Foundry Technology
Introduction
Human progress can be attributed to many factors. The invention of the wheel is one such turning point (no pun intended!). The industrial revolution is another turning point. Foundries and castings have played an important role in the industrial revolution. The Copper age, Bronze age, and Iron age were so called because humans knew how to cast these metals from that time. And with the industrial revolution, more and more sophistication was introduced in the casting processes. It also bought about the increased use of alloys – which are nothing but a blend of different metals. Casting, which was - and still is - one of the most important processes of moulding metals, is very old. It is believed that the casting process originated in the foundries of China about 2500 years back, and was introduced in Europe later. Some scholars believe that casting is even older, and newer archeological research is lending credence to this claim. The earliest furnaces in a foundry were very simple to operate, perhaps with charcoal and bellows to blow air. As technology advanced, foundries have changed too. Today, there are various furnaces found in foundries, ranging from induction furnaces, crucible furnaces, cupola furnaces to electric arc furnaces.
The word foundry is derived from the transitive verb ‘found’, which is nothing but the art of melting material and casting it into a mould. A foundry is therefore a mechanical manufacturing facility that produces metal castings by pouring molten metal into a pre-formed mould to yield a solid cast. Foundry technology therefore primarily insinuates the study of the casting process. The primary metals cast include iron and steel from the ferrous family and aluminum, copper, brass and bronze from the nonferrous family. Foundry castings are therefore divided into ferrous and non-ferrous categories. Foundries are oftentimes classified based on what kind of castings they produce, so a foundry that predominantly casts iron is called an iron foundry, a foundry that produces bronze castings is called a bronze foundry, and so on.
Foundry Processes
The basic aim of a foundry is to produce castings. The processes employed in the foundry include gravity and pressure die casting, investment casting and centrifugal casting, but the general characteristics of any foundry can be defined with respect to the production of sand castings by conventional moulding. Sand casting is the most common method of metal casting, accounting for approximately 75 percent of all metal cast. Primary foundry processes involve making the pattern, mould, core, forming a cavity in sand with a pattern, filling the cavity with molten metal, and then releasing the casting by breaking away the sand. Patterns are full size models having the shape of the exterior of the casting to be produced and may be made of wood, brass, aluminum, or other material. These are the basic steps; depending upon the type of casting material and product requirements, other steps like heat treatment, annealing, etc may also be involved.
While a good foundry can provide assistance in the casting design process, it is typically the end customer that provides the desired design. Today, application of computer simulation of metal flow and solidification characteristics allows foundry owners to offer better product optimization to the end customer.
The basic foundry processes include pattern making, mould making, core making and metal melting and pouring.
Pattern Making
Once a design has been received, the casting producer must design and build the necessary tooling to produce the casting. For sand casting, the tooling consists of dies for any required cores and patterns to make sand moulds. In essence, the pattern is nothing but a replica of the object that needs to be cast. It is usually made out of board, wood, metal or model board. The patterns incorporate placement of cores and include shapes forming channels in the mould through which molten metal flows to fill every cavity of the finished mold. In other words, the mould cavity is made with the help of a pattern. The size, shape, and location of these channels, called sprues, gates, and risers, are essential parts of the pattern design process.
Mould Making
The next step in a casting foundry is mould making. The purpose of mould is simple – it is the actual cavity with shapes of the final object into which molten metal is poured. Mould making usually occurs in the area where molten metal is poured. The extent of automation of mould making depends upon the size, complexity, and number of castings to be produced. For a large volume production, permanent moulds work best. Permanent mould casting is a process for producing a large number of castings with one single mould that is reusable.
Core Making
Cores are forms, mostly made of sand or sand-clay mixtures, which are placed into a mould cavity to form the interior voids and surfaces of castings. They define the final casting shape, with the sand used inside the cores giving strength and rigidity to the casting structure. The better the quality of the sand, better defined the shape of the casting.
Metal Melting and Pouring
Another key production step in a foundry is metal melting. Melting is the process of preparing the raw molten metal for casting. This is one of the key aspects in a foundry where stringent quality control is required, as the quality of the melt directly affects the quality of the finished product / part. There are various processes like degassing, filtering, oxidizing unwanted chemicals, etc. undertaken before the molten metal is transferred to the pouring station where it is ultimately poured into moulds. There are numerous technologies available to produce molten metal. Iron foundries often use cupola furnaces, while steel foundries can choose either electric-arc or electric induction furnaces, which are more suited to batch-type and intermittent operations. Non-ferrous foundries may use electric-induction furnaces and, due to the lower melting temperature of the metals, have additional options in gas- or oil-fired furnaces. Typically, a foundry will also use an electrically heated holding furnace to maintain temperature in molten metal, transferring large amounts of molten metal from the melting furnace to the holding furnace, and then taking smaller amounts to the pouring location as needed so that a constant pouring temperature can be maintained for all similar castings.
Evolution of Foundry Technology
Many foundries sprang up after the industrial revolution, mostly for the manufacture of the cast iron. The industry depended heavily on the skills of the mould and the pattern maker, and experience of the craftsmen in casting material properly. Their skill enabled complex forms to be produced with minimum defects. However, enhancements in metallurgical engineering and furnace technology, coupled with advances like CAD and computer simulation has allowed foundries to be relatively independent of personal skills. Indeed, most of the modern foundries, including those in India, are now process driven. Advances in foundry technology have allowed casting of not only metals, but ceramics and other material. Development in melting systems has enabled combining melting with other metallurgical processes like metal filtering and degassing. Improvements in furnace design and types, automation in mixing of metals and their alloys enable foundries to offer a better mix of products. In countries like India and China, inexpensive labour is another benefit.
