Gray Iron Castings
Gray iron castings manufactured by the automated green sand molding process represent the dominant cast products of today's technology. These castings are suited for the many shapes designed into components and parts by engineers because they are low cost, easily machined, strong, wear resistant, have good dampening ability, and exhibit properties of high flexibility.
Automatic green sand molding of Class 25, 30 and 35 gray iron castings is the preferred process for moderate to high quantities of castings that weigh under 150 lbs. The castings resulting are close to net shape. The automated aspect of the process further reduces cost and improves repeatability. Typically cast parts afford tolerances of +/- 0.030" or better on first article inspection and +/- 0.015" part-to-part in production for dimensions under 6".
Cored and noncored gray iron castings come in a weight range from less than 1 lb up to 120 lb in mold flask sizes of 14" x 19" and 20" x 24". Single order and shipment quantities generally range from 50 to 5000 parts. Iron pouring capacity is 50 tons per day. Preproduction engineering and planning sessions should precede order placement.
Quality castings are a consequence of casters following job-specific process instructions and the use of a written quality system requiring constant monitoring and documentation of all general processes.
What is Gray Iron?
Gray Iron is the oldest and most recognized type of cast iron. It has been produced in various forms for several thousand years. It is primarily composed of graphite flakes and either pearlite or ferrite or a combination of both. Other alloys or additives are often added to the mixture to impart specific properties to the Gray Iron.
What is a Gray Iron Casting?
A Gray Iron Casting is a part that has been made by pouring molten metal into a temporary sand mold that has been imprinted with a pattern.
When were Gray Iron Castings invented?
The Chinese first produced Gray Iron Castings over 2,500 years ago. The Chinese applications for Gray Iron Castings included weaponry, stoves, common household goods, tools, building materials, and statuary. The earliest recognized western production of Gray Iron Castings dates back to 1450 AD in England. (Historical information provided the American Foundry Society.)
Are there different types of Gray Iron Castings?
Yes, the metallurgy of the Gray Iron can be adjusted to make the cast metal harder or softer, dependent on the application. Additionally, alloy additions and secondary processes such as heat treating and annealing can affect the physical properties of the Gray Iron Casting.
What benefits do Gray Iron Castings provide?
There are a number of important benefits that the use of Gray Iron for casting provides. Gray Iron Castings can be:
- Machined more easily
- Used for damping or controlling vibration in wide range of applications
- Formulated so their metallurgy meet specific applications' requirements
- Used in applications that require dimensional stability
- Used in applications that require high strength to weight ratios
- Produced economically in high volumes using Disamatic equipment, and
- Tested for quality using non-destructive methods/LI>
- Designing a casting that are currently welded or assembled from several parts
How are Gray Iron Castings made?
There is a specific series of steps used to make Gray Iron Castings. The four common steps are:
- Create a wood or metal pattern of the part or parts to be cast.
- Use the pattern to create a sand mold that holds the shape of the part after the pattern is removed.
- Pour molten Gray Iron into the sand mold.
- Remove the sand mold after the casting has cooled, leaving the new raw Gray Iron casting.
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