Rodney Aggregates Whangaripo Quarry is located northeast of Warkworth. The site has been quarried on and off since the 1930s, and was revamped into a full-scale operation in 2006 in a JV partnership between Fulton Hogan and GBC Winstone. By ALAN TITCHALL.
THE QUARRY is a major aggregate supplier to the North Auckland and Rodney districts – producing from a very high quality greywacke deposit, and a wide selection of products spanning from quality asphalt and concrete aggregates through to base courses and bulk fill.
“This resource is the highest grade greywacke I have dealt with over my 23 years of quarrying,” says Steve Hancox, quarry manager, Rodney Aggregates.
Suffice to add, demand is increasing every year and the team is constantly looking for ways to improve and increase production.
The main crusher is a Jawmaster 1211 with a cone crusher and a vertical shaft impactor (VSI) crusher, which is the focus of this story, or as Steve puts it – a story of two parts.
“I have been involved in trialling different rotors in the past and although they achieved small gains in productivity, the change in grading had a negative impact on quality.
“We had an opportunity to trial a REMco rotor in our old VSI machine and we did it reasonably scientifically so that we could quantify any gains.
“Using the original rotor, we ran the plant in a steady state and then stopped it with the belts full. We took belt cuts of the infeed and outfeed to check the grading at the lab. We then installed the REMco rotor, which has five ports as opposed to three, and repeated the process.
“We normally ran the crusher at a full 200 amps, but the new rotor was only pulling around 160 at the same feed rate. We gradually increased the feeder speed to bring it back up to 200 amps.
“I did the belt cuts myself and I noticed, carrying the bags to the ute, that they were heavier as there was more product going through the machine, using the same amount of power.”
Suffice to say, the REMco rotor stayed in the machine.
The VSI had been the bottleneck of the plant’s operation, Steve explains. “The primary and secondary crushers would pause constantly throughout the day as the VSI wasn’t matched to their output.
“The result was ‘stop start’ production all day long resulting in a variable feed being supplied to the VSI. Our PAP7 grading bounced around all day going from fine to coarse.
“With the increase in production from the new rotor, the plant is now balanced and runs at a more consistent pace resulting in a more consistent product which shows in our QA testing.”
According to the quarry’s comparative figures, the new rotor has pushed up production considerably.
“It actually improved by 30 percent and, effectively, we got a plant upgrade without spending any capital. It was just an operational cost to replace a rotor that we had to do a couple of times a year anyway.”
Another bonus was how long the wear parts lasted and even the rotor itself, Steve adds.
“We used to pull the old rotors out every six months for a rebuild, the new one went for 14 months. So, the net result, was more production, better quality, and less down time.”
The second half of the story
Eventually, the quarry replaced its VSI crusher with a new one.
“This was driven by the maintenance time we had to spend on the old VSI, which required using heavy lifting gear to take the hopper and the top of the machine off just to change the distributor plate, which is just one bolt,” says Steve.
“This process took three guys three to four hours each time. We had procedures and permits for doing this task safely, and we were managing the risk.
“I knew you could get self-lifting VSIs so I first approached Jon McAllister from CMS to see if REMco could retrofit a lid lifter on our old machine.
“This process sort of snowballed and Jon ended up brokering a trade-in deal on a brand new REMco VSI crusher. It was an offer too good to pass up on.”
Logan Cann from BDC Engineering looked after the structural side of the project and planned the installation, which Steve says was challenging given the other structures that needed to be worked around.
“We not only expect to get longer life out of a bearing cartridge but being oil-filled means it is also capable of running at a higher rpm.”
Steve says the business case for a new machine was driven by safety aspects.
“Our justification for the capital spend was based solely on the safety aspects of this machine. Using engineering controls to eliminate risk.
“Daily inspections on the old machine involved hatches on the top for looking down into the machine with a torch and then you had to reach in to feel for wear underneath. Now we just push a button and the lid lifts up giving access to the entire rotor. The first distributor plate change we did took one person just half an hour.”
The quarry team are “stoked with their new VSI” and only have good things to say about it, he adds, and appreciate the lid lifter has made their jobs both easier and safer.
“I am not saying our project is a solution for all sites, but trialling something a bit different has definitely paid off for us.”
- Article commissioned by CMS
This article was first published in the April-May issue of Q&M.