One of the first of the two new generation twin-engine Wirtgen W210 milling machines, bought by the UK specialist road planing contractor Power Plane Ltd, has made substantial time and cost savings on a round the clock runway resurfacing project at Cambridge Airport. The new W210 completed the job under budget and 30% ahead of programme, while saving 25% on fuel and over 30% of the contract value on the absence of backup plant, which is normally required on high profile, non-stop runway and motorway restoration projects.
Despite the W210 being about 25% more expensive than an equivalent size single engine milling machine, Power Plane also forecasts the company will save about half the capital value of the new machine in owning and operating costs over its four-year life. The W210 is a huge leap forward in milling machine technology and incorporates numerous new beneficial features not found on any other competitive manufacturers’ milling machines. As a bonus for Power Plane, the W210 is also far friendlier to the environment. It has a much lower carbon footprint than a less productive standard single engine milling machine as it can operate on just one of its two engines.
Power Plane, working for main runway repair contractor Colas, used its Wirtgen W210, fitted with an optional fine milling cutter drum, to remove about 90,000m2 of slurry seal from the surface of the 2km long, 45m wide pavement quality concrete runway. The slurry seal was between 3mm and 6mm thick down the central band of the runway, increasing to a double thickness of 12mm along the edges. The airport is operated by Marshall Aerospace and its design consultant, Capita Symonds, was concerned that the grooved finish, produced by conventional planing, would not allow the new slurry seal coating to properly key to the planed surface and would wear too quickly.
Conventional planing with a normal milling cutter drum generally produces a rough finish of 5.5mm deep grooves at 15mm spacing. But the consultant required a much better and smoother finish for the new slurry seal to bond too. Power Plane proposed using its new W210 fitted with the special and optional Wirtgen fine milling drum, the only one of its type in the UK. The Wirtgen LA6x2 fine milling drum has a quadruple helix with a total of 672 picks. This compares with 274 picks with a single helix, 8mm groove spacing drum and 168 picks on a 15mm spacing drum. It produces a surface with shallower grooves or ridges of only 1mm deep, spaced at 6mm and leaves a much finer finish to accept the new slurry seal. The twin cutting tool per line design enables the planer to move at a much faster forward cutting speed than a normal drum, while producing a much smoother finished surface. It also cuts any protruding aggregate softly, compared with a drum with fewer picks, which can catch the aggregate and flick it out of the surrounding material.
The fine milling drum is part of what Wirtgen calls its Flexible Cutter System. This allows the same width drums, but with different tool or pick spacing, to be changed comparatively quickly, so improving the utilisation and flexibility of the W210. "The FCS allows us to change the cutter drum in just two hours, compared to a minimum of eight hours on a conventional planer," says Power Plane managing director Ian Chattington. "We also have an optional Wirtgen ECO cutter drum on our other W210 with 18mm pick spacing for faster and deeper milling down to a maximum depth of 320mm."
Power Plane's proposal to use its Wirtgen W210 with 2m wide fine milling drum was accepted and the company started in the early evening of Wednesday 2 June on its non-stop contract to remove the old runway slurry seal. Power Plane, based at Wolvey, Leicestershire, had two teams working with the Wirtgen W210 on 12 hour shifts and had finished the non-stop work within six shifts by about midday on Saturday 5 June. This was nearly 30 hours ahead of programme at an average of about 1,400m2/h, including five changes of picks.
Colas, which was given a full nine and a half day possession closure of the runway, followed on behind Power Plane assessing the condition of the exposed concrete runway and identifying and correcting any defects in the pavement and joints. On completion of all the repairs Colas covered the entire runway with a new 3mm thick coating of slurry seal to the new Defence Estates 045 Specification (2010). "The finish provided by the fine milling drum allowed for a smooth uniform layer of slurry to be applied to the planed surface. Through experience, a normal milling drum leaves small 3-5mm ridges, which would have been visible through the slurry," says Colas airfield manager Simon Downing, who returned the runway back to Marshall Aerospace 14 hours ahead of programme on the afternoon of Friday 11 June.
