U.S. patent number 3,626,043 [Application Number 04/836,343] was granted by the patent office on 1971-12-07 for lubrication process.
This patent grant is currently assigned to Belgonucleaire, S.A., Centre d'Etude de l'Energie Nucleaire. Invention is credited to Alfred Jean P. Flipot, Armand Georges Smolders.
United States Patent |
3,626,043 |
Flipot , et al. |
December 7, 1971 |
**Please see images for:
( Certificate of Correction ) ** |
LUBRICATION PROCESS
Abstract
The specification discloses processes for lubricating compaction
presses, including automatic presses having double-sided rotary
press heads, with solid lubricants.
Inventors: |
Flipot; Alfred Jean P. (Geel,
BE), Smolders; Armand Georges (Olmen, BE) |
Assignee: |
Belgonucleaire, S.A.
(Bruxelles, BE)
Centre d'Etude de l'Energie Nucleaire (Bruxelles,
BE)
|
Family
ID: |
25656691 |
Appl.
No.: |
04/836,343 |
Filed: |
June 25, 1969 |
Foreign Application Priority Data
Current U.S.
Class: |
264/37.29;
419/38; 427/222; 264/39; 427/133 |
Current CPC
Class: |
C10M
7/00 (20130101); B30B 15/0011 (20130101); B30B
11/08 (20130101); C10M 2207/129 (20130101); C10M
2217/042 (20130101); C10M 2207/281 (20130101); C10M
2229/05 (20130101); C10M 2201/18 (20130101); C10M
2207/286 (20130101); C10M 2201/042 (20130101); C10M
2207/404 (20130101); C10N 2050/08 (20130101); C10M
2207/283 (20130101); C10N 2050/10 (20130101); C10M
2205/14 (20130101); C10M 2201/16 (20130101); C10M
2201/066 (20130101); C10M 2205/04 (20130101); C10M
2201/041 (20130101); C10M 2205/026 (20130101); C10M
2207/282 (20130101); C10N 2010/06 (20130101); C10M
2207/125 (20130101); C10M 2201/00 (20130101); C10M
2205/06 (20130101); C10M 2205/16 (20130101); C10M
2207/40 (20130101); C10N 2010/00 (20130101); C10M
2229/02 (20130101); C10M 2205/20 (20130101); C10M
2205/17 (20130101); C10M 2217/043 (20130101); C10N
2010/04 (20130101); C10M 2201/061 (20130101) |
Current International
Class: |
B30B
11/02 (20060101); B30B 11/10 (20060101); B29c
001/04 () |
Field of
Search: |
;264/111,338,300,37,39
;117/5.3,5.1 ;25/DIG.15 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: White; Robert F.
Assistant Examiner: Sokal; Allen M.
Claims
What is claimed is:
1. A method of lubrication comprising, in sequence: providing
lubricant dispersed on carriers which yield on compression and tend
to return to their original shape on release of compression;
introducing said lubricant dispersed on the carriers into a
compacting chamber of a compacting press; lubricating the interior
walls of the chamber by compressing the carriers in the chamber by
the mechanical action of compaction members in the press in the
substantial absence of working material, normal residues of working
material excepted; releasing the compression on the carriers;
removing the carriers from the chamber in the form of flowable
particles, a film of lubricant being left on the interior of the
chamber; introducing working material into the chamber for
compaction therein; and reusing the flowable particles removed from
the compaction chamber in a subsequent compression step for
lubricating the interior of the chamber.
2. A method in accordance with claim 1 wherein the compressions of
working material and carriers are performed alternately.
3. A method in accordance with claim 1 including periodic
introduction of carriers bearing fresh lubricant into the
process.
4. A method in accordance with claim 1 wherein the carriers are of
elastomeric material.
5. A method in accordance with claim 1 wherein said working
material is uranium oxide powder.
