Note: Descriptions are shown in the official language in which they were submitted.
-- 1 --
L IC~TING GREASE
This invention relates to a lubricating grease suitable
for open-gears.
Open gear lubricants are a special type of lubricant
and have been marketed commercially for many years. As the
name implies, the gears to be lubricated are open to the
atmosphere and may thus be required to operate over a wide
temperature range and in the presence of moisture. The
lubricant is normally placed on the gear teeth and it has
to have the quality of spreading uniformly over the teeth
without dropping off. In one form of existing lubricant,
bitumen is used as a basic component and in another form a
lubricating base oil is thic]cened with carbon black and
atactic polypropylene. These existing lubricants are,
however, dark in colour and therefore dirty to use and do
not have extreme pressure (EP) properties.
The present invention provides a clean, light coloured
grease with EP properties.
According to the present invention a lubricating grease,
suitable for use as an open gear lubricant, comprises a
lubricating base oil, from 2 to 20%,by weight of total com-
position of a clay thickener; from 2 to 12% wt., by weight of
total composition oE an alkali metal borate as extreme pressure
additive; and a combination of an olefin polymer selected from
the group consisting of atactic polypropylene and polyisobu-
tylene and a light coloured particular mineral which is zinc
oxide, as tackifier and filler, the polymer and particulate
material each being present in an amount of from 3 -to 12%
wt. by weight of total composition and the polymer; particulate
mineral ratio being from 1.5:1 to 1:1.5 by weight.
The lubricating base oil may be a mineral or synthetic
base oil. For simplicity and cheapness it is preferably a
lubricating base oil derived from petrole~m. Thus, the base
oil may be a refined oil obtained from petroleum having a
viscosity of from 10 to 900 centistokes at ~0C.
The clay thickener may be of the type well known in the
grease-making art, i.e. a colloidal clay whose particles are coated
with an oleophilic substance. An example of a clay thlckener is a
material consisting of platelets of montmorillonite coated with a
quaternary ammonium salt~ Such materials are sold under the Trade
Marks "Baragel" and "Bentone", The clay thickener may be present in
an amount of from 2-15% wt by weight of the total composition.
The grease may also contain, in conventional manner, a
dispersant for the clay type ~hlckener~ e~g. from 0.1 to 3% wt of
propylene carbonate.
One of the problems associated with clay-thic~ened greases is
that of finding additives which are compatible with the clay and its
polar coating. However, for open gear lubricants, a clay thickened
grease without addltives is of little value.
In one aspect of the present invention, .herefore, it has been
found that the combination of a polymer and a particulate mineral is
an additive combination which is compatible with the clay and which
imparts to the grease good spreading properties without giving rise
to excessive drop off from the gears. It has been found that the
ratio of polyMer to particulate mineral is important in this respect
and that the required optimum balance of properties is obtained if
the polymer:particulate mineral ratio is Erom 1.5:1 to 1:1.5, and
preferably 1:1. The total quantity of each material is from 3 to
12~ wt by weight of total composition.
The polymer is preferably an olefin polymer having elastic
properties. The polymer may be a polyisobutylene (e.g. a material
sold under the Registered Trade Name "Vistanex") with an average
molecular weight of 40000 (viscosity average molecular weight
(Flory)), or more preferably an atactic polypropylene9 molecular
weigh~ approximately 3QOOO and a melt viscosity of 5000 to 10000 cPs
at 170C and 2.7 sec~1-
The term "mineral" i9 to be understood as including both
naturally occurring and synthetic materials.
Another important aspect of the inventlon is the choice oE
extreme pressure additive which, again, should be compatlble with
the clay thickener and should, preferably, provide extreme pressure
qualities beyond those of existing open gear lubricants.
It has been found that an alkali metal borate alone gives good
extreme pressure qualities. Alternatively the alkali metal borate
may be used in combination with an aromatic disulphide, particularly
dibenzyl disulphide. Again it has been found that the weight ratio
of borate and disulphide is relevant to obtaining an optimum EP
performance and the preferred weight ratio of borate to disulphida
is from 5:1 to 7:1 and pr~f~rably 6:~. The ~o~al quantitieQ of
material are from 2 to 12% wt of borate, and may be 0.2 to 2% weigh~
of aromatic disulphide, if this is present, by weight of total
composition.
The alkali metal borate is preferably borax and it has been
found that the borate confers anti-rust properties as well as EP
properties. Despite its solubility in water, it has also been found
that the borate is not leached out to any substantlal extent by
moisture and that the finished grease gives less than 1~ wt washout
in the water washout test at 79C (ASTM D1264 or IP Method 215).
The borate may be inccrporated into the grease using the
technique known for incorporating alkali metal nitrites lnto clay
thickened greases. Thus a solution of borate in water may be formed
into an emulsion with a portion of the lubricating base oil and a
portion of the clay thickener, The water may then be evaporated off
leaving a dispersion of borate particles in the base oil which may
then be blended with the remaining base oil and the other components
of the grease. The size of the borate particles is believed to
depend on the relative proportions of borate and oil. With a
dispersion of about 50% borate in oil che particles may have a size
of about 1 to 5 microns diameter, but sub-micron particles may be
obtained by lowering the concentration of bora~e in the borate/oil
dispersion.
