veneer
As veneer 0.5 to 8 mm thick sheets are made of wood referred to, which are separated by various sawing and cutting process from the stem. In the 16th century the word veneer was borrowed from the French fournir , “to fit” , “to deliver ”. It referred to the process of covering less valuable wood with finer, thin wood sheets.
Manufacturing / cutting process
The simple veneers are usually produced by peeling off round wood (peeling veneers). Sliced, seldom sawn veneers are also used for decorative surfaces (sliced veneers or sawn veneers).
Rotary veneer
Scheme of the veneer production
System for fully automatic loading and drying of veneer
Peeled birch veneer
Before peeling, the logs, depending on the type of wood, are boiled in large steaming pits (logs lie completely in the water - the temperature can be below 100 ° C, so the water does not have to boil) or steamed (logs only have contact with water vapor; Depending on the process, the temperature is over 100 ° C) to make the wood more pliable. This changes the natural color of the wood, sometimes considerably. A few types of wood are soft enough to be processed further without this process - i.e. raw. The trunk is then debarked and then clamped like a roller to rotate. The trunk then rotates quickly around its own axis against a cutter bar, which separates a veneer band from the trunk; similar to unwinding a kitchen roll . The veneer tape is then divided into narrow, individual sheets of veneer by vertically striking or rotating knives (so-called clippers). The veneer sheets in thicknesses of primarily 0.5 mm to 1.5 mm are processed into panel-shaped wood-based materials such as veneer plywood , laminated wood or rod plywood . A specialty is the processing of the veneers into molded plywood , another is the production of veneer from bird's eye maple , with a structure that, due to the appearance of these burl buds, only comes into its own on the outer circumference of the trunk, almost only in the peeled veneer. Another specialty is burl wood, which is obtained from burls that are often formed at the grafting points (grafting points) through uncontrolled growths. So-called root veneer is rarely made from the roots of a tree, but is a colloquial and incorrectly used term for burl veneer. If the trunk is clamped eccentrically rather than in the middle and the axis of rotation is therefore not in the middle of the trunk , the pattern resembles a sliced veneer the more the axis of rotation is away from the center of the trunk.
Staylog production
This type of production is very similar to eccentric rotary cut veneer production, but is mostly marketed and processed as sliced veneer. The trunk is not clamped directly, but on a swivel bar made of cast steel, which forms the axis of rotation, which is therefore outside the trunk. This is also known as eccentric slicing or peeling. In this way, either a particularly narrow veneer image or a particularly wide, flat image can be produced.
Sawn veneer
The oldest production method of veneer is sawing . The veneer sheets are cut from the trunk with a saw, often lying with the trunk over an open pit in pre-industrial times. One person stood in the pit, the second on a scaffolding above the trunk, which was sawed with a frame saw . At the beginning of the 19th century the first steam powered veneer saws were developed. In England and America, these were huge, highly specialized circular saws with saw blade diameters of up to 4 meters, while in continental Europe the form of gang saws prevailed. Around 1900 the maximum development maturity of such machines was reached, the loss-free production of sliced veneer, however, meant the end of the industrial saw veneer production.
Since when sawing veneers, depending on the saw blade used and depending on the veneer thickness produced, approx. 50% to 80% of the trunk turns into sawdust and waste, this is a time-consuming method with high material loss. But there are some good reasons why saw veneers with typical thicknesses of 1.2–2.5 mm, 5 mm, 7 mm and 10 mm are still produced and sold today:
- The sawn veneer retains its light, natural color and is not changed in color by the often days of cooking to make it supple for the knife process, as is the case with knives.
- The susceptibility to cracks and breaks that is always present with sliced veneers, especially on the side facing away from the knife, is completely eliminated with sawn veneers.
- Due to their high hardness, many woods can only be processed into sawn veneer from a certain thickness. There is no other method, for example , to process palm wood , ironwood or snakewood into veneer.
- Longevity of the objects with the possibility of processing given by the thickness of the veneer.
- For the restoration of antique furniture (which was veneered with sawn veneer at the time) you need veneers of the same thickness in order to be able to repair damage.
For many discerning craftsmen, saw veneer is used again today when it comes to the production of high-quality individual pieces of furniture: Customers often demand permanent solutions for the construction of expensive design furniture, the almost paper-thin sliced veneer is no longer after a damage to a table top, for example can be repaired or refurbished. The use of sawn veneer helps to produce durable furniture that can often be used for generations. However, since furniture is built more and more short-lived these days, this is becoming less important.
Sliced veneer
When cutting, the tree trunks are first boiled or steamed and then clamped on a so-called sledge. It either moves horizontally (older machines) or vertically (newer machines) against a knife. With the latest generation of machines, some manufacturers use a moving knife instead, with the trunk remaining in a fixed position. With each cutting process, a sheet of veneer is produced, which is between 0.4 mm and 0.7 mm thick for thin-cut veneer. Strongly cut veneer, which is becoming less and less important due to the economy in handling the raw material wood and alternative products, is sliced up to a thickness of approx. 6 mm, which, however, requires a very heavy machine (mostly horizontal slicing machines from 1960– 1975). The veneers cut in this way have the advantage over sawn veneers that there is no loss due to the saw cut, but such thick veneers can only be used for inferior applications such as blocking wooden surfaces, since the strong cracking (knife cracks) during production makes permanent surface treatment impossible .