Description
BACKGROUND OF THE INVENTION
Compacting presses have in the past been plagued by early wear-out
attributable to the abrasive character of the solid particulate
material which is fed to them. The difficulty of abrasiveness
exists with many inorganic solids, and with some organic solids,
but particularly with powdered metals. Because the maintenance of
tight tolerances is critical to successful operation of the
compaction presses now in use, accelerated wear rapidly impairs
their efficiency. The problem has been sufficiently acute to force
either the frequent replacement of die sockets, punches and punch
sockets, or the equipping of the presses with replaceable hardened
bushings in the punch sockets, tungsten carbide dies and high
carbon or carbide-tipped punches.
While these expedients have circumvented or reduced wear problems,
they have not eliminated them, and there is no question that there
is a definite need for further improvements. This need becomes
evident when one considers the demands of high speed rotary
compaction presses designed to turn out 750, or even 1000 to 1500
parts per minute, high pressure impacts on the order of 50 tons
p.s.i., and particular working materials, such as tungsten powders
used in forming electrical contacts, ferrites used in forming
electronic computer memory cores, carbides used in forming studs
for insertion in pneumatic tires, ceramic materials included in
compacted filter elements and other materials.
Lubricants have been applied in various ways to combat tool wear.
For instance, in the compaction of ceramic powders to form pellets,
a lubricant is added to the feed material prior to compaction, and
during the pelletizing operation, some of the lubricant rubs off of
the feed material granules onto the compacting members of the
pelletizing apparatus, lubricating same. However, when the
resultant pellets are subjected to after-treatment in an oven to
further densify them, the decomposition or volatization of the
residual lubricant in the pellets can foul the oven, the product or
the atmosphere surrounding the oven.
Lubrication of the inside walls of the compacting chamber in a more
direct fashion has also been attempted. Many presses are fitted
with upper and lower punches, the latter being arranged to pass at
one point in their operating sequence through a supply of lubricant
so as to become coated with a film of the lubricant. The punches
then move, bearing the dragged-out film of lubricant, into contact
with the die and transfer a portion of the lubricant film thereto.
This method limits the effective height of the compaction chamber
and tends to deposit more lubricant in the lower portion of the die
than in the upper portion. Thus, if the lubricant is supplied in
sufficient quantity to properly lubricate the upper portion of the
die, there may be sufficient excess in the lower portion to unite
with the finer particles in the powder feed to form a thin deposit
which obstructs lubricant feed and/or blocks up the lower
punch.
Liquid lubricants and dry lubricants in volatile solvent have also
been applied to the walls of compaction dies by spray-guns which
are synchronized with the operating rhythm of the press. Nonuniform
application is also a problem with this system. The problem
increases in magnitude as the complexity and height of the
compacting chamber increases.
Thus, the need which exists may be more particularly defined as a
need for the discovery of a process for lubricating the compacting
members of a compacting press which is successful in retarding
wear, is effective in bringing the lubricant to the exact place
where it is needed without undue waste, spillage or misplacement,
and minimizes contamination of the compacted product.
BRIEF SUMMARY OF THE PRESENT INVENTION
Briefly stated, the present invention fulfills the aforementioned
need by providing a process of lubrication in which solid lubricant
and solid particulate working material are alternatively subjected
to compression in the same die of a compacting press.
More particularly, the invention is directed to the lubrication of
manual or automatic, single or multiple, rotary or nonrotary
compaction presses for use in the compaction of organic or
inorganic solid particulate working materials by successively
compressing solid lubricant material in the die of the press with a
compaction member (e.g., the punch) in the substantial absence of
the working material for causing a portion of the lubricant
material to adhere to the internal working surfaces of the die
while the remaining portion of the lubricant material, which is in
excess of that which will adhere to said internal working surfaces,
does not adhere to the die, ejecting the excess lubricant material
from the die, introducing abrasive solid particulate material into
the die, and compacting the abrasive solid particles in the die
with the adhered lubricant material in place on the internal
working surfaces of the die.
In the present specification and the appended claims, "solid," as
applied to lubricants, refers to lubricants which exist
substantially in the solid phase under the conditions of
temperature and pressure which prevail in the compaction press
during their introduction thereto and removal therefrom. If there
is a temporary liquification of the lubricant while the press is
closed, followed by a return to solid phase when it opens, the
process will still operate. However, many of the available solid
lubricants, including those which are preferred, appear to remain
in the solid phase throughout the press cycle.
