The difference between pickling, phosphating, and passivation

In an effort to prevent corrosion or simply improve appearance, engineers will often specify an additional finishing treatment process for a portion, or all, of a metal part’s exterior surface after it has been machined or fabricated.

No matter what the reason, each of these metal surface treatment finishing processes plays an important role in the manufacturing process:

Pickling

The definition of pickling

Acid is used to remove oxide scale chemically according to a certain concentration, temperature, and speed, which is called pickling.

Pickling classification

• According to the type of acid: sulfuric acid pickling, hydrochloric acid pickling, nitric acid pickling, hydrofluoric acid pickling. Pickling must choose different media according to the material of the steel, such as pickling carbon steel with sulfuric acid and hydrochloric acid, and pickling stainless steel with mixed acid of nitric acid and hydrofluoric acid.
• According to the shape of steel: wire pickling, forging pickling, steel plate pickling, strip steel pickling, etc.
• According to the type of pickling equipment: tank pickling, semi-continuous pickling, full continuous pickling, tower pickling.

The principle of pickling

Pickling is the process of chemically removing the oxide scale on the metal surface, so it is also called chemical pickling. The iron oxide scale formed on the surface of the steel pipe is an alkaline oxide that is insoluble in water. When they are immersed in an acid solution or sprayed on the surface of the acid solution, these alkaline oxides can undergo a series of chemical changes with the acid.

Because the iron oxide scale on the surface of carbon structural steel or low-alloy steel is loose, porous and cracked, and the iron oxide scale undergoes repeated straightening, stretching, and conveying along with the strip steel on the pickling line, these pores and cracks further increase and expand, so while the acid solution chemically reacts with the iron oxide scale, it also reacts with the base iron of the steel through the cracks and pores. That is to say, at the beginning of pickling, three kinds of chemical reactions between iron oxide scale and metallic iron and acid solution are carried out at the same time.

1. The iron oxide scale reacts chemically with acid and is dissolved (dissolution).
2. Metal iron reacts with an acid to generate hydrogen, which mechanically peels off the iron oxide scale (mechanical peeling action).
3. The generated atomic hydrogen reduces iron oxides to ferrous oxides that are easy to react with acid, and then react with acid to be removed (reduction).

Passivation

The Principle of passivation

The passivation mechanism can be explained by film theory. That is to say, passivation is due to the action of metal and oxidizing substances, which produces a thin and dense passivation film on the metal surface with good covering performance, and can also be firmly adsorbed on the metal surface. Passivation film firmly adsorbed on the metal surface. This film exists as a separate phase, usually a compound of oxidized metal. It plays the role of completely separating the metal from the corrosive medium, preventing the metal from contacting the corrosive medium, so that the metal basically stops dissolving and forming a passive state to achieve the role of anti-corrosion.

Advantages of passivation

1. Compared with the traditional physical sealing method, the passivation process has the characteristics of absolutely no increase in the thickness of the workpiece and no change in color, which improves the precision and added value of the product, and makes the operation more convenient; 　　
2. Since the passivation process is carried out in a non-reactive state, the passivation agent can be added and used repeatedly, so the life is longer and the cost is more economical.　　
3. Passivation promotes the formation of the oxygen molecular structure passivation film on the metal surface, the film layer is dense, the performance is stable, and it has a self-repairing effect in the air at the same time, so compared with the traditional method of applying anti-rust oil, the passivation formed The passivation film is more stable and corrosion-resistant.　　

Most of the charge effects in the oxide layer are directly or indirectly related to the thermal oxidation process. In the temperature range of 800-1250℃, the thermal oxidation process with dry oxygen, wet oxygen, or water vapor has three continuous stages. First, the oxygen in the ambient atmosphere enters the formed oxide layer, and then the oxygen diffuses into the inside through the silicon dioxide. When it reaches the Si02-Si interface, it reacts with silicon to form new silicon dioxide. In this way, the oxygen entry-diffusion-reaction process continues to occur, so that the silicon near the interface is continuously converted into silicon dioxide, and the oxide layer grows into the silicon wafer at a certain rate.

