DESIGN OF A GARDEN LEAVES SHREDDER

1. Garden Leaves Shredder
2019
Tinashe Jambo (JMBTIN001)

2. Introduction
• Garden leaves shredder is used to reduce the volume of collected
leaves.
• The crunched leaves take up less storage space.
• The crunched leaves can be used for compost as mulch.

3. Aims and Objectives
Design a functional garden leaves shredder, driven by an electric motor:
• With a satisfactory shredding ratio ( previous project 1:0.8 )
• Effectively crunch wet and dry leaves
• Create suction in the shredding chamber to draw in leaves
• Capable of crunching small branches < 10 mm
• Blow out crunched material into a collection bag

4. WORK BREAKDOWN STRUCTURE

5. Literature Review: Shredder Mechanisms
Disk Mechanism
Shear type Shredder
Mechanism
Cylindrical Drum
Trimmer lines
Spiked wheel and Drum

6. Literature Review: Selected Options
Disk Mechanism
Shear type Shredder
Mechanism
Advantages:
Higher Shredding ratio
Low maintenance
Low cost design
Compact design
Safe
Disadvantage:
Clogging of leaves around blades.
Advantages:
Very High Shredding ratio
More efficient
Disadvantage :
•Clogging of leaves around blades.
•Expensive cost design
• High maintenance cost

7. Existing Garden Leaves Crunchers
Ryobi RG1500
Disk Shredder mechanism with precutting blades.
Cons: Clogging of leaves in the chamber (No suction and discharge
mechanism)
Ecoshredder
Disk Shredder mechanism with precutting blades.
Cons: Clogging of leaves in the chamber
(No suction and discharge mechanism)

8. Existing Garden Leaves Crunchers
Patriot CSV 2515
Y hammers behind cutting blades to expel shredded items and create
suction
Cons: Clogging of leaves around the blade.

9. Literature Review: Benchmarking
Metric Unit Ryobi RG1500 Patriot Products
CSV-2515
Eco-Shredder
ES1600
Mulch Ratio 10:1 20:1 10:1
Power Source mains Mains Mains Mains
Type Type Mulcher Mulcher Mulcher
Speed Rpm 3300 3600 2800
Power Hp Hp 2 1.5 2.5
Power Kw 1,5 1,12 1.9
Torque
Weight Kg 48 43 49
Maximum
branches
mm 60 63 76
Price R 3899 15255 3000

10. Literature Review: Target Specs
Metric Unit Marginal Ideal
Mulch Ratio 10:1 20:1
Power Source mains Mains Mains
Type Type Mulcher Mulcher
Speed rpm 2800 3600
Capacity kg/hr 100 300
Torque hp Nm 2 2.5
Power kW 2.2 2.2
Weight kg 49 40
Maximum branches mm 30 40

11. Literature Review: Cutting Forces
Leaves : 0.45 N
Methods Novel way of measuring the
fracture toughness of leaves and other thin
films using a single inclined razor blade
Kai Yang Ang 1, Peter W. Lucas 2 and Hugh Tiang Wah Tan1
1 Department of Biological Sciences, National University of
Singapore, 14 Science Drive 4, Singapore 117543, Republic
of Singapore;
2 Department of Anthropology, George Washington
University, 2110 G St NW, Washington DC 20052, USA

12. Literature Review: Cutting Forces
Branch : <50 N , < 10mm Branch

13. Literature Review: Torque Power
𝜎 =
𝐹
𝜋
𝐷2
4
=
7.7
𝜋
0.012
4
= 0.6 MPa
Shear Stress, (Yield Strength of an 10 mm diameter branch)
Torque
𝜎𝑡 =
32∗𝑇
𝜋𝑥 D 3
𝑇 =
𝜋𝑥 D 3 ∗ 𝜎𝑡
32
= 0.06 𝑁𝑚
•Torque Required to shred leaves is minimal.
•Design will be for worst case scenario where
branches are shredded.
•Consider Reducing Branch diameter to lower
power requirements.

14. Literature review: Fan Design
•All concepts utilize a fan to blow out crunched material.
•The fan creates suction at the inlet and drives shredded leaves
into the collection bag.
TYPE Characteristic
Forward curved blades Low speed , High pressure and power
Sensitive to solid particles
Backward curved blades High increase in static pressure
High speed application
Gas streams with moderate solid
particles
Radial Blades Suitable for solid particles,
High pressure ,
Self cleaning

15. Literature Review: Mechanism Concepts
Concept A:
Stacked Rotating Blades
Concept B:
Disk type Shredding
mechanism
Concept C: Shear type
Shredding mechanism
Concept D:
Cylindrical Blade

16. Literature Review: Concepts
Concept A: Concept B: Concept C:

17. Literature Review: Final Concept

18. Detailed Design
𝜎𝑡 =
32∗𝑇
𝜋𝑥 D 3
Minimum shaft diameter for EN8 Steel, 280 MPa Yeild Strength
is 8 mm.
•Any shaft diameter above 8 mm will be suitable.
•Engineering Judgement was used to select sizes.
•Taking into account safety factors and budget.
𝐷 = (
32∗𝑇∗4
𝜋𝑥𝜎𝑡
)
1
3= 8𝑚𝑚
The available 2.2 kW motor at 1400 rpm gives 15 Nm torque.

19. 3D CAD MODELLING
Material Flow

20. Drawings

21. Assembly and Testing
Initial Testing Eliminating Vibrations Final Testing

22. Product Specifications
Specification Unit Value
Mulch Ratio 5:1
Power Source mains mains
Type Type Leaf Shredder
Speed RPM 1400
Capacity kg/hr. ± 20
Torque Hp 3
Power kW 2.2
Weight kg 40 ± 3kg
Maximum branches mm <10

23. Budget
Item Budgeted Actual Variance % Variance Fav/Unfav
Material 1165 287.5 -877.5 75 Favorable
Square Tubing 220 700 480 218 Unfavorable
Belt Drive(Pulley,
Belt)
300 398.91 98.91 33 Unfavorable
Bearings 960 1286.85 326.85 34 Unfavorable
Wheels 300 377.2 77.2 26 Unfavorable
Fasteners 690 277.55 -412.45 60 Favorable
Total (ZAR) 3635 3328.01 -306.99 8 Favourable

24. Thank You. Any Questions?