LEWCO, Inc. was recently challenged to design two conveyor ovens that could not only handle a high production rate of a soil testing laboratory, but also accommodate their limited floor space. The result: two custom electrically heated, vertical conveyor ovens. The ovens will be used to dry moisture from the soil samples prior to testing. The samples will be carried by sheet metal trays indexed by a series of sprockets and chains. Each oven contains 296 trays with a total live load capacity of 8,000 lbs. At the current index rate of 15 seconds, a given tray takes 8 hours to pass from load end to the unload end. The oven is equipped with three top mounted heater boxes. The heater boxes provide independent temperature control zones each with a process controller and a redundant high limit controller.
The oven incorporates a custom LEWCO designed Human Machine Interface (HMI) that communicates to a programmable logic controller (PLC). From the HMI, the operator can monitor a number of things including the status of the oven, control modes and set the temperature and product dwell time. The oven data will also communicate via Ethernet to an enterprise control system.
The oven was equipped with three different operating modes dual, single, and maintenance. For maximum production the oven may be placed in dual operator mode where there will be one person loading and one person unloading the oven. During off peak production times the oven may be placed in single operator mode where one person will both load and unload the oven. Finally there is a maintenance mode which allows the oven conveyor to run continuously.
LEWCO provided a solution to suit this continuous oven application. According to Controls Engineer Alisha Fannin; “We had quite a few meetings with the customer to determine just how the oven was to operate. Creating a specially designed PLC program and HMI to enable the different operating modes and yet maintain a simple and clean user interface proved to be challenging. However, keeping the customer involved throughout the design process enabled us to supply an oven capable of meeting their diverse needs.”
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