Definition of a Changeover for Tube and Pipe Mills
There are many machine configurations that can speed up a changeover, such as rafted sections, quick change fasteners, etc. However, most important is just a matter of having your mill and tooling in good dependable condition and organizing the rest of the efforts of the changeover process.
Many ask the question, "How long should a changeover take?" This is a wide-open question, with no specific answer. Why? Because the variables are too numerous and wide spread. Not all mills are of the same configuration. Some are more operator-friendly than others. Some have more passes, which require more tooling than the next. Is the mill in good, dependable condition? Some claim to change the mill over in an hour but spend hours, if not days, chasing all the problems the mill or tooling might have before good tubing is produced.
Other factors that affect the speed of a changeover are:
- How many men are available for a changeover?
- What is the mechanical dexterity of the men?
- Do they have the right tools to do the job?
- Do they have all the tools, tooling, pieces and parts organized, ready to use and go on the mill?
- Are there mill changeover procedures to follow, or does each man go his own way?
- Are there set-up procedures to follow to properly set-up the tooling as it was designed. Or, do they just set it up by a seat-of-the-pants approach?
- Are there tube mill operating procedures in place for all to follow, so all are working toward a set standard?
The mill and tooling are fixed items, which if maintained properly, will perform the same each and every time they are used. The large variable is the human factor. How we maintain, set-up and operate the mill. I'm sure everyone has seen the scenario. Jim has his way of setting up the mill, and George has his way, which he says is better. Night shift has their way, day shift yet another and so on and so forth.
The whole process is predictable and can be repeatable each and every time. This is why written procedures must be a part of any operation. These procedures not only allow for predictable and consistent set-ups, but can be used for trouble shooting when trouble arises and training of new personnel.
Mill Integrity and Alignment
It is very important that the condition of the mill and its alignment can be counted on during a changeover. If the mill is in poor condition, and out of alignment, your changeover times will undoubtedly take longer.
The entry table has a very important job to do. It must guide the material, centered, to the first breakdown pass. Material introduced off-center from the start will cause problems all the way through the mill.
- Are the guide rolls in good condition? No grooves or broken out sections.
- Check the shafts the guide rolls mount on for proper O.D.
- Check the bearings of the guide rolls.
- Check the lead screw adjustment. Ensure it is tight, not to allow side to side end play, allowing the guide rolls to hold the strip steady on center.
- Check the blocks the shafts mount to. Make sure they are tight within the assembly.
- Ensure the unit is centered with the center line of the mill.
- Make sure the unit is at the proper height.
- Ensure the unit is as close as mechanically possible to the first breakdown pass.
Ensure the following:
- O.D. of the shafts is within tolerance.
- No broken out keyways.
- No loose bearings, bearing blocks, inboard and outboard stands.
- No bent shafts.
- Top shaft parallel to bottom shaft, all passes.
- Shaft shoulder alignment is within tolerance, top shaft to bottom shaft.
- Stand to stand, section to section, are in alignment, vertically and horizontally.
- Driven shaft sleeve I.D. in outboard stands, not oversized, out of tolerance.
Faster changeover features of outboard stands.
- Type of driven shaft fastener, to allow for quick removal and installation.
- "C" type washer.
- Hydraulic nuts.
- Wing nuts.
- Hold down of outboard stand.
- Flip up clamps.
- Slotted bases on outboard stand.
- Single point adjustment, for top driven shaft, ensures coordinated adjustment of inboard and outboard stands during changeover and set-up. This feature also ensures the top shaft stays parallel with the bottom shaft.
Side Pass Stands
Ensure the following:
- O.D. of shafts is within tolerance.
- Shafts are tight within the blocks they are mounted to.
- Blocks are tight within the gibbs that retains them.
- In and out, side to side adjustments are tight, and no end play.
- Up and down adjustment in good repair, supporting the unit plumb.
- Tie bars, where used, should be in good repair with all fastener parts intact.
- Units that are adjustable in height are set to proper metal line.
- Convert brass washers, where used, on the top and bottom of the side rolls to thrust type bearings. This eliminates the wear variable of the brass washers.
- On "M" style mills, using solid tooling, the metal line drops, thus requiring the side roll passes to be lowered to match the new metal line. Part of a good tooling maintenance and set-up program, is knowing exactly how much to drop or raise the metal line of different roll sets at the time of set-up, not to just guess at their height. This not only saves valuable set-up time, but affects the quality of the end product as well.
Equipment Features for quick changing of side rolls
- "C" washers to release the tie bars.
- Top plates that hold tooling in place can be of "Flip top" design, where applicable.
Ensure the following:
- Is the unit in good mechanical repair and dependable? This can be very detailed, for there are many various weld box configurations and features out in the industry. Use common sense in evaluating the integrity of the components.
- For those units which have the weld rolls held in by clevises - have extra clevises on hand, with weld rolls already installed for fast set-up during a changeover, and for quick replacement during a run.
- Metal line is affected by roll changes here as well on certain weld box designs. Know the O.D. of the weld rolls that are being installed and how that will affect the metal line of the weld box.
- Set the weld rolls up with a plug gauge. The plug gauge should be the same diameter as the welded tube size, to match the radius of the weld rolls. This is especially effective in three- and four-roll weld boxes.
Turks Head Units and Straighteners
- The same application of ensuring the integrity of the unit as previously described applies here as well.
- For those units with clevis mounted rolls, have extra clevises ready to go to speed-up changeovers.
- Set the rolls up with a set-up plug. This is same principal as described for the weld box. Once set, check for even clearance between all rolls. The use of a plug gauge is especially effective for square and rectangle set-ups.
- Is all the tooling organized, ready to install on the mill?
- What equipment is available to help install the tooling?
- Jib cranes with tooling fixtures can save valuable time, and are safer for the operators during the removal and installation of roll sets.
Tooling Maintenance Program
- Is there such a program in place? Or, does the tooling just get removed from the mill, put on a shelf or in a box until the next time it is to be installed on the mill?
- Proper tooling maintenance is essential in aiding in faster changeovers. The tooling, like the mill, must be in good condition, so as to not cause problems during the installation and set-up.
- Do you know how much life is left in the tooling?
- Will it make this next run?
- What condition are the pieces and parts, such as the spacers?
- Are they to the correct length?
- Do you have rim clearance figures from the last successful run, so as to start where you left off the last time? This can save valuable time in fine-tuning the mill and running prime product with minimum scrap.
- Included in a tooling maintenance program is more than just the tooling itself. It should include:
- Prints of the tooling
- Set-up charts
- Rework records
- In house maintenance inspection sheets
- Rim clearance sheets
- Cost record
It is quite obvious that the material covered in this document needs to be in place no matter what type of equipment is used. Even if a company has all the latest in quick-change equipment, this equipment will still need procedures in maintenance, set-up and operation to make it successful.
You must be consistent and have a disciplined process for it to be effective. Many programs are setup, but then not monitored or disciplined. The standards that need to be set in any operation require the participation of everyone involved. This includes management, maintenance, operators, supervisors as well as the general laborers. All need to share in the responsibility of making the process work.
Robert A. Sladky
Vice President Tube Mill Engineering