Paddle mixer

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DESCRIPTION

The paddle mixer are the mechanical devices which are used fot the mixing of the liquid materials.

The paddle mixers are similar to the plow type but the paddles mounted on the shaft differ in design from that of plow mixer.

Paddles can be oriented so as to impact lateral/back and axial mixing.

The paddles are generally operated at high speed than the plow mixer.

The speed has to be determined from running trials and the right speed can be result in good mixing.

Higher speed can cause segregation resulting in heaiver product thrown near the walls and lighter products near the center. 1,2

HISTORY

Jeff and Trevor Baillie started invention of paddle mixer in 1981,focusing on weighing solutions based on engineering principles. For the last 30 years paddle mixer has built its reputation as a leading supplier of robust Packaging &Bulk Handing Equipment. Our innovative engineering and continous product improvement have led to designs that will stand up to the rigors and demands your product line will throw at it. 1-4

CONSTRUCTION

Both the plow and paddle type has double shaft with two horizontal impeller. The paddle or blade overlap those on the other shafts.

In operation the impellers counterrotate, fluidzing and mixing of the materials.

To evaluate the sutability of such mixers, it is recommended that the test trails are conducted on the mixture to judge the duration and the quality of the mixing. 1,2

PRINCIPLE

The paddle mixer works on the principle of kneading action and by applying the shearing forces for mixing of liquids.

WORKING

In a paddle mixer the flat blades are attached to a verticle shaft which rotates at low speed of 100 rpm. For the mixing the low viscosity liquids simple flat paddles are used.

But for mixing high viscosity liquids the big paddles, often shaped to fit closely to the surface of the vessel are used.

The paddles of different sizes and shapes are used in the pharmaceutical industry according to the charcater and viscosity of the product.

The paddle mixers can also be used for kneading and for mixing pastes since the kneading action shows or allows phase changes from dry to paste when liquid is added.

Due to the rotation and the paddles used the mixing of the liquids takes place.

The Paddle Mixer is a batch powder or continuous mixer. It is housed within two parallel drums containing counter-rotating overlapping shafts with paddles fixed at a pre-determined angle, giving a high mixing efficiency. The paddles have close tolerance to the troughed walls, providing an area of low shear force. Both bulk blending and dispersive mixing is possible within the Paddle Mixer, regardless of product density or particle size. The process is reasonably gentle. 1,2

Paddle mixer

TYPES

Sigma blade and plantery paddle mixers

  • Sigma blade and plantery mixers are also used for solid solid mixing
  • High speed impellers are set into the cylindrical or vertical shell at the bottom which are more efficiency
  • Produces pricese blend and also break agglomerates rapidly.
  • High mechanical is built up produced with in the powder material.

Fluidised zone twin shell paddle mixer

  • Fludised zone twin shell paddle mixer produces homogenous mixture independent of its particle size, sensity and shape
  • It shows gentle mixing, short mixing cycle
  • Low operating cost, minimal product degradition
  • Highest production capacity.

Rotating twin shaft paddle mixer

  • It is a recent development
  • In this the feed is loaded from the nozzles which are present at the top of the vessel
  • After completion of the mixing the trough is rotated 180 degrees and the material is discharged from the bottom of the vessel
  • After the discharge of the material again it is rotated to the same position for the new feed.
  • In this design the essential air tight process are equiped with critical cleaning.
  • It is used for higher sensitive products to avoid oxidation it is equiped with the vaccum orinert atmosphere.

