By Timothy McCrea, Market Segment Manager – Aftermarket, Hägglunds – Bosch Rexroth Corp.
Hydraulic systems are proven, versatile and dependable technologies used in mining operations on equipment such as auger drives, drilling machines, mobile crushers, apron feeders, breakers, belt conveyors, and more. In particular, radial-piston, direct drive hydraulic motors are well-suited for these applications because of their low-speed/high-torque (LSHT) capabilities, their space-saving design, and technology engineered to deliver reliable, long-lasting performance and reliability for moving heavy loads under difficult operating conditions.
As with any system in a harsh environment, routine service is critical to maintaining the uptime of radial piston motors. Hydraulic direct drives are engineered for longevity; however, preventative maintenance (PM) is often overlooked for this type of equipment until it is too late. When breakdowns occur, they can take valuable equipment off the line or even shut down operations.
Implementing a few effective maintenance and service best practices can prevent major breakdowns — plus it saves time, money, and effort compared to allowing equipment to deteriorate, then shipping it off to a repair center. More importantly, these best practices can help mining operators ensure that the drives powering vital equipment provide the years of operation they were engineered to deliver.
Value of hydraulic direct drives
Large LSHT hydraulic direct drive systems are often used to power demanding mining applications where heavy masses of materials need to be moved under variable speeds. Mining equipment such as fixed or mobile crushers, bucket wheel drives and augers have specific needs in equipment design and flexibility. These include the ability to withstand rugged environments and shock loading, two of the most common operating conditions. In addition, hydraulic direct drives must be able to resist wear and tear without adding bulk and weight.
LSHT radial piston motors meet these challenges, producing extremely high torques in a small compact package. The radial piston motor mounts directly on the machine’s driven shaft, while other hydraulic drive components can be located away from the machine. For mobile equipment, all the hydraulic components may be distributed on the machine platform itself.
Some of the better radial piston hydraulic drives are designed to prevent equipment damage via set points and limits that prevent over-torque in case of upstream or downstream equipment failure. Diagnostics and machine health indicators are additional advantages available on these types of radial piston hydraulic drive systems. Given the central role hydraulic direct drives play in the smooth operation of mining equipment, they should be included in any effective maintenance strategy.
Risks of “breakdown maintenance”
When periodic predictive maintenance practices are not in place (or only performed intermittently), even the best, most well-engineered hydraulic system will break down. “Breakdown maintenance” follows with serious impacts, such as:
- Equipment deterioration is a direct result of neglect, increasing energy costs and reducing efficiency.
• Small issues — such as fluid leaks from worn-out seals — become big issues when preventable fixes are overlooked.
• Safety incidents and injuries occur more often due to sudden failures or jams on conveyors and other systems moving loads over long distances.
• Maintenance teams are under pressure to complete fixes on a time crunch, thus potentially overlooking standard safety practices, and
• Emergency repairs are more difficult to schedule, often incur higher costs and can take technical personnel away from regular duties to support removing and transporting damaged direct drive equipment.
In addition, if a facility or location generally follows breakdown maintenance, failures in multiple pieces of equipment can happen right on top of each other. These types of failures typically have longer repair times if systematic neglect forces repair of surrounding components and equipment as well as the hydraulic direct drives.
Best practices for maintaining hydraulic direct drives
There are several essential maintenance practices that, if followed consistently, can prevent many potential hydraulic direct drive failures and keep you from operating in breakdown maintenance mode.
Periodic inspection and maintenance checks: This lays the foundation for maintenance best practices. Equipment inspections should follow a standard schedule. Standard intervals should be monthly at a minimum, whereas some of the best facilities conduct weekly inspections. Inspections should document danger signs, such as main pump pressure changes, fluctuations in desired motor speed, increased oil temperatures compared to standard operating levels, increased case drain flows, hydraulic oil leaks and oil reservoir levels.
Large-scale operations in industries, such as mines and paper mills, use these inspections not only to prevent breakdowns but also to capture data about machine performance to improve both their maintenance and production processes.
