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What is stainless steel passivation?
What is passivation and how does the passivation process work? How to passivate stainless steel parts after machining? These are questions machine shops and manufacturers of component materials such as stainless steel, titanium and tantalum often ask.
Passivation is a metal surface treatment process widely used to prevent corrosion. In stainless steel, the passivation process uses nitric or citric acid to remove free iron from the surface. Chemical treatments form a protective oxide or passivation film that is less likely to chemically react with air and cause corrosion. Passivated stainless steel prevents rust.
Passivation type
Today, the industry standard for surface passivation offers three types of passivation. Each type is based on the chemicals used for passivation. The three types of passivation are:
nitric acid
Nitric acid and sodium dichromate
citric acid.
The choice of chemicals for passivation usually depends on customer requirements. Each passivation type has its own advantages and disadvantages. See our article Nitric vs. Citric passivation for more information.
Why passivate stainless steel?
Passivation is a post-fabrication best practice for newly machined stainless steel parts and assemblies. Benefits include:
Anti-rust chemical film barrier
Extend the life of the product
Remove contaminants from product surfaces
Reduced maintenance requirements.
How does passivation work?
Stainless steel is an iron-based alloy usually composed of iron, nickel and chromium. The corrosion resistance of stainless steel comes from the chromium content. When chromium is exposed to oxygen (air), it forms a thin film of chromium oxide that coats the stainless steel surface and protects the underlying iron from rust. The purpose of passivation is to enhance and optimize the formation of the chromium oxide layer.
Immersing stainless steel in an acid bath will dissolve free iron on the surface while leaving the chromium intact. The acid chemically removes free iron, leaving a uniform surface with a higher chromium content than the underlying material.
After exposure to oxygen in the air after the acid bath, the stainless steel will develop a chromium oxide layer over the next 24 to 48 hours. A higher proportion of chromium on the surface allows a thicker, more protective chromium oxide layer to form. Removing free iron from the surface eliminates the chance of corrosion starting.
The resulting passivated layer provides a chemically non-reactive surface that prevents rust.
A pump is a mechanical tool that gives enough pressure to move the liquid through the system at the desired flow rate. Therefore it is a means to change mechanical work into fluid energy. The pump can be widely classified as a centrifugal pump and positive displacement pump. So far, centrifugal pumps are the most widely used pumps.
What are Pump Housings?
Simply put, the pump housing is a cast component that holds a pump. The pump can be very miniature or massive. But regardless of size, all pumps mainly function by accepting fluid through an inlet and sending it through outlets after increasing the pressure. The housing pump is a casing that attaches all parts consisting of pump work. The pump housing is very important wherever the pump is exposed to elements. A good example where sturdy pump housing is needed is a submersible pump.
The pump housing is one of the most expensive pump parts and must be carefully chosen.
Choosing the right pump housing directly affects reliability and uptime. The pump housing that is disposed of correctly also plays an important role in improving its performance. In many systems, the pump receives a fluid that is very hot or very cold. Therefore, the choice of material is also important.
Casting of Pump Housings
Pump housing contribute to the pump fee to a large level. There are various challenges faced by casting housing pumps. One of the most important challenges is corrosion because of the fluid. While throwing pump housing, the manufacturer must ensure that the pump housing wall is sturdy enough to withstand the pressure and pressure imposed on the pump. Casting manufacturers also need to ensure that the housing casting pump is resistant to corrosion. The pump housing diameter must be large enough to accommodate pumps with enough permits for efficient installation and operation.
Material used for Pump Housings
Ductile cast iron is one of the most popular casting materials for pump housing. However, they can be made from cast iron or gray iron too. Cast iron houses mainly tend to withstand wear very well and need more rare replacement.
Usually, after the manufacturer of casting housing pumps receive CAD images, molds are made from the material needed pump housing thrown into the tolerance needed.
Housing Pump - Testing
Pumps and pump houses undergo a lot of wear because of the nature of these components. Therefore it is important to test these two entities for fatigue, corrosion, and reduction in thickness. There are regular laboratories that carry out the pump housing test.
