6. Are there any other options?
I personally like the idea of an index movement; that is, movement of the parts a given distance per timed interval. You can place a workpiece into a quench or cooling chamber while moving a part into the high heat and (if necessary) another part into a preheat zone while loading a part into an entrance vestibule.
7. Do you have an opinion on what would be better, a horizontal conveyor belt or vertical chain system (the pieces have holes which permit hanging them)?
Conveyor belts can be made to accommodate index movement as well as continuous product flow. With monorail (hanging-style) furnaces, heat losses become an issue. I have also seen vertical furnaces in which the product enters and is conveyed in a looping fashion through the furnace via an internal conveyor. These work surprisingly well.
8. What measurements can/have to be taken in order to prevent temperature loss when inserting or exiting a piece?
In industry, thermocouples are placed on parts sent through the furnace to develop a thermal profile of the furnace as a function of position. This method would also indicate temperature loss.
9. There will be a minimum distance between the furnace door and the working volume of the furnace. If I wish to keep the dimensions of the furnace as small as possible, this distance is the limiting factor. I thought of solving this by using three separate conveyors. The conveyor in the working volume moves backward and forward to put the pieces in the optimal position (with a minimum safety distance). Is this a possible option?
Sounds complex and mechanisms that move inside hot furnaces are high maintenance.
10. Do you know of any other ways this is solved? Any estimates on this distance?
In designing a furnace, there is something called an insulated throat that separates the door from the heated chamber on each end of the heating chamber. The minimum recommended distance is 9 inches (230 mm), although longer throats further reduce heat loss.