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Ancel,
That makes sense. I am beginning to see why the laser printers I have looked at use heaters inside the rollers.
Harvey
Harvey asked :
>>I am not sure I understand why slowing the rollers causes them to pick up more heat energy. In my laminator (Harbor Freight) there are two heaters, placed on opposite sides fo the rollers. The heaters are attached to aluminum structures that enclose the roller assembly all around, except for the slots for the paper path.<<
During development of the Apache PCB mod, I effectively slowed the rollers to a net zero movement.
Before long the rollers' area closest to the heaters started to smoke a lot.
When I powered down cooled and dismantled the rollers they had developed a white powdery surface which shed when wiped. After cleaning this sediment the rollers had become oval shaped and frangible.
I swapped them out with the 'cold rollers' (quad roller laminator) and wrapped them in kapton tape to keep them serviceable.
In summary; the reflected heat from the metal enclosure is not as much as the direct radiant heat from the heater coils and (with an almost parked roller) this creates a temperature on the roller surface than can exceed the roller's spec, if the roller does not rotate away from the heater and cool off.
Because the temp sensor is on the exposed side of the roller away from the heaters, it depends on the hot side of the roller rotating into contact with it, if this doesn't happen fast enough, the temp sensor sees a temp well below the hottest part of the rollers and does NOT shut off the heater, resulting in overheating.