Tube and Pipe
Split Rolls
The
Best
Value
in the Industry Guaranteed. solid
roll tooling, the industry standard for years, is not your
only
tooling choice for tube and pipe production. One option
available from Roll-Kraft is Tube and Pipe Split Roll
Tooling. Using split
rolls can reduce your overall tooling cost, while increasing
the cost effectiveness of your tube and pipe operation.
Very simply, split rolls are tube rolls made in two
sections and bolted together into one unit. For all
practical purposes, they look and work the same as solid
rolls. However, the differences between the two are
numerous. Rework procedures are different, the “size” of
reworked rolls is not the same, and downtime is reduced when
using split rolls, due to fewer mill adjustments between
regrinds.
Let's look at split roll theory and its
advantages. After reading this information, you may decide
that converting your mill(s) to split roll tooling can be
beneficial to your manufacturing operation.
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.
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. 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 down hill from
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.
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.
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 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.
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 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.
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