If discoloration is on all surfaces of all parts, check vacuum pressure to be sure it is in the proper range. If discoloration is dark black, has the chamber or carriage recently been stripped with caustic? A failure to properly rinse and dry after caustic cleaning often results in a chamber full of black parts. If discoloration is randomly distributed about the chamber, check these possibilities. The chamber and fixtures may need to be stripped clean. Vacuum levels may be higher than is normal (lower pressure). This can draw volatiles from chambers walls, carriages, and parts which may not outgas at higher pressures. These volatiles react with the depositing aluminum and cause it to discolor. Has the basecoat been properly cured? Undercured basecoats are often a cause of discoloration. Oven temperatures and bake times should be closely monitored. Also, check that the coating has not been applied more heavily than is usual. If so, it may have failed to cure adequately. If the burned part seems to consistently occur in one area of the chamber, check the filaments near that area. Are they properly connected? Do they burn brighter or more dimly than others in the chamber? Many burned parts are the result of poor current distribution throughout the chamber. Filaments should light as evenly as possible across the carriage. Here is the reason. If some filaments burn more brightly than others, it will be difficult or impossible to determine the proper firing point which should be used. If one uses the brightest filaments as a determiner, then filaments which are not getting as hot will not fire off all of their evaporant or might drip evaporant off the filament onto parts. Chances are that the coating will be inadequate and the filaments which are lighting improperly will have a diminished life. If the decision is made to use the dimmer filaments as a guideline, by the time they have gotten hot enough, long enough for them to evaporate their charge, the hotter filaments will have already fired and will have been pouring excess heat into the chamber, probably resulting in burned parts. As you can see, even the lighting of filaments is a prerequisite for good coatings. Also, if a filament burns out during a firing cycle, it will sometimes cause a dark area. If the burn always appears on the same area of the part, check the fixturing. Does the burned area pass close to the filaments at any point during the rotation? As a rule, parts should never pass closer than six inches from the filaments.
The Spanish film "Intacto," like the recent Sundance entry "The Cooler," believes that luck is a commodity that can be given and received, won or lost, or traded away. Most people have ordinary luck, some have unusually good or bad luck, and then there is a character like Tomas (Leonardo Sbaraglia), who is the only survivor of an airplane crash, beating the odds of 237 million to 1. (I am not the statistician here, only the reporter.) The movie involves a man named Sam (Max von Sydow), who survived the Holocaust and now operates a remote casino at which rich people bet against his luck, usually unsuccessfully. So unshakable is his confidence that he will remove one bullet from a chamber holding six and then bet that he will not die. That he is alive to be a character in the movie speaks for itself. 2b1af7f3a8