Bend it. Twist it. And tie it in a knot

The compression gives wood a new structure and amazing flexible features. During the compression the wood fibre will be folded like an accordion. Afterwards you can do with the wood whatever you want. You can bend it. You can twist it. You can even tie it in a knot. When the wood dries up it keep that shape you have given it.

With compression machines from Compwood you get a thoroughly tested technology and nearly 30 years of know how and experience.

Heating

Wood suited for compression

Wood for compression has to meet the same quality demands as for normal furniture manufacturing. The planks have to be without larger knots and other defects. Wood with smaller knots can be compressed but the knots can produce problems in the bending part. The ideal moisture content in the wood is 20-25%.

Ash, black cherry, beech, elm, red oak, silver maple and walnut are very suitable for compression.

The planks have to be plane and cut in dimensions, which fits in the compression machine – max 3 meter.

Heating

To prevent the wood to get crushed it’s necessary to soften it before compression. For that purpose we use an autoclave with steam. The wood will be heated up to about 100° C – hereby you kill dry rot as well. It’s possible just to bend a part of the compressed wood if needed.

If the wood has to be stocked before compression you have to protect it against sun and against mould. Stock the wood cold or treated with remedy against mould.

Compression

In the compression machine the planks will be compressed till a length of approx 80% of its original length. When the pressure decrease the planks will expand again to approx 5% of the original length.

Within this process all axial fibre has got crosswise walls and the massive planks can now be bended.

A typical compression cycle takes about 9-10 minutes if the moisture content is approx 20-25%.

Compression machines from Compwood

We offer compression machines with different chamber dimensions. Choose in proportions to your needs of capacity and wood dimensions.

If you mainly produce round wood for chairs or table legs cross dimension of 40 mm, you can choose a chamber size with a cross section of 135 x 90 mm. In that case the chamber can contain 6 planks of 45 x 45 a time.

The capacity will typically be from 0,5 – to 4,5 m3 hardwood tree for every eight hours referring to wood species, moister content, the quality of the wood and choice of machine.

Bending

It’s possible to work with the wood immediately after the compression, but it can also bed stocked for later use. If you put the wood on stock you shall keep it in cold room or wrap it in plastic to avoid the wood to dry out. The compressed wood can be stored in 6-12 month. Mould attach shall be avoid in the same way as raw wood.

How to bend compressed wood

In traditional bending technique with steam you often need hose clamp of steel. Unfortunately that technique gives pressure marks in the soft wood.

With compressed wood you can stretch the outside of the wood 3-5 times more and therefore you normally can avoid hose clamps.

Even though the compressed wood is soft you still have to use power to bend it. For more massive planks you have to use tools, moulds and tension tools.

Even larger bending radius can be bent into the shape you want without use of hose clamps. You only need to fasten the wood to a form with clamps.

Thin list of compressed wood can be bend only by using your hands.

Drying

When the wood is bended, it has to be kept in form until its dry. The bended wood can take harder and faster drying than normal wood without getting chinks. After drying the wood recover the majority of its original stiffness.

Processing

When the wood is dry you can work with it like normally wood. You can glue it and surface treats it with oil, stain, varnish or paint. However some type of stain can give discolorations. In general we refer to specifications from colour and varnish manufacturer.

If the compressed wood is going to be used in high humidity – indoor or roofed outdoor – you have to treat it with wood preservation as you do with normal wood. Furthermore the form of the wood has to be locked to prevent movement’s contingent on humidity.

Strenght

The strength for bending, pressure and pull is for beech and ash approx 10% lower than for non-compressed wood. The impact strength is 20% higher.