Rohit, sorry for taking so long to respond.
Actually there are more than two oven variations. First they can be electrically heated or by burning combustible gases. They can also be radiant, recirculating air, or a combination of the two. Additionally the air can flow against the direction the wire moves, with the wire, or with it in the evaporation zone and against it in the curing zone.
To keep it simple, lets call the area that the wet wire enters after leaving the enamel applicator, the wire chamber
Some ovens are designed for a single wire making multiple passes (anywhere from 5 to about 20 or so) through the oven chamber. Other ovens may have multiple wires making multiple passes through the same chamber. Years ago it was not unusual to have as many as 24 lines running on the same oven.. In most cases the wire sizes were similar and the enamel coating the same. This was because most takeups were gang type and if the sizes or enamel varied you would have to compromise your temperature and speed setting to achieve average conditions. When all wires were the same and enamels the same you could set up the system to maximize conditions – speed, cure, wire quality, etc.
The newer enameling systems generally have from 1 to 4 lines but they run 10 – 20 times faster than was capable 20 years ago. With some of the new systems you have the flexibility to easily run different wire sizes and maximize performance as well as flexibility. Additionally the newer machines are almost always equipped with inline wire drawing so instead of having a 100 Kilo payoff spool, you might have a 1,000 kilo payoff package. Inline wire drawing allows you to have less bare wire inventory plus the payoff line speed is a fraction of the speed of the enameled wire. (May be 2mm at payoff and 0.4 mm at take-up.)
The oldest type of ovens are radiant heating. The wire chamber may have been heated by gas burners, electric heaters, etc. In some cases the heaters were attached to the wire chamber and sometimes just near it. There was very little air movement through the wire chamber and speed was limited because of that.
The first circulated air oven were inclined or vertical and fresh air passed over the electric heaters or gas burner, entered the wire chamber and naturally exited with the wire. At some companies these ovens were referred to as “Smokies” because that is what they did.
The first variation of the circulated air oven occurred when the fume laden air was pulled by a fan back across the burner or heater and then went back into the wire chamber. Some of the fumes were burned by either the flames form the burner or making contact with the electric heating element. This was a very inefficient way to clean the air. About 1947 the first catalyst was developed for enameling ovens. The metal mat catalyst had a precious metal coating; platinum and palladium. When the solvent vapors contacted the active sites on the catalyst the solvents were ignited. Because the air was cleaner, the wire could run faster.
GE recirculating ovens also incorporated radiant panels in the evaporation zone. Air flow was with the wire and the wire chamber was wider at the entrance than at the exit. This meant that the air flow was hotter and faster at the wire exit than entrance. Now that you had different temperatures, the wire chamber was now referred to as the evaporation chamber and the curing chamber. The evaporation chamber is were the wet wire is exposed to heat, solvents evaporated and then as it progresses to the other end of the oven or cure chamber, the semi dry wire is cured.
In the 60’s Acrometal developed the bi-directional recirculating oven. In the evaporation zone the air moved in the direction the wire moved. Just below the half way point of the oven was a section called the interchange. In the curing zone the air moved against the direction of the wire. The evaporation air stream and the curing air stream met at the interchange where it was then returned to the air heating section and through the catalysts. Since the catalyst burned the solvents while cleaning the air, the heat released from the burning solvent was recovered and used to cure the wire. This reduced fuel or electrical consumption.
You have asked which type oven works best. The answer to that is what kind of product are making? Copper, aluminum? What type enamel? Single enamel, dual, triple, bondable, etc? Are you make standard spec or special dimensions.
Depending upon those answers can have an effect on what type oven is best.
Richard
