The Bronze Casting Process
The Bronze Casting Process

The Bronze Casting Process

Everything You’ve Ever Wanted to Know About Bronze Casting Today

Are you looking to have your first-ever bronze part cast for a new product, or have you been in the business of manufacturing items with bronze components for decades? Either way, Cast Technologies has the bronze casting process experience and equipment to handle whatever you need.

What Metals Are Used In The Bronze Casting Process?

Bronze can generally be defined as a mixture (or alloy) of copper and tin. However, other metals and substances are added within the bronze casting process sometimes, including aluminum, manganese, zinc, lead, nickel, iron and even silver. The exact mixture will vary according to the desired quality of the finished item. In ancient times, the mix of metals most likely depended on what scrap metals and other materials were available. Today, the recipes are much more exact and are scientifically chosen to have the qualities best suited to the product or part.

Why Bronze Casting Is So Popular?

Bronze has many qualities that have made it a popular choice of metals since ancient times. It’s harder than copper or iron. Depending on the specifications of the “recipe” used to make it, bronze may be especially strong or corrosion-resistant or hard. So whether the bronze will be used in a statue, as a ball bearing or as a boat propeller will call for a decision to use one alloy or another.

What are the Advantages of Cast Bronze?

Bronze is highly durable — so durable that bronze items made thousands of years ago are still in existence and often still in excellent shape. Bronze’s corrosion resistance makes it perfect for equipment that will be used outdoors and that needs to withstand weather extremes. Bronze is also among the easiest of metals to weld, which is an advantage in many different industries. Its lower melting point, relative to iron, is yet another advantage. Striking bronze does not create a spark, which makes it ideal for use around flammable materials or vapors.

Common Bronze Casting Methods

At its simplest, bronze sand casting consists of pouring molten bronze into a hollow formed into sand. You can imagine pressing an item (called a pattern) into wet sand and then pouring in the liquid metal and letting it cool and set. That is the most basic method of sand casting. However, there are countless refinements to the process that metal workers have invented throughout history. These refinements allow sand casters to create intricate three-dimensional bronze items of almost any shape desired. 

Bronze Casting Terminology

When it comes to the bronze casting process, there are several terms to learn. Here are some of the most common terms you’ll hear in connection with foundry processes:

  • Green Sand Casting:

    The name may be slightly misleading, as the sand used in this process isn’t green in color. Green sand is usually a mix of water, sand and clay. This is a simple, inexpensive and common casting process, but it has its limits. The surface of a metal component cast in green sand will not be perfectly smooth. If an absolutely smooth surface is required, the component will either need to be machined after casting, or another method of casting the bronze must be chosen.

  • Lost Wax Casting:

Wax casting is a method of bronze casting that involves first making a wax model and then building a mold around it. After the mold sets, the wax is melted away, leaving behind a space to hold the molten bronze. The bronze is allowed to cool fully, and then the mold is removed, leaving behind an object of cast bronze.

  • Ceramic Casting:

Ceramic casting is related to lost wax casting. It refers to a ceramic coating being formed around a wax model.

  • Investment:

You may run into the term “investment” and wonder what it means in the context of bronze casting. In the foundry world, this term refers to the method of creating a very hard shell around a wax model. The wax model is dipped into a ceramic slurry multiple times, each time building up a very thin layer that must be allowed to dry before the next dip. The process is repeated until a thick, hard ceramic shell forms around the wax. This is similar to a traditional method involving plaster. With either method, once the wax is melted away the hollow form is ready to accept the molten bronze.

  • Casting Flask:

The flask is a frame, usually of metal or wood, that contains the green sand.

  • Cope and Drag:

These refer to the top and bottom halves of the casting flask. The pattern (model) of the desired part will be placed inside the casting flask and the sand will be firmly packed around the pattern. When the sand in both the cope and drag are packed solid, the pattern is removed and the flask is combined and firmly connected so that the hollow cavity is ready to be filled with the molten metal.

  • Sprue:

The sprue is simply a tunnel made in the sand. It provides a path for the molten metal to flow into the mold. Once the component is unmolded, the cooled metal in the tunnel can be machined off. 

  • Riser:

The riser is much like the sprue. But instead of the melted metal being poured through it, it serves as a reservoir. The idea is that as the metal starts to cool, it contracts, possibly leaving an unwanted void in the casting. The reservoir of hot metal contained in the riser can fill that void. If all goes well, any cavity formed by a lack of metal volume will be in the riser, not in the casting. Once the component has cooled and is removed from the mold, the cooled metal of the riser, like the sprue, can simply be cut or machined off.

What Industries Use Bronze Castings?

Bronze’s qualities make it suitable for a wide variety of applications and objects. You are nearly certain to have multiple cast bronze items near you at any given moment. The automotive, nautical and aerospace industries make extensive use of bronze parts. 

Besides Industry, How Else Is Cast Bronze Used?

You’ll find bronze in coins, furniture trim, musical instruments, bells, screws, guitar strings, decorative objects, medals and of course statues. Some statues have been displayed outdoors for many generations, demonstrating the strength and endurance of bronze.

What Is the History of Bronze Casting?

Bronze casting is so important that a historical period was named after it. The Bronze Age began as many as 4,000-5,000 years ago, although Chinese and Middle Eastern artifacts show some bronze was being cast even earlier. However you date it, it’s clear that the ability to mine, melt and combine materials into bronze tools, weapons and art helped shape and change civilization. Whenever a culture developed bronze weapons, they had an immediate advantage over any neighboring cultures that were still depending on stone tools. More primitive groups of people had every motivation to learn how to work metal so they could better compete.

But bronze wasn’t used only for weapons. The agricultural revolution predates the Bronze Age, but you can imagine how elated Neolithic farmers must have been at the prospect of cast bronze plows and other agricultural implements. Up to that point, they were limited to farming with wooden and stone tools. The adoption of bronze hoes, plows and other tools allowed farmers to more easily clear land, cultivate the soil and harvest crops. 

Metal was also quickly adopted in the arts. We still have many examples of ancient metal figures, jewelry and other decorative items made thousands of years ago. It seems that our ancient ancestors were quick to understand the usefulness of this metal and to find ways to incorporate cast bronze into almost every part of life — just as we do today.

How Do Modern Bronze Foundries Work?

Even though the basics of sand casting are similar to what has been done down through the ages, sand casting bronze is today much safer, thanks to modern automated equipment. Advances in technology allow us to make much more intricate items than were possible in the past. In addition, we now have the ability to make further refinements to cast bronze implements. A cast bronze item can be machined to add intricate details as needed. 

Cast Technologies is the largest brass and bronze sand casting foundry in Illinois. Founded in 1887, the foundry today pours more than 30 different brass and bronze alloys, in addition to aluminum and other alloys. The foundry can produce components that are as small as a few ounces to others that weigh hundreds of pounds. 

Are You Looking For Advanced Bronze Sand Casting Capabilities?

Contact us to learn what Cast Technologies can do for you. We can help you at every stage of your project, from choosing the ideal alloy and casting technique to designing the pattern. We also have a CNC machine shop on-site to allow for complete finishing of your components. Talk to us about your projects and plans and let’s get started.