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RUNNING REPORT
MOVING UP A WEIGHT CATEGORY
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Eoghan Daly reports from the north-east of Scotland on the flagship excavator at Limehillock Quarries
second-generation family
Abusiness established in the north-east of Scotland in 1973, Limehillock Quarries runs a sizeable operation from its HQ at Spey Bay, Moray. Richard Murray spearheads the operation, which includes seven active quarries and gravel deposits, together with demolition work and, through other firms in the group, a wide range of associated activities.
They include LAS Plant Hire, which offers plant and tool hire, together with access platform and crane hire, from depots at Inverness and Spey Bay. In 2017, the long-established and well-respected haulage company Baillie Brothers became part of the Limehillock Group.
However, quarrying remains the core activity of the business, which produces a variety of materials from its various sites. They range from the production of common aggregates to more valuable deposits of magnesium and calcined limestone; they even operate a marble quarry. In addition to serving their own processing needs across these sites, contract crushing and screening continues to be a key activity for the firm.
BUYING DECISION
Very much a staunch JCB customer over the decades, as the British firm’s excavators and wheel loaders are in use across its various quarrying operations, Limehillock Quarries’ management
Below and inset: Weighing close to 45t, the Doosan DX420-7 took over primary loading duties on the Limehillock Quarries’ fl eet from a smaller JCB JS370 excavator.
team had a difficult decision to make last year. Their JCB JS370, with additional ballast, was working well loading a series of crushers and screeners at the face, but this application was at the top end of its performance envelope. A step up to the next excavator weight class was the obvious route to take, to get the best from their extensive fleet of tracked processing equipment.
The trouble was that such a 40-tonne-plus excavator was not available from JCB, and there was an on-going concern about the operating costs of running a larger machine, to say nothing of its purchase price. However, after much detailed consideration, it was decided to introduce a Doosan DX420-7 to the quarry fleet, which in standard spec weighs 43.5 tonnes.
Richard said, “Previously our largest excavator was a JS370 and, even though we did decide to increase the size of the machine, it was important not to increase too much, as a larger machine would have implications for transport. This is why the DX420 strikes the right balance of capacity and still remains in an ideal size class for movement between our quarries.
“We have been using JCB machines since 1975 and they have been really great for the company. Our JS370s have been excellent and we have had no issues with service. Since Doosan have been showing around the country, we decided they deserved a closer look. That led us to ask the question: would it be worthwhile to change to a machine that is more expensive than those we would have bought?
“Of course, this can only be answered over the longer term, but for us the machine looks right and is well built for quarry work. We also saw the commitment to service from
“EVEN THOUGH IT
HANDLES LIKE A MUCH Doosan dealer Balgownie as being a strong SMALLER SIZE argument in favour of the machine. This is MACHINE” the fourth machine I have bought from them, the others working on the plant hire side of the business.”
Its large working envelope and the stability to work at full reach, enables the DX420-7 to provide a fast, comfortable and effi cient way to load a mobile crusher.
SITE VISIT
The Doosan has been the flagship excavator at Limehillock Quarries for just over a year now, in the extremely capable hands of operator Gordon Souter, whose previous mount was the JS370. We met them on a contract crushing job, where the team were clearing a large site down to formation
DOOSAN DX420-7 DRIVELINE
Routine service items are easy to get to, with good access up top, over the AdBlue tank and then past the diesel refi ll point, to the engine compartment.
level, to enable the construction of a whisky storage facility.
Running on narrow 600mm quarry track shoes on a standard fixed undercarriage, the width of the DX420-7 is 3.35m. A wide load, but still more practical than moving a 50-tonne-plus machine about this rural upland region. In practice, the big Doosan is frequently relocated around the firm’s various quarries without any real issues.
This somewhat over-sized undercarriage, together with the standard eight-tonne counterweight, helps to provide a high level of operational stability when working at full reach. Configured with a 6.7m mono-boom and a 3.25m long dipper, the machine also carries a Geith quick-hitch.
When feeding a crusher, the excavator is equipped with a narrow but deep bucket, which minimises the possibility of in-feed blockages. A wider digging bucket is used when it is being used for excavating and handling material in the firm’s sand and gravel deposits. This DX420-7 also has a ripper tooth in its arsenal of attachments, together with auxiliary lines to run a high-capacity hydraulic breaker.
