US3779747A - Process for heating and sintering ferrous powder metal compacts - Google Patents

Process for heating and sintering ferrous powder metal compacts Download PDF

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US3779747A
US3779747A US00285965A US3779747DA US3779747A US 3779747 A US3779747 A US 3779747A US 00285965 A US00285965 A US 00285965A US 3779747D A US3779747D A US 3779747DA US 3779747 A US3779747 A US 3779747A
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compact
temperature
heating
sintering
level
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R Conta
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Gleason Works
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Gleason Works
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/10—Sintering only
    • B22F3/1017—Multiple heating or additional steps
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
    • B22F2998/10—Processes characterised by the sequence of their steps

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  • heating in the induction field is used to UNITED STATES PATENTS raise the temperature of the entire compact to a level 3,708,645 1 1973 Osborn 219/1041 above 1,8 0 F and this temperature is maintained for 3,331,686 7/1967 Bonis ct al. 75/226 a sufficient period of time to deoxidize and sinter the OTHER PUBLICATIONS compact.
  • the present invention particularily relates to processes for heat treating and sintering powder metal compacts to prepare the compacts for final forming operations which increase the density and establish the final shapes of the compacts as finished parts, but the discoveries of this invention may be applied to processes which sinter powder metal parts as a final step in a finishing technique.
  • the invention is specifically concerned with improvements in heating and sintering of compacts formed from ferrous metal powders used in the production of high strength finished parts such as bevel and spur gears, and the like.
  • the present invention provides for improvements in heat treating processes for ferrous metal powder compacts so that such compacts can be economically and efficiently heat treated in a continuous process which carries each treated compact to a final forming operation where its density is increased to approximately percent of theoretical value and its shape is established for a finished part.
  • the present invention provides for an overall decrease in time and energy required for heat treating such compacts through a use of induction heating in an efficient and economical manner for at least a part of the heat treatment of each compact.
  • the improved process of the present invention is based upon a discovery that the incubation period (or the time it takes for the compact to effectively couple with a magnetic field of an induction heating system) of a given compact in a relatively low frequency induction field can be substantially reduced or eliminated by preheating only the outside surfaces of the compact to a temperature level which produces an irreversible change in characteristics of the compact with respect to its ability to respond to the induction heating field. It is not known just what mechanical or chemical changes take place when a compact is preheated prior to introduction into an induction heating field, but it can be observed that the preheated compact responds much more readily to induction heating, thereby significantly reducing the total power required in an induction heating cycle to raise the temperature of the compact to a sintering level.
  • Preheating can be carried out with known radiant heating equipment in a very short time which raises the temperature of only the skin surfaces of the compact prior to induction heating.
  • the surface temperature is raised to a level above 300 F, and there appears to be a preferable threshold level of about 400 F at which incubation time is nearly eliminated, but somewhat lower temperatures may be utilized if the preheating treatment is carried out for a longer period of time.
  • preheating of a 295 gram compact will require about one minute or less to raise its surface temperature to the preferred 400 F level.
  • the compact After this preheating treatment, the compact can be immediately introduced into an induction heating field, or it can be cooled and stored for a subsequent use in an induction heating field since the effect of preheating appears to be an irreversible one with respect to reduction or elimination of the characteristic incubation period for a compact in an induction field.
  • the basic process of the present invention is one of increasing the rate at which ferrous metal powder compacts can be efficiently heated in an induction heating field by preheating the powder metal compact sufficiently to raise the temperature level of the material in its outer surfaces to at least 300 F prior to subjecting the compact to an induction heating field which then can rapidly raise the temperature level of the material of the entire compact to a level at which sintering takes place.
  • An overall process for forming ferrous metal powder compacts into high strength finished parts includes the steps of (a) preheating each compact sufficiently to raise the temperature level of material in its outer surfaces to at least 300 F (and preferably to about 400 F), (b) subjecting the compact to an induction heating field which rapidly raises the temperature of the material of the compact to a sintering level (between I,800F and about 2,500 F for a ferrous metal), (c) maintaining the temperature of the compact at the sintering level for a sufficient length of time to deoxidize the compact and to cause powder particles therein to coalesce, and (d) cooling the compact from said sintering level to a temperature at which the compact can be immediately formed into a finished part 1,500 l,900 F). Step (d) can be omitted for processes in which sintering produces thefinal form of the article.
  • FIG. 1 is a sehematic illustration of a continuous process by which a compact of ferrous powder metal is prepared and treated in accordance with the present invention for use in a final forming operation;
