I’m sure there are guys out there with more current knowledge than I but this is what I know or have experienced.
1) Are you rolling the strip while it is dry? - Answer - Yes.
My experience is rolling it wet. I have used a two stand with a single edging stand and have some knowledge of 3 stand mills but with dual edgers. Rolling with lubricant (a) washes away any dust that occurs, (b) keeps the wire cooler, (c) reduces wear on your flattening rolls as well as the edging rolls. You would not draw copper dry so I am not sure why one would try these extreme shapes dry. Not only do you get dust on the finished product, dust may build up in the edging rollers affecting the corner radii of the shaped product! Lubricant flushes the dust away.
2) Is the ETP rod used as is from the mill or has it been shaved? - ETP rod first drawn to required size. - Answer - No shaving.
Is this an ETP continuous cast product? What size rod are you talking about. Two of the most difficult wire products to make are fine magnet wire and shaped magnet wire. There are some basic reasons for this; the quality of the purchased rod has to be very high, the quality of the material you are going to draw to a very fine size or flatten has to be very good, the end specs for the product are generally very difficult. Transposed cable may be the most challenging of the shaped wire products to make. You have to start with a quality product that has a high quality surface with minimum imperfections, scale, inclusions. You cannot take a great rod product and damage it during processing and expect it to remain high quality.
3) You say that the rod is soft, does that mean soft as it came from the rod mill or was it annealed prior to rolling? - Answer - Soft as it comes from rod mill with an UTS (Ultimate Tensile Strength) of 235 N/mm2. (34,084 psi).
OK, again what is the diameter of the rod being flattened? What are your finished sizes? I am pretty certain that unless you can make the size in a single pass that you might need an intermediate anneal, especially when going wider than 10:1 width to thickness ratio. This is especially true since you have a single edger and corner radii are critical in most cases.
4) What is the final use of this strip? - Answer - Enameling and CTC (Continuously Transposed Cable Copper).
People will tell you all the time how hard their products are hard to make but magnet wire is the most challenging of wire products because in addition to a very thin “paint” coating it has a series of physical and electrical tests that it must pass. Plain enameling of round wire is hard enough, but shaped wire is even harder in most cases. Shaped wires are used to make coils but transposed cable is usually comprised of about 5 to 84 strands of shaped magnet wire to make a cable and you are bending each piece in multiple directions multiple times in a given length. A picture explains it better than I can so please check www.superioress*x.com/magnetwire.aspx?id=3634 .
5) Are you flattening it in a single pass? - Answer - No.
So you are not making the final shape in a single pass, how many passes are you making for a typical size?
6) Your W(idth) to T(hickness) varies from about 10:1 to about 20:1 worse case which seems like a lot of variation without an intermediate anneal, so you are annealing after rolling but are you doing any annealing as a strip but before the final size? - Answer - No.
I may have misunderstood. You are not annealing the copper during the flattening process? Are you annealing it after reaching the final size but before enameling? Do you have a pre-annealer on your enameling system? If you are annealing the wire before enameling, are you getting adequate elongation etc. after annealing and before covering with paper, etc.
7) How many mill stands do you have? - Answer - 3 flattening and one edging. The dust generally pops up during edging.
Shaping the edges and corners requires a lot of force. A 3 stand mill with two edge stands allows you to make a rough edge, flatten some more, complete the edge and then the final flattening stand takes off just a few thousands to complete the desired thickness. A single edge stand often results in over-edging which stresses the edger and will sometimes cause width variations.
Are your edges full radius? - Answer - No
Since you do not have a full radius edge that means you have specs for a distinct corner radius. You have to edge enough to form the corners, but at same time cannot over edge. Are you seeing any copper dust building up in the edge rolls?
9) Do you have an edging stand or two? - Answer – One.
See comment 7 above about having 2 edging stands.
• Shaving the rod would reduce the number of surface imperfections, scale, etc that will pop off during the flattening process. It would also make your corners smoother with less “orange peel” appearance. Unfortunately this would require more equipment and another manufacturing process.
• Since you are flattening and edging dry, you will produce dust which is actually scale, oxide, etc. popping off the rod as it is being deformed. Wet rolling and edging will wash away the copper oxides, dust and fines.
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Another though about edging is that it takes a lot of force to properly form corners. However the edging rolls are genearally mounted vertically and for all purposes "cantilevered" This means the the top bearings for the edging shafts are several inches below the groove on the edging rolls. If you try to edge or reduce the width by much more than 35-40 thousands, you put a lot of stress on the edgers and they will in some cases actually move resulting in a variation in width. Additionally if you are able to over edge the wire you have to worry about the flat strip looking like a dog bone - fatter on edges, thiner in middle. The final flatenning roller fi it does much more than a hard kiss cannot correct the dog bone shape without altering the corner radius.
If the rod is manufactured by a continuous cast process and passes through a non-acid pickle, then the surface will be inherently dusty compared to shaved rod. This will be exacerbated by the increased surface friction if it is rolled dry to form strip.