Our facility uses sand casting processes to produce brass door knockers and other decorative hardware items.
Sand casting is a form of art that is enjoyable as well as challenging. Numerous steps are involved in the process. Each step must be carried out properly or the completed piece will not be up to expectations and may need to be scrapped.
The process involves heating metal beyond its melting point bringing it to a liquid form. The molten metal is then poured into a green sand mold which forms it into its new shape. When the metal solidifies the sand mold is broken away leaving the metal casting behind.
Green sand consists of a mixture of sand, clay and water. This sand mixture is packed firmly into a box containing a pattern of the part to be produced. This box known as a flask is made in two halves. It is designed to be taken apart after the sand is packed in it.
The pattern of the part to be made is situated at the center of the flask where the two halves come together. After the sand is packed the two halves of the flask are separated and the pattern removed. This leaves a cavity in the sand the shape of the part to be produced. With the mold cavity formed hand tools are used to cut sprues and gates into the mold. This is the pathway that the molten metal follows through the mold and into the cavity.
When the cavity, gates and sprues are completed the two halves of the mold are put back together and the mold is complete. The completed mold is then taken to the pouring area. In daily practice we prepare as many molds as the crucible can hold brass for. The molds are lined up in the casting area to await the pouring.
Now with our molds all set we will need to melt some brass. In our facility we work with a propane gas fired furnace and fire clay crucibles. We fill the crucible with pieces of brass and place it into the furnace. When the temperature gets around 1600 degrees farenheit it begins to melt. Around 1650 degrees it is liquid. When the brass is roughly 1680 degrees the dross is skimmed from the top of the crucible and some flux added. When the brass is over 1700 degrees it is ready to pour.
Cautiously we lift the crucible filled with glowing red molten brass from the furnace. Carrying it to the mold we line up our pour. Tipping the crucible the brass flows out and down the sprue, into the gate and ultimately into the mold cavity filling it completely.
At this point everything is left to cool. We clean up our mess and take a short breather. When the castings have had enough time to cool enough to solidify it is time to remove them from the mold. The sand is broken away leaving the new casting exposed.
When castings come out of the mold they have a rough surface. Sprues and gates are still attached. Additional work must be performed to convert this casting into a finished product. This typically involves cutting, sanding, buffing and machining.
This process must be repeated for every component used to make the door knocker assembly. Most door knockers consist of two castings, a body and a clapper.
When the product is assembled and complete, a solid brass door knocker like this must be protected by a clear lacquer or similar substance to prevent the surface from tarnishing and deteriorating. The clear coating will keep the door knocker looking good for many years to come.