Strategizing to Cut Wear Costs
Check out these new products, systems and tips to handle critical anti-wear applications
By Russell A. Carter, Contributing Editor
Full ceramic wear materials offer an alternative to metal, with excellent abrasion resistance and no threat of corrosion, but they can’t be formed or cut like metal can, and also can be challenging to install correctly. Likewise, elastomers offer unique characteristics that make them very effective in many applications, but selecting an elastomeric product with optimum abrasion resistance for site-specific applications can be tricky.
However, even though abrasion may
always be the eventual winner against any
of these materials, there are many options
available to mineral producers to prolong
the life of wear components, reduce the
cost of these consumable items, and soften
the overall impact of abrasive wear on
production volume and cost. One strategy
employs a three-pronged approach:
• Buy the best.
• Plan before you buy.
• Plan after you buy.
Buy the Best
“Buying the best” doesn’t necessarily mean buying the most expensive or well-known wear components, it means buying the product that best fits specific operational needs, budget and available resources. In some cases, this could entail buying a more expensive, longer-lasting item for installation in critical areas where failure or excessive maintenance demands could impact production; or a less-expensive product when quick changeout and avoidance of unscheduled downtime aren’t principal factors.
It pays to keep abreast of new product introductions and upgrades in the wear materials market. Suppliers are constantly improving the physical characteristics of their wear products, which often expands their horizons for applicability.
Last year, for example, SSAB introduced
its new Hardox 500 Tuf, touting
the attractiveness of its strength, hardness
and toughness combined in one
type of wear plate. According to SSAB,
it offers the best properties of Hardox
450 and Hardox 500, making it tough
enough to perform as a structural material
in heavy-duty dump bodies and
buckets. Offering performance proven in
cold climates and freezing conditions, its
superior wear and dent resistance allow
for increased service life and the ability
to withstand heavy impact, said SSAB.
Specific characteristics include:
• 85-100% longer estimated service life compared to Hardox 400;
• Guaranteed impact energy of 20 ft-lb at -4°F (27 J at -20°C);
• Narrow Brinell hardness window of 475–505 HBW; and
• Highly dent and crack resistant when hit by sharp and heavy objects.
However, not all applications will require Hardox 500 Tuf. SSAB noted that XCMG, one of China’s biggest construction machinery manufacturers, recently built what it claims is the biggest wheel loader bucket in China, with a capacity of 17 m3. Use of Hardox plate and Strenx structural steel increased overall bucket lifetime by 70%, according to the manufacturer.
The first of these buckets is being used with a large electric-wheel loader in the Eastern open-pit mine in Shuozhou, Shanxi, which is the biggest coal producing area of China. “The original bucket had worn out and the end-user needed a reliable replacement. We have been using Hardox wear plate and Strenx high strength steel for years, but it’s the first time that we worked together with SSAB’s K1 service center in Kunshan. After having the design drawings of the bucket, K1 developed the entire solution recommending steel grades, thicknesses and welding procedures. We welded based on all the ready-made components provided by K1,” said After-Market Service Engineer Cai Tuo of the Earthmoving Division of XCMG.
After the first bucket with Hardox 450 in the main body, Hardox 400 in the side bars and Strenx 700 in the structural part of the main body had been used in the coal mine for three months (2,000 working hours), a survey showed the wear loss to be 2 mm, with an original edge plate thickness of 80 mm. The service life was expected to exceed five years, compared with three years for the previous bucket.
In another sector of the market, SSAB announced its new M43 hardenable steel is formulated to provide a new level of convenience, as it can be quenched in plain water without an immediate need for tempering, yet still reaches high values for hardness and impact strength. SSAB said M43 can be quenched in water instead of aqueous quenching fluids or oil for a cheaper, safer and more environmentally friendly process. It saves energy and time in production and reduces CO2 emissions. Heat treatment results in a fully martensitic, fine-grain microstructure with excellent hardness to toughness ratio. SSAB M43 can reach three times higher toughness than a medium- alloyed chrome-vanadium or chromemolybdenum steel.
