🔹 1. Introduction

Large-scale surface mines rely on continuous and cyclic excavation systems.
Three major high-capacity mining machines used in overburden removal and soft-rock excavation include:

1. Bucket Wheel Excavators (BWE)
   
2. Draglines
   
3. Continuous Miners (CM)
   

These machines operate with different mechanisms and are selected based on:

• Deposit type
  
• Rock hardness
  
• Bench geometry
  
• Production requirement
  
• Capital cost
  

🔹 2. Bucket Wheel Excavators (BWE)

BWEs are massive continuous excavation systems used in:

• Lignite mining
  
• Soft overburden
  
• Large opencast mines (Germany, India)
  

2.1 Construction & Components

• Bucket Wheel with 10–20 buckets
  
• Boom carrying wheel
  
• Crawler system
  
• Counterweight
  
• Discharge conveyors
  
• Operator cabin
  

2.2 Working Principle

The rotating bucket wheel cuts material continuously and dumps it onto belt conveyors.Flow:
Wheel → Buckets → Chutes → Boom Conveyor → Main Conveyor → Dump

2.3 Production Capacity

BWEs are continuous miners with capacities:

• 2,500 – 20,000 m³/hr
  
• Some up to 240,000 T/day
  

2.4 Advantages

✔ Very high production
✔ Lower operating cost per tonne
✔ Continuous operation
✔ Suitable for soft overburden

2.5 Limitations

✘ High capital cost
✘ Not suitable for hard rock
✘ Limited flexibility
✘ Requires large flat working area

🔹 3. Draglines

Draglines are large excavators used primarily for overburden removal in coal mines.

3.1 Components

• Boom
  
• Bucket (10–60 m³)
  
• Hoist rope
  
• Drag rope
  
• Walking mechanism
  
• Power house
  

3.2 Working Cycle
 1. Swing bucket to digging position 

 2. Drag bucket towards machine

 3. Hoist bucket 

 4. Swing loaded bucket 

 5. Dump 

 6. Swing back empty bucketCycle time = 40–80     seconds.
3.3 Dragline DeploymentUsed in:

• Stripping operations
  
• Dragline benches
  
• Side casting of OB
  

3.4 Advantages

✔ Versatile digging range
✔ No need for trucks
✔ Ideal for stripping
✔ Very low operating cost

3.5 Limitations

✘ Cannot load into trucks

✘ Requires large working radius
✘ High capital cost
✘ Slow walking speed

🔹 4. Continuous Miners (CM)

Used mainly in:

• Underground coal
  
• Soft sedimentary rock
  
• Trench excavation
  

But also applicable in surface box cuts and shallow deposits.
4.1 Components

• Cutting head
  
• Gathering arms
  
• Conveyor
  
• Crawler tracks
  
• Operator cabin
  

4.2 Working Principle

The rotating drum with picks cuts material continuously while conveyors load it onto shuttle cars or belts.
4.3 Advantages

✔ Continuous cutting
✔ High productivity
✔ Reduced workforce
✔ Low dust (with water sprays)
4.4 Limitations

✘ Not suitable for hard rock
✘ High pick consumption
✘ Limited to soft ores

🔹 5. Comparison of BWE, Dragline & CM

Parameter	BWE	Dragline	Continuous Miner
Operation	Continuous	Cyclic	Continuous
Material	Soft	Soft/medium	Soft
Use	Overburden/ore	Overburden	Soft ore
Capacity	Very high	High	Moderate
Flexibility	Low	Medium	High
Capital Cost	Very high	High	Medium
DGMS Use	Lignite & OB	Coal OB	UG Coal & Soft ores

🔹 6. Selection Criteria

• Deposit hardness
  
• Working conditions
  
• Bench height
  
• Required output
  
• Mobility requirement
  
• Capital investment
  
• Mine life
  

🔹 7. Diagrams (Text Format)BWE (Conceptual)

