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De-rust and Anti-rust
Writer：dl-admin2010-07-10 00:00
HEAT：896
All technical kinds of metalwork oil seal, is generally include cleaning, drying, packing, storage, and several other links. Each link is directly related to the quality of the storage is good or bad. Based on our practice in the above process in several years, we give a brief introduction.
Before storage products with rust, it is needed to remove the rust, or it will affect the seal quality. This is because the product under effect of further development of the electrochemical corrosion. Therefore, we also introduce how to de-rust in the following. Thus you can get a good result in the use of our anti-rust TO-40 and de-rust TO-30 products. Our company is Shenzhen Tony Electronics Co., Ltd.
1. Cleaning
Cleaning is an important part of oil seal. In terms of machining or assembly, or in product seal up for keeping, seal removing, we will meet it at all. There are many kinds of feculence: dust, cutting materials, abrasives, grinding paste, polishing paste, cutting liquids, hand sweat, salt trace, acid or alkali, plant and animal oils, and mineral oil, etc. These materials include not only water-soluble, but also non-water soluble. If you could clean these dirt materials at all, it will affect the processing, assembly and quality of oil seal. As the cleaning quality is not high, even if you use high quality anti-rust oil, it will not achieve the desired effect, because this is common practice in production. So cleaning is an important step of oil seal before you seal.
The most common detergent (clean agent) can be divided into two kinds. One is water-based detergent, including the added surfactant and non-added surfactant; the other is petroleum solvents and organic solvents.
2. Water-based detergent
Water-based detergent is mainly used for clean oil, and it can also clean the scrap metal attached on the surface of metal chipping, scum, abrasive and carbon residue mixed in the oil. Alkali detergent has a good result for clean the hand sweat stuck on the surface of metal. Because it contains high alkaline materials, so it can make plants oil or animals oil saponification, the cleaning effect is better.
Water-based detergent should have these capabilities: 1) solubility and high alkalinity; 2) dispersivity for solid greasy oil dirt; 3) emulsification and dispersivity for liquid greasy oil dirt; 4) easy to clean up; 5) has low surface tension and has lubrication capability; 6) stable; 7) the effective concentration is lower; 8) non-toxic; should not cause pollution; 9) if it is required in electrolytic cleaning, it has a good electrical conductivity.
Water-based detergent should have these capabilities: 1) solubility and high alkalinity; 2) dispersivity for solid greasy oil dirt; 3) emulsification and dispersivity for liquid greasy oil dirt; 4) easy to clean up; 5) has low surface tension and has lubrication capability; 6) stable; 7) the effective concentration is lower; 8) non-toxic; should not cause pollution; 9) if it is required in electrolytic cleaning, it has a good electrical conductivity.
3. Oil-based solvent cleaning
Petroleum has a strong capability for cleaning oil, it can easy to dissolve out the oil on the metal surface, but this flammable material easy burn, must prevent it from fire. Common petroleum solvents are gasoline, kerosene, light diesel oil, etc. The most popular among these is gasoline, because it volatilizes fast, easy to dry. Though the advantage it has, but the defect is moisture in the air will cause condensation. When gasoline evaporates and absorbs heat that makes the temperature down on the workpiece surface, concreting moisture drops on the metal surface, and will cause the metal to be rust. This is the common question in Southern district of our country. The amount of condensation more or less is in connection with gasoline distillation technics. If use rubber solvent oil (SY1027-67), its distillation range that is in the range of 80 ~ 120 ℃, due to its initial boiling point is higher than gasoline, so condensation phenomena is less than gasoline. In many solvent-dilution type of rust preventive oil, people select rubber gasoline as the solvent. If you use 200# gasoline (GB 444-64) as the solvent, it can solve condensation problem, because it is close to kerosene, not only bad smell, but also “heat hand”. Somebody uses kerosene or light diesel oil as the solvent for cleaning, but it is difficult dry, unless it can be allowed into the seal oil.
