Look behind the scenes
According to the German automobile club ADAC, there were 538 roadworks on German motorways in September 2018, causing traffic jams and delays. But not all road closures have to take long: A Dutch company has developed a technology for quickly clearing roads for traffic after repairing minor surface damage. A special fast-curing, resin-based repair asphalt is mixed in a special vehicle directly on site and applied to the surface. The great advantage of this method is that the surface is ready for traffic again in less than an hour.
“To get the special mortar ready for use, the cold asphalt mixture is stored in a tank with an agitator and pumped through the mixer, in a special vehicle directly on site,” explains Max Waser, Engineer Internal Sales at NETZSCH Pompen Nederland. “The same vehicle then spreads gravel from a reservoir over the cold asphalt.” Until April 2018, a rotary lobe pump was used for the first step of pumping the mixture of resin, sand and silver sand. The pump had to be operated at speeds of around 250 to 300 rpm and suffered high levels of wear due to the highly abrasive medium. “This especially affected the elastomer lobes – in the end the company for the application of road surface coatings had to replace them every two to three weeks, so the vehicle was often out of operation,” explains Waser.
Those responsible therefore decided for this application to replace the previous rotary lobe pump with a more suitable progressing cavity pump with lower pulsation and less wear. A NEMO® progressing cavity pump of type SY from NETZSCH was selected: Due to its displacement principle allowing smooth pumping with low shearing and pulsation, this pump type is ideal for use on the specialized repair vehicle to convey the cold asphalt which has a temperature of 20°C and a viscosity of 7,000 to 10,000 mPas. “We selected the largest possible pump model for our customer which makes optimum use of the space on the vehicle and also ensures low rotation,” explains Waser. “This allowed us to achieve values of around 50 to 75 rotations per minute, meaning particularly slow and precise pumping.” However, the capacity of the pump was doubled to 1 m³/h at this speed.
he NEMO® progressing cavity pump from NETZSCH has now been used by the Dutch specialists since April 2018. With a pressure of 5 bar, it pumps 1 m³ of the abrasive resin/sand/silver sand mixture per hour. Thanks to the stainless steel components and the EPDM elastomer components, the pump has been running without problems so far. That it works without malfunctions in contrast to the previous model has not only positive effect on the operating hours of the machine, but also to the curing time of the repair asphalt: “If the components of the medium are mixed well continuously, which is supported by the coupling rod with mixing elements, the mortar now needs less time to fully cure. So the road can be cleared for traffic even sooner,” explains engineer Max Waser.