Development of an airinjection press for preventi

Authors: Hideaki Korai Nan Ling Hiroshi Saotome Takahiko Iida Tomoko Hamano Kensuke Kawarada

Publish Date: 2012/06/21

Volume: 58, Issue: 5, Pages: 417-422

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Abstract

An airinjection press which has holes punched in the heating plates injects highpressure air through the holes of one plate into particleboard and discharges the air through the other plate during press heating The press can manufacture particleboard from highmoisture particles by controlling blowout of the boards In this study the optimum diameter and spacing of the airinjection holes and the effects of pre and postpressing were investigated An optimum hole diameter was not found for the modulus of rupture and thickness swelling for a spacing of either 25 or 50 mm In terms of internal bond strength the optimum diameter of the holes arranged at a spacing of 25 mm was 1 mm but the internal bond strength was not changed by the diameter of holes spaced 50 mm apart Air injection under all hole conditions reduced the formaldehyde emission from the board Prepressing was tested for further increase in the modulus of rupture and internal bond strength but was found to have no effect More efficient use of the airinjection press was achieved by injecting air from the early stages of pressingWhen manufacturing particleboard vapor can become accidentally trapped between the wood particles during the hot pressing process and cause a blowout on the board when the press is opened 1 2 Since this damage occurs at the final stage of the manufacturing process all preceding procedures are wasted and productivity is severely reduced The effective method at present for preventing blowout is to use completely dry particles 3In a previous study 4 a hot press was developed that discharges the vapor trapped inside the particleboard and thus prevents blowout The press has holes punched in the upper and lower heating plates Highpressure air is injected through the holes of one plate to the inside of the board and is discharged from the holes of the other plate The highpressure air forces out trapped vapor and prevents blowout of the board This press is called an airinjection pressIn another study 5 the effects of the diameter of the airinjection and discharge holes on the performance of the boards were investigated It was estimated that large holes of 5 mm could discharge more vapor than small holes of 1 mm and would prevent blowouts more effectively However the study showed that 1mm holes actually prevented blowouts effectively and resulted in higher internal bond strength than 5mm holes This is likely because large holes cause the discharge of binder as well as vapor whereas the smaller 1mm holes reduced the discharge of binder and increased the internal bond strength The optimum air pressure for manufacturing boards of aimed performance was also determinedTo manufacture boards of optimum performance it is necessary to clarify the optimum diameter and spacing of the airinjection holes In this study hole diameters of 1 2 3 4 and 5 mm and spacing of 25 and 50 mm between the centers of adjacent holes were tested to determine the optimum hole diameter and spacing for manufacturing boards Furthermore the airinjection forces out vapor which is likely to contain unreacted formaldehyde 6 Therefore the airinjection press is expected to reduce the formaldehyde contents in the boards and provide a new means of reducing formaldehyde emission It is important to reduce it for preventing sick house syndrome 7 8 9 The effects were also examined in this study and minimizing formaldehyde emissionThe effects on board performance were also investigated in terms of pressing conditions before and after air injection to improve board performance For example a board was pressed for 2 min without injecting air the process is hereafter called “prepressing” and then pressed for 8 min while injecting air The performance of the board was compared with that of a board manufactured without prepressing but with pressing for 8 min while injecting airAirinjection holes on the lower plate of 1 2 3 4 and 5 mm in diameter at a spacing of 25 and 50 mm between the centers of adjacent holes were used There were 121 holes in an area of 250 × 250 mm for the 25mm spacing and 36 holes for the 50mm spacing Holes were also punched on the caul plate upper plate through which the highpressure air and vapor were discharged Also on the caul plate were 121 and 36 holes in an area of 250 × 250 mm for the 25 and 50mm spacing respectively Grooves that were 15mm deep and 1mm wide were also cut connecting the holes on one side of the caul plate to discharge the highpressure air The diameter and spacing of the holes on the caul plate were the same as those on the lower plate For example the hole diameter and spacing on the caul plate would be 1 and 25 mm respectively if the hole diameter and spacing on the lower plate were 1 and 5 mm respectively See refs 4 5 and 10 for further details on the airinjection press

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