Doors and paper honeycomb core
Paper honeycomb core has been a popular filling material in doors for many years. Not only solid, but also moulded doors very commonly are filled with paper honeycomb core.
Even fire retardant doors and steel doors are at times filled with paper honeycomb core, for this the paper honeycomb core has smaller cell sizes than for common internal doors.
There are clear benefits to using paper honeycomb core as filling material for doors.
Paper honeycomb core is packed and stored in a compressed state onto pallets. When used during production the paper honeycomb core is expanded to it’s final form, generally some 10 times larger.
The benefits of lower transportation costs and lower storage costs and space requirements are significant.
Hollow core door comprises a framed door in filled with structural paper formed into a honeycomb pattern to provide support and rigidity which is glued in place between the door skins. As there are no solid materials within its frame, these doors are lightweight and are an affordable alternative to solid core timber doors. The door surface is usually wrapped with veneer to achieve a uniform appearance. Often, the veneer is sanded and varnished to create a striking appearance. However, hollow core doors are not suitable for exterior use for safety reasons as they are easy to break. Honeycomb paper The honeycomb shaped inner core material is made from layers of paper or cardboard, bonded together in parallel and uniformly spaced. When it is expanded for use, it forms a honeycomb configuration with hexagonal cells. It is manufactured from recycled paper and generally is non-toxic. The honeycomb sheets can be made of various thicknesses and cell sizes to cater for a variety of applications. It can replace the solid filling materials used in solid core doors.
A typical section of hollow core timber door.
Honeycomb structure enhances resistance to perpendicular crushing forces. The following are key features of honeycomb in-filled timber doors or panels:
CAUSES OF WARP AND TWIST IN TIMBER DOOR PANELS “Warp” is any distortion in the panel itself and does not refer to the relationship of the door to the frame or jamb in which it is hung from. Warp is mainly due to timber expansion and contraction caused by temperature and humidity changes. The term “warp” also includes bow, cup, and twist, and they are measured by the deviation from a straight-edge or string placed on the suspected face of the door at any angle (i.e. horizontally, vertically, and diagonally) with the door in its installed position. The chances of warpage are higher in longer panels, because of its higher length to width ratio. HINGE BLOCK OUTER FRAME LOCK BLOCK PAPERHONEYCOMB CORE VENEER
Warp or twist are caused mainly by expansion and contraction of timber. Occurrences of warp and twist can be minimized with infill like honeycomb papers, especially for tall panels. During the production stage of the honeycomb paper, moisture content is about 14% (8% from paper, 6% from glue). This can be reduced and its pressure strength increased through an expander cum dryer in the manufacturing process. The highest pressure strength can be achieved at 3% moisture content.
Relationship between moisture content and pressure strength.
Honeycomb papers stretched mechanically and dried