Valves are an integral part of any industrial unit or system. Industrial valves are used to regulate the flow of the medium through pipelines, isolate certain areas of the pipeline, check the system integrity of a unit, and more. This is the reason why industrial valves need to be of the highest quality, leak-proof, efficient, and durable.
The debate of which is better between cast steel and forged valves has been going on for ages. For the longest time, cast steel valves dominated the industrial space. They were a cost-efficient, quick-to-manufacture, high-quality valves that performed well in different industries. But then forged valves hit the market and the landscape was changed. Forged steel valves promised more strength, longevity, and better performance. They were also great for high-temperature, high-pressure applications. Hence the debate of which is better began and is still ongoing today.
In this blog, we will go through the definitions of cast and forged steel valves, how they are made, what makes them different, and which one is better for what application. Read on to find out more.
Cast steel valves are manufactured using a process called ‘casting’. This method requires the steel to be melted and then molded into the desired shape. Modern cast steel valves are very competitive in terms of strength, longevity, quality, and wear resistance. For example, SIO Cast Steel Valves are used extensively in petrochemical plants, power generation plants, waste processing units, water treatment plants, railways, and more.
Cast steel valves can be made from high-grade steel or metal alloys depending upon the nature of the application. Since they are made through molds, you can customize these valves easily to have complex shapes or intricate details. They can be made in any size and a single valve can have many different components.
Casting is a process whereby metal is melted and then the molten liquid is poured into different molds. However, there are different ways of casting metal like sand casting, pressure casting, investment casting, cavityless casting, gravity casting, shell mold casting, low-pressure casting, and more. Here we are going to discuss two of the most common types of casting used to make cast steel valves.
Sand casting is the most common type of casting method used to make cast steel valves. In this method, the molded pattern for the valve is fitted to the bottom of the sandboxes. These boxes are then filled with casting sand. The sand is then pressed firmly into the molds. Then the sandboxes are turned upside down and the molded patterns are removed. But since the sand was pressed around these molds, the impression of the mold is imbedded in the casting sand. Check the video of sand casting here.
Two parts of the sandbox are then fitted on top of each other and bolted together. Melted steel is poured on top of the bolted sandboxes that seeps through holes in the top of the box. The bolted sandbox is then cooled. Once the sandbox is unbolted and removed, the steel cast valve component is revealed. Cut off any access steel around the component and it is ready to be used. Sand casting is used to create larger valve components as this tends to be a more expensive form of casting.
Investment casting is a process that is used to manufacture smaller, more precise components of cast steel valves. In this process, the first mold is made using hard wax, lost wax, lost foam, or similar material. This wax mold is then dipped in wet ceramic slurry until it becomes really thick. Once dried, the wax is melted so that the ceramic mold is left behind. Check the video of investment casting here.
The ceramic mold is heated to a temperature of about 1000 degrees and molten metal is poured into the hot ceramic mold. Once the metal cools, the ceramic mold is broken using vibrations leaving behind precise metal components. Investment casting is used to create smaller parts up to 100 kg and 1.5m of maximum length. This method is also more cost-effective than sand casting but cannot be used to create larger components.
Forged steel valves are manufactured using a process called ‘forging’. Forging is based on the application of thermal energy to solid blocks of steel and then using mechanical forces to further process the steel into a finished product. This process is used to make valves that are extremely strong and tough. For example, SIO Forged Steel Valves are used in mining and mining processing, agriculture and livestock handling, aeronautics, automobile industry, brickworks, stormwater plants, rendering plants, asphalt plants, power and water industry, pharmaceuticals, chemical industry, cosmetic industry, and more.
Forged steel valves are perfect for handling high-temperature, high-pressure services. However, you can only some metals can be used in forging. This method is used to make smaller, specialized valves. Larger forged steel valves have to be made in components. The components are then welded or connected through flanged connections to make the complete valve.
The process of forging is completed in a number of steps. First, the raw material that is in the form of blocks, ingots, or billets is cut into smaller pieces. The pieces are then heated to reach the required temperature at which the metal will be ductile and malleable. Once the metal is heated, it is then transformed into the required shape by applying mechanical forces. In olden times the pressure was applied manually through power hammering. Now automatic machines like hydraulic presses are used to get the job done.
Once the metal is shaped into the desired form, it undergoes machining, finishing, and heat treatment to get the finished product. Forging has the following classification based on the temperature applied to the raw metal:
This type of forging is done at room temperature without applying any additional heat to the metal. The metal has lower malleability than in case of hot or warm forging so a greater mechanical force is required to shape the metal.
In this type of forging the metal is heated to temperatures ranging from 800 to 1000 degrees centigrade. The metal becomes ductile at this temperature but no as much as in hot forging.
When the metal is heated to temperatures over 1000 degrees (but still below 1300 degrees), it is called hot steel forging. The metal becomes so malleable at this temperature that only a moderate amount of mechanical pressure is required to mold it into the desired shape.
There are also two types of forging depending on the method used to shape the metal components of the valve.
In closed die forging, the melted metal is placed in the bottom die and it is almost the exact shape and size of the final forged part. In open die forging, the melted metal is moved through multiple dies that shape part of the metal into the desired shape through hammering or stamping. Here is a diagram that shows the difference between these two types of forging.
Now that we know how cast steel valves and forged steel valves are made, let us take a look at some of their merits and demerits.
Choosing the right valve for your application depends on a number of factors. While forged valves are great at handling high-temperature, high-pressure applications, they are expensive and cannot be easily standardized. Cast valves are cost-effective and can be produced in greater numbers easily. However, there is always a risk of a void in the valve’s construction. To find out which kind of valve is the best you need an experienced valve manufacturer that can advise you on the most appropriate steel valve which meets specific plant needs. Get in touch with us so we can help you do just that.
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