Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE INVENTION
This invention relates to rock drill lubricant
compositions having low air mist emitting properties. In
particular, this invention is directed to rock drill
lubricants which will minimize the quantity o~ oil mist
exhausted with the air from a rock drill, particularly
when used in confined areas.
The construction and mining industries, faced with
the task of excavating large quantities of rock or ore,
depend upon rock drilling operations to accomplish this
often horrendous task. Many excavating operations involve
drilling blast holes, blasting or fragmentation and then
removal of the fragmented rock by earth moving equipment.
Drilling the blast holes stresses the importance of
effective rock drilling operations. The most widely
accepted method for drilling blast holes in rock formations
and for some broaching operations is the compressed air
powered rock drill. Broaching consists of drilling a
number of holes close together and then breaking out the
rock between them. To meet the requirements of the mining,
quarrying and construction industries the percussion
technique has been adopted to many sizes and models of
rock drill. These percussion drills operate on a principle
similar to that employed in drilling with a hand-held star drill
and hammer. A reciprocating piston activated by compressed -~
air strikes the drill steel and the resulting blow crushes
the rock under the cutting edges of the drill bit. Except for a
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few specialized drills, the drill steel is rotated a few
degrees after each power stroke and the cuttings are
periodically or continuously removed from the hole by
compressed air or water or a mixture of both.
All drills using the percussion technique have
similar demanding lubricant requirements. In addition,
the range of severe and adverse operating conditions
encountered and the numerous type of rock dril]s utilized
presents many problems to the lubrication engineer. Many
suppliers formulate special lubricants for rock drill use.
A review of a variety of rock drill applications
exemplifies the severe conditions to which these machines
are subjected and are still expected to provide trouble
free performance. Highway construction often requires
large and at times spectacular rock cuts through rough and
mountainous country. Mining and quarrying operations,
although less apparent, depend solely on the excavation of
ore or rock for their raw materials. Other transportation
systems, including railroads, highways and canals as well as
the construction of dams, hydroelectric plants, and water
supply and sewer systems often involve the removal of rock by
rock drill operations.
In above-ground operations ambient temperatures
and moisture conditions vary from subzero and dry as in
the Artic to hot and humid as in the tropics. In underground
mining and tunneling projects, temperatures and humidity
often remain relatively constant. However, problems
relating to rock dust, fogging and ventillation become prime
considerations and,accordingly,operating methods useful above
ground must be modified.
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Rock drills may be classified into several general
types. Jackhammers or sinkers are handheld tools and are
used primarily for downhole work. They seldom weigh over
100 pounds and depend on their weight and that of the
operator for feed pressure. Rock cuttings may be removed
by air, water or a combination of the two. Stoppers are
similar to jackhammers or sinkers and are used primarily
to drill upward holes for mine roof bolting, working
overhead ore and other overhead drilling. To
reduce entry of water and rock dust into the drill
some have an anvil or tappet between the hammer and the
drill steel. In other instances, air is blown out through
the front head to protect the drill.
Drifter drills are the most widely used and are
generally classified by piston diameter, usually ranging
from 2 5/8 inches to 5 1/4 inches. The larger drifters
are usually mounted on hydraulic booms which in turn
are mounted on a wheeled or crawler chassis. At times, these
larger drifters and their associated mountings are referred
to as blast hole drills. When several drills are mounted
on a single mobile unit, the resulting arrangement is
generally referred to as a jumbo.
Downhole drills are used for large diameter,
deep hole drilling with the bit and percussion mechanism
combined into a single unit which operates at the bottom
of the hole. Operating air is supplied through the drill
pipe that supports the drill.
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Percussion rock drills are designed to operate
on air pressures of approximately 90 pounds per square lnch.
In addition to supplying the drilling energy, the air
carries very fine droplets of misted oil to the moving
parts of the drill. With few exceptions the drills are
totally lubricated by the air and oil mixture. Adequate
lubrication of rock drills depends upon a relatively small,
constant flow of misted ~il to the drill. Hence the location
of the air line oiler with respect to the drill is another
factor which requires consideration. While the oiler
should not interfere with the operator, long distances from
the drill should be avoided since the oil particles would
tend to reclasify and collect as slugs in the line.
Attempts to compensate for intermittent oil mist flow
caused by excessive distances between the lubricator and
drill by increasing the oil feed rate can cause other
operating problems. For example, fogging at the exhaust
from the drill and "dieseling" often result from excessive
oil feed rates.
