Process and apparatus for treating the surface of an elongated, steel alloy form to facilitate cold working thereof

A process for cold working an elongated form of a steel alloy includes the step of forming a matte texture on substantially all of the surface of the elongated form. The matte texture is characterized by a plurality of random, minute, shallow indentations, uniformly distributed on the elongated form's surface. The process provides an elongated form of steel alloy that has a significantly improved capability to carry lubricant into a cold working tool or die, thereby benefiting the cold workability of the elongated form. An apparatus for carrying out the process according to the invention, in line with one or more other processing operations is also disclosed.

BACKGROUND OF THE INVENTION 
This invention relates to processes for cold working an elongated form of a 
steel alloy, and in particular to a process and apparatus for treating the 
surface of such an article to facilitate cold working thereof. 
An elongated form of a steel alloy, such as wire, rod, or bar, can be cold 
worked to provide useful product sizes and shapes. Here and throughout 
this application, the term "cold working" means the plastic deformation of 
metal under conditions of temperature and strain rate that result in 
strain hardening of the metal and which is typically, but not necessarily 
conducted at room temperature. Cold working of an elongated form includes 
such operations as drawing, extruding, cold heading, or a combination 
thereof. Prior to being cold worked, an elongated form of steel alloy is 
treated to remove surface conditions such as oxide scale or residue that 
result from upstream processing, e.g., hot or cold rolling. As a result of 
such pre-cold-work processing, a smooth surface is formed on the 
elongated, steel alloy form. 
One of the known processes for providing a smooth surface on the elongated 
steel form is the removal of a thin peripheral layer of material by 
shaving, peeling, or broaching the elongated, steel alloy form. Here and 
throughout this application, the term "shaving" includes any operation 
that is also commonly referred to as "scalping". The shaving, peeling, or 
broaching process exposes a new surface on the steel alloy form that is 
very smooth and reflective. Steel wire that has been previously 
cold-worked can be bright strand annealed prior to further cold working. 
Such processing also leaves a very smooth and highly reflective surface on 
the wire. 
An elongated steel alloy form having a smooth, reflective surface is 
difficult to cold work because such a surface is not conducive to carrying 
lubricant into the cold working tool or die. Consequently, the elongated 
form of steel alloy is subject to scratching or galling and the cold 
working tool or die is subject to damage. 
Some machines that perform surface layer removal leave superficial, machine 
tool marks on the surface of the elongated form. These tool marks act as 
high pressure points that also adversely affect the drawability or 
extrudability of the steel alloy form. Tool marks that are left on the 
surface of the elongated form can remain visible after cold working and 
present an unsightly appearance. 
After the surface layer removal process, steel alloy bar, wire, or rod has 
been treated by acid etching, annealing, and then acid cleaning, or by 
annealing, shot blasting, and then acid dipping, to provide a dull, etched 
surface that is more conducive to retaining lubricant during a subsequent 
cold working operation. However, the use of acids to provide surface 
etching and scale removal leaves much to be desired for a number of 
reasons. Acids are highly corrosive and are difficult to dispose of in an 
environmentally safe manner. Acid cleaning is not readily adaptable to 
in-line or strand processing. Furthermore, many steel alloys are subject 
to intergranular attack when the surface is acid cleaned. 
The use of shot blasting with metallic shot to treat the surface of an 
elongated steel alloy form also leaves much to be desired. Shot blasting 
work hardens the surface of such forms which adversely affects their 
cold-workability. Also, shot blasting leaves a metallic residue on the 
surface which can cause corrosion unless it is removed by acid cleaning. 
The drawability and extrudability of an elongated steel alloy form are 
adversely affected when the surface is excessively cratered and torn by 
the shot blasting process. Furthermore, the surface indentations provided 
by shot blasting are relatively sharp, jagged voids that can easily trap 
lubricant, precoat, or coolant used during the cold working process. 
During elevated temperature thermal treatment of the elongated form after 
cold working, localized corrosive attack can occur in the indentations, 
thereby resulting in undesirable surface pitting. 
