Note: Descriptions are shown in the official language in which they were submitted.
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DRY WIRE DRAWING LUBRICANTS
IR 3328B
Field of the Invention
The present invention relates to dust free, dry wire
drawing compounds, and processes for their manufacture,
particularly to dry wire drawing compound lubricants
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characterized as dry, free-flowing, non-powdery, non-
dusty, compositions and constructions having at least
one reproducibly controlled dimension which form viscous
lubricating films directly or after reduction in size.
S Backaround of the Invention
Wire drawing is a process employed to produce wire
from rod by pulling the rod and wire through one or more
dies in order to reduce the cross-sectional area until a
final product of the desired cross-section is achieved.
"Rod" is a term used to denote hat-rolled, undrawn
stock used in the wire drawing process. "Wire" is the
term used to denote the product of drawing, i.e., rod
which has been reduced in cross-sectional area.
Dies used in the wire drawing process must be of
sufficient hardne$s to withstand the pressure, heat, and
abrasiveness developed by the wire passing through the
die. Most wire drawing dies are constructed of_special
alloys such as tungsten-carbide or similar hard materials
or alternatively, the die surfaces, which may contact the
moving wire, are coated with thermally stable, abrasion
resistant coatings. Direct contact between the die
surface and the moving wire surface must be kept to a
minimum, or preferably prevented entirely, in order to
maintain the desired surface characteristics of the wire
and prevent excessive die wear and damage.
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Typical dies designed for wire drawing operations
consist of four zones which may be described as follows:
Zone 1, or the approach zone, consists of a circumferen-
tial angular opening encircling the moving wire which
allows the wixe drawing lubricant to enter the die. The
angle of the approach zone's interior surface, relative
to the moving rod or wire surface, is typically 6 degrees
to 25 degrees. The selection of approach zone angle
depends on the size and composition of the wire to be
drawn, draw speed, number of reductions required, and
lubricant formulation and physical form. The lubricant
must b~ in a form which allows it to enter the approach
zone along with the wire. Zone 2, or reduction zone, is
the location within the die in which plastic deformation
of the rod or wire occurs. It is in Zone 2 that
reduction of cross-sectional area is achieved during
drawing. Zone 2 is a continuaus extension of Zone 1,
encircling the moving wire. The angle of the interior
surface of Zone 2 relative to the moving wire determines
both the degree of cross-sectional reduction and is a
major factor in controlling the thic3eness of the wire
drawing lubricant film which remains on the wire surface
as it exits the die. This residual lubricant is
essential when a number of dies are used in a series to
effect muTti-step cross-sectional reductions. Zone 3 is
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referred to as the bearing zone. It serves principally
to assure fir_al shaping of the wire. Zone 4 is the
pressure relief zone. Pressure developed between the
wire and die surfaces can reach many thousands of pounds
per square inch during the dxawing operation. It is
necessary that this pressure be released at the die exit
in a manner which avoids damage to the die. Without a
pressure relief zone, cracking of the die can occur.
Dies may be used in combination with a single die
stand. These are referred to as pressure dies and are
designed to increase the pressure on the wire drawing
lubricant in order to force additional lubricant onto the
surface of the wire and thus increase the residual
lubricant film thickness.
As noted above, it is essential that the rod or wire
be prevented from coming in contact with the die surface
during wire drawing. This is accomplished by maintaining
a continuous film of lubricant between the die surface
and the surface of the moving wire. When dry wire
drawing lubricants are used, the rod or wire is pulled
continuously through a bed of dry wire drawing lubricant
contained in a "soap box" or "die box." fibs soap box has
an entry port and an exit port through which the wire
passes. The exit port of the soap box is camprised of a
first die located such that the die is~ below the surface
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level of the wire drawing compound contained in the soap
box. Periodic additions of wire drawing compound are
made to the soap box to assure that its first die is
always submerged in wire drawing compound.
When a series of dies are employed for multi-step
reductions, there may be additional soap boxes associated
with specific dies. The purpose of these additional
boxes is to supply additional surface lubricant coating
to the wire if needed.
The wire being pulled through the die system travels
at speeds of a few feet per minute, up to thousands of
feet per minute, depending on the die system, wire
composition, cross-sectional area reduction required,
cooling capacity, and lubrication available. At these
high speeds it is necessary that the undrawn rod surface
be roughened so that lubricant in sufficient quantity
will adhere to the surface and be carried into the die.
Roughening of the rod may be accomplished by applying
chemical comtings to the rod prior to its introduction
into the wire drawing system. The most common coating
compositions are based on lime, borax, or phosphates.
