Hi A
Premise: I'm shooting from the hip (as usual)
Why do you say the "valve" in your sentence are the "hinges"? From the information you give, they appear to be literally "valves" as in a clamshell design, so that "the refrigerator cabinet is composed of a shell manufactured in two halves", or something to that effect. "Incastro negativo" is new to me, but I spent some time wrestling with the type of system that could be used to assemble the two "valves" and wondered whether they could be simply fitted together in a sort of co-penetrative fashion that could, I suppose, in a month of Sundays, be described as an "incastro negativo"...
Cheers
An Unsquashed Beneficiary of Geordie Generosity