You are wise to be cautious. At least one screw application handling poultry litter for a power station was catastrophic. The first thing is to establish is where and why the wear is likely to occur. With screws it is more common to experience wear on the tips of the flights than the flight face, usually this is when the screws form and run on a static bed of material that may be hard and unyielding or have a tip clearance that will trap hard lumps. Thick, heavily constructed flights is the wrong approach, as this normally leads to higher power loss, excessive bending of the screw and more wear. The ‘Moving Hole’ discharger is an excellent method of discharging poor flow products from a holding bin, but will it deliver a steady, controlled stream of loose materials, or allow the material to fall away into the screw in ‘clumpy’ surges that may temporally flood the screw, even though the average loading is less than 30%? Wear is a power function of pressure and contact velocity, so a large screw with a short pitch, running slow and having a thin tip is usually a good start. Double runs of hard weld deposit on the flight tips provide excellent protection where this is a main concern. Face wear can also be virtually eliminated by welding radial runs of hard metal deposit on the flight faces to form surface ‘wear boxes’ that prevent product slip on the face. I have not used ‘Unideg’, so cannot comment on this, but ‘Belzona’ has given good results in the past. My choice would be to go with the weld deposit as it can be refurbished if necessary. ■