The invention is illustrated by the following ~.xamplesO
~e:~
A lubricating grease was prepared having the followlng
composition:
-- 4 --
% wt
Clay thickener 6.5
Propylene car~onate 0.9
Atactic polypropylene 5.0
Zinc oxide 5.0
Borax 5 0
Dibenzyl disulphide 0.~
Lubxicating base oil 76.8
The clay thickener was the material sold by Berk Chemicals Ltd. under
the Registered Trade Mark "Baragel". The atactic polypropylene had a melt
viscosity of 5700 cPs at 170C, 2.7 sec . It was sold by Chemie Linz AG
as grade APP8. The zinc oxide had an average particle size of 0.2 ~m and
was sold by ~5Orris Ashby Ltd. as "Zincoli" Red Seal grade. The borax was
a laboratory grade of sodium tetraborate, Na2B4O7 lOH20, sold by BDH
Chemicals Ltd. The lubricating base oil was a refined mineral lubricating
oil having a viscosity of 30 centistokes at 40C and a viscosity index
of 100.
The grease was prepared in three stages as follows. Firstly, a
concentrate of the thickener and filler was prepared by dispersing the
zinc oxide; Baragel and propylene carbonate in 60% of the base oil, at
ambient temperature.
Secondly, the borax was dispersed in 20% of the base oil in a second
mixing vessel. The borax was dissolved in water at 90C and added to the
base oil at 90C. A small quantity of Baragel and propylene carbonate
were added to stabilise the water in oil emulsion. The temperature of
the emulsion was then increased to 140C whilst mixing vigorously to boil
off the water. The resultant dispersion of borax in oil was then cooled
to 100C and added to the grease concentrate.
Finally the polypropylene was dissolved in the remaining base oil at
160 C. When the polypropylene had dissolved the temperature of the blend
was reduced to 120C and the dibenzyl disulphide added and dissolved~ The
total blend was then added to the grease concentrate.
The resultant grease was then homogenised on a Manton Gaulin
Homogeniser at 2000 psi to provide a smooth structure.
The grease was submitted to the following tests to evaluate its
suitability as an open gear lubricant:-
_ 5
O n Gear Riq
The rig consists of a gear driven by and lightly loaded against a
pinion. The gear axes are vertical. Running conditions are as follows:
Gear: Cast Iron, 3DP 40 tooth. 3O5 inches wide
Pinion: Steel 16 teeth
Pinion Speed: 40 rpm
Load: 12.5 lbf ft torque load on gear shaft.
A total of 110 g of grease is applied to the gear. Grease is applied to
the driven face of each gear tooth. The rig is then run for two hours.
At the end of the test only the minimum amount of grease should have
dropped off the rig and the driven surfaces of the pinion and gear should
be completely covered with grease.
Open Gear Rig 2hr run drop off: 8O0% wt
coverage: Complete coverage of teeth
Cone Penetration: (IP Method 50/69) Unworked = 235
Worked = 275
Four Ball EP Performance (IP Method 239): Mean ~lertz Load = 67.9 kg
Initial Seizure Load = 158 kg
Weld Load = 355 kg
Water Washout (IP Method 215) 79C: = below 1~0%wt
Dynamic Anti Rust Test (IP Method 220) = rating 2,2.
Example 2
A series of greases was prepared according to Example 1 the only
variant being the ratios and amounts of atactic polypropylene and zinc
oxide.
Each grease was tested for its spreadability over the teeth of the
open gear test rig described in ~xample 1 and for the amount of grease
which dropped off the gears during the tests.
The results are shown in Table 1 below~
6 ~ 98~
r
Table 1
~ . . . _ .:
i
~wt Zlnc Oxide 20 15 10 5 10 15
%wt Polypropylene 5 5 5 5 10 15
~ . _____ ._i_._~ .. .... ... . _ _
% Drop Off 15 10 9 3 11 27
Coverage insufficient total some bare
coverage of coverage of spots on
gear teeth gear teeth gear teeth
~ .
Taking the results of Table 1 in succession from left to right it
will be seen that, as the ratio of zinc oxide to polypropylene decreases
from 4:1 to 1:1 there is a steady improvement in % drop off and in
coverage, the best result being at a 1:1 ratio and 5% wt of each. If
the ratio is kept at 1:1 and the amount of each is increased, however,
~rop off increases and coverage becomes less certain.
Example 3
A series of greases was prepared according to Example 1 the only
variant being the ratios and amounts of borax and dibenzyl disulphide~
Each grease was tested for EP properties using the 4 Ball testO
The results are shown in Table 2 below.
Table 2
--. . _ . j ___ .~_ _. t
%wt Borax 1 7.5 - 5.0 5.0 2.5 5.0
%wt DBDS ¦ - 2.2 0.5 loO 2.0 0.8
4 Ball EP (IP 239/73) ¦
Mean Hertz Load kg 1 53.956.850.2 63.0 63.6 67.9
Initial Seizure Load kg ¦141 79 126 141 89 158
Welding Load kg 1398 335 282355 398 355
J
; Table 2 shows that good EP properties were obtained using borax
alone. When mixtures of borax and DBDS were used, the optimum borax:
DBDS ratio was about 6:1.
Exam~e 4
Two lubricating grease were prepared as in Example l except that
7 ~
no dibenzyl disulphide was added.
For grease A the omission of the dibenzyl disulphide was the
only difference; for grease B there was the additional difference
that the filler was added after the polypropylene.
The greases were also tested as in Example 1. The compositions
of the greases and the test results are shown in Table 3 belowO
Table 3
. _ .
Grease A B
_ .
Clay thickener %wt 7.2 10.5
Propylene carbonate " 1.0 1.5
A,actic polypropylene " 5.0 5.0
Zinc oxide " 5.0 5.0
Borax " 4.9 5.0
15 Lubricating base oil " 76.9 73.0
__
Cone penetration, unworked 247 219
worked 274 283
Cpen gear rig, 2 hr. run.
drop off % wto 8.2 8.2
coverage complete complete
4 ball EP performance, Mean
~ertz Load, kg 55.7
Initial Seizure Load kg 141
25 Welding Load kg 251 _
