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Frequently asked questions

Adhesives

• I have a vacuum press system and I need to know what adhesives can be used?

  The most versatile bonding system suitable for use with an 'air bag' would be our two-part UF resin system for rapid cold pressing of wood veneers, laminate and shaped profiles. Borden UL39 UF resin, suitable for hot or cold press applications can be used with two powder hardeners:

  • UH21 – the fastest powder hardener ideally suited for use with air bags, offering a rapid set under pressure at room temperature. With a pot life (usable life) of around 60 minutes, it will produce a cured bond within 60-90 minutes at around 15-20°C.
  • UH191 – the variable powder hardener that allows one to adapt the mix ratio of hardener to suit production. If you require a long open time (pot life) to allow for coating larger panels, laying up laminates or veneers without pre-curing of adhesive then use UH191. This facility allows a mix ratio of between 5% and 20% producing either shorter pressing cycles (short pot life and rapid set) or longer pressing cycles (long pot life and extended pressing cycle) to be obtained to suit your production.

  UF resin systems produce a far superior bond quality, are more tolerant of many surfaces than PVA's, gap filling and hold profiled, laminated structures rigidly without 'spring-back'.

• Why do I need to weigh the powder hardeners?

  Because powders are of varying density and difficult to measure consistently by volume, it is strongly recommended that the hardener ratio is measured by weight. Mixing can be done by hand for small batches or by mechanical mixer. In both cases it is advisable to allow the mixture to stand after mixing to allow entrapped air to escape. Bubbles or foam in a glue line can cause a weak bond.

• Why is moisture content of timbers important?

  Ideally the moisture content of the substrates should be 6-14% with no more than 3% difference between the two surfaces to be bonded. Otherwise stresses are built into the joint which may result in wood or joint fracture. If the timbers are too dry, there is a tendency for the adhesive to be absorbed too readily into the surface, resulting in glue starvation. Correspondingly, if the timber is too damp it will extend the cure time on aqueous-based adhesives & in effect dilute the coating of adhesive applied with the consequence that the final bond quality may be reduced.

• Why is surface preparation important?

  Before you start to bond substrates together, just take a moment to prepare the surfaces – good housekeeping practices will minimise any failures & produce quality bonds Always ensure the surfaces to be bonded are free from dust, dirt & oils prior to bonding. Abrade dense surfaces with P80 to open up the fibres allowing adhesive to soak into surfaces – oily timbers need to be freshly sawn & can be wiped with a suitable solvent (acetone) prior to coating. Bonding veneers to metal surfaces require a suitable casein latex primer to be used to etch into metal surface producing a surface to which UF resin will adhere to in. Keep all substrates at room temperature & within the specified moisture contents, especially during the colder months of the year as large variations can produce stresses. Also make sure the adhesive being used is suitable for the final application (i.e. water-resistant, structural, gap filling, etc).

• Why do you only recommend using UF resin for veneering?

  We don't – PVA's are suitable for veneering application when used in hot or cold presses & offer many benefits to production including easy to use, no mixing required & on application of heat, undergo a cross-linking reaction improving heat & moisture resistance as well as hardness of the glueline. Generally full bond strength is obtained over a 24 hour period & being thermoplastic, the final bond has a degree of flexibility & can be soften in areas of high heat application. Depending on the individual application, PVA's also offer economic production rates at ambient temperatures, whereas UF resins do require elevated temperature. From experience, we generally recommend PVA's for use in smaller panel work where they are not exposed to large variants in heat & moisture & not to be used in highly stressed joints subjected to heavy loads. Only the special cross-linked grades are water resistant.

  UF resins are our preferred choice when veneering as they offer a more tolerant system than PVA's to the many varied wood surfaces being bonded. Being a two-part chemically reactive system at elevated temperature, final bond quality can be obtained rapidly allowing a larger volume of work to be produced over a shorter time.

  Why are they tolerant? UF resin systems can be adapted to suit various veneer types (i.e. porous, dense, burrs & curls, etc) that are bonded to the many panel stocks available. By carefully selecting the resin & hardener types, one can minimise production issues & produce high quality veneered surfaces. Offering gap filling properties, water & heat resistance durable bond, rigid bonds with minimal flex & economies of scale over larger panel production UF resin systems can be adjusted to suit nearly all applications. With a range of powder, liquid & separate application hardener systems available UF resins are well placed to meet the ever increasing demands of today's woodworking industries.

• Bonding of difficult timbers – what do I need to be aware of?

  As mentioned, a few simple preparation techniques & careful selection of the correct adhesive will help minimise production failures when bonding substrates.

