Steel and concrete combined make durable, strong structures. But when it comes to demolishing such structures these two elements pose different challenges. In the past demolition contractors used dedicated crushers to handle the concrete and dedicated shears to cut the steel, or crushers that also had small rebar-cutting shears built into them.
Nowadays though, many manufacturers offer a single attachment that can do both jobs. Called by a variety of names – multi-processors, combi-cutters, demolition processors, universal processors – these hydraulically powered devices use interchangeable jaw sets to tackle just about any demolition application. Yet there is still room in the marketplace for the dedicated, single-purpose tools. And simpler, less expensive mechanical shears and crushers also continue to be bought by contractors who don’t need the speed and all-day productivity offered by the hydraulic tools.
As a general rule if a contractor is using an attachment to cut steel more than 50 percent of the time, he should probably go with a dedicated steel shear, says Uwe Kausch, Stanley LaBounty product line manager. If he’s processing concrete more than half the time, then the universal or multi-processor type attachment is usually best.
Shears: the heavy metal tool
Shears excel at cutting up metal such as I-beams, storage tanks, pipes and railroad cars as well as other materials such as tires and trees. Shears bring a lot of cutting force to the task, but they’re limited in what they can do beyond metal work. “Using a shear to crush concrete may have some limited benefit on a small job, but you lose the advantage of multiple sets of teeth the crusher uses for faster, more efficient product reduction,” says Kevin Loomis, hydraulic applications manager, Atlas Copco Construction Tools.
“The ideal way to process any material is to have the jaws entirely surround the material to be processed, and then have the tool power to shear or crush all of it.” says Michael Ramun, marketing representative for Allied Gator. “With today’s high labor costs, the most efficient contractors will use these tools on all of their carriers from their largest machines all the way down to their compact excavators and skid steers.”
And shears are designed to exert maximum force just as the jaws are about to close, which is what’s needed to cut steel, says Poul Rosengaard, sales and marketing consultant for Caterpillar. This is the opposite of what’s needed to crack concrete – jaws that exert maximum force when wide open.
Crushers and pulverizers: from walls to rubble
Crushers and pulverizers also turn large chunks of concrete into smaller sizes suitable for loading. Concrete crushers and pulverizers are configured with teeth across a large portion of their work surface. The teeth focus the crushing forces and aid in overall product size reduction. Compared to a shear the teeth in a crusher are abrasion resistant and also help prevent the jaw from slipping off the material, says Tim Atchley of Ingersoll-Rand.
Most crushers and pulverizers also have the ability to cut small-diameter steel with a pair of shearing blades in the throat of the tool. These cutters usually will not accept large beams or angle iron, but are instead used to snip rebar or mesh materials found in reinforced concrete.
Multi-processors: the jack of all tools
“With a multi-processor and a couple of jaws, you can do almost everything that needs to be done on a demolition site,” Rosengaard says. “And obviously it’s a lot cheaper to replace a jaw on a multi-processor than it is to buy a completely dedicated concrete cutter or crusher.”
With a multiprocessor, the rotating unit and the hydraulic cylinders remain fixed to the carrier and the contractor swaps out various jaw sets to attack the full range of demolition applications from shearing to concrete cracking to pulverizing.
Multi-processors now dominate the market compared to dedicated tools, says Rosengaard. When cutting steel you need a larger multi-processor than you would a dedicated shear, he says, but the multi-processors still do a good job and are widely used to cut steel.
Mechanical vs. hydraulic tools
Mechanical shears and crushers use the carrier machine’s bucket cylinder to provide the force to do the job. A mechanical crusher or shear won’t generate as much crushing force as hydraulically powered jaws, and not having a regeneration circuit means cycle times are slower.
“Hydraulic pulverizers will outperform mechanical ones by about three to one, says Russell Walton, regional manager and product manager for demolition tools at BTI. Rosengaard adds that the mechanical tool’s lack of rotation means it is possible to damage it or the stick or boom of the carrier machine if you try to twist or pry the concrete to break it.
Yet manufacturers still make the mechanical versions. They’re lighter, less expensive and don’t require as much hydraulic plumbing on the carrier machine. So for light-duty or occasional work, the lower-cost mechanical shears and crushers may give you the best return on your investment, says Chuck Bellew, general manager for Construction Attachments. Kausch also sees a profitable role for the wide-jawed mechanical concrete pulverizers, when they’re used to reduce concrete rubble from demolition sites.
Rotation and the angle of attack
Most manufacturers offer shears, crushers and multi-processing tools with or without 360-degree continuous rotation. But Rosengaard estimates the rotation ability boosts productivity by at least 25 percent.
A rotating tool also has crossover relief ports, Walton says. So when the jaws close down over the material, they will rotate rather than twist the boom or the stick of the carrier machine. About the only concern contractors have with rotation is the possibility of damaging the rotation mechanism – an expensive component.
And being able to take a bite from any angle means more precise work and less repositioning of the carrier machine and material, Atchley says.
Measure the job before the machine
Your primary consideration in choosing a unit will be the material you want to cut, Atchley says. Manufacturers state the crushing force of their tools, but this is not usually a good metric to use in comparison shopping, says Ramun. There are no industry standards for this and different designs achieve maximum power at different times. The best way to compare units is to carefully review both the crushing force and the literature or charts that specify the size and type of material that can be cut or crushed as well as the tons of force achieved. Keep in mind there are different densities in concrete and steel, and as your cutting teeth wear they will become slightly less efficient.
Two other considerations are the weight of the attachment and the hydraulic capacity of the carrier machine. Rather than mount large tools in place of an excavator bucket (commonly called a third member attachment) the bigger units are sometimes mounted in place of the stick or “second member” to enable the machine to carry an attachment that would otherwise be too heavy. The trade off with second member attachment is that you gain power with the bigger attachment but lose the reach the excavator stick offers.
Most demolition tools will require a bi-directional hydraulic circuit (for opening and closing jaws) capable of pressures exceeding 4,000 psi, Loomis says. A typical add-on hydraulic kit designed for a breaker or a compactor will only flow oil in one direction, will not support pressure much over 3,000 psi and will not work with most shears or crushers, he says.
If you’re not sure of your carrier machine’s capability, Loomis says you can form an educated guess about your hydraulic attachment circuit by checking these items:
· If it’s bi-directional you will have an activating pedal or lever in the cab that has two ranges of motion with a neutral position between them. A single electric foot pedal in the cab will usually indicate flow in one direction only.
· Inspect the markings on the hoses that connect auxiliary tubes to the carrier. If the stated hose pressure is below 5,000 psi, then the kit is probably not going to work with a shear or crusher without modification.
Finally, both hoses need to be originating from a common valve section on the carrier’s main control valve. If one of the lines is connected to the hydraulic reservoir, you probably do not have a bi-directional hydraulic circuit.