POWDER METALLURGY IN THE MANUFACTURE OF HUNGARIAN MACHINE PARTS

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP80-00809A000700060354-1
• Release Decision: RIPPUB
• Original Classification: R
• Document Page Count: 11
• Document Creation Date: December 22, 2016
• Document Release Date: October 5, 2011
• Sequence Number: 354
• Publication Date: May 23, 1952
• Content Type: REPORT

Sanitized Copy Approved for Release 2011/10/06: CIA-RDP80-00809A000700060354-1
r
.CLASSIFICATION RESTRICTED
CENTRALS LLIGEN EI AGENCY
INFOKMATION FROM
FOREIGN DOCUMENTS OR RADIO BROADCASTS
COUNTRY Hungary
SUBJECT Economic - Metallurgy, heavy inuustry
HOW
PUBLISHED Monthly periodical
WHERE
PUBLISHED Budapest
DATE
PUBLISHED
LANGUAGE
1x1. DOCe...T eexrq.r 1-I.Ane. 1119 l.. ixt .ATlogl OV[...
el TM. V.ITED -i.T[. ..ft. THE .G. L. Ol br10.Mr ACT .0
r. s. ITS e., n co.r. .n . ua, e. uuo-o. m A.snuio. a. rxun.uno.
or
ur
n.nx. ro ~. uu... rum. a rw
.umo n u.. uoou cno. or rxu ro..u ..oxurt.o.
kR- Vol III, No 4,5 and 6, 1951.
SUPPLEMENT TO
REPORT NO.
PONDER METALLURGY IN
TER MANUFACTURE OF HUNGARIAN MACHINE PARTS
In response to the need for intcrmation on the part of engineers, tech-
niciane, and planners engaged in the various fields of metalworking and machine
engineering, this article diecussee the possibilities for the utilization of
powder metallurgy in general and the manufacture of small-sized machine parts
in particular, with primary emphasis on the manufacture of complicated iron
and steel parts. Due to reduced porosity, the machine parts produced by means
c" powder metallurgy approximate, in quality, castings and rolled products.
Powder metallurgy also reduces the costs of labor and materials in the
manufacture of machine parts, due to the complete or partial elimination of
machining operations.
Engineers and technicians engaged in the various fields of machine en-
gineering and metalworking have, in general, not yet become acquainted with
the pcseibilitiea. Inherent in the utilization of powder metallurgy for the
reduction of production costa.
The purpose of this article is to acquaint experts, especially on the
planning level, with the essential features of po'-der metallurgy, its methods,
and poaeibiiitiea. A knowledge of powder metallurgy will be helpful in solv-
ing some problems or design and in selecting the :ost suitable process for
the manufacture of machine parts.
Although the products now fabricated by means of powder metallurgy con-
stitute only 0.1 percen' of all metal products produced in the entire world,
this percentage is increasinv very rapidly. To illustrate the importance of
STATE
ARMY
DISTRIBUTION
Sanitized Copy Approved for Release 2011/10/06: CIA-RDP80-00809A000700060354-1
STAT
STAT
 Sanitized Copy Approved for Release 2011/10/06: CIA-RDP80-00809A000700060354-1
r
this new branch of industry and the role it plays in modern eachl.ne manufac-
ture, it will suffice to point out that in highly industrialized. countries, a
motor car now contains about 100, and a modern airplane more than 4,000 machine
parts produced by means of powder metallurgy.
1. By means of powder metallurgy, it is possible to produce materials
that cannot be manufactured in any other manner. This process enables us to
_'egulate the porosity of certain products. As a result, ferrous powders may
be used to produce metals which possess the qualities of bronze and lead. We
use this process, for instance, in the manufacture of self-lubricating axle
bearings, filters, condensation rings, etc_
2. Parts an be molded into finished or semifinished dimensions ~ungar-
lan; tolerance J 117, h7, thus entirely or partially eliminating machine
operations, with ccn_equent great savings in material and working time. In
this manner, produt'1on costs of parts can be reduced in some :;asee by four
fifths
It is,thereto:e, cf some interey' to cite a few typical applications which
illustrate the advantages afforded by prcier metallurgy. The following have
advantages.