The resultant rough coating is commonly referred to as a
"lubricant carriers coating.
Mechanically descaled rod may be sufficiently rough
without further coating or, if necessary, may be
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roughened with additional mechanical treatment.
Lubricant applicators can be used to force lubricant onto
the rod surface by pressure.
The dry wire drawing compound lubricants must flow
freely in the soap box in order that fresh lubricant be
exposed to the moving wire. If the wire drawing compound
fails to move freely by gravitational force or mechanical
agitation in the soap box, it will compact into a dense
mass through which the moving wire will form a channel.
This is a condition known as ~~tunneling." Once tunneling
occurs, there is a loss of contact between the wire and
the dry lubricant and, as a result, the die system is
starved for lubricant and damage to the wire and die
surface will occur.
As the dry wire drawing compound lubricant enters
the die at the approach zone, it is converted by heat
and/or pressure into a film of plastic-like consistency.
If converted to a liquid, it would offer little, if any,
protection against the wire moving laterally through it
and contacting the die surface. Further, the majority of
a liquid lubricant applied to the wire in this type of
drawing system would be lost immediately upon exiting the
die and would not be available as residual lubricant for
protection of other dies in a multi-die system.
The composition of the dry wire drawing compound
lubricants has been discussed widely in the patent and
technical literature, some examples of which are set
forth hereinafter in the detailed description. In a
broad sense, dry wire drawing compounds are typically
based on a combination of fatty acid soaps, excess base
or free fatty acid, and, as required for specific
applications, various thickeners, pressure additives,
pigments, fillers, and thermal stabilizers. The most
commonly used dry wire drawing compound lubricants are
based on calcium soaps or sodium soaps. A manufacturer
of dry wire drawing compound lubricants typically offers
several hundred different formulations, each designed to
satisfy the technical requirements of specific wire
drawing applications.
Historically, dry wire drawing compound lubricants
have been produced as fine powders in order to meet the
stringent requirements of th8 wire drawing proce$s.
However, these powdered materials are very dusty, lending
to worker irritation and unclean work areas.
Various approaches have been tried to alleviate the
dust problems associated with dry wire drawing compound
lubricants. These include tableting,~extruding, flaking,
beading, and wetting. None, however, have been totally
successful.
Wetting of the compound with a liquid to suppress
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dustiness introduces a non-active diluent which
frequently has a deleterious effect on one or more
essential properties of the lubricant, such as lowering
of the melt point or reduction in free flowability.
"Beading"~ is a process of manufacturing dry wire
drawing compound lubricants disclosed in Canadian Patent
1,006,497. Although this patent discloses a composition
which is "essentially dust-free," it states that "the
presence of fines in minor amounts ... can be tolerated
without loss of operating efficiency." In practice,
these beaded compositions are less than completely dust
free as would be expected from the presence of fine
particles. Removal of the fines by screening or washing
would add costly manufacturing steps. Further, the beads
formed by rolling are not uniform in dimension in any
direction, resulting in separation during shipment and
use.
Flaking of dry wire drawing compound lubricants by
casting a molten mass of the lubricant onto a chill roll
is essentially ineffective. Th~ resultant flakes are too
large, typically one-half inch in diameter X12 mm), to
perform effectively in wire drawing systems. Grinding of
the flakes to produce smaller particle size invariably
leads to production of a fine powder fraction and dust.
Tableting is an expensive process and, again, the
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particle size, typically one-quarter inch in diameter
(6 mm) or greater, is unsatisfactory.
Extruding of dry wire drawing compounds on
conventional screw eXtruders, operated in a conventional
manner, such as are used in making palletized plastics or
plastic additives has been tried in the dry wire compound
lubricant industry without success. While the pellets
produced ware dust free, the work energy required to form
them hardened the pellets so that they would not melt or
reduce to useful size in the wire drawing process.
It is completely surprising that the process of the
instant invention solves all of the problems of previous
attempts at making effective, dust free, dry wire drawing
compound lubricants, especially since no permanent
additional additives such as water-soluble binders which
could interfere with or change the lubrication properties
of.the dry wire drawing compound lubricants are_required.
Sll_mn!ary Of the Inypll't' i nn
This invention pertains to a method for the
manufacture of dust-free, dry wire drawing compound
lubricants and metal soap compositions having at least
one reproducibly controlled dimension which possess all
of the beneficial properties of powdered lubricants and
none of the undesirable properties of powders, such as
dust generation. The process comprises the steps of
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conglutinating and shaping the dry wire drawing compound
composition under controlled pressure. The
conglutinating and shaping steps may be performed
sequentially or simultaneously.
