CASTING 101

A short Story on the origin of Metal Castings

According to biblical records, Casting technology reaches back almost 5,500 years BC. Gold, pure in nature, most likely caught Prehistoric man’s fancy…as he probably hammered gold ornaments out of the gold nuggets he found. Silver would have been treated similarly. Mankind next found copper, because it appeared in the ash of his camp fires from copper-bearing ore that he lined his fire pits with. Man soon found that copper was harder than gold or silver. Copper did not bend up when used. So copper, found a ‘nitch’ in man’s early tools, and then marched it’s way into Weaponry. But, long before all this…man found clay. So he made pottery – something to eat from. Then he thought, "now…what else can I do with this mud…" . Early man thought about it, "I’ll use this pottery stuff, ( the first patterns ), to shape my metal into bowls ".

The first American foundry, Saugus Iron Works, located near Lynn, Massachusetts, began operation in 1642. The Saugus Iron Works was also America's second industrial plant. A number of foundry men played major roles in the American Revolution. Patriot Paul Revere operated a foundry in Boston. Seven foundry men signed the Declaration of Independence (Charles Carroll, James Smith, George Taylor, James Wilson, George Ross, Philip Livingston, and Stephen Hopkins).

The metal casting industry is the manufacturing backbone of America. It plays a critical role in every major manufacturing sector in the United States--whether it be energy, transportation, agriculture, aerospace, or national defense.

Today, approximately 3,000 foundries operate in the United States, employing nearly 200,000 people. American foundries ship roughly 14 million tons of castings per year at a value of $25 billion.

The metal casting industry is the largest recycler in the United States. Foundries recycle 20 million tons of scrap metal and reuse 100 million tons of sand each year.

Man had discovered the Casting Industry.

A casting, is the essential foundation of civilization. With it, man unlocked his future, placing him on the path toward conquering his environment. History tells us this happened in Mesopotamia, today's modern Iraq. The oldest casting in existence today is believed to be a frog, cast in copper. The frog’s complexity indicates that it was preceded by other simpler casting efforts. Things went slow back then. Tin, came around in the 16^th Century, but man used earth's ores for 4500 years prior. The Chinese get the nod for iron castings around 1000 BC. India made steel about 500 BC. Civilization in general, was casting brass by then, ( brass = copper / plus zinc ) , which was many centuries before the Christian era. All along this path all the techniques for casting and molding processes were being discovered, and recorded into history. All of these processes would be pictured forever in time through the labors of early man.
 

CONVENTIONAL MOLDING PROCESSES:

A.) SAND CASTING( also called, GREEN- SAND MOLDING )

Sand casting is the most commonly used casting platform throughout the entire Casting Industry, World Wide. Simply put, there is a top, a bottom, and a middle to a mold. The pattern, or impression device, sits in the middle of the mold, and later is surrounded with sand . These are the basic, universal casting components, which can be applied to all casting processes.

The top and the bottom of the pieces of the mold form the flask. The flask assembly, the top and bottom, "holds the whole thing together". The upper or topmost section of the flask of the mold (flask) is called the cope, while the bottom of the mold (flask) is called the drag. The impression device, in the middle, is called the pattern. The sand around the pattern is called the, holding medium. The mold maker uses the pattern to make the impression in the sand. He then sets the pattern aside. At that point, the molder closes the cope and drag, forming the mold. What the mold maker wants is the void left from the impression of the pattern, in middle of the sand, inside the mold. So, he fills that void with a molten material.

Basic casting like this, is also called, "Green Sand Molding, or Green Sand Casting". These are the most basic molding methods, currently used in today’s casting practices, regardless of the metal alloy, or any molten - liquid material being poured. Like was said in the Preface, Man has been casting things since before Biblical times, using these very concepts.

All casting techniques employed in the rest of the Casting and Molding Processes are in many ways, just like sand casting, or green sand molding. With some thought and imagination, you can always see the cope and drag principle of casting we already discussed. The different techniques or casting and molding processes are used to achieve a desired end product, which has a special need in the market place. This special need prompted man to develop special processes.