Apparatus for shot blasting is relatively massive and is not conducive to 
in-line or single strand processing. Also, a significant amount of energy 
is required to operate a shot blasting apparatus because shot blasting is 
an airless process that uses a large centrifugal wheel to propel the metal 
shot. 
Another known method of enhancing the cold-workability of an elongated 
steel alloy form is to coat it with a thin layer of a more malleable 
material such as copper. Although copper coating can significantly enhance 
the cold-workability of many steel alloys, the coating must ultimately be 
removed from the cold-worked product. The removal of the copper coating is 
costly and poses significant problems in connection with environmental 
safety because it requires the use of highly corrosive chemicals. 
Air-driven abrasive media such as sand, aluminum oxide, or glass beads have 
been used for treating the surface of a metal article to remove oxide 
scale, paint, or dry surface residues and to condition the metal surface 
for good adhesion of a paint or coating. In particular, air-driven glass 
beads have been used for peening metal surfaces to provide a beneficial 
compressive stress in the peened surface layer. Air-driven glass beads 
have also been used to provide a dull or matte finish on steel alloy strip 
that was flat-rolled from round wire. 
SUMMARY OF THE INVENTION 
The problems associated with the known processes for cold working an 
elongated steel alloy form, such as wire, rod, or bar, are solved to a 
large degree in accordance with one aspect of this invention, whereby 
there is provided a novel process for cold working an elongated form of a 
steel alloy which has a smooth, reflective surface. The cold working 
process includes the steps of forming a matte texture on substantially all 
of the surface of the elongated form, applying a lubricant to the 
elongated form such that the lubricant contacts the matte textured 
surface, and then cold working the elongated form. The matte texture is 
characterized by a plurality of random, minute, shallow indentations, 
formed over substantially all of the surface of the elongated steel form. 
The matte texture significantly increases the lubricant retention 
capability of the surface of the elongated form, thereby facilitating cold 
working of the elongated form. 
In accordance with another aspect of this invention there is provided a 
process for treating an elongated form of a steel alloy, such as wire, 
rod, or bar, to facilitate cold working of the elongated form. The process 
according to this aspect of the present invention includes forming a 
smooth, reflective surface on the elongated form of steel alloy, and then 
forming the above-described matte texture on substantially all of the 
surface of the elongated form. 
In accordance with a further aspect of this invention there is provided an 
apparatus for treating the surface of an elongated form of a steel alloy 
to facilitate cold working thereof. The apparatus includes means for 
forming a smooth, reflective surface on the elongated form, surface 
texturing means for forming a matte texture comprising a plurality of 
random, minute indentations on substantially all of the surface of the 
elongated form, and means for pulling the elongated, steel alloy article 
longitudinally through said smooth, reflective surface forming means and 
said surface texturing means.

DETAILED DESCRIPTION 
In the method according to the present invention a smooth, reflective 
finish is formed on the surface of an intermediate size of an elongated, 
steel alloy form, such as wire, rod, or bar. Among the known operations 
for providing such a surface are shaving, peeling, broaching, or back-die 
shaving. In such an operation a thin, peripheral layer of material is 
removed from the surface of the elongated form of steel alloy. Another 
technique that provides a suitable surface is bright annealing of wire or 
rod that has been cold drawn. Bright strand annealing is a preferred 
bright annealing technique because it is readily adaptable to in-line 
processing. 
After the smooth surface is formed on the elongated steel alloy form, a 
matte texture is formed on substantially all of the surface of the 
elongated steel alloy form so as to provide uniform coverage thereon. The 
matte texture is characterized by a plurality of random, minute, shallow 
indentations, uniformly covering the surface of the elongated form. The 
randomness of the indentations is important because directional 
indentations, such as longitudinal lines or circumferential spirals, are 
significantly less effective for carrying lubricant into and through a 
cold working tool. The coarseness of the matte texture also is important 
because if the matte texture is too fine or too coarse, lubricant will not 
properly adhere to the surface of the elongated form. Preferably the 
roughness of the matte textured surface is about 30 to 50 microinches Ra. 
