Wood veneers

Another widely used overlay adhesive is the contact type. These specialized adhesives, in the same group as mbber cement, may be of the solvent-base or water-base types. They are often used to bond overlays such as wood veneer, vinyl (poly(vinyl chloride)) films, or high pressure laminates such as countertop overlays. 

Plywood is a panel made from wood veneers (thin shces or sheets) bonded to one another. Generahy each ply is oriented at right angles to the adjacent ply, and the two face pHes should have the grain direction parahel to each other. Thus most plywood wih have an uneven number of pHes, such as 3, 5, 7, or more. An exception to this is a four-ply constmction in which the two core pHes are oriented parahel to one another and perpendicular to the two face phes. 

Lumber core is a five-ply panel, usually about 19 mm (3/4 in.) thick, in which the bulk of the thickness, about 16 mm (5/8 in.) is edge-glued lumber. Yellow poplar and red gum are desired species for lumber core. Cross-pHes of lower value wood veneers are laid at right angles to the core grain direction, followed by two thin surface pHes of the decorative face veneer in a parallel direction to the core. This assembly is pressed and bonded to form a panel of exceptional quaHty, provided all steps are accompHshed in a desirable manner. 

Plywood furniture core panels, also about 19 mm (3/4 in.) thick, were normally made of a number of layers of relatively thick, 1.5—3.0 mm (1 /16—1 /8 in.) lower value wood veneers combined with thin surface pHes of the decorative veneer. These assembhes were laid-up from glued veneers and then pressed while the bonding occurred. Both lumber core and plywood core have been almost totally displaced in recent years by particleboard or medium-density fiberboard, both discussed herein. This change resulted from the increasing availabiHty and improved finishing characteristics of composites and from decreasing suppHes of core lumber or veneer of suitable quaHty. 

A small amount of particleboard is made with a fire-retardant treatment for use in locations where codes require this material, as in some offices and elevators. Particleboards receive overlay and finishing treatments with ease. Wood veneers, melamine overlays, printed paper overlays, vinyl overlays, foils, and direct grain printing can all be done quite simply. A small amount of particleboard is also made in the form of shaped, molded articles such as furniture parts, paper roU plugs, bmsh bases, and even toilet seats. There is another small increment of particleboard made by the extmsion process. These products are made in small captive operations owned by furniture manufacturers which consume all of this production in their furniture. The extmsion process differs from conventional flat-pressed particleboard in that the wood furnish is forced between two stationary heated surfaces. The mats are formed from one edge and this edge is alternately formed and pushed between the heated platens, which are maintained at a distance equal to the thickness of board produced. This is an old, slow, small-scale process, but is stiU in use in at least one location. 

Laminates aie materials made up of plies or laminae stacked up like a deck of cards and bonded together. Plywood is a common example of a laminate. It is made up of thin pHes of wood veneer bonded together with various glues. Laminates ate a form of composite material, ie, they ate constmcted from a continuous matrix and a reinforcing material (1) (see also Reinforced plastics). 

With the advent of these compounds in the 1960s, the hitherto more conventional insulating materials, such as phenol formaldehyde (popularly known as Bakelite) and wood (veneered impregnated) have been almost replaced by them. These compounds offer better electromechanical properties than conventional materials. Below we describe the basic mix and properties of these two basic compounds, for a brief reference. 

At one time urea-formaldehyde was used extensively in the manufacture of plywood but the product is today less important than heretofore. For this purpose a resin (typically U-F molar ratio 1 1.8)-hardener mixture is coated on to wood veneers which are plied together and pressed at 95-110°C under pressure at 200-800 Ibf/in (1.38-5.52 MPa). U-F resin-bonded plywood is suitable for indoor application but is generally unsuitable for outdoor work where phenol-formaldehyde, resorcinol-fonnaldehyde or melamine modified resins are more suitable. 

Monocoque structure fabricated by molding wood veneer with glue to shape under pressure was successfully used as early as 1916 in the LWF Model V complete molded fuselage and probably most famously in the monocoque fuselage... 