Pure petroleum solvent has not ability of clean sweat, and when it volatilizes, it will cause rust because of condensation. Therefore add 3 to 5% of the replacement-type anti-rust oil, and it is quite effective in practice. During the hot and humid season, because gasoline will vaporize, condensation of water will cause thin displacement-base oil film to emulsify, and changed to be emulsion liquid membrane (ELM). This layer membrane must be dried or not before oil seal, it depends on further practice. If chose high distillate as petroleum solvent for cleaning, this phenomenon can be avoided entirely.
For mechanical parts, the use of water-based products for anti-rust is more economical than oil-based products. Water-based anti-rust product is a kind of anti-rust material of water diluent, which is characterized by low cost, safety for use, when it is covered the metal surface, it can formed a protective coatin after water vaporized. Currently, water-based anti-rust product usually used for anti-rust in working procedure, individual product can be sealed up for keeping long term after working procedure.
4. Drying
It must remove attached water or solvent on metalwork surface in the shortest possible time after complete cleaning. It is needed an effective drying method. General drying method is heating, that is, put the metalwork into a drying cabinet or an oven with a humidity regulator and blast, or blow hot compressed air and make it dry. Workpiece cleaned with hydrosolvent, it can use boiling water for drying, that is, immerse the wet workpiece into the hot getting boil water in a period of time, then hang the workpiece into the air, quickly vaporize the water by temperature of workpiece itself. If necessary, it can also use compressed air for drying, or put the workpiece into the oil tank at a temperature of 105～110℃. Chose HJ-10, HJ-20 machine oil or other machine oil, and fill up the tank. Take workpiece out, there will be a very thin film covered on the surface layer, generally it can put anti-rust oil on the surface of workpiece, without cleaning anymore
Pay attention, workpiece must complete dry at temperature of 105～110℃, otherwise will affect the oil seal quality.
5. Derust
It is usually necessary to remove corrosion materials on the surface of metalwork before seal. This is the only way to ensure the quality of seal storage. Ordinary, these corrosion materials play the role of anode in the course of atmosphere corrosion, will accelerate the electrochemical process, and impel the development of corrosion. On the other hand in terms of chemical composition, they are metal oxides, hydrates, salts, etc., so there are quite hygroscopic, due to chemical cohesion, even in low humidity situation, it also makes condensed water film on the metal surface, and so it creates the conditions for the electrochemical corrosion.
In the mechanical products production process, the general corrosion of metal surfaces comes from two aspects: one is after heat treatment, due to the medium caused by heat treatment; another is atmospheric corrosion which is referred to as rust.
Medium corrosion of heat treatment in the production process, atmospheric corrosion and metal materials or processing defects often are indistinguishable. Although the use of advanced physical methods such as electron probe, scanning electron, energy spectrum, infrared analysis, etc., can help us to distinguish, but in general working conditions, it is impossible to do like this. In the production process, people use by ordinary instrument such as low multiple magnifying glass or metallurgical microscope, etc., for determination, discrimination. It is necessary to understand the general characteristics of corrosion, and no definitive regularity of the shape of corrosion. After removal the rest of anti-rust, if the bottom is seems dark, we can determine it is heat treatment corrosion or other chemical medium corrosion. In the production process, in order to distinguish more accurately, it must investigate on the scene, to understand the whole technological process of product.
De-rust methods can be divided into two kinds: by mechanical de-rust and by chemical de-rust. In spite of any kind, it will more or less decrease the workpiece precision, decrease the workpiece brightness. Which method is the best depends on need of the workpiece, that is, according to the different parts of workpicec and the precision level.
De-rust methods can be divided into two kinds: by mechanical de-rust and by chemical de-rust. In spite of any kind, it will more or less decrease the workpiece precision, decrease the workpiece brightness. Which method is the best depends on need of the workpiece, that is, according to the different parts of workpicec and the precision level.