Sliced veneers are primarily applied as visible veneers on inexpensive carrier material (mostly chipboard , plywood , MDF or HDF ).
Micro veneers or veneer papers are produced in thicknesses from 0.08 mm. The production requires machines that cut in the direction of the wood fiber instead of at (approx.) 90 ° to it. Micro veneers are popular in Japan, among other places, where they are also made by hand. Such thin veneers require laminating foils or papers as a base, since the veneers themselves are too fragile and almost transparent.
use
The following product types are differentiated according to their areas of use:
Fine or face veneers
These are used to cover sheet material or other material in order to create a noble wood look. Sliced veneers are usually used for this, and more rarely expensive sawn veneers. Particularly beautiful results can be achieved with expensive grain veneers, which are obtained from growths.
The veneer can be joined to different images:
mirrored (overturned)
laid, also pushed, lined up
head down
For more examples of the use and application of precious wood veneer, see precious wood .
Lower veneers
For high-quality work, these are inserted as an additional separating layer between the base material and the face veneer rotated by 90 ° in the grain direction. This prevents damage to the carrier material from shining through the face veneer or the glue joints of the (possible) edge strips from becoming visible. Bottom veneers usually consist of sliced veneers of lesser quality and thicker than the top veneer that is later visible.
Blind veneers
Blind veneer is the name given to surfaces veneered with so-called counter-veneer that are no longer visible after the workpiece has been installed, for example the inside of a base. This is necessary because the underlay could warp over time due to one-sided veneer. Inferior quality veneers with optical defects are generally used for this.
Barrier veneer
This is the name given to veneers that block the panel during the manufacture of panels, i.e. are intended to prevent further movements and changes in the carrier panel. This applies in particular to the blockboard and the multiplex panels . This consists of long and narrow wooden sticks onto which the barrier veneer - based on the grain direction - is glued, offset by 90 °. For barrier veneers, peeling veneers of thicker thickness than normal sliced veneer are usually used because of the larger widths available.
Chipboard
Completely analogously prepared chipboard or thin wood from poplar and other European and tropical softwoods used to manufacture wooden boxes , baking pans , disposable cutlery , spanning trees and other Christmas decorations, as well as wooden crates . Because of the different use, there is no mention of veneer .
Matchsticks
To produce the wooden shafts for matches , a veneer of suitable thickness is first peeled off from trunk sections, from which the individual shafts are then cut. Aspen is mostly used as wood . The shafts are then impregnated to make them flame-retardant in order to prevent them from after-glowing and through-glowing.
processing
Before processing, veneers are usually joined to veneer covers (fixed dimensions) so that they can be applied to a panel in one step. To do this, the individual sheets of veneer are trimmed and then either glued butted or sewn with a zigzag-shaped glue thread.
Economical meaning
Only the most valuable woods are used for the production of the top veneer, and these are mainly hardwoods . Beech and oak currently dominate here, each with around 30 percent market share. Maple has a ten percent market share. Birch , cherry , ash and the conifers move within a range of five to seven percent each. In Germany around 30 companies with around 1,000 employees are mainly active in the veneer sector. The main buyers of veneers are mainly industrial processors (especially the furniture industry ). Other customers are interior fittings and the carpentry trade as well as boat building / yacht building and the automotive industry .
history
The veneer technique was already used by the Egyptians in the 18th dynasty (1332 BC). Noble woods were just as popular as they were rarely in Egypt , which was poor in forests . This forced the Egyptians to use the most economical processing possible. They cut the wood into fine boards and then attached them with glue and at the same time with fine wooden pegs on optically less attractive wooden surfaces. In 1922 veneered furniture was found as grave goods for Tutankhamun - contemporary witnesses of an ancient veneer technique.
In some epochs of art history, e.g. B. Louis Seize or Biedermeier would not be conceivable without decorative veneers in the traditional way. Many of the woods used were not available in sufficient quantities or simply too expensive for massive construction methods. Decorative techniques such as multi-stitched wooden pictures or inlays were only made possible by veneers in the broadest sense. In France the professional title for the first time in 1657 Ebenist (ebony from the French. Ébène,) proves that was used for a cabinetmaker who produced mainly veneered furniture.
With large doors and molded wood products, our furniture today makes it clear what an important role veneer has played, although the trend towards deceptively real decorative foils may affect this use in the long term.
supporting documents
- ^ State Study Academy Dresden, Fabian Knorr (PDF; 512 kB)
- ↑ Thinnest Wood Shavings You Have Ever Seen - Japanese Woodworking on YouTube
- ↑ Alexander P. Hardt: Pyrotechnics , Pyrotechnica Publications, Post Falls Idaho USA 2001, ISBN 0-929388-06-2 , pp. 74 ff.
literature
- André Wagenführ, Frieder Scholz: Pocket book of wood technology. Specialized book publisher at Carl Hanser Verlag, Leipzig 2008; Pp. 127-259. ISBN 978-3-446-22852-8 .
- Georg Himmelträger: Veneer . In: Reallexikon zur Deutschen Kunstgeschichte , Vol. X (2014), Sp. 1220–1225.
