| 摘要 |
A method for producing a duct from a planar board having two opposed substantially parallel edges with metal foil facings on opposed major surfaces of the board is disclosed. The method comprises making planar cuts through one of the metal foil facings and at least most of the planar board there below to produce a blank with 3 parallel“V shaped grooves which are parallel to angled edges of the blank. A duct is formed by folding the blank so that the“V”shaped grooves form three of the edges of the duct, and the angled edges form the fourth of the edges.
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