Graphite-bronze brush materials used in the electric industry; friction
washera made of copper, leaf, zinc, graphite, and ccrrindum used in machine
tools for the manufacture cf automobile' and airplanes; and p,roua, self-
lu-bricating ".le a.1^g= which cver-:ome many ?ilftt:ultiee in cases where sys-
tematic lubrica ion 1- impc~rible. Axle teasing. s_th iron bases are of special,
interest, because -hey can be sube.l* .'.ed for axle bearings ride of other metals.
Fuel filters cf considerably reduces .eight, ob`.ainei by tontrolled porosity,
for automobile. marine, sir-raft, and etto ienery diesel engines; noncorroding
steel filters as substitute. for nonferrous metals; porous iron washers to re-
place lead washes in imter pipe'; an?.i ei:!ramtly hard contact materials of
nonweldable metals for the elect: oteclrnice1 industry, produced by embedding
such metal! as .-If-am in nickel, copper, sliver, e_.
The new process i.e employed prlma.:ily in the manufacture of small parts
weighing 80 to 100 grams and used in the light-machine, v,!:)-_-A-le, and household-
appliance industries, including sevl ng-machine parts, office machine parts,
sprockets for bicycles, bicycle brake hubs, gears for oil pumps, roller-bearing
racevays, valve lifters, meat-grin`'er hives and dicks, lock parts, keys, etc.
It may be pointed cut, ho'wever, that the article is devoted mainly to the
manufacture of iron and steel machine parts. Even within this restricted field,
it is not proposed to deal with porous machine parts but only with machine parts
of complicated construction and of slig~,t porosity, designed to approximate the
strength of solid metals. This branch of power metallurgy has Just begun to
come to the fore as a competitor of other metalworking procesees.
For exploiting the possibilities of powder metallurgy with respect to the
manufactur- of ma-`nne Wage the desimlers must first become acquainted at
Sanitized Copy Approved for Release 2011/10/06: CIA-RDP80-00809A000700060354-1
 Sanitized Copy Approved for Release 2011/10/06: CIA-RDP80-00809A000700060354-1
r
least with the general outlines if its technology. To proceed further, they
must become successively acquainted with it-, inherent ]'mitations, the poten-
tialities of its physical and mechanical properties, and its strong points.
Producing the Powder
The first step shown in Figur. i :!-'--'.rates the process for producing
metal powder for machine parts. Different methods may be employed for this
purpose, pending on the requirements of economy and future use.
Preparing the Powder
The second step consists of the preparation of the powder, which involves
the following processes, preliminary sieving, heat treatment, milling of the
heat-treated powder, final sieving, and mixing,
Pressing Process
The third step consists of compressing the powder.
The hydraulic or
mechanical presses used for this purpose develop pressures of from 2 to 10 tons
square centimeter, Compression ii followed by efntering in a gaseous atmos-
phere in electric ovens at temperatures ranging from 800 to 1,300 degrees centi-
grade. If necessary, compres?'.on and sintering are repeated, sometimes followed
by a copper bath and finally by calibration. The powder is routed along one
of the four basic courses illustrated, depending on strength and other require-
ments. These four basic sequences, however, -frequently undergo variations, which
depart from the routings illustrated in variations 1, c, 3, and 4.
Subsequent Operations, Flnilhly processes
Any remaining operations that are ne?ceessxy, such as me-,hlning, polishing,
final hea., treatment (hardening, temperng, cs,eharien1ng;, or oil impregnation
(as in the case of axle bearings), are performed in the fourth step.
Details of Variations in Third Stec
Variation 1. The pressure is varied between and 8 tone per square
centimeter, depending on the degree of porosity to be obtained. Lower pres-
sure is used, for i.nstance, in the ar_ of machine parts which are to be im-
pregnated with oil 'axle bearings), ~?_eater pressure is required for parts
which will operate under greater stress.
Variation 21 In the manufacture of machine par-ta requiring greater strength,
preliminary pressure ranges between 4 and 6 tons per square centimeter; pre-
liminary sintering takes place at temp.mraturea between 800 and 900 degrees centi-
grade; final compression ie varied between 4 end 6 tons per square centimeter;
and final sintering is done at temperatures between 1,100 and 1,300 degrees centi-
grade.
