Locomotive oil filter

Provided is a novel locomotive oil filter for use in locomotive applications. The filter is comprised of a pulp which is comprised of lignin-containing fibers derived from a fiber source having a lignin content of at least about 10% by thermomechanically pulping a fiber source under temperature/pressure conditions of 300.degree. F.-350.degree. F./50 psig-120 psig and a refiner energy utilization of about 8-35 HPD/ADT. The locomotive oil filter comprising the pulp of such lignin-containing fibers overcomes the severe problems of filter swelling and plugging due to water in the locomotive oil, while also providing one with improved filtration capacity and good filtration. The use of such lignin-containing fiber pulp also gives one the economic advantage of substitution for the more expensive cotton linter generally used heretofore in railroad/locomotive lube oil filters. The pulp of lignin-containing fibers can be used in combination with other suitable pulps, e.g., high alpha cellulose content pulps, in making the filter media.

BACKGROUND OF THE INVENTION 
1. Field of the Invention: 
The present invention relates to the manufacture of filter media for 
application in locomotive lubrication oil systems. The present invention 
also relates to the filtration of locomotive lubricating oil employing 
such filter media. 
2. Description of the Prior Art: 
Railroad locomotive lube oil filters must meet certain physical 
characteristics in order to perform adequately and overcome the problem 
often encountered with water getting into the lube oil. The problem of 
water in the lube oil is a very common and serious problem if one does not 
use an appropriate lube oil filter in the locomotive engine. The result of 
using an inappropriate filter is that the water softens and swells the 
filter, the filter becomes very limp and the bottom edge of the pleat 
extrudes into the center tube of the filter, thereby causing blockage of 
the line or at least a decrease in flow rate i.e., high pressure drop. In 
order to test filter materials to determine whether they would be 
appropriate for use in locomotive engines, a water extrusion resistance 
test has been formulated in order to test the water extrusion resistance 
of the filter medium. In the test, one first tests the flow resistance of 
the filter paper to lube oil at a certain temperature and flow rate. Then, 
the paper is tested for flow resistance against a water-in-oil emulsion 
(generally about 1% water in oil emulsion) at the same temperature and 
flow rate. A ratio of the respective pressures measured, i.e., pressure at 
X gpm of emulsion/pressure at X gpm of lube oil, is indicative of the 
suitability of the filter media. The industry generally considers anything 
over about 1.1 as generally not suitable for application in locomotive 
lube oil filters. 
Due to the problem of water often appearing in the locomotive lube oil, to 
date the industry has adopted the use of a one side coated filter paper 
made of cotton linter fibers. The filter used is essentially that 
described in U.S. Pat. No. 3,116,245 issued to Robert W. McNabb and Howard 
L. Dahlstrom. The use of cotton linter fibers results in a filter medium 
exhibiting good resistance to water extrusion and good filtration 
characteristics. The problem with using cotton as a source, however, is 
the cyclical variance in supply. Even when cotton is available, the price 
is prohibitive, e.g., $1200/ton, as compared to other wood pulps, such as 
the Kraft wood pulps, which average about $300/ton. The use of Kraft pulp 
in filter media for application in the filtering of locomotive lube oil is 
unsuitable, however, as the filter medium can exhibit poor-resistance to 
water extrusion. To provide a filter media which replaces at least a 
substantial part of the cotton generally used would be of benefit to the 
industry, providing the filter medium can perform adequately as a 
locomotive lube oil filter, i.e., exhibit adequate water extrusion 
resistance. 
Accordingly, it is an object of the present invention to provide filter 
media for use in the filtering of locomotive lube oil which comprises a 
substantial portion of fibers other than cotton fibers. 
It is yet another object of the present invention to provide such filter 
media which exhibit good filtering characteristics and improved filtration 
capacity. 
It is still another object of the present invention to provide such filter 
media which is much less expensive than filter media made from 
substantially all cotton linter fibers. 
Another object of the present invention is to provide a process for 
filtering locomotive lube oil employing such filter media. 
