Current press release

EXTRUSION COATING LINE FLEXIBILITY AS A RESULT OF DIFFERING DEMANDS WITHIN THE INDUSTRY

18.10.2011

As a consequence of ongoing technological developments and the availability of new materials, application changes are occurring with increasing rapidity and the related product life cycles are becoming ever shorter. Manufacturers in the extrusion coating and laminating business have no choice but to react to these market shifts. Accordingly, their machinery must be able to handle a variety of differing applications and therefore future demands have a significant effect on production line design.
Numerous factors have an influence on the configuration of extrusion coating lines and they all relate to the end product. Therefore, the first question to answer before ordering a new production line is what kind of article is foreseen for manufacture? Only when this has been established can the proper equipment be selected.

Selecting the proper equipment
Unwinding

Single unwinding stations represent the simplest solution in this area. However, they can only handle one substrate roll and thus splicing is not possible. Therefore, due to the fact that to obtain a perfect profile the extrusion coating process requires continuous production, this type of unwinder is only used for products with lower quality requirements, or for additional substrates such as grids that cannot be spliced.

In principle, semi-automatic, double unwinding stations consist of two single unwinding stations with a pressing unit that enables the splicing of two webs using double-sided adhesive tape. Depending on the substrate to be handled, speeds of up to 60m/min are available in the course of roll changeover, which often results in ramping-down during this procedure.

Turret unwinds are the most versatile type of unwind and in an extrusion coating line represent the state-of-the-art. Turret rotation and the acceleration of the new bobbin to line speed allow the completion of roll changes at full speed. The two webs are joined with double-sided adhesive tape and the outgoing web is cut with a knife. This results in an overlap of the two webs at the start of the new roll measuring approximately 500mm in length.

For the unwind, differing types of substrate mean varying winding diameters, core diameters, unwinding widths and both-side unwinding. The clamping of roll cores can either be carried out with winding shafts or shaftless. The most flexible system in terms of different roll widths and core diameters is the shaftless type with moveable chucking heads, which also avoids the handling of winding shafts.

Some substrates such as thin aluminium foil are more difficult to unwind than others. This material is highly sensitive with regard to tension variations and during the production process the single layers can adhere to each other. Should the gap between the roll to be unwound and the next guide roll be too large, the foil can easily break and cause line downtime. Therefore, a special following roll, which maintains the distance between the bobbin and the next guide roller to a minimum, has to be installed.

Zero speed splice unwinds are highly sophisticated systems in which splicing is completed while the unwind is stopped. However, this does not mean that the entire line is at a standstill, as during splicing an accumulator situated downstream of the unwind supplies the coating unit with material. Depending on the type of splice unit (butt splice, thermowelding, etc...) a very short joint is produced, thus reducing scrap to a minimum. The disadvantages of this type of unwind are the relatively high price, the space requirement and the fact that it can only be used for certain materials.

The control of web tension is one of the most important issues in web handling. Adjusted tension must be constant at all times, as fluctuations cause creases or other web defects. Tension control inside the unwind is provided by dancer equipment. The dancer must be weight compensated and should be as light as possible, in order to reduce the inertia mass moment. A possible solution in this connection is the use of carbon fibre dancer rolls, which help to keep the tension control stable even in the case of imperfectly round running rolls.

Lightweight elastic materials such as 20gsm nonwovens require very low web tension (approx. 30 N/m), whereas 80gsm paper requires a tenfold higher value and products like paperboard need more than 1,000N/m. It is impossible to build a single line that can handle both the extremes created by very low and very high tension, but it is possible to create a line that can handle the range from 30-600N/m and thus process most standard products. Pull roll modules with sensitive web tension measuring devices and a sophisticated control system are required to achieve this result.

Treatment stations
One of the most important parameters of the finished product is the adhesion between the different layers or substrates. In case the extruded film does not stick to the substrate, primer stations can be used to apply an additional functional layer on the web.
Also corona treatment or flame treatment stations are used to improve the adhesion between the substrate and ten coating layer.

Extrusion

For example, the configuration, size and type of extruders are dependent upon layer structures and their output and thickness requirements. To select the correct number and size of extruders, one must know the products, material types and the required output.

In combination with feedblocks and different selector plugs, differing layer structures can be realized. Most common are 3- and 5-layer feedblocks, but higher layer numbers are also possible. Moreover, should the production of various product widths on one line be foreseen, there is a need for a deckling system to modulate the open die lip length.

The simplest answer is external deckling with an adjustable cover, which is pressed against the die lip. This is a cheap solution and for some applications is absolutely sufficient, although it has its handicaps, as the material inside the die cannot exit the die in the area where the deckling is mounted and therefore material degradation can result.

