One of our mechanical engineers shares his experience working on the tools in a component rebuild centre. How has it made him a better engineer?
By Colin Sheldon
Recently, I was lucky enough to attend 12 days in a Component Rebuild Centre (CRC) for a major mining contractor/service provider. It has been a long-time goal of mine as a mechanical engineer to gain an insight into the trade side of the industry and be able to spend time on the tools. I have always been around mining equipment in my working career but purely from a supervisory/management/engineering perspective.
Bluefield takes pride in having team members who have experienced the shop floor opportunities and challenges within a mining environment. This background “at the coal face” gives Bluefield the ability to understand issues and nuisances more easily than your typical service provider.
During this secondment, I was fortunate enough to assist with the disassembly and assembly of excavator hydraulic cylinders (boom, stick & bucket), haul truck suspension cylinders (front & rear), grader front axles, haul truck rear wheel groups (spindle, hub & final drive), wheel loader final drives, haul truck steering links, as well as dozer SCAB (steering clutch and brake) units. There were six major takeaways for me:
The importance of seals
After stripping some cylinders and seeing the state of the gland and piston, the important role the humble seal plays is obvious. They cop an absolute barrage from contaminants, pressure spikes, and tolerance deviations but even in their impacted condition they still performed their role in the cylinder. We were able to note dieseling on the seals (inadequate bleeding of the system/aerated fluid), extruded edges (excessive pressure or excessive internal clearances), as well as evidence of damage on previous install.
One interesting chat revealed a previous practice where custom seals were manufactured following the actual measurement of the cylinder components, which consistently gained a greater component life for the cylinder as opposed to the use of factory seals. A side note: it is also important to make sure you install the backing ring on the correct side of the pressure seal (my bad – lucky old mate spotted that before it went together).
Make the job as easy as possible
To ensure the job was completed as quickly and as safely as possible, the workshop had multiple custom stands, work platforms, tools, jigs and fixtures, which enabled ergonomic access to subcomponents and the ability to rotate, lift and manoeuvre components with ease. I was also interested to see how easy the HYTORC electric torque wrench was to operate (I have only used hydraulic units in the past).
The ease with which the fitters could go about their work on components (some upwards of 5T) made me reflect on the difficulty mine site fitters have to contend with. We as an industry often set-up our maintainers to do their jobs with less than adequate tooling or equipment which exposes them to situations that can seriously impact their health and safety.
Noticing wear and failure trends during disassembly
The tradespeople in the CRC who disassembled multiple components over and over were able to notice and recognise patterns in the wear experienced within the assembly. Additionally, they noticed different wear rates dependent on the service hours and rebuilt history of the component.
This chance to look inside and recognise what is happening is a major advantage and should feed back into asset plans and maintenance strategies. This also comes with the sheer volume of components that this CRC sees which gives them the necessary sample size to make informed decisions.
At mine sites, we often only get to see the component stripped ourselves if we request a strip-down report following a failure, we don’t get to observe the internal signs as to what is happening to our components.
Risk to components following contamination of a system
For hydraulic components, we were able to identify areas of damage and wear which were attributed to contaminants in the system. Documented failure reports also showed repeat failures whereby an initial failure took place, only for the newly installed component to fail within a short period as well.
Discussing the necessary cleaning steps for excavator hydraulic systems really opened my eyes to the level of action needed to be taken to ensure the integrity of the fluid and system following a contamination failure. These steps included: pulling hoses, pigging those hoses and any steel tubing, dropping the oil, and getting inside tanks to clean them thoroughly – all which take a very long time to complete!
In my experience, mine sites don’t typically go that degree of cleaning, which ultimately reduces the service life of your components.
Storage and preservation should always be a priority
As a mine site mechanical engineer, I often didn’t readily think about the need to preserve or properly store components that had failed or had been removed from service having reached the strategic hours etc. However, seeing the process within the rebuild workshop - if the proper covers, blanking plates etc. aren’t used when storing these on site before dispatch, environmental conditions can cause more damage that increases the cost of repair.
In particular, cylinder barrels that have not had ports covered leave questions as to the internal condition of the clevis end of the barrel, which is difficult to inspect regardless. Ensuring storage standards are maintained for used components being returned is important to consider to reduce the overall cost of repair.
How to measure properly
I used to think I knew how to use Vernier Calipers, micrometers, dial gauges in my novice home mechanical projects. How wrong was I – especially when dealing with critical measurements and the short tolerances they demand. The skilled tradies I worked with showed me the right way to measure by ‘feel’ instead of cranking the micrometer ratchet until it practically locked in place. It is a real skill to have.
A massive thank you to Bluefield and particularly Gerard for arranging this time in the CRC and for the truly special opportunity to swing spanners with some of the most skilled and knowledgeable tradespeople I have come across. I consider myself very lucky to have experienced what I did. It has made a lasting impression and a less-than-handy engineer very happy.