These and other objects, as well as the scope, nature and utilization of 
the invention, will be apparent to those skilled in the art from the 
following description and the appended claims. 
SUMMARY OF THE INVENTION 
In accordance with the foregoing objectives, there is provided herewith a 
locomotive lube oil filter comprised of a lignin-containing fiber pulp. 
The lignin-containing fibers are derived by thermomechanically pulping a 
fiber source having a lignin content of at least about 10 percent under 
pressure conditions of about 50 psig to 120 psig, at temperature 
conditions of about 300.degree. F. to 350.degree. F., and a refiner energy 
utilization in the range of about 8 to 35 HPD/ADT. The resulting 
lignin-containing fibers are characterized by having most of their 
original lignin content and by having a smooth wall structure, 
substantially free of fiber-bonding surface fibrils and being 
substantially non-self-bonding to adjacent like fibers in the absence of 
elevated temperatures. 
By employing a filter medium comprised of a substantial portion of the 
lignin-containing fiber pulp in accordance with the present invention, the 
severe problem of swelling and plugging due to water in the lube oil is 
obviated. Moreover, the use of the lignin-containing fiber pulp in 
accordance with the present invention also results in a filter medium 
exhibiting improved filtration capacity and good filtration. As well, one 
achieves the advantage of an less expensive filter medium. 
The lignin-containing fiber pulp can be used in combination with other 
suitable pulps, e.g., high alpha cellulose content pulps, or cotton 
linter. It is generally preferred to use the lignin-containing fiber pulp 
in amounts of at least 30 percent. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The lignin-containing fiber pulp utilized in the locomotive lube oil filter 
of the present invention is that pulp obtained by the processes described 
in U.S. Pat. Nos. 4,455,195 and 4,455,237, which patents are herein 
expressly incorporated by reference. The pulp is produced under selected 
and controlled thermomechanical conditions. It has been surprisingly found 
that filter media comprised of a substantial portion, e.g., at least about 
30 percent, of such lignin-containing fiber pulp, do not suffer from the 
problem of swelling and plugging, and easily pass the water extrusion 
resistance test. Such filter media are, therefore, advantageously suitable 
for use in locomotive lube oil applications. 
The source of the lignin-containing fiber is not specifically critical and 
may be taken from a wide variety of lignin-containing fibers, although 
some may, of course, be preferable to others. These sources include 
debarked wood (both softwood and hardwood varieties) and other 
lignin-containing materials, such as bamboo, bagasse, certain grasses and 
straws, and the like. For purposes of the present invention, the 
fiberforming material should have a lignin content of at least about 10% 
and preferably around 15% or more (most pulp woods have a lignin content 
in excess of 20%). At the present state of development, the preferred 
fiber source is debarked wood, either northern or southern softwoods or 
hardwoods, with some preference toward northern softwoods. 
After removal of bark, which is not used in the process for obtaining the 
pulp, pulp wood logs are cut into chips of a size suitable for 
thermomechanical processing. Desirably, the typical chip size is in the 
range of 3/8 inch by 1/2 inch by 3/4 inch, with the fibers aligned with 
the long axis of the chip. Of course, in any chipping process, the size 
and shape of the chips is highly randomized. Nevertheless, the objective 
is to seek a typical chip having a minimum dimension of about 3/8 of an 
inch and a maximum dimension of about 3/4 of an inch, which can be 
reasonably approximated by screening of the chips to one inch maximum 
screen mesh and 1/8 minimum screen mesh. 
The screened chips, typically after cleaning by a conventional water wash 
procedure, are reduced to pulp fibers following general techniques of the 
Asplund U.S. Pat. No. 2,008,892, the disclosure of which is incorporated 
herein by reference. A first step in this process is the preheating of the 
chips by steam, and this is advantageously carried out in a vessel such as 
a horizontal tube digester. The digester, which is a conventional piece of 
equipment, may be provided at the inlet with a rotary valve or similar 
device (also conventional) for accommodating the in-feed of wood chips 
while maintaining the vessel under superatmospheric steam pressure. 