The misted oil in the compressed air supplied
to the rock drill is the main source of lubricant for
all of the internal drill components. The lubricant is
expected to form an adequate film on moving parts. This
oil film must seal clearances, prevent rust and corrosion
and protect the heavily loaded components from wear. A
proper rock drill lubricant must have several important
characteristics. Since some of the oil mist exhausts
from the rock drill, the oil cannot possess a disagreeable
odor or contain toxic or nauseous additives, particularly
when being used in a confined area. To assure correct oil
feed rates, sealing characteristics and film strength, the
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viscosity grade of the oil used must be selected on the
basis of the ambient temperature. The lubricant must have
rust and corrosion protection quallties in order to
preserve clearances in the rock drill and prevent the
formation of abrasive rust particles. In order to protect
the heavily loaded parts in the drill, anti-wear and extreme
pressure characteristics are also considered essential and
must often be provided b~ additives when the film strength
of the base oil alone is not sufficient. Since the
oil must adhere to the part being lubricated, even in the
presence of water, adhesiveness of the lubricant is a
necessity. The rock drill lubricant must also be resistent
to deposit formation in order to avoid the formation of
hard carbonaceous materials or vanishes which would
prevent proper valve functioning in the rock drill.
Rock drill lubricants should also be able to emulsify
water that enters the drill in order to maintain the
protective oil film that resists rust and corrosion as well
as preventing metal-to-metal contact. Finally, the
lubricant must demonstrate an anti-foam action to eliminate
the possibility of drills running dry as a result of foam
in air line oilers being mistaken for a satisfactory oil
level. Thus, a rock drill lubricant must be specifically
tailored to meet the demanding lubrication requirements of rock
drills.
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As the air exhausts from the rock drill, one means
to assure that proper lubrication is being maintained is to
test for the presence of oil in the exhaust air by holding a
piece of white paper near the exhaust parts. When using rock
drills in confined areas such as mines and other underground
excavating sites, stray fog and fine oil mist from the rock
drill lubricant can create an occupational health hazard to
the work crew. Recent U.S. legislation, such as the Federal
Occupational Safety and Health Act (OSHA), is evidence of
the increasing awareness of providing healthy working areas
for industrial workers. Therefore, not only must the rock
drill lubricant not possess a disagreeable odor or contain
toxic or nauseous additives but ideally the lubricant should
be so formulated that stray fog and fine mist generation
from these lubricants is minimized.
Although polymeric additives are known to surpress
mist generation in lubricants, their utilization in rock
drill lubricants to date has not achieved the mist surpres-
sion required, particularly when drilling in confined areas.
It is therefore an object of this invention to
provide a rock drill lubricant which will have a low stray
fog quality when utilized, particularly when used for
lubricating rock drills in confined spaces.
SUMMARY OF THE INVENTION
There is provided according to this invention a
process for reducing the stray fogging of a rock drill
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lubricant during rock drill operations which comprises
supplying to a compressed air powered rock drill, for use as
a lubricant, a rock drill lubricant composition comprising a
major portion of a mineral oil base, rock drill lubricant
having a viscosity of 100 to 3000 SUS at 100F and a minor
portion, sufficient to reduce the stray fogging qualities of
said rock drill lubricant composition, of an amorphous
ethylene-propylene copolymer having an amorphous structure a
number average molecular weight of between about 10,000 and
100,000, a propylene content of 20 to 70 mole percent and a
w/Mn of less than about 5
The ethylene-propylene copolymer found useful
for this purpose has an amorphous structure, a number average
molecular weight, preferably between about 30,000 and 80,000,
and a propylene content of preferably 30 to 55, mole percent.
Minor quantities of this copolymer, between about 0.01 and
1.0, preferably between about 0.04 and 0.35, wt.% of the
rock drill lubricant composition are found to be effective
in reducing the air misting of the rock drill lubricants to
a satisfactory level. Concentrations of the copolymer
higher than 1.0 wt.% may beused but there is no apparent
further improvement in product quality or mist surpression.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Broadly, we have found that the stray fog
generation of a rock drill lubricant can be significantly
reduced by incorporating therein small quantities of an
amorphous ethylene-propylene copolymer. Further, this
particular copolymer maintains the stray fogging at accept-
able low levels during prolonged rock drill operations.