Phosphating

Phosphating treatment is a kind of chemical reaction to form a layer of film (phosphating film) on the surface of a surface treatment process.

The phosphating process is mainly used on the metal surface. The purpose is to provide a protective film for the metal surface to isolate the metal from the air and prevent it from being corroded. It is also used for the primer before the painting of some products. With this layer of phosphorus, The chemical film can improve the adhesion and anti-corrosion ability of the paint layer, improve the decoration and make the metal surface look more beautiful, and can also play a lubricating role in the cold working of some metals.

After phosphating treatment, the workpiece will not be oxidized and rusted for a long time. Therefore, the application of phosphating treatment is very wide, and it is also a commonly used metal surface treatment process, which is more and more used in automobiles, ships, machinery manufacturing, and other industries.

Classification and application of phosphating

Normally, a kind of surface treatment will show one color, but phosphating treatment can show different colors by using different phosphating agents according to actual needs. This is why we often see phosphating The processing is gray, colored, or black.

Iron-based phosphating: After phosphating, the surface will appear iridescent and blue, so it is also called color phosphor. The phosphating solution is mainly made of molybdate, which will form an iridescent phosphate film on the surface of steel materials. It is also mainly used for coating the bottom layer to achieve the anti-corrosion ability of the workpiece and improve the bonding force of the surface coating.

The distinction in between pickling, phosphating, and passivation

Phosphating treatment refers to a chemical treatment approach in which a metal surface is contacted with an acidic service consisting of dihydrogen phosphate, and a chemical reaction occurs to form a steady insoluble inorganic substance movie on the metal surface area. The formed film is called a phosphating movie.

The modern-day phosphating procedure is normally: degreasing → water washing → rust elimination → surface conditioning → phosphating → water washing → drying.

Degreasing: The grease on the parts not only hinders the formation of phosphating film but likewise impacts the adhesion and rust resistance of the coating when it is painted after phosphating.

Passivation treatment is the last procedure step in chemical cleaning, and it is a crucial step. After the boiler is marinaded, cleaned with water, and washed, the metal surface area is very clean, extremely activated, and prone to corrosion. Therefore, passivation treatment needs to be performed immediately to form a protective movie on the cleaned-up metal surface area to slow down deterioration.

Purpose: Comprehensive pickling and passivation treatment of stainless steel to eliminate all types of dirt such as oil, rust, oxide scale, welding spots, etc. After treatment, the surface area ends up being uniform silver-white, which significantly enhances the corrosion resistance of stainless steel. It appropriates numerous types of stainless steel parts, Plate and its devices.

Features: Simple operation, convenient usage, cost-effective and useful. At the same time, high-efficiency rust inhibitors and fog inhibitors are contributed to prevent metal from over-corrosion and hydrogen embrittlement and to inhibit acid fog.

The passivation procedure is normally: degreasing → water cleaning → delighting → water washing → passivation → water cleaning → drying.

Phosphating and passivation are both surface anti-rust effects.

Pickling is the procedure of using dilute hydrochloric acid, sulfuric acid, and phosphoric acid to eliminate rust from rust on the metal surface. It is often used in the shipbuilding industry. For pipeline rust elimination, the inner wall of the pipe is normally rusted when the pipeline is installed. When the rust can not be eliminated manually, Will utilize this technique. In addition, electroplating parts ought to be cleaned up by marinading throughout commercial production. The phosphating process typically occurs more often in automated assembly lines, mainly to increase the bonding force between the metal surface area and the very first coating. For instance, in auto production, the procedure of degreasing → washing → (rust elimination) → surface area conditioning → phosphating → washing → drying-electrophoresis is usually adopted, which usually does not have the function of rust avoidance, however, due to the higher pollution, the use is less.

Wuxi T-Control Industrial Technology Co. Ltd. is a professional manufacturer of pickling and phosphating lines. It has rich overseas engineering experience, stringent quality control, 24-hour reaction after-sales service, and sensible prices, which have been acknowledged by industry clients.