Wood chips generally of the indicated size are preheated at a temperature 
not less than about 300.degree. F. and more desirably at a temperature in 
the range of about 330.degree. F. to about 350.degree. F. This corresponds 
to a pressure range of about 50 psig to about 120 psig, with the preferred 
range being from about 90 psig to about 120 psig. Desirably, the chips are 
moved progressively through a partially filled (1/8 to 1/2) digester, 
while being continually agitated. This assures highly efficient heat 
transfer between the steam and the wood chips and a uniform preheating. 
Typically, a three minute retention time inside the horizontal tube 
digester is adequate, and this is believed to bring the inside of the chip 
to within about 10.degree. of the steam temperature. 
The preheated wood chips are ground into pulp fibers in a disc refiner, 
while the chips are maintained in a pressurized steam atmosphere and in a 
substantially dry condition. Grinding is performed in a disc refiner of 
the general class disclosed in the aforementioned Asplund patent. More 
specifically, a C. E. Bauer, No. 418 counter-rotating 36 inch disc refiner 
is a preferred piece of equipment for this purpose. This machine utilizes 
a pair of oppositely rotating 36 inch discs arranged in communication with 
the horizontal tube digester and arranged to receive preheated wood chips 
from the digester (preferably under the same pressure conditions), in 
which case a pressure valve device is not required to be located between 
the digester and the disc refiner. 
In accordance with known principles, when the wood chips are subjected to 
shear and abraded by the counter-rotating refiner discs, they are subject 
to further heating, as a result of the energy input of the grinder itself. 
It is known that, under certain conditions of preheating of the chips and 
operation of the disc refiner that the lignin content of the chips becomes 
softened and plasticized, allowing easy separation of individual fibers 
with minimum damage and destruction of the fibers. A desired degree of 
refining is controlled by adjustment of the peripheral gap between the 
refiner disc. In general, the narrower the gap, the more energy 
utilization that is required to refine the pulp and enable the fibers to 
emerge from the gap. Typically, such energy utilization is measured in 
Brake Horsepower Days per Air Dried Ton (HPD/ADT) of the raw material. For 
the production of pulp fibers ideally suited for the filter media of the 
present invention, it has been determined that the energy utilization in 
the disc refiner should be not less than about 8 HPD/ADT and not more than 
about 35 HPD/ADT. In many cases, achieving the desired energy levels 
requires setting of the gap at minimum size--virtually zero clearance, 
although for certain woods, such as southern softwoods, it may be 
desirable to widen the gap slightly to limit the energy to around 35 HPD. 
After refining, the fibrous pulp is discharged from the refiner, through a 
suitable blow valve or the like, which enables the fibrous material to be 
taken from a pressurized condition to a nonpressurized condition. 
After the disc refining operation, the pulp fibers are mixed with 
sufficient water to derive a slurry of about 0.5 to 1% solids, suitable 
for screening of the fibers. In this respect, fibers produced according to 
the procedures outlined are significantly longer and stiffer than more 
conventional pulp fibers, and are not readily screened on conventional 
pulp screens, without excessive rejection of good fibers and unnecessary 
loss of yield. Because of the fiber characteristics of the pulp thus 
produced, it is desirable to utilize a rotary-type screen having slots 
aligned circumferentially (rather than axially as is more typical). A 
so-called "Ultrascreen" marketed by Black-Clawson is effective in the 
process. Such a screen having a slot width of approximately six mils 
enables effective screening of the pulp, with reliable rejection of shives 
and other foreign matter, without excessive rejection of good fiber. 
