Test Apparatus for Measuring Sound Power Levels of Drills

39 Pages·2012·1.62 MB·English

Information Circular 9166
Test Apparatus for Measuring
Sound Power Levels of Drills
By William W. Aljoe, Robert R. Stein,
and Roy C. Bartholomae
UNITED STATES DEPARTMENT OF THE INTERIOR
Donald Paul Hodel, Secretary
BUREAU OF MINES
David S. Brown, Acting Director
Library of Congress Cataloging in Publication Data:
Aljoe, William W.
Test apparatus for measuring sound power levels of drills.
(Information circular/United States Department of the Interior, Bureau of Mines; 9166)
Bibliography: p. 34-35.
Supt. of Docs, no.: I 28.27: 9166.
1. Rock-drills—Noise. I. Stein, Robert R. II. Bartholomae, R. C. III. Title. IV. Series:
Information circular (United States. Bureau of Mines); 9166.
TN295.U4 [TN279] 622 s [622'.8] 87-600273
CONTENTS
gage
Abstract........................................................................................ 1
Introduction.................................................................. ................ 2
Test system considerations................................................................. 4
Control of drill operating parameters................................................. 4
Control of the acoustical environment................................................. 5
Data collection and analysis............................................................ 7
System description.......................................................................... 8
System operation.............................................................................. 12
Drill test program......................................................................... 12
Test sequence............................................................................. 12
Data input and startup procedure..................................................... 13
Data collection and display........... ............................................... 14
Control subsystems....................................................................... 15
IBM-XT microcomputer.................................................................. 15
Westinghouse PC-700 process controller........................................... 15
Drill rig positioning control...................................................... 16
Carriage lock control................................................................ 16
Feed thrust and hole depth control................................................ 17
Drill hammer control................................................................. 18
Drill rod rotation control.......................................................... 18
Flushing water control............................................................... 20
Other drill test commands.............................................................. 20
le location program........................................................................ 21
Selection of hole position............................................................... 21
Validation of input data.................................................................. 22
Selection of hole depth................................................................... 22
Data analysis program........................................................................ 22
Direct data analysis and graphics...................................................... 23
Test selection............................................................ .............. 23
Raw data retrieval....................................................................... 23
Basic system graphics................................................................... 25
Expanded data analysis through spreadsheets.......................................... 27
File conversion procedure.............................................................. 27
Advantages of spreadsheet analysis................................................... 28
Initial test results......................................................................... 29
Pneumatic versus hydraulic percussion drills........................................ 30
Rotary versus percussion drills......................................................... 32
Discussion...................................................................................... 34
References..................................................................................... 34
ILLUSTRATIONS
1. Noise sources on typical hand-held percussion drill.............................. 2
2. Noise sources on typical jumbo-mounted percussion drill......................... 3
3. Typical noise radiation pattern....................................................... 6
4. Components of automated drill test fixture and control system................... 8
c;. Drill test rig in reverberation chamber, top view................................ 10
Drill test rig in reverberation chamber, profile view........................... 10
Drill test rig in reverberation chamber, rear view showing control room.... 11
8. Drill test rig in reverberation chamber, control valves and process
sensors.................................................................................. 11
