Sand Casting
Aluminum, Brass, Bronze, 300 Series Stainless Steel, 400 Series Stainless
Steel, Precipitation Hardened Stainless Steel, Carbon Steel Alloys, Ductile
Iron, Grey Iron, Zinc
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.
Palmer
Associates proudly represents BSL
Castings for sand casting.
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 and cast urethane resins, which 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.
Please see alloy chart for information on alloy characteristics, such as tensile
strength, yield and elongation.
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. Sand
casting is usually the least expensive of all casting production processes.
- Quantities of parts produced can range from a prototype of one to thousands.
- Surface finishes of 250 RMS to 400 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
an 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 or 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 specifications 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.
Production Speeds
- Jolter Squeezer sand molding process can produce 12 molds/hour.
- Hunter Automatic (Horizontal Flask) sand molding process will produce 120
molds/hour without cores.
- Disa Automatic will produce 300 molds/hour without cores. Cores can be added,
but please note that it will slow down the production process.
Sand Castings Pattern Description
Sand casting patterns can be made out of wood (low volume), repro plastic (poured
off of master wood pattern) & machined metal match plate pattern ( high volume).
Sand castings can be a good solution for your casting needs whether the casting
will need to be made of Aluminum, Brass, Bronze, Steel Alloys, Ductile Iron,
Grey Iron & Zinc. Typically metal match plates are used for the high volume
(Hunter & Disa automatic).
Mold revision changes are relatively inexpensive for wood & repro plastic
patterns. Below are 3 different processes, some sand casting tooling examples &
tooling production machinery images to give you an idea of how the process is
completed.
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