Chemical de-rust can be divided into two types: chemical or electrochemical. When we select the method, we must according to the requirement of metals and different instances, and should pay attention to the specific ingredient and technical process.
It can use chemical de-rust for big parts or fixed equipment. Removed the oil attached at the rust place, spray a coating layer of de-rust agent (Shenzhen Tony’s product as TO-30), after a few seconds, check the rust whether is removed or not. If the rust is complete removed, turn over the part, add de-rust agent. After de-rust, clean up with pure water, then scrub with PH9~10 cleaning solution, operate compactly in order to avoid rust appears again. It must to avoid sunshine or light in order to prevent from evaporation of water.
After de-rust with corrosive chemical agent, it should immediately completely clean, counteract, and anti-rust, this process may be continuous, in order to avoid corrosion of the hidden dangers afterwards again. If it is the acid de-rust agent, generally use a neutral medium plus inhibitor of alkaline solution to counteract, then if select dehydrated water film anti-rust oil, it can omit drying process, and also play a seal storage effect.
Reactive film layer with good attached ability which formed from materials on metal surface be concerned with chemical reaction or electrochemical reaction, it is known as chemical conversion coating. Over a variety of chemical conversion coatings have a better protective properties than metals, so it can also be used to anti-rust after de-rust process, and to reinforce the metal corrosion resistance. Because liquid of the formation of chemical conversion coatings has more or less reaction for the metals, so in some conditions, it is known as deactivation usually. About specific content please see reference metal surface treatment information.
When in the selection of chemical de-rust or chemical conversion coating, pay attention not only to the case of hydrogen will separate out, but also pay attention to hydrogen embrittlement, especially for high strength structural steel should be cautious, in some cases these steels do not allow acid immerge in acid trough, because these steels will cause hydrogen cracking (cause the steels crack), even wipe out hydrogen by reheating at last, cracking will not disappear. When refinery was halted in order to repair, it is needed to blow water steam in the steel tower, not only to wipe out petroleum product, but to avoid hydrogen cracking in the tower, because in this case, when somebody entrances into the tower, he (or she) will fall down and even die, sometime it will cause explosion in case of operation (ignite fire).
Because magnesium alloy has a very low negative potential, so should pay attention to de-rust, in the use of mechanical methods, we must use special glass sandpaper (i.e., woodworking sandpaper) and alumina (corundum emery cloth), do not allow by use of silicon carbide or boron carbide cloth. When blowing sand, use common quartz sand, other metal use’s sands are strictly separated. These stipulations are to avoid conductive carbon or other metals enchased in the magnesium alloy to form a corrosive cell in the de-rust process. Also in chemical de-rust, it should choose non-conductive material as a tool to avoid corrosion because of they contact with.
6. Seal
When in the selection of chemical de-rust or chemical conversion coating, pay attention not only to the case of hydrogen will separate out, but also pay attention to hydrogen embrittlement, especially for high strength structural steel should be cautious, in some cases these steels do not allow acid immerge in acid trough, because these steels will cause hydrogen cracking (cause the steels crack), even wipe out hydrogen by reheating at last, cracking will not disappear. When refinery was halted in order to repair, it is needed to blow water steam in the steel tower, not only to wipe out petroleum product, but to avoid hydrogen cracking in the tower, because in this case, when somebody entrances into the tower, he (or she) will fall down and even die, sometime it will cause explosion in case of operation (ignite fire).
Because magnesium alloy has a very low negative potential, so should pay attention to de-rust, in the use of mechanical methods, we must use special glass sandpaper (i.e., woodworking sandpaper) and alumina (corundum emery cloth), do not allow by use of silicon carbide or boron carbide cloth. When blowing sand, use common quartz sand, other metal use’s sands are strictly separated. These stipulations are to avoid conductive carbon or other metals enchased in the magnesium alloy to form a corrosive cell in the de-rust process. Also in chemical de-rust, it should choose non-conductive material as a tool to avoid corrosion because of they contact with.