An important economic advantage of the aforementioned Asplund-type pulping 
procedure is the extremely high yield of fiber. The fiber yield may be as 
high as 95% of the dry wood starting material, as compared to chemical 
processes for high performance pulp, which yield as little as 35% useable 
fiber. To a large extent, this results from the fact that the fiber output 
of the pulping process retains substantially all of the lignin and 
hemicellulose content of the original unpulped fiber source. The chemical 
processes, on the other hand, substantially remove lignin and 
hemicellulose, which results in an immediate loss of yield. Moreover, 
because of the essentially fragile nature of the resulting fiber product, 
additional significant losses occur throughout subsequent processing. The 
presence of the lignin and lignim related materials in the fiber output is 
significantly advantageous in the ultimate filter media when the fiber 
production has been achieved under the conditions of the aforedescribed 
process. Thus, under proper pressure and temperature conditions, the 
lignin materials are in a plasticized state during the refining operation, 
which not only enables a relatively long, relatively undamaged fiber to be 
produced, but the resulting fiber is extremely stiff and tough, and has a 
very smooth outer surface. This structure is exceptionally ideal for 
filter media utilization, as it exhibits exceptionally low bonding 
characteristics and, because of its structure resembling "uncooked 
spaghetti" it results in an extremely porous, bulky media when laid in 
random form, as by wet laying or air laying for example. Directly related 
to the high bulk characteristic, is an extremely high freeness, in the 
area of 760 and above. This equals or exceeds the freeness of the highest 
quality high performance chemical pulps. 
For the purposes of the present invention, the filter medium contains a 
substantial portion, i.e., at least about 30 weight percent, more 
preferably at least about 40 weight percent and most preferably from 40 to 
75 weight percent, of the lignincontaining fiber pulp. The remaining 
constituency of the filter medium, if any, can comprise any suitable 
fibers and/or pulp which will not result in failure of the water extrusion 
test, i.e., a ratio of greater than about 1.1. Examples of such suitable 
pulps are the high alpha cellulose pulps such as the Buckeye "HPZ" pulp, 
XJ pulp from Merciner, Placetate from Merciner and Esparto (which is 
bleached grass pulp). The remaining constituency can also comprise cotton 
linter fibers if one so desires, such that a filter medium comprising a 
mixture of substantial portion of lignin-containing fibers and cotton 
linter fibers is within the scope of the present invention. 
Kraft wood pulps may be present in the filter media in minor amounts, i.e., 
less than 5 to 10 weight percent, and preferably less than about 5 weight 
percent. The presence of greater than about 10 weight percent Kraft wood 
pulp results in a filter medium exhibiting insufficient water extrusion 
resistance to be used commercially. 
In the manufacture of filters for commercial use, typically, although not 
necessarily, the pulp mixture is generally prepared as a slurry, beaten 
sufficently to assure uniform distribution, and then wet laid on a 
paper-making screen. Also typically, the wet web is dried and then 
impregnated with a binder resin. Alternatively, the filter media may be 
produced using air-laying techniques. 
The resin, typically, is only partially cured by the web manufacturer. The 
ultimate filter manufacturer, later usually converts the web material into 
an accordion pleat configuration, quite frequently forming a cylinder of 
accordion pleats accommodating a generally radial flow of the lube oil to 
be filtered. At this stage of production, the resin in the web material 
may be fully cured to provide a relatively permanent set to the 
manufacturer's configuration. 
The resulting filter medium in accordance with the present invention 
exhibits excellent water extrusion resistance, while also providing an 
economic advantage of a less expensive filter medium than the cotton 
linter filters now used in the industry. The cost of the lignin-containing 
fiber pulp used in accordance with the present invention is only about 
$450/ton as opposed to the $1200/ton cost of cotton fibers. Besides the 
economic advantage, the use of the lignin-containing fiber pulp results in 
a filter medium exhibiting improved filtration capacity and good 
filtration efficiency. 
The following examples are given as specific illustrations of the present 
invention. It should be understood, however, that the specific details set 
forth in the examples are merely illustrative and in nowise limitative. 
All parts and percentages in the examples and the remainder of the 
specification are by weight unless otherwise specified.

