TERM: "Placera en lämplig försättskaka framför ugnsöppningen (gäller ej i kombination med Hexadoor eller blädderblock)."

They seem to be referring to the piece of material you put in front of the opening of the oven. Here is an illustration of how they are known in Swedish:

http://www.corgab.se/images/kakortabell.jpg

The illustration is from this company, who state that they have a wide range of ”försättskakor, halvkakor, invärmningskakor samt invärmningsbågar:”

http://www.corgab.se/produkter.html

The equivalent English term seems to be ”full cover cake, 1/2 cake and 1/4 cake, etc”:

”Full door opening is 9"w x 9.5"h. 1/2 cake is 6"w x 6.5"h. This package comes with a full cover cake, 1/2 cake and 1/4 cake for each door ”

http://www.hubglass.com/garagepipewarmers.html

”Försättskaka” seems to be ”full cover cake” - since the shapes seem to match - so the sentence is about placing a suitable full cover cake over the opening.

Does this seem right in the context?