Pump damage can lead to costly downtime, repairs. Knowing the cause of damage can help in selecting pumping equipment to reduce the chance of failure. Here, we take a look at four common causes of pump damage and how to avoid them.
cavitation
Cavitation is the result of insufficient pressure on the pump suction or available net positive suction head (NPSHa) causing liquid in the pump to become vapor at low pressure.
At low pressure, this creates air bubbles that burst as the liquid moves from the suction side of the impeller to the delivery side.
The implosion of the bubbles creates a shock wave that puts pressure on the inner surfaces of the pump, causing vibration and mechanical damage, and eventually failure.
When this happens repeatedly, cavitation can cause pitting and fractures in the impeller, volute and casing, which weakens the metal, increases resistance to flow and reduces pumping efficiency. Shock loads from cavitation can also shorten shaft and motor life.
Cavitation and the associated problems it causes can drastically affect pump life, shortening it by 10-15 years, and in extreme cases even longer.
Cavitation is easiest to avoid during the design phase, ensuring that the selected pump has sufficient NPSHa to keep the liquid above its vapor pressure.
NPSH needs to be calculated for each application because different liquids have different vapor pressures and will vary with pressure and temperature.
This can be used in pump selection as manufacturers will be able to give any of their pumps the required Net Positive Suction Head (NPSHr) to match the specification.
corrosion
Corrosion in pumps is the result of a chemical reaction between the metal and the fluid being pumped.
This reaction can lead to uniform corrosion of wet surfaces - mainly in pumps made of non-stainless steel materials - or localized corrosion of a small number of components - most often on metal-attached and passivated surfaces that form an oxide layer.
When corrosion does occur, pump performance and efficiency can be affected, increasing the need for more frequent maintenance and more downtime, and if left untreated, can lead to failure.
The key to mitigating corrosion is choosing a pump made of the material best suited for the application.
Cast iron is one of the cheapest options for pump material and is often used for the casing.
It has good corrosion resistance to neutral and high pH liquids, making it a popular choice for general purpose, irrigation and mining pumps. However, it is not suitable for low pH applications which are more prone to corrosion.
Stainless steel is one of the most commonly used materials for pumps because of its good corrosion resistance in a variety of environments where other carbon and low alloy steels would corrode.
Under certain conditions, such as exposure to water in the presence of chlorides, pitting corrosion may occur on lower grades of stainless steel.
However, this is not a problem with higher grades of stainless steel which have high corrosion resistance.
Therefore, corrosion is the easiest to avoid when choosing a pump.
Material selection will determine corrosion resistance in a particular application as well as the overall cost of the pump, including initial cost, maintenance, replacement, downtime, life cycle and reliability.
dirt
Fouling occurs when particulate matter adheres to the internal surfaces of the pump, most commonly in the distribution lines connected to the inlet or outlet.
When this happens, pumping efficiency and flow are reduced and may eventually lead to failure. This is an unavoidable problem, but is more prevalent in applications where the pumped fluid contains particles.
However, various cleaning methods can be used to maintain the pump and increase efficiency and capacity.
Put on
Wear is unavoidable when running a pump, however, there are a few factors that can cause excessive wear that can accelerate pump aging.
Particulate matter in the pumped fluid not only causes fouling, but also increases the rate at which the pump wears.
These particles scour and roughen the pump's internal surfaces, reducing pumping efficiency over time as it works harder to move fluid.
Eventually, the pump will wear out to the point where it can no longer generate enough lift and can cause excessive vibration.
Wear can also be the result of an improperly sized pump, which can lead to pressure imbalances that place excessive stress on bearings and seals; turbulent flow; fluid velocity; wear ring degradation; and erosion and corrosion.
By ensuring that the pump is sized and made of the right material for the application, the rate of wear can be reduced, and regular maintenance is done to catch and fix any problems before they lead to unplanned downtime or pump failure.
