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Questions and Answers
What type of cutting action is primarily involved in manual harvesting?
What type of cutting action is primarily involved in manual harvesting?
What characteristic of serrated sickles allows it to maintain its effectiveness without frequent sharpening?
What characteristic of serrated sickles allows it to maintain its effectiveness without frequent sharpening?
What cutting velocity is required for a dull edged single element blade to perform effectively?
What cutting velocity is required for a dull edged single element blade to perform effectively?
In shearing type cutting, which of the following statements is true?
In shearing type cutting, which of the following statements is true?
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What principle do reciprocating cutter bars most commonly use in agricultural harvesting?
What principle do reciprocating cutter bars most commonly use in agricultural harvesting?
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What is the typical angle between the cutting edges in reciprocating cutter bars?
What is the typical angle between the cutting edges in reciprocating cutter bars?
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What factor can significantly limit the speed of a reaper during operation?
What factor can significantly limit the speed of a reaper during operation?
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Which type of cutting mechanism involves a single high-speed cutting element?
Which type of cutting mechanism involves a single high-speed cutting element?
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What is the primary function of a slider crank mechanism in machinery?
What is the primary function of a slider crank mechanism in machinery?
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Which of the following factors contribute to vibration in farm machinery?
Which of the following factors contribute to vibration in farm machinery?
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How can the rotary unbalanced mass be balanced according to the provided principle?
How can the rotary unbalanced mass be balanced according to the provided principle?
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What happens if the reciprocating counterweight is offset from the line of motion?
What happens if the reciprocating counterweight is offset from the line of motion?
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What does complete dynamic balancing aim to achieve?
What does complete dynamic balancing aim to achieve?
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In which condition is counter balancing generally deemed unnecessary?
In which condition is counter balancing generally deemed unnecessary?
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What does the centrifugal force of the rotating counter weight fail to achieve?
What does the centrifugal force of the rotating counter weight fail to achieve?
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Which farming equipment typically requires more attention to counter balancing?
Which farming equipment typically requires more attention to counter balancing?
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What is a primary factor affecting the efficiency of the cutting mechanism?
What is a primary factor affecting the efficiency of the cutting mechanism?
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What is the typical stroke length used for a knife bar in reapers?
What is the typical stroke length used for a knife bar in reapers?
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At what speed does the reciprocating knife-bar typically operate in grass mowers?
At what speed does the reciprocating knife-bar typically operate in grass mowers?
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What is the required reciprocating speed of the knife bar relative to the forward speed for grass mowers?
What is the required reciprocating speed of the knife bar relative to the forward speed for grass mowers?
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Why is it unnecessary to use knife-clips in modern grain harvesting machines?
Why is it unnecessary to use knife-clips in modern grain harvesting machines?
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What limiting factor affects the maximum speed of the pitman and reciprocating cutter-bar type mechanisms?
What limiting factor affects the maximum speed of the pitman and reciprocating cutter-bar type mechanisms?
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How does the moisture content of stalks affect harvesting?
How does the moisture content of stalks affect harvesting?
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What is the minimum number of strokes required to effect shear by impact alone?
What is the minimum number of strokes required to effect shear by impact alone?
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What is the primary function of a typical four-bar mechanism?
What is the primary function of a typical four-bar mechanism?
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How can the unbalanced horizontal shaking forces in a four-bar mechanism be addressed?
How can the unbalanced horizontal shaking forces in a four-bar mechanism be addressed?
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What is a requirement for two members to be termed dynamically equivalent?
What is a requirement for two members to be termed dynamically equivalent?
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What mechanism relies on the principle of scissor action for cutting?
What mechanism relies on the principle of scissor action for cutting?
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For what purpose is the pitman and reciprocating knife-bar mechanism primarily used?
For what purpose is the pitman and reciprocating knife-bar mechanism primarily used?
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What type of balance can easily be obtained in a four-bar mechanism?
What type of balance can easily be obtained in a four-bar mechanism?
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What is the primary resistance faced during the operation of a shearing-type cutting mechanism?
What is the primary resistance faced during the operation of a shearing-type cutting mechanism?
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What effect does introducing a mirror-image mechanism have on the four-bar mechanism's shaking forces?
What effect does introducing a mirror-image mechanism have on the four-bar mechanism's shaking forces?
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Study Notes
Cutting Mechanisms in Harvesting
- Cutting plant operation involves four actions: slicing, tearing, high-velocity impact, and shearing.
- Slicing uses a sharp, smooth edge.
- Tearing uses a rough, serrated edge.
- High-velocity impact uses a sharp or dull edge.
- Shearing uses a two-element scissor-type action.
Manual Harvesting Actions
- Manual harvesting typically involves slicing and tearing actions.
- These actions lead to plant structure failure due to compression, tension, or shear.
- The serrated sickle combines slicing and sawing.
- It doesn't require frequent sharpening.
Single Element Impact Cutting
- Single element impact cutting is a common economical method.
- It uses a high-speed cutting element, often for rotary lawn mowers, forage choppers, and tractor mounted cutters.
- The single element impact requires 10 m/s for a sharp edged blade.
- A dull edged blade requires about 45 m/s velocity for impact cutting.
Rotary Cutter Actions
- Rotary cutter knives rotate in a horizontal plane.
- Flail shredder's knives rotate vertically.
- Shearing type cutting happens due to shear forces.
Reciprocating Cutter Balance
- Cutter bar is a major source of vibrations in reapers.
- The slider crank mechanism is commonly used.
- Imbalances in un-balanced mass of the machine and rotating components cause vibrations.
- They can lead to early fatigue failure in components like the knife.
- Balancing techniques involve counterbalancing masses to reduce vibrations.
Balancing Requirements
- The balancing mass should be positioned opposite to the unbalanced mass for optimal effects.
- Balancing may be complete (dynamic) or partial (static).
- Field mowers, with relatively light frames, require careful balancing.
Four-bar Mechanism Balancing
- Balancing is difficult for mechanisms without rotational symmetry.
- A typical example is the four-bar mechanism.
- Techniques involve mirror-imaging of components or replacing parts with equivalent ones.
- The main issue is introducing components with opposite effects to balance shaking forces.
Shearing-Type Cutting Mechanism
- Shearing-type cutting utilizes scissor action to cut materials.
- It minimizes bending and crushing.
- The shearing strength of the material is the key resistance factor.
- The pitman and reciprocating knife-bar are common examples.
- This mechanism involves triangular knife sections on a reciprocating bar.
Cutting Speeds for Reapers
- Reciprocating knife-bar speed in reapers is not significantly high, typically below 100m/min.
- Speed is usually higher in grass mowers (up to 170m/min) due to factors like feed rate and shearing resistance.
- Higher speeds require more emphasis on balancing mechanism design to mitigate vibration issues.
- Moisture content of grain influence the shearing resistance.
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Description
Explore the various cutting mechanisms used in harvesting operations, including slicing, tearing, and shearing. Understand how different actions affect plant structure and the efficiency of manual and mechanical harvesting techniques. This quiz examines the principles behind rotary cutters and impact cutting methods.