Variation 3; This variation is identical with the previous one, except that
after final sintering, cold-calibrating compression is employed for precision.
Variation 4s This variation may be applied to parts which have been routed
via variation 1, 2, or 3. In this case, however, the machine parts are copper-
plated to increase strength and reduce porosity.
Sanitized Copy Approved for Release 2011/10/06: CIA-RDP80-00809A000700060354-1
 Sanitized Copy Approved for Release 2011/10/06: CIA-RDP80-00809A000700060354-1
Before proceeding to fill in the details of the above outline, it is first
necessary to study the various pulverization processes comm,nly used to pro-
duce the powders necessary for powder metallurgy.
The iron or metal powder required for vacuum technology, for compressed
iron powder cores for the communications industry, etc., is produced from gas
phases by means of the carbonyl method. The product thus obtained has great
purity. The granules are spherical and have a diameter of C.1-5.0 micrc?ns.
However, this method ce very costly; the heavy investment required for it pro-
hibits the extensive marketing of powder thus produced, except for special
purposes.
Although the electrolytic method of pc-id,T production is somewhat more
extensively used than the carbonyl method previously described, its more ex-
tensive use 1E profitable only at lo:ation3 which have immediate access to cheap
electric power. The fern-shaped granules thus obtained, having a dendritic
construction, measure 5-;0 microns; thus purity of this powder, as well as its
excellent cempreseitiiity, also render it suitable for use in vacuum technology
and for the msn?.Lfac'ure of compressed iron ponder cores and permanent magnets.
The so-called vortex-mill !"Hametag"? process, a mee:hsni.;al method of
powder production, c,akee It possible -o pulverize broken wires, plate scraps,
granulated metal-,, d steel shavings. :n this process, cc,arsely broken shav-
ings, wires, or, plate scrape. are pulverized in a closed drum by '.w: counter-
rotating propeller- The powder thus obtained is widely used on the manufac-
ture of machine parts and self-lubricating axle bearings.
The disadvantage of this proces, is the relatively small output of the
equipment flC-_0 kilograms per hour!: furthermore, the e -called edge hardness
of the resulting machine parts Is net perfect. This deficien?::y is attribut-
able to the disk shape of the granules, which does not assure eatlafact:ory
binding after compr ?:sicn,
The me t wi,iely ueel process ;,on?i-'s cf :cr:.!rg molter. metal through thin
jets and pulve.ra,ing it.ty a high .prn _us spray of ',rater or air. Before the
ps.rticlee sclid.ify, they fall revolving ?hovels, which cut them into a fine
powder. This pr=cees, which yields one to tone of powder per hour, assures
an adequate supply of powder metal for the lerge-scale production of. machine
parts, If *,he basic material is pig iron of high certon content, cast iron, or
steel, the concentrated oxide layer ocver.ng the individual granules will cause
decarburization ;refining) In the -itctance when air '._ the medium used in the
powdering process. As a result, carbon monc.xide it produced in the form of
minute gee globules in the centers of the granules. Af :sr subsequent annealing,
the powder thus obtained has excellent prop-rtiee for compresecon,
The metal powders pro?iuced by be foregoing method-A. must then be prepared
for the pressure-molding process in the tethaclog?ral sequence indicated (see
Figure 1, Step 2 This preparation con=_Ist.e of sieving and grading, removing
the oxygen abscrbed during the pulverization process, milling the powder con=
lseced by the det:Mldization process, alloying, and adding lubricants to facilitate
compression, etc.
Pressing
The compacting of meted powders is performed under a pressure of 2-10 tons
per sq,iare centimeter in a special hydraulic or mechanical press. in the
STAT
Approved for Release 2011/10/06: CIA-RDP80-00809A000700060354-1
 Sanitized Copy Approved for Release 2011/10/06: CIA-RDP80-00809A000700060354-1
F
following, surface will be taken to mean the greatest cross section of the part
to be produced, perpendicular to the direction of the applied pressure. The
density of the finished product depends on the magnitude of the pressure nrplied;
consequently, it is possible to regulate porosity. Although low pressures (2-3
tons per square centimeter) are applied for the molding of self-lubricating axle
bearings with a final porosity of about 30 percent, steel machine parts of great
strength and minimum porosity are moulded under pressures of 6-10 tons per square
centimeter. The application of higher pressures 12 not economical because of the
excessive strain on the presses and tools.