  1. Timbers with absorbent surfaces – use a viscous UF resin system, possibly adding extenders & fillers, avoid end grain gluing, increase the spread rate (more glue on) looking for a consistent squeeze out bead around the joint on pressure applications.
  2. Timbers with dense surfaces – lightly sand the surfaces to open up timber pores & improve adhesive penetration into fibres. Apply adhesive to both surfaces to be bonded & ensure there is sufficient open time to adequately wet the surfaces prior to pressure applications. Be aware, if the open time exceeds the guidelines given, the adhesive may pre-cure prior to pressure being applied. The addition of a wetting agent may also assist bond quality on certain timbers.
  3. Timber with case hardened surfaces – lightly sand surfaces prior to adhesive application, add a wetting agent or use an adhesive that wets the surfaces more readily (i.e. resorcinol or animal-based adhesive).
  4. Timbers with resinous or greasy surfaces – guidance as above for case hardened surfaces but for optimum results sand immediately prior to use as, if left, the natural resins will again rise to the surface. Lightly degrease surfaces with suitable solvent cleaning agent.
  5. Timbers with acidic surfaces – ensure moisture content of timber is below 12%, some particularly acidic timbers may retard the setting times of resorcinol resin systems & the surface can be neutralised with a weak alkali solution such as 1% sodium carbonate solution.
  6. Timbers prone to staining – ensure glues & hardeners do not come into contact with ferrous fixings & fitments, avoid high acid systems & particularly separate application hardeners. Please note, however the surface on some sensitive timbers can be affected by a variety of factors including UV lights & some surface finishing products (i.e. lacquers, stains, etc).

• I have problems bonding burr and curl veneers – do you have any advice?

  Traditionally Burr & Curl decorative veneers are used in the production of traditional or reproduction furniture and with the use of such veneers ‘checking’ on the surface is always a potential problem unless appropriate measures are employed for successful bonding. With no definite grain direction, decorative veneers tend to move when hot pressed and the attention to the following guidelines will assist in providing the require results:

  • Liquid resin when used with our 1298 flexible hardener can provide a degree of flexibility at the crucial stage when the panels are released from the press. The initial give in the glue line helps to stabilise the panel & compensate any movement in the veneer. Whilst 1298 is not a panacea for all eventualities, it makes a significant contribution towards panel quality.
  • 1298 should be presses low & slow, that is pressing for the longest possible time at the lowest temperature will ensure the equilibrium is gradually adjusted to maintain panel stability.
  • Bearing in mind that the heat will be retained for sometime in panels stacked from the press, it is beneficial to stick battens between each panel to allow air to circulate gradually reducing them to ambient temperature.
  • The moisture content of the veneers should normally be between 8-12%.
  • 1298 exhibits a high degree of initial tack & is suitable for wetting the most difficult veneer species.

  Can be used with EXT99, an inert filler to reduce adhesive penetration through the veneer surface.

Abrasives

• What is the meaning of open and closed coat?

  When referring to open and closed coat this is normally associated with coated abrasive products for the wood working industry. Open coat means that individual abrasive grains are spaced at a predetermined distance from one another covering approximately 50 – 70% of the abrasive surface.  Open coat would be the coarse grits (P36 – P120/P150) and ideal for stock removal. In the case of closed coat abrasive, the spacing of the abrasive grain will be denser covering approximately 95 – 98% of the abrasive surface. Closed coat products are used in the finer grits when de-nibbing and finishing.

• What does the 'P' stand for on the back of a coated abrasive product?

  The 'P' stands for FEPA (Federation of European Producers of Abrasive). FEPA is an association of European manufacturers of abrasive products and members include the largest companies in the world. This means that all the members have to comply with standards laid down by the federation including bonding, backing and Grit size.

• What is the benefit of antistatic sanding?

  When two surfaces come in contact with each other i.e. the work piece and the sanding belt friction increases, creating static electricity. As a consequence the static charge prevents a large proportion of the dust to be extracted. Dust on and around the machine and belt clogging can be a problem. Abrasive manufacturers have now developed a way of neutralising the electric charge in both the backing and the bonding process allowing the dust to be collected much more affectively. The dust on and around the machine is reduced dramatically which in turn helps prolong the life of the belt and creates a much cleaner working environment.

• What is a Non-Woven abrasive product?

  Non-woven's are among the most versatile abrasive product. They are primarily used in the metalworking industry for a multitude of surface conditioning, de burring and finishing processes. Non-woven abrasives have a 3 dimensional open structure, which is achieved by combing and needling nylon fibre to form a web. Abrasive grain – primarily aluminium oxide and silicon carbide and resin are bonded throughout the web and then passed through a drying and curing stage. The grain is distributed throughout the structure of the product and as the nylon breaks down, fresh abrasive grain is exposed, ensuring a constant finish. Non-woven abrasive are a perfect solution to apply the final finish to any surface. Non-woven's are also used in the automotive industry, solid surface finishing and de nibbing wood products.

• How is coated abrasive manufactured?

  Coated abrasives give users the best value and results for finishing the surfaces of a wide variety of materials. They consist of a backing (typically paper, cloth, fibre or film)  to which abrasive grains are bonded. The choice of abrasives used depends on the work piece properties and type of treatment and ranges from garnet, emery, silicon carbide to various forms of aluminium oxide, zirconia alumina and ceramic aluminium oxide.

  Coated abrasives are made in a continuous process on production lines known as ‘makers’, which can be up to 300 metres long. The abrasive grains are applied by an electrostatic process. These can be natural or synthetic minerals, such as silicon carbide or a variety of aluminium oxide, according to the use of the abrasives. A second layer of adhesive bond, called the size coat, is applied to anchor the abrasive grains securely. The abrasive is cured in a drying chamber and passed to the end of the production line where it is wound into jumbo rolls weighing up to 2,500 kilos. Throughout the manufacturing process, electronic measurement systems monitor the consistency of the different application operations and guarantee uniform quality.