Our technology

History

Wood bending by steam heating has been known since ancient times. Typical examples of traditional steam bending are the application of planks for ship planking, stick handles and Thonet chairs. Steam bending requires a high degree of craftsman skills due to the fact that bending has to take place right after steaming while the wood is still hot. For instance, the rear legs of a Thonet chair have to be bent within a few minute after the wood has been removed from the steam chamber. For years, research has been carried on in order to find other and better methods for industrial bending of solid wood and the decisive breakthrough came in 1988 with the compression machine.

Compressing process

Compressed bendable hardwood is produced and used in the following way:

Up to 3000 mm long and 80 x 120 mm cross section, sawn and planed planks of hardwood are heated and plastified and then compressed approximately 80% of the original length in a hydraulic compression machine. All axial fibre cell walls have been cross folded and the solid wood can be bent. The compressed planks can be either stored cold or worked with right away. The traditional steam bending technique demands instant bending of the wood while it is still hot. Compressed wood, however, does not need to be heated before bending, which provides with the possibility to execute the bending right on the spot. On the pictures below you can see how the structure of the wood is changed during the compressing process.

Before compression

After compression


 

Properties and advantages of compressed hardwood

Process specific properties

  • It stands huge changes in shape and can be bent in cold condition in 3-D direction
  • It is produced entirely without chemicals or glue
  • It can be stored without time limitation in dry conditions (packed in foil), but should not be stored in damp conditions
  • It is harder and more resistant to impact than ordinary wood
  • It is more flexible, however, stable when dry
  • It is sliceable and flexible in thinner dimensions when highly compressed
  • It can be machined, sanded, sawn easily like normal wood when still moist and bendable
  • It can be routed along the grain direction when dried
  • The quality of the bent components is remarkably better (No marks from steel straps. Lower degree of stretched fibres etc.)

Production related advantages

  • Thick pieces and hard-to-bend wood species can be bent with less wastage in short time and with large capacity
  • Pre-bending is rendered superfluous
  • The bending can be carried out by means of simple tools and wooden moulds, which only take little time to learn how to use
  • Less dryings cracks and smaller costs for finishing
  • Less tearing when moulding as less wringled inside the curved parts
  • No color differences and fine lines (compared to laminated parts or finger-jointed curved parts)
  • Stronger than finger-jointed and curved parts as curving follows the direction of the grains
  • Possibility for storage of compressed planks for up to 12 months for "just in time" production and for small production runs

 Strategic advantages

  • New possibilities within design and product development
  • Opens easy access to curving solid wood
  • Unique, high value added products

 


THONET vs. COMPWOOD comparison

COMPWOOD

  • Cold bending
  • No time limitation in bending
  • Wood heating without high pressure for short time
  • Neither ruptures nor creases arising during bending
  • Can be bent on the spot

 THONET

  • Only warm bending
  • Time limitation in bending
  • Wood heating under high pressure for long time
  • The inner side is subject to ruptures, the outside to creases
  • Can be bent only in factory