Typical hardness and toughness values are 58 HRC and 25 J/cm2 at +20°C. For even greater toughness, low-temperature tempering is enough to reach greater than 30 J/cm2 with hardness still at a level of 56 HRC. Shearing, blanking and piercing can be performed without risk of micro-cracking, avoiding more time-consuming and expensive processing.
Another new product, introduced last year by FLSmidth, is FerroCer Impact, a wear liner material designed to help mining companies reduce production downtime. As Helgi Gudbjartsson, the global launch manager, pointed out in a blog post, in mineral processing applications, different wear liners are applied in different situations, depending on factors such as type of ore, drop height, material lumpsize distribution, and angle of impact. Each wear liner has its own advantages and disadvantages. Common types include hard-metal liners, heavy-duty rubber or rubber/ceramic composite liners, each with their own strength and weakness.
These positive or negative characteristics have a significant impact on maintenance procedures and costs. A general issue facing the industry is the loss in production time because of wear liners frequently needing to be replaced and the time it takes to install new liners.
A typical example could be for common ore such as gold, copper or nickel, with a hard impact velocity of more than 7 m/s. In such a situation, the wear liner may have an average lifetime of one or two months at most. The replacement procedure can take a whole shift, putting the process flow on pause for several hours resulting in significant production losses.
With units of wear liners weighing between 20 kg and 40 kg each, safety is also a concern. A special lifting mechanism is often needed in addition to the scaffolding, allowing maintenance personnel to safely access the installation points. FerroCer Impact specifically addresses the challenges related to wear liner longevity and installation time as well as the safety of personnel involved, according to Gudbjartsson. A unique composite structure of steel and ceramic components, FerroCer Impact provides the advantages of both ceramic and metallic materials. Combining the superior abrasion resistance of a ceramic with the strength, toughness and malleability of a metal, it handles hard and abrasive materials in medium- to high-impact applications.
FerroCer Impact panels are lighter and less bulky than traditional metallic liners. Each panel comprises a number of ceramic inserts enclosed within a matrix of cast metal. The matrix protects the more vulnerable side faces of the inserts and ensures that only the wear face of the ceramic is exposed to material impact. The tapered geometry of the ceramic inserts and corresponding holes within the matrix act to wedge the inserts within the matrix and prevent material particles and fluids from causing them to be ejected from the matrix.
This design also enables the remaining wear life of the ceramic inserts to be visually assessed. As the exposed surface of the insert is progressively worn away, its area and face width increase. There is a direct correlation between an insert’s face width and height so that the one can be readily calculated from the other. The panels’ low weight (approximately 5 kilograms) and compact shape make them quick and easy to install using nothing more than standard hand tools.
In one nickel processing plant, the FerroCer Impact panels were installed in a conveyor discharge chute downline from the primary crusher unit where the material drops 6 m from one conveyor belt down to another. The hardness of the nickel ore is approximately 5 on the Mohs scale. During an initial measurement after installation, the plant operated for 319 days at full production of 900 mt/h with lump sizes of up to 250 mm in diameter — a significant increase from the previous liner, which had lasted less than three weeks on average.
On a different site, FerroCer Impact panels were installed in a chute downstream from the primary crusher of a gold mine where the drop height is 2 m and the lump size up to 400 mm in diameter. The previous liner type, consisting of heavy-duty rubber bars, typically lasted no longer than six weeks. After the first 17 weeks in operation, the wear measurements taken on-site indicated the new FerroCer panels would last at least another 80 weeks, giving them a tenfold service life increase over the previous liner solution.
Plan Before Buying
Apart from selecting the best anti-wear material for a specific site need, another effective ploy is to identify a type or brand of equipment intentionally designed to be wear-resistant. Case in point, as illustrated by process equipment supplier Weir Minerals: Centrifugal pump impeller vanes are designed to meet the incoming flow and accelerate the fluid. A problem occurs when the slurry approaches the impeller of the slurry pumps, as there is an abrupt change in flow direction. The small, fine particles follow the fluid as it transitions from the pipe into the impeller, but the large particles do not. They continue to move in a straight line, impacting the vane-leading edge as the slurry moves through the impeller. The high relative velocity between the rotating vane and the incoming particles results in leading-edge wear on the impeller. Loss of vane length due to impacting of the large particles results in a loss of pump performance. Eventually the pump will no longer be able to generate the head and flow required for the duty and the impeller will need to be replaced.