9. Drill test software program selection menu........................................ 12
ILLUSTRATIONS—Continued
Page
Main data input menu for drill test program..................................... 13
Drill rig carriage and boom positioning system................................. 16
Drill carriage lock system.......................................................... 17
Feed thrust and hole depth control system....................................... 17
Drill hammer control system......................................................... 19
Drill rod rotation control system................................................. 20
Data input menu for hole location program....................................... 21
Data input menu for analysis program............................................. 23
Printout of drill test data......................................................... 24
Graphs of hammer pressure, feed thrust, feed rate, and sound power versus
elapsed time.......................................................................... 25
Sound power spectrum and spectrum waterfall graphs............................ 26
Data input menu for Spreadsheet Formatter program............................. 27
Average frequency spectra: pneumatic and hydraulic percussion drills.... 30
Frequency spectra for percussion drills, beginning versus end of hole.... 31
Average frequency spectra: pneumatic and hydraulic percussion drills,
pneumatic rotary drill.............................................................. 33
Frequency spectra for pneumatic rotary drill: beginning versus end...... 33
TABLE
Maximum values and accuracy of ADTF control parameters........................ 13
UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT
cf m cubic foot per minute in/s inch per second
dB decibel Kb kilo byte
dBA decibel, A-weighted kHz kilohertz
ft foot lbf pound (force)
ft2 square foot Mb megabyte
ft3 cubic foot mi n mi nu t e
f t/mi n foot per minute pet percent
gpm gallon per minute psi pound (force) per
square inch
h/d hour per day
s second
Hz Hertz
V volt
in inch
TEST APPARATUS FOR MEASURING SOUND POWER LEVELS OF
DRILLS
By William W. Aljoe,1 Robert R. Stein,1 and Roy C. Bartholomae2
ABSTRACT
This Bureau of Mines report describes in detail the design and opera­
tion of a test apparatus for measuring the sound power levels of drills
used by the mining industry. The two major components of the test ap­
paratus are a computer-controlled automated drill test fixture (ADTF)
and a large (45,000-ft5) reverberation chamber that houses the ADTF.
Design specifications and performance capabilities of the ADTF and the
reverberation room are given. Initial test results for three types of
drills—a pneumatic percussion drill, a hydraulic percussion drill, and
a pneumatic rotary drill—are given to illustrate the types of experi­
ments that can be conducted with the test appartus.
^Mining engineer.
^Supervisory electrical engineer.
Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA.
2
INTRODUCTION
Percussion drills used in the mining
industry produce noise that can cause
exposures of 10 to 20 times the limits
Drill steel
allowed by Federal noise regulations.
Typical noise levels experienced by per­
cussion drill operators are 110 to 120
dBA. Approximately 60,000 percussion
drills are being used in the mining in­
dustry CO, 3 and many more are used in
the construction industry. Given the
severity of the percussion drill noise
problem, it is not surprising that con­
siderable efforts have been made toward
its control.
The primary noise-generating mechanism
in all percussion drills is the repeated
hammering action of an oscillating steel
piston on the end of a long, slender
striking bar (drill rod). This action
causes vibration of both the drill rod
and the cylindrical piston housing,
thereby producing drill rod noise and
drill body noise. On pneumatic drills,
the high-pressure air used to oscillate
the piston is exhausted to the atmosphere
through ports in the drill body, thus
producing air exhaust noise. Figure 1
depicts these three major noise sources
on a typical hand-held pneumatic (stoper)
drill. Figure 2 shows the various noise
sources associated with a typical
machine-mounted (jumbo) drill; however,
the drill body, drill rod, and air ex­
haust are still by far the most serious
noise sources on the drill.
Numerous attempts have been made in the
past by the Bureau of Mines and other re­
searchers to control percussion drill
noise through the use of retrofit noise
control treatments (2fJ0 and new drill
design features (7-10). These attempts
have been moderately successful, result­
ing in noise reductions of up to 15 dBA
at the drill operator position. Unfortu­
nately, some of the noise-controlled
drills were rather impractical from an
operation standpoint (e.g., reduced
drilling rates, muffler freezing, exces­
sive weight and bulk).
^Underlined numbers in parentheses re­
fer to items in the list of references at
FIGURE 1.—Noise sources on typical hand-held percussion
the end of this report.
drill.
3
Piston-striking bar impact
Leakage air noise
Air motor noise
Body noise
J ' Exhaust noise
Bit-rock impact
FIGURE 2.—Noise sources on typical jumbo-mounted percussion drill.