As defined by MIL-STD-753C, a passivation process is a final treatment/cleaning process used to remove iron from the surface of corrosion-resistant steel components, resulting in a more uniform passivated surface formation for enhanced corrosion resistance.
Stainless steel differs from other metals in that the composition of the metal actually changes when you get close to the surface. During passivation, free iron is removed from the surface into solution, leaving behind a higher chromium content. A good chromium to iron ratio is generally considered to be 1.5 to 1 or higher.
What is passivation?
Passivation is a chemical treatment of stainless steel and other alloys that increases the corrosion resistance of the treated surface.
Passivating equipment and systems has many benefits:
Passivation removes surface contamination
Passivation improves corrosion resistance
Passivation reduces the risk of product contamination
Passivation allows you to extend system maintenance intervals
Composition of stainless steel
To understand the passivation of stainless steel, the key is to look at the stainless steel itself. All stainless steels are alloys of iron, nickel and chromium. Chromium makes up at least 10% of the metal. It is this element that makes stainless steel corrosion resistant. Steelmakers often add molybdenum to enhance the protective properties of chromium in highly corrosive or high temperature applications.
In addition to the chemical composition of the metal, the different layers that make up stainless steel also vary in composition. On the surface is a passivating layer, sometimes called a passivation film, which is responsible for providing corrosion resistance. It is a very thin layer of highly stable metal atoms that does not corrode or rust easily. Only a few atomic layers thick, the ratio of chromium to iron (Cr/Fe) is at least 1.5 to 1. Chromium combines with oxygen to form a chemically inert "passive" surface.
Below the passivation layer is a transition region with a higher nickel concentration. Like the passivation film, the thickness is only 3 to 4 atomic layers. The nickel in this section protects the passivation film by preventing a chemical reaction with the iron in the layer below. It also acts as a protective barrier for the base metals that make up the bulk of stainless steel. The percentages of chromium, nickel and iron vary depending on the intended use of the article.
Why do you need passivation?
Although passivation occurs naturally in corrosion-resistant and chromium-rich alloys, under the right conditions, new stainless steel vessels or components will require passivation before being placed in service. Fabrication, machining, and welding leave behind contaminants such as metal oxides, inclusions, fabrication debris, and tramp iron that impair the metal's natural resistance to corrosion.
Lock parts castings, door and window components are the most commonly used casting products in the construction industry, including locks, locks, hinges, handles, etc. These locks are usually small in size, weighing between 10 and 250g, very precise in size, with high tolerance requirements, important linear dimensional tolerances are usually +/-0.15mm, for critical areas, tolerances can be +/-0.03mm, The surface finish in the visible area must be very smooth. Locks can be produced by several different production methods such as zinc die casting, fusion film casting, MM, etc., but only investment casting can provide the best mechanical properties and the best price/performance ratio, and provide the best safety performance and longest Service life The life of doors and windows.
Door and window locks are assembled from multiple lock pieces, so the dimensional tolerance and mechanical strength of the parts are particularly important for the smooth function and safety of the lock. Precision lock parts are one of our foundry specialties, and we supply millions of precision cast lock parts and door and window components to world-renowned door and window manufacturers. With more than ten years of experience, we have an in-depth understanding of the quality requirements and manufacturing processes of door and window components, and provide door and window customers with turnkey solutions and assembly services from investment casting, post-casting processing, heat treatment, and surface treatment.
Stainless Steel Castings for Floor Texture Solutions Stainless steel castings are typically produced in Type CF8 (304), an 18-8 austenitic stainless steel with excellent corrosion resistance. Type CF8M (316) stainless steel is also available for certain applications. At JCCASTING Stainless Steel Foundry, you can choose 304 and 316 stainless steel to cast the ground grain, because we have the ability to produce different grades of stainless steel castings. After casting, we can polish the cast stainless steel floor texture parts to a smooth finish.
