Getting past the rebar
Shuffle conveyor system eliminates downtime for C&D recycler
One of the more recent services offered by Robert J. Spence Construction, based out of London, Ontario, is concrete demolition. Pete Spence, owner and president of the company which was founded by his father in 1958, says demand has become increasingly popular from companies, farmers and private individuals who are getting rid of larger and larger amounts of crumbling infrastructure waste, as well as those tidying up property.
Prior to 2012, Spence purchased a 4043 T crusher from Ohio-based Screen Machine Industries to handle concrete with rebar in it, and separate metal from the concrete after it was crushed, using an overhead magnetic belt conveyor. Using the 4043 T, concrete exits a high stacking conveyor while rebar goes out the side into a bin.
According to Paul Tamlin of Mayfran International, an Ohio-based company specializing in the manufacture and supply of engineered solutions for scrap and coolant management and material handling, one of the challenges of crushing concrete with rebar and steel in it is simply that it is very hard on equipment.
For Spence, concrete chunks were being pre-broken by an excavator mounted pulverizer with a 36-inch Moley Magnetics magnet, to get the majority of rebar out. But a lot of rebar was still going through the 4043 T crusher, which was presenting a challenge. Every once in a while, a piece of rebar or steel would become stuck in the rubber conveyor belt which removes material from under the crusher.
Generally, when this happens, it will likely cause damage to the belt, to the point where, if continued, it will eventually require a shut down and possible replacement. In the case of such downtime, there will typically be support equipment, which now has no machine to feed and may be forced to shut down as well.
For Spence Construction, each downtime event to replace their belt was costing about $14,000 in combined machine time, belt cost and the labour to do the job. After several instances of downtime, and after going through four belts in the first 800 hours of operation, Spence thought there had to be a better way. This led him to Paul Tamlin at Mayfran International.
THE SHUFFLE CONVEYOR SYSTEM
One of the products Tamlin introduced to Spence was Mayfran’s patented shuffle conveyor, a system Spence had already heard about from a friend who owns a metal stamping plant. In the metal stamping facility application, the shuffle conveyor is situated in a pit, seven feet deep and six feet wide under a row of stamping presses used to stamp out parts for the automotive market. All the scrap steel from the stamping presses falls below the floor and lands on the shuffle conveyor, which then conveys it out of the plant and loads it into lugger bins via a Mayfran steel hingebelt conveyor system.
The thing that most impressed Spence about the shuffle conveyor initially was that there was no place for scrap to get caught.
“The conveying surface is a steel tray which moves back and forth in a linear motion causing material to move forward,” explains Tamlin. “The tray accelerates forward and then decelerates quickly, causing material to move forward. The return stroke of the tray is just the opposite as it accelerates quickly in the return motion and decelerates slowly, which again causes material to move forward.
“A lot of people confuse this with a vibratory conveyor, which it is not,” says Tamlin. “The heartbeat of our shuffle conveyor systems is a patented shuffle drive gearbox which creates this motion, and systems are designed to convey horizontally or even up a slight incline.”
Tamlin says the linear motion of the tray also helps to scour or clean the tray as material is sliding on its surface, rather than jumping along as with some vibratory conveyors.
After being contacted by Spence Construction, Tamlin visited the company to review his application and to see if his was a suitable job for Mayfran to take on with the shuffle conveyor.
“Mayfran’s expertise in engineered conveyor solutions for customers came into play in this particular application, as Spence wanted to be able to keep the original belt conveyor system operational but have the conveyor belt protected by the impact of the steel rebar coming through the crusher,” explains Tamlin.
“The solution was to put in a short shuffle conveyor, about 8 feet long – made from AR plate in the machine – over the conveyor belt. This would extend under the crusher rotor so as to accept all material coming through the crusher and then convey it onto the conveyor belt in a manner as not to damage the belt. Spence’s material typically is a mix of concrete, stone, rebar or even clay.”
Once a concept was created and agreed upon between Spence Construction and Mayfran International, the final design parameters were determined. The system needed the capacity to handle a maximum of 350 tons per hour, and would need to run via hydraulic motor provided by the existing hydraulic flow and pressure of the crushing machine. Plus, it had to fit over the existing conveyor belt.
In order to ensure material throughput it was decided the tray would be tilted down on an angle towards the conveyor belt. This would improve material speed and direct material if it bounced forward, under the crusher onto the belt. The tray is also supported on torsion style struts, which means there is no metal to metal contact on the suspension system, thus reducing wear and maintenance.
In order to get detailed dimensions, a site visit was done to create a 3D model of the working envelope and the structure of the machine.
“This allowed us to go back to the office and complete the design so as to be able to review it thoroughly with Spence construction before metal was ever cut or the machine taken out of service for the installation,” said Tamlin.
When design and manufacturing were finished, the installation was completed in partnership between Spence Construction and Mayfran. Greg Johnson of Mayfran International designed the system for manufacturing and also helped to install the system to ensure it was done according to his original design intent.
The system has now been operational since the spring of 2014. During its first “crushing season,” Spence’s system was monitored to see where it could be improved. One improvement made was to install a scraper bar that travels back and forth across the tray while the system is in operation, which keeps the tray free of clay and improves material flow. A camera was also installed under the crusher, over the conveyor, allowing operators to see the conveyor in action, including any sparks and steel coming through the crusher and bouncing off the tray.
Since the shuffle conveyor has been installed, Spence Construction feels they have an advantage over competitors when it comes to crushing. He now has more uptime and more jobs, which means a better bottom line.
A final impact to the bottom line is this. Machines only make money when they are operating. According to Tamlin, after more than 2,000 hours, the belt which was worn at the time the shuffle conveyor was installed has not been replaced in Spence’s 4043 T crushing plant since.