The distinction between pickling with hydrochloric acid and sulfuric acid

Benefits and disadvantages of marinading hydrochloride

(1) Advantages of pickling with HCl

Although the pickling solution can be either sulphuric acid or hydrochloric acid, hydrochloric acid is mainly used in pickling line production. Due to the fact that the pickling operation can be performed at room temperature, hydrochloric acid has strong chemical solubility to metal oxides, and can successfully pickle a range of metals.

Under the greenhouse, the dissolving pickling of the iron matrix of steel workpiece with hydrochloric acid is much faster than sulfuric acid, and the pickling time is much shorter, so it is simple to manage the pickling procedure efficiently. Therefore, making use of hydrochloric acid to marinade steel workpieces is less most likely to cause "extreme deterioration" and "hydrogen embrittlement".

At room temperature, the surface of the workpiece after marinading is less residue, the surface area quality is greater.

Improve the quality of hydrochloric acid concentration is one of the procedures to enhance the speed of pickling, hydrochloric acid marinading less hydrogen precipitation, so the "hydrogen embrittlement" phenomenon is lighter.

For numerous oxides of iron, the solubility in hydrochloric acid is little, and the solubility in sulfuric acid is relatively large, therefore, using hydrochloric acid is much easier to manage the iron ion content variations, so regarding preserving a greater pickling speed.

For the exact same concentration and temperature level of hydrochloric acid and sulfuric acid, the marinading speed of hydrochloric acid is 1.5 to 2.0 times faster than that of sulfuric acid.

(2) Disadvantages of marinading with HCl

Utilizing hydrochloric acid production expenses are high, unstable, corrosive fog must be installed with the excellent effect of the slander gas equipment, waste acid treatment, and resource recycling procedure are really complex. And sulfuric acid is cheap, simple to transport and store, high concentration of product acid, in a really high pickling temperature level, almost no steam. This is because there are trusted commercial treatment methods for waste acid and wastewater, so before the 1960s, continuous pickling of strip steel was nearly inevitably made with sulfuric acid.

Benefits and downsides of sulfuric acid pickling

(1) Advantages of marinading with sulfuric acid

The production expense of sulfuric acid pickling is lower, and at the same time, it is easier to recycle the waste acid of sulfuric acid than hydrochloric acid

Raising the temperature level can extend the pickling efficiency of sulfuric acid, which is conducive to reducing acid intake and production expenses.

The storage and transportation of focused sulfuric acid do not require the use of acid-resistant materials.

(2)Disadvantages of pickling with Sulfuric acid.

Sulfuric acid in the pickling process of the workpiece iron base of the engraving big, easy to produce hydrogen embrittlement. When the temperature level is expensive, it is simple to trigger "over rust" of the iron matrix and increase the possibility of "hydrogen embrittlement", for that reason, it is necessary to add a corrosion inhibitor to control it.

In order to improve pickling performance, it is required to perform heating and warming operations.

After the workpiece has been marinaded with sulfuric acid, a layer of dark black iron salts remains on the surface, which is not easy to tidy.

Concentrated sulfuric acid can quickly trigger chemistry, so unique care needs to be taken when managing and utilizing it.

Understanding more about steel pickling techniques in detail

Steel is an alloy utilized in a broader range of applications for various purposes. It contains elements such as carbon, iron, manganese, cobalt, vanadium, chromium, and molybdenum that are understood for their special homes. On the other hand, there are some techniques used for improving the quality of steel with high success rates.

What is a steel pickling?

Marinading includes metal treatment processes to remove impurities and other undesirable substances from steel. It uses an acidic option called as "pickle liquor" that contributes more to eliminate the oxide layer with optimum results. Most steel processing business uses hydrochloric acid and sulfuric acid while performing pickling.

On the other hand, the exact may vary depending on the type of metal which gives ways to undergo major modifications. Acid cleaning has some constraints because it does not apply to all steels. As a result, steel production companies choose some alternatives to get a solution to the issues as soon as possible. This, in turn, paves methods to save time in the production process.

