Profit Pointer for Tube Mill Set Up
By Robert A. Sladky, Vice President, Tube Mill Engineering, Roll-Kraft Nebraska U.S.A.
Using the Set-Up Chart
The chart shown below is an example of a Set Up Chart furnished to you with your set of rolls from Roll-Kraft. It lists all the information necessary to properly set up your tube mill through the three stages of tube production:
(1) Forming, (2) Welding and (3) Sizing
We will be referring to this chart throughout this bulletin, illustrating various examples to help you understand and use it during set up.
Roll & Spacer Installation
Correct Tube Mill Set Up begins with the correct installation of the roll spacers and the tube rolls. Begin by checking and installing the inboard spacer. It should be noted that the correct spacers to be used on the mill should be selected and measured in the tool room before you begin setting up the mill. The check being performed at this time is a final check to ensure that none of the spacers to be used have been interchanged with others used in another location. Proper length is critical to mill alignment. All spacers, especially those used on the inboard side of the mill, must be within ± .001” of the required length. The Set Up Chart lists the required spacer lengths of all spacers (see Note 1 on chart). After checking the inboard spacer length, install it on the shaft. Next, install the tube roll on the shaft. Check the length of the outboard spacer and install it on the shaft. Secure the assembly — spacer, roll, spacer. Repeat this procedure for each driven pass on the mill. If side roll spacers are required, check their length. Install the spacers and side rolls on each idle stand. Remember, all the tie bars, end caps and nuts must be torqued properly to prevent premature wear of the spacers, roll faces, bore and shaft. When you have completed installation of all the spacers and rolls, you are ready to check the set up for each pass on the mill.
The first step in setting up your mill properly after roll installation is checking the entry table. A well maintained entry system will assure that the strip is formed symmetrically about the centerline of the mill. (This is particularly important when you are shaping a material that is difficult to form or your breakdown rolls are of edge form design.) Keep in mind that the entry table is a guide for the strip into the Number 1 breakdown pass. (It is not to be used to correct the alignment of the strip coming off the uncoiler.)
Breakdown Pass Clearances
The radial clearance between the top and bottom rolls of each driven breakdown pass is equal to the gauge of the strip to be run through the mill. Set the clearances on all driven breakdown passes to this dimension. Many times mill operators ask “how tight is too tight?” when they are setting up this clearance. At this point of our set up (before the strip is threaded into the mill) it is best to use gauges to measure this clearance at the drive points on each roll. This is illustrated in Figure 1. Another method that may be easier than using gauges is the use of a self-made measuring tool. This tool is nothing more than a small section of the actual strip that will be formed on the mill. Place the strip between the top and bottom roll and set the clearance. After the strip has been threaded, we will check for thinning and proper “feel”. Clearance for the side rolls is measured at the bottom rim of both rolls as shown in Figure 2. The dimension is found in the Set Up Chart (see Note 2 on chart). In our example, we have three sets of side rolls in the breakdown section. They are designated as EF1-2,2-3, and 3-4. Use taper gauges or gauge blocks to measure the rim clearance. Adjust as necessary.
Fin Pass Clearances
In the lower left hand corner of the Set Up Chart are diagrams illustrating the rim clearances for the Number 4, 5 and 6 driven fin passes (see Note 3 on chart). This can also be seen in Figure 3. In our example, the rim clearance is .062". The fin side pass rim clearance, labeled as 4-5 and 5-6 in the chart, is also .062". Please note that the rim clearances for the fin side passes are listed in a different section of the Set Up Chart than the driven passes (see Note 4 on chart). Figure 4 illustrates this clearance. Holding or lead rolls should also be set at this time.
In order to accurately measure the clearance between the welding rolls, make a solid plug to the size indicated at the bottom center of the Set Up Chart (see
Note 5 on chart). Adjust all weld rolls to the plug gauge diameter. Check the rim clearance between the rolls and adjust as necessary. In the upper right hand corner of the Set Up Chart, there is a section entitled “Welding”. On the line marked “Weld Rolls”, the rim clearance is abbreviated CL. In our example, that dimension is .062".
The sizing section of the mill consists of the sizing rolls and the turkshead section. The lower right hand corner of the Set Up Chart contains the required rim clearance information for the sizing driven rolls. It is arranged in the same format as the clearance data for the fin driven rolls (see Note 6 on chart). Adjustment is done in the same manner as the fin section. In our example, the rim clearance is .010". This is illustrated in Figure 5. The first side pass in the sizing section is often referred to as the Ovaling Guide. The abbreviation used in the Set Up Chart is OG. The other passes are labeled S1-2 and S2-3. The rim clearance specified in our example chart is .031". As with the fin section, the side roll rim clearances are listed separately from the driven rolls (see Note 7 on chart). The turkshead rolls are set using a plug gauge in the same manner as the weld rolls. In the Set Up Chart, the turkshead data is in the box labeled “Sizing” and abbreviated TH. The rim clearance is listed as .031" and the plug diameter required is in parentheses (.750" dia.). Adjust the rolls to the plug gauge and check the rim clearance.
