Insulation materials
Pressboard for Transformers and Electric Motors
Pressboard is a natural product made from cellulose fibres and has been used in transformer and motor construction for many years.
Pressboard and pressboard paper are among the oldest and most proven electrical insulation materials. The natural cellulose product combines good electrical insulation with high mechanical strength at an attractive price.
Pressboard is available in numerous thicknesses and grades. Key quality criteria are density, temperature resistance, tensile and tear strength and dielectric strength. Per DIN EN 60085 pressboard belongs to thermal class A up to 105 C.
A special property is its absorbency: pressboard soaks up impregnants and transformer oil very well, preventing air inclusions and improving heat dissipation.
Diamond Dotted Paper for transformers
For transformer construction, printed pressboard papers are also used, known as Diamond Dotted Paper, DDP or DPP. The paper is printed with epoxy resin in a diamond pattern that bonds the winding layers during curing. Structure, DDP TU and delivery formats are covered on the Diamond Dotted Paper page. For rigid barriers and spacers, pressboard is also available as pressboard sheets from 1.0 to 6.0 mm.
Delivery formats and processing
At Hauler & Hermann pressboard is available as slit rolls, large formats or finished stamped and formed parts. On our slitting lines we convert pressboard from a strip width of 4 mm, see cutting. As stamped parts we process pressboard into cut parts, discs and formed parts to drawing. Combined with polyester film we also supply it as pressboard PET laminate with increased dielectric strength.
Selection criteria for purchasing and design
Material choice depends on the required thermal class, mechanical load, thickness and whether the part is impregnated or oil-immersed. If class A up to 105 C is not sufficient, we advise on alternatives such as polyester film for class B or Nomex aramid paper for class H. Request thicknesses, formats and prices via our contact form.
Frequently asked questions
What thermal class does pressboard have?
Per DIN EN 60085 pressboard belongs to thermal class A, suitable for continuous temperatures up to 105 C. For higher temperatures, polyester films, aramid papers or laminates are used.
What is Diamond Dotted Paper (DDP)?
DDP is pressboard paper printed with epoxy resin in a diamond pattern. During curing the resin bonds the winding layers in the transformer and mechanically stabilises the winding without an extra process step.
In which formats is pressboard available?
As slit rolls from a strip width of 4 mm, as large formats for in-house cutting, and as finished stamped and formed parts to drawing.
Why is pressboard still used despite modern plastics?
Pressboard is economical, mechanically strong and absorbs impregnants and oil very well. Particularly in transformer construction this absorbency is a technical advantage many plastic films cannot offer.
More Products
Pressboard Sheets for Transformer Construction
Pressboard sheets are rigid cellulose boards from 1.0 to 6.0 mm thick, used above all in transformer construction.
Learn more →
Diamond Dotted Paper (DDP) for Transformer Windings
Diamond Dotted Paper is insulating paper with a diamond-pattern epoxy resin coating that bonds the winding layers of a transformer together during curing.
Learn more →
Pressboard PET Pressboard Laminate
This three-layer laminate consists of polyester film with pressboard on both sides.
Learn more →Do you have a specific requirement?
Talk to us. We will find the right insulation solution.