Printing Machine and Devices | Propellers of a ship | Propeller, Types of Propellers and Construction of Propellers

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Printing Machine and Devices

 A printing machine is also known as the printing press, equipment used to print out copies of the original document by means of forcing the inked surface on the belt of the paper or cloth, or polymer sheets. Any form of text or image is imprinted on a series of sheets with perfect dimensions. German Johannes invented the printing press in 1440, and from then this device was modified and redesigned to improve its performance and capacity.
A simple diagram can explain how the laser printer works in your office or home, which is on the principle of static electricity.

Propellers of a ship

Ships use propellers to generate pressure difference and provide motion in the water. Nickel-aluminum bronze alloy is used to make them corrosion-resistant.  (80 Cu; 10 Al; 5 Ni; 5 Fe) is an appropriate alloy combination when the propeller is used in seawater.  Its coefficient of thermal expansion is 9.4 millionth per Fahrenheit.    

Three blade propeller

The number of blades depends on the capacity and the ship’s masses so that enough acceleration can be produced from the propulsion system. For heavy loads and high speeds, the blades are bolted rather than direct welding to the shaft hub.

A four-blade propeller model shown here is categorized by direct welding the blades to the shaft hub rather than bolting. Such a model is preferred only for low-speed and medium-capacity ships. The word propeller is used for ship-driving systems because they make the fluid flow in the axial direction. The shape of the blades is one of the important identities of the propeller which looks entirely different from turbines and anchors. The angle of the blades is always less than 90 degrees.

Four blade propeller

Types of Agitators

Propeller agitators are commonly made of three-bladed attached to the main shaft. They are flexible in operations and mostly used in the mechanical mixing of low to medium-viscosity fluids. These types of propellers are also called marine-type propellers. The diameter of the propellers depends on the rotational speed and diameter of the batch reactor or the agitator’s vessel. Depending on the agitator vessel size and the fluid viscosity the power consumption of the propeller agitator may exceed more than 50kW.

Turbine impellers operate at low speeds and are much larger than propellers. A turbine has an excellent feature in designing the flow pattern where a change in design can divert the flow pattern of fluid by radial flow or axial flow in the reactor vessel. Based on the configuration of the impeller blades these flow patterns can be achieved. The radial design makes the fluid flow at high velocity in a radial direction whereas axial impellers use pitched blades, making the fluid flow parallel to the shaft in the downward direction and then push the fluid toward the wall of the agitator’s vessel. For gas dispersion operation radial turbine impeller is used and an axial turbine impeller is used for chemical reactions, suspension solid, and miscible liquid mixing. 

Types of agitators models, application, and comparison:

Agitator modelsApplicationAdvantagesDisadvantages
Paddle:
Flat paddle finger paddlesGate paddles
Solid mixing slurry mixingHeavy duty mixingAdjustable to 2 or 4 blades excellent for low-speedHigh power consumption efficient liquid circulation
Counter-rotating paddlesPaste mixingEfficient in the laminar condition lendingVibrates at high speed not suitable for liquid mixing
TumblingBlendingPaste and viscous material mixingNot suitable for  fluid solutions
Disk and conePolymers and dispersion preparationViscous solution mixing with 60 revolutions per secondPaste mass cannot be handled
Free shaft suspensionSugar processingSuspension, Thickening operationHigh power requirement
Impeller typeEmulsion preparationsGood temperature control creates axial flowGood phase mixingNot for viscous materials
Turbine agitator
Straight bladePitched bladeVaned diskCurved blade
Liquid and gas reactionsExcellent for dispersion operations creates good radial flowOnly for less viscous liquid below 15 to 20 Ns/m2
Slotted rotary
Rotating disk
Powders and
cosmetics
Unique particle size and homogeny product formationMinimum axial flow operates better only for 0.1 to 0.01mm particle size solids
Screw
Screw in cone
Food and snack processingHomogenization of highly viscous materialsNot suitable for miscibility operations
Helical
Ribbon typeHelical screw
Polymer and paints processingHandles viscoelastic liquids that are more than 20 Ns/m2Less radial flow patterns
GateBlending operationsGood speed control handles pseudoplastic liquidsNot suitable for gas-to-liquid operations
Anchor
Round anchorCombine anchor and gate
Milk and fat processingEfficient heat exchange between the reactor walls and reaction mass (fluids)High power consumption requires heavy-duty gearbox
PropellerDairy and food processing chemicals processingLess  Metzner โ€“Ott shear rate constantHomogenizationGood miscibilityThe motion of liquid starts on one spotted spots formation at high rotation speeds occurrence of solids settling at low speeds

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