Materials used as raw materials in the process are
dry wire drawing compounds, usually in powder form,
comprising metal soaps, unreacted basic compounds, free
fatty acids, and, as required for specific applications,
minor amounts of various adjuvants such as fillers.,
pigments, dyes, extreme pressure additives, stabilizers,
thickeners, waxes and polymers, esters, ethoxylates and
metal wetting agents.
A wide range of temperature can be employed in the
pressure forming step, with the restriction that it is
below the melt point of the metal soap component of the
dry wir~ drawing composition. At least one dimension of
the shaped article formed by the pressure forming step is
reproducibly uniform.
A wide range of forming pressure energy may be
employed with the proviso that it be no greater than the
energy later required to reduce the product of the
process to smaller particles during use by pulverizing,
softening, or melting.
The most preferred application for the novel
products of the invention is in wire drawing through
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stationary or roller dies. As used herein terms such as
"dust free" or "non dusting" refer to the shaped wire
drawing compound constructions which are essentially free
of dustable particulates as formed. Minor amounts of
dustable particulates may be generated during cutting
operations to form the construction to the desired
length(s), but these may be readily removed, typically
by exposing the canstruction to a vacuum during the
cutting operation.
Detailed pescr~pt~on of the Invention
A method has now been discovered for the production
of conglutinated and shaped dust-free dry wire drawing
lubricant compounds, the shaped lubricant compound
products thus obtained having at least one reproducibly
controlled dimension. The method may be carried out
using a variety of equipment such as screw extruders,
roller extrusion presses, or roller presses. The
grinding action which occurs in pellet production on
pellet presses, whether on stationary dies with rotating
roller pressure or rotating dies with stationary roller
pressure, effectively reduces agglomerates resulting in
a more uniform wire drawing compound product which in
turn results in more uniform coating on the wire.
The dry wire drawing lubricant compounds useful in
CA 02096884 2000-06-27
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this invention have been widely described in the
literature such as the following. One such publication,
an article by Richard Platt titled "Choosing a Powdered
Lubricant fo:- Ferrous Wire Drawing" in Wire Technology,
May 1989, discusses the general composition of dry wire
drawing lubr:Lcant .and provides a table of properties
relating the composition to residual film thickness.
Another arti<:le titled "Lubrication of Ferrous Wire" in
Ferrous Wire, Volume 1, "The Manufacture of Ferrous
Wire," published by the Wire Association International,
Inc., discusses various types of lubricants, their proper
selection, a:nd some of the terminology - thus, the
industry accepted terms descriptive of the lubricants
which leave a thick residual film on the wire is "lean,"
while those leaving a thin film are referred to as
"rich." The"rich" lubricants are higher in fatty acid
content than the "'lean" lubricants. A further
classification diEOCUSSed by Platt divides the dry wire
drawing compounds into soluble sodium soap compounds and
insoluble calcium soap compounds. A "lean" soap
formulation typically contains 30% fatty acid while a
"rich" soap formulation typically contains 70% fatty
acid. Both of th~ase articles disclose that other
additives me~y be present to help maintain viscosity
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during the drawing process, to act as extreme pressure
lubricants, to provide anti-corrosion characteristics,
and to add color. U.S. Patent No. 2,956,017 (Franks)
discloses calcium soap compositions useful fn dry wire
drawing compoynds. Franks further notes that combination
of the calcium soaps with diamide waxes is beneficial.
U.S. Patent Na. 4,404,828 (Blatchford) discusses the wire
drawing process utilizing dry wire drawing lubricant
powders, the classification and composition of dry wire
drawing powdered lubricants, the dust problem associated
with powdered lubricants, and so on.
The dry wire drawing lubricant compounds useful with
the present invention are those which are based on metal
soaps, particularly calcium soaps and sodium soaps as
described in the aforementioned references. The process
described herein is also beneficial in the reprocessing
of "spent" wire drawing compounds - that is, those
materials which have been rejected by the die system or
have passed through the die or dies and have become
separated from the wire. They may be unchanged in
chemical composition or modified by heat exposure, metal
pick up or other forms of contamination. Such materials
are frequently in the form of scales or flakes, string
like materials or powder. These spent materials may be
recovered by vacuum systems, for example, and reprocessed
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alone or blended with virgin wire drawing compound to
produce satisfactory shaped constructions of dry wire
drawing compounds, frequently without intermediate
purification steps.
The method of the invention comprises the steps of
(A) conglutinating the dry wire drawing lubricant
composition and (B) shaping the conglutinated product
under controlled pressure to provide a dust-free shaped
lubricant product having at least one reproducibly
controlled dimension, pulverizable by the wire drawing
process. Steps A and B can be carried out sequentially
or simultaneouly.