Human progress can be attributed to many factors. The invention of the wheel is one such turning point (no pun intended!). The industrial revolution is another turning point. Foundries and castings have played an important role in the industrial revolution. The Copper age, Bronze age, and Iron age were so called because humans knew how to cast these metals from that time. And with the industrial revolution, more and more sophistication was introduced in the casting processes. It also bought about the increased use of alloys – which are nothing but a blend of different metals. Casting, which was - and still is - one of the most important processes of moulding metals, is very old. It is believed that the casting process originated in the foundries of China about 2500 years back, and was introduced in Europe later. Some scholars believe that casting is even older, and newer archeological research is lending credence to this claim. The earliest furnaces in a foundry were very simple to operate, perhaps with charcoal and bellows to blow air. As technology advanced, foundries have changed too. Today, there are various furnaces found in foundries, ranging from induction furnaces, crucible furnaces, cupola furnaces to electric arc furnaces.
The word foundry is derived from the transitive verb ‘found’, which is nothing but the art of melting material and casting it into a mould. A foundry is therefore a mechanical manufacturing facility that produces metal castings by pouring molten metal into a pre-formed mould to yield a solid cast. Foundry technology therefore primarily insinuates the study of the casting process. The primary metals cast include iron and steel from the ferrous family and aluminum, copper, brass and bronze from the nonferrous family. Foundry castings are therefore divided into ferrous and non-ferrous categories. Foundries are oftentimes classified based on what kind of castings they produce, so a foundry that predominantly casts iron is called an iron foundry, a foundry that produces bronze castings is called a bronze foundry, and so on.
Foundry Processes
The basic aim of a foundry is to produce castings. The processes employed in the foundry include gravity and pressure die casting, investment casting and centrifugal casting, but the general characteristics of any foundry can be defined with respect to the production of sand castings by conventional moulding. Sand casting is the most common method of metal casting, accounting for approximately 75 percent of all metal cast. Primary foundry processes involve making the pattern, mould, core, forming a cavity in sand with a pattern, filling the cavity with molten metal, and then releasing the casting by breaking away the sand. Patterns are full size models having the shape of the exterior of the casting to be produced and may be made of wood, brass, aluminum, or other material. These are the basic steps; depending upon the type of casting material and product requirements, other steps like heat treatment, annealing, etc may also be involved.
While a good foundry can provide assistance in the casting design process, it is typically the end customer that provides the desired design. Today, application of computer simulation of metal flow and solidification characteristics allows foundry owners to offer better product optimization to the end customer.
The basic foundry processes include pattern making, mould making, core making and metal melting and pouring.
Pattern Making
Once a design has been received, the casting producer must design and build the necessary tooling to produce the casting. For sand casting, the tooling consists of dies for any required cores and patterns to make sand moulds. In essence, the pattern is nothing but a replica of the object that needs to be cast. It is usually made out of board, wood, metal or model board. The patterns incorporate placement of cores and include shapes forming channels in the mould through which molten metal flows to fill every cavity of the finished mold. In other words, the mould cavity is made with the help of a pattern. The size, shape, and location of these channels, called sprues, gates, and risers, are essential parts of the pattern design process.
Mould Making
The next step in a casting foundry is mould making. The purpose of mould is simple – it is the actual cavity with shapes of the final object into which molten metal is poured. Mould making usually occurs in the area where molten metal is poured. The extent of automation of mould making depends upon the size, complexity, and number of castings to be produced. For a large volume production, permanent moulds work best. Permanent mould casting is a process for producing a large number of castings with one single mould that is reusable.
Core Making
Cores are forms, mostly made of sand or sand-clay mixtures, which are placed into a mould cavity to form the interior voids and surfaces of castings. They define the final casting shape, with the sand used inside the cores giving strength and rigidity to the casting structure. The better the quality of the sand, better defined the shape of the casting.
Metal Melting and Pouring
Another key production step in a foundry is metal melting. Melting is the process of preparing the raw molten metal for casting. This is one of the key aspects in a foundry where stringent quality control is required, as the quality of the melt directly affects the quality of the finished product / part. There are various processes like degassing, filtering, oxidizing unwanted chemicals, etc. undertaken before the molten metal is transferred to the pouring station where it is ultimately poured into moulds. There are numerous technologies available to produce molten metal. Iron foundries often use cupola furnaces, while steel foundries can choose either electric-arc or electric induction furnaces, which are more suited to batch-type and intermittent operations. Non-ferrous foundries may use electric-induction furnaces and, due to the lower melting temperature of the metals, have additional options in gas- or oil-fired furnaces. Typically, a foundry will also use an electrically heated holding furnace to maintain temperature in molten metal, transferring large amounts of molten metal from the melting furnace to the holding furnace, and then taking smaller amounts to the pouring location as needed so that a constant pouring temperature can be maintained for all similar castings.
Evolution of Foundry Technology
Many foundries sprang up after the industrial revolution, mostly for the manufacture of the cast iron. The industry depended heavily on the skills of the mould and the pattern maker, and experience of the craftsmen in casting material properly. Their skill enabled complex forms to be produced with minimum defects. However, enhancements in metallurgical engineering and furnace technology, coupled with advances like CAD and computer simulation has allowed foundries to be relatively independent of personal skills. Indeed, most of the modern foundries, including those in India, are now process driven. Advances in foundry technology have allowed casting of not only metals, but ceramics and other material. Development in melting systems has enabled combining melting with other metallurgical processes like metal filtering and degassing. Improvements in furnace design and types, automation in mixing of metals and their alloys enable foundries to offer a better mix of products. In countries like India and China, inexpensive labour is another benefit.
If you are looking to outsource foundry work like castings, it is a good idea to choose someone who is experienced as well as tech savvy. To ensure the quality of castings, they must also possess good infrastructure and industry standard software.