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pretty sound advice here, as usual. I may be able to add something regarding the metallising inquiry. For restoring lost dimension to press fits, seal areas, or damaged shafts,..... the least amount of heat input is what is desirable. The low temp coatings will vary somewhat (150�F to 450�F) from one type of equipment and process to another. The most expensive (twin wire arc)sprays the coldest. Whether you use a two step powder, an exothermic powder, flame sprayed wire, or arc sprayed wire..... the bond will be mechanical and the bond strength will vary between processes. Todays equipment and consumables are capable of yielding bond strengths that are quite high. I often demonstrate this by pounding the daylights out of our freshly sprayed sample. The bond created by these various processes creates the bond in much the same way as soldering processes create a bond. The 'new rub' is what is truly referred to as cold spray wherein kinetic energy creates the bond w/o heat being applied to the powder or the substrate. In the old days, when gravity fed torches where the rage, spray rates where very slow, part temps naturally were much higher, and bond strength was considerably lower. These torches are still available for sale to the price concious. Those torches earned a bad reputation that still lingers in the minds of those who have not kept up with the technological advancements. A good supplier will have quality powders for the $16.00 to $23.00 per pound range. Wire can range from $4.00 to $23.00 per pound based on chemistry. The hot process or spray and fuse torch is sometimes easily confused with the other processes. That torch will create a metallurgical bond and the welding powder actually bears a tensile strength rating. (A weld rather than simply a coating is realized.) Part temps will reach 1600�F to 1800�F and may sometimes be as high as 2400�F in certain instances. Using the proper techniques, these high temp torches can be used to repair damaged keyways and for shaft build-up. Powders will range from around $21.00# to 32.00# typically. High volume users will obtain some of those same powders for as little as $10.00# to $15.00#. I would enjoy fielding questions pertaining to these processes either on this forum or privately. This is a field that I personally find to be quite exciting. It is the fastest growing segment of the welding industry right now and many of these methods are approved repairs by many of the major manufacturers such as Caterpillar, Boeing, Rolls Royce, and even the U.S. military. Many of these applications are for O.E.M. specs on new parts to enhance the performance of a certain material. It is, afterall, an endeavor in surface engineering.
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