OEMs and end users can pick from an expanding range of products, selection tools and installation techniques
By Russell A. Carter, Managing Editor
At a factory in France, a new hydraulic excavator is assembled, tested and disassembled for shipment to an Australian iron ore producer. A few thousand miles to the west, a drilling jumbo hammers away at a hardrock face underground in Canada’s Sudbury Basin. At a surface mine in the Southwest U.S., a high-speed conveyor dumps thousands of tons of copper ore each day onto a transfer point. And at a nickel mine in Finland, a tweak to the profile of a gyratory crusher’s wear mantle results in a 15% increase in crusher throughput.
Apart from the single obvious connection between these examples—all are hardrock related—is another: The equipment involved in each application benefits from advances in materials and techniques that protect against abrasive and/or impact wear—and future versions will likely gain even more reliability and productivity as wear materials continue to evolve and improve.
Selecting the Right Steel—and Installing It
Predicting the service life for various materials under diverse conditions can be challenging. Each variety of rock is composed of a unique set of minerals that influence the specific type of wear damage. However, some recent developments in wear-resistance technology directly pertain to the most basic elements of use: selection of the right material and proper installation.
For example, after five years of development, Swedish steelmaker SSAB—suppliers of the well-known Hardox line of wear steel products—recently introduced a new version of its WearCalc software, which allows convenient calculation of the relative service life of Hardox materials. Combined with comparative material and production costs, this permits quick selection of the optimum materials for the job.
The previous version of WearCalc only predicted sliding wear but WearCalc 2.0, according to SSAB, now can predict erosive and impact wear as well for all types of Hardox plate. The erosion model is based on research involving aggregate and large rocks. At macro level, WearCalc 2.0 predicts whether makeup of the abrasive materials will cause particle edges to penetrate the steel surface or to break. At micro level, the model uses mineral hardness to calculate erosion on different types of wear plate.
The software covers two types of impact damage: severe damage involving crater formation and extruded lips during impact, and milder damage resulting in plastic deformation of the surface.
The algorithm takes size, shape, impingement angle and velocity of the material into account. Although the software requires the entry of several parameters to obtain accurate results, SSAB said the developers have taken pains to ensure the user interface remains easy to use.
The results are presented in a table in which mild steel is normally used as a reference value. A report generator creates a report with the input parameters and result table. This file can be edited in Microsoft Word and saved or e-mailed. Access to WearCalc software is arranged through SSAB’s technical managers.
Another upgrade of a useful software tool, SSAB’s WeldCalc Version 2.0, was introduced at the CONEXPO-CON/AGG trade show held in Las Vegas, Nevada, USA, in March. WeldCalc is an application for calculating and presenting wear-plate welding recommendations. The user enters the desired mechanical properties, welding process and plate materials involved. Based on this information a “tolerance box” is calculated, showing the allowed span of heat input and preheat/interpass temperature. The new, Web-based version also allows the user to save or export results. Logs can be opened, edited and re-saved.
SSAB also has revised and expanded its welding handbook. “We thought the time had come to update our technical recommendations,” said handbook author Daniel Stemne. “This also gave us an opportunity to expand the contents to include a number of new practical and theoretical topics. In short, the welding handbook contains our broad collective knowledge in many areas of welding technology involving Hardox wear plate and Weldox structural steel plate.”
The handbook also covers more general subjects—from joint preparation and magnetic arc blow to heat treatment of welds, and repairs. It also contains chapters on various topics including filler metals, shielding gas and discontinuities in welded joints. Although it was written principally for technicians and engineers, others may also benefit from the book, according to the company.
SSAB also noted that in addition to providing multiple hardness grades of Hardox wear steel, its product line now includes both thick and thin plate. Although thicker plates connote higher weight and possibly less efficiency this isn’t always the case, according to the company, which points out that larger machines are generally more efficient. But increasing machine size means greater mechanical forces and production throughput—and this leads both to greater wear and to a demand for longer component service life to improve economy and uptime.
SSAB has responded by investing heavily in quenching, tempering and rolling mill equipment and procedures to produce thicker, through-hardened plate of consistently high quality, following its belief that thicker specialized plate can enhance efficiency and economy by providing greater strength and wear-resistance for the same standard-plate thickness and weight. Thicker plates, according to SSAB, allow the manufacture of components that last longer, deliver greater uptime and cut lifecycle cost.
