Next up on the work order is straight flange:
An inch and a half straight flange is the default. But customers can order whatever length straight flange they want. And they do. The trickiest straight flanges are the ones that aren’t there. Zero straight flange. The circumference measurement is taken at the top of the icr. Very difficult. Also difficult are straight flanges of 3 inches or more. That is a long stretch of metal to keep straight. The flanging machine I normally run is rated to do a 2 and 1/2 inch max straight flange, so for ones longer than that I have to get creative.
You wouldn’t think making something straight would be that difficult. But there are no dials on a flanging machine that tells us we have the straight flange straight. So we eyeball it while the head is spinning. I had a hard time learning how to do this. Roy H., who trained me, told me to line the edge of the spinning head up with the lines of the cement blocks in the wall in front of my machine. Now I can glance at a head and tell how straight the flange is. But it took a long time to learn this.
When I think the flange is straight I stop the machine to check it. I do this by placing a straight edge across the head, then reading my protractor off it. It has to read between 88 and 92 degrees. I am allowed by ASME code to be toed in or out 2 degrees. Except for one of our biggest customers that wants no toe in or toe out at all. Also, the straight flange is held by the ASME code to plus or minus a quarter-inch in length. So a 1 and 1/2 inch straight flange can be between 1 and 1/4 and 1 and 3/4 inch long.
Our engineers have some convoluted formula for figuring blank size. If the metal circle is too large to begin with, then there is too much straight flange, which not only makes the head needlessly difficult to flange but also creates excess metal to be machined off. If the the circle is too small, then we come up short on the straight flange. The formula has to account for the size of the head, the length of the straight flange, the size of the icr, the depth of the radius, even how much the metal will stretch while being pressed. Extra metal can always be cut off, but if there isn’t enough metal there isn’t much you can do about it. So they tend to order slightly bigger circles than required, to ensure there is enough metal. That means we spend a lot of time machining off a lot of excess metal.
You have to be careful with heads with only a 1 inch or less straight flange because the head will be in size before you realize it. I am used to a 1 and 1/2 inch straight flange, since that is what most heads call for, so when you have a head with only a 1 inch straight flange and you form it with the 1 and 1/2 inch you are used to, then you are in trouble because that head will be way small. On the other hand, a straight flange longer than 3 inches can be very difficult, especially if the metal is thin. By the time you flange that much metal above the icr roll it is usually hardened, or wrinkled, or bowed. And if extra large blanks were ordered to ensure there is enough metal, you can easily end up with 4 or more inches of straight flange. I have actually formed a head with 6 inches of straight flange. That was a challenge.
Of course,the straight flange and the circumference have to agree. If you have a head with the correct circumference but it is toed out 5 degrees, then by the time you straighten the flange that head is small. Or if you have a head with a perfectly straight flange, but it is still a half-inch big in circumference, then you aren’t finished, you have to make the head smaller, which will mess up the perfectly straight flange. It’s a constant struggle.
One other note about the straight flange. It can be measured inside or out, depending if the circumference is to be measured inside or out. The customer determines which measurement he wants, and the straight flange has to agree with this. You wouldn’t think it would make any difference, but it is much easier forming a good straight flange if you measure it on the outside. Don’t ask me why. “Flanging machine bery mysterious.” I paraphrased Mathiessen from “Far Tortuga”, and I meant to write ‘bery’.