Three-roll mills

Three-phase furnaces, 12 304 Three-roll mills, 18 65 Three-screw pumps, 21 73 Three-stage (ternary) cascade refrigeration systems, 21 549-550 Three-stage refrigeration systems,... 

Average temperatures (40-70°C) in combination with high-shear dispersion equipment, of which three-roll mills are a good example, appear to afford the best results in terms of pigment dispersion in wetting systems, such as offset varnish. Fig. 33 shows a curve in which the degree of dispersion reaches a distinct maximum at one particular temperature. 

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...

Fig. 35 Influence of the binder on the CPVC and of the binder and the CPVC on the viscosity of P.Y.13 in sheet offset vehicles of different composition at constant dispersion conditions in a three-roll mill.

Fillers may be added to low-viscosity resins by conventional sigma-blade mixer or the same type of equipment used for mixing paint systems. Three roll mills are generally employed for more viscous systems to obtain thorough wetting of the filler by the resin matrix. 

Cone and drum plasticators as well as two- and three-roll mills are other ways of making concentrates. These along with Z mixers are probably best suited for low-viscosity polymer carriers, plastisols, or paste concentrates. Some concentrates based on wax and stabilizer carriers are produced on this type of mixer. 

Figure 20.1. Common dispersing equipment for liquid color (a) horizontal media mill (b) three-roll mill (c) dissolver mixer.

The choice of a mill may depend on the desired characteristics of the liquid color needed. If a heavy viscosity is acceptable, the three-roll mill is an excellent tool. The premixed liquid color is introduced at the first nip. After passing through that nip, about half the liquid clings to the second roll and is carried around to the second nip. About half that liquid clings to the third roll and is scraped off and collected by a doctor blade (also called the apron). That is the finished liquid. Since the liquid is split twice, about three-quarters of the liquid that passes through the first nip is returned to be reprocessed at the first nip. 

Three-roll, one-roll, and stone mills constitute a more mature dispersion technology still in use with medium viscosity millbases. A three-roll mill consists of the feed, center, and apron rolls. In roll mill operation ... 

The three-roll mill ean handle viscosities up to 200 Poise, and therefore can be used for materials not suitable for ball and sandmills... 

Due to the introduetion of easily dispersed pigments and fillers, three-roll mills have lost some of their importance. This may change in the future when solventless systems of higher viseosities become more common... 

In the third stage, the viscosity changes from high to low due to the addition of diluent. The viscosity range which can be handled by high speed mixers is similar to the range of a three-roll mill, i.e., up to about 200 Poise... 

It may be possible to diperse the pigment in a slowly evaporating solvent such as isophorone or Solvesso 150 by using a differential three-roll mill. This technique is similar to the plasticizer dispersion technique except the plasticizer is replaced by a solvent. 

Add silver-flake flUer (Ferro s 26LV) to the resin mixture at 80% by weight and blend in a three-roll mill until homogeneous. 

The same thermosetting polystyrene SMP was used in this study. In addition to the 40% by volume of glass microbaUoons, 0.15% by volume of multiwalled carbon nanotubes was also added, which was the same as in Reference [38]. The multiwaUed carbon nanotubes (Cheap Tubes Inc.) have a density of 2.1 g/cm, diameter of 20-30 nm, and length of 20-30 pm. Similar to Reference [38], a two-step procedure was used to prepare the syntactic foam. First, the carbon nanotubes were added to Part A of the polymer. The mixture was mixed with the assistance of an ultrasound mixer for 30 minutes at a frequency of 20 kHz (Sonics Vibracell VC 750W) and a three-roll mill for one pass (NETZSCH type 50) (see Rgure 3.26). Second, microballoons and hardener (Part B of the polymer) were added to the carbon nanotube/Part A mixture and mixed with a spatula for 15 minutes. It was then poured into an aluminum mold of... 

Hardeners such as dicyandiamide need to be ground using equipment like a three-roll mill (Figure 21.70) to ensure proper distribution. Mixing is important and high shear and static mixers are used. Wet resins dissolved in solvents can be coated by many techniques (Figure 21.71) normally onto a silicone coated release paper, supplied with a differential... 

Three-roll mill See triple roller mill. 

Raza, M. A. Westwood, A. V. K. Brown, A. P. Stirling, C., Texture, Transport and Mechanical Properties of Graphite Nanoplatelet/Sihcone Composites Produced by Three Roll Mill. Compos. Sci. Tech. 2012, 72,112-118. 

Finally, testing with a three-roll mill and simplex single-worm and simplex twin-worm refiners is essential. Only testing for adeqnate color dispersion, surface roughness, plasticity, and temperature assure the proper selection of refining equipment. 

This section discusses subsequently the Stephan mixer, the rotor-stator mixer, the planetary mixer, the mortar with pestle, the beaker mixer/blender, the three roll mill, the coffee grinder, the Topitec mixer and Unguator mixers. 

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