Die suppliers have produced different solutions to deckle the die from inside. In such cases T-channel dies must be used and precisely fitting deckling blades are moved into the die channels containing the melt. Special versions of these dies even have deckling blades with several adjustable bars, in order to influence the neck-in of the extruded material. These solutions are more expensive, but they offer numerous advantages with regard to constant material flow. Up to 50 per cent of the die can be deckled thus providing maximum product width flexibility.

The extrusion coating unit

The coating unit is a central element in the line and consists mainly of a cooling roll and a pressing unit. The different extruded materials demonstrate a variety of behaviour in connection with neck-in, stability, draw ratio, oxidation, etc. and in order to be able to run these materials on one line, it is essential that the relative position between the pressing nip and the die exit can be adjusted with regard to both height and machine direction.

Substrates can have different thicknesses and may either be flexible or rigid. The most important factor with regard to their combined production on one line is the nip between the cooling and pressing rollers. Compact materials such as films or paper can be pressed with adjustable force, but thick and soft materials, e.g. felt or foam have a tendency to crease in the coating layer following compaction in the coating nip and subsequent relaxation. Therefore, their processing requires adjustment of the gap between the cooling and the rubber pressing roller.

Overcoating is common in extrusion coating. Problems arise when the melt comes into contact with the rubber pressing roller, as it tends to stick to the roller and entwine it. Roll suppliers provide various rubber compounds with anti-adhesive characteristics, but none is suitable for every application. However, an endless PTFE tape running through the overcoating area can prevent the melt from sticking to the roller and also supports overcoating during cool-down, which results in straight edges and less fold-over.

Rolls with different shore hardness and diameter are required to achieve greater flexibility in the case of running patterned substrates and the smaller footprints for higher line pressure in the nip. For this reason, rubber roller exchange should be as straightforward and fast as possible. Therefore, the rollers need to be equipped with quick couplings for water cooling and easy to remove bearing blocks.

Cutting systems

Before winding up, the product requires edge trimming and may even be cut into several part-bobbin rolls. Therefore, a suitable cutting system is required, which can involve a razor blade, crush or shear cutting. In addition, a fail-safe edge removal system is needed to prevent downtimes of the entire line.

Winding systems

As already mentioned the extrusion coating process is continuous and therefore the winder must also be capable of undergoing roll changes without alterations in the production speed or line stops. Several different winder types are available on the market for continuous production. The wound roll may either be driven on the surface, the inside (centre driven), or from both positions, while the material can be transferred to the roll in direct contact or with a gap. Each winding system has its advantages and disadvantages, but it would go beyond the scope of this article to compare them all in detail.

Surface-driven drum winders have the simplest design. They are extremely robust and can produce the largest diameters and hardest rolls, but have a weakness with regard to elastic materials.

Turret winders provide the highest flexibility and therefore the handling of the widest product spectrum. They allow centre, surface, or combined centre-surface winding with taper curves for winding tension and nip force. Gap winding for sensitive or post-crystallizing materials is also possible. With all these settings available, adjusting the winder is a complex procedure, as each material may well require its own parameters. Consequently, a sophisticated control system with recipe storage is essential.

In summary it can be said that line configurations to cover a complete range of products are feasible, but the correct choice of equipment has to be made. Extensive discussions with the machinery supplier are therefore a must to ensure that investment spending translates into profits on the bottom line.

Mario Höllnsteiner, product manager, coating
Martin Kaltenecker, head of sales department

Lenzing, 12.10.2011

New BCF TEXTURIZING TECHNOLOGY cuts raw material costs by twenty per cent

03.08.2011

Carpet manufacturers have confirmed that replacing their old BCF equipment with new SML texturing technology has resulted in enormous raw material savings. In fact, they have been able to produce at least equal carpet quality with 20 per less raw material input. The key to these cost savings is the SML texturizing jet, which provides excellent crimp that permits a 20% reduction in yarn titer without any lowering of product standards.

Apart from material economies, the patented texturizing system allows SML customers to run their complete product range with just one system. This is because there is no need to change the texturizing jet or other components when switching to a yarn with a different titer. This again saves money.

SML has so much experience in this field, that it is able to offer a three-year warranty on the jet’s function and wear resistance. This is possible because the texturing jet shows almost no abrasive wear.

No integrated lamellas are used and therefore, as opposed to a lamella design, the air exhaust has a much shorter, screen-type insert, which drastically reduces the number of components and hence potential wear. In addition, special materials and surface treatments are utilized.

The unique design of the cooling drum also plays a major role in providing excellent crimp. The multiple plug wrapping on the drum with a very smooth surface allows plug cooling for a minimum of 15 seconds resulting in excellent cooling of 7 meters of plug, i.e. 700 meters of yarn. The square cross-section of the plug enhances guidance and cooling conditions and this extended stabilization on the cooling drum facilitates outstanding yarn properties. Testing has shown that this texturizing system is highly flexible, titers down to 300dtex can be processed without part changes.

