a guess

I think it is related to a conveyor that transfers a work piece into a sintering furnace for sintering/firing a work piece. And the sintering may have to be performed two times.

In the absence of any other context, here is my imagination taking over (based on some logic, of course) :-)

The below 2 websites are not about press transfer machines per se, but I think some of the same terminology can be used as in “reversible conveyor direction” (正転逆転 = forward and reverse)
http://www.blodgett.com/conveyor_ovens.htm
Reversible conveyor direction
http://www.bakeequipsolutions.com/CONVEYEROVENSPIZZA.html
reversible conveyor direction

- Also, press machines heat designs on all sorts of objects from clothing to mugs, etc. using heat (if this is what your question is referring to, that is.) There's a video below of a fairly simple conveyor operation that is "curing" transferred-on designs).
- I am imagining that the machine you mention goes in both forward and reverse directions, effectively being able to "double-heat" whatever is being made.

http://www.youtube.com/watch?v=jjKN40yWE3Q

As another idea, it may be about being "double-stacked" / or "double-tiered"/"double-layered"/"double-decked" for being able to handle twice the number of objects at the same time.... I find that a lot online, too.

I've seen 「2度焼き」mean "main firing" or just "firing" in a few instances.
Here is an example below.

Also, see the link below for "firing conveyor"