The step of providing the matte texture is preferably performed in-line 
with one or more of the surface smoothing processes, such as back-die 
shaving or bright strand annealing. Such in-line processing provides a 
very efficient mode of surface treating an elongated form that is to be 
subsequently cold-worked. 
In carrying out the surface texturing step of the present invention, 
minute, nonmetallic, nonporous, spheroidal particles are propelled at high 
velocity onto the surface of the elongated, steel form. The spheroidal 
particles impinge on the surface of the elongated, steel form to produce 
the random, minute, shallow indentations that are characteristic of the 
desired matte texture. Here and throughout this application the term 
"spheroidal" means a shape that is regularly or irregularly rounded and 
does not include sharp angles. The term "spheroidal" encompasses, but is 
not limited to, round spheroids, oblate or prolate spheroids, ellipsoids, 
tear-drop shapes, and pear shapes, as well as combinations thereof. The 
particles are preferably embodied as glass beads about 100-170 mesh in 
size. 
The spheroidal particles are carried toward the surface of the elongated, 
steel form in a stream of fluid such as compressed air that is supplied 
from a high pressure source. Thus, the density of the spheroidal particles 
must be low enough to permit their being readily carried by a pressurized 
fluid, preferably by compressed air. The fluid stream is preferably 
supplied at about 60-100 psi in order to impart the desired high velocity 
to the spheroidal particles. In carrying out the process according to the 
present invention, the velocity of the spheroidal particles is controlled 
to provide the desired surface roughness without measurable peening or 
work-hardening of the surface of the elongated form. Work hardening of the 
surface of an elongated, steel alloy form adversely affects the cold 
workability of the elongated form. The particle velocity can be controlled 
by adjusting the pressure at which the carrier fluid is supplied. To 
obtain substantially full and uniform coverage of the elongated, steel 
form surface, it is preferred that a plurality of streams of the minute, 
nonmetallic, nonporous particles be used. As will be described in 
connection with a preferred apparatus according to this invention, the 
particle streams are arranged around the elongated form and each of the 
streams is angularly displaced from an adjacent stream around the 
elongated form and directed generally radially toward the elongated form. 
After the matte texture is formed on the surface of the elongated form, and 
prior to further processing, a lubricant is applied to the elongated form. 
The lubricant is applied in any known manner so as to contact the matte 
surface of the elongated form, to which the lubricant readily adheres. 
Although any known lubricant that is suitable for cold working operations 
can be used, it is preferred that the lubricant be compatible with the 
particular cold drawing, cold extrusion, or cold heading process to be 
performed on the elongated, steel alloy form. 
The lubricated form is then cold worked as by cold rolling, cold drawing, 
or cold extruding to reduce its cross-sectional area without removing 
material therefrom. Instead of, or in addition to, such cold reduction, 
the lubricated form can be cold headed. It will be readily appreciated, 
however, that the matte-textured, elongated form need not be cold worked 
immediately after the surface-texturing step. Rather, it can be sold as a 
finished or semifinished product form. 
Referring now to FIG. 1 there is shown a schematic representation of an 
apparatus for carrying out the method according to the present invention. 
The apparatus includes a surface treating line 110 and a wire drawing line 
140. In the surface treating line 110 a pay-off stand 112 supports a coil 
114 of steel alloy wire 116. The surface treating line 110 includes an 
optional roller die 118, a surface layer removal tool 120, an air wipe 
122, a surface texturing apparatus 124, a lubricant applicator 132, and a 
capstan 134. The Wire 116, before reaching the surface treating line 110, 
will have been processed as by hot or cold rolling to an intermediate size 
or diameter. The wire 116 is pulled by capstan 134, longitudinally through 
the optional roller die 118 and through the surface layer removal tool 
120. If desired, a straightening die or a drawing die can be used in place 
of roller die 118. The surface layer removal tool 120 is a tool or machine 
that is designed to remove a thin surface layer of the wire 116. Depending 
on the nature of the elongated form, i.e., wire, rod, or bar, the surface 
layer removal tool 120 can be embodied as a broaching tool, a shaving 
tool, a peeling machine, or a back-die shaving tool. In the embodiment 
shown in FIG. 1, the surface layer removing tool is embodied as a back-die 
shaving tool. The surface layer removal tool 120 removes a thin peripheral 
layer of material from the surface of the wire 116, thereby exposing a new 
surface on the wire which is very smooth and reflective. 
