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Fasteners of Laminated Pressboard and Solid Wood

12. January 2020 17:45

Lignostone laminated densified wood, made from beech veneers,
is formed into high-strength precision fasteners.

By Bill Esler, Editor, IWF Network News

New versions of precision threaded bolts and nuts made of specially processed wood materials have been developed by Röchling Engineering Plastics. Due to wood's natural insulating properties, the fasteners, along with densified wood laminate panel, are critical components for electrical devices. Due to its special material properties, Lignostone is mainly used as insulation material in transformer construction and as thermal insulation for tank supports in ocean tankers carrying liquified natural gas. The fasteners are also favored for connecting various types of plastic panels. 

For more than a century, the Haren, Germany-based firm Röchling Engineering has been manufacturing Lignostone, an impregnated grade of wood material used in transformers. Lignostone laminated densified wood consists of beech veneers (Fagus sylvatica), which are joined together with thermosetting synthetic resins under pressure and heat. Röchling developed expertise in the application of this bonding technology and manufactures semi-finished products and components, such as pressure rings, pressure beams, shield end rings, shield rings along with the fasteners, producing them customer specifications.

Röchling Engineering says selected red beech veneers of the highest quality are used,  subject to its stringent quality specifications, drawn from sustainably managed forests. Thanks to the excellent conditions in Western Europe for growing beech within a period of around 120 years, "top grades of this product from logs of suitable length felled in the right locations offer extremely good homogeneity that enables them to withstand the extremely high electric stresses."  In addition to electrical insulating properties, Lignostone is also strong,  due to its intact capillaries (woody structures) with continuous load-bearing fibers this material offers unsurpassed mechanical strength values, which depend on the direction of lamination and the densification.

More recently Röchling Engineering developed Trafoboard, a panel material made from laminated pressboard with phenolic resin bonding for use in oil-filled power transformers. The material has also been fabricated into an alternative to fasteners (above) for transformers that are made from laminated pressboard with casein and polyester resin bonding. 

Trafoboard HD-PH, the international plastics processor Röchling Engineering Plastics SE & Co. KG, Haren, Germany is the first manufacturer in the market to offer fasteners made from laminated pressboard with phenolic resin bonding for use in oil-filled transformers. Röchling Engineering says the unique phenolic resin bonding in Trafoboard offers the highest electrical properties and can contribute to increased operational reliability of oil-filled transformers.

Trafoboard HD-PH consists of highly densified pressboard layers made of pure cellulose according to IEC 60641, which are bonded permanently by means of phenolic glue. Along with good mechanical and electrical properties, the material has very low moisture content and very good drying behavior. Röchling worked closely with the University of Applied Sciences Osnabrück on its development. Compared to conventional fasteners made of laminated pressboard, Trafoboard HD-PH has very high mechanical strength even at high application temperatures of 90 °C (near boiling). Röchling says Trafoboard high homogeneous strength reduces the risk of cracking and delamination. 

High-precision fit
The low shrinkage behavior of the fasteners and nuts made from Trafoboard HD-PH also ensures a high-precision fit, facilitating the construction and dimensioning of transformers with more accurate tolerances. Compared to polyester resin-bonded laminated pressboard, no styrene is released when machining on CNCs and other systems, releasing no unpleasant smells for employees and contributes to work safety. Learn more at Röchling Engineering Plastics 




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