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MIM production at PAMCO
Stainless Steel Powder/MIM Production at PAMCO Pacific Metals Company (PAMCO) started life as a pig iron producer at Hachinohe in the north oOapan in 1957 under the original name ofNisso Steel Manufacturing Ltd using locally available iron sand as its source of raw material. However, within 10 years the availability of iron sand dwindled and the company began to diversify using its excellent seaport location to import ore, and the smelters previously used for pig iron, were converted for smelting first of ferromanganese and silicon- manganese, and later also ferronickel. In fact such is the scale of ferro nickel production at Hachinohe today that it merits the company o'perating its own ore carrier to transport raw material across the 'nickel highway' from New Caledonia, Philippines and Indonesia to Japan. It was the company's success with ferronickel - it is Japan's largest producer and ranks number 5 in the world - which also saw the introduction of stainless steel production, and with this further diversification came the name change in 1970 to Pacific Metals. In the same year the company expanded ferronickel
capacity. i.e. 13,000 tonnes/month, but that this would be increased during 1990 to around 20,000 tonnes/month with the construction of a new continuous casting plant. 60% of stainless steel output at Hachinohe is in the form of blooms, slabs, billets and ingots, which are further worked into sheet and bar. 30% is in the form of wire rod, and the remaining 10% in round bars and stainless steel powders.
POWDER PRODUCfION PAMCO first began to investigate the water atomization of 300 series stainless steel powders in the mid-1970s, starting at the outset with a facility developed in-house and based essentially on large scale atomization by using charges of 30 tons of refined ferro nickel and pig iron from one of the three ASEA-SKF furnaces which are transferred in a ladle to the two water atomization stations. Mr Yoshiyaki Kato, manager ofPAMCO's powder metallurgy section, told MPR that water atomization technology developed in-house allowed for
FIG. 1 ASEA-SKF furnace at Pacific Metals Co Ltd
the complete control of particle shape and size, thereby allOWing grades to be produced for PM 'parts, filters, and for usc as a refining additive in the company's own ferronickcl and ferrochrome production. Total powder production was said to be running at 150 tonnes/month of conventional stainless steel grades and a further 30 tonnes/month of other types of powders. One of the important advantages in operating an atomization plant on this scale is consistency and high productivity, but another major advantage is the source of the molten raw material, said Yoshiyaki Kato. He further stated that because no scrap is used at any stage in the smelting and refining process, purity of the water atomized stainless steel powders is guaranteed giving the powder superior compressibility, machinability and weldability, and corrosion resistance. PAMCO was one of the first companies to introduce high pressure water atomization into the mass production of powders in 1982 by incorporating a specially developed nozzle system and water pumps capable ofgenerating pressures up to 1000 kgf/cm z compared with conventional atomization pressures of 100 200 kgf/cm z. This allowed the company to produce bulk quantities of ultra-fine high alloy steel and stainless steel powders with an average particle size of less than 10 micron. The process has been further refined to allow pressures of up to 1500 kgf/cm z to be used for atomization of 30 tonne melts. Even at this high pressure the company states that it has complete control of particle shape
FIG. 2 Argon-oxygen-decarburization (AOD) converter instal/ed in the stainless steel plant
smelting capacity by constructing an Elkem 40,000 KVA closed furnace, which is said to be the largest of its type in the world, and shortly after an ASEA-SKF furnace (Fig.1), degassing unit, ADD converter (Fig.2) together with Mannesmann continuous casting units were added to make Hachinohe unique in its approach to a totally integrated facility for producing austenitic grades of stainless steels. On MPR's recent visit to PAMCO's huge facility, production of all types of stainless steel materials FIG. 3 Steam drying furnaces in PAMCO's modern powder finishing was said to be running at full plant 476
and size distribution. For example, one of the fine powder grades in production - PF20A - uses a special atomization system which provides advanced shape control thereby allowing the production by water atomization of powder particles with tap densities approaching those achieved in gas atomization. One application for such a powder is metal injection moulding. The care taken to produce a consistently pure and uniform water atomized powder in 30 ton batches is not lost in the finishing process such as drying, sieving. blending and packaging. These MPR June 1990
FIG. 4 Sieving station and charging ofpowder into coded 2.5 tonne stainless steel containers
