Major overhauls to large mining excavators typically require 15 to 30 days of downtime when performed
in the field. Having the work done in a shop environment can decrease downtime by as much as 25%.

In return for their productivity, mining excavators demand a level of attention and maintenance commensurate with their importance to the mining plan. For their part, hydraulic excavator builders are steadily advancing machine design to provide better maintenance access for quicker service, longer maintenance intervals and improved component reliability. For the customer, the combination of improved technology and a well-planned-and-executed excavator maintenance program can offer surprising benefits, providing a useful shovel life of 100,000 hours or more—a significant gain, as up until recently mining excavator OEMs commonly used 50,000– 60,000 hours as a reasonable service life.

Not too long ago Hitachi Construction Machinery, for example, reported that several units in a fleet of 10 EX3500 excavators at the Kaltim Prima coal mine in Kalimantan, Indonesia, had racked up more than 88,000 operating hours, with an average availability of slightly more than 91%; while the mine’s four EX1800 shovels were closing in on 90,000 operating hours at average availability of 92.4%. Some of the shovels in that fleet now have more than 100,000 operating hours. Kaltim Prima has since also determined to achieve 100,000 hours on its Liebherr R 996 shovels and backhoes.

In 2006, a Hitachi representative at Mining Media’s Haulage & Loading conference and trade show reported on Newmont Mining’s program to achieve 100,000 or more operating hours for its Nevada and Latin American operations, encompassing Hitachi units ranging in size from the EX1800 to the EX5500.

The keys to success in this type of maintenance program, said Hitachi’s Eric Berkhimer, come from three sources: the OEM, which must provide a well-designedand- built machine, provide technical and parts support to the dealer, and both technical and operator training; the dealer, which must provide superior technical and parts support and be available when needed for additional assistance; and the customer, who must operate the machine(s) responsibly and repair them properly and efficiently. Typically, said Berkhimer, a program such as Newmont’s should follow certain guidelines for success, including:
• Extensive use of nondestructive testing;
• Ensuring that OEM-recommended modifications and improvements are performed;
• Carrying out repairs in accordance with OEM guidelines and using OEM parts;
• Establishing dedicated crews to maintain the shovel fleet; and
• Maintaining a relationship with a dealer that can provide strong technical and training support.

A significant increase in excavator service life, said Berkhimer, can pay off by allowing the customer to postpone purchasing decisions while continuing to use its familiar shovels—a known quantity— and barring catastrophic failure, to operate within a known cost structure.

Looking at Longevity
To find out what general parameters excavator manufacturers use in assessing major service and overhaul intervals for their mining- class machines, E&MJ asked several OEMs to comment on the topic. While understandably reluctant to provide exact hour intervals, costs or similar quantitative figures due to the extreme variation in conditions, usage and maintenance capabilities from site to site, Liebherr and Komatsu nevertheless offered some insightful observations on what their customers can expect with regard to maintenance responsibilities, overhauls and shovel longevity in general.

Dr. Burkhard Richthammer, product and marketing manager for Liebherr’s hydraulic mining excavator business based in Colmar, France, with input also from Fabrice Gresser, after-sales and product support manager, pointed out that variations in component and overall shovel service life results from the machine’s duty load—is it working in hardrock ore or softer waste, and how abrasive is the material it’s loading; operator skill; and maintenance organization capability quality and strategy. They listed a number of initiatives that OEMs such as Liebherr have taken to increase excavator service life before the machine leaves the factory, including:
• Designing components to a targeted lifespan, based on precise calculations and experience database, combined with an economical intermediate rebuild program to decrease overall component life cycle cost.
• Implementation of new technologies into major components such as gearboxes, slew rings, track chains and track rollers. Liebherr, for example, has within its inhouse component manufacturing facilities even more specialized facilities for continuously researching and testing improvements on all type of components.
• Developing and offering reliability features that range from machine-health diagnostic systems to grease monitoring systems that reduce or prevent instances of under- or mislubrication.
• Developing systematic and OEM standardized maintenance approaches within service support organizations.
• Conducting intensive Finite Element Analysis during the design stage of components and steel structures to further understand load cases prior to manufacturing.
• Use of high-quality materials resistant to high stresses where required; e.g., castings in areas with high stresses, often with special material properties to ensure targeted lifespan.