  • FIG. 2 is a temperature-time graph which depicts the various stages of heating and sintering treatments suggested for the process of FIG. ll;
  • FIG. 3 is a graph illustrating reduction in incubation period for compacts subjected to preheating for different time durations
  • FIG. 4 is a graph illustrating the effects of various durations and temperatures of preheating on incubation time
  • FIG. 5 is a graph showing a temperature-time profile which indicates a range of preheat times and tempera tures that will nearly completely eliminate incubation time for a 295 gram compact.
  • FIG. 1 depicts the invention with reference to an overall continuous process for producing finished metal parts from a ferrous metal powder.
  • FIG. 2 graphically illustrates the same continuous process shown in FIG. ll. This process is especially useful in producing high strength gear forms which exhibit equal or superior characteristics to present day gears manufactured by a method of cutting and removing material from a blank.
  • the gear forms which can be produced by the process of the present invention include various known bevel gears as well as spur gears and other types of gear designs and gear tooth forms.
  • Station I of FIG. 1 comprises a place at which a ferrous metal powder is compacted at ambient temperatures to increase its density and to create a coherent preform or compact which can be easily handled in subsequent steps of heating and forming.
  • the compacting technique does not form a separate part of the present invention and may consist of any known isostatic or mechanical method for increasing metal powder density to about percent to 90 percent of its theoretical full density.
  • the ferrous metal powder Prior to compacting, is selected or prepared to provide for a controlled admixture of carbon for reacting with combined oxygen and for forming an alloy with the ferrous metal of the powder.
  • the powder is prepared in accordance with techniques described in co-pending application Ser. No. 190,353, filed on Oct. 18, 197i in the name of Philip J.
  • Guichelaar under the title Method For Producing High Strength Finished Forms From Ferrous Metal Powders, and commonly owned with the present application. This technique suggests, for example, the use of a commercially available, water atomized, annealed metal powder having a high ferrous content of about 98 percent by weight of the powder. About 0.20 to 0.60 percent by weight of graphite is admixed with the metal powder, and the mixture is subjected to isostatic compacting to produce a preform or compact having about to percent of the theoretical full density for the selected metal.
  • a lubricant or binder be added to a powder mixture when isostatic techniques are used for compacting, and therefore, a subsequent step for removing such a lubricant or binder is not required, as is the case with certain other compacting methods.
  • the preform After compacting, the preform is delivered to suitable apparatus for carrying out a series of heating treat ments in accordance with the present invention.
  • These heating treatments may be included as a part of a continuous process which provides for continuous delivery of compacted preforms from a compacting machine to the heating apparatus which will carry out critical steps of heating as the preforms move through a series of heating zones within the apparatus.
  • Stations ll, ill, IV and V represent the stations at which heating treatments will be applied to compacts moving through heating zones contained therein.
  • the hot compacts 'be rapidly delivered to 'a final forming or forging press at station VI.
  • final forming can be included as part of an overall continuous process, and means would be provided for unloading hot compacts from the final heating station V for a rapid transfer into the forming press at station VI.
  • a continuous process of the type depicted in FIG. 1 can be carried out in a time period of about 6 to 10 minutes (for relatively small gear parts) from the time of initial compacting until a finished form is produced at station VI.
  • the heating and sintering stations ll V provide for certain treatments which are necessary to carry out reactions and physical changes in a powder metal compact before it can be formed into a high strength finished product.
  • the stations ll V are arranged to maintain an inert (or reducing) atmosphere around each compact as the compact advances from station-tostation, Induction heating is used at staion Ill to add substantial heat energy to a powder compact in a relatively short period of time so as to bring the material of the compact to a sintering temperature at or above 1,800 F.
  • ferrous metal compacts exhibit a characteristic incubation period at the beginning of a heating treatment in a low frequency induction field, and this period is of sufficient duration to resuit in a costly expenditure of energy without attainment of a desired rapid change in the temperature of the compact.
  • the incubation period is substantially reduced or eliminated by subjecting each compact to a preliminary step of preheating prior to the step of induction heating. Preheating is carried out at station ll with known radiation heating equipment, for example, which functions to raise the surface temperature of the compact to at least 300 F but less than the sintering temperature which will be attained in the induction heating zone.
  • preheating By preheating only the outside surfaces of the compact, it is possible to reduce the time required for preheating, and yet, a very desirable and apparently irreversible change is effected by such treatment whereby the compact will then respond to relatively low frequency (at least 1 KH induction heating with very little or no incubation period delay. It is also desirable to preheat only skin surfaces of the compact to avoid an unnecessary stressing that may resuit in cracking of the compact during subsequent heating and sintering operations.