For some types of surface layer removal techniques, a coolant is applied to 
the wire 116 in order to control thermally induced stresses therein during 
the surface layer removal operation. The air wipe 122 removes any residual 
coolant from the wire 116 to provide a surface that is dry. The air wipe 
122 can also be embodied as a vacuum device for removing the coolant from 
the wire surface. 
After the air wipe 122, wire 116 passes through the surface texturing 
apparatus 124. The surface texturing apparatus 124 includes an enclosure 
125, a reservoir 126 which holds the minute non-metallic, non-porous 
spheroidal particles, and a plurality of spray or blast nozzles 128. The 
surface texturing device 124 also includes means for mixing the particles 
from reservoir 126 with compressed air, preferably in the blast nozzles 
128. The particles are propelled through the blast nozzles 128 by the 
compressed air, so as to impinge on the surface of the wire 116 as it 
passes through the enclosure 125. The blast nozzles 128 are arranged 
around the pass line of wire 116 through enclosure 125 such that the 
surface of the wire is fully and uniformly contacted by the particles. 
As shown in FIG. 2, the blast nozzles 128 are preferably arrayed in a 
helical pattern about the pass line of wire 116 to provide a plurality of 
particle streams. The preferred arrangement, shown in FIG. 2A, includes 
twelve nozzles each spaced a preselected radial distance from the pass 
line of wire 116 and each angularly displaced from an adjacent nozzle. The 
inside diameter of the orifice 129 of a blast nozzle 128 and the radial 
distance of the blast nozzle 128 from the wire 116 are selected such that, 
for a given air pressure, the velocity of the spheroidal particles at the 
surface of the wire 116 results in sufficient surface indentation to 
provide the desired surface roughness without any measurable peening or 
work-hardening of the wire surface. The surface texturing apparatus 124 
can also include an air wipe 130 to remove dust or other residue on the 
wire 116 that results from the surface texturing process. Preferably, the 
surface texturing apparatus 124 and the surface layer removal tool 120 are 
aligned on a common axis, such that the pass line of the wire 116 through 
the surface layer removal tool 120 and the surface texturing apparatus 124 
coincides with the common axis. 
Upon exiting the surface texturing apparatus 124, the wire 116 passes 
through a lubricant applicator 132 and is coiled onto a capstan 134. The 
capstan 134 is powered and rotates to pull the wire 116 through the 
various devices on the surface treating line 110. It is readily apparent 
that wire 116 is subject to significant tension as it is pulled through 
the surface treating line 110. That tension is desirable to the extent 
that it helps keep the wire 116 on or very close to the common axis of the 
surface layer removal tool 120 and the surface texturing apparatus 124, 
and hence equidistant from the array of blast nozzles 128. Of course, the 
tension on wire 116 must be controlled so as not to exceed the tensile 
yield strength of the wire. 
After the wire 116 has passed through the surface treating line 110 and is 
coiled on the capstan 134, it is transported to the cold working line 140 
which includes a lubricant applicator 144, a cold working tool 145, and a 
powered capstan 148 which pulls the wire 116 through the cold Working tool 
146. A pay-off stand 141 supports the coil of the surface treated wire 
116. The wire 116 passes through the lubricant applicator 144, through the 
cold working tool 146, wherein its cross-sectional area is reduced, and is 
taken up and coiled on the capstan 148 in a known manner. The cold working 
line 140 shown in FIG. 1 is configured as a cold drawing line, cold 
working tool 146 being embodied as a cold drawing die. 
Shown in FIG. 3 is a schematic representation of another embodiment of the 
apparatus for carrying out the method according to the present invention. 