Comprehending more about steel pickling line

A steel pickling line targets at clearing any pollutants, rust, and scale from steel through communicating strips. Nevertheless, technologies are enhancing these days and wire surface treatment is capturing the attention of many providers because it leads to numerous benefits. A totally automatic closed wire surface area treatment has 4-5 trolleys which can assist take full advantage of the steel production to a big extent. The technique is to bring in consumers from different parts of the world.

The wire surface treatment uses computer-controlled cranes that will keep an eye on the development of wire rod coils. Apart from that, it even needs phosphating to eliminate the surface area oxides created during the hot rolling process. Besides that, the surface of the wire rod is easily vulnerable to rust and needs pickling to control it considerably. The primary benefit of the steel pickling line is that it offers approaches to guarantee maximum protection.

What are the features of the steel pickling & phosphating line directly type?

Steel pickling & phosphating line straight type includes specific features that permit steel-producing systems to achieve goals in the production. The first thing is that it is a totally enclosed production process that will reduce the contamination of the environment. Besides, it is a fully automated technique that supplies several advantages to industries. Some of them include stability, automation control, popular performance, and really low maintenance.

What is the steel picking circle type?

The circle type pickling type involves certain applications that make it possible for steel production systems to minimize undesirable issues. They consist of packing, pre-cleaning, marinading 1, pickling 2, marinading 3, immersion cleansing 1, high-pressure cleansing, surface area conditioning, phosphating, immersion cleaning 2, hot-dip, organization, saponification, drying, and unloading. Apart from that, it consists of the exact same functions as straight-line type pickling which shows methods to experience the desired outputs. Most of the time, industries that participated in the pickling of steel will assess the requirements of steel producers correctly to prepare the operations according to needs.

What is a pre-treatment line in steel pickling?

A pre-treatment line uses marinading options for traditional processes that provide methods to increase productivity levels. It consists of an environmental management program with an automated operation mode. The technique is an appropriate one for minimizing the production expenses while performing marinading works. A few of the applications utilized at the same time include poisonous gas detection systems, distributed control systems, and so on. All of them enable steel production units to get top quality products with much better services. It is possible to prevent safety threats and other problems with pre-treatment line pickling methods that can assist increase the quality of steel products.

About Wuxi T-control steel pickling business

Wuxi T-control steel pickling business provides services for clients with the most innovative methods. Based in China, it has a well-experienced R & D group that supplies solutions for numerous industries with integration methods. It is well-equipped with modern-day centers to plan the tasks in a comfy environment. Also, the business follows high requirements in the pickling process that can assist get rid of pollutants efficiently. The costs are an affordable one that enables the steel-producing businesses to ensure that their products feature the best grades while offering them on the markets.

How to call the company?

Those who would like to know more about marinading services can contact the company through e-mail. The business uses free assessments for consumers to know more about the techniques and other things in detail. This will help a lot to choose services that fit their budgets. It gives ways to set up whatever with a programmable reasoning controller and other innovative equipment consequently revealing methods to get the very best outcomes. It is a licensed business that renders services with experienced and expert teams. With marinading services, steel units can focus more on their objectives efficiently that assistance witness comfort.

 Assembly line type

The assembly line system completely breaks through the standard manufacturing procedure, takes on the annular, closed and also programmed mode, and also at the same time considers the on-line environmental protection scheme, understands the continual automatic procedure setting, considerably improves the production effectiveness, lowers the manufacturing expense and enhances the production atmosphere.

Assembly line technical needs

1. The basic make-up of assembly line: The pickling line contains the primary frame, circular track, packing car, process storage tank, hanging mobile vehicle, maintenance terminal, an electrical control part, environmental protection system, and so on.
2. Assembly line tools requirements: The tools choice or self-built part of the assembly line will satisfy the site's ecological requirements as well as functional demands, satisfy the technological accessories, and also style needs.
3. Production line control: The efficiency and technological demands of the assembly line tools will be collaborated to make sure the system runs dependably under the established process as well as working conditions.
4. Production line style needs: The style and manufacture of the production line shall be taken into consideration according to the purchaser's demands, real site, ecological conditions, financial investment range, upkeep, and also other factors.

