Tuber, you posted “Has a porous wheel ever been used/considered? The wheel would pick up enamel at one spot and apply the enamel at another. We used to use the concept in the medical industry to apply small amounts of liquid to blood sampling tubes.”
I don’t know if one has been used or not but I would be concerned that if a porous wheel worked that the performance would vary when the solids in the enamel clogged up the porous wheel. I am pretty certain that clogging would occur because with felt applicators, the felts would eventually clog.
In the 70’s Acrometal had a roller dies less applicator which had for each enamel three rolls. The first was the grooved applicator roll which had an enamel bar which supplied enamel to the grooves. Since the size of the grooves was fixed, you varied the amount of enamel in a groove and or the rpms of the roller. On some machines you could also change the rotational direction of the roll with it rotating with the wire for smaller wire and against the wire for larger wires. The oven was cross strung with 10 lines per side of the oven and they made 5 to 7 passes (total 50 – 70 wire) for the base coat enamel. The overcoat applicator was 2 passes. When you needed more passes you dropped lines.
The concept was that the applicator roll applied the enamel and two wiper rolls removed the excess. The wiper rolls generally rotated against the direction of the wire. A meniscus was formed between the wire and wiper roll and pulled enamel off the wire. A soft brass blade was used to wipe the enamel from the roll so that the roll was always clean at the point where the wet wire contacted it.
A roller die less applicator cost a lot more than a die applicator however its operating cost was less. A 20 line oven designed for 8 total passes required 160 dies for a simple set up. Since the wire range on an oven might be 10 – 12 awg sizes, you could easily a minimum of 2,000 dies and at a cost of $2.00 to $6.00 (1970’s) you could easily spend $12,000 to $20,000 just to have enough dies for each oven system’s range of wire sizes. Additionally the dies would wear out and require either resizing or replacement. You could easily after your initial investment, spend several thousand dollars more per year per oven.
Vertical oven applicators had opposed wiper rolls. With the horizontal applicators, the wires were on top.
I don’t know how many companies used these but I know that Hudson Wire was very successful with the roller dieless applicators.
The roller dieless evolved into the felt roller dieless applicator. A set of felt holder took the place of the grooved rollers. The wiper rolls were still there to wipe of excess enamel. This worked good for horizontal systems and pretty good for vertical ovens. Biggest problem was regulating enamel flow/pressure and finding the correct or best wiper roll speeds. The Acrometal V12 and V18 that we had were operated at speeds that were about 40-50% greater than the typical GE oven at that time. When we made our own V21 we got a substantial speed increase. The ovens were sensitive to variations in the enamels; when they ran good they were great and when they ran bad they were horrible. On a good week running 18 awg polyester we could make 150 to 200,000 pounds with 3-5% scrap. On a bad week we would be up and down and lucky to make 50K of good wire. Again the smallest variation in the enamel was critical!