The apparatus shown in FIG. 3 is a single processing line 310 including an 
optional roller die 318, a surface layer removal tool 320, an air wipe 
322, surface texturing apparatus 324, lubricant applicator 332, a first 
capstan 334, a second lubricant applicator 344, a cold working tool 346, 
and a second capstan 348. Capstan 33 is powered and rotates to pull the 
wire 316 through the surface layer removal tool 320, the surface texturing 
apparatus 324, and the optional cold working tool 334. The second capstan 
348 is also powered and rotates to pull wire 316 through the cold working 
tool 346. 
In the single processing line 310 a pay-off stand 312 supports a coil 314 
of steel alloy wire 316 which has been previously processed as by hot or 
cold rolling to an intermediate size or diameter. The wire 316 passes 
longitudinally through the optional roller die 318 and through the surface 
layer removal tool 320. The wire 316 then passes through the air wipe 322 
which removes residual coolant from the wire surface. Upon exiting the air 
wipe 322, wire 316 enters the surface texturing apparatus 324 which is 
similar to that shown in FIG. 1 and described above. Upon exiting the 
surface texturing apparatus 324, the wire 316 passes through the lubricant 
applicator 332 and is coiled onto first capstan 334 in a known manner. If 
desired, an optional, intermediate cold working tool can be interposed 
between the lubricant applicator 332 and the first capstan 334 to provide 
an intermediate cold reduction of wire 316. 
The wire 316 is then uncoiled from first capstan 334 and pulled through a 
second lubricant applicator 344, through the cold working tool 346, and is 
taken up and coiled on the second capstan 348 in a known manner. The first 
capstan 334 and the second capstan 348 are operated in coordination so 
that the tension on the wire 316 at any point in processing line 310 does 
not exceed the tensile yield strength of the wire 316. 
The distinctive and beneficial nature of the matte textured surface 
provided by the process and apparatus according to the present invention 
will be better understood with reference FIGS. 4, 5, 6, and 7. Each of 
those figures is a photomicrograph at 100X of a partial, transverse cross 
section of a specimen of AISI Type 302 stainless steel wire. In each 
photomicrograph the lighter area is the wire material. 
FIG. 4 shows the surface profile of Type 302 wire which has been back-die 
shaved, but not further treated. The surface of the wire shown in FIG. 4 
is very smooth and thus not very conducive to cold working because of its 
limited ability to carry lubricant into and through a cold working tool or 
die. FIG. 5 shows the surface profile of Type 302 wire which has been 
blasted with metal shot. The surface of the wire shown in FIG. 5 is very 
rough and jagged, and thus not very conducive to drawing or other cold 
working processes. Shown in FIG. 6 is a surface profile of Type 302 wire 
which has been annealed and acid cleaned after having been back-die 
shaved. FIG. 6 illustrates the undesirable intergranular attack at the 
wire surface that results from such processing. 
FIG. 7 shows the profile of the surface of Type 302 wire that has been 
back-die shaved and then surface textured by glass bead blasting in 
accordance with the present invention. This surface is characterized by a 
plurality of random, minute, shallow indentations which significantly 
improve the lubricant carrying capability of the wire surface without 
measurable work hardening thereof. It has been found that this matte 
textured surface facilitates cold working of the wire to a significant 
degree. 
It is apparent from the foregoing description and drawings that the process 
and apparatus according to the present invention provide a unique 
combination of advantages over the known techniques for surface treating 
and then cold working an elongated form of steel alloy. For example, the 
process according to this invention is readily adaptable to in-line 
processing with other surface treating and/or cold working operations to 
provide efficient, continuous processing of wire, rod, or bar. The process 
is capable of high processing line speeds, e.g., from at least about 300 
fpm up to about 700 fpm, and possibly higher. The process is not limited 
to large diameter wire, rod, or bar and it does not measurably increase 
work hardening of the metal surface. Moreover, this process significantly 
improves the drawability and extrudability of peeled, shaved, or broached 
wire, rod, or bar while avoiding the physical and mechanical disadvantages 
of shot blasting and the chemical and environmental problems associated 
with acid treatments. 
The terms and expressions that have been employed herein are used as terms 
of description and not of limitation. There is no intention in the use of 
such terms and expressions to exclude any equivalents of the features 
described or any portions thereof. It is recognized, however, that various 
modifications are possible within the scope of the invention claimed.