SIGMA BLADE
DEFINITION:
The mixing elements are two nos. Z type steel casted blades.. They contra rotate inward fitted at close or specified clearance with the container to give thorough and uniform mixing. There is a gland pusher of gun metal bush which ensure minimal friction and extend the life of mixing elements (Blades). Two counter rotating mixing arms rotate at different speeds (usually in the ratio of 3 to 2) in the trough, the intersection of which forms a saddle and the arms meet tangentially just above the saddle.
The mixing action is a combination of bulk movement, shearing, stretching, folding, dividing, and recombining as the material is pulled and squeezed against blades, saddle, and side walls. Continually new layers of material are compressed and folded over one another and are subjected to shearing forces. New surfaces are formed and the components can penetrate. The blades, which are ground and polished, successively sweep all points of the trough surface during each revolution, at the same time dividing the batch continuously across the saddle piece and thereby achieving a perfect mix.
DIAGRAM:
SIGMA BLADE MIXER
Single Arm Sigma Mixer
Mix dough in less time! That's the bottom line for MIKRONS Single Sigma Arm Mixers. featuring a unique, heavy formed component agitator, these mixers can handle your most demanding product requirements. Built for durability and reliability, these mixers feature an overall frame and drive construction of heavy duty materials.
Solid stainless steel is used for the mixing bowl, canopy, agitator and shaft, and coolant jacket.
Solid stainless steel (bowl, agitator, canopy)
Heavy duty tubular stainless steel framework
Single end direct mount drive
2 speed TEFC motor
4 operator and starter panels
Hydraulic bowl tilt (dual cylinders)
Pneumatic flour gate in canopy
Sanitary liquid inlet in canopy
Operator panel/push button or touch screen with PLC interface
 * |
Sigma - The most widely used blade for the process industry
|
|
 * |
Dispersion Blades - Provides a smooth folding action and is excellent for mixing a fiber reinforced product. Available in 135 degree or 180 degree spiral.
|
|
 * |
Masticator Blade - Used for a superior dispersion of products difficult to mix such as rubber, plastics or abrasive materials.
|
|
 * |
Naben Blade - Also known as the Fishtail Blade. Suitable for mixing cellulose materials.
|
|
Double Arm Sigma Mixer
|
Double arm sigma blade mixers are engineered specifically for kneading, mixing, and homogenizing wet, pasty, and highly viscous products. The mixer consists of two counter-rotating tangential rotors in specially shaped trough, curved at the bottom to form two longitudinal half cylinders with sufficient overboard volume.
The blades rotate at different speeds in opposite directions causing the product to be transferred from blade to blade and from end to end, resulting in a figure eight pattern.
The main trough is of fully welded construction. The rotors are taper bored and key-fitted onto stub shafts working on anti-friction bearings. They are driven by gear on both sides in heavy duty models and pitched to achieve end to end longitudinal movement of the material resulting in thorough kneading action. The shaft sealing is achieved by stuffing box arrangement with teflon impregnated gland packing.
Options:
Mechanical or hydraulic drive system
Jacketed mixing troughs or heating and cooling
Designed for pressure, vacuum, or inert gas operation
Remote operator control
Specialized die heads / special extrusion spouts
Automated operation of cover via hydraulic piston
Cored blades of various design
|
Applications:
Sealing compounds,
asphaltic derivatives,
mastics, hot-melts,
floor coverings, colorings,
rubber base, master-batches,
chewing gum,
rubber compounds,
silicone,
lubricating greases,
dispersed pigments,
butyl, gums and adhesives,
ceramic paste,
polyester compounds,
greasy inks,
pencil leads,
explosives,
powders to granulate,
PVC coatings
Extruder Screw Sigma Mixer
The extrusion screw is located in the saddle section and runs in a cylindrical trough tangential to and below the 2 mixing blades.
The extruder mixer is designed to handle difficult to discharge products such as hot melts and butyl sealants, as well as other medium to high viscosity pastes. This type of mixer combines the action of the Double Arm Sigma Blade Mixer with an extrusion screw placed in the lower part of the mix trough. During mixing, the extrusion screw is run in reverse which imparts a third mixing action on the product, increasing mixing efficiency.
|
|
|
When the product has finished the mixing cycle, discharge/extrusion is performed simply by running the extrusion screw in a forward direction.
The double arm sigma blades normally continue to run throughout the extrusion process providing a thoroughly mixed product at all stages of the production cycle.
By changing the extrusion die heads, the product can be discharged in round, square, "spaghetti", or any form desired.
Speed variation of the extrusion screw allows adjustment of the product flow, depending on the viscosity.
As an option, a die cutter can be installed outside the die head. This bevel-faced cutter provides transverse cutting and can be pneumatically driven.
Extruder Screw Sigma Mixer
Types of Sigma Blades
Optimum Agitator Design
All agitators are available in carbon steel and stainless steel construction.When the process requires additional heating or cooling special agitators with grooved cored centres are available. Our kneaders are available for both Overlapping and Tangential applications.
