Vitreous – Wooden Laminates

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Vitreous and Wooden Laminates
Vitreous – Wooden Laminates
A perfect preamble to Printers Blankets study
  • Vitreous – Wooden Laminates manufactured during a decade in Brasil provided the perfect preamble to printers blankets study.
  • Invited into a Petrobrás sponsored nationalisation project, the secondary oil production stage required the development of fibreglass reinforced epoxy pipes. As a result, Petrobras had more than 400 km of these newly developed pipes installed in a few years. They injected water at 1,200 psi to oil fields which original pressure had already been spent during primary exploitation.
  • Next came composite development for a Permali Gloucester Ltd subsidiary. (By then Permali specialised in electric insulating materials, including “Permaglass” and “Permawood”, with production facilities in the UK and France.) More than twelve different complete projects were successfully carried out, using five or six different manufacturing processes. Some of these projects had the strong advice of Dow Chemical specialists. Their documentation contained an inestimable wealth of product and processing data, including frequent updates on the latest curing agent specialities.
  • Local composite development was the option to avoid imports from Europe or the USA. It focused on a combination of the following properties: chemical and heat resistance, mechanical modulus, or dielectric strength.
A Major Project
  • Siemens and BBC local development obligations towards the Brazilian Authorities led to the development of a variety of composites. The Itaipu bi-National Power Station at the Paraguay border required a variety of custom developed fiberglass composites. The 500 to 765 kV transport lines to the main consumption centers used wooden laminates. Meet one of the eighteen Itaipu generators.
  • During composite production, several techniques used to create sharply transient temperature gradients enabled to optimise a particular operation. In this way the objective, for example, of fiber wetting optimisation had no real impact on finished products’ performance.
    The discerned use of temperature gradients was a mighty ally to vacuum techniques when composite dielectric properties were top priorities. It did assist in reducing drastically laminate void content.
  • Conformity Certificates were issued with every batch delivered, keeping the CQ laboratory busy. At customer’s option, an external inspector witnessed Sample testing.
Vitreous and Wooden Laminates - A perfect preamble to Printing Blankets study

A token to a fruitful partnership.

Major Challenges
  • Company’s traditional business consisted of compressed wooden laminates.

    Its manufacture used a heat-assisted process, shaped by inter-veneer paper sheets impregnated with phenolic resin.

  • Production consisted on a range of wooden-laminate-grades to meet the particular mechanical and dielectric specifications of Siemens, GE, Asea, or Embraer.
  • The business was OK , except for occasional nasty complaints. Some wooden laminate batches would exhibit a “puzzling” fibre degradation, causing their properties to fall short of customer’ specifications.
Air and Water
Multipurpose processing agents.
  • Identification of the undulatory nature of wind travel inside the veneer pretreatment oven constituded the first step:
    Moisture on individual veneers should fall into a precise value, within a narrow range.
    Careful veneer moisture control carried after the pretreatment drying cycle showed far too irregular moisture distribution over the veneer surface. Contrarily to expectations air flow developed wave patterns as it happens with open environment wind, forming nodes and anti-nodes.
    Designing curved veneer supports prevented the free air flow between opposite oven walls.
    These supports ensured now that a gentle warm air flow swept both surfaces of every single veneer.
    It was finally possible to adjust the drying time so that each veneer would keep exactly the desired moisture content.
  • Actually, this control was crucial throughout the production process of highly densified wooden laminates:
    Upon arrival and during storage, moisture absorption of pre-treated wooden veneers would favour mould development and other wood decay problems.
    Veneers which moisture was kept within a very narrow range was the pre-requisite to obtain properly densified laminates.
    Too low moisture would not provide sufficient plasticising effect.
    Fracture of the wooden cell walls would occur instead of the desired densification without structural damage.
    Too high moisture content would cause the finished laminate to darken markedly in comparison with the original veneers’ shade.
    The laminate would also have its mechanical properties severely reduced.
    Fibre degradation happened due to the steam pressure-cooking-effect during the hotter part of the compression cycle.