6. Seal
Different types of workpieces and products, different storage conditions, different storage period, all these should choose different kinds of anti-rust oil. There are several methods of oil seal: brushing method, dip method, oil cooking method, immersion method, spraying method, shower method, etc. Dip method is one of the commonly used for small and middle workpieces oil seal. If choose heat coating anti-rust grease, it needs to strictly control the heating temperature of oil tank and the time of workpiece immersed, because temperature and time determine thickness of oil coating, the higher temperature and longer time, the thinness oil coating; contrary, the thickness oil coating. If choose liquid anti-rust oil and solvent dilution type, it does not need heat, in this case it is only to immerse the workpiece into the oil complete, let the oil penetrates into every part of workpiece. But when you choose solvent dilution kind of anti-rust oil, you should pay attention to constantly replenish the amount of evaporation off the solvent, in order to avoid excessive coating thickness.
If choose brushing method, it should use the brush to brush coating, the brush should not be too soft, but also not too hard, because too soft brush can not make anti-rust oil cover the surface equality, and too hard brush can harm metal surface. For brush liquid anti-rust oil or solvent dilution, because their good fluidity, so it can use soft brush. Efficiency of brushing method is too low, so brushing method is only use in case of part oil seal or large workpiece oil seal.
Spray method is sprayed anti-rust oil on the surface of metal by air gun with compressed air. Although liquid anti-rust oil can be sprayed, but in practical applications mostly are solvent-dilution kind anti-rust oil (Shenzhen Tony Electronics Co., Ltd. TO-40 anti-rust agent sprays anti-rust oil on the surface of workpiece), especially hard coating oil for oil seal of large equipment and simple tools (or parts). It will form condensation from moisture in the air during spraying. To this reason, relative humidity should be controlled below 70%. In addition, personal use compressed gas should be the result of purification treatment in order to remove water and oil and so on.
Immersion method is mainly used for seal machine inner parts or precision workpiece, metal is completely immersed in the anti-rust oil. When complete immersion method is chosen, besides to select correct oil, should also pay attention to reserve some space in the container for expansion because of thermal conversion, the container is sealed tight, which prevent the leakage of oil, and avoid oil contact with air for a long-term. As the technical requirements of such oil, for instance, high require in anti-rust oil, especially demand of against the corrosion. Oil composition will be more low viscosity, high-refined oil.
Solvent dilution kind hard coating anti-rust oil are generally not immediately packed, it should be let the solvent volatilized suitability. Water emulsion (W Em) anti-rust oil when oil seal is done, generally it is needed to volatilize water, in order to finish this process, it is better to add a drying process after oil seal.
Cold brush grease is used by means of brushing, generally should not heated, but sometime it is needed to heat before brush because the cold brush grease is somewhat hard when the temperature is low. Pay attention to equality when brushing, or there are different thickness of oil coating on different parts, and can cause discoloration on thicker part.
Cold brush grease is used by means of brushing, generally should not heated, but sometime it is needed to heat before brush because the cold brush grease is somewhat hard when the temperature is low. Pay attention to equality when brushing, or there are different thickness of oil coating on different parts, and can cause discoloration on thicker part.
When select oil seal, pay attention to its adaptability of a variety of metals, especially various kinds of non-ferrous metals. Tdlytriazole oil though effective for copper alloy oil seal, but it will consume in the long-term use, may be caused by high vapor pressure. Therefore, according to regularly test the effect, add it suitability.
For bearings, gears, springs, gauges, bushings, powder metallurgy, precision instruments, weapons, tools, machine, and so on, whether they have plated or not, or passivated, TO-40 anti-rust oil cited foreign technology and produced by Shenzhen Tony Electronics Co., Ltd. can achieve satisfactory results.