Examples of usage would be: Air movement components ( fan blades), hubs, shafts, tubes, rectangles, squares, holes, no holes, the list is endless.

A1.) GREY IRON CASTINGS

This process is very much like sand casting and green sand casting processes. It can be done as flask-less molding. The difference being that the molten material is gray iron.

Grey Iron is white iron to which 2% to 3% carbon has been added to reduce the hardness and brittleness of iron. See GREY IRON in Glossary.

Examples of usage would be: pump bodies, housings, impellers, sewer covers, gears, blanks, bases, pads, motor mounts etc.

B.) FLASK-LESS, MOLDING

This process is a sand casting, or a green sand molding variation, that has been automated for speed and high volume out-put, of identical castings. Despite any misconceptions, a flask-less molding does use flasks. The flasks, " holds the whole thing together ". A Flask must be used on all sand molding for the containment of the sand, while the sand is firmed about the pattern. In flask-less molding, in either a vertical or a horizontal stance, a sand filled flask is rebuilt and used over and over, in this totally mechanized, and automated sand molding process. In sand casting or green sand casting, a tight fitting, individual – most likely sand filled flask – is used for each mold produced.

The Industry has sand molders, use machines named "Hunter" or "B&P", to identify the makes and models of their flask-less molding equipment. The benefits of these systems are very impressive … uniformity, high density molds, high out put of products, elimination of mold shift, just to mention a few, all of which drastically reduce labor expense.

Flask-less Molding provides a mold hardness that is consistent though out the mold. The operator can adjust to different cope, drag heights and total squeeze pressure to accommodate different mold densities and mold hardness to meet the molding application. The operator can adjust the sand fill allowing the adjustment for variations in each pattern. It is possible produce complex molds and mold with deep pockets, which are difficult with traditional, normal sand casting procedures

Rapid core setting, easy inspection of cores used, utilization of existing tooling, high casting quality, reduced finishing time, quick pattern change, exceptional mold to mold consistency, high productivity are some of the many reasons to use flask-less molding.

Examples of usage would be: Any thing you can make in a sand mold, but you want it made for high volume, high production.

C.) DRY SAND MOLDING

Large components are very difficult to cast to exact size and dimensions. Hence, some foundries use dry sand molds to produce such parts. Dry sand molding is the green sand process modified by baking the mold at prescribed temperature. Engine blocks, large gears, big housings, construction parts, are examples of dry sand process candidates. Ferrous and non-ferrous metals are cast in this method. The key to this process is the proper baking time in relation to the binder and the moisture content. The other factors are the size, weight, and mass, of the component being cast. Wynn Danzur can explain the profitable advantages of this process to you. Some good examples are, the great strength of the part cast, exactness in dimension, much smoother finish, etc., but most important is how these processes will benefit your casting jobs.

Examples of usage would be: engine blocks, transmission housings, big gear boxes, etc.

D.) SAND SLINGING

is the rapid process of mechanically filling the flasks with sand. The sand is propelled into the flask, like a sling-shot. This yet, just another method for compacting the sand into the cope and drag of the flask. Some sand slingers are stationary, some portable, and are some moveable. The big plus with this process, is the elimination of sand waste, which is the universal sand foundry problem.

Examples of usage would be: Examples of usage would be: large pump bodies, gear boxes, boat engine blocks, gears, Large valve bodies, etc.

E.) STACK MOLDING

is another high production, sand casting, or green sand molding process. The piston ring people know this method well. Simply explained, the bottom of a given flask in a stack provides the cope of the flask below, while the top, provides the drag of the next layer…"pan caked- casting ".

Examples of usage would be: piston rings

F.) DRY OR BAKED "SAND CORE" MOLDING

very intricate automotive and agricultural castings are formed with this process. Accuracy, is the key word here along with close tolerances. A binder is mixed with un-bonded sand, it is then formed to the mold or pattern and baked. This is an expensive process, that achieves high level accuracy, in all dimensions.

Examples of usage would be: Examples of usage would be: engine blocks, transmission housings, gear housings, pump housings etc.