Hydraulic fluid selection and condition: As with other hydraulic systems, be sure to use the manufacturer’s recommended fluid with the viscosity level the hydraulic direct drive is engineered to use. Environmental factors can influence this selection. Mining operations will have temperature extremes based on their locations, especially in high-temperature environments. If equipment manufactured for use in Canada is shifted to use in New Mexico, double-check the hydraulic system specifications as to whether a change from a moderate viscosity fluid, such as ISO 46, to a denser viscosity, such as ISO 68 or 100, is advisable.
Equally important is regular monitoring of hydraulic fluid conditions for contaminants, discoloration or particles — along with other sensor data that the direct drive may offer. Oil condition is a critical warning sign that there may be components in the motor that are wearing or damaged. This is particularly important in pits and quarries for example, with their high level of dust, gravel and other contaminants.
Servicing filters and seals: Filter changes at specific intervals are important to reduce contamination buildup and, in turn, reduce wear in all hydraulic system components. Direct drive manufacturers will specify the type of filter their system should use, and they may provide more detailed recommendations — filter medium and micron level, for example — depending on the level of dust and contaminants present in the operating environment.
In addition, most hydraulic systems have fittings that use O-rings to prevent leakage; however, due to the shock loading, vibration and nature of leaking in aggregate operations, these O-ring seals may tend to wear out more frequently. Periodic maintenance inspection will find those leaks so you can replace used and worn O-rings, tighten loose fittings or replace any damaged fittings.
Use OEM parts: With radial piston motors, it may be assumed that a local repair shop has the expertise to complete a repair to OEM specifications. However, to achieve OEM-level it is critical to ensure the right parts are used. It’s quite common to see motors repaired with used parts taken from a scrapped component, or with aftermarket parts not necessarily designed to perform under the harsh conditions of high shock load equipment. In addition, sometimes motors have parts that require a special proprietary coating which may improve service life or efficiency. These coatings are used on internal wear parts designed specifically for high shock load applications where there is a risk of cavitation. Cavitation can cause a reduction of oil film between the metal wear parts. In addition, these proprietary coatings were developed to deliver long life in applications requiring extremely slow and extremely high motor speeds where oil viscosity levels can be reduced. This detailed knowledge may not be available from third-party local repair shops working on a wide range of industrial hydraulics equipment.
It’s important to specify that any repairs should use original OEM parts supplied from the manufacturer and not those pulled from a scrapped motor. In fact, some hydraulic direct drive manufacturers do more than repair their equipment: They can provide fully remanufactured drives and radial piston motors with “like new” warranties to ensure long-term performance.
Choose OEM-certified service suppliers: The specialized design and operating characteristics of hydraulic direct drives call for a higher level of expertise and resources, which can only usually be supplied by OEM-certified facilities that concentrate on this equipment. Third-party repair facilities will not have the original manufacturer specifications to properly repair, calibrate and test the motor to new condition — and in fact, will not typically be able to perform a fully warrantied remanufacture.
They are also the kind of facility that can provide the most effective and up-to-date PM programs and technicians factory-trained to inspect, service and maintain the OEM’s equipment. Certain proprietary components that cannot be duplicated or obtained from scrapped drives and motors may only be available from OEM-certified facilities; in addition, there may be specific equipment tolerances that only the factory or OEM service shop are equipped to work with.
Preventative maintenance programs: Many of the best practices described here can be incorporated into comprehensive PM programs that identify risks and correct issues before they lead to failures or downtimes. Effective PM programs include annual major inspections and quarterly minor inspections carried out in the field by factory-trained and certified technicians.
Good PM programs include detailed inspections of all accessible equipment, oil temperature, pressure and non-intrusive motor temperature inspections, pump settings, speed and motor parameter setting inspections and validation against operating specifications, case drain flow measurement, oil analysis as well as shaft coupling and O-ring inspection and replacement. An effective PM program will also supply a detailed report of findings, recommended maintenance, spares and follow-up actions.
Filed Under: Design World articles, Hydraulic equipment + components