🌾 Threshing and Threshers
Understand the principle of threshing, major types of threshers, and the machine parts that affect threshing and cleaning efficiency.
Harvesting does not finish post-harvest work. Once the crop is cut, grain still has to be detached from ear heads, panicles, pods, or plants. That separation step is threshing, and it strongly affects labor requirement, grain damage, and cleaning quality.
What Threshing Means
Threshing is the process of detaching grain from ear heads, panicles, pods, or harvested plants.
It may occur through:
- rubbing
- impact
- stripping
The aim is to separate grain efficiently without causing excessive breakage or leaving too much unthreshed material.
Principle of Threshing
Threshing depends on breaking the bond between grain and the plant part holding it.
This bond is broken mainly by:
- impact of spikes, beaters, or bars
- rubbing or wearing action between cylinder and concave
The ease of threshing depends on:
| Factor | Influence |
|---|---|
| Crop type | Different crops need different threshing action |
| Variety | Bond strength differs among varieties |
| Moisture content | Wet material is usually harder to thresh cleanly |
| Stage of maturity | Overripe or immature crop behaves differently |
Threshing efficiency depends not only on machine type but also on crop moisture and feed condition.
Types of Threshers
Threshers can be classified in different ways.
Based on power source
- manual threshers
- power-operated threshers
Manual units suit small-scale work; power-operated units greatly increase capacity and reduce drudgery.
Based on feeding method
- throw-in type
- hold-on type
In throw-in threshers, the crop is fed directly into the cylinder zone. In hold-on types, the operator holds part of the crop while the panicle or pod end is threshed.
Based on crop flow
- through-flow
- axial-flow
In through-flow machines, crop flow is largely perpendicular to the cylinder axis. In axial-flow units, movement is parallel to the cylinder axis.
Main Parts of a Thresher
The three essential functional units are:
- concave
- threshing cylinder
- cleaning unit
Concave
The concave is the curved or partially surrounding grating against which the cylinder acts. Grain falls through it once separated.
Threshing cylinder
This is the main active threshing element. It rotates and provides impact or rubbing action.
Common cylinder types include:
- peg-tooth
- wire-loop
- rasp-bar
- angle-bar
- hammer-mill type
Each type suits particular crops and threshing conditions.
Cleaning unit
The cleaning unit removes straw bits, chaff, dust, and other foreign matter from the threshed grain. It commonly uses sieves and an aspirator or fan.
Factors Affecting Threshing Quality
The quality of threshing depends on machine setting as much as machine type.
Important variables are:
- cylinder speed
- number and shape of beaters
- concave clearance
- feed rate
- direction and uniformity of feeding
- moisture content of crop
If settings are too harsh, grain breakage rises. If they are too mild, unthreshed grain increases.
Threshing and Cleaning Efficiency
Two performance measures are commonly considered.
Threshing efficiency
Threshing efficiency reflects how much grain has actually been detached from the crop mass.
Cleaning efficiency
Cleaning efficiency reflects how clean the grain is after separation from straw, chaff, dust, and impurities.
A good thresher must do both jobs well: detach grain efficiently and clean it effectively.
Summary Cheat Sheet
| Topic | Key point |
|---|---|
| Threshing | Detaching grain from ear head, pod, or plant |
| Main actions | Impact, rubbing, stripping |
| Main parts | Concave, cylinder, cleaning unit |
| Cylinder types | Peg-tooth, wire-loop, rasp-bar, angle-bar, hammer-mill type |
| Key variables | Cylinder speed, concave clearance, feed rate, crop moisture |
| Threshing efficiency | Measures detached grain performance |
| Cleaning efficiency | Measures purity of grain output |
Lesson Doubts
Ask questions, get expert answers