Rolls are used in web-conveying production installations in the paper, converting and steel industries. With installations operating at increasingly higher speeds and product quality standards constantly on the rise, precise alignment of the rolls has become a must.
In the past, roll parallelism was measured with optical systems such as theodolite, total station or mechanical methods such as contact angle measurement. The measuring process is hindered by the time-consuming nature of these methods, error propagation, relative inexactness and inaccessibility of the rolls. Measurement of rolls in structurally separated areas was virtually impossible.
An inertial method of measurement can solve these problems. For this purpose, PRUFTECHNIK developed a revolutionary and unique measuring device for roll parallelism: PARALIGN. The in-built laser gyro technology, commonly used in aerospace navigation systems, makes roll alignment faster and more precise than ever before.
The parallelism of rolls has an huge influence on the productivity of a paper mill. The problems affect everything from wires and felts, which have to be replaced within a fraction of the specified service life as a result of poor roll alignment, to increased frequency of web breaks due to decreased roller parallelism.
Many paper machines today operate at nearly twice the speed as they were designed for ten years ago. To meet the increasing quality standards, the alignment tolerances have been narrowed accordingly.
Creases, incorrect rolling or a non-symmetrical thickness profile can be minimized.
PARALIGN makes it possible to take advantage of even short machine downtimes to conduct the traditionally time-consuming job of roll measurement. The following examples demonstrate the benefits of our roll alignement system.
PARALIGN in the wet end
The lower press felt in the wet end of a papermill producing newsprint paper showed a remarkable shrinking after only two weeks of production: Both lateral edges reduced the width of the felt, thus the lifetime of the felt decreased dramatically. After two weeks of production it had to be replaced. Usually the lifetime should be five weeks. In addition to the increased spare costs the production department suffered from further machine downtimes.
In figure 1 the compact structure of the wet end can be seen clearly. In this multi layer environment an optical system can only be used under a huge loss of time and accuracy caused by the additionally needed measurement equipment like mirrors and prisms. Here PARALIGN was able to convince the production management by its unparalleled brief measurement time and its self explaining measurement protocol.
Another advantage: PARALIGN does not need any line of sight between the rolls themselves or between the rolls and the outer reference line. Thus all rolls could be measured without loss of accuracy.
From measurement to correction
After measuring the alignment condition, the offsets were corrected according to the readily available PARALIGN protocol. The lower press roll was chosen as the reference roll. The corrections were confirmed on the same day by a second PARALIGN measurement. After the corrections the lower press felt could keep its planned lifetime as the shrinking effect did not occur any more.
The figures 2 and 3 show the PARALIGN protocols of the said wet end before and after the corrections. The improvement in roll parallelism can be seen clearly.
PARALIGN in the drying section
A paper mill for magazine paper came to us with the following problem:
One of the drying wires had to be changed after four weeks instead of a regular lifetime of twelve months. Because of the housing, a traditional measurement system can hardly access the rolls. On the other hand, the temperature gradient in the hot drying group makes the use of optical systems very difficult. The deflection of light near the hot drying cylinders is different to the deflection at room temperature outside the machine.
PARALIGN measurement in record time
The key argument for the production management to use PARALIGN was short measurement time. The critical felt rolls were placed in the cellar of the machine, so that it would take very long to place the mirrors and prisms required by an optical system in order to access the rolls. In addition, the repeatability of the measurement, for example after correction, is hardly possible. Within two hours the alignment condition of this drying group was measured with PARALIGN.
According to the readily available protocol several alignment scenarios were simulated together with the maintenance department of the paper mill. Based on a cost-benefit analysis one of the scenarios was chosen. On the same day the maintenance team corrected the respective rolls including guide and tension roll. The corrections were proved immediately by a second PARALIGN measurement.
Three months after the service the satisfied customer contacted us to confirm that the felt showed no abrasion or other irregularities. The lifetime of the felt was increased to the regular period. Picture 2 and 3 show the PARALIGN protocols of the said drying group before and after the alignment. The improvement of roll parallelism can be seen clearly.
Reducing paperbreaks in the calender section
In the calender section the paper is smoothened and brightened. A paper mill for premium magazine paper showed quality problems in the calender section. Figure 1 shows an example of a calender unit.
The unit is placed between the ground and the first floor of the machine hall. Because of the lack of space in front of the unit it was hard to access all rolls with traditional optical systems. Thus optical measurements were not so accurate and time consuming due to the necessity of additional measurement equipment like mirrors and prisms.
The plant engineer took PARALIGN as an alternative to the traditional methods. The system works also in narrow spaces with the same accuracy. In addition, no line of sight between the rolls is needed for the measurement.
The PARALIGN measurement was performed in a very short period of time – the results were well defined: The idlers of the calender showed huge horizontal offsets. Thus asymmetric tensions on the paper occurred. The reason for the quality problems was found.
The PARALIGN protocols (fig. 2 and 3) show the said calender before and after the corrections. The improvement in roll parallelism can be seen clearly. After the alignment the quality standards of the paper met the requirements while the machine availability increased due to the reduction of paper breaks.
The problem of roll measurement in the steel industry is well-known. Misalignment can have different causes:
For the plant operator, this can result in increased maintenance downtimes and, due to inferior product quality, potentially dissatisfied customers.
Conventional methods for roll measurement often prove to be difficult and time-consuming due to inaccessibility of the rolls. Roll measurement with PARALIGN takes only a fraction of the time otherwise needed. The corrections conducted based on the protocol can be measured and confirmed immediately. The following examples show typical PARALIGN applications in the steel industry.
Poorly aligned rolls in a push-pull pickling line in the cold rolling mill can lead to strip misalignment; in the worst case scenario, the strip touches the frame, causing machine downtime.
In this example, the rolls 11 and 12, with horizontal misalignment of 1.5 cm, exert transverse forces on the material, which impairs the strip alignment. Correct alignment of the rolls minimizes the risk of strip misalignment and reduces the risk of downtimes. The depicted component was measured with PARALIGN within 2 hours.
Although the tandem line has no rolls with high wrap, the requirements for the roller alignment are higher here than in the hot wide strip mill, since the strip is much thinner. The result of misaligned rolls in the tandem line is, in addition to strip misalignment, an asymmetrical thickness profile. Besides the position of the support rolls, the position of the rolls to the strip tension and profile thickness measurement is important.
After removing the working rolls, the depicted tandem line can be measured in about 1 hour.
Due to the high wrap, rolls in the vertical annealing furnace can affect the path. The annealing furnace, however, is completely inaccessible and cannot be measured using conventional methods – no problem for PARALIGN. A vertical annealing furnace of the galvanization line was measured in about 4 hours.
The quality standards required by customers who purchase converting products have increased significantly in the past few years. Even in the case of a film with a thickness of 10 µm, a thickness deviation of only a few percent is not tolerated.
This also applies to the printing sector: to convey the impression of a high-quality product to the end customer, the register alignment must be exactly right.
Complaints of printing machines that cannot operate at the specified speed due to alignment problems are common. The result: production losses, day after day.
Our customers therefore often require precise alignment of new installations, with tolerances of only a few tenths of a millimeter. Such a requirement generally cannot be met with conventional measurement instruments.
Many renowned manufacturers have trust our gyro technology for the installation of new plants. It pays off. Will you be the next?