EXAMPLE 1 
Handsheets were made having the following constituencies: 
A 
40 percent lignin-containing fiber pulp 
40 percent HPZ pulp 
20 percent esparto 
B (Comparative): 100 percent cotton 
C (Comparative): 
47 percent lignin-containing fiber pulp 
23 percent Westvaco bleached hardwood kraft 
30 percent bleached kraft pulp made from redwood chips 
D 
47 percent lignin-containing fiber pulp 
30 percent placetate (bleached alpha pulp made from softwood fiber) 
23 percent esparto 
E 
47 percent lignin-containing fiber pulp 
25 percent placetate 
20 percent esparto 
8 percent bleached kraft pulp made from redwood chips 
A water extrusion resistance test was performed on each handsheet to test 
the materials applicability as locomotive lube oil filter media. The runs 
were conducted by first testing the flow resistance of the handsheets to 
82.degree. C. lube oil at four flow rates ranging from one to four gallons 
per minute. The lube oil was then taken and mixed with water in a 
Commercial Waring Blender to form a one percent water in oil emulsion. The 
flow resistance of the handsheets to the emulsion at 82.degree. C. was 
then tested at the same four flow rates. The flow resistance was monitored 
in each instance, and the results are tabulated in Table 1 below. Also 
noted in the Table is the water extrusion resistance ratio (pressure at X 
gpm of emulsion/pressure at X gpm of oil), as well as the Frazier CFM. 
TABLE No. 1 
__________________________________________________________________________ 
Water Flow (Extrusion) Resistance 
Average 
Frazier 
Handsheet 1 gpm 
2 gpm 
3 gpm 
4 gpm 
Ratio 
CFM 
__________________________________________________________________________ 
A Oil 82.degree. C. 
2.45 
psi 
5.75 
psi 
9.7 
psi 
14.5 
psi 21 
Emulsion 82.degree. C. 
2.50 6.00 10.1 15.2 
Ratio 1.02 1.04 1.04 1.05 1.04 
B Oil 82.degree. C. 
3.1 
psi 
6.4 
psi 
11.3 
psi 
17.1 
psi 14 
Emulsion 82.degree. C. 
3.3 7.1 11.7 18.4 
Ratio 1.06 1.11 1.04 1.08 1.06 
C Oil 82.degree. C. 
2.8 
psi 
6.1 
psi 
10.6 
psi 
16.1 
psi 
Emulsion 82.degree. C. 
3.2 7.4 14.2 20+ 
Ratio 1.14 1.27 1.34 -- 1.25+ 
D Oil 82.degree. C. 
2.1 
psi 
5.1 
psi 
8.6 
psi 
13.3 
psi 
Emulsion 82.degree. C. 
2.2 5.3 9.1 13.7 
Ratio 1.05 1.04 1.06 1.03 1.05 
E Oil 82.degree. C. 
2.0 
psi 
5.0 
psi 
8.4 
psi 
13.1 
psi 26 
Emulsion 82.degree. C. 
2.3 5.4 9.1 14.3 
Ratio 1.15 1.08 1.08 1.09 1.10 
__________________________________________________________________________ 
As can be seen from the foregoing Table 1, the filter media of the present 
invention have a ratio in the water extrusion resistance test of about 1.1 
or less. This is comparable to the water extrusion resistance of an all 
cotton fiber filter medium (Run B). If more than just a minor amount of 
kraft wood pulp is utilized in the filter medium, however, the ratio 
exceeds 1.1 greatly (Run C). 
EXAMPLE 2 
The handsheets A and B were tested for filtering capacity in mgms/sq.in. 
and filtering efficiency using standard testing methods, in order to 
compare the filtering capacity and efficiency of locomotive lube oil 
filter media of the present invention with a conventional all cotton 
locomotive lube oil filter medium. 
The results are tabulated below, and demonstrate that while the efficiency 
is comparable, the filtering capacity of the filter medium of the present 
invention is much improved. 
TABLE No. 2 
______________________________________ 
Handsheet: A B 
______________________________________ 
Capacity (mgms/sq.in.) 
55 30 
Efficiency (percent) 87 91.8 
______________________________________ 
Although the invention has been described with preferred embodiments, it is 
to be understood that variations and modifications may be resorted to as 
will be apparent to those skilled in the art. Such variations and 
modifications are to be considered within the purview and the scope of the 
claims appended hereto.