Cam-Operated Kiln Control System

The objectives of the study were to compare the accuracy of a temperature recorder-controller equipped with nitrogen gas-filled bulbs and pneumatic transmitters to a system having vapor-filled bulbs and to a recording potentiometer with thermocouples; to investigate the possibility of a reduction in the drying time of partly air-seasoned, heavy-segregation 4/4-inch redwood lumber of the “Clear” and “A” grades by gradual rather than step-by-step changes of kiln conditions; to determine whether results obtained in a 5,000 board foot-capacity kiln could be duplicated in a commercial kiln; and to determine the effectiveness of single-point control in a 100-foot triple-zone kiln. The nitrogen gas-filled, expansion-type kiln recorder-controller gave more accurate temperature control up to 140?F, than commonly used vapor- or liquid-filled systems. Large fluctuations around a preset temperature could be prevented by proportioning control valves. A continuous change in kiln conditions by cam control resulted in a shorter drying time that when a step-by-step kiln schedule was employed. A cam-controlled system may also save time in kiln personnel and prevent errors that may be encountered with hand-set kiln instruments. Multizone compartment kilns may be controlled by a single-zone recorder-controller if handset valves leading to the steam coils of other zones can be adjusted to equalize the temperature throughout the kiln. Such control is not recommended if easy readjustment of these hand valves is not possible.

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