Sigma Blade Agitator
This design is best suited for all round use. This may be positioned with either tangential or overlapping action.
Dispersion Blade Agitator
This design is best suited for all round use. This may be positioned with either tangential or overlapping action.
|
|
Masticator Blade
Used for a superior dispersion of products difficult to mix such as rubber, plastics or abrasive materials.
Double Naben Blade Agitator
Naben Blade - Also known as the Fishtail Blade. Suitable for mixing cellulose materials and highly viscous products such as gum.
180 Degree Spiral Blade Agitator
This agitator requires less power than sigma blade and it is used for sanitary applications.
|
Double Naben Blade MIXER
DEFINITION:
Naben Blade - Also known as the Fishtail Blade. Suitable for mixing cellulose materials and highly viscous products such as gum.
DIAGRAM
WORKING PRINCIPLE:
DISPERSER BLADE MIXER
DEFINITION:
A disperser is a type of mixer used to rapidly break apart lumps of powdery material, uniformly distributing and wetting them in a liquid. It is also used to dissolve soluble solids in a liquid.
DIAGRAM:
disperser blade mixer
WORKING:
A disperser works on the principle of energy transfer. A disc type blade is mounted at the bottom end of the mixing shaft and rotated at a relatively high tip speed. (Tip speed is the speed at the outer tip or edge of the rotating disc. Tip speeds typical of dispersers are measured in feet per minute, calculated by multiplying the constant 3.14 times the diameter in feet of the disc times the revolutions per minute of the mixing shaft. The industry terminology for tip speed is peripheral velocity.) The solids and liquids are drawn into the rotating disc by the suction it creates. This suction usually results in a visible whirlpool from the top of the mixture down to the top of the disc. A similar whirlpool is created below the disc extending from the bottom of the tank to the underside of the disc. The whirlpools are actually two individual vortices, although common industry practice refers only to the visible upper one known as the vortex.
When the solids/liquid mixture enters the vortices and is sucked into the high-speed disc, the energy (horsepower used to drive the disc) is instantaneously transferred from the disc to the mixture. This intensively focused energy transfer creates tremendous, instantaneous velocity changes in the mixture as it progressively contacts the disc. (Think of the mixture as a series of individual horizontal layers descending downward from the top and upward from the bottom on to the face of the rotating disc.) As each layer contacts the disc it is instantaneously accelerated from the slow moving vortex into the very high speed of the disc and projected outward away from the disc and toward the wall of the tank. The rapid tearing apart of layer upon layer of the mixture is shear force, commonly referred to as shear.
What is the difference between a disperser and an agitator?
Both the disperser and the agitator will mix. Mixers are sometimes compared to pumps. The performance of a pump is usually measured in the horsepower required for its gallons per minute discharge capacity. A disperser is a high-powered, low volume pump. Considering its substantially higher horsepower per gallon requirement, a disperser is an inefficient mixer. An agitator is a low-powered, high volume pump - it is an efficient mixer. A typical dispersion application (such as dispersing pigment to make paint) requires about 1 HP for every 10 gallons compared to an agitator application (such as thinning the pigment dispersion with solvent) requires about 1 HP for every 100 gallons. Although the agitator is the more efficient pump, it does not create sufficient shear to disperse most solids into the liquids.
Moderate shear dispersers operating at about ½ the normal blade speed of high shear dispersers are sometimes used in place of agitators when some shear is required. Typically the discs have larger teeth to promote better pumping and require about 1/3 the horsepower of a high shear disperser but still 3 times more than an agitator.
APPLICATIONS:
Reduction of production time as no additional shear ring dispersing is required
Short, reproducible treating times when adding dry substances
Constant standard of quality because of an absolutely lump-free solution
Narrow droplet spectrum by a homogen distribution of the shear energy
Independent from any change of the viscosity
Reducing cost for raw material as different product qualities may be handled, independent from the dispersing and wetting characteristics
Reduction of the amount of emulsifiers because of a better disintegration and dispersion
Complete desagglomeration and suspension
Optimum performance requires the following criteria:
1) Start with a clean tank
2) Correct blade to tank ratio
3) Proper formulation
4) Suitable blade in good condition
5) Highest appropriate blade tip speed
6) Correct tank Geometry (length compared to width)
7) Sufficient horsepower
8) Proper technique of adding raw materials.
9) Proper rheology
safety measures
1) Read the operation and safety instructions supplied by the manufacturer. If they are not available call the manufacturer and request additional copies.
2) Be certain that all operators are properly trained on the use and drilled on the potential dangers involved with the disperser
3) Do not operate the machine unless all the appropriate safety features are in place and functioning properly. On hoist mounted units that raise and lower the blade, these features include but are not limited to: A) mixing shaft guard; B) Tank holder with limit switch; C) Limit switch on lift to prevent machine from operating with blade or shaft within reach of the operator.
The disperser is a very fast and powerful machine. Serious and fatal accidents can occur in a split second of carelessness. Human reflex is no match for the instantaneous danger of operating a disperser unsafely. Never sacrifice safety for convenience.
