Cord calendering

Recent Developments in Rubber Mixing and Cord Calendering in Tire Production... 

A FUNDAMENTAL APPROACH OF THE CORD CALENDERING PROCESS 35.5.1 Introduction... 

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. 

Fig. 5. Calendered unidirectionaHy reinforced single-ply cord—mbber lamina where 9 is the helix angle, E is lamina, and Tis tire.

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

The product quality, however, is related to the calendering process. Thickness gradients across the calendered product, thickness variations along the product, as well as cord density distribution determine the quahty of the product and are tremendously related to the process parameters. 

Cord tension variation 250 N per total width both in calendering direction and across... 

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. 

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. 

Beside roll deflection and therefore thickness gradients in the product high pressure in the calender nip may cause varying positions of the cords in the calendered sheet in case of cord coating. 

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... 

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

FIGURE 35.44 Typical thickness deviation across the calender direction for various products (textile cord sheet). 

Only in the calender area the cord tension is high enough to resist the pressure caused by the mbber flow in the calender nip region. Therefore, a constant cord density can be maintained by means of locally high cord tension. 

Cord and belt formation Washdown, spills, leaks Organics and sohds from dipping operation oil from seals, in roller mills, calenders, etc. 

Air blisters generally occur due to trapped air during the processing of the rubber in the calender or extruder or during hand building up of the products. The remedial measures to be undertaken are 1) Modify process temperature or pressure, 2) Feed the calender or extruder with adequate rubber stock, 3) Prick out visible blisters when the compound is in unvulcanized state, and 4) Use bleeder cords between metal and the rubber sheets applied at the welded places in the rubber lining process. 

Fig. 15.1 (a) A four-roll, inclined Z calender for double casting of tire cord, (b) A four-roll,... 

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