Hardox wear plate, Weldox structural steel plate and Toolox pre-hardened tool and machine steel are available up to a thickness of 160 mm (6-1/4 in.) depending on hardness grade. At the other end of the thickness range, SSAB also has launched Hardox wear plate in 3-mm thickness, offering the same features as other Hardox thicknesses with less weight and bulk.
A Win for Work-Hardened Wear Steel
In the UK, a recent name change for an established specialty steel supplier has been accompanied by a commercial achievement in the mining equipment sector. As of January, Abraservice UK, formerly known as IMS UK, is now a subsidiary of Abraservice Holding, itself a 100% subsidiary of IMS SA. The group claims to be the largest independent distributor of special steel grades across Europe with manufacturing facilities in Germany, Italy, France and the UK.
Among the range of specialty steels offered by Abraservice UK is CREUSABRO, which the company describes as combining extreme resistance to abrasion with a high level of toughness, developed to optimize wear resistance against abrasion, impact, heat and corrosion. This is made possible, according to Abraservice UK, by the specific chemistry and heat treatment processes used during the manufacturing process.
Nick Taylor, Abraservice UK’s sales manager, said the ability of CREUSABRO 4800 to work-harden offers an increase of up to 50% service life compared with conventional 400-HBW steel grades. It also endures temperatures up to 450°C, a level not achievable with standard wear steels. CREUSABRO 4800 is designed to provide a combination of wear resistance, controlled hardness and ease of processing, achieved by a combination of an enriched chemical analysis (Cr, Mo, Ti) at a controlled quenching rate.
Likewise, the ability of CREUSABRO 8000 to work-harden offers similar increases in service life compared with conventional 500-HBW grades, said Taylor, who noted that following the results from a recent comparative abrasion test program, Liebherr Group now offers customers an option to purchase hydraulic excavators and other earthmoving equipment fitted with buckets employing CREUSABRO 8000 wear parts. The test program, carried out at the Assarel copper mine in Bulgaria which is renowned for extremely abrasive conditions, showed that use of CREUSABRO 8000 steel increased the wear life of excavator buckets by more than 46%.
Taylor explained that buckets used on excavators are conventionally manufactured using high yield strength steel for the body with 400- and 500-HB water-quenched steel wear plates welded into position. This typically provides sufficient strength and an acceptable level of abrasion resistance. In the comparison test, two identical mining buckets were used on a Liebherr 994 excavator. Both buckets were produced by Liebherr in its manufacturing plant in Colmar, France, and were manufactured as two-part front-shovel buckets with a back door for unloading the excavated material. The individual parts of both buckets were manufactured from materials shown below.
To assess the overall difference in performance between the bucket equipped with CREUSABRO 8000 wear parts and the bucket using conventional steel wear parts, the testing schedule monitored:
• Thickness of the wear parts over a common period of time;
• Thickness of the cross-sectional beam on the static back of the bucket;
• Tonnages of material moved over the same period; and
• Working conditions and parameters.
Both buckets were tested by digging directly at the mine face, working with both unblasted and blasted material. The face comprised a range of different minerals including sulphur bornite and malachite azurite cuprite as well as a variety of grain sizes. The shovels ran 23 hours per day, seven days a week.
The bucket equipped with CREUSABRO 8000 was in service from October through March; the other bucket from April to October. The latter bucket operated for 2,540 hours before requiring maintenance. At that time, severe wear was observed from the abrasive sliding and impact of the material. Due to the concentrated wear on the bucket from the high tonnages of material excavated, the wear protection strip extremities were totally worn away on the back of the bucket and measurements also showed that beam thickness, originally 120 mm, had been reduced to 22 mm. Other consequences resulting from the continual wear on the inside faces of the bucket were loss of mechanical resistance and distortion leading to risk of rupture and critical maintenance requirements. However, no repairs were required on the outside surfaces.
The CREUSABRO 8000 wear parts-equipped test bucket was used for 2,600 hours; on inspection it required no maintenance and went on to operate for 3,700 hours at which point minor maintenance was required—primarily, just cleaning. Some grooving in the structural base of the bucket was observed, but the level of maintenance required was minimal. Wear protection strips on the static back of the shovel bucket were in good condition, and there was no visible dimensional difference between the initial alignment on the back of the shovel bucket and the current alignment.