  • preheating can be carried out over a relatively broad range of temperatures for durations of time which generally decrease as the temperature is increased, it is preferred that the surface area of a compact be raised to a temperature of at least 400 F to obtain a relatively rapid preheating treatment at a reasonable cost.
  • FIG. 3 shows the reduction in incubation period for com acts preheated at 0.5, 1.0, and L5 minutes, in the type of radiation heating equipment just described, and as thereafter subjected to induction heating at power densities of 1.6, 3.2 and 4 8 KW/inF.
  • the compact After preheating, the compact can be moved directly to the induction heating station Ill where it is subjected to an induction field which has the effect of raising its temperature to a sintering temperature level.
  • sintering can be carried out at about 1,800 F, it is preferred, in certain processes, that a higher temperature, on the order of 2,350 F be used to assure a full deoxidation reaction of the compact to remove at least percent of combined oxygen from the powder mixture.
  • the desired deoxidation reaction, together with coalescence of powder particles can be achieved by maintaining the sintering temperature for approximately 2 to 5 minutes after the temperature is reached.
  • the temperature of the compact must be adjusted prior to forming since the compact is not in an ideal condition for forming at the sintering temperature level.
  • Forming is preferably carried out at a temperature of l,500l,900 F, and this requires a cooling of the entire compact. Since outside surfaces of a large compact tend to cool more rapidly than its inner core areas, it is necessary to cool the outside surfaces to a temperature below that required for forming, followed by a reheating of the outside surfaces to the desired forming temperature. Thus, the cooling step of the process can be considered a temperature adjusting step since there may be a step of reheating involved in reducing the temperature of the sintered compact down to a forming temperature. Cooling and temperature adjusting take place at station V with known means for transferring heat from hot compacts as they pass through the sta tion. After cooling to about 1,500 to l,900 F, the compacts are immediately transferred to a forming press for final forming operations which increase the density of the compacts to about 100 percent of theoretical density for comparable bar stock.
  • FIGS. 3 through 5 portray certain relationships determined from the heat treating process of the present invention as applied to a ferrous metal powder isostatically compacted to a nominal density of 6.3 grams per cc for each compact tested.
  • Each compact weighed 295 grams, and the powder used was of a water atomized type marketed by A. O. Smith-Inland'as 4,600 powder with 0.35 percent graphite added.
  • the properties of this type of powder are represented in Table 1 below:
  • the powder compacts produced as above were subjected to a range of preheating temperatures ranging from 200 F to l,000 F (temperature of skin surface of compact at end of preheating treatment), and compacts within each temperature range were heated for time periods varying from one minute to twenty minutes.
  • the effects of these various preheating treatments are depicted in FIG. 4 wherein line 10 represents a plotted line determined from preheating times of l, 5, l0, l5, and minutes to a compact surface tempera ture of 200 F.
  • lines I2, 14, 16, 18, 20 and 22 of FIG. 4 represent averages obtained for preheating of compacts to the higher temperatures indicated on each line for the periods of time which can be plotted from the graph.
  • preheating to incubation time can be seen in terms of a substantial reduction in incubation time as preheating temperatures are increased.
  • results of the tests depicted in FIG. 4 would suggest that a commercial process would prefer a minimum preheating temperature of a com pact to about 300 F, although temperatures in the range of 400 to 500 F offer even more noticeable reductions in incubation time.
  • Incubation time was determined by rapidly moving a preheated compact to an induction field having a constant power density of 3.2 KW/in. and the end of the incubation period was defined to be when a 2 percent shift in power factor from the unincubated state had occurred between the power supply and the induction tank circuit.
  • FIG. 5 represents a temperature-time profile which shows a range of preheat times and temperatures which will produce a nearly complete elimination of incubation time for a 295 gram compact.
  • the enclosed area of the graph of FIG. 5 indicates a range of time and preheat temperature combinations which produce approximately 400 F surface temperatures for the compact material.
  • Incubation time within the enclosed area of the graph was nearly zero for induction heating treatment which included power densities at 1.6, 3.2, and 4.8 Kw/in
  • compacts have been preheated and allowed to cool to room temperature to test for reduction in incubation time in an induction field.
  • each compact is subjected to said heating and sintering treatments in a continuous process which subjects the compact to preheating of its surfaces to about 400 F, followed by rapid induction heating of the entire compact to about 2,300 to 2,400 F, followed by continued heating and sintering at about 2,300 F to 2,400 F, followed by an adjusting of the temperature of the entire compact to about 1,850 F, after which the compact is formed while hot and before there is a reoxidation of the material of which it is composed.
  • a process for increasing the rate at which ferrous metal powder compacts can be efficiently heated in an induction field comprising the steps of preheating the powder metal compact sufficiently to raise the temperature level of the material in its outer surfaces to at least 300F but less than the sintering temperature for the material, and thereafter subjecting the compact to an induction field which rapidly raises the temperature level of the material of the compact to a level at which the compact can be sintered.