Horizonatal paddle mixer

Characteristics:

Best mixing homogenity, shortest mixing time, high mixing efficiency, double drive unit, total volume: 0.3-30cbm, batch working capacity: 0.1-15cbm, batch output: 0.1-20tons, mixing time: 2-10mins, driven- power:3kw-150kw, material: 316L, 321, 304, mild steel

Mixers need to be customized according to the different cases, the cases are as below:
1. Agglomerated material larger than 5mm is contained in the raw material
2. Bulk density of the raw material bigger than 3kg/l
3. Materials that are easy to get damp and not allowed to be exposed to the atmosphere, the mixer need to be vacuumized or negative pressure
4. Fill compressed air to the mixer barrel, and keep the pressure
5. Material with a large friction coefficient, mixer need to do a special Wear-resistant surface treatment
6. Material is not allowed to contact with the metal surface during mixing process
7. Mixer need to be heated up to 200 Celsius degree
8. Heavy duty (loading material into mixer before turning on it) is required.
Double shaft paddle mixer
Standard valve for double shaft paddle mixer is twin pneumatic planar flap valves. When close the valve, the planar flaps match the mixing barrel perfectly, this makes no mixing dead zone and better mixing effect.

According to the properties of raw materials, the paddle can be adjusted and designed accordingly, for example adding wear-proof plate, Teflon plate, and saw-toothed paddle.
Double shaft paddle mixer can be also added high speed breaking bar inside the barrel, scattering material following its flow.

High speed paddle mixer

High-speed mixer is suitable for churning and mixing the concentrated slurry of granular dry&wet materials in the starch,alcohol and fodder industries. It makes the surface of wet material entering the drier hard to be affixed by wall. It is charaterized by a compact structure, the small floor area,a large treatment capactiy, a good mixing effect and high efficiency.

Two shaft paddle mixer

Main Features

a. It consists of three parts: Transmission part, Agitator and Twin U-shape Cylinder. The transmission part is the decelerator drives the agitator to run with lines of chain or gear driving. Agitator is two shaft paddles, the shafts reversely rotates at the same speed. The paddles on the shaft arranged with a special angle ensure the materials can splash to three directions including radial, loop, axial, forming a compound effect of cross circle, shearing mixing ect to achieve uniform mixing in the short time. Alloy small blade in this paddle acan be easily replaced.
b. Twin U shape cylinder is with a door for cleaning. The exterior side can be with jacket for cooling or heating.
c. The discharging valve at the botton of the cylinder can be pneumatic one, electric one or manual one. And it can aso be designed with big door or small door for discharging according to production technology.
d. The machine can also be equipment with high-speed crashing device.It is needed when the material agglomerating. "Crushing Stick" with triangle tooth enclosure maintains high rotating speed of over 1400rpm, which smashes and depolymerizes the agglomerating materials in the material weightlessness area.

Application

a. The machine is with wide application range for mixing powder-powder, powder-granule, especially suitable for materials with big specific gravity difference or particle size difference.

b. The machine is widely used in industries such as pharmaceutical,food, feedstuff, chemical fertilizer,sand paste etc.. 3,4

PHRMACEUTICAL APPLICATIONS

  • Paddle mixer are used for drying and cooling of the bulk powders.
  • Suitable for cohesive materials
  • Used in pahrmaceutical industiries and boitechnology labs
  • It is a continuous process used in food and chemical industries.

ADVANTAGES

  • Good radial and rational flow
  • It is cheap
  • It is so veratile
  • It can be used as continuous and batch process
  • Low cost
  • It is simple and easy to handle
  • Satisfactory blending
  • No segregation of materials
  • Short mixing time
  • Gentle mixing
  • Higher throughoutput.

DISADVANTAGES

  • Small pumping capacity
  • High power requirment
  • Poor perpendicular flow
  • High vertex formation at very high speed. 1-4

REFERENCES

  1. Edward L. Paul, Victor Atiemo-Obeng, Suzanne M. Kresta, Handbook of Industrial Mixing: Science and Practice, Volume 1, 2003.
  2. Michael D. Holloway, Chikezie Nwaoha, Oliver A. Onyewuenyi, Process Plant Equipment: Operation, Control, and Reliability, 2012.
  3. Remington, Alfonso and Gennoro, Science And Practise Of Pharmacy- powders. 20th edidtion.
  4. Mehta RM, Pharmaceutics-I: Mixing and Homogenisation (1996), Page no: 113.

About the Author

Saraswathi.B's picture
Author: Saraswathi.B

Assistant Professor in St. johns college of pharmacy

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