When under pressure, the metal powders used for the manufacture of machine
parts do not manifest the same behavior as do liquids. Frict:cn is generated
between the powder porti:les and along the surfaces of the tools, thus hindering
the uniform tranimiesion of the pressure,
+ When dealing with complicated machine parts, 'he eroIre pressing technique
sus.. be adjusted to compensate f;r the particular ::hara:..terlsti s displayed
by each type of?metal ,>o-der, Ccnsegrently, a detailed discussion of this prob-
lem appears to be necessary.
If metal pox :r is to be :ompacte to form a solid cylinder, and the com-
pacting pressure :s exerted in only one direr_t.lon (see Figure 2) the density
of the ,ompact powder decrease- in direct proportion ae the length of the cyl-
inder exceeds its diameter. If the 1?/d rati;
su-
crease in density 'will exceed le per:.ent st. the point tfsrth3t from then pressure
punch. If the lj3 ratio cee 20 percent.
is greater than 2, the decrease will exceed 20 percent.
However, if pressure is exertei from :w. sides, as illr.trited In Figure 3,
densities are obtained which are su_t3b1e for purposes of machine production; in
case the 1/i ratio is equal to one, the decrease in density will be lees than
5 percent. Figure K graphically illustrates this point, it also reveals that
the friction generated by the intera_t_on of 'he granules and by the movement of
the granules, sgecnst the eurfso' of the fc.m:rg tools be ier_
tssrln, t:: srln -seed :,iSs sn-
tially by aiding a lubr?i- :nt. such as g_;F?ri`t or =t the pander.
To offs-- the decrease in density re=nlt+na f-rm the friction generated by
the inters,-:tioc of the granules, and
ili.ta'e the eves ? toad of ?.
to the eatremt'l.a of the d.e, tar, fe p pfirst
methoi; are tmplcyed. in the first
method, illuetra'_d is Figure 3, the fie t?:,:y destgnei to receive the powder
remains sta+:Laa3ry, wale -ne. upper sin' hoer punches exert pree-u from two
directions. "'he >F:-ad me-tied is leetened to redut 'be effict~ of the generated by the movement, of the g_a._uje6 against the el ewalls of the dieetion
(see Figures Sant 6;. It will be seen in Figure 5 that., in this case, the die
body is mvv.3bvthep':tier under sprit -er: i n phi^h 1.., va:-ied according to the
powder used. Figure 6 th u=tratec a v:':t,+.,on in shi_b the motion of the die
body corresponds to the motion of the pcnicha,
The properties of the metal powders described in the foregoing cause
difficulties in the manufacture of Irregularly shaped ma::hlne parts. Finished
briquettes of i regular shaper- ';.t 11 bt cf appre:ramstely uniform density only
when the degree of campressicn Is uniform throughout the piece,
When dealing st:h an irregularly shaped part ieee Figures 7u, b, and c),
the resulting varterlc.i in density , ar, be tolera-tei. In the event, however,
that a part require, steps which exceed one fourth of the total thickness,
the product will be unfit for use because of even der.:3lty. In sucb -aces,
the procedure illustrated in Figure 7a should be used, in which four punches,
moving independently of one an-the!r, assure the uniform density of the finished
briquette. On the other hand, it is not possible to assure uniform density
when compressing similar parts with the punch depicted in Figure 7c.
Sanitized Copy Approved for Release 2011/10/06: CIA-RDP80-00809A000700060354-1
 Sanitized Copy Approved for Release 2011/10/06: CIA-RDP80-00809A000700060354-1
A comparison between Figures 7a and 8a reveals that punches 1 and 2 will
have to compress sections of powder of the same height but to different degrees,
which will positively cause unevenness.
To eliminate unevenness, the equipment illustrated in Figure 8b has been
employed for filling in the powder.