Production line operation demands:

To make sure the safe, as well as typical operation of the system, the complying with operational needs, will be fulfilled:

• Supply 220V/380V three-phase four-wire power supply, 50Hz, 200KW voltage fluctuation
• Give tap water stress of 0.15-0.2 mpa with a flow rate of 15 m3/ h;
• Provide steam stress: 0.5-0.7 mpa; Temperature of 150 ℃,180 ℃; Flow price of 3000 kg/h;
• Provide pressed air pressure: 0.2-0.4 mpa; Flow 0.3-0.5 m3/min.
• Provide industrial water (reuse water): the storage tank capability is 50m3/h (nonstop supplement), PH worth is 7-8
• Give natural gas calorific value: >= 8000kcal/m3 (natural gas can be made use of to completely dry if readily available).
• The stress of 0.03 MPa diameter Φ 32.
• Ecological specifications of the temperature:-- 10 ℃,50 ℃. Loved one moisture is less than 90%.

Demands of the assembly line to the workshop and also auxiliary centers are as complies with:

the floor of the craft trough rack/trench will be anticorrosive therapy. Doors and Windows must be made from anti-corrosion products, the home shelf must be well anti-corrosion procedures.

The track position of the electric flat vehicle shall be well-drained pipes as well as the security rail centers will be thought about (the purchaser will be accountable for it).

The acid pool, phosphorus slag reduced level swimming pool, saponification swimming pool as well as follower shall be well secured from rainfall as well as drainage, and also the safety railings shall be well shielded (the purchaser will be accountable for it).

Process circulation and also criteria of the assembly line.

The device adopts the sequential procedure circulation, without roundtrip or recurring procedure, making the assembly line running the easiest and most cost-effective.

Procedure flow diagram:

feeding:

pickling1 → pickling2 → pickling3 → pickling4 → pickling5 → The typical temperature level immersion wash 1 → high-pressure laundry → Hot-dip laundry 1 → phosphating → The regular temperature level immersion laundry 2 → Hot-dip clean 2 → saponification → completely dry.

Keep in mind:

1. This is a reference procedure, which may need modification in actual production.
2. Customers can change craft trough and choose the needed procedure slots.

Reviewing the Environmental Benefits as well as Manufacturing Improvements Effected by Wuxi T-Control Wire Rod Pickling Lines

As a surface area therapy procedure, industrial-grade pickling is defined as a chemically energetic cleaning operation. The process essentially uses caustic acids to search away post-procedure surface pollutants. Metal oxides, surface scale, dust, and warm treatment sustained tarnishes, they all break down as well as come free when a workpiece is dealt with.

Suppose the subject steel is a continuous production line of cord poles? Classed as the thinnest, most dimensionally minimized lengths of slim steel, a by hand run post-processing line might probably clean away the persistent range and also corrosion caused by a previous treatment cycle, however, the procedure would certainly be reasonably sluggish as well as inefficient. Furthermore, acid pickling procedures would generate horrible chemical by-products, including clouds of dangerous fumes. Keep in mind, acidified condensates are especially harmful, particularly as they collect on the revealed surfaces and also trigger destructive exhaustion. What, then, is the remedy? Is there an elegant, machine-based system that can address every one of these problems?

Introducing the Wuxi T-Control Pickling system

By automating the pickling process, performance margins climb and expand healthily. Next, pull the system containers inside an encased housing, acidified fumes are removed. Employee safety and security are ensured, environmental concerns are considerably reduced, as well as operational performance scores gain strength. As a result of all of this cutting-edge device refinement, succeeding handling costs drop. It's, as affordable production kinds like to claim, a win-win situation. Taking the lead in this commonly difficult, metallurgically prejudiced post-processing system, Wuxi T-Control Pickling Lines are swiftly transforming the market. From the lowered toxin levels to the higher volume-outcome, as enabled by the automatic nature of the devices, the system provides a variety of key advantages, the majority of which can not be matched by any other competitor, especially those that rely on older, obsolete technologies.

