Faster, More Efficient Changeovers for Tube and Pipe Mills and Equipment
Definition of changeover: Going from running good tube of one size to running good tube of another size (not just changing out the tooling).
- There are many machine configurations that can speed up a changeover, such as rafted sections, quick change fasteners, etc. However, just having your mill and tooling in dependable condition and organizing the rest of the efforts of the changeover process go a long way.
- Many customers ask how long a changeover should take. This is a wide open question with no specific answer. The variables are too numerous and widespread. Not all mills are configured in the same way. Some are more operator-friendly than others. Some have more passes, which require more tooling. Is the mill in dependable condition? Some customers 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 Changeover Speed:
- How many employees are available for a changeover?
- What degree of mechanical dexterity do the employees exhibit?
- Do they have the right tools to do the job?
- Do they have all the tools, roll tooling, pieces and parts organized and ready to go on the mill?
- Are there mill changeover procedures to follow, or does each employee go his own way?
- Are there procedures to properly set up the tooling as it was designed or do they just set it up by the seat of the pants approach?
- Are there tube mill operating procedures in place for all to follow, so all are working to the same standard?
- The mill and tooling are fixed items, which if maintained properly, will perform the same way 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 must be predictable 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 setups, but can be used for training new employees and for troubleshooting when problems arise.
Mill Integrity and Alignment
- The condition of the mill and its alignment must be reliable. If the mill is in poor condition and out of alignment, the changeover will undoubtedly take more time.
- The entry table has a very important job to do. It must properly guide the material into the first breakdown pass. Material that is not centered 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 that 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 and does not allow side to side end play, allowing the guide rolls to hold the strip on center.
- Check the blocks that the shafts mount to. Make sure they are tight within the assembly.
- Ensure the unit is centered in the mill and 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 or bearing blocks in the inboard and outboard stands
- No bent shafts
- Top shaft parallel to bottom shaft for all passes
- Shaft shoulder alignment within tolerance, top shaft to bottom shaft
- Stand to stand, section to section, are in alignment both vertically and horizontally
- Driven shaft sleeve I.D. in outboard stands is not oversized or 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 setup. This feature also insures 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 gibs that retains them.
- In and out, side to side adjustments are tight with 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 height-adjustable 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, requiring the side roll passes to be lowered to match the new metal line. Part of a good tooling maintenance and setup program is knowing exactly how much to increase or decrease the metal line of different roll sets at the time of setup. This not only saves valuable setup time, but affects the quality of the end product as well.
Equipment Features for Quick Changing 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:
The unit is in good mechanical repair and dependable. This can be very detailed, for there are various weld box configurations and features out in the industry. Use common sense when evaluating the integrity of the components.
- For units that have the weld rolls held in by clevises: Have extra clevises on hand with weld rolls already installed for fast setup 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 up the weld rolls with a plug gauge. The plug gauge wants to 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 units with clevis mounted rolls, have extra clevises ready to go to speed up changeovers.
- Set up the rolls with a set up plug, using the 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 setups.
- Is the tooling organized and 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 a program in place or does the tooling just get taken off 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 to prevent problems during installation and setup.
- Do you know how much life is left in the tooling (will it make it to the next run)?
- What is the condition of other pieces and parts, such as the spacers (are they the correct length)?
- Do you have rim clearance figures from the last successful run, so you can 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.
- A tooling maintenance program should involve more than just the tooling itself. It should include prints of the tooling, setup charts, rework records, in-house maintenance inspection sheets, rim clearance sheets and cost records.
The subject matter covered here needs to be in place no matter what type of equipment is used. Even if a company has all the latest quick change equipment, this equipment will still need procedures in maintenance, setup and operation to make it successful.
You must be consistent and disciplined for the process to be effective. Many programs are set up but not monitored or disciplined. The standards that need to be set in any operation require the participation of everyone involved. Everyone needs to share the responsibility in order to make changeovers faster and more efficient.
Author: Robert A. Sladky, Vice President Tube Mill Engineering, Roll-Kraft.
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