One of the key engineering challenges we face in modern manufacturing is choosing the right materials for our products to ensure maximum product life at the most appropriate cost to our market segment. This is as true for bronze and brass alloys as it is for the other components in any product and we often get asked by our customers for help with their material selection. The key mechanical considerations when choosing the correct bronze alloy are the ultimate tensile strength, the yield strength, the elongation and the hardness, while consideration may need to be given to the shear strength, compressive strength and maximum and minimum operating temperatures, as with any metal.
The best way to describe the ultimate tensile and yield strength measures in terms of a ductile material such as a bronze alloy, is as a measure of how much force a material will withstand before it deforms in a plastic manner (yield) and ultimately “necks” or loses cross-sectional area due to the plasticisation of the test specimen (ultimate tensile). Eventually the specimen will break.
Elongation measures the ductility of the material. This is normally done at the time of the strength test.
Hardness is measured on the Brinell scale. The Brinell test was devised by Johan Brinell in 1900 and involves applying a 3000kgf force on a 10mm ball to a test specimen and measuring the indentation the ball makes in the specimen. With the increased use of mild steel in many manufactured products (for example worm gears), it is important that the hardness of the bronze is taken into account when designing any system.
Ultimately, it is worth taking the time to work out which material is suitable, both for safety of design and for cost grounds. The temptation as an engineer is to hit it with a heavy hammer and over-design the part. This certainly means it will last a long time, but if there is extra cost, then it might price the product out of the target market and put said engineer out of work!
The difference in cost between alloys has become more dramatic in recent times due to the higher price of commodities, particularly nickel and tin. This means the difference between our cheapest alloy and our most expensive can be 250%! In terms of material substitution and potential cost savings, you are more likely to be looking at the 10 – 15% range, but still worth looking at.
Of course, you may be at the other end of the scale and looking to improve the quality of your product with a more durable alloy.