OPERATOR FEEDBACK
Perched on a pile of extracted rock at the warehouse development site, the DX420-7 was loading a Terex Finlay J1170 crusher, a combination that had already built up a considerable stockpile of processed material. With the ability of the big Doosan to work at full reach, there is a large volume of material within its grasp, resulting in fewer relocations of both excavator and crusher. Gordon was delivering smooth and surprisingly fast loading cycles, accumulating a full load every time, after the bucket effortlessly penetrated the pile of rock.
He said, “Even though it weighs almost 45 tonnes, its speed of operation enables it to work like a much smaller machine. It gives this level of speed without affecting breakout force, which is very impressive regardless of which bucket I’m using, and also when
Above: Operator Gordon Souter highly rates the fi rst Doosan excavator to enter the Limehillock Quarries fl eet, following over 40 years allegiance to JCB. Right: This excavator is equipped with a wide array of additional LED work lights, to help with full shifts in little daylight this far north during winter months.
This latest generation of Doosan excavator is powered by a six-cylinder, Stage 5 ultra-low emissions Scania engine. It is rated at 257kW at a modest engine speed of 1800rpm, which is much of the basis for the excavator’s decent fuel economy.
The engine drives a hydraulic system that provides an oil fl ow of 335 litres per minute from each of the two main pumps, all controlled by Doosan’s latest engine/hydraulic management system. It enables the operator to select between four work and four power modes, which can be further fi ne-tuned through the cab’s main control monitor.
From the perspective of daily checks and routine service points of this driveline, everything seems to fall easily to hand. Its operator particularly appreciates its refuelling system and the ease of access to the Ad-Blue tank.
The DX420-7 is fi tted with Doosan’s Connect telematics system, the resulting service history and operating data being easy to comprehend and use.
Below and inset: The fl eet of Limehillock Quarries is dominated by Terex Finlay mobile crushing equipment, together with JCB excavators and wheel loaders, plus Liebherr loaders.
I’m extracting rock with the ripper tooth.
“The Doosan cab is very well finished and gives a very high level of comfort, which makes it a pleasure to operate over the course of a full day. The heated air seat and working position is generally excellent, while the sense of space inside the cabin is also very welcome. The cab design provides good visibility too and a glance at the 360-degree camera system gives total awareness of everything that is going on around the machine.
“The Doosan is a first-class machine and I couldn’t find fault with anything in either its design or the way it performs. It has good digging power and is smooth to operate with a well laid-out cab and a high level of comfort. To be honest, there is nothing I would change about it.”
OTHER FLEET
The Doosan DX420-7 is part of the quarry’s production fl eet, which is dominated by JCB excavators and wheel loaders, but also features Liebherr wheel loaders. As a consequence of the number of quarry locations and the diversity of projects undertaken, when it comes to contract crushing and demolition, a number of low-loader combinations support these activities. Their fl agship HGV tractor unit is a Volvo FH16 750 Globetrotter XL with an 8x4 axle confi guration, ideal for heavy haulage duties. In addition to a four-axle Nooteboom low loader, the FH16 is also used with tipping trailers and step-frame units.
CONCLUSION
Over the last year or so, the Doosan has performed well across different applications and has settled well into the varied but challenging role, as Richard explained, “The DX420-7 is normally working at the head of a full train of crushers and screens and is the right size for this type of work. It wouldn’t be viable to run a larger machine in the 50-tonne class, as the greater investment involved is not in line with the application.
“The fuel efficiency has improved a lot on the machine as the months have passed and, in relation to its size class and the work it can do, it is efficient. It is a little thirsty on the Ad-Blue side though, and a filter kit to do a complete service is more expensive than we would have paid for our JCB excavators. That said, we are dedicated to using genuine filters and keeping the machine original, which can only help aftermarket value by having a fully traceable service history.
“We will be looking at all the running costs over the machine’s working life, and taking resale value into account, before we can say if buying a more expensive excavator has been a sensible long-term decision. But for now, we are very impressed by the early indications.
PROCESSING FLEET
Over the decades Limehillock Quarries has remained loyal to Terex Finlay crushers and screeners, which have been found to produce consistently high levels of output and overall reliability. Heavily reliant on mobile processing plant, Terex Finlay kit suits the operations at Limehillock Quarries particularly well. The fi rm runs a comprehensive fl eet of crushers and screeners, to enable a machine train to be formed to suit specifi c production requirements.
