Metal rust prevention

1、 Selection of antirust oil

The variety of antirust oil is complex, and the selection principles are as follows:

1. According to the metal type, different antirust oils have different antirust effects on different metal materials. Some have good antirust effects on ferrous metals, but the effect on copper is average. These are often described in the product description of antirust oils, which should be selected carefully.

2. According to the structure and size of metal products, solvent dilution type or grease type can be selected for those with simple structure and large surface area, while oil type is better for those with complex structure, holes or cavities, because the removal of antirust film during unsealing should also be considered.

3. According to the environment and use of metal products, it is necessary to distinguish whether it is short-term process rust prevention or long-term rust prevention with short-term lubrication at the same time, whether it is long-term storage rust prevention for humid environment, or it may be stored in coastal warehouses or even transported by sea for a certain period of time, so it has good salt spray resistance. The selection should be targeted in this regard.

Of course, the rust preventative oil with reliable quality shall be selected first. Due to the small amount of antirust oil currently used in China, many antirust oils are produced by small local factories or even made by users. At present, some major domestic antirust additives are not stable in quality or oil solubility. Therefore, visual inspection shall be conducted before use to compare with the previous batches in terms of appearance, color, whether there is layering or uneven. If the appearance of several batches differs greatly through visual inspection, their quality should be doubted. For users with large amount of antirust oil, they should be equipped with wet box test equipment to verify the antirust effect of antirust oil.

2、 Antirust oil application method

For different antirust grease, there are the following application methods:

1. Dip coating: immerse metal products in liquid antirust oil, take it out and drain it. Some antirust oil needs to be heated to a certain temperature when it is too thick.

2. Brush coating: apply the antirust oil on the surface of metal products with a brush, especially for large products and products with complex shapes.

3. Spraying is fast and uniform for large metal products.

4. Immersion, small metal products can use this method.

Generally speaking, the rust prevention work is completed after the above antirust oil is applied for short-term or process rust prevention. However, for long-term storage and rust prevention, packaging is also required to protect the antirust film from damage in transportation and storage and reduce the invasion of corrosive media. Generally, materials with good sealing performance and soft film, such as plastic film, aluminum plastic film, wax paper, are commonly used.

3、 Classification of antirust grease

It can be divided into: antirust oil between processes, long-term storage antirust oil, antirust machinery oil, antirust instrument oil, etc;

According to its state, it can be divided into three categories: liquid antirust oil, solvent diluted antirust oil and antirust grease. The antirust oil is divided into five types: fingerprint type antirust oil, solvent dilution type antirust oil, grease type antirust oil, lubricating oil type antirust oil and vapor phase antirust oil. The antirust oil has antirust property, zinc solubility, washability, oil film thickness, workability, oil viscosity, etc.

4、 Cleaning before rust prevention

The surface of processed metal products will be attached with a lot of dirt, such as acid, water, salt, dust, cutting fluid, hand sweat, etc. They may corrode the metal themselves, and also make the antirust oil can not be evenly and tightly adsorbed on the metal surface to isolate environmental corrosives, so it is necessary to clean them first.

General cleaning materials include petroleum solvent (gasoline, kerosene, solvent oil, etc.), chemical solvent, alkali solution, water, etc. Petroleum solvent has good effect on cleaning oil stain and some organic matters, but it has poor effect on inorganic matters and water-soluble matters. When using, operators should take protective measures for their skin and breathing, and have good ventilation. Because such articles are flammable, open fire and high temperature should be prevented. Chemical solvents, such as chloroform, have higher degreasing capacity than petroleum solvents, and also have good solubility in asphalt, resin and wax, but they are expensive, volatile and toxic, so they should be used with caution. For oil stain, salt, inorganic matter, hand sweat, etc., the effect of cleaning with alkaline cleaner, steam or water solution is also very good. They are cheap and have low risk. In a word, different cleaning media should be selected for the dirt on the metal surface. At the same time, attention should be paid to the cleaning of these cleaning media. In order to save money, cleaning media with a lot of dirt should not be used to clean the metal surface, so that there will be more dirt on the metal surface. The metal products shall be dried after cleaning, generally including drying, blowing and draining.

