Classifications

• • 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
• • 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
  • B22F3/22—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip
  • B22F3/225—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip by injection molding
• • 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
  • 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
  • B22F3/1021—Removal of binder or filler
• • 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
  • B22F3/22—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip
• • 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
  • B22F2201/00—Treatment under specific atmosphere
  • B22F2201/10—Inert gases
• • 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
  • B22F2201/00—Treatment under specific atmosphere
  • B22F2201/20—Use of vacuum
• • 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

Definitions

• the present invention relates to a method of preparing a cemented carbide or a cermet alloy, and more particularly, it relates to a method of preparing a cemented carbide or a cermet alloy by shaping cemented carbide powder or cermet alloy powder into a prescribed configuration by an injection molding method, thereafter removing an organic binder and sintering the compact.
• a cemented carbide and a cermet alloy are materials having high melting points.
• a powder metallurgy method of press-molding or CIP-molding a powder raw material and thereafter sintering the same has generally been employed.
• manufacturable configurations are significantly restricted.
• Japanese Patent Publication No. 62-33282 discloses a method of kneading metal powder or ceramics powder with an organic binder and shaping the same into an article having a complicated configuration by injection molding.
• Cemented carbide powder or cermet alloy powder is fine powder whose particle diameter is about 1 ⁇ m. Further, such an alloy has large gravity. In addition, tolerance for carbon concentration in the alloy is small. Due to such material properties of the cemented carbide or the cermet alloy, deformation and imperfection are easily caused during debinder processing. Besides, it is impossible to obtain an alloy of good quality, due to an influence exerted by residual carbon which is caused by decomposition of the organic binder. In order to avoid such problems, it is necessary to perform debinder processing for an extremely long time. Due to presence of the aforementioned problems, an injection molding technique for a cemented carbide and a cermet alloy has not yet been substantially put into practice.
• An object of the present invention is to provide a method which can obtain a cemented carbide or a cermet alloy of high quality by efficiently shaping cemented carbide powder or cermet alloy powder by an injection molding method, and through subsequent debinder processing and sintering processing.
• Another object of the present invention is to provide a method which causes no deformation and imperfection of a compact in debinder processing.
• Still another object of the present invention is to provide a method which can perform debinder processing in a short time.
• the method of preparing a cemented carbide or a cermet alloy to be the premise for the present invention comprises a step of mixing/kneading cemented carbide powder or cermet alloy powder with an organic binder, a step of shaping this mixed powder into a prescribed configuration by an injection molding method, and a step of thereafter removing the organic binder from the compact and sintering the same.
• the removal of the organic binder is first performed in an inert gas atmosphere as a first removal step, and then performed in a vacuum with a pressure of less than 1 Torr (1.3 10 ⁇ 3 bar) in continuation as a second removal step.
• the organic binder contains a plurality of types of binders, which are divided into a group removable under a low temperature and a group removed under a high temperature.
• Compositions of the respective binders contained in the organic binder are selected to satisfy such a condition that the loss rate of the high-temperature removal group is within 5 % when the low-temperature removal group is lost by 30 % of the whole in an inert gas atmospheric pressure heating loss test (TG) for only the organic binder.
• TG inert gas atmospheric pressure heating loss test
• the rate of the binder belonging to the low-temperature removal group with respect to the overall organic binder is set to be at least 30 % and not more than 90 %.
• a temperature for transition from the first removal step to the second removal step is selected to satisfy the following condition:
• the condition is such a condition that the amount of removal of the binder belonging to the low-temperature removal group is at least 30 % with respect to the overall organic binder, while the residual rate of the binder belonging to the high-temperature removal group is at least 5 % with respect to the overall organic binder.
• a binder for serving as the main component of the low-temperature removal group is preferably prepared from wax having hydrophilic polar groups, with a melting point of not more than 80°C. Sintering is preferably performed in a vacuum under a pressure of not more than 0.05 Torr (6.6 10 ⁇ 5 bar).
• the compact may be once cooled after the organic binder is removed, to be thereafter sintered.
• An injection-molded compact is formed by powder and a binder, substantially with no voids.
• the binder first escapes by expansion of the binder, and then debindering progresses due to evaporation from the surface.
