During the Liberation War of the 1970s, hundreds of kilometres of minefields were laid in Zimbabwe along its borders with Zambia and Mozambique. Although the war occurred decades ago, its impact is still being felt today – Zimbabwe is one of the most highly mine-impacted countries in the world, with more than 1,550 people estimated to have lost their lives or been injured by mines since the war, and more than 120,000 cattle accidents across the whole frontage since 1980.
The plastic M14 AP mines, which are 40mm tall, 56mm in diameter and extremely difficult to detect, run close to houses, schools and agricultural land, and work to clear these minefields is often undertaken via teams of people on their hands and knees (pictured above).
An unlikely partnership was formed more than five years ago between The HALO Trust, a Scottish-based charity that has been demining in Zimbabwe since 2013, and Mining Machinery Developments (MMD), which designs and manufactures material processing equipment for the mining industry. This partnership saw MMD design and fabricate a donated mobile demining sizer rig to the charity, Hazardous Area Life-support Organisation, at the Hillhead show in Derbyshire, UK, earlier this year.
In action
The rig, 14.3m long, 4m high, and weighing approximately 29,000 kg, is made up of a hopper, belt feeder, metal detector, two sizers (crushers) and a discharge conveyor. Material, such as earth and anti-personnel mines, is deposited into the hopper and transported up along the belt feeder. The material is then crushed down to approximately 45-50mm diameter by the first sizer and then further reduced to 25-30mm diameter by the secondary sizer, before being transported along the discharge conveyor. The sizers (pictured below) incorporate shock protection, preventing the equipment from sustaining damage from exploding mines or ordnance left behind after the conflict.
Mark Vickers, mobile equipment designer at MMD Design and Consultancy, explains: “The sizers both work at the same time, so you have a primary sizer and secondary sizer. The top, primary, sizer receives the raw material and reduces it down into a smaller size, and then we take it into the secondary unit, where it is processed again to ensure that 100% of the anti-personnel mines have been crushed or destroyed.”
The sizers, which both run at 90rpm, work by subjecting material to stress, bending, tension and shear forces. They are designed to handle wet and sticky material, as well as hard rock and organic material. The conveyor, meanwhile, has a throughput rate of 80tph. Andy Withers, director at MMD Mineral Sizing Europe, says that because the rig is destined for Zimbabwe, it is primed to deal with “very small anti-personnel mines” that aim to maim and injure, as opposed to large mines that are intended to kill and destroy. This is where the integrated metal detector plays its part to halt the operation if large explosive ordinance is detected.
Vickers continues: “We are not looking to size any large anti-tank mines or large pieces of metal. So, when the metal detector spots a large lump of metal, it immediately stops the feeder. Alarms on the rig and via a remote control notify somebody that there has been metal detected.”
When it comes to personnel, a shift team would include a minimum of six, including a supervisor, sizer operator, two plant operators and two deminers. The HALO Trust was clear during the design process that it didn’t want anyone within 50m when operating (unlike the artist’s impression pictured above). The design team at MMD therefore developed a remote control, which has a TV screen built in, so that operators can monitor the rig from a safe distance. If the metal detector goes off, operators can use the CCTV system to inspect the belt feeder.
“At that point, they can either discharge the material by reversing the feeder, requiring specialist manual disposal, or they can say, ‘no, it’s a false alarm’, and start the feeder up again. The whole point of the screen is to carry out a visual investigation before they make a decision on whether to approach the rig,” adds Vickers.
Key components
ABB provided two 37 kW four-pole, flange-mounted motors to drive the sizers, which can withstand up to 5g of force, and a variable speed drive to regulate the speed of the conveyor that feeds material into the rig (https://is.gd/iwucol). Westbury Controls helped to develop, engineer and build a control system for the rig (https://is.gd/ovomur), alongside contributions from Siemens and Conveyor Units.
Once the testing, design and development stages were completed, manufacturing, fabrication and build took place at MMD’s site in Derbyshire. Withers says MMD has invested an enormous amount of engineering expertise to customise the ‘350 Series’ sizers, which were “designed purely and simply for this project”. In particular, the sizer’s tooth profile and shafts were specifically created to ensure that no mines could pass through the rig without being destroyed.
“It’s a completely new avenue for us – the project was born out of a simple phone call from The HALO Trust, to see whether our sizers could help where their impact crushers were failing,” Withers explains. “However, we have also now sold the 350 machines into normal mining production systems, but the main development was for this project.”
MMD has designed the rig so that it can be hitched up to a tractor unit and towed along “clear paths” in the minefields. When the time came to test the rig, Collins Earthworks loaned its yard to MMD and supplied soil for the procedure. Vickers explains: “A lot of our core mining equipment is too large to do any research and development testing directly in the UK, so we do a lot of in-field testing.
“But we were quite fortunate: due to the mobility of the rig being road legal, we could have it transported and tested locally. The HALO Trust also brought some mocked-up land mines to push through the sizers to demonstrate the equipment’s effectiveness.”
The rig, powered by a diesel generator, is capable of carrying out a 24/7 operation, but the sites being worked on in Zimbabwe are often governed by daylight working hours. MMD expects to see the rig working in early 2019.
BOX OUT: Traditional methods
There have been a variety of methods used over the years to clear minefields around the world – from the traditional metal detector, hand removal, and mine rollers, to the use of rodents and robots.
Andy Withers, director at MMD Mineral Sizing Europe, explains that anti-personnel mines in Zimbabwe have “very little metal” in them, so using traditional methods such a metal detector often proves difficult.
“It is very risky, time consuming and labour-intensive. One individual I met in Zimbabwe had suffered a serious hand injury a few weeks prior, despite having years of experience. By using this rig, you withdraw all the people from the area. Up to now, with all the tests we have done on a prototype machine, we have had a 100% success rate, and we look forward to seeing HALO deliver this to the field.”