The motion of the lover punch is synchronized with the motion of the upper
punch, as shown in Figure 8b and 8c. Figure 8d, on the other hand, illustrates
the manner in which the finished briquette is ejected from the die, while Figures
9a b, and c illustrate problems of tool construction.
With respect to the machine part illustrated in Figure 10a, uniform den.iity
can be obtained by the following method,
1. Preliminary pressing is done under relatively slight pressure to ob-
tain the form as shown in Figure 10b.
2. This is followed by preliminary sintering at about 1,100 degrees centi-
grade.
3. Finally, finish pressing is accomplished under high pressure to obtain
the form shown in Figure 10a, followed by final sintering.
The foregoing discussion justifies the conclusion that the various shapes
of machine parts which can be prcduced by means of powder metallurgy are limited
by the following principal considerations:
1. Powder does not behave in the same manner as do liquids or plastic
substances, that is, powder does not fill out overcomplicated forms, does
not flow around, does not fill out corners,and can be shaped only in the di-
rection of the pressure,
2. Only such shapes can be obtained which will allow the punches to com-
pact the powder in the direction of the pressure and permit the resulting bri-
quette to be ejected from the dim,
The following are secondary limitations.
1. An unfavorable distribution of density will be obtained in the case of
solid cylindrical parts when the ratio of the length to the diameter exceeds 3:1
for bronze and copper and 2;l for iron. If these ratios are exceeded, deforna-
ti.on will follow after sintering.
2. There can be no undercut,)rojections in the side of the die, such as those
which are usually found in certain types of conventional dies, for the purpose
of facilitating chip clearance in the course of subsequent turning and grinding
of the casting (see Figure lln). However, there is no need for such a procedure
in powder metallurgy, because the machining or polishing operation is entirely
eliminated, since the ports are usually made to final dimensions.
3. In shaping the di-, any shoulder-forming angle must be chamfered as
illustrated in Figure llb. Since the compressing of a perfectly sharp shoulder
is impractical, a minimum radius of 0.2 millimeter must be applied in such cases.
4. The hamfer required at the ends of the castings must form the smallest
possible angle with the horizontal, since acute chamfers are easily broken (see
Figure 12).
Sanitized Copy Approved for Release 2011/10/06: CIA-RDP80-00809A000700060354-1
 Sanitized Copy Approved for Release 2011/10/06: CIA-RDP80-00809A000700060354-1
r
5. Only holes with axes parallel to the axis of pressure can be cored in
the powder-metal die. Holes with axes running athwart the axis of pressure must
be machined subsequently.
6. Feather edges, very narrow or deep notches, thin bosses, and gears are
difficult to compress under a modulus of 1.5. Such machine parts will easily
break when they are ejected from the die. Abrupt changes in cross-section thick-
ness cause considerable cracking along the junctures on shrinkage of the metal
after the sintering process.
Taking these considerations into account, machine parts are frequently de-
signed to make a few machining operations necessary after the powder-metallur-
gical process has been completed.
The foregoing is represented by Figures 13a and l313 in which the part
shown is a feed attachment for it sewing machine. Figure 13a represents the
part when the powder-metallurgical process has been completed; at this stage
the teeth are still missing. The teeth are cut in a subsequent machining opera-
tion. Figure 13b shows the part in its final, finished form, produced by con-
ventional machining operations.
Figures 1" and 14b illustrate bobbin parts of a sexing machine made accord-
ing to two different technologies.
Where parts were previously manufactured of tempered alloys, they are now
being made from steel powder containing 0.6 percent of carbon, pressed twice
(6 tons per Square centimeter, plus 6 tons per square centimeter), a:d cali-
brated.
Figures 15a and 15b illustrate the manufacture of the brake drum of a bi-
cycle, which entails a steep brealsiff amounting to 20 degrees and subsequent
undercutting to a diameter of 19.7 millimeters.
from A 34 11 polished rods see Figure 15a7 is now The
manufactured factuz previously by py powde wderuced
metallurgy from steel containing 0.8 percent of carbon, pressed !price (6 tons
per square centimeter each time), followed by calibration.
