"BRASS" as defined in Merriam-Webster's Collegiate Dictionary

Main Entry:  brass
Pronunciation:  'bras
Function:  noun
Etymology:  Middle English bras, from Old English bras; akin to Middle Low German bras metal
Date:  before 12th century

1: an alloy consisting essentially of copper and zinc in variable proportions
2: a:  the brass instruments of an orchestra or band - often used in plural
  b:  usually brass memorial tablet
  c:  bright metal fittings, utensils, or ornaments
  d:  empty cartridge shells
3: brazen self-assurance:  GALL
4: singular or plural in construction
  a:  high-ranking members of the military
  b:  persons in high positions (as in a business or the government) - brass adjective

As defined in the above Merriam-Webster's Collegiate Dictionary, brass is an alloy or mixture consisting mainly of copper (Cu) and zinc (Zn). It should not be confused with bronze however, which is an alloy of copper and tin (Sn). The entire product line at Symphony in Brass is made of 100% brass and finished in various techniques to give it a decorative and weather resistant finish. Almost all of Symphony in Brass' products are produced by sand casting of brass into intricate shapes and sizes which is described below for your understanding of our manufacturing process.

Diagram


Typical Cross-Section of a Two-Part Sand Casting Mold

The above diagram represents the most basic casting process used today. This process is used worldwide regardless of metal, alloy or molten liquid material being cast. Man used this concept at the beginning before Biblical times to manufacture objects for decoration, weapons, utensils and hardware. This process is commonly known as sand casting since sand, which is held together with a binder, is the medium to form the mold cavity.

Definitions

Core:  A sand shaped insert placed in the mold cavity to produce internal features on the part.
Cope:  The upper half of the sand mold.
Drag:  The lower half of the sand mold.
Flask:  A box made of wood or metal to contain the sand.
Gates:  Multiple openings in the mold to allow the molten brass to flow into the mold cavity.
Gating System:  A passage where the molten brass flows into the mold. The gating system is made up of the pouring cup, sprue, runner and gates.
Mold:  A cavity or matrix by which molten brass is shaped into a desired product.
Parting Line:  The line where the top and bottom halves of the sand mold meet.
Pattern:  A representation of the final product used to imprint the shape into the sand.
Risers:  Reservoirs called risers inside the mold, which is filled with the molten brass to compensate for shrinkage or "feed" the mold cavity during the solidification process.
Runner:  The horizontal part of the gating system, which supplies molten brass to the gates.
Sprue:  The vertical part of the gating system, which is connected to the pouring cup at the top and feeds the runner with molten brass at the bottom.
Vent:  An opening in the mold to allow the escape of hot gases.

Simple Casting Process Description

The flask is comprised of a bottom and a top half and together, they form the flask assembly. The upper section of the flask assembly is known as the cope and the lower section is termed the drag. The first step in the casting process is the mold must first be made. The drag or bottom half of the flask is filled with sand, which is pre-mixed with a binding agent to keep it intact. Inside the drag, there is a pattern, which will create the impression that will form the mold cavity (the patterns for the top and bottom may be different depending on the object that is to be cast). The sand is compacted around the pattern by manual and mechanical means to ensure all the air is removed and that a smooth mold cavity is formed around the pattern. This procedure is repeated with the cope or upper half of the flask. Depending on the complexity and size of the part and the number of castings being made at one time, the pouring cup, sprue, runners, risers and gates will also be imprinted onto the sand or an expendable core will be used that will burn away. Once the sand has set, the cope and drag are flipped to remove the pattern thus leaving a void in the sand. Cores may be added, if necessary to create hollow and internal features on the final product. The next step is to close the mold and lock it in place using weights or clamps to keep the mold from splitting open at the parting line during the pouring process.

Now that the mold is complete, the molten brass is poured into the mold cavity via the pouring cup or hole. Once filled, the entire assembly is allowed to cool and solidify. Depending on the size of the casting, cooling time can take several hours (in industry, some castings take over a week to solidify!). Once the molten brass has solidified, the flask assembly is taken apart. The sand mold is then broken apart to expose the product by hand tools, vibration, rotary drums or a combination of these techniques. At this point, the gating system is also removed, and the cores are disposed of.

Once the product is cool to the touch, they go through a rigorous cleaning and finishing process. The parting line on the casting is blended and any spikes or splinters are removed by mechanical means. Once the rough finishing is complete, the parts are polished to a smooth finish in various grinding and buffing stages. Depending on the colour (natural brass, verdigris or black) the products go through a final finishing process to give it the desired colour. Once complete, the final products are ready for shipment around the globe.

This is a very simple explanation of the casting process since explicit details is beyond the scope of this website.


 
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