The term "lubricant" is used herein in a special expanded sense. It
refers not only to materials whose sole function is lubrication but
to those which have additional functions. It refers to lubricants
consisting of a single material having lubricating properties as
well as to mixtures of materials, some of which may and others of
which may not have lubricating properties. Thus, the term
"lubricant" includes particles of a carrier material in (meaning
"in" or "on" or both) which is dispersed a solid or liquid material
having lubricating properties and which is available at the
surfaces of the carrier particles in an amount which is effective
to have a significant wear-reducing effect on the compacting press
in which the present invention is practiced.
Where the material having lubricating properties is dispersed in a
carrier mainly in the sense of being dispersed throughout the
bodies of the carrier particles, the particles must have sufficient
pores or other channels of communication between their interiors
and the surfaces thereof to make the material having lubricating
properties available at the surface thereof. Where the material
having lubricating properties is dispersed on a carrier mainly in
the sense of being distributed on the surfaces of the carrier
particles, the porosity of the carrier is not of critical
importance. However, the presence of porosity (including cellular
formations) in the carrier at the surfaces of the carrier particles
facilitates the preparation of the lubricant.
The weight of material having lubricating properties, based on the
weight of the carrier in which it is dispersed, will generally
range from about 0.1 percent to about 20 percent, but any minor
amount (less than 50 percent by weight) which is effective in
significantly reducing wear may be used, with about 1 percent to
about 10 percent being preferred. Where the dispersed material
having lubricating properties is a liquid, it will be necessary to
restrict the quantity thereof, relative to the carrier, to an
amount which will not deprive the lubricant of its substantially
solid character. The upper limit of liquid which can be tolerated
will vary with different liquids and carriers, but can be readily
determined by gradually adding liquid to the carrier with agitation
until periodically withdrawn samples of the wetted carrier begin to
show signs of localized excesses of liquid manifested as droplets
of the liquid filling the interstices between the carrier
particles.
The materials which impart lubricating properties to the lubricant
may be organic or inorganic or both. For instance, a fatty acid
soap is a desireable lubricant. Inorganic lubricants may also be
used; for instance, graphite may be dispersed on small carrier
beads (e.g. 1 mm.) of polystyrene. Liquid materials having
lubricating properties for dispersion in a carrier include for
instance synthetic and natural oils such as animal, marine,
vegetable and mineral oils which have been refined, if necessary,
to remove any deleterious materials contained therein. Also, it
will of course be understood that the carrier and any other
materials included in the lubricant will be free of abrasiveness
and other undesireable properties.
The size of the particles of solid lubricant may vary widely, and
the size to be used may be readily chosen by those skilled in the
art. Generally speaking, the smaller the particles, the better, as
this results in the best flowability and the highest degree of
contact between the lubricant particles and the walls of the
compacting chamber. Thus, the size of the particles should be a
small fraction (e.g. less than 10 percent) of the height, width or
depth of the compacting chamber.
The shape of the lubricant particles may also vary widely. Thus,
the particles may be spheres, powder particles, granules, spangles
or any other form. Spheres are preferred because of their readily
flowable character and the resultant convenience involved in
feeding them to the compacting chamber of the press. Less force is
required to convey the spheres if they are nonadherent in respect
to one another prior to compression, and thus in some cases the
force of gravity will be sufficient to move them from any suitable
dispensing mechanism into the compacting chamber or zone.
The lubricant particles are "yieldable." That is, when they are
compressed, they undergo a change in shape which brings them into
more complete contact with the walls of the compaction chamber,
while tending to conform generally to the shape of the chamber
while under compression. The change in shape may persist after the
compression ceases, as will be the case where the lubricant is a
solid fatty acid per se. The change of shape may also not persist,
as where the lubricant includes material having lubricating
properties, e.g. fatty acid, dispersed on elastomeric carrier
particles, which tend to return to their original shape after
compression is released.
The quantity of lubricant employed will usually be sufficient to
fill the compacting chamber or zone with the compacting member(s)
(e.g. punch) in retracted position and the lubricant in its
uncompressed form (the form which it has prior to compression).
