Once I was speaking to a friend who had operated both portable and tracked systems in his operation. Based on his experience, he had some pretty strong opinions about his preference. But in all fairness, his operation did not favour using a tracked system. Did it crush and screen his material? Sure. But it wasn’t the best tool for his application.
Another friend of mine uses a portable system to recycle concrete but a tracked screen to scalp out the dirt before he accepts and crushes the material, to save wear in his jaw and increase the cleanliness and value of his end product. He uses the tracked machine as a tool. Smart.
So what are the major benefits of each type of system? On the surface, the arguments for each are pretty straightforward.
Easily the biggest benefit of tracked plants is they provide captive power sources, which enable the equipment to be deployed to remote locations where line power simply isn’t available, and to be easily relocated within the job site. Such plants can also be set up and operating in minutes – versus hours or even days – capturing precious and valuable time and lost production.
If the engines are used as a direct drive to large horsepower crushers (such as a cone crusher), they also eliminate the need to toil with the large, cumbersome electrical cables that must be connected to the electric motor(s). Such plants are generally also safer to set up.
Having each plant equipped with individual power units also gives the added flexibility to separate or split the system and only turn on the engines required for a specific job, which can help offset liquid fuel costs. For example, if you only need to produce 40mm base material, you will likely be burning fewer engines and less fuel than if you are producing 20mm asphalt rock.
Historically, with most tracked systems, diesel engines are coupled with hydraulic motors and control valves. This simple circuit eliminates mobile cone crusher stations, expensive starters, cables and connectors, etc.
Then there is the service aspect. Chances are the same mechanic that services your loader can also service the engine on your tracked crusher or screen. Also, compared with electrical systems, hydraulic systems do not require a rocket scientist – or at least a journeyman – to maintain them.
However, let’s not assume too much. Wheeled portable plants provide clear advantages too.
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WHEELED MOBILES
Electric motors commonly found on wheeled portable plants are more efficient than their hydraulic counterparts, and they tend to be more reliable regardless of climate. Historically, electrical wheeled plants have provided more uptime than diesel tracked plants.
Electrical plants provide more space and weight to equip larger and more productive crushers and screens because they are not penalised by the tracked assemblies, engine and engine comportment, etc. Higher production equates to lower tonnes/man-hours.
Depending on where you are, engine emission permits and trying to stay compliant with constantly changing tier ratings can mean electrical power provides an advantage. If a larger single or dual generator to power electric motors is the desired configuration in a portable system, this will still prove an easier challenge than trying to permit multiple diesel engines in many areas.
From a service standpoint, while a skilled journeyman is required to maintain the electrical system, such systems will not incur downtime stemming from a dusted engine due to a neglected
air filter, a bypassed oil filter or a blown hydraulic hose.
Do you remember when, at the turn of the century, the aggregates industry started heavily marketing self-contained wheeled systems? While many producers jumped on this bandwagon to reap the same benefits the tracked systems provided – such as a more nimble operation, the ability to be more flexible, etc – several producers I was involved with on large self-contained systems have long been pushing us (the suppliers) to develop similar solutions that provided the same conveniences without the baggage of the engines.
I have even witnessed a few retrofitted plants, replacing engines with electric motors.
The reality today is that, around the world, unstable liquid fuel costs and geopolitical issues alone are shifting market demand towards increased development of electric-driven, “self-contained” portable systems. Even simple tracked machines that were previously diesel-hydraulic configurations are now supplied with standard or optional electric power configurations.
Such plants, when equipped with on-board generators, electric motors, etc, obviously come at a price premium. The idea is to “track” the machine into position and then drive on-plant electric motors.
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HYBRID CONFIGURATIONS
So does this mean electrical systems are always the best choice? No. In my opinion, the simplicity of a diesel-hydraulic configuration cannot be overlooked in many scenarios. When one does the maths and considers all the variables, diesel plants will usually provide benefits when they are used as mobile crushers on demolition sites or to screen piles of recycled materials, rented on a month-to-month basis out of dealer rental fleets and used by inexperienced operators, used to process material in remote locations or even as complete systems that must be relocated 10 to 15 times per year and broken into multiple configurations.
Tracked machines and portable plant are both great tools but both were designed to appeal to a specific market segment. There is some application overlap but generally speaking, with a little soul searching and number crunching, the right decision on which system to use in your operation will become clear.
Paul Smith is the international marketing manager for the Astec Aggregate & Mining Group.