In addition to Liebherr’s acceptance of the specialty steel as a wear-parts option for its buckets, Abraservice UK notes that Assarel subsequently placed an order with Liebherr for five new buckets, to be lined with CREUSABRO 8000.
Another product in Abraservice UK’s portfolio is Dillidur Impact, a wear-resistant steel claimed to have exceptionally high resistance to cracking. It has a nominal hardness of approximately 340 HBW in its delivery condition, and its mechanical properties are obtained by water quenching and subsequent tempering. Dillidur Impact is recommended where strong resistance to abrasion is required together with toughness to resist impact wear.
According to the company, this wear-resistant steel is also more flexible with regard to pre-heating and post-heating processes and is easier to weld compared with standard 400- and 450-HBW water-quenched grades, especially where high thickness is an issue.
Conquering Corrosion with Chrome
Dallas, Texas-based Chromium Corp., a subsidiary of GAF-ELK Corp., has been in the steel business since the 1920s and specializes in providing various types of electroplated, hard chrome-coated wear steels. Its CRODON wear plate is a dual-layer wear system consisting of a thin, tough upper layer and a base metal layer of mild steel, stainless steel, or through-hardened AR plate. The upper layer adds virtually no weight but greatly improves service life and performance. CRODON product groups are differentiated by the backing material used. Each product group is application engineered to meet the needs of specific environments.
CRODON Standard wear plate uses mild steel as base material and is recommended as an economical solution for abrasion, sticking and light to moderate impact. CRODON Advantage wear plate uses stainless steel base material, and is most appropriate for corrosive conditions, especially when the CRODON wear plate needs to be cold formed or rolled with a radius in the external diameter, subjecting micro-sections of the base material to corrosive materials. CRODON Plus wear plate offers AR400 through-hardened steel as a base. According to the company, it provides two advantages not found with CRODON Standard or Stainless wear plate: the CRODON wear surface works synergistically with the AR400 base steel to improve resistance to impact by a factor of 12 or more; and because the base material itself also is wear resistant, it allows the operator to predict when material needs to be replaced once the CRODON wear surface finally wears through.
CRODON Premier wear plate employs AR500 through-hardened steel base. It is targeted for non-impact applications that experience extremely high abrasion. Once the wear-resistant CRODON hard coat surface is worn through, the AR500 base allows extra time before the assembly needs to be replaced, giving the operator longer life and maximum flexibility to schedule maintenance.
According to the company, independent test results have shown that CRODON excels in bulk material handling situations where the proper liner choice can significantly reduce common flow problems, such as bins, chutes, hoppers and other bulk solids handling equipment. CRODON’s low frictional resistance make it an efficient material for chutes, for example, where its use as a liner could reduce the need for steeper hoppers and lessen chute build-up. CRODON also maintains its low frictional resistance even as the surface became smoother, allowing for the hopper flow pattern and the chute velocity to remain unchanged.
The Finnish Line
Helsinki, Finland-based Rautaruukki Corp., which uses the marketing and branding name Ruukki, also offers steel products that have garnered attention from mining equipment suppliers and users. Its Raex line of wear-resistant steel is recommended by the company for use as wear material on excavator buckets, for bucket cutting-edges, and for general wear applications across a wide variety of mining applications.
According to Ruukki, Raex’s toughness derives from the company’s unique direct water-quenching (DQ) process, which quickly cools steel from 900°C to room temperature immediately after rolling. It produces an extremely hard and tough microstructure and allows production of thinner materials with easier weldability and improved steel surface quality and thickness accuracy. Raex is available in nine grades ranging from 270–390 HBW up to 450–540 HBW, from 2.5- to 40-mm thick and in cut lengths or heavy plates depending on the specific HBW grade. Ruukki states that Raex 400 is 2.5 times harder than ordinary structural steel, while Raex 500’s hardness is triple that of ordinary structural steel.
Last year, Ruukki launched its patent-pending Optim 700 MC Plus product, a new high-strength structural steel with improved cold-forming properties and high impact strength. Along with mathematical modeling to calculate the optimal composition of the product in the concept stage, Ruukki’s cooling and thermo-mechanical rolling process expertise is applied to create a fine-grain steel offering a doubling of impact toughness, easy weldability, superior low-temperature performance and high tensile strength.
Ruukki’s steel service centers can provide pre-bent and laser-welded components, as well as finished parts or products.
