Laminated shapes

Although MDF was originally considered as a flat sheet material, recent developments have created an opportunity for the manufacture of curved components and panels from MDF using three different processes.

A. Thin MDF lamination

Thin MDF, now readily available at thicknesses down to 1.8mm and sometimes lower, can be laminated into shapes using heated moulds following the well established procedures used for manufacturing laminated panels from wood veneers.

Layers of polyvinyl acetate (PVAC) or urea formaldehyde (UF) adhesive are applied between the pieces of MDF required to build up the required thickness. The shapes are formed between the two surfaces of matching moulds heated to 60 - 80°C using a low voltage system or radio frequency (RF) electrodes. Pressures of 500 - 700 kN/m2 should be used to bring the MDF layers into close contact.

As a general rule, the time required for the heat to reach the inner gluelines is 1min/mm with additional time required for the cure of the glue.

B. Chemical pretreatment

An alkaline chemical pretreatment process which has the effect of plasticising the MDF enabling it to be formed into shapes for archways, shaped head windows and curved panelling generally, is now available. According to the inventor, the properties of the MDF are not affected by this pretreatment. An additional advantage of this process is that the surfaces of the plasticised boards can be embossed.

C. Formable MDF

The process of back cutting wood strips to enable them to be formed has been adapted to MDF by several manufacturers who now offer a forming grade board. Parallel saw cuts across one face of the board, cutting through approximately 90% of the thickness of the board, impart a high degree of flexibility to the board. The rigidity of the formed component is achieved by adhesive bonding two layers of forming grade board back to back.

Based on current experience with this type of board, shapes with minimum radii of 17, 22 and 26mm can be formed from 6, 8 and 9.5 mm thickness boards. Simple shapes can be formed by clamping the two adhesive back coated layers of board round a preformed mould using steel or fabric band clamps. For more complicated shapes, the use of matched moulds is recommended with pressure applied to the moulds using hand cramps or more uniformily, using a flat plate press.