Pressed Wood Products A group of materials used in building and furniture construction that are made from wood veneers, particles, or fibers bonded together with an adhesive under heat and pressure. 

Electric road vehicles have been reduced to insignificance, as mentioned already by, vehicles with combustion engines. Another electric vehicle — the electrically driven submarine — presented a continuous challenge to lead-acid battery separator development since the 1930s and 1940s. The wood veneers originally used in electric vehicles proved too difficult to handle, especially if tall cells had to be manufactured. Therefore much intense effort took place to develop the first plastic separators. In this respect the microporous hard rubber separator, still available today in a more advanced version, and a micro-porous PVC separator (Porvic I) merit special mention 28]. For the latter a molten blend of PVC, plasticizer and starch was rolled into a flat product. In a lengthy pro-... 

The closest relative to the wood veneer surprisingly has retained some of its properties, which differentiate these separators from pure synthetic ones primarily, a positive effect in reducing the water loss in starter batteries [39, 70-72], This impact tends to decrease as the antimony content in the alloys is lowered, but it still represents an advantage over other leaf separators, unless a microporous pocket is required by the alloy anyway. 

One commercial adhesive is marketed with the following claims High Strength Adhesive Durable Bonding Fast Acting Bonds Metals, Rubber, Ceramics, Plastics, Glass, Wood, Veneers, Fabrics, Vinyl, Cardboard, Cork, Leather, Nylon, and Other Similar Surfaces. 1 How can one substance act as a general purpose adhesive with affinity for so many types of surfaces ... 

A thin layer of Masonite (wood veneer) is attached to an insulating layer of glass wool. The Masonite is 2 mm thick. It has the following properties ... 

Hill and (letin (2000) modified the surfaces of wood veneers with methacrylic anhydride (Figure 6.6a) and formed lap joints using either styrene or methyl methacrylate in the presence of the free radical initiator azoisobutyronitrile. Significant improvements in bond strength were found when compared to unmodified wood. 

UV curable coatings are applied to a variety of flat, rigid substrates, such as particle board, medium- and high-density fiberboard, wood veneers, polycarbonate, poly(methylmethacrylate), paper, and metal sheets and foils. An example of a formulation for UV curable coatings is in Table 7.1. 

Lumber banding consists of gluing lumber strips, 1/2 to 2 inches in width, on the particleboard edges. These strips are normally used in applications where the particleboard is to be covered with wood veneers. The solid wood strip can be machined to decorative edges and, with the veneer surfaces, the panel is fully as functional and attractive as a solid wood panel, but at a lower cost. The lumber bands are normally bonded to the particleboard with polyvinyl acetate or urea-formaldehyde adhesives, cured rapidly by either contact or high frequency heating. 

Plywood construction refers to the composition of the inner plies or layers. The faces are usually always veneer but the cores may consist of four different types of wood materials all inner plies of (1) wood veneer ... 

With the advent of the polymer or plastic age, scientists had yet another group of chemicals to coat and treat the ancient raw material, wood. During World War II, phenol-formaldehyde, based on the research of the Forest Products Laboratory, was used to treat wood veneer and to form the composite into airplane propellers. Today, this same "Compreg" is used for cutlery handles throughout the world. 

Skived film — A PTFE film prepared by peeling from a sintered billet using a sharp cutting tool in a similar fashion as, for example, wood veneer. 

Decorative laminate is defined in ISO 472 but in common usage has come to mean sheet materials consisting of decorative surface papers impregnated with melamine resin and consolidated under heat and pressure with plies of core paper permeated with phenolic resin. In a wider sense the term can be applied to many associated products—including laminates in solid colour laminates with facings such as metal foils, textiles, or wood veneers polyester laminates direct faced boards and composite boards comprising thin laminates bonded to substrates of various kinds. 

Wood Veneers. Wood veneered laminates are available in two forms, which may be described as natural and surfaced . 

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