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Mechanical Engineering (AREA)
  • Powder Metallurgy (AREA)
US00285965A 1972-09-05 1972-09-05 Process for heating and sintering ferrous powder metal compacts Expired - Lifetime US3779747A (en)

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JP (1) JPS5717041B2 (sv)
AU (1) AU470373B2 (sv)
BE (1) BE804426A (sv)
BR (1) BR7306517D0 (sv)
CA (1) CA1006717A (sv)
CH (1) CH586086A5 (sv)
DE (1) DE2342051C2 (sv)
FR (1) FR2197677B1 (sv)
GB (1) GB1407557A (sv)
IT (1) IT998333B (sv)
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Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3894892A (en) * 1972-09-05 1975-07-15 Gleason Works Process for heating and sintering ferrous powder metal compacts with radio frequency magnetic field
US3899821A (en) * 1973-08-09 1975-08-19 Kawasaki Steel Co Method of making metal piece having high density from metal powder
US3981725A (en) * 1974-03-06 1976-09-21 The Gleason Works Process and system for forming finished parts from powder metal
US4050932A (en) * 1975-04-07 1977-09-27 General Motors Corporation Colloidal graphite forging lubricant and method
US4051590A (en) * 1972-10-19 1977-10-04 Cincinnati Incorporated Method for hot forging finished articles from powder metal preforms
US4414028A (en) * 1979-04-11 1983-11-08 Inoue-Japax Research Incorporated Method of and apparatus for sintering a mass of particles with a powdery mold
US5134260A (en) * 1990-06-27 1992-07-28 Carnegie-Mellon University Method and apparatus for inductively heating powders or powder compacts for consolidation
US5157232A (en) * 1990-05-18 1992-10-20 Tocco, Inc. Method and apparatus for inductively heating asymmetrically shaped workpieces
US5403540A (en) * 1990-10-29 1995-04-04 Corning Incorporated Heating of formed metal structure by induction
US20040005237A1 (en) * 2000-07-20 2004-01-08 Fuping Liu Post-delubrication peening for forged powder metal components
CN111375758A (zh) * 2020-04-23 2020-07-07 王伟东 一种钛或钛合金粉末的烧结方法

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JPS5538983A (en) * 1978-09-13 1980-03-18 Sumitomo Electric Ind Ltd Production of high density powder molding by powder hot forging process
JPS5554503A (en) * 1978-10-13 1980-04-21 Toyota Motor Corp Production of powder forging
FR2502640B1 (fr) * 1981-03-24 1986-02-28 Do Nii Chernoj Metallurgii Procede d'obtention de fer spongieux, four pour sa mise en oeuvre et fer obtenu par ledit procede
JPS57192202A (en) * 1981-05-22 1982-11-26 Toyota Motor Corp Rapid manufacturing method of sintered product
US4435213A (en) * 1982-09-13 1984-03-06 Aluminum Company Of America Method for producing aluminum powder alloy products having improved strength properties
DE3530741C1 (de) * 1985-08-28 1993-01-14 Avesta Nyby Powder AB, Torshälla Verfahren zur Herstellung pulvermetallurgischer Gegenstaende
DE102012208170A1 (de) * 2012-05-16 2013-11-21 Fct Anlagenbau Gmbh Vorrichtung zur Wärmebehandlung eines Werkstücks

