AHSS – Advanced High Strength Steels Used in the Design of Dumper Trucks – A Case Study (CBMM Mine Dumper Truck) Authors: Hugo Rosa - CBMM Fábio Silva - SSAB Fábio Soave - Rossetti

OPERATION DATA

Annual material transportation – 2013 forecast Ore: 8 million tonnes Overburden: 4 million tonnes Trips per year: 300,000 (old truck load capacity 40 tonne) Distance (avg): 1.0 km Fuel consumption: 389,300 liters

THE APPLICATION

General - Dumper trucks used at CBMM mine in Araxá - Transported ore: stick (UHMW liner) - Dumper design

- Half pipe - Capacity: 20 m3

- Box material: Y.S. 350 MPa - Subframe + reinforcements: A36

CBMM requirements for the new dumpers: - Stronger: more load resistance/ longer service life - Lighter: increase payload

WHAT WERE THE PROBLEMS?

Breakage of support chains that resulted in the misalignment of the tailgate.

WHAT WERE THE PROBLEMS?

Subframe cracks with propagation along the longitudinal beam.

WHAT WERE THE PROBLEMS?

Cracks in the fenders due to stress concentration in the weld.

WHAT WERE THE PROBLEMS?

Dumper body floor plastic deformation (dents). Deformation of dumper floor from ore impact during loading, which caused loses in the UHMW liners, leading to material sticking to the dumper (increasing dead weight).

WHAT WERE THE PROBLEMS?

Breakage of subframe attachments to the truck chassis due to low material strength and the attachment design.

WHAT ARE THE GOALS?

- Increase the availability of the trucks. -

- Reduce the dumper body weight, increasing the payload capacity proportionally.

- Reduce maintenance costs. - Reduce transportation costs.

Dumper Box S355 Steel (Y.S. 350 MPa) • Floor - t 9.5 mm • Sides - t 6.3 mm A36 Steel (250 MPa) • Box structure

Subframe A36 Steel (Y.S. 250 MPa) • Longitudinal beams - t 8 mm • Reinforcements - t 6.3 mm • Cross members - t 4.75 mm/9.5 m

ORIGINAL PRODUCT

NEW PRODUCT PROPOSAL

Lighter Dumper Body • Material and design changes • Reduce welding

Stronger Subframe • Change material • Keep existing design • Reduce some components

NEW DUMPER BODY

Lighter Dumper Body • Floor: Hardox 450 - t 6 mm • Sides: Hardox 450 - t 4 mm

• Structure parts: Domex 700 (reduced

thicknesses)

• New design

NEW SUBFRAME

Stronger Subframe • Domex 700 MC Steel • Longitudinal beams t 8 mm/reinforcements

6.3 mm • Cross member t 4.75 mm/9.5 mm • Basically the same design • Fixtures/attachments redesigned to be more

resistant to fatigue

NEW PRODUCT

MATERIAL SELECTION FOR THE NEW PRODUCT

Y.S. (MPa)

T.S. (MPa)

Hardness (HBW)

Hardox 400 ~1000 ~1250 370-430 Hardox 450 ~1200 ~1400 425-475

Box sides, floor, tailgate, front panel

Y.S. (MPa)

T.S. (MPa)

Hardness (HBW)

Domex 700 700 min 750-950 ~270

Subframe, top beam (rail), box reinforcements

WHY USE DOMEX IN THE SUBFRAME

Benefits:

•Stronger structures handle overload without cracking, dent resistance •Reduce reinforcements/welding • Increased service life •Reduced maintenance

A36 (250 MPa) Domex 700 MC (700 MPa)

WHY USE HARDOX IN A DUMPER BODY

OEM benefits • Thinner gauges due to higher strength and better wear properties • Workshop friendly – excellent weldability • Good bending properties • Less reinforcements needed • Less welding in the process

End user benefits • Weight reduction/increased payload • Stronger structures/higher load capacity • Increased service life (wear) • Dent resistance • Reduced maintenance

Properties • Yield strength • Hardness • Excellent impact toughness • Excellent impact resistance • Very good flatness/surface quality • Consistent and homogeneous properties

WELDABILITY

Both Domex and Hardox have excellent weldability - No need for a special welding process. No preheating required for Domex and Hardox 450 (<t 20 mm). - Generally, consumables used for mild steel can be used.

Thinner plates are often used due to high strength - Fewer consumables - Faster welding - Increased productivity - Lower welding costs

FLEXIBLE DESIGN ADVANTAGES FOR AHSS

E1=E2 F1 >F2

Max value: 1050 MPa

Max value: 542 MPa

Flexible Design - The hardest and strongest steel possible for this application provides the greatest benefits. - It is not only strength/hardness that are necessary but also a very good combination of impact resistance and workshop performance.

SUPPORT PROVIDED IN MATERIAL SELECTION AND DESIGN

Frame

Plate

Hitting zone Hammer

10

20

30

40

Plas

tic d

efor

mat

ion

[mm

]

0 HARDOX 400

S 355

Steel t (mm) LRM (kg) HARDOX 400 4 250 A36 4.75 160 A36 6.3 220

PRODUCT COMPARISON

Truck (Actros 4844 2010) = 11,074 kg Dumper + liner (Rossetti 2010) = 7,426 kg Total weight = 18,500 kg

Old

Truck (Actros 4844 2013) = 11,530 kg Dumper + liner (Rossetti 2013) = 5,470 kg Total weight = 17,000 kg

New

1.9 tonne (25%) lighter

1.5 tonne more payload

Expected benefits

- 10,800 fewer trips (extra load 1.5 tonne) - 1,200 fewer labor hours

- 4% savings in total transportation costs in the mine

Actual results - 5,880 fewer trips (extra load 0.8 tonne) - 650 fewer labor hours - 2.2% savings in total transportation costs in the mine

- 3.7% fuel reduction

- 1,500 kg unloaded - 700 kg (loaded only with 800 kg) * Improved engine (new truck)

BENEFITS ACHIEVED WITH THE LIGHTER AHSS DUMPERS IN THIS CASE

PAYBACK

PAYBACK < 2 Months

REDUCTION IN CO2 EMISSIONS

Per truck reduction in fuel consumption = 600 liters/year 1 liter of diesel* = 2.61 kg of CO2

Reduction in C02 emissions - fuel (truck/year) = 1.6 tonnes/year Reduction in C02 emissions - steel (1 t steel =1.5 t C02) = 2.85 tonnes TOTAL C02 emissions/year (13 trucks) = 60 tonnes/year (60 Ton C02 = 17 passenger cars/year) Considering car mileage 20.000km per/year * Source: www.learningtools.com.br

CONCLUSIONS

• Total transport cost reduction of 2.2%.

• Too early to evaluate fully, but no cracks or breakage until now. The new product is proving to be robust.

• Although still only loading an extra 0.8 tonnes instead of the 1.5 tonne potential, payback was achieved in less than 2 months.

THANKS