THREE-ROLL

Sheet can be produced by melt extmsion, but in this case a three-roll stack of quenching roUs is generally used (Fig. 2). More than three roUs may be used where necessary. The roUs may be mounted vertically or horizontally. The web is extmded through a slot die in a thickness close to the desired final thickness. The die is in very close proximity to the first chill roU or chill-roll nip. The web may be cast horizontally directly onto the upper chill roU of the stack as shown (Fig. 2), or it may be extmded into the first nip directly. The roUs quench the sheet and provide the surface polish desired. In some applications, matte or embossed roUs maybe used to impart special surface characteristics for certain functions. Where the utmost in optical (glazing) quality is desired the trend has been to mount the roU stack horizontally. The hot melt is then extmded vertically down into the first nip. This avoids problems associated with sag of a horizontal hot melt no matter how short the distance between die and quench. 

Fig. 8. Sheet extrusion A, die inlet B, die C, three-roll finisher D, support roUers E, edge-trim cutter F, puU roUs and G, saw or shear (15).

The Bradley pneumatic (air-swept type) Hercules mills Bradley Pulverizer Co.) are centrifug ring-roll-type pulverizing mills which can be fitted with either two or three rolls. These mills are suitable for the pulverization of many materials to produce as coarse as 98 percent minus-20 mesh to as fine as 99.5 percent minus-325 mesh. The size of the pulverized product can be varied by adjusting the fineness selector mounted on top of the mill. Capacities range from 225 kg/h (500 Ib/h) to 90 Mg/h (100 tons/h). When combined with the superfine Bradley IU 4C classifier, this mill can make a product finer than 11 [Lm. 

According to U.S. Patent 3,002,891, the following describes pilot plant production of bromelain. Stripped pineapple stumps were passed four times through a three roll sugar mill press. 

The calendering configuration of rolls may consist of two to at least seven rolls. The number of rolls and their arrangement characterizes them. Examples of the layout of the rolls are the true L , conventional inverted L , reverse fed inverted L , I , Z , and so on. The most popular are the four-roll inverted L and Z rolls. The Z calenders have the advantage of lower heat loss in the film or sheet because of the melts shorter travel and the machines simpler construction. They are simpler to construct because they need less compensation for roll bending. This compensation occurs because there are no more than two rolls in any vertical direction as opposed to three rolls in a four roll inverted L calender and so on. 

Hose may be hand built using a three roll wrapping machine. The centres of the three rolls form an equilateral triangle. The hose during construction sits on the junction between the two lower rollers and pressure is exerted to consolidate the composite by the upper movable roller. An extruded inner liner, after fitting to a solid inner mandrel, is placed into the machine between the rollers and then the various layers of rubber coated or resorcinol-formaldehyde-latex treated, fabric are applied in a spiral form, with overlap. Once the reinforcement layers have been added the cover rubber is applied and a cloth, usually nylon, is spirally wrapped around the constructed hose using the roller system. The hose is now ready for vulcanisation. 

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.

Taking the example of a three-roll calendering machine, the successful calendering operation is ensured by the following basic features. 

In setting up the three-roll calender for topping one side of the fabric even surface speeds of rolls are used for the pair of rolls forming the fabric nip and a friction ratio of 3 2 between those forming the rubber nip. 

In the case of a three-roll calender, an alteration to the fabric nip does not affect the rubber layer thickness, since it is a movement of the bottom roll in relation to the fixed bearing middle roll. With a four-roll calender the stack or the breast roll type where the two top rolls are adjustable, the opening or closing of the fabric nip does, in practice, frequently result in a disturbance of the top roller nip. 

It is interesting to know that experience has shown that difficult fabrics with respect to tension variability can be best handled on a three-roll calender. 

Fig. E6.1b Alternative design solution of a roll pump from building block 1. On the top we see two two-roll pumps one co-rotating and the other counterrotating. The latter is a toothless gear pump where the pumping mechanism is viscous drag rather than positive displacement. In the middle we have three three-roll configurations, and at the bottom a four-roll pump.

A further development is the Calendrette—a three-roll machine fed by an... 

---