Roll temperatures

Use fully killed or fine grain steel, controlled rolling temperatures high Mn/C ratios eliminate sharp corners in design, remove defects from steel heat treat steel. For cryogenic operations use high nickel alloy steels or austenitic stainless steels, depending on temperature. 

Calendering can achieve surprising accuracy on the thickness of a sheet. Typically the tolerance is 0.005 mm but to achieve this it is essential to have very close control over roll temperatures, speeds and proximity. In addition, the dimensions of the rolls must be very precise. The production of the rolls is akin to the manufacture of an injection moulding tool in the sense that very high machining skills are required. The particular features of a calender roll are a uniform specified surface finish, minimal eccentricity and a special barrel profile ( crown ) to compensate for roll deflection under the very high presurres developed between the rolls. 

The structure of millscale consists of three superimposed layers of iron oxides in progressively higher states of oxidation from the metal side outwards, viz. ferrous oxide (FeO) on the inside, magnetite (Fe304) in the middle and ferric oxide (Fe203) on the outside. The relative portions of the three oxides vary with the rolling temperatures. A typical millscale on 9.5 mm mild steel plate would be about 50/tm thick, and contain approximately 70% FeO, 20% Fej04 and 10% FejOj. 

Fig. 32 Effect of the roll temperature and the number of passes during the dispersion of 20% P.V.19, (3-modification, in a sheet offset vehicle at constant pressure between the rolls on the viscosity of the printing ink.

Fig. 33 Effect of the dispersion temperature (roll temperature) and the pressure between the rolls during dispersing of Pigment Red 53 1 in a sheet offset varnish (pigment concentration 20%) in a three-roll mill on the degree of pigment dispersion. This correlation is illustrated by showing the viscosity of the printing inks at a shearing rate D = 220 s...

A mat chill roll with a high surface roughness should be used to minimize sticking problems. The chill roll temperature should be kept at about 30-40°C for Ecovio whereas Ecoflex can be run at lower chiU roll temperatures. 

Figure 4. Hot plasticity of sulfide inclusions during hot rolling of steel as a function of oxygen content, Mn/S ratio, rolling temperatures, and substitution by stronger sulfide formers. The hot plasticity is measured in length-to-width ratio of elongation after hot rolling, in longitudinal sections.

Tile is manufactured in several ways. In each method, a continuous sheet is formed gauge refinement and planishing are carried out in subsequent calendering steps. Stresses that could lead to poor dimensional stability are avoided. The efforts to prevent stresses are governed by formulation, stock and roll temperatures, conveyor speeds, etc. After the final calendering, a resin—polymer—wax finish is applied to the surface of the sheet which is then buffed before it moves to the punch press. Frame scrap and tile rejected because of defects are returned to the mixers and recycled. 

It is desirable to operate with the lowest roll temperatures for... 

Aluminum particle rolling directly into continuous strip. Molten metal is sprayed into particles about the size of rice in a controlled environment, then brought to a desired rolling temperature and continuously rolled into instant coiled sheet This process can handle alloys which normally cannot be cast in ingot form. 

Preparation of Blends. The blends were prepared by milling the desired quantity of polyether additive with a portion of a masterbatch chosen from those described in Table II. Both the temperature and procedure used for the milling operation were critical. As is discussed in a subsequent section, temperatures that can be attained on a steam-heated mill were generally too low to attain good properties. Consequently, most milling was carried out on a 4-inch oil-heated mill at the desired temperature. The temperatures given are the mill roll temperatures. However, when the stock temperature was measured, it was about the same as the mill roll temperature. 

Fig. 15.3 Pressure profiles in the calender gap at various cylinder axial positions, with rigid PVC (Vestolit Z 1877) at equal roll speeds of 5cm/s and roll temperature of 185°C minimum gap, 0.6 mm roll diameter, 30 cm width, 50 cm. Note the drop in pressure in the cross-machine direction with distance from the centerline, which drops to zero at the end of the rolled web. [Reprinted by permission from W. Unkruer, Doctoral Thesis, KV, Technischen Hochschule, Aachen, 1970.]...

Mixed stocks should be used promptly or stored at temperatures below 18°C (65°F) to prevent scorching, and great care should be taken to exclude moisture. Typical roll temperatures for calendering recommended for VITON E-60C or related FLUOREL types are38 ... 

The amount of acid used per ton of stainless steel varies widely, depending on the surface area per unit weight, the temperature of the treated surface, the pretreatment conditions (annealing and rolling temperatures) and the grade of the stainless steel. Industry estimates vary widely, ranging from about 5 to 50 pounds of nitric acid consumed per tome of stainless steel produced. 

Mill scale (rust) and pitting. The three layers of iron oxide scale formed on steel during rolling vary with the operation performed and the rolling temperature. When mill scale is placed in an electrolyte, any defect in the mill scale surface becomes the anode the remainder of the mill scale, which is usually many times larger than the defect, becomes a very strong cathode. An electric current can easily be produced between the steel and the mill scale. This electrochemical action will corrode the steel without affecting the mill scale. 

The passage of hot melt between the rolls creates a pressure forcing them apart and the calculation of tolerances using a statistical model has been described (417). There is a rolling bank of feed material created in the gap or nip set between the first pair and also the second pair of rolls. Passage of the material is controlled by roll temperature, surface finish and the ratio of the roll speeds at the nip. The final calender nip controls film thickness. 

The setting of roll temperatures depends on the cure systems used. Typically, stocks with diamine (e.g., Diak No. 3) are calendered at temperatures of top and middle rolls set 15°C to 20°C (27°F to 36°F) lower than stocks with bisphenol and peroxide [51]. 

Dry Film Lamination The resist lamination was performed using a Model 712 Hot Roll Laminator supplied by MacDermid, Inc., Waterbury, Connecticut. The heart of the lamination system is an aluminum-cored fuser roll which is about 2.3 inches in diameter and is coated by 0.1 inch thick additives-filled silicon rubber. Figure 3 shows a schematic of the fuser roll. All dry film lamination experiments were performed using a conveyor speed of 20 inches per minute an air-assisted pressure of 0 PSIg and a fuser roll temperature of 103 C. The hold time between surfece treatment and resist lamination was kept constant at 60 minutes. 

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