After experts at Weir Minerals witnessed this problem repeatedly in mineral processing plants, and wanted to improve the wear performance of its Warman mill circuit pumps, a company engineering team devised an innovative solution to decrease the impact wear on the vane leading edge — the Warman throatbush with pre-swirl vanes.
The pre-swirl vanes change the flow of the slurry, swirling it in an counterclockwise direction, with the rotation of the impeller, before it enters the impeller. This induced rotation of the incoming flow reduces the relative velocity between the impeller vanes and the slurry.
Elsewhere, conveyor equipment supplier ASGCO recently added Semi-Ceramic Pulley Lagging to their pulley lagging product line. The addition of Semi-Ceramic Lagging allows the company to offer a product range that provides customers with a choice between full ceramic coverage for a high-tension drive pulley, as well as less than full (40%) coverage with for smaller pulleys, non-drive pulleys and bend pulleys. The new lagging product, according to the company, provides a solution when conventional rubber lagging wears prematurely. ASGCO explained that the ceramic tiles are embedded in rubber on all sides and separated by a horizontal groove for channeling water and dirt, and a unique backing method provides exceptional bonding for rubber-to-metal applications.
Plan After Buying
Eventually, even the toughest wear components become damaged or reach the effective end of their service lives and require replacement. When it comes time to perform a planned shutdown, the stakes can be high, with significant dollars linked to each minute of downtime. Coordinating all the resources, equipment, tools and parts to keep everything on track can be challenging for even the most experienced team. Metso recently listed four key actions that need to be considered.
Baseline Performance – Assessing shutdown performance and understanding where delays occur is critical. With so much going on during a planned shutdown, it is not realistic to catch and record every improvement opportunity. But what if one could record an entire shutdown and then review it to find every delay? It can be done if one has the right tools and expertise. A lean production tool called Single Minute Exchange of Dies (SMED) or time and motion analysis, frequently used by mining companies, uses time-lapse video sequences to examine repetitive tasks, such as mill and crusher relining. Cameras are strategically positioned to capture the entire process. Maintenance and reline experts then analyze the video sequences to highlight issues and recommend improvements.
Evaluate Tools – Maintenance on
crushing and grinding equipment can be
hazardous to crews without the proper
tooling. Having the right tools that can
facilitate maintenance while improving
safety is another important element to
maximize performance. Observations from
shutdown crews or data collected from a
formal SMED analysis are used to develop
special tooling that will save time and mitigate
safety risks. The customized tools
listed below can be a better solution:
• Customized concave setting fixtures for gyratory crushers
• Special liner lifting devices for Vertimills
• Concave removal trays for crushers
• Custom work platforms, stands and ladders
Plan, Share and Execute – Small planning adjustments can make the difference between a successful changeover and one that runs hours over schedule. Planning is about making sure that all resources, parts, and tools are available to execute work in a safe and optimal manner. This includes having the right checklists on hand such as pre-planning, tools and previous shutdown checklists. Prior to execution, sharing the plan with the entire team can help raise and solve any unanswered questions. A plan is only useful if everyone is on the same page. Executing the plan is easiest when everyone knows what needs to be done ahead of time. When last minute decisions are eliminated, safety risks and delays are minimized.
Review to Improve – Even after a successful shutdown has been completed, it doesn’t end there. One of the most important things to do once the shutdown is completed is to take a step back and once again assess performance by holding a post mortem analysis. Did everything go according to plan? Were there any new safety concerns? How did the shutdown compare to the last one? Were there other unforeseen delays or other issues? In some cases, new problems and possible solutions can be easily identified. In other cases, another SMED analysis may need to be done. In any event, holding a post mortem to assess performance and set targets for the next shutdown is often a neglected step, but if done right can be served as a cornerstone to continuous improvement.