Masonite process

The slurry is pumped iato another stock chest, where wax ia emulsion form, usually about 0.5—1.0% wax-to-fiber weight, and 1—3% PF resia are added. PF resia is also added on the basis of resia soHds-to-dry fiber. Thea a small amouat of alum is added, which changes the pH (acidity) of the slurry, causiag the resia to precipitate from solutioa and deposit on the fibers. Resia is required ia greater quantity than ia the Masonite process because only light bonding occurs between fibers prepared ia a refiner. The fiber slurry is thea pumped to the headbox of a Fourdrioier mat former, and from this poiat the process is similar to the Masonite process. 

Commercial Masonite and Asplund boards and the asphalt-impregnated insulation board were sampled before any commercial heat treatment. The corresponding "thermomechanical" pulps had been produced by pressurized refining of steamed chips. The higher pre-steaming temperature used in the Masonite process resulted In a yield of about 85% as compared to a fiber yield of about 94% of the Asplund pulps, the remainder being dissolved. 

The first industrial hardboard was developed by W. Mason in the mid-1920s he found that a mat of wet fiber pressed in a hot press would produce a self-bonded flat panel with good strength, durabiUty, and stabiUty. The product was patented in 1928, trademarked as Masonite, and commercial production began. Over time several other processes for producing hardboards have been developed from modifications of the original process. Brief descriptions of these processes foUow and a flow chart of the process is shown in Figure 5. 

Alternatives to grinding include explosive depressurization, which is involved in the Iotech (5) and Masonite (16) processes, ultrasonics (17), osmotic cell rupture, and conventional chemical pulping techniques. Explosive depressurization appears especially promising because of its effectiveness and relatively low energy consumption. 

Three major furnish preparation processes (Figure 1) are now in use today. These are the original Masonite wet-form process, the wet form process using pressurized refining, and the dry form process. 

The Masonite Wet-Form Process. Masonite Corpor-ation was founded to exploit Mason s patents and still practices the original furnish-preparation process shown schematically in Figure 1. Cooking is accomplished by charging chips into a vertical cylinder outfitted with a slotted plate at the bottom that supports the chip stack. Below the plate is an hydraulically-operated valve that provides passage to the atmosphere. 

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