With ever increasing machine speeds and improved paper qualities the demands on reeling equipment is continuously increasing.
Today, reeling problems and in consequence remarkable production losses can be found throughout the paper industry.
Often, there are several reeling processes throughout a production line and therefore, the paper loss per wound roll plays a major role in determining the over all efficiency or, so to say, the loss of profit.
Not just the influence of the different winding parameters are discussed but also the impact of various layouts of the equipment being in touch with the paper. Not just a centre wind assist but also the stiffness of a reel spool and/or the surface of the drum have a major impact on the quality of a wound roll.
All three measures to achieve better reeling results are being discussed and reference is made to improvements achieved in practice. Herewith, the proposed paper gives the opportunity to possibly envision parallels to existing installations of the audience in an easy and practical way.
After walking through the basics and different equipment responsible for sensitive reeling, the paper leads to the state of the art reeling concept SIRIUS, featuring all the measures discussed above and in which all major experience regarding reeling of paper has been realised to the extend possible to the benefit of the customer.
SENSO REELING TECHNOLOGY
For optimum printing results, papers require, above all, suitable, surface properties. During winding, these properties have to be preserved in the best possible way. In this paper we will learn about measures that can be taken against the harmful air boundary layers that are transported along with the web, and we will also hear about the mode of operation of a centredrive and the part played by the dimensioning of the reel spool. Besides theoretical considerations, practical examples will be given to show how existing plants have been optimised. Finally, I would like to present our new product to you, which is called "Sirius" to you.
Figure 1. Senso reeling technology
With ever-increasing machine speeds air boundary layers on the top side and underside of the running paper web play an ever greater role. These air masses cause a back pressure ahead of the reel drum and in the ingoing nip. The consequences are an air film on the reel drum and air enclosures in the paper roll.
Figure 2. Air boundary layers
A practical example shows, in an impressive way, the impact that the reel drum surface makes on this. Following the rebuild of his machine, a manufacturer of newsprint increased the speed from 1180 to 1330 m/min. Suddenly the paper web formed an air film on the reel drum. The consequences were an unstable web run with a poor edge face and occasional wrinkles. The grooved reel drum was exchanged for one with perforations and a different groove shape. Trouble-free operation was achieved immediately. The perforations ensure a more effective discharge of the air and therefore prevent the web from forming an air film.
Two years later, improved newsprint was manufactured on the machine in addition to standard newsprint. Porosity decreased from 100 to 28 ml/min. The papermakers were now dismayed to see an air pocket between the two top paper layers and the roll. On 52-gram paper with the very low porosity, longitudinal wrinkles occurred in areas where the paper was thicker. This paper could no longer be used.
This problem was addressed by redesigning the reel drum. It was now fitted with an elastic cover with a drilled surface and a flat groove. This eliminated the air pocket and the wrinkles. The elastic surface of the roll adapts itself to the roll contour and thereby largely prevents the winding-in of air into the roll. Residual air is transported to the edges defined by the special groove.
Figure 3. Influence of reel drum
The decisive factor for the quality of a roll is how stresses are distributed across the roll diameter. The red lines show the development of tangential and radial stress in a paper roll which was wound in the traditional manner with a constant web tension without a centre drive. The black lines represent the development at a different web tension level. The critical area is the one shown in yellow. There, the tangential stress has dropped into the negative range. Layer displacements can occur here, which may, depending on paper grade, lead to crepe wrinkles and bursts that damage the paper surface or produce glossy areas. What is desired is a development as shown by the green lines.
Figure 4. Roll stresses
On each reel the nip load can be controlled to a better or worse degree. I do not wish to go into this generally well -known tool in greater detail today. An additional effective instrument to improve roll build-up, particularly in the reel centre, is the centre drive.
This representation shows the theoretical relationships regarding the influence of wound-in tension with a centre drive. In general, the web tension T0 is maintained constant ahead of the reel drum. This requires that the sum of the peripheral forces F1 plus F2 should remain constant. If a positive torque is introduced via the reel drum, i.e. the peripheral force F1 is greater than zero, then the wound-in web tension T1 is smaller than the free web tension T0. If the reel drum does not transmit any peripheral force to the paper web, then the wound-in web tension is equal to T0. The yellow arrows represent an extreme case in which the reel drum receives a negative torque. The wound-in web tension is then higher than the free web tension.
We can see that the distribution of the drive torques on the reel drum and centre drive decisively determines the wound-in web tension. Less peripheral force on the reel drum and a high centre torque result in hard reel centre winding. For the sake of completeness let us mention the following: As, on the winding system that we are discussing here, the paper roll forms a nip with the reel drum, the stress generated by this nip must be added to the wound in tension.
Figure 5. Wound in tension effect of centre wind assist
Now let us look at a case taken from a commercial application. A producer of coated paper has reported a very large air pocket under the outer paper layer. With an extension of 300 - 400 mm in the direction of paper travel, this air pocket was especially pronounced here. This caused wrinkles in the centre and therefore produced broke. With these particularly smooth papers, a „soft" reel drum alone does not help. Through the installation of a centre drive, correspondingly hard reel centre winding was achieved and the air pocket was reduced to a size that no longer causes any disturbances. The slab on the spool decreased to below 40 mm, and the production gain was 30 t of more saleable paper per day. An investment that paid for itself after 6 months.