Austrofil BCF lines are manufactured in a “horizontal” design, which provides a clearly ordered production process and a straightforward start-up procedure. The line can be easily operated from ground level and only one person is needed for start-up and operation.

Two pre-intermingling positions enable customers with a tricolor line to produce a wide selection of tonal variations. Yarns can be pre-intermingled singly or in combination, which results in mixed (mélange) or sprinkle effects. This method also allows different color blends through individual adjustments to the pressure at both positions. Accordingly, the customer has an opportunity to create fresh innovative effects in the final carpet.

The tricolor BCF line also possesses great flexibility, as it is possible to produce two differing yarn types simultaneously. These yarns can vary with regard to titer, the number of filaments, the required quenching speed, the amount of spin finish and the production speed.

As BCF lines are often operated in rough ambient conditions, a special e-container is employed by SML to ensure reliability and high uptime. This replaces traditional switch cabinets. The e-containers are centrally air-conditioned and provide top protection for all electronic parts (e.g. against corrosion due to spin finish vapor). The operator friendly “SMILE” control system, based on B&R hardware is developed entirely in-house.

Austrofil spinning lines are known all over the world as some 200 machines have been installed in the last 15 years. This has resulted in high levels of engineering competence and expertise.

SML focuses on design quality, reliability, quick delivery, low maintenance, immediate spare part supply and highly efficient customer service. Customers not only receive SML’s support in the start-up period, but also during the subsequent years of production. Indeed, the good relations between SML personnel and customers have resulted in numerous follow-up orders. SML stands for a genuine partnership in a fast-moving business world.
Christian Moser

„EcoCompact“ , the new stretch film standard

01.10.2010

„EcoCompact“ , the new stretch film standard

Visit SML at K2010, Hall 16, B47

The current success encouraged SML stretch film lines, to define a new standardized machine of a price-performance ratio second to none. The target has been to build a line, that offers a great number of features, which makes it interesting for a wide number of customers, and to reduce the price by means of standardization.

This new line produces stretch film of 4 x 500mm films at a net production capacity of around 1,200 kg/h and it runs at speeds in excess of 600 m/min.

Due to limited space availability in the industry the footprint of this line was minimized. The components are arranged very space efficiently on two levels. With extruders, air-conditioned e-cabinets and water pumps on the upper level we could compress the footprint to only 140 sq m floor space. This is only half of the space of a conventional stretch film line. But neither the number of dimension of installed equipment, nor the proven quality of SML components was compromised.

The line is fully equipped with 3 or 4 extruders, a choice between a 3 layer or a 5 layer feedblock, infrared gauge and a complete recycling unit with reel feeder!

We have installed our robust W4000 turret winder with automatic core and roll handling system. This proven winder, in combination with cut resistant guide rollers, provides perfect winding quality for machine rolls as well as for jumbo rolls up to 60kg. We have also included our ThinCore technology into the package of this winder.

Energy efficiency is one of the key features for a long use of the line in today’s energy competitive environment. With the combination of a High Speed Extruder and efficient conventional extruders, both boosted up with high value infrared heaters, this line does not fear any efficiency competition.

This new package, named “EcoCompact” is demonstrated and introduced into the market on the K’2010.

coreless machine rolls in top quality

05.11.2009

On the recently presented winder model 4000 of SML Maschinen GmbH, Austria, it is possible to produce coreless machine rolls. Installed in a 4-up stretch film line, the winder is capable of producing 4 x 500mm wide rolls weighing up to 16 kg each, either with or without paper cores. Running without cores does not impair roll built-up or winding quality.

Eliminating paper cores amounts to considerable savings for the film producer.
The advantages for the users of the film are more film on the roll and no cost for disposing empty cores, says Mr. Rauscher, product manager of cast film division.

SML GOES HIGH SPEED

21.09.2009

HIGH SPEED stretch-film-line has been taken into operation...

On 20th and 21st of October 2009 the latest innovation from SML Maschinengesellschaft mbH – the HIGHSPEED stretchwrap-extrusion-line was successfully put into operation and presented to an international specialised audience.
SML has reached its ambitious goal und has convinced the customers yet again that SML is the global technology leader in the range of the high speed film extrusion lines!

The new high speed line is designed for a mechanical speed of 1000m/min and an extrusion capacity of 2500 kg/h for 5 layers. Due to its speed potential, the aim is to run a constant maximum output at all standard film thicknesses of between 15 and 23µm. One special feature of this line is the new HSE extruders which produce the main layers of the film. The HSE extruders are achieving an extremely high throughput and are able to process standard polyethylene as well as metallocenes in the best melt quality. Above all a key priority was to develop a line with efficient energy consumption and less space requirements.

SML with its head office in Lenzing, Austria is specialised in building high-performance extrusion equipment and operates 3 additional offices in Kuala Lumpur (Malaysia), Beijing, (China) and Moscow (GUS).