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Sand Casting Process
Aluminum, Brass, Bronze, Steel Alloys, Ductile Iron, Grey Iron, Zinc, Standard Casting Alloys
 Sand combined with a suitable binder can be packed or rammed rigidly about a pattern. When the pattern is removed, a cavity corresponding to the shape of the part remains. The upper half of the pattern is called the cope and the bottom, the drag. Each half is formed separately then, the cope is placed on top of the drag portion. A metal jacket or flask is placed around the mold which holds the four sides in place. (This is done so the sand mold will not come apart while pouring metal into the mold.)
Metal is poured into the mold and the metal fills the cavity area that represents the shape of a part. To allow for adequate solidification time of the metal, the mold will cool for 20 minutes to one hour. Following the cooling period, the sand molds are broken open to remove the part with its metal feed system, gates and risers.
The parts are removed from the gating system with a band saw or cutting abrasive wheel. The cast components are then sand blasted or, a wheel-a-brater is used for cleaning them. The castings are now ready for machining and any other secondary requirements.
Sand cast parts can have undercuts, formed by cores to produce intricate features. Cores can also be used to make square, round or D-holes in a casting.
There are several types of patterns used to produce sand castings; wood, match plate metal pattern, cast urethane resins are the most common types of patterns.
The sand cast process can be used from prototypes to high volume quantities. Higher quantity parts may have multiple cavities in the mold to reduce casting costs.
Benefits of Sand Casting
- All ferrous and non ferrous alloys can be cast using the sand cast method. Aluminum, brass, bronze, carbon steel, stainless steel, and irons both gray and ductile to name a few.
- Casting weight can vary from ounces to 50,000 pounds or more.
- Pattern costs are the most economic compared to other casting processes. Sandcasting is usually the least expensive of all casting productionprocesses.
- Quantities of parts produced can range from a prototype of one to thousands.
- Surface finishes of 250 RMS.
- Painting, plating, anodizing and hard coat finishes can be applied to sand castings. The finish will vary according to the cast material.
- Cast letters, numbers and logos are possible with sand castings.
Machining Sand Castings
Sand Castings can be machined to tolerances of +/-.001 or better. Machining stock is added to the casting, .060 to .120 to achieve required final dimension. Depending on the length and size of the casting, machine stock will vary.
Castings can be quoted to print specification by utilizing our in-house machining capabilities.
Casting Sizes
The sand casting process is capable of casting parts from one or two square inches to 20 feet by 20 feet or larger.
Molding Sand Castings
The jolt squeezer molding method is capable of casting between 12 to 20 molds per hour. The size of the mold flasks average 20” x 28” by 12”.
Automatic molding machines like the Hunter can cast up to 120 molds per hour. Disamatic molding machines can produce 300 molds per hour.
All sand cast manufacturing processes vary due to the possibility of a core being added to the mold or, the volume (square area) size of a part. This will slow the molding process, therefore resulting in fewer molds per hour.
Tolerances
General tolerances on a sand casting are +/- .030 for the first six inches with and additional .003 per inch over six inches.
Tolerances must be modified (increased) when dimensions are affected by parting line (P/L), cores and on moving mold parts.
Draft
All walls on sand castings that are perpendicular to the parting plane require draft or taper. This draft is not always constant as it will vary with the length of draw of pull.
Draft will add metal to the casting thereby increasing its size and weight. Typical draft on a sand casting is 1° per wall or side. Draft adds mass which increases weight to the casting.
Wall Thickness
Many conditions and specification affect the ability of foundries to cast a desired wall thickness, i.e.; fluidity of alloy, metallurgical quality. Design, surface finish, pattern and molding equipment. Wall thicknesses vary and generally are from .125 to .250 thick.
This is a basic over view of the sand cast process.
For more detail on your design please contact Dick Palmer
toll free:
888.494.0414 or email: (dick@castingreps.com)
Please see alloy chart for information on alloy characteristics, such as tensile strength, yield and elongation.
Mr. Palmer may be reached by calling toll free:
888.494.0414 or email: (dick@castingreps.com)
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