"Conglutination" is a term used to describe the
process of sticking together a mass of individual
particles as though glued together. The conglutinating
"agent" is a combination of heat and pressure, with or
without water being present. If water is present, it may
be water remaining in the metal soap composition
generated during the reaction of the metal hydroxide with
the fatty acid or it may be added to the process, far
example, at the pressure forming step. If water is
present it will normally be present in the range of from
about 0.5 to about 10.0 weight percent of the finished
product weight. The maximum water present in any given
comgosition of wire drawing compound is dependent on the
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end use of the wire drawing compound and varies with the
wire composition, process configuration, and wire speed.
Elevated temperatures may be employed to facilitate
conglutination and pressure forming to the desired shape
and physical strength of the finished product. Elevated
temperatures used in the process will be below the melt
point of the metal soap used in the dry wire drawing
lubricant. Preferred temperatures range from about 50 to
about 120 degrees,Centigrade, most preferably 70-90.
These elevated temperatures refer to the temperature of
the dry wire drawing compound composition as it enters
the forming equipment or gresent in the forming
equipment. The elevated temperatures of the lubricant
composition may be residual heat from the soap forming
step or may be added by exposing the composition to
elevated tempermtures or by supplying heat to those
portions o~ the forming equipment which contact the dry
wire drawing compound during forming. Where the pressure
Forming equipment comprises a portion of a continuous
pxocess, the residual heat of the soap production is used
beneficially. Pellets exiting the die plate may be
advantageously cooled by passing air across them to lower
their temperature and minimize sticking to each other or
to surfaces of the process equipment. These exiting
pellets may also be subjected to a vacuum, at or close to
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the cutter bar which cuts the pellets to the desired
length, in order to reduce or eliminate fine particles
which may be generated during the cutting or breaking
action.
The pressure to be applied to the conglutinated or
conglutinating product to form the shaped, dust-free dry
wire drawing compound covers a wide range and is
determined by the metal soap composition of the dry wire
drawing compound, the strength required for the shaped
articles to withstand the rigors of shipping and handling
and still be useful in wire drawing, and the process
forming equipment being used. It is also influenced by
the temperature being employed and by the presence or
absence of water. It is the physical strength required
of the final shaped product which determines how much
pressure is to be used. For example, pellets (or other
constructions) of dry wire drawing compound produced by
th~ process of this invention should be strong enough to
reaiat breakage ar deterioration to powder during
shipping and handling (generally able to withstand
pressures of at least about 10 pounds per square inch)
but pulverize readily when in cantact with the moving
wire (generally satisfactory if pulverizable at a
pressure below about 300 pounds per square inch). It is
essential that such pellets be reduced in size rapidly
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during the wire drawing operation in order that they can
enter the approach zone of the die where softening and
melting to a plastic film begins. Some pellets,
particularly those below 1 mm diameter, can enter the
approach zone or go directly into the melt without
pulverizing.
While the action of the wire moving through the
pellets in the soap box is the primary force which
pulverizes the pellets, it may be desirable at initial
startup of a wire drawing line to add a small amount of
pulverized wire drawing compound to the soap box to
insure complete coating of the wire prior to the
pulverization process reaching equilibrium. Another
means of accomplishing this is to use lubricant
applicators which are well known in the art for breaking
up lubricants and forcing the powder onto the wire.
A particular advantage of the shaped constructions
of Wire drawing compounds described herein is that they
form a "blanket" over pulverized material in the soap
box. The larger shaped constructions rise to the top of
the soap box while the pulverized materials remain at the
bottom of the soap box surrounding the wire. This
blanketing action suppresses the release of finely
pulverized wire drawing compound to the atmosphere. A
23 further advantage of these shaped constructions is that
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the coatings deposited on the wire are more uniform than
those produced using conventional powdered wire drawing
compounds, possibly due to segregation of powdered
material into non-homogeneous layers during shipping and
handling; the.uniformly coated wire in turn is easier to
process in post drawing operations.
The shaped dust-free wire drawing lubricants
produced by the inventive process may be produced in a
wide variety of shapes, such as cubes, balls, cylinders,
pellets, or flakes. It is, however, essential that at
least one dimension be reproducibly controlled and not be
so large as to be unusable in the wire drawing operation.
In general, large diameter wire can be processed with
large or small constructions of shaped wire drawing
lubricants produced by the inventive process, while small
diameter wire will normally require smaller constructions
of wire drawing compounds. A typical size for products
of this invention which can be used successfully in wire
drawing is one having a diameter or thickness of from
about 0.5 to about 10 mm. All other dimensions will be
approximately 5-7 times the controlled dimension, or
legs.
