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PRODUCTS FINISHING — PFonline.com 31 THE VOICE OF FINISHING 80 YEARS percent longer) to cure, cutting production half. If each rack or cart is worth $1,000 and the line does two racks per hour in an eight-hour shift, the line completes 16 racks, or $16,000, in a perfect operation. The line completes 8.73 racks per shift, or $8,730–$7,270 less than what might have been possible with a better oven. Time is Money If the system is a continuous moving line, the same holds true. If a system is bought to do 6 feet per minute, but cannot cure the part properly in the time allotted, the line must be slowed down. Less product can go through the shop in a day, which potentially means less revenue. If the line is run at 6 feet per minute for eight hours a day, the total feet of travel in a day is 2,880 feet. To compare, if the line can only run at 5 feet per minute for the same amount of time, the total feet of travel per day is 2,400 feet. That is a difference of 480 feet a day. How many parts can be produced in that length? And how much revenue can be earned per part? Say the system produces revenue per hour. Let's pick a dollar volume—$10,000 per hour at a 6 feet per minute line speed. The line travel is 2,880 feet per eight-hour shift, or 360 feet per hour. At 5 feet per minute, there is 480 feet less of product through the line a day, and 480 feet equates to 1.33 hours or $13,300 at 6 feet per minute. So you lose more than $10,000 per shift by decreasing the line speed to 5 feet per minute. Another way of looking at it is breaking down the revenue per foot. At 6 feet per minute, the line can earn $80,000 in 2,880 feet, or $27.78 per foot. At 5 feet per minute, multiplying 2,400 feet per shift by $27.78 per foot, the total revenue per shift is $66,672. This is a loss of $13,328 in potential revenue. Changes in this line speed can directly impact the revenue. Here are some things to consider before purchasing: Airflow. In many batch ovens, heated air is intro- duced from a supply duct on both sides of the oven. Air is directed at the part on a cart in the middle of the oven. Heated air impinges upon the part from both sides. This airflow style, known as center flow, is an effective way of heating a part. However, some ovens have a crossdraft airflow where air enters from one side of the oven, is pulled over the part and exhausted on the other side. Another airflow style is downdraft where heated air comes from the top down to side ducts or a floor-mounted duct. Products cure the most effectively when the heated air directly impinges upon the part. If the heated air does not go directly to the part, some heat is lost. Analyze the required airflow and make sure to purchase an oven that meets this criterion. Air changes. In addition to airflow style, look at air velocity, the number of air changes and cubic feet of air per minute; the more air changes, the quicker the air is reheated. Air moves through the oven quicker and should impinge upon the product more, providing a quicker temperature rise or cure. For powder applications, be aware of air velocity until the powder is melted and will not get blown off the product. For wet coatings, consult a coating supplier in regards to flash-off time, solvent pop. Heating capacity. The burner is an important function of the oven because it heats the air. The There are multiple ways to heat an oven, the most common of which are natural gas and electric heat. Completing a batch fve times quicker could add two or more batches per day, which means more product through the shop and more money saved. IMPROVING YOUR OVEN