Almost all hardwood plywood is available in several optional cores or substrates. This is the material over which a thin decorative face and back veneer is applied. Core selection is often a compromise between performance characteristics and price.
There are three categories of cores: veneer, composite and hybrids or “combination cores”.
Veneer Cores are comprised of an odd number of wood veneers laminated in alternating grain directions to achieve the desired panel thickness. Core veneers may be softwood or hardwood and the grades may vary significantly. While they will be balanced from the center out, individual core veneers may be of varying thickness. In addition to the species, grade and number of core veneers used, how the cores are assembled affects the finished panel quality and costs.
• 1 Step, or Conventional Construction is the least expensive way to manufacture a veneer core panel because all laminations including the face and back veneers are assembled and pressed at one time. The drawback to this method is that imperfections in the core veneers can transfer to the surface as high or low spots on the face and back.
• 2 Step, or Calibrated Blank Construction is more costly because it takes more time to construct. Core veneers are assembled and pressed without the face and back. The resulting “blank” is then sanded to a calibrated tolerance before going back to the press with face and back veneers applied. The resulting panel is smoother and has better tolerances.
Composite Cores are either particleboard or medium density fiberboard (MDF).
• Particleboard is perhaps the least expensive core for hardwood plywood because its particles are less refined than MDF, yet it is perfect for many applications. It is smoother and more uniform than veneer cores and available in Class A fire ratings as well as no-added-urea-formaldehyde constructions.
• MDF is manufactured from highly refined wood particles into an extremely dense panel that in addition to being very smooth and uniform in thickness, will machine more like solid wood than either particleboard and veneer cores. MDF is also available in Class A fire rating and NAUF. MDF is available in both thin and thick panels.
Combination Cores are a hybrid of veneer and composites that take advantage of the best properties of both by using veneers to build the center portion and thin MDF on the outer layer of a core, directly under the face and back veneers. Combination cores are proprietary to, and branded by hardwood plywood producers.
These cores are popular with case good manufacturers for their ability to support high value, very thin face and back veneers, especially in geographic areas with very low humidity which can cause veneers to split or “check.” These cores typically carry a Class C fire rating, and can be ordered in no-added-urea-formaldehyde formats.
Source: States Industries. For more information visit StatesInd.com, (800) 626-1981.