Abstract: The invention relates to a continuous dryer for veneer. In addition to terature sensors near the inlet and middle zones to determine heat demand and to control heat input in these zones, the dryer also has an infrared detector at the exit end to determine surface temperature and thus to determine residual moisture of the veneer. The signal from this infrared detector is processed to give a control signal for blowers in the drying zones near the exit. By this means, more precise and reliable control in final moisture is achieved. Variations in dryer load, initial moisture, wood density, and sheet thickness can be better tolerated.

Abstract: A continuous drier for plywood sheets is provided at its inlet end with a nsing device measuring the width and the spacing of the plywood sheets entering the drier. The values measured by the sensing device are transmitted to a control device, which by means of a calculator regulates the speed of a conveyor transporting the plywood sheets through consecutive sections of the drier in such a manner that the plywood sheets follow each other closely on the conveyor without overlapping. Each of the sections is provided with a heater and a ventilator which blows air over the heater, and the hot air is directed by installations onto the plywood sheets. In order to compensate the effect of the varying speed of the conveyor with respect to the drying of the plywood sheets, the control device preferably controls also the volume of the streams of hot air by varying the speed of the ventilators. This will result in a considerable saving of the driving energy.

Abstract: A continuously operating multistage drying installation is provided for drying a workpiece. The drying installation includes a conveyor belt for transporting along a predetermined path a workpiece having two opposite longitudinally extending surfaces and containing excess moisture. A first stage drier is located at an upstream portion of the path. This drier includes guide rollers for turning the workpiece over at least once so as to expose both of its surfaces to heat within the drier to thereby preliminarily dry the workpiece. A second stage drier is provided at the path downstream of the first stage drier for finishing the drying of the workpiece to a desired moisture level while maintaining the workpiece free from being turned over to thereby avoid cracking the surfaces of the workpiece due to pressure applied to the demoisturized and consequently relatively brittle surfaces thereof.

Abstract: Plyboard or the like passes through the successive drying zones of a multone drier, has a varying initial moisture content and presents to the drier a fluctuating degree of loading (surface area). The drying action is varied by adjusting the drying-gas temperature and/or the transport speed of the goods through the drier, so as to quickly match the drying action to the fluctuating drying demand. Instead of measuring initial moisture content per se and degree of loading (surface area) per se, temperature measurements are performed, from which equivalent information is derived, and from which in turn are calculated the values of drying-gas temperature and/or transport speed which must be set on the temperature and speed controllers of the drier.