There is no objection however to using smaller amounts, so long as
the amount is not reduced to the point where the effectiveness of
lubrication is impaired. A quantity of carrier particles having a
very high loading of material having lubricating properties may
under certain circumstances have the same lubricating effect as a
larger quantity of carrier with a lower loading of material having
lubricating properties. In any event, the quantity of lubricant
should be sufficiently large to contact all of those surfaces of
the compacting members which contact the material to be compacted
when the compacting members are in their fully extended (maximum
compression) position.
It should be evident that the invention is applicable to virtually
any solid material which is capable of being compacted in a press.
A number of examples of such materials have been given in the
foregoing discussion of the background of the invention and others
are set forth in the text and examples which follow. Those skilled
in the art will readily apply the invention to the compaction of
other particulate solid working materials.
By "alternately," as applied to the sequence of compressing the
solid particulate working material and the solid lubricant
particles, it is meant to include a mode of operation in which
lubricant and working material are compressed in turn, first
lubricant, then working material, then lubricant, then working
material and so on on a repetitive or continuous basis. However,
the term is also intended to include a mode of operation in which
several compressions of working material intervene between each
compression of lubricant and vice versa, although the latter mode
will not be likely to be used as often as the former.
The expression "in the substantial absence of the working material"
as applied herein to the compressing of the lubricant material,
means that the whole of the compacted working material from a
preceding compaction step, with the exception of any residue of the
working material which is normally left behind in the compaction
chamber, has been removed from the compaction chamber prior to
compression of the lubricant. Moreover, before the next charge of
working material enters the compaction zone, the excess lubricant
is removed from the zone. Thus, excepting for the presence of
normal residual amounts of the working material and the lubricant
which are left behind in the zone after each has been compressed
and ejected, the working material and lubricant are compressed
separately from one another. Thus, employed in respect to such
compression steps, the term "separately" is to be construed as not
excluding the presence of the aforementioned residual amounts.
The terms "compacting" and "compaction," as employed herein, are
intended to refer to operations in which particles of a solid
working material are subjected to mechanically applied pressure by
compacting members in compacting apparatus. The shape and the
degree of cohesiveness which are imparted to the resultant product
do not constitute limitations on the invention. However, it will be
apparent that the invention is useful in pelleting operations as
well as in operations for the formation of more complex shapes, and
that the superior performance of the invention will be particularly
evident in the lubrication of compaction dies which are deep and/or
have complex shapes.
The invention may be better appreciated upon consideration of a
preferred embodiment disclosed in the drawings and in the text
which follows.
BRIEF DESCRIPTION OF THE DRAWING
The drawing is a schematic view of the rotating table, die
openings, feeder mechanism, knock-off bars and ejection chutes of a
double-side rotary compaction press.
DESCRIPTION OF PREFERRED EMBODIMENTS
Although the invention is, as suggested above, applicable to
virtually any type of compacting press, it can be applied with
particular advantage to presses of the double-sided rotary type
depicted in the drawing. Such presses are well-known to those
engaged in the manufacture of shaped powder metallurgy parts (e.g.
carbide snow-tire studs). Such presses have a horizontally disposed
rotary table which has a plurality of vertical die openings through
the table disposed at angularly spaced intervals near its
periphery. In one type of such press which is manufactured by
Wilhelm Fette, Schwarzenbek-Hamburg, Germany, the table is caused
to rotate in registry with discs which are located on the same axis
as the table above and below it. These discs carry upper and lower
punches associated with each die opening, which are adapted to be
extended and retracted, as the table and discs rotate in
coordination, by the striking of stationary cam members fixed on
the frame which supports the rotating discs and table. During each
rotation of the table and discs, the end of each punch strikes four
different cams which cause it to extend and retract twice. The
extension and retraction of the upper and lower punches are phased
so that the lower punch extends and retracts while the upper punch
is retracted for ejection of a compacted product and refilling of
the compaction chamber or die with a fresh charge of powder. These
double-sided rotary presses have two product ejection stations
adjacent the two locations on opposite sides of the apparatus where
the upper punches retract and the lower punches extend for ejection
of the compacted shapes. A short distance further around the
apparatus in the direction of rotation of the table are two filling
or working material feeding locations, again on opposite sides of
the apparatus, where the upper and lower punches of each die both
assume a retracted position to receive the fresh powder. Still
further around the table, again in the direction of rotation, are
two compression stations on opposite sides of the apparatus at
which the upper punch is extended (and at which in some
circumstances the lower punch may be partially extended) for
compaction of the powder to form a shaped article.