Figures 16a and 16b represent the upper eccentric of ase-wing machine. The
hole having its axis parallel to the direction of pressure must be machined
subsequently, since its relatively small diameter involves danger of die break-
age in this special case.
Sintering
The Powders, when pressed into proper shape and removed from the die, have a
strength similar to chalk; they must be handled carefully lest the edges break
off or-become marred. (So-called peripheral stress is one of the characteristic
features of various metal powders). To endow machine parts with the durability
required for practical purposes, the pressing process must be followed by sin-
tering. This process should take place in reducing or neutral atmosphere to
prevent intermediate oxidation. Usually, an electric furnace with molybdenum
resistance elements is employed for sintering. The temperature varies from 800
to 1,300 degrees centigrade, and sintering lasts from 2 to 60 hours.
Sintering assists in forming the durability and mechanical properties of
the finished part; in this respect, sintering is of even greater importance
than the pressing process. The temperature and duration of sintering determine
the porosity of the substance and also the ^oheei? .between the individual metal
particles. The diffusion that takes place at various temperatures during sin-
tering is explained by research engineers as follows
-7-
RESTRICTED
Sanitized Copy Approved for Release 2011/10/06: CIA-RDP80-00809A000700060354-1
 Sanitized Copy Approved for Release 2011/10/06: CIA-RDP80-00809A000700060354-1
The amplitude of atomic oscillations increases at the sintering tempera-
ture to such an extent that the magnetic fields of force of the atoms along
the edges of the crystals become diffused and the atomic chains of the two crystal
particle: become connected. Once this connection has been established, it
persists even after the cooling process has been completed. This increase in
amplitude and atomic oscillation are also present within the crystal, but here,
a state of equilibrium exists. The possibility of oscillation is much greater
along the surface of the crystals, since only a unilateral stress exists and the
space for movement is larger. The surface of the crystals is'sharply articulated.
There appear peaks and deep indentations, with the atoms representing the peaks
taking up positions in the indentation of another crystal.
These phenomena have been substantiated by experiments perf:irmed in con-
nection with sintering, in which a vacuum was used instead of a protective hy-
drogen atmosphere. Since the gas charge hindering surface diffusion (the sur-
face being defective, or its hollow portions having been occupied by foreign
particles) was eliminated, better results were obtained in this case than when
a protective hydrogen atmosphere was used. (The use of the vacuum has not been
generally adopted because of the technical difficulties involved).
Experiments have been conducted to prove that In the fusion of two metals
in their solid state, the first step consists of the migration of electrons
from one atomic orbit to the other. A current of 3.5 amperes was passed through
pressed iron-powder rods, resulting In an increase of temperature amounting to
2-3 degrees centigrade. Despite the rise in temperature, considerable additional
stability was found in the pressed parts, which was attributed to the electronic
flow.
The higher the temperature at which diffusion takes place, the greater the
rate of diffusion. Its magnitude depends on the duration of the sintering proc-
ess, on the number of atoms participating in it, and on how closely individual
crystals have approached one another during the pressing process. The porosity
remaining after the crystals have cohered decreases slightly during the in-
crease in granulation occurring in the recrystallization which takes place dur-
ing sintering.
Figure 17 illustrates the extent of diffusion and the increase in stability
values as influenced by the duration of the sintering process. Fig-ire 18 illus-
trates the effect of the temperature of the sintering process on stability.
Figure 19 sbcwe the electric resistance of metal powder prior and subse-
quent to the sintering. From these indications, certain conclusions may be
drawn with regard to the extent of granular bonding. This figure also illus-
trates the considerable difference which exist in the resistance values be-
fore and after sintering.
The resistance of metal powders decreases by about one half when the
nreaeure increases from 2 tons to 6-8 tons per square centimeter; there is
little or no change if the pressure is further increased. Therefore, an in-
crease in pressure beyond 8 tons per square centimeter is not economical.
Figure 20 illustrates the effects ofirepeated compression and sintering
on density and stability values. It is not economical to increase the number
of operations beyond two or three at the most. An increase in compression
pressure especially is not economical, since the density of the piece sub-
,lected,to sintering will not incre'se essentially even if greater pressure
promises such an increase (see curve, 6 tons per square centimeter).
