Calendering line

The calender was developed over a century ago to produce natural rubber products. With the developments of TPs, these multimillion dollar extremely heavy calender lines started using TPs and more recently process principally much more TP materials. The calender consists essentially of a system of large diameter heated precision rolls whose function is to convert high viscosity plastic melt into film, sheet, or coating substrates. The equipment can be arranged in a number of ways with different combinations available to provide different specific advantages to meet different product requirements. Automatic web-thickness profile process control is used via computer, microprocessor control. 

A Calender Line for Coating of Textile and Steel Cords.1008... 

The purpose of this section is to explain in a qualitative way how the product quality is related to the calendering parameters. Therefore a simplified calender model is presented. The model describes the pressure buildup in the calender nip region as a function of compound viscosity, clearance, calender line speed, rolling bank height, as well as geometrical data. The general layout of a typical steel and fabric cord calender is explained by means of the result of the presented calender model. 

Pressure between two calender rolls Calender line speed... 

From the diagrams in Figures 35.34 through 35.40 it might become clear that all parameters will have a tremendous influence on the calendering process and therefore on the calendered product. The calender line speed seems to have the least influence on the calendering performance. 

In modem calender lines both compensating devices can be found. It is common that wide calender rolls are crowned in such a way that under working conditions the crowning compensates the roll deflection due to high shear forces. Crowning specifications can be understood by means of the presented theory. Since the lowest nip forces can be achieved at high clearance settings, low line... 

There are various textbooks available on the calendering process,which is referred for an extensive explanation. In this section the impact of the presented theory on the general layout of a dual-purpose calendering line for textile cord and steel cord coating is considered. 

Major changes in calender line speed to be avoided... 

Figure 35.43 shows a general layout of a dual-purpose calender line for coating steel cord and textile cord. The heart of the production line is the four-roll calender in an S-configuration. Two mbber sheets are formed in the upper and lower nip. The thin sheets are guided to the middle nip and the cords are coated in the middle nip between the two rubber sheets. Generally outer roll bending is applied on rolls 2 and 3 to compensate the roll deflection caused by the nip force in nip 2. Rolls 1 and 4 can be set crossed respectively to rolls 2 and 3. 

FIGURE 35.43 Example of a general layout of a dual-purpose calender line for coating textile and steel cord. 

Figure 35.44 typically shows the capability of a modern calender line to produce a 1450 mm coated sheet without a big thickness gradient across by applying the proper cross axes settings for various products. The products fulfil the requirement mentioned earlier in this paper. 

The calender is included in a calendering line (see Figure 5.13) made up of ... 

Figure 5.13. Principle of a calendering line with a five-roll calender...

In a calender line, the polymer melt is transformed into films and sheets by squeezing it between pairs of co-rotating high-precision rollers. Calenders are also used to produce certain surface textures which may be required for different applications. Today, calendering lines are used to manufacture PVC sheet, floor covering, rubber sheet, and rubber tires. They are also used to texture or emboss surfaces. When producing PVC sheet and film, calender... 

On any calender line there are several possible sources of contamination, the first being the raw materials used. In most resins there will be a small number of discoloured grains, which are accepted up to a specified level. On occasions a manufacturer s equipment fails and produces resin with more than normal contamination of this kind. Some particles may not be discoloured but may fail to disperse and so cause small lumps in the film (known in clear films as fish eyes ). On the other hand, lumps may not necessarily be attributable to faults in the resin—they can arise also from poor dispersion of plasticizer, or from degradation taking place at some stage in the process. 

Capital investment for a calender line may be about 5 million. Operating cost may be about 500 per hr. Calendering is a very highspeed method of producing plastic film and sheet, but high-speed economy must be balanced against quality of the finished product. 

Figure 9.2 Calender line starting with mixer...

Figure 9.3 Examples of the arrangements of rolls in a calender line...

Coated substrates involve different materials such as coated credit cards, paper, woven and nonwoven textiles, plastic or aluminum films and sheets, and roll coverings. Calender lines can process one coated side, both sides, or laminated (multiple substrates coated between each substrate). Calender with three rolls is usually sufficient for one-sided coating. However four rolls are used for extremely thin coatings. The 4-roll calender can be used for double-sided coating that is applied simultaneously on both sides. Specialized calendering equipment is used for certain products such as credit cards, floor tiles, and window curtains. 

A web thickness between 0.002 to 0.020 in. (0.05 to 0.50 mm) is generally the kind of plasticized film and sheeting produced by calender lines. For extremely light gauges, those under 0.001 in. (0.02 mm), calendering... 

Variations in these multimillion-dollar calender lines are dictated by the very high forces exerted on the rolls to squeeze the plastic melt into thin film or sheet web constructions. High forces at least up to 6000 psi (41 MPa) could (if rolls were not properly designed and installed) bend or deflect the rolls, producing gauge variations such as a web thicker in... 

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