The next several items on the work order can be covered briefly.
Finish Inside: Mill finish and Finish Outside: Mill Finish merely means there is no polishing done on this head. I’ll get into polishing when I post about my 7-year vacation from flanging when I operated a polisher.
Form Code: Cold Formed & Pickled means there is no heat treatment performed on this head. All stainless steel heads get pickled, or acid cleaned. Carbon steel, aluminum, and other exotic metals don’t. Titanium get sand-blasted.
Diameter: 90 inches OD is self-explanatory, with the OD meaning the measurement is to be taken on the outside of the head. We check the diameter until we come close enough to being in size that we need to start checking the circumference. Then during the final inspection we check the diameter to check for out of roundness. By ASME code we are allowed to be 1 per cent of the diameter out of round. That means this 90 inch diameter head could be as much as 7/8 inch out of round. We are rarely more than 1/4 inch out of round, usually 1/8 inch or less. Also, it’s good to compare the final diameter to the final circumference and make sure they agree, just to ensure we are reading our tapes correctly. It is easy to be off by an inch, especially when checking an inside circumference with a wheel. When you have so many numbers whirling through your head all day it is easy to mis-read a wheel or a tape.
RD: 90 inches specifies the shape of the dish. This is mainly for the press operator, to inform them which dies to use. We just find the radius template the press operator used to press the head and check the final radius with it. We can use too much side roll pressure and distort the radius just below the icr, causing crush up. Or we can make a head small. When we pull it back out into size the radius gets deeper than how the press operator pressed it. This causes endless disputes between flanger operators and press operators. If the radius of a head ends up too deep or too shallow, the blame shifts back and forth. We claim the head wasn’t pressed deep enough or was pressed too deep to start with. The press operator will claim we crushed-up the radius if it ends up too shallow, or that we made the head small and pulled it back out if the radius ends up too deep. A lot of finger pointing.
ICR: 1 inch denotes the size of the inside corner radius.
In this drawing, the icr is the curved part of the head with the D.R., or dish radius, above it and the S.F., or straight flange, below it. We flanger operators bend the metal on the edge of a pressed head around an icr roll and make the metal below the icr, the straight flange, straight. The customer can request any size icr. On the flanging machine I usually operate, we can fashion an icr from three-quarter inch up to thirteen and a half inches. On the larger flanging machines the corners can be much larger. The general rule is that an icr can be bigger than requested, but not smaller. We have many different sized rolls we can bolt onto the machine for different icr’s. If a customer requests a size that we don’t have a roll for, we can use the closest icr roll we have, then either make the corner tight by using a lot of side roll pressure or leave the corner loose by using little side roll pressure.
The icr is the critical area of a flanged head. The icr roll is bolted onto the end of the drive shaft, and the rotating shaft is what makes the head spin in the machine. This is where the head gets thinned out, because the metal as it spins is squeezed between the forming roll and the icr roll. Also, if the head has grease in it, or if the operator tries to flange too quickly, or if the operator tries to trim the edge too quickly, the head can skid and the icr roll will mar the surface. This is especially bad on stainless steel heads, since these skid marks will rust. Also, if the flanger operator uses too much pressure he can leave rough ridges on the outside of the icr. Also, if the flanger operator makes a head small and has to pull it back out, it is the icr area he works. He can make humps in the icr doing this. Which he has to roll out. And pulling a small head back out into size can also make the icr too big. So the operator will have to tighten the corner back up once the head is no longer small. There is a lot of work to maintaining a good icr.
Rolling out humps in an icr of a head that has been made small and pulled back out into size is one of the hardest things to learn on a flanging machine. There is a real skill to doing this. Of course it’s better not to make a head small to start with, but inevitably you will. Geoff L. tried installing a laser on a flanging machine that would warn you if you were making the head too small. But that never worked. There are just too many variables to consider. A sixty inch standard head with a one inch icr is much different from a sixty inch elliptical head with an eight and five eighths inch icr. And the flanging machines vibrate too much, disrupting the laser. And carbon steel heads stir up too much dust, making the environment too dirty for the lasers to work properly. It just didn’t work out for our shop.