• debindering of 30 % progresses by such a process, pores communicating with the surface are formed in the interior of the compact. Gas generated in the interior of the compact is removed through the pores, to further promote debindering. However, if the gas is generated in the interior of the compact in a debindering state of less than 30 %, the compact is cracked or blistered.
• Wax for serving as a plasticizer and high polymer resin for serving as a binder are required as the binders. Since wax evaporates at a low temperature with no decomposition, it is possible to relatively easily perform debindering. On the other hand, high molecular weight polymer resin is apt to cause imperfection in the compact in an initial stage of debindering, since the same generates a large quantity of gas by decomposition.
• high molecular weight polymer resin which will start no decomposition even if the temperature reaches such a level that the wax is removed by at least 30 % of the whole, and this high molecular weight polymer resin is mixed with the wax.
• debindering of at least 30 % is facilitated by evaporation of the wax alone, to form continuous pores in the interior of the compact. After the pores are formed, decomposition of the high polymer resin is made to start.
• Hoechst wax, carnauba wax, montan wax, ozokerite wax, auriculine wax, candelilla wax, beeswax, microcrystalline wax and the like can be cited as major wax materials of the low-temperature removal group.
• Low density polyethylene, low molecular weight polyethylene, ethylene-vinyl acetate, polypropylene, acrylic resin and the like can be cited as binders of the high-temperature removal group.
• the atmosphere pressure is maintained in excess of the atmospheric pressure, thereby preventing the compact from imperfection.
• the atmosphere pressure is brought into a decompressed state, or a state close to a vacuum, thereby facilitating evaporation of gas from the surface and desorption of gas generated in the interior of the compact.
• the debinder processing is performed in two stages of a first removal step and a second removal step.
• the first removal step is carried out under an atmospheric pressure atmosphere
• the second removal step is carried out under a vacuum atmosphere.
• the bonding agent In transition from the first removal step to the second removal step, the bonding agent must be left by at least 5 %. If the residual amount of the bonding agent is not more than 5 %, the compact will collapse before bonding strength is attained between the powder particles.
• the atmosphere for the debinder processing is now described.
• the first removal step is carried out in an atmosphere of inert gas such as N2 or Ar.
• an oxidizing atmosphere such as the air
• surface oxidation of Co, Ni and the like inevitably progresses during progress of the debindering. If such surface oxidized layers are present, bonding strength by reduction is inevitably lowered in the second removal step.
• carbon concentration in the alloy is ununiformalized and a liquid phase appearance temperature in sintering is ununiformalized, to significantly reduce dimensional accuracy.
• the types of wax are now described.
• the surface of cemented carbide powder or cermet alloy powder is hydrophilic.
• wax such as n-paraffin is hydrophobic. Therefore, wettability between wax such as n-paraffin and cemented carbide powder or cermet alloy powder is inferior.
• the inventors have studied various wax materials, to find that the amount of the binder can be reduced by employing a certain type of natural wax having hydrophilic polar groups.
• wax at least having a melting point of not more than 80°C. So far as the wax has hydrophilic polar groups with a melting point of not more than 80°C, its effect remains unchanged whether the same is a synthetic or natural one. While stearic acid or the like may be employed as a lubricant, the effect of the present invention remains unchanged even if such a minor additive is employed.
• WC powder having a particle diameter of 2 to 4 ⁇ m 80 % of WC powder having a particle diameter of 2 to 4 ⁇ m, 10 % of TiC powder having a particle diameter of 1 to 2 ⁇ m, and 10 % of Co powder having a particle diameter of 2 to 4 ⁇ m were mixed in a wet ball mill for 3 hours, and dried. 6.0 % of beeswax and 1.0 % of low molecular weight polyethylene were added to 100 % of this mixed powder, and these were kneaded at 120°C for 30 minutes. Then, this raw material mixture was cooled/solidified and thereafter pulverized, to prepare raw material particles of 0.5 to 2.0 mm in particle diameter.
• injection molding was performed with a mold (20 ⁇ 20 ⁇ 6 mm) having the configuration of a throw-away tip, to prepare a compact.
• the compact was arranged in a furnace, and the interior of the furnace was held at 1 atm. (1 bar) in an Ar atmosphere.
• the temperature in the furnace was raised up to 425°C at a programming rate of 8°C/h. under a condition of an Ar flow rate of 3 l/min., to perform debinder processing.
• the temperature in the furnace was raised up to 700°C at a programming rate of 50°C/h. in a state maintaining the interior of the furnace not more than 0.5 (0.7 mbar) Torr with a vacuum pump, and the furnace was held at the temperature for one hour, and thereafter cooled.
• the debinder processing was terminated. Then, the interior of the furnace was brought into a vacuum state of 0.05 (0.07 mbar) Torr and the temperature was raised up to 1400°C at 200°C/h., and the furnace was held at the temperature for one hour, and thereafter cooled.
• the as-formed sintered body had absolutely no imperfection, and was excellent in view of alloy characteristics.
• a heating loss test for the binders used in this Example was carried out whereby the beeswax was lost by 95 % before reaching 425°C under conditions of N2 and 1 atm (1 bar). On the other hand, the loss of the low molecular weight polyethylene was 13 % at 425°C.