The indication that the lubricant constructions have
,.
at least one reproducibly controlled dimensions includes
the use of a blend of two or more sets of pellets, each
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set of pellets varying in the size of the reproducibly
controlled dimension(s).
A preferred shape of the product is a cylindrical
pellet having a diameter of 2 mm and a length of no
greater than 10 mm. Two most preferred embodiments are
pellets having a diameter of 1.6 mm and a length of
approximately 10 mm and pellets having a diameter of
1 mm and a length of approximately 5 mm.
Some representative examples follow:
Examples A-D:
Representative dry wire drawing lubricants ware
prepared in a stirred reactor to a final temperature of
90 degrees centigrade and formed into dust-free pellets
on a roller extrusion press. The compositions are shown
in the following Table I.
The caller extrusion press used in the experiment
comprised a flat die plate having a plurality of Z mm
diameters perforations 3 mm in length. A series of two
rollers moved transversely across the top openings of
each of the perforations every 2 to 3 seconds. The
rollers were suspended approximately 0.75 mm above the
top surface of the die plates. The lubricant
compositions of examples A through D were fed
continuously into the space between the roller surface
and the die plate. The lubricant composition was
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converted from essentially powder to continuous extruded
strands through each die plate perforation. A breaker
blade, rotating below the die plate and adjusted for
distance from the die plate and speed of rotation
controlled the length of each generated pellet. Thus,
the extruded strands, 1 mm in diameter, were cut or
chopped to a controlled length of approximately 7 mm
average.
The water reported in Table I is used in the
formulation to convert the metal oxides to metal
hydroxides which in turn react with the fatty acids to
form soaps. The additives are conventional fillers,
thickeners, anti-corrosives, and the like.
TABLE I
DRY WIRE DRAWING SOAP COMPOSITION
Soluble Sodium Insoluble Calcium
soaps (weig] t ~1 : Sops ,~~weiaht ~
Rich Lean Rich Lean
Example A B C D
Fatty Acid 72 49 58 32
Metal Oxide 9 5.5 30 50
Additives 13 39.5 2 3
Water 6 6 10 15
It was found that the pelletized dust-free
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pulverizable dry wire drawing compounds of examples A
through D could be pulverized back to powder by applying
a force of approximately 20 pounds per square inch (psi).
The pellets of examples A through D were sufficiently
cohesive to resist breakage during packaging and
shipping.
Evaluation of the pellets of examples A and C were
carried out on production size wire drawing equipment.
The results are shown in Table II. The "Controls" were
the same lubricant compositions but in unpelletized form.
With the insoluble calcium soap (example C), an
additional 10 weight percent water was added at the
pressure farming stage to produce pellets containing
approximately 5 weight percent unreacted water after
partial drying.
TABLE I I
Example A: E~, 12 a C:
Type of Die Stationary Roller
~ of Reductions ons ___
Wire Speed 350 feet/min. >1500 feet/min.
Lubrication Quality equal to Control equal to Control
Dust Generation:
fox Pellets none none
for Control copious copious
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Examples E-F°
A test was run to determine applicability of the
process to reprocessing of "spent" material. Following
some wire drawing operations, spent lubricant (a rich,
soluble, sodium soap) was collected from the floor under
the wire drawing machine and from the soap box, care
being taken to exclude metal particles and non-soap
products. The spent material was dusty and had an
analysis similar to that of Example A above, except
that the fatty acid content was about 77%, the metal
oxides about 15%, the additives about 8%, and the water
leas than 1%. This material was repelletized on a lmm
die, some as is (Example E) and some (Example F) mixed
with virgin material (75% spentj25% virgin), the virgin
material being about 79-81% fatty acid, about 10-13%
metal oxide, about 4-6% additives, and less than 2%
water. Pellets made from both materials showed positive
lubrication results in a one hour evaluation.
Example G:
A aeries of evaluations were made to determine the
strength of pellets produced according to this invention,
"strength" referring to resistance to pulverization to
powder where exposed to pressure between opposing platens
in a machine (an Instron 4204 Tester) designed to
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evaluate physical properties of dry materials. The tests
were run on pellets made from various rich and lean,
sodium and calcium based, compositions, with diameters
varying from 0.8 to 6.2 mm and lengths varying from 3.4
to 13.3 mm. The results in all cases showed that the
pellets were resistant to pulverization at pressures
below about 17 psi and were readily pulverized at
pressures between about 17 psi and about 292 psi.