Figure 6. Effect of center wind assist
As we have heard before, the paper in the centre of the reel is exposed to the greatest radial stresses. The extreme values occur due to reel spool deflection at the edges. An important characteristic for the deformation of the reel spool is edge inclination. It is not rare for the paper to be overstressed at the edges. This becomes apparent through the frequent occurrence of crepe wrinkles in the edge rolls of the last set. In such cases the immediate action that can be taken is often only to wind up less paper on the reel spool so that the deflection becomes smaller, or to leave a correspondingly large amount of residual paper on the reel spool, which is precisely what we really want to avoid.
Let us look at the applications listed below a little more closely. In the case of customer A, the printing shop complained about an above-average number of breaks. A precise analysis showed that crepe wrinkles were found on most of the torn rolls. These were primarily the edge rolls of the last set. Urgent action was called for. Among the various possible countermeasures, the most cost-effective variant was selected: a changeover to reel spools larger in diameter and thus more rigid against deflection.
The edge inclination reduced from 1.7 to 0.7 mm/m produced a pleasing result: The number of breaks in the printing shop went down by 40 %.
In case B, a thick rest was left on the reel spool to avert complaints. By means of larger reel spools, success was achieved here in reducing the slab on the reel spool by 50 mm while maintaining roll quality.
Figure 7. Stress on reel center
If we look at the paper production process as a whole, we note a decisive change: the trend from offline to online processes. For new plants, online coating is the rule, online calendering no longer remains the exception. Probably one of the most significant changes can be observed in winding technology. The number of winding operations on an LWC line decreases from the previous nine wind-up and unwind operations to now, just one.
"All-Online" is the future
The greatest challenges for winding technologists are the enormous change in the process parameters of the paper wound up on the PM. Whereas, on an offline production line, the paper is wound up in two supercalenders at speeds below 1000 m/min, in the online process 2000 m/min at the PM wind-up is required for the supercalendered paper. Added to this is the drastic increase in the number of layers to be wound up for ever-larger reel diameters. Traditional winding concepts are overtaxed by this task.
Figure 8. Changes in processing LWC
With a novel wind-up system, the way is now free to the fully integrated paper production process. This system combines the previously described elements:
Figure 9. Sirius R125/2
In October 1997, this system went into operation for woodfree coated grades at an European Mill. A roll diameter of 3 .55 m and a roll weight of 120 t have become a reality. On re-reelers this trendsetting technology has proven successful at operating speeds up to 2500 m/min.
Figure 10. Sirius R125/2
The heart of the machine, however, is a new loading principle. In contrast to conventional technology, the nip load is generated by a moving pressure roll and the roll diameter growth is compensated by a path-controlled parent roll movement. The result of this clear separation of function of linear load generation and parent roll movement is a precise and sensitively controlled linear load.
The special advantages of this principle are:
The various winding parameters, web tension, linear load and centre torque, can be adapted independently and within a wide range to the respective requirements.
Figure 11. Separation of the functions
How does the functional sequence look like?
In a transfer arm the new reel spool is accelerated to synchronous speed, the parent roll moves away from the drum, the empty reel spool swivels into the position for the start of winding, a novel machine-wide turn-up system separates the web safely and cleanly. The reel spool on which paper has begun to be wound is lowered completely onto the reel spool rails.
While applying the desired nip load, the pressure roll compensates for the parent roll growth necessary due to the fixed bearing centre of the loading arms. After the wound parent roll has been decelerated, the winding roll is transferred to the main winding carriage. The diameter growth of the roll is now compensated for by the path -controlled main winding carriage. On insertion of a new reel spool into the transfer arm, the system is again ready for the next reel spool change.
Figure 12a. Sirius - Operational sequence
Figure 12b. Sirius - Operational sequence
Additionally, and in order to underline the contrast of the above-mentioned operating principle to conventional reeling systems, I would now like to show you an animation of the this sequence.
Loading of the empty reel spool
What gain in quality can the papermaker achieve by SensoReeling?
Figure 13. Quality advantages by SensoReeling with Sirius
I would like to close with this graph, which shows the paper loss as a function of the parent roll diameter with different amount of remaining paper on the spool.
If, for a parent roll diameter of 2600 mm, we compare a rest on the reel spool of 2500 m with 500 m at 3600 mm roll diameter, this results in a reduction of the paper losses by more than 3 %. For a modern newsprint machine this is approx. 8000 t per annum extra production. On offline production lines for coated papers, in which winding is performed at several points due to the process, these slab losses naturally occur much more. Particularly large improvements in efficiency can therefore be achieved on a changeover to online production.
The diagram also shows us: the large potential lies in the reduction of the remainder of paper on the spool, with a particularly strong impact on small parent roll diameters.
Figure 14. Paper loss by bottom broke