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CASE STUDY – Combined Loading. Drill bit isolators for underground mining – all metal components and elastomer must be safe! Design requirement: 8,000 lb thrust load and 300 lb-ft (3,600 lb-in) torque – these are basically the cutting forces.

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case study combined loading
CASE STUDY – Combined Loading
  • Drill bit isolators for underground mining – all metal components and elastomer must be safe!
  • Design requirement: 8,000 lb thrust load and 300 lb-ft (3,600 lb-in) torque – these are basically the cutting forces.
  • Detailed FE analysis but ALWAYS verify with hand calculations!!
slide2
Bit Isolator

Drill Depth up to 48”

Chuck Isolator

2010 SME Annual Meeting & Exhibit

Phoenix, Arizona

35 mm 1 3 8 in isolator load requirements
35 mm (1 3/8 in) Isolator Load Requirements:

Drill Bit

Drill Bit Isolator (

Thrust Load = 8,000 to 10,000 lb

Bending Load= 125 lbs)= K*d

Drill Rod

Torsion Load= 300 lb-ft

Chuck Isolator

HOT SPOT!

2010 SME Annual Meeting & Exhibit

Phoenix, Arizona

slide4
Results showed that in combination, the bit isolator and the drill chuck isolator provided a 7 dB(A) reduction in sound pressure level at the operator position.

2010 SME Annual Meeting & Exhibit

Phoenix, Arizona

a weighted sound level spectrum
110

105

100

95

90

A-weighted Sound Level (dB)

85

80

75

70

65

60

250

315

400

500

630

800

1000

1250

1600

2000

2500

3150

4000

5000

6300

8000

10000

Overall

1/3-Octave-Band Center Frequency (Hz)

A-weighted Sound Level Spectrum

108.9 dB(A)

Baseline:

T2 - 45 NR BISO, 45 NR CISO:

104.4 dB(A)

T5 - 55 NR BISO, 55 NR CISO:

102.7 dB(A)

104.4 dB(A)

T7 - 70 NR BISO, 70 NR CISO:

2010 SME Annual Meeting & Exhibit

Phoenix, Arizona

slide6
1 3/8” Drill Bit Isolator – Design Review:

Drill Bit isolator:

Chuck isolator:

2010 SME Annual Meeting & Exhibit

Phoenix, Arizona

1 3/8" DBI, R. Michael, PE

slide7
Critical Area!!

Look at metal components: Where would you expect max stress to occur?

1 3/8" DBI, R. Michael, PE

results fe analysis 1 3 8 dbi
Results: FE Analysis 1 3/8” DBI

All cases, thurst load = 8,000 lb, torque = 300 lb-ft (3,600 lb-in)

HOT SPOT!

1 3/8" DBI, R. Michael, PE

slide10
Max Principal, s1

Min Principal, s1

slide11
Max shear stress, tmax

VERIFY FEA RESULTS WITH HAND CALCS!!!!

slide12
Verify Principal Stresses with Hand Calculations or Mohr’s Circle!!

Thrust Load = 8,000 to 10,000 lb

Torsion Load= 300 lb-ft

HOT SPOT!

y

x

slide13
HAND CALCS:

From Axial Load

(Compression)

From Torque

slide14
HAND CALCS Cont’d:

Principal Stresses:

=-11.95 +/- 35.8 ksi

How do these values compare with FEA results?

Next: use Mohr’s circle to resolve

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