Electric Preboarding Oven Improves Production Efficiency

chromalox rad 1800 w

The Challenge
An old steam preboarding machine used for shaping hosiery needed to be replaced.

The Solution
A specially-built preboarding oven equipped with 108 Chromalox Electric Radiant Heaters rated at 800 watts each was designed by Chromalox application engineers.

In this process, hosiery passes through oven between vertically mounted heaters on metal forms. Air enters the top of the oven in a plenum, then is channeled down over the forms and carried out the bottom. The production rate is 38 to 48 dozen pairs per hour depending upon the wool content of the hose. The oven operates 24 hours per day and is shut down only over weekends. This eventually will be a closed system with some air recycled to temper the air on cold days and lower the relative humidity on very humid days.

Conveyor speed is adjusted by using a variable pitch pulley on the motor drive. A three-position switch, forward, stop and reverse, is located on top of the instrument panel near the operator. The variable pitch pulley was removed from the fan motor because one fan speed would handle all drying speeds.

The oven has three zones, each controlled by an off-on, 30 second time cycle input controller. The first input controller is set at 100% at all times and the other two controllers are varied with the percent of the wool in the hose. The exit controller is always set at low to prevent scorching, as the hose are almost dry when they reach the exit zone. There is a fuse for each bank of three heaters.

Additional ovens are planned using Chromalox Electric Radiant Heaters as heat source. New developments in handling are planned as well, particularly a stripper to remove hose from forms to a conveyor. Management calculates that production efficiency can be increased another 15 to 20%.

Benefits

  • Provides substantially greater production efficiency - about 28% - over the old steam form method.
  • Operating cost is considered reasonable (2 1/2 cents per dozen pair dried).
  • It is completely safe.