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Felt Dies

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11 years 11 months ago #2094 by Archived Forum Admin

Replied by Archived Forum Admin on topic Re: Felt Dies

Peter, here is a long response

In the very beginning the wire was coated by passing the wire through a dip bath. The coating was shellac which was actually made from bug bodies. Then there was the oleo resinous materials. These products were generally very low solid content so a variety of methods were used to wipe the excess material off. One way was the GE roller die (a company named Mohawk also made them)made by the Bettners, first at Waldron die and now at Bettner Die. This die was barrel shaped with 3 grooves and slid on a rod that was powered. Depending upon the size of the wire it may have rotated with or against the wire movement. Each die had a spring steel finger that rode on the die making a triangle that the wire was in. 2 legs or sides of the triangle were in the roller and the spring finger was the 3rd side. The dies mounted on a die rod rode in a block which had enamel pumped into it on the bottom side of the roller die. the wire and fingers were on the top side of the die. The size of the groove varied depending upon the size of the wire that was being coated. We used these dies and variations to make magnet wire sizes from about 25 AWG to 50 or smaller. Typically the wire would make 4 to 8 passes through the oven and applicator. In magnet wire the enamel is put on one pass at a time and the material cured in the oven with each pass and then goes through the applicator again. These dies could be used on horizontal, inclined and even vertical ovens.

Waldron Die was started by Howard Bettner's father. I first knew of them in the late 60's. Later Howard started his own company Bettner die. In addition to the GE roller die there is the dog house die which for lack of a better description looks like a dog house. there are also cathedral dies which are really just tall dog house dies. These dies were made of shaped brass and were also split. Variations included steel heads. What was good about these dies was that with a tool like that used to open spring locks, you could spread the die and then slip it over the wire. Since it was partially split, you could do this while the wire was running. This allowed you to change dies on the fly. Dog house type dies could only be used on vertical ovens.

The steel head dies were for larger wire, plus they provided an approach angle much like a drawing die. The brass dog house dies were only as thick as the original sheet. The steel heads were from 3/8 to ½“ square or thereabouts. Steel head dies were an evolution of the dog house dies due to higher viscosity enamels, increased solids and increased wire line speeds. A variation of this die had a clip that fitted around it so that it would not spread during running.

Still another type of die is the solid die. In their simplest form they were can shaped and were first used on vertical ovens. These dies were tapered inside and somewhat similar to a drawing die. These dies were put on the wire like threading a needle. They were not as easy to use or change as the dog house dies but they could withstand very high hydraulic pressure without opening. Biggest problem was if trash got on the wet wire and dried, the wire might break when it jammed in the next die. Wire speed were generally higher with these than the dog house or steel head dies. Viscosities and solids could also be heavier.

In the late 60’s Acrometal developed a felt applicator and variations that could be used on vertical ovens and their horizontal ovens. The logic was good. A dog house die at that time may have cost about $1 - $2.50. To string up an oven with 20 lines making 7 passes $500 and that did not include spares and was only for a single size of wire. You could easily spend thousands of dollars just to have the minimum number of dies needed to run all of the size ranges of the oven. Arcometal’s felt applicator used 6 pieces of felt that combined size was about 6” x 100” inches and cost about $10. It was not perfect but when it worked well it was very good. Acrometal machines were about twice as fast as other machines. The faster the wire speed the more passes you needed. That’s another story.

I also worked with a Spanish machine called a Plasmica which had felt applicators. About that same time SICME and Aumann were also using felts. These felt machines were for wire sizes between about 25 and 50 awg. I don’t know/remember about the Plasmica’s or Aumann felts but I do know about SICME’s.

SICME felts were very sophisticated. The applicator had a base and a top. The base held two felts which were inserted parallel to each other. These felts varied in size but some were about 7 mm wide x 5 mm tall and 40 mm long. The bottom felts had their fibers oriented like a box of straws. Enamel flow was electronically controlled so that in theory only the amount of enamel needed was supplied to the felt. The felt fibers were like soda straws and the enamel moved through the fibers via capillary action. The top felt was different in that its fiber was not oriented and it provided a wiping action. There was one set of felts for each wire line. It was not unusual for the wire to make 10 to 20 passes through the felt applicator. Due to the high number of passes and the small amount of enamel that got on the wire with each pass, the wire speed were quite high; for some sizes as high as 1,500 meters/minute. The felts could be obtained in various densities so that they could be used for different enamels. Fibers getting on the wire only occurred if the wire was rough and ripped them out. For the most part they worked very good.

The holy grail for magnet wire is a high solid, low viscosity, enamel that can be sued for all sizes of wire on all types of machines, etc. It does not exist.

AS solid content of the enamels increased, felts became problematic because the fiber – straws would clog with the solids, etc.

The solution was to go back to solid dies and some of these even had carbide inserts,

GE used a term DV which was the diameter in mm times the speed in meters/minute. 18 AWG for instance is 1 mm in diameter. If you ran about 15 meters/min which was about standard in the 60’s for that size, the DV would be 15. for 30 AWG a good DV in the 60’s would be about 30 to 40. Today there are machines that run 30 AWG at DV greater than 200.

The other holy grails were to be able to coat in a single pass and there have been processes such as extrusion, powder coating, and UV curing and they have been limitedly successful as that the finished product had limited applications.