In normal practice, both of the two sets of ejection, filling and
compression stations of double-sided rotary presses are processing
solid particles of working material into shaped compacts at the
same time. Any lubrication which is supplied is accomplished by one
of the above-described prior methods or by other methods which form
no part of the present invention. In an informative discussion of
double-sided rotary presses, entitled "High Volume Production of
P/M Parts," International Journal of Powder Metallurgy, 3(4) 1967,
pp. 33-43, hereby incorporated herein by reference, it is pointed
out that such presses may have as many as 27 punch and die sets
and, depending on the powder feed, can produce as many as 250-750
compacts per minute with compression capabilities of up to 100
tons. The development of presses capable of turning out 1000-1500
parts per minute has been predicted.
In accordance with the preferred embodiment of the present
invention, one side of a double-sided rotary press is fed
particulate solid lubricant, while the other is fed particulate
solid working material. In this way, each die and its corresponding
punches is alternately lubricated and used to form a compact. The
invention can be applied just as readily to presses having any
plurality (e.g. three or more) of sets of ejection, feeding and
compression stations, with the number of sets which are
appropriated for lubrication purposes being determined by the
severity of the lubrication requirements.
The schematic illustration of the application of the invention to
double-sided presses which is set forth in the drawings includes a
circular table which rotates in the direction indicated by the
arrow and has been divided (for purposes of illustration only) into
sections I and II. As shown, the dies in section I of the table are
passing beneath the outlet of a hopper 1 from which lubricant is
dispensed into the open dies. The dies then rotate counterclockwise
to a position, identified by reference numeral 2, where the
aforementioned cams (not shown) partially extend the punches for
precompression of the lubricant. The table and dies rotate further
in the same direction to compression station 3 for completion of
compression and then to ejection station 11 where the lower dies
previously mentioned (not shown) force the lubricant out of the die
so that it will be deflected by a fence 12 into an ejection chute
4. If desired, the lubricant material may be recycled manually or
by automatic recycle means 10, such as a conveyor, from deflection
chute 4 back to hopper 1.
While the dies in section I are being fed with and caused to
compress lubricant, those in section II are being fed with and used
to compress working material which issues from hopper 5 into a feed
frame 6 and from thence into the dies. The dies rotate to a
precompression station 7, compression station 8 and ejection
station 13, where they are urged by deflection fence 14 into
ejection chute 9. Section II of the table then passes beneath
hopper 1, picks up a charge of lubricant, compresses and ejects
same as it passes stations 2, 3 and 11 and then returns to hopper 5
for a fresh charge of working material. In normal operation the
table rotates continuously with each of the dies alternately and
separately receiving, compressing and ejecting lubricant and
working material.
The recycling of lubricant is especially advantageous where the
working material is radioactive and the disposal of contaminated
lubricant is a problem. For best results, recycling should be
conducted with a lubricant which includes a material having
lubricating properties dispersed in particles of elastomeric
spheres of carrier material which are not permanently deformed
during compression.
Among the polymers which may be included in the elastomeric
carriers are polystyrene (preferred on account of its
inexpensiveness), polyethers, polyurethanes, polysiloxanes,
polybutene, polypropylene, polybutadiene, and natural rubber. Any
synthetic or natural polymeric substance having plastic or elastic
properties may be used as a carrier in the practice of the
invention, but elastic carriers are preferred, especially where
there is to be recycling of lubricant. If it is desired to have
rougher carrier particles (which is helpful in holding the
lubricant), they may be of foamed resin or rubber. Their diameter
will generally be on the order of 1 millimeter, but diameters
within as well as above and below the range of about 0.1 to about 5
millimeters may also be used.
