Tube and pipe split rolls are the best value in the industry - Guaranteed.
Split tube and pipe mill rolls are quite simply the very best value: You receive two rolls for only about 20%-30% more than the cost of one roll. To create a split roll, we manufacture two halves of a roll and bolt them together to make one whole roll.
Split rolls look and work the same as solid one-piece tube and pipe mill rolls. However, the differences between the two are numerous. For example: when reworking or reconditioning your solid one-piece tube and pipe mill rolls, you must reduce the roll diameters. This causes the rolls to rotate with the tube and pipe mill shafts at a faster speed. Think of a bicycle sprocket. The smaller the sprocket you use, the faster you peddle. The same applies for rolls. So, if your rolls rotate faster and faster after each rework, the rolls will spin faster causing them to wear out faster. If your rolls wear out faster, you are going to have to buy new rolls more often.
When your rolls are spinning faster and producing less, your mill cannot keep up with the speed difference. Smaller rolls require that you turn up the speed of the mill to keep the same production speed as when the tooling was new. With split rolls, you never have to reduce the roll diameters when reworking. This means your rolls will last at least 10-15 times longer than solid rolls.
Let’s look at split roll theory and its advantages.
Split Roll Theory
The theory of split roll design is very basic. The throat diameter of the roll is maintained after each rework, holding the mill speed constant, with no adverse effect on the roll’s ability to drive the tube. In effect, the roll size, from a shaping and driving standpoint, does not change when a split roll is reworked.
Tool wear and rework are a fact of life in the tube and pipe business. In order to maximize tool life, roll wear must be monitored and rework scheduled on a regular basis. However, using split rolls will benefit your established rework schedule by allowing you to rework only those rolls that require it. To understand this, it is necessary to look at roll wear and the process of reworking split rolls, compared to re-contouring solid rolls.
Tube rolls will wear in the areas of the roll that perform the most work (shaping and driving). On a typical roll, this is in the two radii and the throat diameter (see Figure 1).
Also, fin pass and sizing rolls wear quicker than breakdown rolls. When a solid roll is reworked, the throat diameter is reduced to restore the contour to its original shape (see Figure 2). This reduction in throat diameter can have some adverse effects on mill setup and tube production.
In addition, on driven passes, the bottom line of the tube (metal line) drops, in order to make full contact with the reworked bottom roll. If the mill does not allow for shimming of the bottom driven roll shafts to correct for the drop caused by rework, the metal line alignment of the mill will be drastically affected.
For example, if the fin section is reworked and cannot be shimmed up to match the metal line of the breakdown section, the strip will run downhill from the last breakdown to the first fin, causing buckling, bending, and marking of the tube.
If the fin section can be shimmed, the decreased speed of the reworked solid rolls can be controlled only if the mill has multiple drives and RPM trim control to adjust the RPM for each drive. For instance, if the breakdown rolls are driven separately from the fin pass section, the fin passes can be adjusted faster to coordinate with the rest of the line speed. If this shimming and speed adjustment is not possible, the breakdown passes would have to be reworked, regardless of the amount of wear.
As you can see, reworked solid rolls require substantial readjustment of your mill before production can resume. On the other hand, split rolls can eliminate most of this readjustment and get your mill back on line in a shorter period of time.
As mentioned, a split roll is made in two sections and joined together as one roll. Wear patterns and wear rates are the same as those seen on solid rolls, but when rework is required, the re-contouring is performed differently. Figure 3 is a cross sectional view of a typical split roll in two sections.
To rework this style of roll, the sides are ground to narrow the overall width. Then, the original contour is re-cut into the roll by taking material from the flanges, without reducing the throat diameter. The only change required to the mill setup is the installation of longer spacers to compensate for the narrower reworked rolls. The potential problems seen with solid rolls (the shimming up of driven passes and variable roll speed) are eliminated. Figure 4 illustrates the reduction of width on a split roll after numerous regrinds.
Deciding to Use Split Roll Tooling
The real benefits of using split rolls can only be realized if you are set up for large production runs. The savings in setup time alone can justify the use of split roll tooling because downtime on large runs is money. In addition, the extended life of the roll tooling will offset the extra initial cost.
With experience in designing and manufacturing split rolls, we will help you perform a comprehensive analysis on your mill to determine if split roll tooling can be economically beneficial to your tube or pipe operation.
Tube Mill and Pipe Mill Requirements for Using Split Roll Tooling
By design, split rolls are wider than solid rolls for an equivalent tube size. The extra width is found in the flanges. Due to this fact, the tube mill or pipe mill that is being considered for conversion to split roll tooling must have sufficient roll space. Roll-Kraft’s Engineering Department can assist you in analyzing your present mill to determine if split roll tooling can be installed.
Another important consideration is the number of motor drives on your mill. As mentioned, breakdown rolls usually do not wear as quickly as fin and sizing pass rolls. Therefore, conventional solid rolls can be used for breakdown passes, only if the mill has individual drives for each section (breakdown, fin, and sizing). A single-drive mill would require a complete set of split rolls in order to keep mill speed constant. One benefit from using split rolls on such a mill is extended tool life. The number of regrinds far exceeds the number possible with conventional solid rolls and would offset the higher initial cost of split rolls.
A two-motor drive mill should also use a complete set of split rolls. On such a mill, the second drive is for the sizing section. Mixing solid rolls for breakdowns (remember, the speed will change after rework) and split rolls for fin passes (roll speed is constant after rework) does not allow for mill speed adjustment. This can result in marking the tube. A partial set of split rolls can be used in this case. Like a single-drive mill, cost savings can be realized from longer tool life.
A three-motor drive mill is ideal for split roll tooling. Solid rolls are used in the breakdown passes, and split rolls are used for the fin and sizing passes. Although roll speed will change when the breakdown rolls are reworked, their speed can be adjusted without changing the speed of the rest of the mill. Keep in mind that if you are using solid rolls, the breakdown passes are reworked to control mill speed when the fin passes are reworked, even though the amount of wear would indicate it is not necessary. Using solid rolls for breakdowns, with split rolls in the fin and sizing sections, reduces the number of times the breakdown passes are reworked. This extends tooling life and saves money.
Another possible combination of split and solid roll tooling in a three-drive mill is the use of split rolls in the bottom breakdown section. Bottom rolls wear quicker than the top rolls in this section of the mill. Therefore, it makes sense that the bottom rolls will require rework before the top rolls. If you are using solid tooling, both rolls would have to be reworked at the same time to maintain compatibility with one another.
Finally, if split rolls are being used on the bottom only, they can be reworked when required, maintaining compatibility with the top rolls and eliminating the need to shim the mill because throat diameter is not reduced.
Use our contact form below to learn more about how split rolls from Roll-Kraft may be able to improve your tube mill or pipe mill operation or call us toll-free at 888-953-9400.
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