Discovery Guide: Learning to use Cold-Bend™ Hardwood
Art Liestman
The Compression Technology
Cold-Bend™ hardwood undergoes extreme physical, longitudinal thermo-mechanical compression without any chemical treatment or adhesives used in the process. This innovative material consists of solid hardwood that has been selected and milled to yield clear lumber with carefully controlled moisture content. Cold-Bend™ hardwood remains unmodified in any way except for the extreme end to end compression and the careful quality selection and moisture control required for its exceptional bending qualities.
Wood Selection and Preparation
The wood used for compression must be clear and straight-grained, essentially requiring veneer quality temperate hardwoods such as ash, oaks, cherry, maple, and walnut. Softwoods and imported lumber do not work in this process due to their cellular structure, grain characteristics and kiln drying. We must begin with partially air dried lumber. After sawing from the log, the green, wet boards are partially dried over a period ranging from a few months to years, then sawn and planed to the required dimensions for processing.
The Manufacturing Process
The patented and trademarked Cold-Bend™ hardwood process begins by steaming the planks under pressure in a long stainless steel autoclave. The plasticized boards are then placed in the compression chamber of the Cold-Bend™ hardwood press, which compresses the wood lengthwise to about 75 to 85 percent of its original length while maintaining the other dimensions. This process alters the wood at the cellular level, with the normally rigid cell walls sliding into or folding over on themselves.
To understand this transformation, imagine the difference between a 10 inch (250mm) plastic drinking straw and a 8 inch (200mm) hospital straw, which illustrates the contrast between regular hardwood and compressed hardwood. The compression can also be thought of as producing a bellows effect in the cell walls, fundamentally changing how the wood responds to stress and bending forces. In the case of our planks of wood though, we are taking 10 foot (3m) planks, and compressing them to 8 feet (2.4m). That is a very dramatic reduction in length, essentially densifying the lumber end to end. But density is not the main point here. It's the bellows effect that is achieved that makes the lumber so flexible.
Compression Resting and Stabilization
Once removed from the press, the wood returns to about 10 percent of its original, trimmed length during a process called "Compression Resting." The wood is immediately set into a second press where the forces are allowed to equalize throughout the compressed planks. After compression and resting, the wood retains amazing flexibility as long as it is kept moist, making it suitable for .storage of months to years, followed at any time by resawing (if needed), then cold bending by hand.
Unique Bending Properties
The compression allows the wood to both stretch on the outside of the curve, something wood cannot otherwise do, and further compress on the inside of the curve without requiring backing straps, heat, or steam. The wood maintains its flexibility until dried, so it can be bent onto or over a fixture while moist, then dried to fix the shape permanently. Once dried, the wood becomes rigid and is identical to the original wood, except that it has likely taken on an cool new curved shape.
Strength and Performance Characteristics
About 5 to 10 percent of the original strength of the wood may be lost during the compression process, which is insignificant in most applications and usually performs better than other shaping methods like steam bending, lamination, and sawing curves. The resulting material maintains the appearance, workability, and finishing characteristics of the original hardwood species while offering unprecedented cold-bending capabilities.
Production Specifications and Availability
Maximum net production size reaches 3.75 x 6.25 inches x 100 inches, but the material is more typically produced in planks that are 1 to 2 inches thick x 6 inches wide x 8 feet long. Cold-Bend™ hardwood is manufactured in only one location in the Americas, in Gig Harbor, Washington, by Pure Timber LLC. Cold bendable compressed wood is available in a range of species and sizes to meet various project requirements.
There is a press or 2 in India or Asia within furniture plants. They primarily produce items like Windsor chair backs or supply furniture manufacturers. Pure Timber LLC remains the only wholesale or retail supplier of Cold-Bend™ hardwood worldwide to consumers, woodworkers, and production factories. This exclusive manufacturing arrangement ensures consistent quality and availability of this revolutionary woodworking material.
Art Liestman