Fixing the Wire Rod Contaminant Conundrum

Here's the issue: If a hot rolling method is utilized to create a coil of wire, then the little cross-sectional area of the wire will collect some type of range. This corroded pollutant is difficult to eliminate because of the width of the discharged work surfaces. One option is to utilize pickling bathrooms, then to instantly coat the freshly combed metal wire with a safety phosphate finish. This finish won't rust, won't collect a scaly coating since it's protected. In other words, the cable has actually been "pickled" (acid cleaned) and phosphate-coated (enclosed by a thin crystalline skin) so that it's clean and also totally secured from additional atmospherics-induced responses.

The acid-cleaned cable is also somewhat oily, to the point that it gets a superior anti-galling coefficient. The clean, layer shielded, and also lubricated coils are said to be post-processed full. Additionally, they proceed to a secondary production procedure, such as a wire drawing process. Now, all of this job already conjures up a number of innovative tools lines. Include in that, though, the idea of a die-implemented cross-sectional location modification. That suggests, instead of a plain round shape, a special die setting up outputs cable rods that have a geometrically complex area. With extremely in-depth cable accounts like these, warm or chilly rolling sustained impurities end up being even tougher to remedy. Once more, the Wuxi T-Control Pickling Line makes short work of such manufacturing challenges.

Deconstructing the Immersion Mechanics

Having a look at the blueprints of the device with a vital eye, it breaks down right into several plainly delineated stages. As explained previously, everything is enclosed. Like a vacuum cleaner heater and also quenching bath, the first chamber is sealed, hence holding the acid haze securely back as it increases from a bank of immersion tanks. Regarding its design, it's a large steel structure with pathways in place for service technicians to keep track of as well as preserve the equipment. Inside, a manipulator and also hook system does as the wire pole transport system. This system transports the fouled workpieces with a crosslinked setup of passages.

Remarkably, the assembly line is liquid-based, not developed out of conveyor belts as some may anticipate. Sequentially continued, the wire is hot rinsed and pressure-flushed by caustic liquids. Meanwhile, as an acid mist climbs from the containers, it fills the chamber. It's at this factor while doing so that problems, quite actually, rise. That destructive ambiance gets attracted to the acid mist pipe and counteracted in a downstream purification tower. Back with the transportation manipulator, the wire is steadily stripped and also descaled as it proceeds with all number of immersion-style flushing as well as rinsing tanks. It's a stealthily intricate series, one that can be varied to fit different steel qualities and descaling settings. In order to maintain that clockwork-like computerized sequence, a dedicated control system takes charge of every procedure variable. Every operation, every system specification is finitely controlled, as implemented by this streamlined control hub.

Stage two of the post-processing technique kicks the process up additional gear. The manipulator carries the acid-descaled cord poles onwards to a saponification storage tank, which utilizes an alkaline-based hydrolysis method to help prepare the slim steel surface for its phosphate finish. Without this important treatment phase, the next phase would yield substandard results; The zinc-based surface just wouldn't stick completely to the wire.

Recapping the Processing Benefits

Eco, steel pole pickling is a chemically unpleasant procedure. It's a traditionally messy as well as an inefficient method. Caustic hazes escape right into the ambiance and also harm local ecologies. It's the very same in financial terms, with acidic and also alkaline fumes maturing revealed surfaces. The damages have to be made up, so there are costly prices to offset, too. By switching over to Wuxi T-Control, by purchasing and also running an automated cord pole pickling line from this established Chinese design business, metallurgical services acquire a considerable manufacturing side. That side likewise minimizes environmental problems since the whole control-system controlled procedure is safely included inside a specifically sealed device real estate.

With the ability of descaling after that phosphate coating 300,000 lots of steel cable per year when fully operational, this equipment cuts factory expenses while raising workers' safety and security. The equipment automates a once messy and also environmentally dangerous production procedure to make sure that cord ropes as well as cable-based steel items can be descaled and covered wholesale without sustaining all sort of unpleasant by-products. Certainly, the computer-regulated tools are incomparably scalable and affordable, as confirmed by the flexible control system as well as the equipment's capability for exchanging out different immersion tank mediums.