Mixer roll mills

Polyvinyl chloride Rigid PVC Plasticized PVC Dry blends Liquid or paste dispersions Intensive high-speed mixers Roll mills or disk Impeller mixers... 

The mainstays of the rubber industry for over 70 years has been the two-roll (open) mill and the Banbury (internal) mixer. Roll mills were first used for rubber mixing over 120 years ago. The plastics and adhesives industries later adopted these tools. 

Ceramic feedstocks for extrusion can be produced either in a batch process, or continuously. Which approach is taken depends on the details of the application and the material to be prepared. In the ceramic industry at present, four different types of machines are generally used High shear mixers, roll mills, screw extruders and shear rolls. 

Experiments were run with natural and synthetic rubber by using an internal mixer, roll mills, and an extruder. As the gelation is a mechano-chemical process, independent of the elastomer structure, the reaction was applied to plastomers masticated while in the viscoelastic state [188]. The reaction takes place with poly(methyl methacrylate), poly(vinyl acetate), and polyethylene. No evidence for the cross-linking of polystyrene was observed. The addition of aluminum isopropoxide aids the formation of block copolymer. This technique was applied to the system polyethylene-poly(vinyl acetate). 

Two-Roll Mills These mills contain two parallel rolls mounted in a heavy frame with provision for accurately regulating the pressure and distance between the rolls. As one pass between the rolls does little blending and only a small amount of work, the mills are practically always used as batch mixers. Only a small amount of material is in the high-shear zone at any one time. 

Polyethylene can be compounded on any of the standard types of mixing equipment used for visco-elastic materials. For laboratory purposes a two-roll mill is suitable operating temperatures varying from about 90°C to about 140°C according to the type of polymer. On the industrial scale, compounding is undertaken either in internal mixers, or more particularly, extrusion compounders. 

Blending of polymer, plasticiser and filler may be carried out using two-roll mills or internal mixers as commonly used in the rubber industry. Alternatively, since the raw polymer is supplied as a free-flowing powder a dry blending process similar to that now widely used with PVC (see Chapter 12) is also used. 

In most of these routes, premixing is carried out in a trough mixer at room temperature to give a damp powdery mass or mush . This may then be fluxed on a two-roll mill, in an internal mixer, or in a continuous compounder such as the Werner and Pfleiderer Plastificator. For many operations the compounded mass... 

The filtered dough is then returned to a mixer and the alcohol content reduced to 25% by kneading under vacuum. Further reduction in the alcohol content is brought about by rolling the compound on a hooded two-roll mill. The milled product is then consolidated on a two-bowl calender and sheeted off in hides about j in thick. At this stage the solvent content is between 12 and 16%. 

Compounding may be carried out by either a wet or a dry process. In the wet process, now obsolescent, the ingredients are mixed as a viscous solution in acetone in a dough mixer. The resulting dough is then rolled on a hot two-roll mill to evaporate the bulk of the solvent. It is then necessary to season the resulting hides until the solvent content is reduced to a tolerably low level. 

Dry processes which obviate solvent difficulties are now preferred and are similar to those employed with the major thermoplastics. They include the use of two-roll mills, internal mixers, extruders and extrusion compounders. The use of dry blend techniques similar to that used more recently with PVC have also been used. ... 

As an alternative to the wet process described above, moulding compositions may be made by mixing a powdered resin or a methylol derivative with other ingredients on a two-roll mill or in an internal mixer. The condensation reaction proceeds during this process and when deemed sufficiently advanced, the composition is sheeted off and disintegrated to the desired particle size. This dry process is not known to be used in any current commercial operation. 

Before fabrication it is necessary to compound the gum with fillers, vulcruiising agent and other special additives on a two-roll mill or in an internal mixer. 

Ebonite compositions may be prepared without difficulty either in an internal mixer or on a two-roll mill. In addition to the rubber and sulphur, fillers are invariably present in commercial mixes. These materials have the important function of diluting the rubber phase. Because of this the exotherm will be... 

A two-mill take-off system, the mills sized appropriately for the mixer. The two two-roll mill take-off system is made up of one mill beneath the mixer to take out the heat from the compound (the drop mill) and a second mill used for the final blending process. This system is recommended when time and productivity are major issues. 

The oldest technology involved in the elastomer blending and vulcanization process is essentially a temperature controlled two roll mill as well as internal mixers followed by an optimum degree of crosslinking in autoclave molds (compression, injection, etc.) in a batch process or in a continuous process such as continuously heated tube or radiated tubes. A few examples of laboratory scale preparation of special purpose elastomeric blends is cited here. 

Elastomer-plastic blends without vulcanization were prepared either in a two roll mill or Banbury mixer. Depending on the nature of plastic and rubber the mixing temperature was changed. Usually the plastic was fed into the two roll mill or an internal mixer after preheating the mixer to a temperature above the melting temperature of the plastic phase. The plastic phase was then added and the required melt viscosity was attained by applying a mechanical shear. The rubber phase was then added and the mixture was then melt mixed for an additional 1 to 3 min when other rubber additives, such as filler, activator, and lubricants or softeners, were added. Mixing was then carried out with controlled shear rate... 

The compounds were mixed in three steps The first two steps were done in an internal mixer with a mixing chamber volume of 390 mL. The mixing procedures employed in the first two steps are indicated in Table 29.2. The starting temperamre was 50°C and the cooling water was kept at a constant temperature of 50°C. The rotor speed was 100 rpm and the fill factor 66%. After every mixing step the compound was sheeted out on a 100-mL two-roll mill. The third mixing step was done on the same two-roll mill. The accelerators and sulfur were added during this step. 

The dump temperature of the compound was varied by changing the mixer s rotor speed and fill factor while keeping the other mixing conditions and the mixing time constant. Under the assumption that the final dump temperature is the main parameter influencing the degree of the sUanization reaction, the effect of the presence of ZnO on the dynamic and mechanical properties of the compound was investigated. ZnO was either added on the two-roll mill or in the mixer. 

Mechanical Properties of the Vulcanized Compounds with ZnO Added in the Mixer, Resp. on the Two-Roll Mill at Different Dump Temperatures... 

The material flow in an internal mixer is oriented vertically. On top of the internal mixer a more or less sophisticated feeding system can be found. Underneath the mixer a downstream device, such as a sheeting extruder with one or two tangential screws, or two roll mills are placed. 

The final quality and reproducibility of rubber compounds mixed from scratch on a two-roll mill, or finalisation of compound batches mixed in an internal mixer, depend to a large degree on the skill of the mill operative. In order to overcome to some extent the reliance on operative skill and to ensure reproducible mix quality many mills are now fitted with stock blender units. These consist of a driven twin roller system, of similar overall length to the mill rolls, fitted above the mill frame. 

While the Dove composition described in Table 9.4-2 was processable at reasonable line speeds on a conventional soap processing line (roll mills, extruders, stampers), some equipment modifications were necessary. For example, whereas soap is normally mixed in large agitated tanks, the Dove mixture had a much greater viscosity and therefore required use of a steam-jacketed kneader mixer such as those used to make bread dough, pastes or mastics. 

The mastication equipment most commonly employed is standard rubber instrumentation such as roll mills, internal mixers, extruders or laboratory devices modeled on them (e.g., a single-rotor internal masticator described by Wilson and Watson (43), die model improved by Kargin and coworkers (11) and the Brabender plastograph). 

The polymer was masticated in the internal mixer for 5 min then ZnO and stearic acid were added. Curing agents were added on a two-roll mill and dispersed during 15 min of milling. 

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