Sintering not only establishes the prope1r relationship between granules
of pure iron or other pure metal powders brought into close proximity by the
STAT
Sanitized Copy Approved for Release 2011/10/06: CIA-RDP80-00809A000700060354-1
 Sanitized Copy Approved for Release 2011/10/06: CIA-RDP80-00809A000700060354-1
iESTSIPT6D
pfassing process, but also has the function creating diffusion (alloying) be-
tween the initial substance and the alloying substances admixed with the initial
substance in different' ratios. For example, a mass compresses from a mixture
of soft and cast-iron powder and annealed at a temperature of about 1,200 degrees
centigrade for 3-4 hours vill'yield a uniform, temperable perlite-ferrite
material of crystalline structure.
The carburization of parts manufactured of pure iron powder can take place
either in a sai+ bath or in a gas. Due to the objectis porosity, the carbon
absorption occurring luring the carburization starts on the surface and than
penetrates the interior. Diffusion taking place between the iron particles and
the carbon during subsequent sintering results in a metal of uniform carbon
content.
A process similar to that observed during the sintering of ferrocarbon alloys
occurs when icon powder is mixed with powders of manganese, chrome, etc.
Sintering of the above material does not always take place in the protec-
tive hydrogen atmosphere usually employed for this purpose. In view of the
intense removal of carbon taking place in such cases, it is preferable to cen-
duct the sintering In graphite. tubes under a graphite-powder cover; a suitable
neutral atmosphere for such treatment is a mixture of CO and CO2 or hydrogen
and CO.
Physical Properties Articles Produced by Powder Metallurgy
Figure 21 illustrates the physical and mechanical properties which can be
obtained by using various methods in powder metallurgy.
in addition to tensile stress - strain curves for standard alloys and car-
bon steels, the figure shows the same curves for various powder-metallurgical
products. A comparison of the curves reveals that when great durability is re-
quired, powder metallurgy is endeavoring by four different methods to achieve --
through elimination of porosity -- the physical properties of dense, standard
metals.
The first method is to increase compression. While the tensile strength
of a part produced at lower pressure (4 tons per square centimeter) and pressed
once amounts to approximately 50 percent of that of standard steel, pressure
of 6 tons. per square centimeter increases the tensile strength to 60-70 percent
of that of standard steel. However, as has been pointed out, this method is
uneconomical due to the size of the required presses and the high cost of tools.
Another met':.od involves repeated pressing and sintering. If a pressure.of
6 tons per square centimeter is applied twice and followed by several sinter-
ings, 80 percent of the tensil strength of standard steel has been obtained. This
process cannot be carried beyond the limits pointed out in connection with
Figure 20.
By repressing the compact while it is still warm, it has been possible to
obtain a density approximating 100 percent that of standard steel and a corre-
spoffiigg tensile-strength value. Preliminary pressing at 6 tons per square centi-
meter was followed by preliminary sintering at a temperature of 800 degrees
centigrade. The compact is then repressed at 700 degrees centigrade and receives
a final sintering at 1,200 degrees centigrade. However, this method has certain
limitations. Some tolerances can be maintained only within approximate limits,
and only parts of relatively simple contour can be prodr-ed,
STAT
Sanitized Copy Approved for Release 2011/10/06: CIA-RDP80-00809A000700060354-1
 Sanitized Copy Approved for Release 2011/10/06: CIA-RDP80-00809A000700060354-1
The most suitable method for eliminating porosity is to impregnate the
prepressed and presintered parts with copper (see Figure 21). The pressed and
sintered part is placed in copper powder or chips, after which it is heated
until the melting point of copper is reached. The molten copper is absorbed
by the part through capillary action, and fills up the pores. Since at its
own melting point, copper dissolves iron to some extent (8 percent at 1,100
degrees centigrade), some alloying occurs between the iron and copper. This
alloying increases the tensile strength of the product, possibly even sur-
passing that of standard steels. Results even better than the values shown in
Figure 21 have been obtained by employing special heat-treatment processes
Parts processed by this method offer excellent resistance against corrosion.
