Open-mill mixing

Open-mill mixing is used mainly for special compounds prepared in small volumes. The advantages of mill mixing are its simplicity, the fact that the operator can control the temperature of the material on the rolls, and an easy cleanup. 

Mixing in an internal mixer is best, but open mill mixing may also be satisfactory. An upside down mixing procedure is best with internal mixers. 

As with open mill mixing, when using synthetic polyisoprene in internal mixers, cycle times are reduced and discharge temperatures may be up to 20 °C lower than those obtained with natural rubber, without sacrificing good dispersion of ingredients. 

A machine for masticating rubber, mixing rubber compounds and for warming up rubber compounds prior to calendering, extrusion, etc. See Open Mill. 

Plasticising of mixed compound by working on an open mill or in an internal mixer, preparatory to extrusion or calendering. 

Samples for 180° peel tests were prepared according to standard neoprene recipes (9). Neoprene AC or a graft copolymer prepared from it was mixed on an open mill at room temperature for 20-25 min with the following compounding ingredients in succession ... 

Mixed either in an internal mixer or on an open mill... 

Before introduction of the intensive internal mixers, the mixing was accomplished on open mills — a slow, dirty process requiring skilled operators. An efficient, counter rotating twin shaft internal mixer with elhptical rotating discs was... 

In general, the masticated NR and EPDM were mixed together with other ingredients including compatibilizers and homogenizing agents in an internal mixer or open mills. The rubber compound is cured in an electrically heated press at 160 °C for optimum cure time, which is determined by rheometer. In order to study the... 

Mixing The general methods for incorporating compounding ingredients into dry natural rubber involve the use of either a two roll mill or an internal mixer (e.g. Banbury mixer). Both in the open mill and in the internal mixer, a definite time, temperature, and order of addition of ingredients should be followed for each batch. [59]... 

If the former mechanism can easily be observed in an open mill, the latter is not necessarily apparent because these phenomena occur on a micro-scale. The incorporation involves a decrease in the specific volume of the mix (6). 

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 principle of internal batch mixing was first introduced in 1916 with the development of the Banbury mixer (Figure 2.74a). A Banbury-type internal mixer essentially consists of a cylindrical chamber or shall within which materials to be mixed are deformed by rotating blades or rotors with protrusions. The mixer is provided with a feed door and hopper at the top and a discharge door at the bottom. As the rubber or mix is worked and sheared between the two rotors and between each rotor and the body of the casing, mastication takes place over the wide area, unlike in a open mill where it is restricted only in the area of the nip between the two rolls. 

Compounds may also be mixed on open mills, but this takes considerably more time, batch weights are lower, and it is thus less efficient than use of internal mixers. 

Mechanical mixing of polymers carried out on either an open mill or in a Banbury internal mixer has advantages in efficiency, productivity, and lower cost. However, natural rubber in many instances must first undergo an initial breakdown. 

Use of internal mixers offers a direct and environment friendly technique for preparation of nanocomposites. A two-step mixing in an internal mixer followed by addition of curative on a two roll mill for preparation of elastomer-layered silicate nanocomposites [51]. In the study on the effect of processing conditions (mixer type, mixing temperature) and formulations on the properties of EPDM nanocomposites, it has been shown that open two roll mill mixing results in inadequate dispersion of the nanofiller in the elastomer matrix compared to compounding in an internal mixer. Melt compounding with layered silicates has been reported for NR [52], ENR [46], SBR [53], NBR [54], EPDM [55] and PU [56] systems. 

Mixing. Fluorocarbon elastomers may be compoimded by any standard rubber technique. Open mills may be used, since most commercial gums mix well, except very low viscosity gums, which stick to the rolls, and high viscosity gums, which are very tough. 

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]. 

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