G.) SHELL CORE MOLDS

are the earliest, most automated, and most rapid of mold, and core making processes. This technique is also called the " C " Process or, Croning. Found in Germany after WW II, from a patent issued to Johannes C. A. Croning. The " C "Process uses a fluidized, harden-able sand – synthetic resin mixture to do shell molding and shell core making. Some big advantages are closer tolerances, increased productivity, excellent casting surface finishing, almost "as cast quality ". This process uses a fluidized, harden-able sand – synthetic resin mixture to do shell molding and shell core making. Some big advantages are closer tolerances, increased productivity, excellent casting surface finishing, almost "as cast quality ".

Examples of usage would be: Examples of usage would be: engines valve heads, transmission cases, valve bodies, etc.

H.) OTHER CONVENTIONAL PROCESSES Loam Molds, Chamotte Molds, Compo Molds, Cement-Bonded Molds, Floor and Pit Molds, Sweep Molds( like loam molds), Open Sand Molds, Waterless Bonded Sand Molds, are some of the lesser used, but also very important processes. At

H.1) Oil Based Sand Casting

is very similar to regular sand casting and green sand casting, but a oil based mixture of sand is employed, instead of earth and sands and clays. This concept, provides Die Cast like finish, at a fraction of the cost, because no expensive die casting tools are required. When long life span, and high out put required for the application, a Die Casting is best option.

2. PRECISION MOLDING AND CASTING PROCESSES

A.) INVESTMENT CASTING

or the "lost wax" process has been in use since the construction of the first pyramid.

The Egyptians and Chinese used the process in their early history to make statues and jewelry. The investment casting method was largely ignored as an industrial process for the fabrication of parts until the demand for rapidly finished parts during World War II created the need for near net-shape components that could readily be put into their final form. Then new inorganic high temperature ceramic mold binders were developed to industrialize the process applications to include high strength and corrosion resistant materials such as low to high carbon alloy steel, tool steel, stainless steel, and nickel and cobalt base alloys. Aluminum and brass alloys are available also. It is a process capable of producing intricate shapes weighing from a small fraction of an ounce up to forty pounds or more.

Some examples of usage would be: dental appliances, jewelry, components for the automotive industry, military weaponry, jet engines, aircraft structural parts, machinery components, and many others.

A injection molded wax pattern is used for each part produced which is then encased in multiple layers of ceramic material. The wax pattern is then removed from the ceramic shell mold. The mold is fired in an oven and then molten metal is poured into the cavities left by the evacuated wax pattern. Upon cooling, the resulting precision castings are cleaned and subjected to further processing such as heat treatment. At this point, many parts are in their final form and are ready for use while others may require a small amount of further processing such as machining before reaching their final form.

When properly applied, the advanced technology can offer complex near net-shapes that reduce overall manufacturing costs by minimizing material and labor inputs. Parts designs can be lighter in weight, more complex and are available in a wider range of alloys than those offered by other processes. Stronger materials, better surface finishes, thinner walls, difficult internal configurations and closer tolerances than those available through alternate processing techniques are some of the other advantages of the investment casting process.

The word investment, in INVESTMENT CASTING, denotes the mechanical manner of making a mold rather than the material used. This process employs a three-dimensional pattern – using all three dimensions – to produce a one time destructible mold into which molten metal will be poured. A very simple example would be to pour wax into and egg shell, let it cool, then crack away the shell. People, not especially versed in casting terms, on occasion associate this process with financial matters.

A.1) Lost Foam Process This process is similar to "Lost Wax", better known as Investment Casting, in that both the casting mediums are expended, either melted or evaporated away, leaving the cast part.

A.2)Ceramic Mold Casting

Also known as `cope and drag investment  casting'. The basic process is:

1.  A wood or metal pattern is placed in a flask and coated with a slurry of zircon and fused silica combined with bonding agents.
2. The mold is removed, cleaned and baked. The shells may be used as given, or they may have other materials, such as clay put on as backing materials.
3.  The molds are then used as normal.