MIXING ROLLS
DEFINITION:
Mixing roll mixer is a type of mixer in which deformable material and pastes are dmixed by intense shear by passing them b/w two smooth rolls turning at different speeds
Diagram
mixing rolls
Mixing and blending units
For equal homogenizing of rubber batches.
The stockblender consist of a pair of rolls. It is mounted above the roll nip and each roll is separately driven. Between the rolls of the mill and those of the stockblender a guide fork is situated, which is moved from side to side by a threaded spindle over the entire width of the mill.
Functioning: as soon as a cohesive slab has formed on the working roll of the mill, it is cut by the operator and fed through the guide forks to the stockblender. The stockblender transports the irregular slab and feeds it vertically downwards again into the mill roll nip. As these processes are effected alternately from the left and from the right side, an extremely good mixing effect is achieved due to the reciprocating motion of the fork.
Further advantages:
- Considerable ease of operation as the usually repeated cutting and rolling operation of the compound does not have to be carried out any longer.
- Favourable cooling conditions due to the increased travel of the compound.
- Increased capacity of the mill.
working
A mill is typically assembled on a steel foundation plate, which is again set on rubber-pads or sound-metals adjustable, to isolate noise-levels to the building also to avoid tensions on the mill structure, precisely levelling out of the mill is very important for smooth operationTwo rigid pillars with removable tops carry the rolls, which are placed either in friction/bush bearings or high quality anti-friction roller bearings. Roller bearings are pretty much standard nowadays, as they allow for 20 – 30 % in power-savings. A lubrication system is no longer requiredAdjustment of the front roll used to be made by hand (manual by ratchet) or later motorized by worm gear.Nowadays hydraulic pistons adjust the rolls and also protect rolls from high forces that can build up in between the rolls (roll safety). They also open roll gap immediately when pushing the safety bar in front or back in case of emergency (required by European Safety standards CE).A mixing mill has 2 horizontal rolls set up back to back. They are made of ground chilled cast iron, with surface hardness ranging from 475 – 520 HV (Vickers hardness) up to 520 – 580 HV (or 68 - 72 HSD). The depth of hardened layer ranges from 10 to 16 mm.Rolls are made with a central bore for cooling through a spray-type lance (low cost type cooling) or peripheral drills, where bores are closer to the surface for better cooling and more equal distribution.The rotary joints connected to the spraying lance are supplied from tempering units to provide constant temperature during the mixing process.At the ends of the roll faces the roll nip is being limited by the compound guide cheeks. The compound guide cheeks of split design with “centre tongue” avoid lateral escape of compound from the working area in any case.
MULLER MIXER
DEFINITION:
The Muller Mixer consists of 2 to 4 heavy rollers that move under spring pressure within a pan. A scraping arrangement is also provided. The product dust formed during grinding is confined to within the equipment because of the provision of a hood type cover. The rollers rotate around their own axis and also about the axis of the pan. The number of rollers and their sizes can be customized to the specific applications. The equipment is most suitable for solid particle size reduction.A machine for the mechanical preparation of molding sands and core sands; it mixes silica sands and admixtures, such as molding clay, ground coal, water, and binders. Various types of mixers are used as mullers in the preparation of moldings and core-sand mixtures: standard batch-type mixers, double mixers, oscillating mixers, paddle mixers, and rollerless (vortex) mixers.
DIAGRAM:
Muller Mixer
WORKING:
Standard batch mixers have a fixed hopper, into which the material to be mixed is fed. Two smooth, vertical rollers move over the layer of material with a circular motion as plows guide the mixed material under the rollers. As the rollers move, the components of the mixture are mixed and become evenly distributed. After 3–12 min of mixing, the prepared mixture is removed through a discharge opening in the bottom of the hopper.
Double mixers have two pairs of vertical rollers and two hoppers interconnected in such a way that their sides form a figure eight. The molding materials are fed continuously into the first hopper, are mixed by the rollers and internal plows, and are then transferred by an external plow to the second hopper, where more mixing takes place. The prepared mixture is then removed from the second hopper by an external plow. Double mixers can produce up to 400 tons/hr, and the mixture can be removed either continuously or in batches.
An oscillating mixer has two or three horizontal rollers suspended on oscillators connected to a vertical shaft. As the shaft revolves, the rollers come close to the rubber-faced wall of the mixer’s hopper. The material to be mixed is fed by scrapers into the gap between the rotating rollers and the wall of the hopper. A batch is mixed in 1.5–3 min. The prepared mixture is removed through a small door in the wall of the hopper.
A paddle mixer may have one or two (parallel) shafts equipped with paddles mounted in a helical line and turning inside a trough. When the shaft turns, the mixture is mixed and simultaneously transported along the trough toward the outlet. Such machines can produce mixtures continuously or in batches.
A rollerless, or vortex, mixer has a vertical rotating shaft and a fixed hopper. The working elements are bent springs with heads at the end that press against the side of the hopper and mix the sand.
APPLICATIONS:
- Ayurvedic & Herbal Products
- Pharmaceutical
- Minerals (Mica Powder Mixing)
- Snuff
- Batteries
- Welding rod flux
- Abrasives
- Soaps
- Putty
- Paints
PUG MILLS
DEFINITION:
A pugmill or pug mill is a machine in which materials are simultaneously ground and mixed with a liquid. Industrial applications are found in pottery, bricks, cement and some parts of the concrete and asphalt mixing processes. A pugmill is a fast continuous mixer. A continuous pugmill can achieve a thoroughly mixed, homogeneous mixture in a few seconds. Mixing materials at optimum moisture content requires the forced mixing action of the pugmill paddles, while soupy materials might be mixed in a drum mixer
DIAGRAM:
PUG MILL
WORKING:
Pugmills provide excellent mixing for cement-treated materials because of the violent action of the mixing process. Typically a pugmill will have two horizontal shafts, each with dozens of paddles. The shafts turn in opposite directions, causing one set of paddles to turn clockwise, and the other set to turn counter-clockwise. This motion hurls the particles toward each other in a violent action that allows for uniform mixing.
The pugmill operates on a continuous basis, with an aggregate feed belt, water spray, and cement vane that are all computer controlled to provide accurate metering of the constituents. Pugmills can be set up with more than one silo, so cementitious products (such as portland cement and fly ash) can be blended at the plant.
The mixed material is taken by belt to a surge hopper (or gob hopper) where it will be dumped into a truck to be transported to the job site. The trucks will have tarps to cover the freshly mixed material so that moisture is not lost on the way to the site.
Pugmills on paving projects are typically portable, and can be set up and running in less that a day. Production for pugmills on these projects are normally in the range of 300 – 500 tons per hour.
APPLICATIONS:
- Roller Compacted Concrete (RCC)
- Cement Treated Base (CTB)
- Cold Mix Asphalt
- Hazardous Soil Remediation
- Oil Well Drill Cutting Stabilization
- Flowable Backfill
- Flyash Stabilization
- Lime Addition