• the interior of the furnace was under an Ar atmosphere of 1 atm. (1 bar), and its temperature was raised up to 430°C at a programming rate of 10°C/h. under a condition of a flow rate of 3 l/min., to perform initial debinder processing. Then, the temperature was raised up to 700°C at a programming rate of 50°C/h. while maintaining the interior of the furnace not more than 0.2 Torr (0.3 mbar) with a vacuum pump, and the furnace was held at the temperature for one hour. Thus, the debinder processing was terminated. Thereafter the temperature in the furnace was raised up to 1350°C at 200°C/h.
• the as-formed sintered body had absolutely no imperfection, and was excellent in view of alloy characteristics.
• a heating loss test was performed on the binders employed in this Example, whereby the carnauba wax was lost by 92 % before reaching 430°C under conditions of N2 and 1 atm (1 bar). On the other hand, loss of the low molecular weight polypropylene was 8 % at 430°C.
• WC powder having a particle diameter of 0.1 to 1 ⁇ m 6 % of Co powder having a particle diameter of 2 to 4 ⁇ m and 6 % of Ni powder having a particle diameter of 2 to 4 ⁇ m were mixed in a wet ball mill for 25 hours, and dried.
• 0.5 % of beeswax, 4.5 % of n-paraffin, 0.2 % of stearic acid, 0.5 % of ethylene-vinyl acetate and 1.0 % of low molecular weight polyethylene were added to 100 % of this mixed powder, and kneaded at 120°C for 30 minutes.
• this raw material mixture was cooled/solidified and thereafter pulverized, to prepare raw material particles of about 0.5 to 2.0 mm in particle diameter.
• injection molding was performed with a mold (20 ⁇ 20 ⁇ 6 mm) having the configuration of a throw-away tip.
• This compact was arranged in a furnace. The interior of the furnace was set in an N2 atmosphere of 1 atm. (1 bar), and its temperature was raised up to 380°C at a programming rate of 13°C/h. under a condition of a flow rate of 2 l/min., to perform initial debinder processing. Then, the temperature was raised up to 700°C at a programming rate of 50°C/h.
• the as-formed sintered body had absolutely no imperfection, and was excellent in view of alloy characteristics.
• a heating loss test was performed on the binders employed in this Example, whereby loss of the montan wax was 93 % before reaching 350°C under conditions of N2 and 1 atm. (1 bar), while loss of the low density polyethylene was 0 % on measurement at 350°C.
• Cermet powder (50 % of TiCN, 10 % of TaC, 12 % of Mo2C, 13 % of WC, 5 % of Ni and 10 % of Co) having a particle diameter of 0.5 to 1 ⁇ m was mixed in a wet ball mill for 10 hours, and dried. 7.8 % of montan wax, 2.7 % of n-paraffin, 2.7 % of low density polyethylene and 0.3 % of stearic acid were added to 100 % of this mixed powder, and kneaded at 120°C for 3 hours. Then, this raw material mixture was cooled/solidified and thereafter pulverized, to prepare raw material particles of about 0.5 to 2.0 mm in particle diameter.
• the interior of the furnace was brought into a vacuum of 0.05 Torr (0.07 mbar) and the temperature was raised up to 1400°C at 200°C/h., and the furnace was cooled after the same was held for one hour, and thereafter HIP processing was performed at 1350°C.
• the as-formed sintered body had absolutely no imperfection, and was excellent in view of alloy characteristics.
• a heating loss test was performed on the binders employed in this Example, whereby loss of the montan wax was 93 % under conditions of N2 and 1 atm. (1 bar) before reaching 350°C and loss of the n-paraffin was 100 %, while loss of the low density polypropylene was 0 % on measurement at 350°C.
• a plurality of raw material particle compacts were prepared under the same conditions as those in Example 1. With respect to these compacts, the programming rate in the first removal step of debinder processing and a transition temperature to the second removal step were changed, to examine states after debindering. Table 2 shows the results. Table 1 shows results of heating loss tests of beeswax and low molecular weight polyethylene (PE). As obvious from the results of Tables 1 and 2, excellent states are attained after debindering according to the inventive method, and debindering times can be shortened.
• PE low molecular weight polyethylene
• Table 1 Heating Loss Rate (N2 1 atm (1 bar), Temperature Rising at 10°C/min.) T 250°C 300°C 350°C 375°C 400°C 425°C 450°C 475°C Beeswax (xT) 0.03 0.12 0.32 0.50 0.74 0.95 0.99 1.00 Low Molecular Weight PE (yT) 0.01 0.03 0.05 0.07 0.09 0.13 0.30 0.85 Table 2 Test Result of Transition Temperature to Second Removal Step Test No. Transition Temperature to 2nd Removal step 1st Removal Step Programming Rate Beeswax Loss Rate a ⁇ xT PE Residual Rate b ⁇ (1-yT) State After Debindering 1 300 8°C/h.
• the present invention is effectively applied to a method of preparing a cemented carbide or a cermet alloy by shaping cemented carbide powder or cermet alloy powder into a prescribed configuration by an injection molding method and thereafter sintering the compact upon removal of an organic binder.

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• Manufacturing & Machinery (AREA)
• Mechanical Engineering (AREA)
• Powder Metallurgy (AREA)

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• 1990
  • 1990-09-12 EP EP90913553A patent/EP0443048B1/en not_active Expired - Lifetime
  • 1990-09-12 WO PCT/JP1990/001171 patent/WO1991004119A1/ja not_active Ceased
  • 1990-09-12 CA CA002041668A patent/CA2041668C/en not_active Expired - Fee Related
  • 1990-09-12 DE DE69015150T patent/DE69015150T2/de not_active Expired - Lifetime
  • 1990-09-12 KR KR1019910700490A patent/KR940009337B1/ko not_active Expired - Lifetime
  • 1990-09-13 TW TW079107703A patent/TW225493B/zh active

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