Valves are an essential part of machinery as they are used to control the flow of gas or liquid. Valves also prevent any backflow, which can be a difficult problem to deal with. Through the many different kinds of control valves, the flow of gas or liquid can be obstructed, partially allowed or fully opened. This regulation of flow requires on and off control which can be manual and automated.
The quality of the valve and the type of liquid being dealt with also dictate the efficiency and the temperature of operation and the material of the valve. Creating valves involves two main approaches. Depending upon the manufacturer and the resources available, valves are either cast or forged. Both valves are high-quality, and the function might be similar depending on their use.
The only point of difference between cast valves and forged valves is the way they are made. The creation of these valves can be understood better in detail below.
As evident in the name, forged valves are made through the process of forging. This process involves the shaping of the alloy or metal used for the valve. This forging happens when the material is in its solid form. For forging, heat is used as an agent to bend and shape the metals. Industrial tools are also frequently employed to apply compressive pressure on the alloy or metal to create a specific shape required for a valve.
Forging also involves using dies to manage the shape of the valves and to cut the metal so that it can be used in a valve. Heat is not necessarily the most important factor nowadays because different metals have different malleability, allowing manufacturers to work at different temperatures. The temperature of the forge thus depends on the metal used.
Valves can be forged in the following three types:
1. Rolled ring forging
This uses curved discs or rings to rework the shape of the metal.
2. Closed die forging
Closed die forging works to reshape the metal or alloy into the shape of a die.
3. Open die forging.
Open die forging involves the reworking and reshaping of the metal through different compressive forces.
The Benefit of Forged Valves
In the industry, forged valves have their own set of benefits. With forged valves, there is little chance of getting wasted materials. Disposing becomes a non-issue. Since only one piece of metal needs to be bent into shape, the workload is reduced, and the reworking mainly involves reshaping the metal into the required shape.
Since forged valves are made of a single piece of metal, they are durable and strong. Forged valves are thus better suited to be installed in high-temperature and high-pressure systems. The forging process also helps to refine the grain structure of the metal. This is beneficial as it increases the strength of the metal and also increases the ability of the metal to bear impact.
After forging, the metal or alloy is less prone to issues that damage the valve-like porosity, cracks, and shrinkage. The valves created through forging also have a minimised thickness of valves. This helps the valve as there is little thermal fatigue during the operation of the valve. In case the system is starting and shutting down over and over again, the valve also has to deal with a change in temperature.
Forged valves are more resistant to temperature and do not sustain damage that might come due to the frequent start-up and phase-down. Due to their resistance to temperature change, forged valves are used in power generation by oil and gas as well as in nuclear power plants.
While forging used the metals in their solid form to bend and create a valve, casting relies on completing melting the base metal to create the shape needed for a valve. The metals or alloys used are melted into a liquid at high temperatures, and then this liquid form of metals is poured into specific moulds depending upon the valve being made. The mould is then removed or broken after the liquid has cooled and the metal has set.
The different types of casting processes include the following:
- Sand casting
- Pressure casting
- Low-pressure casting
- Cavityless casting
- Investment casting
- Shell mould casting
- Gravity casting
The Benefits of Casting Valves
Cast valves do what forged valves cannot. No matter how skilled the rework of solid metal is, some shapes cannot be formed through forging. This is where casting comes in. Valves with complicated patterns, sizes and shapes are made through a cast. A mould allows for cyclical production and also provides uniformity to the creation of valves.
In case the valve part requires more details which a forged valve cannot provide, cast valves are chosen. Cast valves require a mould, and since the mould does not distinguish between the type of metal or alloy used, the casting of valves is more flexible than forging, where the rework depends on the physical and chemical properties of the metal and alloys. Whether it is metal or a cast steel gate valve, casting works well with both.
Casting valves are the cheaper solution to create valves. Forging requires labour, and that can prove expensive, which is why small manufacturers prefer casting. Larger valves might be more expensive depending upon the resources and the level of details needed. Casting valves are also beneficial to create as the replacement can be readily made available in case of breakage and deterioration.
The similarities between cast and forged valves are limited when we take into consideration the way in which they are created. While casting is efficient in machinery that does not demand heavy-duty work, forging is the durable of the two. Forged valves are more suited for thermal fatigue as they are more temperature resistant than cast valves. The price might vary initially, but forged valves are more durable in the long run, while cast valves save the initial cost and the cost of repairs.
Therefore, while the essential functions of the cast and forged valves remain the same, the durable, cost-effectiveness and uses differentiate between the two.