Steel calender

Specific terms have been designated according to the function and composition of various roUs. Steel roUs that impose pressure, transmit heat, and emboss a pattern onto the fabric are known as pattern roUs. Flexible surface roUs that transport the fabric and permit pressure transmission to the fabric are termed bowl roUs or bowls. Bowl roUs are usually larger in diameter than pattern roUs. The material used to make these types of roUs is chosen according to the depth of surface smoothness to be placed on the fabric being calendered, and must be compatible with the pattern roU. Cellulose pulp, cotton, wool, cotton—wool mixtures, com husk, and various polymer materials are used as fillers for the roU surface compound. 

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. 

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. 

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

Many rubber products require uncured components which are not rectangular in cross-section. In such cases, at least one calender bowl may have a peripheral design cut into its surface to produce the desired cross section. This method is particularly useful for long production runs, but becomes expensive in terms of bowl change and bowl inventory necessary when many different sections are required. For shorter run working, the calender bowl may consist of a heavy basic mandrel onto which may be clamped solid cylindrical or split cylindrical steel shells into which the appropriate profile design has been cut. Such calenders often have the bowls outside the frames to improve access and facilitate bowl changing. Consequently the bowls are comparatively short. 

The calendering process and its conditions are developed or modified according to the requirements of subsequent operations and the purpose for which the sheet is used. Thus for sheets which are to be open cured, such as in chemical plant lining and custom built items such as inflatables and ebonite pipes, roll coverings for paper and steel mills, the calendering needs to be more exact than the sheets which are used for blank preparation for molding of... 

Cardiovascular Effects. Information regarding cardiovascular effects in humans after inhalation exposure to chromium and its compounds is limited. In a survey of a facility engaged in chromate production in Italy, where exposure concentrations were 0.01 mg chromium(VI)/m3, electrocardiograms were recorded for 22 of the 65 workers who worked in the production of dichromate and chromium trioxide for at least 1 year. No abnormalities were found (Sassi 1956). An extensive survey to determine the health status of chromate workers in seven U.S. chromate production plants found no association between heart disease or effects on blood pressure and exposure to chromates. Various manufacturing processes in the plants resulted in exposure of workers to chromite ore (mean time-weighted concentration of 0-0.89 mg chromium(ni)/m3) water-soluble chromium(VI) compounds (0.005-0.17 mg chromium(VI)/m3) and acid-soluble/water-insoluble chromium compounds (including basic chromium sulfate), which may or may not entirely represent trivalent chromium (0-0.47 mg chromium/m3) (PHS 1953). No excess deaths were observed from cardiovascular diseases and ischemic heart disease in a cohort of 4,227 stainless steel production workers from 1968 to 1984 when compared to expected deaths based on national rates and matched for age, sex, and calender time (Moulin et al. 1993). No measurements of exposure were provided. In a cohort of 3,408 individuals who had worked in 4 facilities that produced chromium compounds from chromite ore in northern New Jersey sometime between 1937 and 1971, where the exposure durations of workers ranged from <1 to >20 years, and no increases in atherosclerotic heart disease were evident (Rosenman and Stanbury 1996). The proportionate mortality ratios for white and black men were 97 (confidence limits 88-107) and 90 (confidence limits 72-111), respectively. 

Hepatic Effects. Chromium(VI) has been reported to cause severe liver effects in four of five workers exposed to chromium trioxide in the chrome plating industry. Derangement of the cells in the liver, necrosis, lymphocytic and histiocytic infiltration, and increases in Kupffer cells were reported. Abnormalities in tests for hepatic dysfunction included increases in sulfobromophthalein retention, gamma globulin, icterus, cephalin cholesterol flocculation, and thymol turbidity (Pascale et al. 1952). In a cohort of 4,227 workers involved in production of stainless steel from 1968 to 1984, excess deaths were observed from cirrhosis of the liver compared to expected deaths (0/E=55/31.6) based on national rates and matched for age, sex, and calender time having an SMR of 174 with confidence limits of 131-226 (Moulin et al. 1993). No measurements of exposure were provided. Based on limited information, however, the production of chromium compounds does not appear to be associated with liver effects. As part of a mortality and morbidity study of workers engaged in the manufacture of chromium(VI) compounds (84%) and chromium(III) compounds (16%) derived from chromium(VI) in Japan, 94 workers who had been exposed for 1-28 years were given a complete series of liver function... 

Polyvinyl Chloride. (Table 15.5) this is the most versatile of the commercial thermoplastic polymers. It is used mainly for rigid and flexible plastics, for rubberlike products, for coatings on steel, cloth, and paper, and in smaller amounts for specialty fibers. It is processed mainly by extrusion and calendering, and in smaller amounts by injection, compression, and... 

A calender is essentially a set of four giant steel rollers mounted in a cast iron frame, usually in an inverted L-shape, in such a way that they can be rotated, and the distance between each pair of rollers adjusted. Consecutive rolls squeeze the material resulting finally in a continuous sheet of the desired thickness. PVC, ranging from rigid to semi-rigid to flexible, is produced continuously in film or sheet up to approximately 1.5 millimetres in thickness and up to and over 2.0 metres in width. 

With the war years, polyvinyl chloride (PVC) resins came under study, and plasticized PVC compounds, based on these resins, became available as calendered sheet lining materials-the material of choice for stainless steel pickling and for chrome plating and other exposure employing mixtures of chemicals including such strong oxidants as nitric and chromic acid which rapidly attack natural rubber. (A higher temperature limit modification now seldom seen is PVDC, for which the continuous temperature limit is said to be 170°-180°F.)... 

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