In addition to major time savings the W210's revolutionary twin-engine design has also contributed to significant fuel savings on the Cambridge Airport contract. "We have achieved about a 25% fuel saving over a standard equivalent size machine," says Ian Chattington. "A conventional single engine planer would normally use between 500-750 litres/shift, but we have saved around 150-190 litres/shift on this job, which equates to an average fuel cost saving of around £100/shift."
This saving is possible as one of the two inter-connecting engines automatically shuts down in situations when the engine load and performance requirements are low or when the machine is idling or loading for transport. The operator can also manually control the use of the second engine, but when they are both automatically and digitally synchronised the combined power of 500kW is available for the most arduous milling tasks. Adjusting the milling drum speed on the operator’s platform, to suit conditions, also contributes towards fuel savings. Wirtgen is currently the only cold milling machine manufacturer to provide this twin engine facility.
The dual engine concept in the W210 has also provided Power Plane with the confidence not to have backup equipment on standby on this and similar high profile runway and motorway projects, as the planer can operate efficiently with just one engine. "Normally on high profile possession type jobs we would have a crane or hydraulic power pack to remove the milling machine in an emergency, or have a standby planer. In theory we have saved 50% on the cost of backup plant and transport on this job as we didn’t need a planer, fitter and low loader on standby for every shift," says Ian Chattington.
The W210 has also shown to be easy, quieter and cleaner to use and is due to a combination of novel features on Power Plane's two machines, including a computer controlled intelligent machine management system. This is called WIDRIVE, which links all the machine's major functions to the operation of the two engines. These include travel, milling drum and discharge conveyor drives and drum water spray, fully floating axle, automatic milling depth and level sensing systems.
The machine's unique Wirtgen levelling system called LEVEL PRO, together with the multiplex sensor arrangement, combined to create a very even, high quality surface and perfect for the new coating of slurry seal. The milling depth and levelling system, uses numerous sensors to automatically monitor and control milling depth. All the relevant parameters are displayed on the LEVEL PRO display, which can be mounted on the operator's main high level control panel or with remote cables on the side of the machine, as is the case with Power Plane's W210. "We can walk alongside the planer and clearly see the milling operation and can quickly make any necessary corrections and adjustments on the touch screen panels, which we have on both sides of the machine," says Power Plane dayshift foreman Carl Taylor. "We also have a parallel tracking system, which keeps the planer parallel and level with the surface. All four tracks are hydraulically linked and if one of them climbs over a hump or drops into a dip, the others compensate to maintain level."
Power Plane's team also says that the W210 is also cleaner than previous models, which is due to its novel VCS vacuum cutting system. "There is no dust with this machine so it's much better and easier for us to work with. The machine is also kept cleaner, making it easier to work on," says Carl Taylor. A pair of spray bars in the cutting drum chamber constantly sprays a water mist onto the pulverised material to cool down the cutting tools. The drum's climbing cutter action throws the excavated material onto the machine's short conveyor prior to transfer onto the main and longer discharge conveyor. At the same time a vacuum or negative pressure in the drum chamber allows the extraction of the water vapour and fine particles of material into a suction hood for transport through hoses. It bypasses the short conveyor and is discharged back into the main stream of material on the main long conveyor for loading into wagons in the normal way. "The VCS has considerably reduced dust and improved the working environment for the operators," says Ian Chattington. "We have VCS on both of our W210s as it keeps them cleaner and contributes towards savings on wear parts."
Power Plane first tested a twin engine W210 in January 2010 alongside one of its own similar sized single engine planers. The trials proved so successful that after just four weeks of comparative testing the company decided to buy two of the latest W210s. "In my view the Wirtgen W210 is a great leap forward in planing technology. Currently there is no other manufacturer of planing equipment in the world that has anything to match it," says Ian Chattington. "We have invested in Wirtgen and its expertise and have access to their vast experience and knowledge base. We believe they offer the best equipment and back up, which will allow us to stay at the forefront of the UK planing market and provide the best service for our customers."