At Bearing Centre, we understand that your steel tools are a costly investment and that their failure can be hugely frustrating, let alone detrimental to the functioning of your business. So how can we be sure that a tool will reach its expected lifespan and perform without a hitch? To answer this, we must consider how it was made. A tool’s durability, or its failure, can be determined before it’s even produced which is why it’s essential that tool manufacturers understand and follow the rules, from initial die design to final finishing.
Taking care to avoid poor manufacturing begins with selecting the right steel for the job. Bearing Centre stocks a wide range of ferrous and non-ferrous metals as well as steel and steel products for any application. Tool steel is the preferred choice for manufacturing hand tools and machine dies – it’s hard, resists abrasion and retains its shape at very high temperatures. There are several grades to choose from depending on the what the tool will be required to do and what type of heat treatment will be used.
The heat treatment of steel, which involves heating the steel to a required temperature and then cooling it down with an appropriate method, has the most significant effect on the operational quality of tools so great care must be taken to follow the correct process. With heat, metals can be manipulated to be harder or softer, tougher and more wear resistant, depending on the tool’s intended application. It’s a tricky, delicate process so it’s no surprise that most tool failures are a result of incorrect heat treatment during manufacture.
Heat, quench (in oil or water) and temper. This is the basic process for manipulating steel but even the slightest variation in temperature, quenching medium or tempering temperature can affect the hardness and quality of the steel. Depending on the application required, it’s vital to get the process correct without putting the steel under excessive stress, making it vulnerable to cracking or fracturing.
Cracking is usually the result of overheating or uneven heating, making the steel brittle and unstable, but quenching at too low a temperature or not tempering immediately after quenching can also be a factor. Certain grades of steel are designed to lower the potential of cracking when quenching with water, while others can be quenched in oil as an alternative. Similarly, if the heat is too low or the tempering temperature too high, the steel will be soft, buckle under pressure and fail much faster than correctly treated steel. ‘Soft spots’ are a more serious problem and are usually a result of a contaminated quenching medium – one that is too warm or not properly circulated.
Heat treatment of steel may result in decarburisation, where the carbon on the surface reacts with oxygen and diffuses, leaving a ‘skin’ on the steel surface that can cause a permanent loss in its potential hardness. Removing the decarburisation can be achieved by machining or rough grinding the surface. This will optimise the tool’s potential service life and minimise future failures.
For tools with mechanical parts designed to handle heavy loads, it’s important to employ the corners and any points expected to be under stress with fillets. The fillets increase the durability of the parts by distributing the weight or stress over a larger area. Of course, using a low grade of steel for the application or overloading the tool will cause fatigue and eventual failure, even with generous fillets.
To guarantee the life and durability of a steel tool, faults during the manufacturing process must be avoided and care must be taken to ensure that correct production steps are followed and finished. And remember, if you require any assistance or need any more information, the Bearing Centre team is always on call.