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Hardwood Record — Veneer & Panel Section 



August 25, 1922 



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By Cnniifsy AiniTicaii Waliuit MjiimfactuiiTS' A^SDciatioli 

 A Four-Piece Matched Panel of Highly-Figured Walnut Stump Wood 



Gluing Panels in General 



The core or crossbands of the panels are coated with 

 glue on a glue spreader consisting of two rollers, the 

 lower one revolving in a bath of glue and the upper one 

 sometimes being coated from another bath of glue re- 

 tained between the upper roller and a trough with its 

 lower edge almost touching the surface of the roller 

 Scrapers or the pressure of the rolls regulate the thickness 

 of the glue layer as desired. 



The panels are built up and placed in the press as soon 

 as possible. Usually with casein glues the panels are 

 grouped with three to five in a set with caul boards placed 

 between sets and at the top and bottom of the entire lot 

 before pressure is applied. The panels are usually left 

 under pressure for 7 to 24 hours and then taken to the 

 drying room. Shorter pressure periods can be used in 

 some cases when necessary. 



One very successful factory using a casein glue has 

 adopted the following standard practice, which is some- 

 what typical : 



With three-ply panels of 1 1 6-inch veneer, cauls are 

 placed every five panels; with plywood 1 1 2 -inch veneer 

 and three or more plies, cauls are placed every four pan- 

 els. About five of these sets, or 20 to 25 panels, are 

 pressed at one time. The time consumed between the 

 gluing of the first panel and the application of pressure 

 is 1 5 minutes. The panels are permitted to remain in the 

 press for about 18 to 24 hours, but if the plant is rushed 

 and all presses are full, a press in which the panels have 

 been pressed for at least six hours is opened and a new 

 stack placed on top. Retaining clamps could well be used 

 instead. 



With glues of the blood albumin type, demanding the 

 use of a hot press, the glue is applied as in the case of cold 

 glue and the panels placed one or more at a time in the 

 hot press. Pressure up to 200 pounds per square inch 

 and temperatures of 2 1 2 degrees Fahrenheit or more are 

 usually applied. The panels are kept in the press until 

 the glue is set, varying from two to several minutes, de- 

 pending upon the thickness of the plies and the panels 

 and type of cauls used. 



Calculation of Pressure in a Hydraulic Veneer Press 



For plywood manufacture determination of the correct 

 amount of pressure to use is important. Results of ex- 

 periments at the Forest Products Laboratory indicate that 

 an excess or a lack tends to produce a weak glue joint. 

 The exact amount of pressure to apply per square inch 

 of panel surface varies with a number of conditions 

 However, pressures of 75 to 1 00 pounds per square inch 

 are within the range of which good results may be ob- 

 tained with most glues and under average factory condi- 

 tions. 



The determination of the amount of pressure applied 

 per square inch of panel on a hydraulic press equipped 

 w^ith a pressure gauge is simply a matter of calculation. 

 With any hydraulic press, the amount of pressure secured 

 per square inch of panel depends upon three factors: The 

 area of the panel, the area of the piston or ram of the 

 press, and the pressure gauge reading. The area of the 

 piston in square inches multiplied by the pressure gauge 

 reading in pounds is approximately equal to the total 

 pressure exerted by the plates. The total pressure exerted 



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