Drying ovens fall short
WEB PROCESSING chief executive Francis Woodruff is known for his candid views on technology. He told Converter about his concerns regarding modern day oven design.
“The concept of efficient drying is and has been well known for many decades and most, but sadly not all ovens sold today, utilise most of the established techniques of air temperature control, velocity, moisture or solvent content to achieve efficient and safe drying.
“However one concept seems to be sadly missing from the design of the majority of ovens resulting in slower running speeds or longer and therefore more expensive than necessary ovens and certainly greater energy usage. At a time when energy is so expensive everything that can be done to minimise its usage should be the target for all designers.
“Work that Web Processing has done over a number of years and with a variety of substrates both coated and impregnated, flocked and laminated has shown that a further saving of some 12-15 percent can be designed into the operating efficiency of the oven.
“If we assume that the air temperature and impingement velocity are operating at their optimum, it will often be found that the concentration of the water or solvent immediately above the web and across most of the web width will be high; high to the extent that the further evaporation of the volatile components of the coating will be reduced.
“By the incorporation of an air extraction system across the web and between each of the air impingement nozzles, this volatile saturated atmosphere can be more rapidly removed from the surface of the web than can be achieved if air removal is only effected along the sides of the oven.
“Clearly the degree of improvement will depend upon a number of factors but, as a generalization, the speed of the line can be increased by 12-15 percent by the installation/operation of this rapid air removal system, or at the design stage the overall length and cost of oven can be reduced by close to the same percentage as the cost of say three metres of oven is more expensive than the addition of the more efficient air removal system throughout the length of the shorter oven.”
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