwich Test), use a piece of filter paper soaking liquid metal processing, and then put the paper between two aluminum plates, under the hating, moisture condition after 7 days.

In the same experiment condition, the difference was to use the ionized water to soak the filter paper, and to see the corrosion of the aluminum plate seven days later. Comparing the two groups of experiments, if metalworking fluid corrosion serious than deionized water group, we thought that metalworking fluid corrosion does not pass. In the test, it is necessary to detect the corrosion of the concentrated liquid (mother liquor) of the metal processing liquid, and also to detect the corrosion of the diluted (the recommended concentration dilution). Corrosion inhibitors commonly used in aluminum processing fluids are silicate, phosphate.

Magnesium:

Magnesium metals are less dense than aluminum (two-thirds of aluminum), but they are strong. Magnesium has two drawbacks: flammable, chemically active, and water can react to produce hydrogen flammable and explosive. This is especially important when you use water based processing fluids. Detection method can be used metalworking fluid and magnesium reaction, collected and measured the generated hydrogen gas volume, so as to determine the strength of the reaction between magnesium and metalworking fluids, you also should pay attention to the degree of corrosion of magnesium.

Ti:

The advantage of titanium is small density and large strength, its strength & weight ratio is the highest in metal objects, and it is corrosion-resistant. But the thermal conductivity is bad, so the heat dissipation is bad. In cutting processing, heat is easily concentrated on the cutting surface and the contact surface. Titanium is flexible, which means that when working, the titanium can be easily deflected when it is processed, unless it is heavily processed. Titanium resist corrosion, but under high temperature conditions, stress corrosion and cracking are easy to test. The test method for this problem is ASTM F945.

Conclusion: in this paper, the analyses on the performance of the four common metal, metal working fluid are discussed in the use of metal corrosion caused by the problem, and liquid metal processing of metal corrosion testing methods. Each metal has different physical and chemical properties, so the corrosion problem should be solved according to the physical properties of metal.

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