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US3331686A (en) * 1964-09-29 1967-07-18 Ilikon Corp Method of heating and forming powdered metals
US3708645A (en) * 1971-10-12 1973-01-02 Park Ohio Industries Inc Method of heating a workpiece of particulate material

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DE592278C (de) * 1928-10-17 1934-02-05 Deutsch Englische Quarzschmelz Verfahren zum Schmelzen von anorganischen Stoffen, die Leiter zweiter Klasse sind, im elektromagnetischen Hochfrequenzfeld
US2228600A (en) * 1938-10-05 1941-01-14 Hardy Metallurg Co Powder metallurgy
US3270102A (en) * 1964-12-23 1966-08-30 Ken Mar Clay Products Ltd Method and apparatus for the production of hardened clay products
US3464252A (en) * 1965-01-25 1969-09-02 Gen Dynamics Corp Method and apparatus for powdered metal forming
DE2024064A1 (en) * 1970-05-16 1971-11-25 Mitsubishi Metal Mining Co Ltd Drop forging of sintered iron alloy for high density

Patent Citations (2)

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Publication number Priority date Publication date Assignee Title
US3331686A (en) * 1964-09-29 1967-07-18 Ilikon Corp Method of heating and forming powdered metals
US3708645A (en) * 1971-10-12 1973-01-02 Park Ohio Industries Inc Method of heating a workpiece of particulate material

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Title
Wick, C. H. Forging Gears From Powder Metal Preforms, in Machinery and Production Engineering, 117; pp. 668 670, 1970. TJI. M17 *

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3894892A (en) * 1972-09-05 1975-07-15 Gleason Works Process for heating and sintering ferrous powder metal compacts with radio frequency magnetic field
US4051590A (en) * 1972-10-19 1977-10-04 Cincinnati Incorporated Method for hot forging finished articles from powder metal preforms
US3899821A (en) * 1973-08-09 1975-08-19 Kawasaki Steel Co Method of making metal piece having high density from metal powder
US3981725A (en) * 1974-03-06 1976-09-21 The Gleason Works Process and system for forming finished parts from powder metal
US4050932A (en) * 1975-04-07 1977-09-27 General Motors Corporation Colloidal graphite forging lubricant and method
US4414028A (en) * 1979-04-11 1983-11-08 Inoue-Japax Research Incorporated Method of and apparatus for sintering a mass of particles with a powdery mold
US5157232A (en) * 1990-05-18 1992-10-20 Tocco, Inc. Method and apparatus for inductively heating asymmetrically shaped workpieces
US5134260A (en) * 1990-06-27 1992-07-28 Carnegie-Mellon University Method and apparatus for inductively heating powders or powder compacts for consolidation
US5403540A (en) * 1990-10-29 1995-04-04 Corning Incorporated Heating of formed metal structure by induction
US20040005237A1 (en) * 2000-07-20 2004-01-08 Fuping Liu Post-delubrication peening for forged powder metal components
CN111375758A (zh) * 2020-04-23 2020-07-07 王伟东 一种钛或钛合金粉末的烧结方法

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AU470373B2 (en) 1976-03-11
BE804426A (fr) 1974-03-04
ZA734867B (en) 1975-02-26
JPS4986205A (sv) 1974-08-19
IT998333B (it) 1976-01-20
DE2342051C2 (de) 1985-01-17
FR2197677A1 (sv) 1974-03-29
JPS5717041B2 (sv) 1982-04-08
FR2197677B1 (sv) 1978-03-10
AU5862273A (en) 1975-01-30
CH586086A5 (sv) 1977-03-31
SE396563B (sv) 1977-09-26
BR7306517D0 (pt) 1974-06-27
GB1407557A (en) 1975-09-24
DE2342051A1 (de) 1974-05-09
CA1006717A (en) 1977-03-15

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