Solving problems on the tube mill
Tube mill machine line face a variety of challenges every day in their effort to produce high-quality tubing in a cost-effective and productive way.
This article examines some of the typical problems producers encounter, some common causes of these problems, and some ideas for how to solve these problems.
Lost Mill Time During Operation and Changeovers
Often, excessive downtime during normal operation or tooling/job changeover can be attributed to one or more of the following causes:
1. No written procedures for setup. Every mill should have written procedures for all operators to follow. The machine, tooling, and steel are fixed factors in the mill setup equation; the only variable is the human factor. This is why it is so important to have written procedures in place to control the process. Written procedures also provide a tool for troubleshooting when problems arise.
2. No setup chart. Tweaking the mill during setup loses valuable setup time. Operators must work the tooling the way it was designed. This means setting up to the parameters of a setup chart.
3. Lack of formal training. Formal training helps operators perform the procedures for carbon steel tube mill machine and maintenance and ensures that all operators are on the same track.
4. Disregard of parameters from previous setup. If the Galvanized tube mill machine has been set up according to the written procedures and setup chart, the operator can write down the numbers from the digital readout on the single-point adjustment (SPA) unit, allowing the next operator to set up where the first left off. Setting up to the numbers can save as much as 75 percent of total setup time, as long as all the other tips discussed in this article are followed.
5. Mill in poor condition. A poorly maintained mill costs valuable time and scrap during setup and operation. The mill must be dependable so that the operator is not chasing mechanical problems during normal operation and setup. A good maintenance program, as well as rebuilds or upgrades when necessary, is essential.
6. Mill in misalignment. Tube mill misalignment, poor mill condition, and inaccurate setup account for 95 percent of all problems in tube production. Most mills should be aligned at least once a year.
7. Tooling in poor condition. Operators must know how much life is left in the tooling before the next scheduled rework. Running the tooling until it cannot produce tubing anymore not only wastes valuable mill time, but produces scrap and affects delivery schedules. All tube production companies should have a tooling maintenance program in place.
Any of these causes of lost time on the mill can have varying degrees of value, depending on the severity of the conditions. The bottom line is, the more of these items that are in control, the less downtime on the mill.
Splitting in the Weld Zone
Weld zone splitting can be a result of some or all of the following:
Overly narrow strip with insufficient material to forge
Poor alignment or setup
Insufficiently worked fin passes, so the edge is not prepared for welding
Poor slit edge
Off-center strip approach (strip rolled over) to the weld box, preventing forging between the weld rolls
Nonparallel edges entering the welding machine
Inappropriate weld power for mill speed
Poor-quality steel with improper chemistry
Irregular Size in the Sizing Section
When irregular size occurs in the sizing section, the problem may not necessarily be in the sizing section itself. The operator also must check the setup in the breakdown, fin, and welding section of the mill to ensure proper presentation to the sizing section. If the forming section sends improperly formed tube to the sizing section, irregular tube size can result.
The operator also should check for bent shafts, oversized bores on the tooling, or undersized outside diameters (ODs) on the driven shafts. The integrity of the side roll boxes also should be checked.
In addition to these checks, the operator should consider the following questions:
Is the weld size in accordance with the setup chart?
Is the weld size round?
Are the strip edges parallel, with no step going into the weld rolls?
Is the weld scarf smooth?
Are rework shims installed under the bottom driven shafts to maintain the metal line?
Are the correct spacers installed on the driven shafts and to the correct length?
Are the bearings and bearing blocks tight?
Are the side rolls parallel?
Is the tube being cooled properly?
Are all the drives coordinated and adjusted to match the rework of the tooling?
Has the chemistry or hardness of the material changed?
Weld chatter is the inability to achieve a clean cut of the outside weld bead after welding. The scarf knife chatters and produces a ribbed or rough cut on the OD of the tube. This is unacceptable in most of the end products produced by the tube and pipe industry.
Several techniques can be used to prevent weld chatter.
The scarf knife should have a slightly larger radius than the tube OD. This will provide a concentric, clean cut.