Over the course of an excavator’s useful life, there are two principal approaches an OEM/customer partnership can take to keep the shovel operating at high availability, according to Dr. Richthammer: a continuous program in which major components are replaced at intervals very close to the end of their predicted lifespan; or a program in which the majority of components are changed out during major overhauls. The continuous program is based on both component condition monitoring, such as oil trend analysis and machine health data, and on predefined component lifespans, based on design and experience data.

Customers must carry out duty-load monitoring to ensure that machines are being used within their design parameters, should provide comprehensive operator training, and conduct preventive maintenance planning and component condition monitoring to avoid dealing with somewhat predictable parts failures.

As a broad guideline, Liebherr predicts that a minor overhaul would normally be necessary for one of its 600-class excavators at approximately 15,000 hours, involving the first engine swapout. A major service requirement would probably follow at about 30,000 hours involving an overhaul of the swing ring and major structural parts. In general, according to Liebherr, the first major components to require changeout are engines, followed by hydraulic pumps and cylinders, followed by structural attachment parts and then chassis. Large mining-class machines should be able to attain service lives ranging anywhere from 60,000 to 100,000 hours, depending on local maintenance and repair capabilities and costs.

Richthammer notes that most overhauls are done in the field, and a reasonable downtime period for a major overhaul can range from 15 to 30 days. Some mines, particularly those with large excavator fleets, perform necessary overhauls in a workshop environment, which generally allows work to be carried out in safer, more comfortable conditions with no delays due to inclement weather. Broadly speaking, a workshop overhaul can generally cut excavator downtime by up to 25% due to better crane capacity, the convenience of workshop facilities and overall working conditions.

For customers facing a major overhaul event, Liebherr recommends close attention to pre-inspection of the machine to determine necessary but perhaps unanticipated repairs, as well as careful upfront planning to eliminate avoidable delays due to part, tool or crane unavailability. A major overhaul should be scheduled anywhere from six to 12 months in advance and supported by a detailed, step-by-step work schedule, with the overall effort directed by a single designated team leader or manager.

From 80K to 100K, and Beyond?
Comments from other excavator OEMs generally follow the vein of Liebherr’s philosophy. Komatsu Mining, for example, acknowledges that 80,000 hours is a reasonable target for overall shovel service life, as well as for large components such as the undercarriage, upper structure and boom, with 100,000 hours of overall service life a realistically achievable goal given proper care and replacement. As Winfried (Winni) Rechenberg, product manager for Komatsu Mining Germany GmbH, notes, Finite Element Analysis now allows OEMs to design much longer-lasting major components, but overhauls are inevitable considering the nature of mine operations and environment, and customers must take responsibility for following OEM recommendations, updates and minor component changeout intervals. This would entail anticipating replacement of pump drive or final drive gearboxes at 20,000 hours; main, swing motor, pilot and traveling motor hydraulic pumps at around 10,000 hours; and various undercarriage components such as sprockets, idlers, bottom and top rollers, track pads and track tensioning cylinders at anywhere from 10,000 to 15,000 hours. (Komatsu and other OEMs emphasize that figures such as these are for calculation and planning only, do not constitute a warranty commitment, and can vary widely by application and working environment.)

Recently, in an interview published on Hitachi Construction Machinery’s Web site, Hiroaki Ogane, general manager of Hitachi’s Mining & Heavy Equipment Development Center, and Atsushi Tamane, senior engineer at the center, discussed how new technology, much of which was developed for the company’s flagship EX8000, is cutting downtime and maintenance costs on the new EX Dash 6 series of mining excavators as well. According to Ogane, all of the recently introduced Dash 6 models, including the EX1900, EX2500 and EX3600 follow a common design concept using many common components, and all EX-6 excavators feature a highly sophisticated monitoring system that allows the operator to diagnose and troubleshoot problems—instead of requiring the operator to refer to service manuals or wait for a maintenance worker to proceed.

Tagane noted that Hitachi has been building hydraulic excavators since the mid-1970s and can draw upon a vast storehouse of historical information to improve its designs and maintenance recommendations. All of its recent miningclass models can be monitored via satellite communications for operating status and equipment failures. Currently, about 50 sensors placed throughout the EX-5 and -6 models provide data for analysis and recommendations for service or part replacement before failure, with the difference in the Dash 6 version being a sharper focus on determining the proper threshold at which the system issues various warnings.