Furthermore, in most cases the quieted many underground ore mining operations
noise levels were still above 100 dBA; because of its compactness, flexibility,
operator exposure would have to be lim­ reliability, and low cost. Space limita­
ited to only 2 h/d to maintain compliance tions and interference with drill opera­
with Federal noise regulations. tion (e.g., operator vision) also dis­
To date, the most effective means of courage the use of acoustical cabs on
protecting the percussion drill operator many types of jumbo-mounted drills.
from noise overexposure has been to iso­ Considering the high-energy nature of
late him or her from the noise source by percussion drilling, the limited success
using an acoustical cab. Noise reduc­ of previous efforts to control drill
tions of up to 20 dBA have been achieved noise at its source, and the limited
through this technique, and in several practical application of acoustical cabs,
cases the noise level measured inside the it is doubtful that the majority of per­
cab was below 90 dBA (6). Acoustical cussion drill operators will work in a
cabs can be applied most successfully to nonhazardous noise environment in the
machine-mounted drills that are used in near future. If the mining industry con­
areas of unrestricted headroom or where tinues to use percussion drills, even
remote control of drill positioning and quieted models, as it has in the past, it
operation is employed. However, many is reasonable to assume that numerous
nining situations require the use of noise overexposures will occur in the
¿mall hand-held drills because of space years to come.
limitations; this precludes the use of Despite the severity of the percussion
acoustical cabs. In fact, the hand-held drill noise problem and the fact that all
percussion drill remains the bulwark of percussion drills are inherently noisy,
4
it is important to note that some drills of Mines, while continuing in this en­
generate more noise than others. Opera­ deavor, does not possess the funding or
tor exposure to noise can be reduced by drill design expertise to embark on a
choosing a less noisy drill or drilling program to develop a drill or drilling
system. Factors that can affect the system that can solve the problem com­
noise produced by a drill include the pletely. However, with the aid of the
source of power (air or hydraulic), input test apparatus described in this report,
energy, degree of wear and leakage, drill it is possible for the Bureau to signifi­
rod size and type, hammer and shank con­ cantly enhance the body of knowledge on
figuration, means of drill steel rotation the subject of drilling noise. For ex­
(rifle bar or independent), and location ample, the test apparatus can provide
of the operator with respect to the valuable but heretofore unavailable quan­
drill. The application and effectiveness titative information on the sound power
of noise control techniques are greatly levels produced by different types and
affected by these differences. models of drills. Noise variations re­
An in-depth understanding of drill de­ sulting from differences in drill operat­
sign characteristics and their effect on ing parameters can also be investigated
noise is an important part of any effort and quantified.
to reduce the noise problem. The Bureau
TEST SYSTEM CONSIDERATIONS
To conduct thorough, systematic studies the drill, and hole flushing medium. Un­
of drill noise, the researcher needs (1) der actual drilling conditions in the
control of the parameters that affect field, control of all these parameters is
drill performance, (2) control of the a very difficult and sometimes impossible
acoustical environment in which the drill task. In short, it can be said that no
operates, and (3) a comprehensive, well- two holes drilled in the field are ever
organized data collection and analysis exactly the same.
system. The Bureau’s test apparatus ful­ In the laboratory, however, it is pos­
fills all three of these requirements. sible to control these parameters such
that any drilled hole is repeatable.
CONTROL OF DRILL OPERATING PARAMETERS More importantly, it is possible to se­
lectively change only one parameter from
The operation of a percussion drill is hole to hole to determine its effect on
affected by many parameters such as the noise and penetration rate. The computer
composition of the drilling medium, controlled automated drill test fixture
sharpness of the bit, type of bit used, (ADTF) facilitates this process by auto­
length and type of drill rod, number of matically maintaining the supply pres­
rod sections, drill feed force, supply sure, rotation flow, and feed force spec­
pressure to the drill, wear condition of ified by the user. These parameters can
5
also be changed by the user during the is another important factor to consider
course of a test if desired. The ADTF when measuring drill noise in the field
also allows the user to select an exact because the sound pressure can vary
hole location (following a preprogrammed greatly from point to point within the
pattern), hole depth, and drill power area of interest. Measurement of drill
source (air or hydraulic) for each test. noise in the laboratory allows for con­
The ADTF achieves this control through trol of some of these variables, but the
the use of standard, commercially- experimental environment must be chosen
available hardware such as pressure, carefully to assure that useful noise in­
flow, and position transducers, a pro­ formation is obtained in a practical and
grammable process controller, and a desk­ cost-effective manner.