Where no elastic carrier is employed in the lubricant, it is still
possible to recycle lubricant. For instance, if solid granules of
unadulterated zinc behenate are employed as lubricant, the pellet
or other shaped mass of zinc behenate ejected from the press may be
converted again to small particles of a size suitable for feeding
to the press, so that they may then be recycled. Such conversion
may be accomplished in any known manner such as on a flaking belt
or with an extruder-chopper apparatus for forming small
pellets.
The preferred lubricant is zinc behenate on a carrier of
polystyrene, but virtually any solid organic or inorganic lubricant
can be used. There are of course the soaps of fatty acids,
including stearates, palmitates, laurates and arachinates of any
suitable metal, such as for example aluminum, zinc, magnesium, and
calcium. Also to be considered are the esters of fatty acids, such
as for example glycerol mono stearate. Other illustrative examples
of lubricants include paraffin wax, molybdenum disulfide, graphite
and so on.
Those skilled in the art will readily select suitable lubricants
and quantities of lubricant based on the efficiency of the
lubricant and various other considerations. For instance, such
factors as working materials of greater abrasiveness, higher punch
speeds and pressures, higher operating temperatures, large dies and
a high recycling factor will increase the amount of lubricant
required and/or correspondingly reduce the number of work
compression operations which may occur between lubrication steps.
Reversal of the foregoing factors will reverse the requirements for
quantity of lubricant and the number of work compression operations
which can be tolerated between lubrication steps. While the
invention has been illustrated with a double-sided rotary press, it
is apparent that the invention can also be used with more
conventional single or multiple punch reciprocating presses for
forming small or large parts, and in such presses there is the
possibility of performing several work-forming steps between each
lubrication step.
The present invention has the advantages of being very simple and
easy to carry out. It can utilize the normal movement of the
compaction members in the press to force the lubricant into contact
with the die and other parts of the compaction chamber both through
pressing and wiping actions, and can be used effectively no matter
how large or small or complex the compaction chamber may be. Excess
lubricant is effectively removed from the compaction chamber before
the next charge of working material, leaving behind a thin film of
lubricant which is effective in reducing the formation of
undesireable deposits of fines separated from the working material.
The thinness of the lubricant film left in the die also minimizes
interference of the compacted product. Further, the present
lubricating method is independent of the granulometry of the raw
material for the compaction operation. Other advantages of the
invention will occur to those of ordinary skill in the art.
By way of illustration and not limitation, the following examples
are presented:
EXAMPLE 1
Polystyrene balls having a diameter of 0.3 mm. are rolled in a
cylindrical container with finely divided zinc behenate until the
balls have picked up an average of 1-3 percent by weight of the
salt.
EXAMPLE 2
Example 1 is repeated, but is continued until a pick-up (average)
of 5-10 percent by weight is attained.
EXAMPLE 3
A double sided rotary compacting press of the type described above
is operated continuously. The product of example 1 is fed at one
feeding station and Uranium Oxide powder is fed at the other. The
powder and the operating characteristics and conditions of the
press are in all respects comparable to those conventionally used
in pelletizing Uranium Oxide, except for the feeding of the
lubricant. The lubricant is fed in sufficient quantity to fill each
of the dies into which it is produced. The extension and retraction
of the punches is the same during the working and lubricating
steps, which are conducted in alternation. The ejected flowable
spheres of elastic carrier bearing excess material having
lubricating properties are recycled and periodically replaced with
fresh lubricant when nearly exhausted. The nearly exhausted
particles are treated to recover residual uranium oxide. The
pellets recovered from the process exhibit excellent uniformity of
dimensions and have a very low order of organic contamination which
is confined to the surfaces and closely adjacent portions of the
pellets rather than being distributed throughout the bodies of the
pellets. The operation of the press is trouble-free.
EXAMPLE 4
The procedure of example 3 is repeated, substituting the product of
example 2 as the lubricant and Uranium Carbide powder as the
working material.
EXAMPLE 5
Ovoid natural rubber particles are coated with calcium stearate to
a loading level of 10 percent and found to possess satisfactory
lubricating properties.
EXAMPLE 6
The procedure of example 5 is repeated, substituting SBR for the
natural rubber. Similar results are obtained.
* * * * *