Advantages of stainless steel casting floor drain
• Attractive Appearance – The bright, easy-to-maintain finish of the cast stainless steel floor drain provides a modern and attractive appearance. The stainless steel finish is unaffected by UV rays and will not discolour in natural climatic conditions.
• Long Term Value - When considering the total life cycle cost of a product, stainless steel is often the cheapest material choice. In addition, casting is also an inexpensive manufacturing process that can create floor drains of different sizes and configurations.
• Environmentally friendly - stainless steel is 100% recyclable, making it the best choice for casting floor drains.
• Ease of Manufacturing - Thanks to today's modern steelmaking techniques, stainless steel castings can be cut, formed, welded and machined as easily as conventional steel.
• Corrosion Resistant - Ordinary steel castings will rust if they are not protected against rust. Due to the inherent corrosion resistance of stainless steel, its appearance and finish will have excellent durability.
NOTE: Cast stainless steel surfaces will rust and may be magnetic.
• Hygienic - The faster, more efficient cleaning capabilities of stainless steel make it an excellent choice for applications involving stringent hygiene conditions, such as hospitals, kitchens and other food production facilities. Maintenance is minimal, and in most applications, occasional cleaning will restore the surface gloss of the material.
The turbine casing is the casing that covers the turbine and directs the exhaust gas into the turbine wheel. The turbine housing is one of the most critical components of the turbocharger, which determines the performance of the turbine. JCCASTING is an OEM stainless steel casting supplier for turbine casings.
JCCASTING's stainless steel casting is an excellent lost wax investment casting process. It is widely used to cast all complex stainless steel products. Compared with other casting methods, stainless steel investment casting of turbine casings can achieve higher dimensional accuracy and better surface quality. More importantly, this casting method can not only meet mass production, but also ensure the consistency of casting turbine casings.
Features of Stainless Steel Cast Turbine Housings
High dimensional accuracy, general linear tolerance CT5-6.
Good surface finish of Ra6.4.
Less machining after casting saves machining time and costs
Tips for Ordering Turbine Housings from a Stainless Steel Casting Company
1) Such steam turbine casings are customized according to customer drawings or samples. Therefore, before sending the RFQ, the purchasing company should prepare the pdf drawings and ensure that all critical dimensions and tolerances are clearly marked in the drawings. And because of its complex shape, it is better to send the 3d file in stp or igs file so that the stainless steel casting manufacturer can check each dimension clearly.
2) Since there are many choices of stainless steel grades, it is necessary to inform the manufacturer of the stainless steel grades to be cast. In general, the nickel content of stainless steel affects the price of castings.
3) For the stainless steel turbine casing to be cast, ensure that the casting method used by the potential supplier is stainless steel investment casting, not sand casting. Only investment casting can provide higher dimensional accuracy and surface finish.
4) If you want to buy a finished turbine casing, it is best to provide both the casting and finished drawings to the supplier. At the same time, it is clear that stainless steel casting suppliers can provide in-house or outsourced machining services.
As a leading stainless steel investment casting manufacturer and exporter in China, JCCASTING Foundry has developed many types of cast or finished turbine casings for customers from the US, UK, Canada, France and more. By working closely with our customers, they are always satisfied with our qualified products. Find a competitive supplier for your turbine housing project, feel free to contact us!
Brass Investment Casting Process
Almost any castable metal can be investment cast. The brass investment casting process is suitable for parts ranging from a few grams to several hundred pounds; however, most parts weigh 15 pounds or less. The first step in investment casting is to create a master mold from wax. This wax pattern can be engraved by hand or machine, and can also be produced by injection molding. A mold is an exact replica of the part to be produced. It is attached to a wax stick called a gate. Hundreds of wax molds can be attached to the same runner, or it can be a single mold. When the master mold is firmly attached, the assembly is turned upside down and dipped into a ceramic slurry called an investment mold. Multiple dips are possible to obtain a uniform coating and desired thickness.