5、 Composition of fingerprint removing antirust oil

Metal parts are easy to rust during processing or storage, especially in hot and rainy wet seasons. The fingerprint rust preventative oil can also be used to weigh the type change rust preventative oil, which can replace or neutralize the sweat stains and a small amount of water left on the surface of processed parts, semi-finished products, or finished products. It is characterized by oil carrying operation, no need for cleaning, and can be diluted in any proportion. It is mainly used for rust prevention between processes or intermediate warehouses, and its concentrate can also be sealed for rust prevention for a long time.

Generally, fingerprint removing antirust oil is made of light lubricating oil, antirust agent, alcohol, ketone and other “water and agent” mixed with surfactant. It can be brushed or sprayed on the metal surface. The water, salt and fingerprint traces that promote rust can be replaced and removed before they can play a role. This antirust oil is mainly used for intermediate treatment in metal parts processing process, or short-term antirust with an indoor turnover period of about 3 months.

6、 Test method for rust resistance of antirust grease

There are many methods to test the antirust property of antirust grease, but in general, it can be divided into two categories:

One type is atmospheric exposure test, including atmospheric exposure, louver box and indoor storage. This method is simple and can be carried out by placing test pieces, parts or even integrated products indoors, outdoors or in louver boxes. This is the most reliable method to actually check the antirust performance of various antirust grease under natural conditions. Because it most conforms to the local actual atmospheric conditions, which can not be simulated by the accelerated test in the laboratory. Therefore, although the test cycle is too long, it is often used in practice, sometimes even necessary.

The other is indoor accelerated test, that is, in the laboratory, various devices are used to simulate actual service conditions, or man-made harsh conditions, such as high temperature, high temperature, salt spray, and harmful gas corrosion process acceleration. The advantages of these methods are fast time, short cycle, accurate control of corrosion conditions, and good reproducibility of test results. However, due to the complexity of atmospheric corrosion conditions, a specific test method can only emphasize one or several factors, so its test results have considerable limitations. The results of each test method can only reflect the performance of antirust grease from one aspect, Therefore, for the evaluation of the same antirust grease, several accelerated tests are generally required to comprehensively reflect the protective performance of this antirust grease from all angles to ensure its use. Even this does not fully represent the actual use.

Since all accelerated tests are carried out under specific corrosion conditions, it is difficult to find a parallel relationship between them and the results of the first type of tests, such as storage test and taste box test, that is, the so-called “conversion coefficient” cannot be obtained, which is proved by many practices. For example, in the evaluation of thin layer oil, the corrosion of a good thin layer oil in the dynamic tide indicator box is often better than that in the louver box test at the same time. The indoor test methods of antirust grease can be roughly divided into direct and indirect methods. The direct method is to place the oiled metal test piece in a specific corrosion medium, accelerate the corrosion, and finally evaluate it according to the surface condition or weight change of the metal. The indirect rule is used to measure the bending of certain physical and electrochemical properties before and after the test or the change in the test process.

7、 Effect of Salt Water Concentration on Rust proof Grease Test

The concentration of brine has a great difference on the test results of antirust grease. From the verification test, when the concentration of sodium chloride is 3-5%, the corrosion speed is the fastest, and the parallelism and reproducibility are good. When the concentration is greater than 8%, the corrosion rate slows down, and the parallelism and reproducibility are poor. Therefore, the concentration used in the standard is 5%. It is generally believed that increasing the concentration of sodium chloride solution is beneficial to improving the corrosion rate, but this is not the case in fact. This is because with the increase of salt concentration, the solubility of oxygen is low, which blocks the cathodic process, that is, the depolarization process of oxygen.