Threading the Mill
After all clearances have been set up for each pass, you can proceed with threading the mill. We have already mentioned the importance of the entry table and its set up; therefore, you should be ready at this time to thread the strip. As illustrated in Figure 6, the ends of the strip should be beveled for easier entry. Also, the burr on the outside edges of the strip (from the slitting process) should face upward to minimize wear on the rolls. With the strip threaded through the mill, set and load each stand. Starting with the first set of breakdown rolls check the set up and re-adjust as necessary. Loading the strip through the mill may have altered your original set up dimensions. Continue through the entire mill, rechecking each pass.
Now that we have threaded the mill, we can address the question of “how tight is too tight?” in this section of the mill. Besides the “right feel” of the strip between these rolls, which is developed with experience by the mill operator, there are two physical signs that will tell us if the clearance in the breakdown driven pass is too tight. The first is marking of the tube. If any markings are noticed they should signal a problem with the setup. Also, thinning of the strip can be determined by measuring its thickness. If the thickness is more than .002" less than the thickness before entering the pass, the clearance is too tight and must be readjusted. Failure to correct this condition will lead to premature tooling wear by eliminating the areas for material clearance. Improper clearance can also be detected when the mill is running by reading the ammeter on the control console, if your mill is so equipped. Clearances that are too tight can be detected by an overload amperage reading.
As the strip exits the 3-4 pass, it is ready to enter the fin section of the mill. Roll-Kraft Set Up Charts will list a diameter that the strip should be at this point (see Note 8 on chart). Diameter of the tube should be .942". Measure the tube diameter as close to the exit point of the pass as possible. If the strip measurement does not coincide with the spec, readjust the clearance. Jog the mill forward and remeasure. Repeat this procedure until the specified diameter is obtained. Perform this procedure of measuring the strip O.D. and readjusting for each fin pass. Do not forget to recheck the rim clearances for the fin side passes. Incorrect settings will produce an out-of round tube.
Recheck the weld rolls and readjust if necessary. Also, if your mill has holding rolls or lead rolls (in our POINTERS Figure 5: Rim Clearance for driven sizing rolls .010 Figure 6 BEVEL EDGES NO.1 PASS ENTRY TABLE example, the mill will have holding rolls), they should also be re-checked and adjusted. Note 9 on our Set Up Chart identifies where this information is located. Your welding equipment, and any equipment used to support that process, should be checked at this time. After we have finished rechecking the entire mill, it will be run to check the entire tube forming process including the weld integrity; therefore, the welding equipment should be ready to go.
In the sizing section, the side roll passes “oval” the tube and the driven passes refine the tube into a “round” shape. Measure the horizontal cross section of the tube after every side roll pass. Dimensions are found in the Set Up Chart (see Note 10 on chart). In our example, the section should measure .750" after passing through the OG. Readjust as necessary to meet the specification in the same manner as the fin section. After every driven pass, the tube should be round. Measure the O.D. in two perpendicular planes to verify this. Readjust as necessary. After the final driven sizing pass, the tube should be the desired diameter. In our example, the O.D. should measure .750". When making round tubing, the turkshead rolls keep the tube straight as it travels to the cut off section. That is the case in our example. The rolls should ride lightly on the tube, exerting only enough pressure to act as a guide. In reshaping, these rolls are designed for resizing and straightening. The Set Up Chart will give specifications to set up those passes.
We are now ready to run the mill for the purpose of checking the integrity of the weld. If all the passes have been set up correctly, the only welding problems that might possibly occur should be a result of a problem with the welding equipment itself. However, if the welding equipment is working properly and the weld is bad, a set up problem may exist. Recheck the fin section and holding rolls for a possible cause.
Record the Settings
Record all rim clearances before and after each production run. Comparing data that is recorded at the start of the run with that taken at the end of the job will help determine wear rates of the tooling. Recording data not only helps in scheduling rework and tool maintenance, but is helpful in setting up the mill the next time that particular size tube is run. One of the keys to productive and profitable tube and pipe production is mill maintenance. A useful, well organized program begins with logging data that helps the operator point to production problems and required rework. The result is increased footage of high quality tube and pipe from your mill.
It should be readily apparent that proper tube mill set up is essential for producing high quality tubing. By following Roll-Kraft's 10 Check Point procedure in conjunction with the Set Up Chart supplied with your rolls, mill set up can be accomplished in a timely, efficient manner. Once you have the mill up and running, frequent checks should be made to ensure that sizes are maintained at every pass and the strip is worked evenly. This will result in extended tooling life and continuous production of high quality tubing.