Worldwide economic activity depends upon industrial production. For optimum industrial working, we require components made of durable and corrosion-resistant materials in many applications. Such materials last longer and are cost-effective.
Stainless steel is a popular metal that has these properties, making it common in the manufacturing industry. You can use many processes to shape the steel as per your needs and applications. One such process is called casting.
Casting is an excellent way of producing durable, detailed, and corrosion-resistant materials. In this article, we’ll discuss this technique in detail.
The Definition and Processes
As per the definition of casting, you have to ‘melt your alloy and pour it into molds or casts of the required shape.’ The steel solidifies in the casts when cooled, so you produce the required parts with high precision.
The method can let you make complex parts made with precise dimensions. These include nuts, fasteners, and bolts. You can use casting to make parts such as valves, pumps, and gears for different industries too.
The Process.
- Pattern Production: You first create a wax or foam pattern, depending on your technique.
- Shell Building: You build a thick ceramic shell around the wax or foam pattern by dipping it in a ceramic slurry and coating it with fine-grain sand multiple times. Once you make the shell, you put it on fire. This hardens the shell and melts out the wax.
- Dewaxing: You eradicate the wax pattern from the shell. By this, you create an internal hollow cavity.
- Melting and Pouring: You melt the stainless steel in a furnace. You then pour it into your ceramic shell. It then cools and solidifies.
- Shell Removal: You remove the ceramic shell once the steel has settled and solidified. You do this either mechanically or by highly pressurized water jets.
- Finishing: The final step is to apply the finishing touches. You can polish, coat, or grind your stainless steel product for the desired surface finish.
Different Stainless Steel Casting Procedures.
There are different types of casting procedures, such as:
1.Investment Casting.
Here, you begin by making a wax pattern. Then, you build a ceramic shell around the pattern and let it solidify into a shell. You then remove the wax and get the resulting mold.
Once you have your mold, you pour your molten metal into it.
This method is also called ‘lost wax casting’.
2.Sand Casting.
You use sand in this technique to make your mold. You pack it around your wax pattern to get the desired hollowed shape. Then, you fill it with molten steel and let it solidify.
This method is cheaper than investment casting. However, it does not retain all complex details.
3.Lost Foam Casting
This technique uses a foam pattern instead of a wax pattern. You build a ceramic shell around the foam pattern. When pouring the molten steel, you first vaporize the foam. This technique produces intricate designs and is used for parts the automotive industry requires.
4.Die Casting.
Here, you use a re-useable steel mold to set your alloy. This is a fast and efficient process; you can reuse your mold multiple times. However, it is unsuitable for complex designs.
5.Continuous Casting.
Unlike the other processes, the mold in this casting technique isn’t stationary.
You pour the molten metal into a constantly moving mold in continuous casting. The mold is generally made of copper and produces a constant length of metal you can then cut into smaller parts. This technique is suitable when you have to produce large amounts of a simple shape like steel bars in less time.
What Variables Can Affect the Results of Stainless Steel Casting?
The results you get through this technique depend on several factors, including:
1.Alloy Selection
Different alloys have different physical and chemical properties, such as melting temperature and fluidity. So, you have to make sure you choose an alloy with good fluidity for your casting process. The alloy you select should be compatible with your mold and give you your desired surface finish.
2.Wax Pattern Design
Your wax pattern design impacts how well your casting process goes. The wax wall’s thickness and shape can impact the molten metal flow and cause defects.
3.Shell-Building Techniques
The shell-building process also affects the casting process. Factors like the thickness of the shell, the composition of the ceramic slurry, and the number of ceramic layers impact the shell’s ability to catch finer structural details.
4.Pouring Temperature
You must optimize the pouring temperature. A low pouring temperature can cause the metals to solidify too quickly, and you may be unable to fill the mold. A high pouring temperature can overheat the metal, and overheated metal causes casting defects.
5.Casting Defects
Several casting defects can happen during the process, including porosity, cracking, shrinkage, and inclusions. These can occur due to the mold design or improper metal pouring.
Types of SS Alloys Used in Casting.
The results of the casting process will depend heavily on your choice of alloy:
1.Austenitic Stainless Steels.
This category is decently formable and stable against corrosion due to high chromium and nickel content. You cast high-strength parts like pressure vessels using austenitic stainless steel.
It has more fluidity, and you can cast it in thin sections or complex shapes. But it can shrink and crack during solidification if the cooling rate is too high.
2.Martensitic Stainless Steels
Martensitic steel has only 11-12% chromium and is the hardest steel alloy available. It is used where you require strength and hardness, such as in the aerospace industry. But this also makes it a poor alloy for casting as it has low fluidity.
It can also form shrinkage cavities and hot tears, which you can control with proper gating and risering techniques. You should also optimize the pouring temperature and cooling rate to lower the chances of defects.
3.Ferritic Stainless Steels
Ferritic stainless steel has less carbon content and resists stress corrosion cracking. It is an ideal material for casting as it has good fluidity and low shrinkage.
However, due to its low thermal conductivity, it can crack and warp during cooling. So, make sure you control the cooling rate.
4.Duplex Stainless Steel.
This is a mixture of austenitic and ferritic stainless steel. Despite austenitic and ferritic steel alloys showing good castability, duplex steel is difficult to cast. This is due to the complex microstructure of the duplex alloy.
5.Precipitation Hardened Stainless Steel.
This is martensitic steel treated with heat to make it harder. As with martensitic steel, casting is difficult and can form cracks during solidification. You must carefully control casting parameters like pouring temperature and cooling rate to cast it.