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The rock drill lubricants whose stray fogging
qualities can be successfully suppressed by admixing there-
with the amorphous ethylene-propylene disclosed herein
include a wide variety of mineral oil base rock drill
lubricants. In fact, where stray fogging of a rock drill
lubricant is a problem, the addition of a quantity of an
amorphous ethylene-propylene copolymer will control the
stray fogging. Rock drill lubricants must be capable of
lubricating all manner of pneumatic percussion tools oper-
ating at ambient temperaturs ranging from -30 to +110F
under either wet or dry condistions. These lubricants
usually are additive-containing naphthenic oils which are
opaque and have a blue bloom. The additive package enhances
the ability of the oil film to resist water wash-off,
enables the oil to emulsify with water to prevent moisture
contact with steel surfaces of lubricated parts, offers rust
protection, suppresses forming in air line oilers, provides
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superior copper corrosion protection and exhibits good
extreme pressure properties. In general, rock drill
lubricants have viscosities covering a broad spectrum, viz,
100-3000 SUS ~D 100F.
The ethylene-propylene copolymers we utilize are
amorphous by infra red analysis and have a narrow
molecular weight distribution. These copolymers may be
prepared as described in U.S. 3,522,180. This patent
discloses that amorphous ethylene-propylene copolymers may be
prepared in a hydrogen moderated reaction at moderate
temperatures and pressures in the presence of a solvent
soluble Ziegler-Natta catalyst. In U.S. 3,522,180, amorphous
ethylene copolymers having a number average molecular weight
of lO,000 and 40,000, a propylene content of 20 to 70 mole
percent and a MW/Mn of less than 5 are disclosed as
viscosity index improvement additives for lubricating
oils. We have found that these same copolymers are
useful as stray fog suppressing additives for rock drill
lubricants. In fact, we have found that the number
average molecular weight of the amorphous ethylene
copolymers we employ may be lO,000 and 100,000 although
we prefer to use those whose number average molecular is
30,000 to 80,000.
The concentration of the amorphous ethylene-
propylene copolymers necessary to suppress the stray fogging
of rock drill lubricants should be between about 0.01 and
1.0, preferably between about 0.04 and 0.35, weight percent
of the final rock drill lubricant blend. Those skilled in
the art will realize that some experimentation may be
necessary to arrive at the minimum concentration required
by both economic and service requirements. In general, the
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more severe the stray fog of oil appearing in the exhaust air
from the rock drill,the higher the concentration of a
given amorphous ethylene-propylene copolymer necessary for
satisfactory service.
Our invention is illustrated in detail in the
following examples.
EXAMPLE I
This example shows the stray fog surpression pro-
perties of a number of polymeric materials when added to a rock
drill lubricant. In a series of tests a small quantity of
each material was added to a rock drill lubricant
composition and the fogging properties of the resultant
blend evaluated by visually observing the quantity of oil
mist formed above a small quantity of the oil while a
stream of air was passing through the oil. The rock drill
lubricant used was compounded from naphthenic oils and
contained an additive package providing water wash-off re-
sistance, rust and corrosion resistance, foam suppression, water
emulsification and extreme pressure resistance. The rock
drill lubricant used in this series of tests had the
following properties:
Gravity, API 22.1
Flash, COC, F 355
Viscosity, SUS ~ 100OF 190.6
SUS ~? 210F 44.3
Pour, AST~, F -35
The fogging characteristics were determined
visually in an apparatus consisting of a vertical glass
cyclinder, 2 inch I.D., 12" long, attached to a stainless
steel plate. After cleaning the cylinder with a light
solvent and blowing it dry, 180 ml. of the oil under test
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were introduced into the cylinder filling it to a height
of approximately 2 1/4 inches. Air was introduced into
the cylinder through a 0.018 inch orifice in the stainless
steel plate at a regulated pressure of 35 psig while the
cylinder was maintained in an upright position. After
allowing one minute for the formation of an oil mist to
stabilize, an observer made a visual evaluation of the
quantity of mist or fog which had formed in the vicinity
of the top of the tube and assigned a qualitative rating
as follows:
Very Good - No mist or fog to barely
mist or fog
Good - Very slight mist or fog
Fair - Slight mist or fog
Poor - Much mist or fog
The additives tested included a polymethacrylate
VI improver (Run 2), an acrylate polymer fuel oil pour
depressant (Run 3), a polyisobutylene tackiness agent
(Run 4) and an amorphous ethylene-propylene copolymer VI
improver having a narrow molecular weight distribution and
prepared in a hydrogen moderated reaction utilizing a
Ziegler-Natta catalyst (Run 5).