7. Packaging
7. Packaging
Seal period of metalwork is directly linked together with packaging, and more important within which is packaging materials, because it directly joints on the surface of oil sealed metal. Suitable packaging materials should have a little water vapor permeability, air permeability and good resistance to oil, to avoid or reduce the infiltration and loss of oil, a certain mechanical strength to prevent crack. But more important is face to metal corrosion, it should arrange metal, oil and packing material can adapt each others. At present, selected packaging materials are paraffin paper, capacitor paper, sodium benzoate paper, polyethylene compound paper and polyethylene film, polyvinyl chloride film and so on.
Paraffin paper is neutral wrapping paper coated a layer of paraffin on both sides, and the coating thickness is about 0.05mm. Paraffin paper quality depends on the base paper quality at first, and according to neutral wrappeing paper regulation (QB601-72) of Ministry of Light Industry Standard, thickness is about 0.08~0.136mm; folding endurance (reciprocating times) is not less than 15 times; vertical and horizontal tensile strength (kg) is not less than 4.5 kg and 3.0 kg; water (%) is not more than 12; acidity (PH) is 6-8; chloride (mg/kg) is less than 0.003; coatings on the base paper is a mixture of paraffin, ozocerite, engine oil, this mixture should be no corrosion, particularly paraffin should be tested. So far, there is no National Standard, all are enterprises’ standards, the names also varies, some as anti-rust paraffin paper, some as neutral paraffin paper. In the indicators for the water extractives PH value, chloride, and sulfate, although they have provisions, but there are different standards. Water extractives PH value in most enterprises is 7.0~7.05; chloride (in NaCl) is less than 0.1%; sulfate (in Na2SO4) is less than 0.25%. An enterprise produces a kind of paraffin paper for a military department, they stipulate PH value of water extractives is 6.3~7.0; chloride ions is less than 75ppm. In the absence of proper determination of paraffin paper on the method of metal corrosion, it is difficult to provide suitable indicators of PH value of water extractives, sulfate, and chloride.
Capacitor paper (QB603-72) has high quality, its acid and alkaline of water extractives are not over 0.007%; chloride is not more than 0.004%; water extractives conductivity is not more than 4×10-5Ω/cm; and the paper has good strength, flexibility, good folding, etc., due to higher prices, generally used for high precision parts such as gauge block, etc., as in packaging.
On sodium benzoate surface, one surface is coated paraffin that contains 2% aluminum stearate, another surface is coated sodium benzoate solution. The reason of add aluminum stearate into paraffin is to increase the hydrophobic nature, and the reason of add sodium benzoate is to increase the anti-rust ability on the metal, because it is a kind of contact form corrosion inhibitor for various metals. The surface coated sodium benzoate solution faces to metal when it is packing.
The main thing is polyethylene paper in plastic compound paper. It is used neutral wrapper paper as the base, through a process of smooth, heat pressing, heat drying with melting polyethylene on one surface. A notable feature of such paper is high strength, moisture-proof, and strong oil resistant. Current production of polyethylene paper, according to the strength of base paper is divided into 1, 2, 3 species, each further divided into 15, 25, 40 (g/m2, 24 hours) according to the humidity, and total are 9 categories. To control the difference of humidity is based on the thickness of polyethylene film. Because neutral wrapper paper is non-corrosive, so both surface can wrap metal, usually people take the plastic surface to wrap the metal as oil seal.
From the current view, high-quality paraffin paper and capacitor paper are compatible with iron and steel, copper, zinc, cadmium and other metals. The sodium benzoate paper will cause the copper discoloration, but this paper is better than paraffin paper and capacitor paper when wrap iron and steel.
