Two-roll rubber mill

Mechanical Mixing of PFAP(II) Compounds. PFAP(II) O-ring seal formulations were mixed in a Brabender internal mixer equipped with a mixer head of 85-mL volume and cam-type blades. The mix order was as follows (1) PFAP(II), (2) silica (Quso WR82, silane-treated surface) (3) magnesium oxide and (4) bis(8-oxyquinolate)zinc(II). This compound then was placed on a small two-roll rubber mill (2 in. X 6 in.) and dicumyl peroxide was mixed in at 57°C. 

The specified rubber compound is mixed and calendered and plied up to tbe desired tbiekness, then sheeted out on a two-roll rubber mill, or extruded. These unvuleanized rubber blanks are then prepared in for subsequent molding operations one of tbe following ways ... 

Thermal process Tyre pieces are steam-heated in a pan in the presence of air for around 2.5 h at up to 260 "C. The rubber product is then cooled, ground and consolidated on a two-roll rubber mill. 

Fig. 3. Typical two-roll rubber mill with features recommended for milling...

The compounding of CR with fillers and vulcanization ingredients was done by a laboratory size open two-roll mixing mill. All the weights are given in parts per hundred parts of rubber and the recipe for the CR compounds is given in Table 4. 

In the case of thermal crosslinking, the corresponding curatives were added to each of the EPDM and CR rubbers on a two-roll laboratory mill at room temperature. A constant friction ratio of 1.2 was maintained between the milling rolls. Approximately 2 mm sheets were drawn out from the mill and cured in a hot press at a pressure of 10 MPa and a temperature of 170°C and 160°C for EPDM and CR, respectively, for their corresponding optimum cure time (f90). 

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. 

The first step of manufacturing a membrane is to prepare a suitable rubber compound either in a Banbury internal mixer or in an open two roll mixing mill by adding different compounding ingredients in the proper sequence during the mixing operation to get a well dispersed compound. 

Roll mUl processing is commonly used to manufacture rubber products and their blends or composites. The manufacture of rubber or elastomer-based composites typically involves melt mixing of compounding ingredients in a two-roll open mill followed by curing [63]. Very recently, Das et al. and Perez et al fabricated MWNT/rubber nanocomposites using roll milling process [64,65]. 

Sample preparation. All ingredients were mixed in an open two-roll laboratory mill at room temperature. The rotors operated at a speed ratio of 1 1.4. Rubber compounds were vulcanized in an electrically heated hydraulic press. The compounds were cured into 0.25 mm thick films at 150 °C for 15 min according to the optimum cure time ( 90) derived from the curing curves previously determined by means of a Rubber Process Analyzer (RPA2000 Alpha Technologies). Rectangularshaped specimens were mechanically cut out from the film samples. 

Two-roll mills are used rnainlv for preparing color pastes for the ink, paint, and coating industries. There are a few applications in heaw-diitv blending of rubber stocks, for which corrugated and masticating rolls are often used. 

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. 

By rolling on a two-roll mill the molecular weight of the polymer can be greatly reduced by mechanical scission, analogous to that involved in the mastication of natural rubber, and so mouldable materials may be obtained. However, bulk polymerisation is expensive and the additional milling and grinding processes necessary make this process uneconomic in addition to increasing the risk of contamination. 

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... 

In order to be effective in imparting various chosen characteristics, all additives employed in a blend must be homogeneously dispersed throughout the blend. The two most commonly employed pieces of equipment for blending rubber and additives are rubber mills and a special type of mechanical mixer known as the Banbury mixer. A typical rubber mill consists of two rolls which rotate toward each... 

There are two types of hot feed extruders, one similar to the screw type cold feed extruder, except that the strip feeding the extruder is taken directly off the two-roll mill. The mill is used to further blend and heat the compound. It is then taken off the mill in strip form and fed directly into the extruder. The second type of hot feed extruder is based on the action of a ram being used to feed the compound into the extruder die (Fig. 16). The compound is placed on a two-roll mill to further blend and heat rubber. It is then taken off the mill in pig form to fill the extruder chamber. 

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 application of two roll mills in the downstream of such mixing lines is preferred, especially if the two roll mills are equipped with stock blenders (Figure 35.14). After discharging, the rubber batch will be sheeted on the two roll mill. By putting the sheet through the stock blender, the free surface from which the ethanol and moismre can be evaporated is rather big allowing the chemical reaction to proceed even at somewhat lower temperatures. A smdy by Zuuring et al. has shown... 

Ambient grinding involves the comminution of scrap rubber, including tires, at ambient temperatures, typically in a toothed-wheel mill, bench grinder, shear mill, or two-roll miU, to give particles... 

The two-roll mill represents the earliest form of rubber processing machine, used by the rubber manufacturer being developed from the masticator of Hancock. Over the years the emphasis of the role of the two-roll mill has moved from being that of the prime means of compound preparation for the majority of the rubber industry, to that of secondary usage. In the modem factory conventional two-roll mills are used for compound blending and for sheeting off of compound mixed by other means. In addition they are used to warm-up compounds from store, and for a number of blending purposes to achieve compound uniformity for other processes. 

In the early days of the rubber industry all mixing was carried out on two-roll mills. Now this situation only occurs occasionally, or when small or expensive batches of material are required, e.g., silicones or fluorocarbons. Mill mixing is an efficient method for breaking down agglomerates and, over a period of time, with good operatives, good homogeneity can be achieved. One batch, however, can take some 30-40 minutes to mix. 

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. 

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