Hardfacing Options Expand
NanoSteel, a supplier of nanostructured steel alloy surface technologies, announced in 2010 the release of its first stick electrode for weld overlay hardfacing applications. SHS 9700E, the newest addition to NanoSteel’s portfolio of Super Hard Steel (SHS) alloys, is described as a premium alloy that features an ultra-refined, near-nanoscale crystalline microstructure that results in hardness up to 70 HRc, with exceptional resistance to abrasive wear. Available in 10- and 50–lb boxes and in bulk, SHS 9700E stick electrode is a hardfacing alternative to MIG and open-arc wire applications with excellent weldability. SHS 9700E, an iron-based steel alloy that does not include nickel, tungsten and molybdenum in its material chemistry, has been designed to be deposited on mild and low alloy steels. NanoSteel recommends that SHS 9700E weld deposits be limited to two layers maximum for most applications. Both single and double layers are claimed to provide exceptional wear resistance of 0.12–0.14 g (+/- 0.03) mass loss in ASTM G65-04 dry sand rubber wheel abrasion tests.
San Diego, California-based Rankin Industries says its Rantube large-diameter tubular hardfacing electrodes are designed to combat parts wear caused by severe abrasion, erosion, impact and heat. Rantube deposition rates are up to 6.5 lb/h for the 7/16-in. (11-mm) size. The ¼-in. size is designed for all-position welding and can be used at low amperage to hardface thin edges. Rantube can be applied to parts made from cast iron, manganese steel and mild steel without preheat, but high carbon and alloy steels may require preheating. Electrodes are available in three diameters and include a graphite end seal for quick arc start; flux coating to prevent damage if dropped and to allow non-heated storage; high-density alloy powder fill; a steel case that seals the tubular section containing alloys to prevent contamination, moisture pickup, and alloy loss if the electrode is dropped; and color coding for alloy identification.
Profiling for Productivity
As illustrated by Metso’s Mining and Construction Technology Group in a recent issue of its Results customer magazine, in certain cases all that is required to maximize wear material performance and machine productivity is a few adjustments to basic design.
Talvivaara, located in northern Finland, is the largest sulphide nickel ore mine in Europe. In cooperation with Metso, Talvivaara recently boosted its primary crushing capacity by as much as 3.5 million mt/y through the technique of crusher cavity optimization.
About 22 million tons of nickel ore is excavated at the mine annually. Broken material liberated by blasting that provides up to 300,000 mt of ore per shot is fed to a 60 x 89 in. primary gyratory crusher and then transported by a 2-km-long conveyor to the secondary and tertiary crushing stages. Bioheapleaching of the ≤8-mm crushed ore particles takes place in four heaps, each 400 x 1200 m in size. Talvivaara produces about 30,000 mt/y of metallic nickel.
The nickel ore is hidden inside black schist, which is extremely slippery material to crush. Soon after initial installation of the primary gyratory crusher, it became apparent that actual crushing throughput would fall far behind the planned figure. This presented a severe challenge to the mine’s economic success.
“The main problem was caused by the profile of the original crusher wear mantle. It was not right for processing slippery ore, and it caused the feed material to jump, decreasing capacity,” said Erkki Kärkkäinen, manager of materials handling at Talvivaara.
Talvivaara contacted Metso’s crusher wear parts specialists at the Tampere office in Finland to find a cavity that could better process the slippery ore and guarantee the capacities required for the mine economy. After several meetings, using Metso’s crusher cavity optimization process know-how, including 3-D mantle design tools, the correct angle for the mantle cavity was found, and the most suitable manganese type selected. Metso’s Tampere foundry casted the huge, two-piece wear mantles in the spring of 2010.
“Our main challenge in designing the right cavity was to determine where to start the curve of the cavity in order to prevent the ore from jumping up, and to secure efficient crushing throughout the whole height of the cavity,” said Mikko Malkamäki, Metso’s wear parts specialist.
The new mantles and outer wear parts were installed in May 2010. After crushing for eight months, results were positive: primary crushing capacity increased by an average of 15%. Given as a percentage, the increase sounds modest; however, when calculating the annual capacity increase, Kärkkäinen calculates that the improvements translates to 3.5 million mt of additional throughput.
The primary gyratory’s original capacity was measured as less than 3,000 mt/h after post-installation testing. Now, after installing the Metso wear parts, it is about 3,500 mt/h. “I believe that with more efficient feeding, we can achieve a continuous production that exceeds 3,000 tons per hour. We currently feed the crusher using big Hitachi dump trucks, dumping 150 tons of ore into the crusher every 2.5 minutes,” said Kärkkäinen.