The screening test results are shown in Table I
below: .
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This serles of tests showed that the mist
forming tendency of a rock drill lubricant can be
supressed with some polymeric materials while little
success is achieved with other polymeric materials.
EXAMPLE II
Those additives of Example I which were
capable of suppressing the mist formation of the rock
drill lubricant were sukjected to further evaluation in
a test which more closely approximates end-use
conditions.
Minor additions of the polyisobutylene
(0.22 wt.%) and the amorphous ethylene-propylene copolymer
(0.16 wt.%) of Example I were added to each of two rock
drill lubricants. Rock drill lubricant no. 1 was that
of Example I while rock drill lubricant no. 2 had the
following properties:
Gravity API 19.5
Flash, COC, F 485
Viscosity
Viscosity, SUS @ 210F 96.3
Pour, ASTM, F +5
The testing of these blends was conducted
by forming an oil mist of each blend, reclassifying
the oil mist, and measurin~ the quantity of oil misted and
reclassified to determine the quantity of oil mist lost
as stray fog. A commercial oil mist lubricator, a C.A.
Norgren Company Model S 3406-6S Micro-Fog Lubricator, was
employed to form the oil mist from the test blends. In
this mist unit clean dry air entering the unit at a
controlled pressure passed through a venturl creating
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a pressure differential between a quantity of oil in an
oil reservoir of the mist unit and the open end of an oil
feed tube passing from the throat of the venturi to
below the surface of the oil. Oil passed up the tube
and into the venturi section where the momentum of the
air caused the oil to be broken up into very fine
particles. A baffle arrangement caused the larger
particles to fall back into the oil reservoir while the
smaller particles, ranging from a maximum of about five
microns to a minimum of less than one micron, were
carried from the mist unit by the air stream into a
manifold assembly. The oil mist passed through the
manifold assembly to a reclassifier manifold where
the oil mistwas reclassified and recovered for
measurement in a collection cup. The oil mist was
reclassified by passing the mist through ten 0.093
inch I.D. lengths of tubing known as reclassifiers
located at the end of the reclassifier manifold. These
reclassifiers served both to increase the mist
velocity and to increase oil particle size with the
result that the oil mist "wetted outn, i.e. was reclassified
into wet spray and droplets which were recovered in a
collection cup located below the row of reclassifiers.
Not all of the oil formed into mist in the mist unit
was recovered in the collection GUp; some was reclassified
and droped out within the manifold assembly and retained
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therein while some of the mist passed through the
reclassifiers and was lost. This "lost mist" is termed
stray fog.
Each of the lubricants was evaluated in three runs,
in the first run of each series the rock drill lubricant
containing neither polymeric material was evaluated, in
the second run the lubricant contained the polyisobutylene
of Example I and in the third, the amorphous ethylene-
propylene copolymer of Example I. In each series of
runs, the inlet air pressure to the mist unit was
maintained at 23 psig and each run was conducted for two
hours. The oil in the mist unit reservoir was maintained
at a selected constant temperature during each run. The
viscosity of the oil under test determined the temperature -
800F for rock drill lubricant no. 1 and 120F for rock
drill lubricant no. 2. All the test equipment was
enclosed in a controlled environment chamber to assure
that the air feed line, the manifold and the mist unit
were maintained at the same conditions.
Prior to the start of each run, the mist unit
and its oil charge were weighed and the mist manifold
assembly and collection cup were cleaned and weighed
individually. Following each two hour run, each of these
three items were weighed again. These weight
determinations permitted the calculation of the following
quantities, viz,:
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1. Quantity of oil misted (mist unit weight loss)
2. Quantity of oil reclassified (collection cup
weight gain)
3. Quantity of oil drop out (manifold weight
gain)
4. Quantity of oil carried off as stray fog
(difference between the weight loss of the
mist unit and the combined weight gain
of the manifold and the collection cup)
The results of these tests are presented in
Table II below. All results are reported in terms of
pounds per hour. Manifold drop out, reclassified oil
and stray fog are also reported as a percentage of the
total oil converted into oil mist.
.
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These tests showed that, although both olefinic
polymers tested reduced both the mist rate fo:rmation and the
c;tray fog loss, not only did the amorphous ethylene-propylene
copolymer reduce the mist rate appreciably more than the
polyisobutylene but this copolymer significantly reduced the
stray fog losses more than did the polyisobutylene.
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