Another method is to mount the assembly in a flask and pour the embedding material. Then let the investment dry, which takes a few hours unless the process is assisted by a fan or vacuum. Once completely dry, the components are turned upside down and baked in an oven or furnace to melt or evaporate the wax. The mold is heated more than necessary to ensure there is no moisture or residual wax inside that would interfere with the liquid brass, then poured into the space left by the wax. To completely fill the mold, the molten metal can be drawn in by vacuum, positive air pressure or centrifugal casting methods. Sometimes gravity is enough. The brass cools, and once hardened to a solid, the investment is removed to release the brass casting inside.
The bonnet is the cover of the opening in the valve body and is the second most important valve component in the pressure valve. Like the valve body, the bonnet is designed in different shapes and sizes.
The valve cover is of the same casting material as the valve body and serves as the cover on the valve body. It is usually attached to the body by threaded, bolted or welded joints. During valve manufacturing, internal components such as the stem, disc, etc. are loaded into the valve body, and then the bonnet is installed to hold everything inside.
In all cases, the connection of the valve cover to the body is considered a pressure boundary. This means that the welded joints or bolts connecting the bonnet to the body are the pressure-bearing parts. Bonnets, while a necessity for most valves, are also a concern. Bonnets complicate valve manufacturing, increase valve size, account for a significant portion of valve cost, and are a source of potential leaks.
Bonnet stainless steel investment casting
Stainless steel casting is an investment casting process that offers many benefits when used to produce precision components such as valve covers. A stainless steel investment casting process can help save costs while bonnets are available through OEM service. Here are some of the benefits you can get when using the stainless steel casting method to make valve covers.
Durability
One of the biggest advantages of stainless steel bonnets over other types of metal bonnets is that they are very durable and strong. Cast stainless steel bonnets can be used in any type of temperature without any problems when used in extreme hot or cold temperatures. When a company chooses to buy high-quality cast stainless steel valve covers, they can count on them to hold up well for a long time. Given the durability and longevity of stainless steel bonnets, they are a very good investment and affordable in the long run.
No corrosion
Cast stainless steel bonnets are not prone to rust or corrosion. This makes the use of cast stainless steel bonnets the preferred choice for industrial applications where conditions can cause the metal to rust or corrode quickly. While cast iron bonnets are also less prone to rust or corrosion, they do not have the strength, durability or high pressure resistance of cast stainless steel bonnets.
Design flexibility
At JCCASTING, we have an unlimited selection of stainless steel grades, giving you the flexibility to configure your castings according to your needs. This includes even very complex shaped or hollow section parts, helping to configure them in a robust and repeatable way. This flexibility also brings the ability to make changes faster and in less time from design to seeing the finished product. Additionally, stainless steel investment casting is a repetitive process that can efficiently produce valve covers. This is because a mold is created, making the process more repeatable and efficient when creating multiple castings.
As a leading stainless steel foundry in China, we specialize in casting, casting process, various surface treatments, etc. Lost wax investment cast stainless steel castings.
A wide range of stainless steel castings to your exact specifications, such as: pipe fittings, marine hardware, valve and pump components, food processing machinery, glass faucets, and more.
As a professional stainless steel investment foundry, we handle large and small orders, so if your requirements are low, you don't need any restrictions, give us samples or even the drawings you need, and we will provide you with the best solution.
Stainless steel casting is a well-known method because it can produce complex shapes. Metals that are difficult to manufacture or form use this method. In this way, it is also possible to manufacture products and parts with complex shapes that cannot be manufactured by ordinary processes. In addition, parts that need to withstand harsh temperatures are manufactured in the process.
The core alloying elements of stainless steel investment casting include molybdenum, nickel and chromium. These elements will perfect the mechanical properties and grain structure of the casting. They also contribute to the heat and corrosion resistance of the casting. Other elements used to make stainless steel castings include silicon, nitrogen, manganese and iron ore.
Making stainless steel castings will first involve melting the steel and then casting it into solid form. After forming, it is heat treated, cleaned and polished. After that, it will be sent to the manufacturer, who will weld and combine it into the desired form.