case study – combined loading drill bit isolators for underground mining – all metal components...
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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.
• Detailed FE analysis but ALWAYS verify with hand calculations!!
Drill Depth up to 48”
Bit Isolator
Chuck Isolator
2010 SME Annual Meeting & ExhibitPhoenix, Arizona
35 mm (1 3/8 in) Isolator Load Requirements:
Drill Bit Isolator (
Thrust Load = 8,000 to 10,000 lb
Bending Load= 125 lbs)= K*
Torsion Load= 300 lb-ftDrill Rod
Chuck Isolator
Drill Bit
HOT SPOT!
2010 SME Annual Meeting & ExhibitPhoenix, Arizona
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 & ExhibitPhoenix, Arizona
60
65
70
75
80
85
90
95
100
105
110
250
315
400
500
630
800
1000
1250
1600
2000
2500
3150
4000
5000
6300
8000
10000
Overall1/3-Octave-Band Center Frequency (Hz)
A-w
eig
hte
d S
ou
nd
Lev
el (
dB
)
108.9 dB(A)Baseline:
104.4 dB(A)T2 - 45 NR BISO, 45 NR CISO:
102.7 dB(A)T5 - 55 NR BISO, 55 NR CISO:
104.4 dB(A)T7 - 70 NR BISO, 70 NR CISO:
A-weighted Sound Level Spectrum
2010 SME Annual Meeting & ExhibitPhoenix, Arizona
61 3/8" DBI, R. Michael, PE
1 3/8” Drill Bit Isolator – Design Review:
Chuck isolator:
Drill Bit isolator:
2010 SME Annual Meeting & ExhibitPhoenix, Arizona
704/19/231 3/8" DBI, R. Michael, PE
Look at metal components: Where would you expect max stress to occur?
Critical Area!!
Critical component – inner member, thin wall, stress concentration!
Results: FE Analysis 1 3/8” DBI
All cases, thurst load = 8,000 lb, torque = 300 lb-ft (3,600 lb-in)
904/19/23 1 3/8" DBI, R. Michael, PE
HOT SPOT!
Max Principal, 1
Min Principal, 1
Max shear stress, max
VERIFY FEA RESULTS WITH HAND CALCS!!!!
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
psi
inin
lbs
A
Py 895,23
)59.0()88.0(4
000,8
22
psiinin
inlbin
J
Tcxy 720,33
])295.0()44.0[(2
)44.0(600,3
44
From Axial Load(Compression)
From Torque
HAND CALCS:
psiy 895,23
psixy 720,33
psix 0
Principal Stresses:
2
2
2,1 2/
2 xyyxyx
22
720.332
895.230/
2
895.230
=-11.95 +/- 35.8 ksi ksi85.231 ksi75.472
HAND CALCS Cont’d:
ksixyyx 8.35
22
2
max
How do these values compare with FEA results?
Next: use Mohr’s circle to resolve