There are two kinds of plastic film for inner packaging: polyethylene film and polyvinyl chloride film. Because these two kinds of plastic film are not special inner wrapping materials, so there is no standard requirement for corrosion of metals previously. Generally, it is believed that PVC (polyvinyl chloride) film could decompose hydrogen chloride, and it can cause metal corrosion, but in actual use it has not been obvious problem, which may be respect of the film contains appropriate stabilizer. From the productive practice, PE (polyethylene), PVC films are still good adaptation for iron and steel, but are not ideal for copper, magnesium and some metals, but they are not ideal for copper, magnesium and other non-ferrous metals. Their thickness is usually used between 0.04~0.06mm, because the thin film is better flexibility, it can joint evenly on oiled metal surface when packaging. The even is relative to thick film. PVC and PE film can be sealed into a pocket by use of high frequency welding or resistance heat welding. When use plastic film for packaging, it is needed external packaging with paper or box, in order to prevent direct irradiation of light from plastic aging, decomposition, embrittlement.
It is reported a manufacturer has produced a kind of PVC film without elasticizer, it has good light-fastness, strong stability, and low permeability, and has good resistance to organic solvents, and it is a promising packaging material.
Similar to PE film is polypropylene (PP) film, its physical and chemical properties and adaptation for metals is also similar to PE film.
In conclusion, the rational selection of packaging materials, especially the inner packaging materials, metals, and anti-rust oil, the adaptability of these three factors is a major event related to seal quality. If there is any mistakes occur, at least it could not ensure seal period, or even it causes rust in batches with severity, and it always meets in production. At present, many anti-rust packing materials are enterprises’ standard, not only indicators are differences, but the test methods are not uniform. Although some packaging materials have Ministry Standard, but there is no consideration for inner anti-rust packaging materials. Therefore, be more carefully when you select packaging materials.
Besides, often there is occur so-called “dry oil spot” corrosion, it is related to package misconduct. Dry oil spot is considered as deterioration caused by mineral oil, because mineral oil was not refined well, when there are light and oxygen in the space, it is easy caused oil spot, and a wavelength of 360 nm light is the main factor to cause light oxidation reaction. If there are SO2 gas and light together, due to light sulfonation reaction, it may also create sulfur acidity. When analysis by X-rays fluorescence spectrometer, it can find in parts of the oil spot component is generated by carboxyl and sulphonate compound because of mineral oil deterioration, their thickness is over 300 angstrom, and there are difference compounds between upper layer and lower layer. To sum up, dry oil spot on the surface of iron and steel is poor refined mineral oil film, the corrosion phenomena due to light oxidation reaction, and generated a thickness which can be seen by eyes. When purchasing anti-rust oil, be sure to go to a professional company.
A method to reduce or avoid the corrosion of dry oil spot is chosen high precision mineral oil, that is, less impurities. As known, there are sulfur-based in impurities of mineral oil, and others are complex compounds of polycyclic aromatics, organic compounds of nitrogen and oxygen. If the mineral oil is refined to a content of sulfur below 100ppm, it can avoid dry oil spot corrosion in a long period.
Another method to prevent and to slow down the corrosion of dry oil spot corrosion is to avoid light irradiation after oil sealed and packaged. For this reason, when choosing PE, PVC, and other transparent film as packaging materials, it want to choose opaque packaging materials again, such as put in carton, wooden box, or cover with an opaque outer wrapping paper, and so on.
Anti-rust oil in inferior quality, there is a oil spot corrosion called wet oil spot corrosion. It is also frequently encountered in the packaging, which usually refers to the oil overlapping and humid conditions, metal corrosion on overlapping surface due to uneven extent oil film. Therefore, it should pay attention when choosing oil and packaging, because between the metal and the inner packaging material also will cause wet oil spot corrosion. Above is the condition of oil overlap resistance.
In wet conditions, packaging will encounter mildew condition. When use of paper-based packaging materials such as kraft paper, carton, which can immersed with organic cyanide RCN or fluoride, then it can avoid mildew. If improve local packaging environment, use low wet permeability packaging materials, such as PVC, PE, aluminum-plastic film, and combine with desiccant, such as silica gel, molecule sieve use in packaging, it can not only to prevent mildew, but also further enhance seal effect of anti-rust oil. In order to prevent mildew, of course, it can choose anti-mildew packaging materials.