top microcomputer. Software designed The two fundamental properties that de­
specifically for the purpose of drill fine the noise-radiating capability of a
test provides the user with continuous sound source are its sound power and di­
on-line information and interactive capa­ rectional characteristics. Sound power
bility via the computer's cathode ray is a measure of the rate at which acous­
tube and keyboard. Safety is ensured by tical energy is emitted by a noise
the presence of several types of auto­ source; it is usually expressed as sound
matic and user-initiated shutdown modes. power level, in decibels (dB), by the
By conducting drill noise tests in the formula
laboratory, it is also possible to exer­
cise almost complete control of the PWL = 10 log (Wac+/Wref),
drilling medium, bit type and sharpness,
drill rod length and type, and hole where PWL = sound power level, dB,
'ushing medium. These parameters can
most never be changed or controlled in Wact = actual sound power, w,
the field due to local geology, blasthole
size requirements, and other production and W reference sound power,
r e f -
considerations. The capability of pro­ lO"12 w.
viding a relatively homogeneous drilling
medium (precast concrete or precut gran­ The most important distinction between
ite) is particularly advantageous when sound power level and sound pressure
assessing the effect of other drilling level, the quantity most commonly asso­
parameters on drill penetration rate. ciated with noise, is that sound power
is a fundamental property of the noise
CONTROL OF THE ACOUSTICAL ENVIRONMENT source itself. Conversely, the sound
pressure level is dependent on the
The acoustical environment of an oper­ distance from the noise source, the
ating mine is rarely consistent because direction from the source, and the acous­
the extent of the mine and the location tical properties of the environment in
of the noise sources change almost daily which it is measured. The relationship
as mining progresses. between sound pressure and sound power
Irregular reflecting surfaces are often levels can be quantified (11):
present, and extraneous noise sources
(other pieces of mining equipment) add to SPL = PWL + 10 log [(Q/4cxr2)+(4/aS)]
the difficulty of measuring the noise + 10,
produced by a drill. Microphone location
6
where SPL = sound pressure level at any For the drill noise research program
given point in an envisioned by the Bureau of Mines, sound
environment, dB, power is the quantity of greatest inter­
est because (1) it allows direct noise
PWL = sound power level of noise comparisons to be made among different
source, dB, types and models of drills, and (2) it
can be used to predict the sound pressure
Q = directivity factor (dimen- levels that will occur in other envi­
sionless) of the source, ronments, given their acoustical
whose value is dependent characteristics.
on the angle from the The directional property of a sound
acoustical center of the source describes its tendency to radiate
source to the measurement more noise in one direction than in
point, others. Directional properties are usu­
ally displayed in a graphical form called
r = distance from the source, a radiation pattern (fig. 3), showing
ft, sound pressure level at a fixed distance
from the source as a function of angle.
a - average absorption coeffi­ It should be noted that figure 3 is for
cient (dimensionless) of illustrative purposes only; the sound
the acoustical environment, pressure levels in the figure do not cor­
including its boundaries respond to measured values for an actual
and objects located within drill.
it, From a purely diagnostic standpoint,
the most complete characterization of any
and S = total surface area, ft2, of noise source can be obtained by isolating
all reflecting surfaces it in an anechoic (free field) environ­
within the environment. ment, i.e., one in which no reflections
ANGLE FROM NOISE SOURCE
60° 70° 80° 90° 100° 110° 120°
E
C
R
U
O
S
E
S
I
O
N
M
O
R
F

E
L
G
N
A
100 90 80 Noise source 80 90
SOUND PRESSURE LEV EL, dB
FIGURE 3.—Typical noise radiation pattern.