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For applications where elastomers are unsuitable, Weir Minerals’ chromium white irons, Hyperchrome® and Ultrachrome®, provide outstanding wear life. We investigate how each is best deployed around the mine.
It’s vitally important to select the right material for the application, as a sub-optimal material will last fewer campaigns and increase the risk of a serious failure that could result in an unplanned shutdown.
In this second entry in our two-part blog series we will explore our range of metals, showcasing their wear resistant properties and which applications they thrive in.
There are a number of applications where rubber simply isn’t suitable. Metal alloys remain the material of choice for dealing with larger, coarser particles, high temperatures and hydrocarbons.
Another scenario where metal is preferred are “high head” areas, where an impeller or some other rotating object is spinning quickly next to the rubber and initiates a process called hysteresis reversion. In this situation, the frequent pressure pulses lead to a heat build-up inside the rubber, degrading it from the inside-out.
High head areas will be present throughout the mine, especially if there are undersized pumps being overworked.
No matter which application you need a metal alloy for, it’s important to understand the different properties of our two types, Ultrachrome® and Hyperchrome® alloys, as using the wrong one could have serious consequences for your operation.
The Ultrachrome® alloys are a series of high chromium white irons that deliver excellent wear resistance in moderate to highly corrosive environments.
These alloys contain varying amounts of chromium carbide, an incredibly hard material measuring 1600 Vickers hardness units which provides excellent wear resistance. Typical mineral ores can range from 300-1100 Vickers hardness units, so the high hardness of the chromium carbide phase is essential for wear resistance.
Our most popular alloy is Ultrachrome® A05, which contains approximately 27% chromium by weight, resulting in a chromium carbide content of about 25% by volume.
With this moderate chromium carbide content, A05 is what’s known as a “near eutectic” alloy. This provides a great balance of hardness and toughness, making it effective for general purpose pumping applications in addition to applications with very large solids – sometimes as large as 300mm in size.
Suitable at pH4 and above, A05 provides modest corrosion resistance to a number of components, such as the impellers, casings, volute liners and throatbushes in the legendary Warman® pump range.
Our Ultrachrome® range also has several “hypoeutectic” alloys - these have a lower proportion of wear resistant chromium carbides, but a higher proportion of free chromium in the iron matrix which dramatically improve corrosion resistance.
A49 has 23% carbide for more corrosive environments, while A53 has around 18% carbide and is suitable for extremely corrosive environments with a Ph of 1, often replacing stainless steel. For applications in which erosion and corrosion are both responsible for wear, A53 can achieve a wear life many times greater than stainless steel, and is frequently used in acid leaching and extraction circuits, such as those in the phosphate refineries and flue-gas desulphurisation (FGD).
Weir Minerals’ Hyperchrome® range consists of a number of hypereutectic iron-chrome alloys, featuring high proportions of chromium carbide to produce incredibly strong metals.
With a higher chromium carbide content than hypoeutectic options, these hypereutectic alloys have historically been avoided, as they typically contain very large chromium carbides (up to 100µm in size or larger), resulting in a very brittle casting. However, Weir Minerals utilises a specific process to refine the carbides and ensure they do not exceed 50µm, in order to provide quality wear resistance and retain useful mechanical strength.
Our most common alloy is Hyperchrome® A61, containing 50% chromium carbide. It achieves outstanding erosion resistance that makes it ideal for conditions with a broad particle size distribution, such as mill discharge slurries.
Conversely, for feeds with larger particles Ultrachrome® alloy is preferred as it is more resistant to the impact force of these particles. Once 20% or more of the feed consists of particles sized 1mm and above, Ultrachrome® alloy achieves a significantly better wear life.
Our latest Hyperchrome® A68, benefits from new metallurgical advances that combine the robust wear resistance of A61 with the anti-corrosive properties of our Ultrachrome® A05, making it ideal for moderately corrosive environments that require a harder alloy than Ultrachrome® can provide.
Having the two together in one material provides a synergistic bonus to overall wear life, which can be found in throatbushes, impellers and volute liners handling mill discharge slurries and tailings.
Failing to use the right material for the job can significantly degrade a component’s wear life and put a plant at risk of an unplanned shutdown.
Perhaps the easiest mistake to make when selecting a wear material is failing to consider the disparate processes and chemicals a slurry feed is subject to upstream of your application. The right wear material isn’t just determined by the immediate parameters of your application, as a wide variety of upstream processes can have significant repercussions for downstream wear, often in ways that are difficult anticipate.
Seemingly small amounts of ‘safe’ chemicals can have an outsized impact on the overall wear life of materials not designed for deployment in corrosive environments.
Another key mistake is using natural rubber in circuits with large amounts of chemicals. A common example is the use of natural rubber to handle slurries containing floatation collector chemicals. These hydrocarbons (often diesel fuel) cause swelling in natural rubber and can cause accelerated wear to rubber components.
When selecting a material for critical components, there’s no substitute for working directly with your OEM to ensure you deploy a cost-effective material which will go the distance.
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