Fiberboards 2867 



are water sprayed to increase moisture content 1 or 2 percent, spread with a 

 quick setting glue to form sandwiches of desired thickness, pressed in a 50-inch- 

 high pile of sandwichs, and unstacked. In the coating line following, boards are 

 cleaned, water sprayed to equalize surface moisture, curtain coated, ovendried 

 at 500°F for 30 seconds, and cooled. Coated boards then pass through a bottom- 

 head planer. Those routed to the asphalt line pass through a roll coater which 

 smoothly applies hot asphalt to both surfaces and all edges, and then through hot 

 rolls (450-500°F) to "strike" the asphalt into the panels. Trademarked and 

 bundled asphalt-coated panels are then warehoused. Painted panels for fabrica- 

 tion into ceiling tile are sanded on the unpainted side, sawn to tile size, drilled, 

 edge machined, roll printed, dried, boxed, and palletized (Dyer 1960). 



Acoustic tile is manufactured in Vi-, Vs-, and 1-inch thickness — the latter 

 laminated. Holes in acoustic tile are either drilled or punched about Vsths of tile 

 thickness. 



Roof insulation is produced !/2-inch thick and in thickness multiples of Vi- 

 inch; it is usually imbedded in hot asphalt or pitch on roof decks. 



Asphalt impregnated sheathing is Vi- or 25/32-inch thick, the latter lami- 

 nated. Panels 4 by 8 feet and larger have square-cut edges for butt jointing; 2- by 

 8-foot panels have a V-joint on the long edge to form a tongue-and-groove joint. 



Embossing. — Decorative patterns can be embossed by passing surface-wet- 

 ted boards under a profiled hot roll (500°F). The hot roll boils the water on 

 contact, softening the board as the pattern is pressed into its surface. Smooth hot 

 rolls are similarly used to iron (flatten) surfaces. Bevels cut in decorative insula- 

 tion board are immediately wetted with paint and ironed with a hot shoe. 

 Embossing and ironing are followed by another application of paint, usually 

 water-based, and white. 



HARDBOARD FABRICATING 



Sanding. — Hardboard printing lines cannot tolerate thickness variations of 

 more than 0.010 to 0.015 inch; hardboard for some furniture applications and for 

 garage door panels also must be accurately thicknessed to fit grooves machined 

 in wood rails. Thickness of S2S wet-formed boards is normally accurate enough 

 for these purposes, but SIS panels must generally be back sanded to thickness. 

 Sanding of dry -process boards not only thicknesses them, but also improves 

 their printability. 



Single-head, wide-belt sanders carrying abrasive grits of 24 to 36 may be 

 located after board humidifiers and before panel trimmers. An open-grit abrasive 

 belt of these grits will sand 40,000 to 50,000 panels. To improve surface quality 

 with little stock removal some finishing lines use 320-400 grit. (See sect. 18-14 

 for further discussion of abrasive machining; see also fig. 18-137 for illustration 

 of a wide planer with solid carbide knives sometimes employed to thickness 

 hardboard.) 



Trimming. — First-pass trimming of hardboard typically yields standard- 

 width boards (4- or 5-feet wide). S2S boards may show chipped edges unless 

 rounded by cutterheads following the trim saws. Shallow grooves may be 

 machined the length of each panel to give a random-width plank effect and to 