Collaboration between Talvivaara and Metso continues: The next challenge is to extend the life of the mantles and minimize the scrap rate. The next mantles will be cast from Metso’s XT750 manganese, and concaves will be cast from white iron.
“Our goal is to double the lifetime of the primary gyratory wears. Whenever possible, it would be ideal to change the inner mantles and outer concaves simultaneously. Consequently, our crusher availability would improved significantly, because changing of wear parts requires a service break of three to five days,” Kärkkäinen said.
The Softer Side
REMA Tip Top recently introduced REMASTAR lining material, based on thermoplastic polyurethane (TPUR), offers new features that offer significant improvement over existing lining materials. REMASTAR is claimed to be extremely resistant to wear, resists grooving and cutting, stays flexible at extremely low temperatures, and is resistant to oils, greases and a wide variety of solvents. REMASTAR, according to the company, has REMA Tip Top’s CN bonding layer, which provides a safe and durable bond to metal or rubber.
The company said REMASTAR has been tested in various applications; in one specific example, as a wear lining material on a magnetic slag belt conveyor where slag intermingled with iron pieces strike the belt with high momentum, causing extreme wear and considerable damage. As a result, the belt had to be replaced frequently. Tests carried out using various commercially available wear-protection linings provided measurable increases in service life, but the serviceability of the belt was not enhanced dramatically until REMASTAR was applied to it as a wear-protection lining. The extended service life of the belt lined with REMASTAR then led to an increased productivity of the whole plant.
Also new to the market is REMA Goo, a solvent-free, two-component polyurethane repair paste which makes it possible to repair damage to conveyor belts in an extremely short time. REMA Goo repair paste comes in a double cartridge, and is applied using a cartridge pistol. Application, according to REMA Tip Top, is simple: The damaged area is mechanically prepared, buffed and cleaned. The double cartridge is inserted in the cartridge pistol, and the included mixing nozzle is affixed. The Goo is then applied to the repair area, smoothed out, and the repair is finished.
Its components are homogeneously mixed during application, and quickly react with one another. Because hardening time depends on the ambient temperature, repair time can be shortened by heating the damaged area. Once applied, Goo stays elastic, does not shrink and is resistant to UV rays. According to the company, REMA Goo cures to the approximate hardness of a conveyor belt’s rubber cover.
Tough Coating for Hydraulics
Recognizing that mining typically places high demands on hydraulic systems due to the highly abrasive and corrosive nature of the operating environment, the German firm Kerpener HT Hydraulik Technik Gülich-Pohl GmbH has developed a new type of material and coating for its hydraulic cylinders that is claimed to be suitable for a wide range of applications. The company says its new HTec coatings have a much higher resistance to abrasion and corrosion than other products currently available on the market.
According to the company, the aim of the new material/surface coating combination is to prolong the total service life of the cylinder’s components, thereby eliminating any need to recondition individual parts of the system during the operating life of the equipment. To achieve this, all components subject to mechanical or corrosive stress are treated with the new coating—except for the seals, which still must be replaced on a regular basis. As well as being used on the piston rod and cylinder inner surface, HTec is also applied to the piston, piston guides and load distribution elements.
An HTec material/coating combination is claimed to be extremely resistant to mechanical stresses. According to a test report produced by RWTH Aachen the actual coating layer exhibits a Vickers hardness of more than 1,700 HV (equivalent to a Rockwell value of more than 80 HRC). Tests also have demonstrated that even when running “dry,” treated cylinders exhibit a service life that is several hundred times greater than that of standard cylinders.
HTec surface tempering constitutes a range of surface treatments that can be adapted to suit the intended purpose and base material. The material is produced in conjunction with the surface treatment using a special manufacturing process. This results in a homogeneous base material and surface finish that is not prone to flaking or peeling. As a result, the technique can be adapted to suit many applications throughout the toughest industrial environments.
HT Hydraulik Technik said the HTec products can be used in an ambient temperature range of –50°C to 600°C. The treated material/surface coating combination is compatible with all mineral-based hydraulic oils, fire-resistant hydraulic fluids and environmentally friendly hydraulic fluids, and can also be used with water. HTec components are suitable for operating pressures of up to 720 bar.