Wood and Ligneous Materials in Door Manufacturing
Wood is a material that is traditionally used for the production of doors. As a natural material, wood has both advantages and disadvantages, which should be considered in the production and usage of doors. The advantages of natural wood include its strength despite the small volumetric mass (in most species it is less than 100 kg/m3); low thermal conductivity, good soundproofing properties and high frost resistance, as well as the fact that it is easy to process and simple to use.
The drawbacks of natural wood include the following aspects: the presence of defects (knots, cracks, pitch pockets, etc.), hydroscopicity (excessive moisture in wood worsens its physical-mechanical qualities), as well as flammability. Wood is used to produce structural door elements and for door veneers. For the production of massive doors the following species of wood are used: oak, various species of mahogany, pine, beech, hazel, cherry-tree and some others. They are used not only for massive doors, but also for the production of veneer (thin layers of natural wood).
The Properties of Commonly Used Species of Wood and Ligneous Materials
Oak – a commonly accepted symbol of eternity – has been used in building industry for hundreds of years. It is a solid and firm tree of a brownish-yellow colour with well defined yearly stratification. The most characteristic traits of the oak are its frequent and thick growth rings. The brown shade of the oak intensifies from the bark to the core. Northern trees that grow on infertile soil have better wood than those growing in the south.
Oak is quite difficult to chip and saw, but is cracks easily. It is almost impossible to polish oak wood due to its high porosity. Pickling stresses the porous fibre structure of oak and makes it especially attractive.
Mahogany. The term “mahogany” is used in relation to various species and families that share a common colour and, partially, wood structure. Mahogany wood is easy to process, and despite having quite a soft wood, it is considered to be quite a popular material in wood-working. This is due is not only its attractive appearance, but also to the high level of its resistance against atmospheric influences and stable form and size. A newly cut down mahogany wood has a yellowish red colour, but in the course of time under the influence of the air and light it darkens and gradually assumes a brown-red or crimson-red colour with conspicuous light and dark threads.
While it is practically impossible to list all kinds of mahogany here, it is worth mentioning that the price and the kind of the tree are determined by the beauty of its fibre pattern, rather that by the place of origin of the tree. Mahogany can be smooth, striped, figured, fiery, marked, packed, knotty, etc.
Mahogany and the frequently used term “meranty” are not the same. Meranty relates to a wood from the group of species that are common in south-east Asia.
Pine has an extremely wide applicability. It is a wood of yellowish-red or pale yellow colour, having high durability and low volumetric mass. Besides, it is easy to process.
In comparison with deciduous species (for example, birch or beech), pine is a softer material; it is less susceptible to humidity impact. In the course of time its wood darkens, and its core becomes sharply distinctive. One of the distinctive traits of the pine is that the unevenness of its surface can become visible if painted. This is due to the fact that areas having unequal gummosity and porosity absorb paint unevenly.
All the mentioned wood types are used not only in the production of massive doors, but are also to make veneer for external finishing of doors. For veneer production the following wood types are also used: beech, hazel, cherry-tree, lime-tree, elm, chestnut, maple, birch, and other types.
‘Veneer’ stands for thin layers of natural wood. They are primarily used in the production of plywood as well as for covering of woodworking products and other articles. Apart from natural wood, various ligneous materials are also used to make doors.
Wood fibreboards are produced by hot pressing an evenly grinded wooden mass impregnated with synthetic pitch, including some additions. The raw material for wood fibreboards is granulated kindling-wood and hogged chips. To improve the quality of wood fibreboards, paraffin, colophony (it increases humidity resistance), synthetic pitch (for strengthening of the board), and antiseptics are added to the wooden mass. There are super firm (950 kg/ m3 density), firm (850 kg/ m3), semi-firm (400 kg/ m3), insulating-decorative (250 kg/ m3) and insulating (to 250 kg/ m3) wood fibreboards. Wood fibreboards can be used in premises with increased humidity level.
The term “orgalite” is quite often used to denote wood fibreboards, the surface of which from one side (the obverse) is polished and painted, covered with a decorating film or plastic. It is used for facing purposes.
Medium-density fibreboard is a wood fibreboard of a medium density. It is the latest technological development in wood-processing industry. The production of wood fibreboards and medium-density fibreboards is similar in many aspects; they are produced by pressing wood fibre.
During the recent years medium-density fibreboard has acquired a wider application, especially in the production of furniture and doors. This is due to the distinct features of medium-density fibreboard – its high hydrophobia (water repellent property), as well as its high environmental sustainability (it does not contain formaldehyde). The surface of medium-density fibreboard is even, smooth, homogenous, dense, and this all makes the external processing of boards extremely simple, especially it concerns the straight painting and thin laminating.
Due to its high endurance, medium-density fibreboard can be used in the production of details that require minimal access and particular precision of carving. Medium-density fibreboard also lends itself to moulding.
Medium-density fibreboard is used in the production of wood fibre (framing of external panels; formed panels too) as well as in the production of frameworks.
Chipboards are produced using the method of hot flat pressing of wood particles that are mixed with the binding substance, essentially with synthetic pitch. A full-fledged primary material for chipboards is any scarcely valuable wood of deal or leafy species.
The exploitative features of chipboards essentially depend on their density, form and size of wood particles as well as on quantity and quality of the binding material. There are boards of a very small (350-450 kg/ m3), small (450-650 kg / m3), medium (650-750 kg / m3), and high (700-800 kg / m3) density.
Chipboards usually are one, three-, and five-layer constructions. It is not recommended to use chipboards in rooms with increased humidity. In such places one should use hydrophobic boards or boards with protecting layers.Chipboards lend themselves to mechanic processing (sawing, rasping, drilling, milling); they can be easily glued and painted. By some physical-mechanical features chipboards surpass natural wood. In particular, they swell less from humidity, are less flammable, do not deform due to change of humidity level; they have remarkable heat-insulating and soundproofing features; finally, they are more biologically stable.The disadvantage of chipboards is that they are heavier than natural wood, and are not as durable as natural wood.
Plywood is a layered wood material which is produced by gluing three or more layers of peeled veneer so that the orientation of fibres in adjacent layers is perpendicular in relation to each other).For the obverse layers of plywood the peeled veneer from birch, alder, lime-tree, aspen, or poplar wood is used, whereas for the inner layers fir, spruce or larch veneer is applied.