8、 Corrosion effect of salt spray resistance test

The corrosion effect of salt spray test is the same as that of other chemical and electrochemical processes, which accelerates with the increase of temperature. The foreign standard methods are specified as room temperature, 20 ± 2 ℃, 35 ± 2 ℃ and 50 ± 2 ℃. The use of room temperature will bring great differences due to time and place; 20 ± 2 ℃ is adopted. For southern China, especially in summer, additional cooling devices are required, which complicates the equipment; Use 50 ± 2 ℃. The materials used and temperature control have certain difficulties; Therefore, 35 ± 2 ℃ is adopted in the standard, because this temperature does not require cooling devices in summer, but only simple heating devices in winter.

9、 Relationship between metal rust and antirust grease

During the storage, transportation and use of metals, due to the influence of water vapor, oxygen, acid, alkali, salt, carbide and other substances in the environmental atmosphere, under certain conditions of temperature, humidity and time, physical and chemical changes will occur and corrosion will occur. Corrosion of metal will cause loss of metal and decline and loss of functions of metal parts. Metal corrosion is caused by oxidation reaction of metal in contact with humid air or electrolyte solution.

10、 Corrosivity of antirust grease

The corrosivity of antirust grease is to test the corrosion effect of grease on metal surface due to different composition of grease and the influence of sulfide, organic acid, free acid and alkali, water or other impurities when the grease is in long-term contact with metal. Some corrosion inhibitors can protect some metals, but may corrode others. The corrosivity of antirust grease is one of the important quality standards. In order to accelerate the process of corrosion test, the test is conducted at a certain temperature.

The types and arrangement order of metal materials are specified in the standard methods. The selection of metal test piece materials is mainly based on the metal materials commonly used by the relevant domestic factories and research institutions. At the same time, these metal materials are finalized by national standards or ministerial standards. In the standard method, it is specified that T 3~T4 red copper, H62 brass, anode cadmium, anode zinc, MZ5 magnesium, LY 12 aluminum, and steel are hung on the test piece rack in the order of T 3~T4 red copper, H62 brass, anode cadmium, anode zinc, MZ5 magnesium, LY 12 aluminum, and steel, The sequence of metal test pieces has a certain influence on the corrosion test of oil products. The corrosion results of single piece test and combined test pieces in the same oil test are also inconsistent, especially for copper and magnesium pieces. In several tests, the single copper strip test is more corroded than the combined test. Therefore, for the sake of uniformity, this method stipulates the above order, which is the same as the standard provisions of foreign methods. However, some units believe that the order of oil products with good quality does not seem to matter much after verification.

The method specifies that the lead strip corrosion test is conducted separately. This is mainly determined by the corrosion characteristics of lead metal. The corrosion of lead in grease is generally large, and there are many corrosion products. Generally, the oil solubility is good. If lead is coexisted with other metals in a test oil, the corrosion of other metals is often affected by the corrosion products of lead, so it is reasonable to conduct the corrosion of lead test pieces separately. Lead corrosion is mostly calculated by weight loss.

The temperature of the corrosion test shall take into account the temperature of the antirust grease in actual use. If the temperature is too high, the grease will not be decomposed correctly. The temperature is too low, the reaction time is too long, and the significance of accelerated evaluation is lost. E.g. 1 OO ℃ × The 3-hour red copper corrosion test is commonly used to inspect the corrosivity of lubricating grease and fuel oil at home and abroad. For antirust grease, the 1 O O ℃ is too high, and the 3-hour time is too short. Therefore, this condition is not suitable for the corrosion test of antirust grease.

This method specifies that the corrosion test temperature of antirust oil is 55 ± 1 ℃, which is because ordinary antirust oil is used at room temperature. Solvent diluted antirust oil and displacement antirust oil contain solvent, and the temperature is too high to exceed the specified temperature, so the test is unsafe. The test temperature of the same type of antirust oil abroad is also specified as 55 ± 1

The test temperature of the antirust grease is 80 ± 1 ℃. At this temperature, the antirust grease can reach the homogeneous liquid state, which is a kind of corrosion to the metal test piece due to the uniform contact between the antirust grease and the test piece. On the other hand, the antirust grease is applied at a temperature of 80.