Calendering applications

As in surface application, calendering can have a positive influence on sizing, if properly developed prior to calendering. However, if the sizing is not properly developed, this can be a negative influence, especially with poorly dispersed rosin size or poorly reacted/fixed AKD size. 

Calendering processes, of great importance in the production of sheet materials from PVC compounds, are little used with polyethylene because of the difficulty in obtaining a smooth sheet. Commercial products have, however, been made by calendering low-density polymer containing a small amount of a peroxide such as benzoyl peroxide to give a stiff but crinkly sheet (Crinothene) which was suitable for lampshades and other decorative applications. 

The main applications for CPVC arise from the fact that the material has a softening point of about 100% and very good chemical resistance. Particular interest has been shown in waste and soil systems which may pass hot water effluents. Calendered sheet may be vacuum formed for uses where hot filling techniques are employed, for example in jam packing. 

Tape may be made by a similar process. In this case the lubricant selected is a non-volatile oil. The preform is placed in the extruder and a rod extruded. The rod is then passed between a pair of calender rolls at about 60-80°C. The unsintered tape is often used for lapping wire and for making lapped tube. Sintering is carried out after fabrication. The current most important application of unsintered tape is in pipe-thread sealing. 

By applying a sufficient high cord tension this can be avoided. However, cord tension might cause some elongation. The duration of application of high cord tension has to be as short as possible in order to avoid creep. The complete upstream and downstream of the calender is mainly dedicated to maintain the preset cord tension. In order to keep the cord tension as low as possible the tension can be set in 3-5 steps. One (or two) in the textile upstream, one in the calender area, and... 

A process for making hollow mbber articles from a single sheet of calendered unvulcanised mbber. The surface of the sheet is semi-vulcanised and the application of a swelling agent causes the sheet to split thus forming the hollow article, the vulcanisation of which is completed thereafter. Homo polymer... 

The correction of calender bowl deflection by application of hydraulic pressure to counteract the forces tending to produce deflection. 

Hose constmcted by wrapping the reinforcing fabric and the calendered cover on to the inner tube which has been fitted over a mandrel of the desired diameter. The application of the fabric, the cover and of the wrapper may be done either by hand or by machine. 

An alternative method to that of using a spreading machine or a calender for the initial preparation of fabrics for application of rubber (for composite product assembly) can be by the use of dip coaters. Application of rubber compound by this method ensures a better penetration of the fabric interstices than can be achieved by conventional frictioning techniques using calenders. More delicate fabrics which would not be strong enough for calender application can also be treated with rubber by this technique. 

Roller die systems can combine a dump extruder with a two bowl calender to produce good quality sheet for application in such products as conveyor belting. Roller head extruders are more integrated with the calender bowls mounted at the front of the extruder cylinder. 

This technique is commonly used to produce films of polyolefins for packaging and other applications, competing with cast and calendered films. Tlie thickness is commonly in the 2CU500 pm range but more rarely can be in the 10-800 pm range. 

Sulfonated EPDMs are formulated to form a number of rubbery products including adhesives for footwear, garden hoses, and in the formation of calendered sheets. Perfluori-nated ionomers marketed as Nation (DuPont) are used for membrane applications including chemical-processing separations, spent-acid regeneration, electrochemical fuel cells, ion-selective separations, electrodialysis, and in the production of chlorine. It is also employed as a solid -state catalyst in chemical synthesis and processing. lonomers are also used in blends with other polymers. 

Many different processes are used to apply a thin layer of liquid-melted polymer, polymer solution or dispersion including rollers, spraying, calendering, and brushing. Here we will look at the industrial application of coatings onto film and sheetlike materials. Figure 18.16... 

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