Pasting roller

Refining. The next stage in chocolate processing is a fine grinding in which a coarse paste from the mixer is passed between steel rollers and converted to a drier powdery mass. Refining breaks up crystalline sugar, fibrous cocoa matter, and milk soflds. 

Modem 5-roU refiners with 2-m wide rollers can process 2200 kg of paste per hour. Output is dependent on particle size. 

Paint-grinding roller mills (Fig. 20-52) consist of two to five smooth rollers (sometimes caUed rolls) operating at differential speeds. A paste is fed between the first two, or low-speed, rollers and is discharged from the final, or high-speed, roller by a scraping blade. The paste passes from the surface of one roller to that of the next because of the differential speed, which also apphes shear stress to the film of... 

When two layers of the substance are displaced relative to one another, the nuclei of phase A, located between them, can be regarded as kind of a roller about which oscillations are executed. - - - when the two layers of phase AB are displaced relative to one another, they transport past the nucleus, in its immediate vicinity, a multiplicity of atoms of both kinds. - - - it follows that all the atoms A passing in the immediate vicinity of the nucieus have sufficient time to combine with the latter and this in fact may be the mechanism of the growth of the nuclei of the new phase. ... 

Sheet molding compound (SMC) consists of randomly oriented chopped fibers in a matrix of resin and filler. SMC is produced in the continuous manner shown in Figure 1-16. Note that the polyethylene film protects the roller system from getting gummed up with the resin-filler paste. The rug-like rolls of SMC are then used in compression molding machines to create large parts such as the sides of cars and trucks. 

In the coating of continuous metal coils, reverse roller coating is often used. In this technique the web is moving counter to the application roller direction, so that the paint is partly wiped off by the moving coil. Shear leads to better flowout. Another type of reverse roller coating is used for the application of stiff paste fillers to chipboard. Application is by forward roller, but this is immediately followed by a reverse roller, which presses the filler into the board and doctors it smooth. 

A matter of considerable importance in the selection of an application method is its efficiency. Spray techniques are usually inefficient, since many droplets drift past the target and are lost. Even electrostatic spraying can waste as much as 35% of the paint. There is some loss of paint in most methods, but roller coating, curtain coating and electrodeposition are very efficient. Electrodeposition is also a very useful technique where corrosion resistance is important, since it applies a uniform coating over nearly all surfaces of even the most complex-shaped article. 

All AB, alloys are very brittle and are pulverized to fine particles in the hydrid-ing-dehydriding process (see Sec. 7.2.1). Thus electrodes must be designed to accommodate fine powders as the active material. There are several methods of electrode fabrication Sakai et al [35] pulverize the alloy by subjecting it to several hydrogen absorption-desorption cycles, before coating the resulting particles with Ni by chemical plating. The powder is mixed with a Teflon dispersion to obtain a paste which is finally roller-pressed to a sheet and then hot-pressed to an expanded nickel mesh. The fabrication of a simple paste electrode suitable for laboratory studies is reported by Petrov et al. [37],... 

Spherical rollers were machined from AISI 52100 steel, hardened to a Rockwell hardness of Rc 60 and manually polished with diamond paste to RMS surface roughness of 5 nm. Two glass disks with a different thickness of the silica spacer layer are used. For thin film colorimetric interferometry, a spacer layer about 190 nm thick is employed whereas FECO interferometry requires a thicker spacer layer, approximately 500 nm. In both cases, the layer was deposited by the reactive electron beam evaporation process and it covers the entire underside of the glass disk with the exception of a narrow radial strip. The refractive index of the spacer layer was determined by reflection spectroscopy and its value for a wavelength of 550 nm is 1.47. 

The mixture is then run on to a sheeting table which is made on the same principle as a paper-making machine, but with the wire replaced for safety by a suitable cloth filter. The pulp passes over suction tubes and between rollers in order to remove as much water as possible, so that the paste when stripped from the cloth contains 20-25% of water. It is dried on trays or else in trucks through which air at 50°C is blown. 

An important feature is the ability of the roller grooves to aid the transport of material through the mill, thus providing a means to control residence time and mill capacity. This transporting action is particularly important with materials which would not readily flow by gravity. Pastes and sticky materials fall into this category. 

Rolling. The paste intended for the manufacture of solventless powder is first rolled between drying rollers (at 50-60°C) and then between gelatinizing rollers, as in the manufacture of ballistite. This operation must be very carefully controlled. 

Uniformity of the paste is a prerequisite for good pressing. This depends chiefly on the uniformity with which the ingredients are mixed under water and on the uniform gelatinization of the mass between the rollers. Insufficient accuracy or defective execution of either operation can be highly detrimental to the pressing process, sometimes rendering it impossible. 

Rolling. It was carried out using horizontal rollers 40 cm dia. and 100-120 cm in length, rotating with a speed of 11 r.p.m. For paste made with dinitroglycol it was sufficient to maintain a temperature of 70-80°C. A charge of about 15 kg was rolled for 18-30 min. The sheets issued from the rollers completely gelatinized. In cannon powders 3-5% water was left in the sheets since this facilitated the formation of tubes. 

Drying of Solventless Double-Base Propellants. Since the manuf of solventless double-base proplnts is potentially hazardous, particularly rolling, drying, extruding machine operations, all such opns are performed by remote control. Following the final mixing, wringing screen opns, the water-wet paste is preheated to 90°F and fed by remote control into differential rollers in sufficient quantity to make two sheets. Hot water or steam is used to control... 

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