Sizing an oven is critical to achieve the desired production rate and heating characteristics. An oven too small limits your production capabilities, while an oven too large adds expense and wastes valuable floor space. The production rate, heating time and part orientation will determine the size of the oven. Allow extra length to account for end effects near the oven openings, future growth and potential changes in process requirements.

The oven size should be based on the maximum desired production rate. Keep in mind preparation and scheduled downtime. For example, the maximum production rate is 10,000 parts per day with two 8-hour shifts. At first glance, one may think 10,000 parts/day x day/16 hr = 625 parts/hr. However, if you deduct 1⁄2 hour to heat up, 1⁄2 hour to cool down, and 2 hours idle time for breaks and lunches each day, only 13 hours of actual production time will be available, requiring a production rate of 770 parts/hr.

Each process has its unique time and temperature recipe. During the initial purchase of your oven, you will need to determine whether the product only needs to be exposed to heated air, or if it needs to soak once it reaches temperature.

Processes like paint curing typically require the product to be only exposed to heat for a specific amount of time, with several time and temperature recipe combinations to choose from. Operating the oven at a higher temperature shortens heating time, while running the oven at a lower temperature increases heating time.

Heat treating processes typically require the part to soak at temperature for a specified period of time. Metallurgists can find design criteria (time and temperature) readily available to achieve the desired material characteristics. Floor space can be reduced by preheating the part using higher temperature air to bring the part up to temperature more quickly. However, care should be taken so the part does not overheat beyond the desired temperature tolerance. A reputable oven supplier will be able to help determine heat-up times based on previous experience, or through product testing in their lab.

Calculating Heat-Up Time

Here's an easy way to calculate your heat-up time using this example: 800 parts/hr, 5" diameter part size and 30 min heating time.

If the parts are spaced four abreast on the conveyor on 0.5 ft centers (allow for air to sufficiently pass through) in the direction of travel, the oven chamber should be approximately 42 ft long (extra length added for end effects).

800 parts/hr x 0.5 ft/5 parts x 0.5 hr = 40 ft

The chamber length can be shortened to approximately 36 ft by placing 6 parts abreast on the conveyor.

800 parts/hr x 0.5 ft/6 parts x 0.5 hr = 33.33 ft

For more information

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