Close examination of the curves in Figure 21 reveals that while the tensile
strength for the various processes approximate fairly closely the values for
standard steels, elongation values, on the other hand, remain very much behind
the elongation values of standard steels.
When a part made by powder metallurgy is to replace a standard-metal part,
its low elongation value, compared to carbon oteel, need not be prejudicial
to its use if the tensile strength is adequate and other factors of economy are
in its favor. While the fatigue limit of standard steels amounts to approximately
50 percent of their tensile strength, the fatigue limit of materials produced by
powder metallurgy is much higher, amounting to approximately 70 percent of their
tensile strength. Powder-metallurgical parts, although possessing relatively
lower elongation, often can be bent better than standard-metal parts which have
a higher elongation value.
So far, low-carbon steel is the basic raw material for parts produced by
powder metallurgy, but rapid progress is being made toward the manufacture of
alloy steel parts.
Today, stainless chrome-nickel steel parts and nickel tempered steel parts
with durability values higher than those of carbon-steel pa-zta sx-e being manu-
factured. For instance, the indexes for a sprocket wheel manufactured of case-
hardened tempered steel are as follove. R,,, 58-61; tensile strength, 50 kilo-
grams per square millimeter; elongation, 10 percent. Experiments which have
been conducted with nickel-alloyed materials impregnated with copper and sub-
!ected to special heat treatments show a tensile strength of 130 kilograms per
square millimeter, with an elongation of 4 percent.
It is possible to machine parts produced by powder metallurgy without
special difficulty, although the edges of the cutting tools are exposed to
greater stress due to the porosity of the material. By using built-up hard-
alloy tips, however, they can be machined economically.
Permissible Variations in Size
Generally speaking, a tolerance of t 0.01 millimeter can be maintained
per 25 millimeters of length in a direction perpendicular to the pressing, and
a tolerance of ?0.1 millimeter can be maintained per 2 millimeter parallel to the di-
rection of pressing. These tolerances can be reduced in case of smaller pro-
ducts by changing tools more frequently or by subsequent calibration.
In the case of products of cylindrical shape, eccentricity of ? 0,02-0.06
millimeter can be maintained. Teeth on spur gears can be held to a tolerance
of ?0.02 millimeter.
STAT
Sanitized Copy Approved for Release 2011/10/06: CIA-RDP80-00809A000700060354-1
 Sanitized Copy Approved for Release 2011/10/06: CIA-RDP80-00809A000700060354-1
Economy of Powder Metallurgy
Production costs of smaller machine parts can be reduced by powder metal-
lurgy. The following brief suimsary represents a condensation of detailed calcula-
tions performed by the author with the cooperatiin of leading experts in the field
of powder metallurgy.
The manufacturing cost of a complicated 50-gram part made by conventional
machining technology is approximately 450 forints per 100. This figure was
arrived at by checking the manufacturing costs of about 200 different parts of
this type.
Selecting from the above parts those suitable for manufacture by powder
metallurgy, the manufacturing tort was cut to approximately 100 forints per
100 parts. If the cost for subsequent machining operations is added, the
total is 200 forints per 100 parts. However, such economy can be expected only
in mass production, due to the high cost of dies.
In view of the fact that a complex We costs about 6,000 forints, the
smallest series should be 10,000 units. The manufacture of even smaller series
is justified only when it would be inexpedient to employ other methods.
The manufacture of self-lubricating axle bearings represents a special-
ized chapter of the technology of powder metallurgy. The same is true of ob-
jects exposed to light stress or of special physical properties.
BIBLIOGRAPHY
M. J. Balshin, Poroehkovoye metallovedyeniye
M. J. Balahin, Poroshkovya metallurgiya
Kieffer and Hotop, Sintereisen and Sinterstahl
H. Silbereisen, "Das pulvermetallurgi ache Fertievngaverfahren," Werkatattste-
chnik and Maschinenbai Vol 40, Ho 6
C. G. Goetzel, Treatise on Powder Metallurgy
Powder Metallurgy Bulletin. 1 September 1948 (lectures delivered at First Inter-
national Congress for Powder Metallurgy at Graz, 1948)
STAT
Sanitized Copy Approved for Release 2011/10/06: CIA-RDP80-00809A000700060354-1