Bucket Wheel OOOOO / \Boom -----( )---- Conveyor \_______/
Dragline (Side View)
Boom /\ / \Bucket O----\___ |
Continuous Miner (Front)
[Cutting Drum] (Rotating Picks) | | < Conveyor >
🔥 8. 25 MCQs with Answers (DGMS Pattern)

1) BWE is used mainly in —

a) Granite
b) Lignite and soft overburden
c) Basalt
d) Iron ore
e) None
Answer: b
2) BWE operation is —

a) Cyclic
b) Manual
c) Continuous
d) Intermittent
e) None
Answer: c
3) Dragline bucket capacity typically —

a) 1–5 m³
b) 10–60 m³
c) 70–120 m³
d) 0.5 m³
e) None
Answer: b
4) Continuous miners are mostly used in —

a) Hard rock mines
b) Gold mines
c) Coal mines
d) Iron ore mines
e) Granite quarries
Answer: c
5) BWE cannot work efficiently in —

a) Soft clay
b) Hard rock
c) Lignite
d) Soft shale
e) Mudstone
Answer: b
6) Dragline walk mechanism is —

a) Tyre
b) Crawler
c) Walking shoes
d) Belt drive
e) None
Answer: c
7) Continuous miner uses —

a) Drag chain
b) Shovel bucket
c) Cutting drum with picks
d) Rope shovel
e) None
Answer: c
8) Dragline operation is —

a) Continuous
b) Cyclic
c) Manual
d) Random
e) None
Answer: b
9) BWE can achieve hourly output of —

a) 50 m³
b) 200 m³
c) 2500–20,000 m³
d) 1 million m³
e) None
Answer: c
10) CM productivity depends on —

a) Bench height
b) Explosive type
c) Pick condition
d) Truck size
e) None
Answer: c
11) Dragline throws material by —

a) Hoisting only
b) Pushing
c) Side casting
d) Pitching
e) None
Answer: c
12) BWEs require —

a) Small benches
b) Large working area
c) Manual digging
d) Narrow roads
e) None
Answer: b
13) Continuous miners eliminate —

a) Drilling
b) Blasting
c) Both A & B
d) Loading
e) Dumping
Answer: c
14) Dragline cycle time —

a) 2–5 sec
b) 10–20 sec
c) 40–80 sec
d) 200 sec
e) None
Answer: c
15) BWEs use —

a) Shovel teeth
b) Hydraulic arms
c) Bucket wheel with multiple buckets
d) Rotary bit
e) None
Answer: c
16) Continuous miners are most suitable for —a) Igneous rocks
b) Soft sedimentary rocks
c) Massive hard ore
d) Basalt
e) None
Answer: b
17) Dragline is widely used in —

a) Limestone
b) Gold
c) Coal overburden removal
d) Granite
e) None
Answer: c
18) BWE flexibility is —

a) High
b) Medium
c) Low
d) Zero
e) None
Answer: c
19) CM cutting head rotates at —

a) 2 rpm
b) 50–100 rpm
c) 200 rpm
d) 500 rpm
e) None
Answer: b
20) Dragline capital cost is —

a) Low
b) High
c) Zero
d) Medium
e) None
Answer: b
21) BWE is part of —

a) Cyclic mining system
b) Continuous mining system
c) Placer mining
d) Offshore drilling
e) None
Answer: b
22) Dragline excavation depth depends on —

a) Track width
b) Rope length
c) Boom length
d) Engine RPM
e) None
Answer: c
23) CMs reduce —

a) Productivity

b) Blasting requirement
c) Dust
d) Gradient
e) None
Answer: b
24) BWE direction of excavation —

a) Reverse
b) Forward slicing
c) Random
d) Upward
e) None
Answer: b
25) Draglines are unsuitable for —

a) Coal OB
b) Very hard rock
c) Soft shale
d) Clay
e) None
Answer: b
                           🔚 Conclusion

Bucket Wheel Excavators, Draglines, and Continuous Miners are among the most productive machines used in surface mining.
Each has unique characteristics, capacities, and applications.
Understanding their working mechanisms and DGMS-selection guidelines ensures safe, efficient, and cost-effective operations.

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