Aluminum and Sand Casting

Aluminum and Sand Casting -

Aluminum casting is a process of pouring molten metal into molds. In sand casting, sand is used as the molding material. Aluminum sand casting is the process of molding aluminum in sand molds.

Sand molds provide a cost-effective way to bind the materials together effectively. The sand is mixed with clay that strengthens the mold when it dries. When preparing to do aluminum sand casting, manufacturers must prepare the sand with a cavity or mold and ensure the aluminum has an opening to enter the mold.

Base Sands

Base sand is used to make the core or mold without a binder. Many different types of base sands are used to make molds. Silica is the most commonly used sand for aluminum casting. It is a naturally occurring element, essentially sandstone, and can be found on beaches or stones. Olivine sand is known to be a safer alternative to silica; it comes from a mineral called dunite. Chromite sand is a mixture of magnesium and aluminum. It is an expensive material, but it’s known to produce molds with fewer surface defects. Zircon sand is a mixture of zirconium oxide and silica. Zircon sand is expensive but proves to be suitable for casing.

Binders

Binders are chemical mixtures that make cores and molds stronger. There are different options for binders in aluminum sand casting. These are:
●Clay and water - Bentonite clay is the most common choice for the sand casting process. However, kaolinite clay is also used throughout the industry. 
●Resins - Resins can be synthetic or natural. Some manufacturers experiment with additives and resin to manipulate the casting outcome.
●Water Glass - Water glass, or sodium silicate, a fast-drying, sturdy binder and can be used at room temperature. Sodium silicate works well with silica sand. 0

Additives and Parting Compounds 
Additives are added to the mold to enhance its properties. Coal powder and fuel oil additives prevent the liquid metal from sticking to the sand particles. Other parting compounds help detach replicated parts from their molds. Parting compounds could be dry silica, talc, and graphite.

Process of Aluminum Sand Casting
Preparing the Mold for Casting.
The process begins with the creation of the mold. The top and bottom of the mold are called cope and drag. The mold pattern is the shape of the desired final object. Once the mold is created it is lubricated. The lubrication will make it easier to take the casting out. 
Manufacturers can use a green sand casting method or an air-set method of casting. The green sand casting method uses wet sand and other organic clays as a binder. When the mold isn’t set yet, the sand looks green. The aluminum sand casting process uses olivine sand. It’s best not to use silica for the green sand method.

The air set method uses sand bonded with other materials and fast-curing adhesives. Manufactures will use bank sand or synthetic sand when using the air set method. The sand is stuffed in the mold cavity, and a plug is formed in it for pouring the liquid metal. The sand is pressed and takes time to settle down.

Applying the Metal to the Mold
Next, the molten metal or aluminum is poured into the cavity through the gating system. The halves of the mold are clamped together with jackets The metal is allowed to sit, cool, and begin to solidify. After cooling, the sand mold is broken down to remove the cast. Sometimes manufacturers use vibrating machines to dislodge the sand from the cast. 
Finishing & Final Steps.
The excess metal is trimmed manually or with a trimming tool. The excess metal can be reused in the sand-casting process. The final product can be polished or powder coated for a shiny, smooth finish.

Applications of Aluminum Sand Casting 
●Aluminum sand casting is used to make a components like air compressor pistons, bearings, blowers, bushings, cams, electronic equipment, and engine crankcases.
●These are also used to make engine oil pans, fittings, low pressure valves, and other machine parts.

The article from link as follow：
https://www.iqsdirectory.com/articles/metal-casting/types-of-casting-processes.html