Vice President Tube Mill Engineering
The sizing section of most tube and pipe mills is normally the last section the tube/pipe will interface with before exiting to the cut off and packaging equipment.
Sizing plays a very important part in the final end product, as it not only does as the name implies, "sizes" or reshapes (squares, rectangles, ovals, and etc.) the tube/pipe, but it also "stress relieves" it at the same time so that the properties are "normalized" within the body of the material.
However, the only way this "double process" can perform or be held under control is by proper set up of the sizing section, per the design of the tooling. It is imperative that the sizing section is set up so the tooling can evenly and equally finish/size/straighten the tube/pipe. Failure to do so will result in secondary fabrication and straightness issues.
In the example of round sizes, so many times operators only check the horizontal measurement out of each side pass station, and the vertical measurement out of each driven pass, and only worry about insuring the tube/pipe is round out of the last driven sizing station or in some cases, not until it exits the Turks head units.
The tooling in the sizing section, in round designs, is designed to oval the tube out of each of the side pass station, and refine it round out of each of the driven stations. It is imperative that this process be set up and maintained throughout the entire sizing section to insure the process of sizing/stress relieving is accomplished.
Above is a sample illustration of a typical "round" sizing section. As illustrated, some mill configurations have a single four-roll Turks head, others have a two-roll horizontal, and two-roll vertical straightening unit.
Out of each driven sizing pass, measure the vertical, horizontal, and diagonal locations and insure these measurements are all the same, "round".
Example: If the horizontal measurement is too wide, simply come in more on the preceding side pass stand. Most set up charts give a "guideline" measurement for the side pass stations in a sizing section. This is a starting point, as the driven passes are the dictator of where the side pass stand will need to be adjusted to obtain a round tube.
Caution: Issues with the diagonal measurement out of any of the driven sizing passes could be caused by any of the "problems and solutions" outlined later in this article, or be in the very first breakdown pass where the formation was not pronounced in the strip at the start of the entire forming process.
The Turks head unit, in round applications, is only designed to straighten the tube as it exits the mill. The unit should be set up with a plug gage, which should be the final tube/pipe size, and the rolls to only lightly ride on the tube/pipe. They are not designed to do any final sizing. Many operators feel that they need to do some minor, "final sizing" to keep the tube straight. If the integrity, alignment, and set up of the entire mill is in place, the tube should be to size as it exits the last driven sizing, and very little adjustment should be required of the Turks head to keep the tube straight. If you have to move the Turks head up or down, left or right any considerable amount to get the tube straight, you have a problem further upstream that needs to be found and corrected.
As outlined above, many mill configurations support reshaping in the sizing section. Some reshaping is done by simply pushing the tube/pipe through a set of multiple Turks heads, whereas other tooling designs start the formation deep within the sizing section for higher quality dimensions, especially in high strength, and heavy gauge materials. Starting the formation of these shapes in the sizing section, and doing only minor "finishing" in the Turks head units, also results in a better drive (bite) on the tube, less marking, and a more refined final product especially when your requirement are for tight corners and flat sides on squares and rectangles.
Most Turks heads have rotating face plates for forming the shapes (squares and rectangles for one example) on the diamond, or on the corner. This aids in dimple free cuts when using a single blade cut off, as the blade enters in on the corner of the tube/pipe. The rotary plate is also used to control twist of the final product.
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