Evolution of Quick Change on Mills

In the age of “Lean Manufacturing”, many tube and pipe producers have faced a seeming contradiction between “just-in- time” production and changeover times of many mills. On large pipe mills, for example, the changeover time is often measured in days and the cost to affect any major time improvement is extremely expensive and usually prohibitive, if not supplied as original equipment, even with the “new math” of “Lean”. Therefore the contradiction is tolerated and changeover improvement is focused mainly on incremental improvements; disciplines involving preparation, training and the use of commercially available power assist tools.

Tube or pipe production below 8” opens up a lot more opportunities and the smaller the tube or pipe the closer we can fold the manufacturing process within a “pull system”. This article will focus on the no-cost to the higher cost solutions that have evolved.

1. First and foremost is PREPARATION – meaning, never letting a changeover catch you by surprise, having all necessary tools on hand, having all necessary roll tooling on hand and have an experienced crew of changeover people ready to ATTACK the change the fervor and exactness of a NASCAR changeover crew. To possess this culture requires a management driven zeal and is not delegated downward very well. Consider the benefit the cost is very low and the payback very large.

2. After enveloping PREPARATION into the working culture, producers have turned to a variety of INCREMENTAL TOOLS and quick change methodologies. These include:

• Power tools suspended (for easy one hand access) over the forming mill, sizing mill and cutoff.

• Half nuts, Jett nuts and “C” washers to expedite the release of the outboard retaining nuts and/or the outboard stand bolts. (we know one goal was 15 seconds to release and remove each outboard stand)

• Flip-Top Clevis on side stands to speed removal of side stands.

• “T” nuts/bolts, cam tighteners, for use on entry guide weld box, seam guide, I.D. Scarf and Ovaling Guide pass. (one goal is to eliminate/reduce use of hand tools for changing/adjusting these devices)

• Single point adjusters with dial/digital indicator (this ties the inboard and outboard stands together and allows adjustment as a unit).

• Weld Box with quick change clevis.

• Turkshead with quick change clevis

• Cutoff die mounted with quick change shoe.

3. Other PARADIGM SHIFTERS, which can enormously help in reducing changeover times, and do not interfere with product quality, are:

• Universal breakdowns means never having to change out these rolls (requires change in tool design philosophy).

• Eliminate seam guides (may require maintaining mill in more precise alignment).

• Practice and perfect threading mill, end-to-end, at a fast jog or slow run (may require precise alignment, use of lead-in-appliances at key points and ability to weld at slow speed while jogging).

• Eliminate outboard stand on Ovaling Guide pass.

4. A discretionary next step in improvement for some producers might be the automation of the single point adjustors, usually through servo controllers for each set of stands.  This approach usually employs a presetting computer to record last set positions and interface between new presets for the next set of tooling or product.

5. Following the incremental march to the cliff-edge, producers often face off whether to take the quantum leap to RAFTING of tooling stands and appliances. This can be done on existing mills but the expense is often close to that of a new mill. This is usually considered and pursued only when this cost is considerably less than that of a new replacement mill installed.

6. A clear trend is that in a majority of new projects today mills are rafted to one degree or another. This is because the cost is small compared with the rest of the total project. The variations on rafting are worth reviewing for anyone considering future specifications. Consider this:

• Simple-Rafting, over posts, located to position each raft in exactly the same position. (often employing lifting rings attached to the raft for crane removal or with design cavities for forklift access)

• Simple-rafting requires a simple means to disconnect the drive source so quick release universals are employed as well with the simple-raft approach.

• Third-Stand-Rafting, as the name implies describes a third stand (driven stand) which is mounted to the mill base, behind the inboard stand (raft mounted) and employs quick coupling techniques to power the raft stands. In this arrangement, various creative scenarios can be applied to move the raft about. Consider also:

  • Raft removal by crane.

  • Raft removal by forklift

  • Raft removal to cart system which also ferries in change raft

  • Raft removal to cart system which rotates to deliver change raft

  • Yet to be specified!

• Advanced Third-Stand-Rafting includes self aligning system for third stand hubs to accommodate pre-setting the off line raft.

What this article cannot describe is the mix and match of incremental and quantum improvements that could be employed. That is left to the reader’s imagination. One note of warning to those embarking on their first quick change effort, the best results often come from mastering PREPARATION alone, and without mastering PREPARATION the results from all the other small and large scale improvement efforts may be inconsequential.