Surface Finishing Techniques for Casting SS Products.
A good surface finish is essential for a casted product. It improves its appearance, corrosion resistance, and durability. Some surface finishing techniques include the following:
1.Shot Blasting.
Here, you use steel shots to remove surface impurities and roughen the material’s surface. By this, you also improve the adhesion of paints and coatings.
2.Sandblasting.
This technique involves fine abrasive particles like sand or aluminum oxide to remove impurities and roughen the surface. It improves the surface texture and prepares the material for painting or powder coating.
3.Electropolishing.
You can give your casting product a shiny and smooth surface by electropolishing. In this process, you electrochemically remove a thin material layer from the surface to improve the surface finish. Doing so also makes the material more corrosion-resistant.
4.Passivation.
In this process, you immerse the casting product in a chemical, typically nitric acid, to generate a protective oxide layer. This oxide layer makes the stainless steel casting more stable against corrosive forces and extends its shelf life.
5.Powder Coating.
In this process, you apply a dry powder, a thermoplastic or thermoset polymer, on the product’s surface and then cure it in an oven. Powder-coated products are durable and resist chipping and scratching. They are also UV and corrosion-resistant.
Advantages of Stainless Steel Castings
Let’s learn the advantages and disadvantages of stainless steel casting, beginning with the benefits:
1.Design Flexibility.
You can make different stainless steel designs through this fabrication technique. These can include intricate geometries and shapes, which wouldn’t be possible through other means.
2.Dimensional Accuracy
The casting process is exact and accurate, so you can make products of the exact height and width you require. Your components can meet tight tolerances and specifications.
3.Improved Mechanical Properties.
Mechanical properties such as toughness, durability, and wear resistance are better in components made by casting. This is due to the heating and cooling of molten metal in the casting process.
4.Corrosion Resistance
Casting improves corrosion resistance as it ensures a uniform and homogenous steel structure. It also reduces porosity, and the surface finish techniques generate a protective oxide layer that resists corrosion.
5.Heat Resistance
The casting process makes heat-resistant components. They do not lose their mechanical properties even at high temperatures, making them ideal for industries like petrochemicals.
6.Cost-Effective
If you choose durable and corrosion-resistant alloys, you’ll get cost-effective stainless steel casting solutions. While casting products have a high initial cost, they last longer, which helps you save money in the long run.
The Limitations of Casting.
There are some limitations to using this technique, such as:
1.High Initial Cost
Stainless steel casting is an expensive process. The initial cost will be more than alternatives like machining sheets of stainless steel.
2.Poor Wear Resistance.
Casted components, typically of austenitic stainless steel, are often not sufficiently stable against wear and tear. Cast iron has better wear resistance than cast steel.
3.Brittleness
The cast steel is generally brittle and can break if shaken vigorously. It wouldn’t shatter usually, but it can break apart in high-stress environments.
Using Casted Stainless Steel.
Some industries that need casted components include the following.
- Aerospace: You can cast aerospace components like their landing gears, as casted components are mechanically better.
- Automotive:. Stainless steel castings are used here as engine components and suspension parts.
- Medical Equipment: You can cast surgical instruments and specific prosthetics as they are biocompatible.
- Food Processing: Food mixers and pumps are often made through the casting process.
- Oil and Gas:. This industry benefits from corrosion-resistant castings of valves and pumps.
- Construction: Castings are used for structural and decorative elements in the construction industry.
Quality Control.
Quality control is necessary for casting metals in 2023. It lets you ensure that your product meets the industry’s standards. Typical tests to perform include:
1.Visual Inspection
You can visually check for cracks, porosity, and surface defects. A magnifying glass or a microscope can assist in your inspection.
2.Radiography
In radiography, you pass x-rays or gamma rays through the material and capture the image on a detector. You can use this technique to detect inclusions, shrinkage, and cracks.
3.Magnetic Particle Inspection
This test involves applying a magnetic field around the casting. You apply magnetic particles to your component’s surface. If there is any surface defect, it will be visible on the magnetic image.
4.Dye Penetrant Inspection
In this test, you apply a dye to the component’s surface. If there is any crack, the dye will seep through it. You then clean the surface and check for the dye. If you can find the dye in some areas, they are cracked.
5.Ultrasonic Testing
Using a transducer, you send high-intensity sound waves through the material in ultrasonic testing. The reflected waves can tell you if there is any porosity or inclusion in the internal structure.
Endnote
Stainless steel casting is a sustainable way to manufacture steel components. You can use different techniques, like sand casting, investment casting, and die casting, to create complicated geometries in your stainless steel components.
The initial cost can be high for casted components, but they are more corrosion-resistant and durable than machined components. Fulfill your industry’s stainless steel requirements through casted components. Contact us for the most premium stainless steel sheets to cast into durable components.
FAQs
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What is the difference between investment casting and sand casting?
Investment casting uses a ceramic shell and is more precise, while sand casting uses a sand shell and is less precise.
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What are the most common defects found in stainless steel castings?
The typical defects include cracks, porosity, and inclusions.
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Is stainless steel casting environmentally friendly?
Yes! You can fully recycle it. The casting can be melted in the furnace and made into a new component, reducing waste generation. However, the manufacturing processes can be energy intensive.
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How does the cost of stainless steel casting compare to other manufacturing processes?
It is more expensive; however, castings last longer as they are more durable, saving you money in the long run.
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What are the latest advancements in stainless steel casting technology?
The latest advancements include computer simulations to predict steel behavior during casting and using 3D-printed molds.