homogenised in the container itself in a recently installed tumbling system (Fig.5). This avoids any risk of contamination with other powders or contact with air which was previously unavoidable. The final stage is also fully automated with the containers being packaged into 25 kg plastic bags or 250 kg drums (Fig.6). The finishing plant has the capacity to handle 300 tonnes/month of metal powders.PAMCO also uses two smaller atomization plants to produce smaller batches of special high alloy steel and other stainless steel grades at a rate of30 tonnes/month. These plants comprise a 1.5 ton vacuum induction melling furnace and a 500 kg induction furnace. Gas atomization is also used for some grades, but is considered too expensive for the fine stainless steel powders. The list of metal powders currently in production at PAMCO is conlinually being expanded. The 304 and 316 stainless steel
FIG. 5 Tumble mixer for homogenising powder mixes in storage containers has replaced the com'entionall0 tonne V-cone blender. The extensive storage area can also be seen operations arc done in a modern, clean (no sign of powder dust anywhere), facility where the moist powder is first dried in screw type steam furnaces (Fig.3) operating under high pressure at around 100C, or in a new type of furnace details of which are confidential but which provides significantly quicker drying. After drying the powder is fed into 2.5 ton capacity coded containers which in turn are automatically lifted above one of four sieving stations (Fig.4) to obtain the desired size fraction of powders, and then stored in racks. Screening of fine powders is done in two special Pulseair air classifiers having 50 kg/hr and 200 kg/hr capacity respectively. PAMCO produced around 250 tonnes of fine powders, mainly 304L stainless steel grade, during 1989. Computers arc used to store the data on each of the coded 2.5 tonne containers and when a particular grade is required an automatic retrieval system operating on rails collects the appropriate container, and delivers it to the blending station for homogenisation. Instead of feeding the powder into a V-cone blender as was previously the case, the powder is MPR June 1990
grades used in PM parts and filters, and flake used in paints, hai'e been supplemented by 400 series powders, 17-4' PH powder, nickel base alloy powders, iron-cobalt. Kovar, and high-speed steels.
METAL INJECfION MOULDING Two of the major problems associated with the metal injection moulding (MIM) process are (1) the requirement for a fine, spherical powder for the moulding feedstock, and (2) the high cost of fine powder when this is based on gas atomized stainless steel or carbonyl iron grades IIsed for MIM components. PAMCO's success in producing powders of less than 10 microns by its high pressure atomization process led it first to establish a small MIM facility at Hachinohe in 1985 to test its powders under production conditions. The
FIG. 6 Automatic packaging station for atomized pOIl-ders
FIG. 7 PAMCO's modern metal injection moulding facility showing three ofthe four40 ton Nissei moulding machines
477
FIG. 8 Selection of MIM parts
de~'eloped by PAMCD
FIG. 9 MIM parts used in spectacle frames made in Japan
FIG. 10 MIM parts used in watch bracelets and Il'atch cases
FIG. 11 The larger Tokyo Vacuum (lefl) and smaller Shimadzu mcuum furnaces used for MIM sinlering results were sufficiently encouraging for the company to decide to venture further with a mass production facility incorporating four MIM lines which was completed in July 1989 (Fig.7). Production of MIM parts was said to be of the order of 100,000 pieces per month based on a core of ten parts the weight of which varied from 0.2 g to 80 g. Some of the MIM parts in production are shown in Figs,8. 9 and 10 and include stainless steels, Fe. Fe-Ni and Fe-Co alloys and Kovar alloy for IC packages. Some nm'e1 but potentially important commercial applications for PAMCD MIM parts include stainless steel links in spectacle frames, links for watch straps, and watch cases. The company has also succeeded in producing a highly complex soft magnet printer head component for computer printers. 478
Mr Akira Kimura, director and deputy general manager of the Hachinohe works told MPR that the company did not see any conflict of interest between itself as a powder producer entering the field of MIM component production, and the PM parts industry which it supplied. He said that the quantities produced were still 'very small', and that MIM did not compete so much with conventional PM parts as with investment casting and machining. A striking feature of the new MIM plant is the 'cle:]n room' conditions in which parts are produced, and the high level of automation which has been introduced in the moulding operation. Yoshiyaki Kato stated that it was essential to automate production in order to improve productivity and to combat escalating labour costs in Japan. In the metal injection moulding process fine
metal powder is mixed with a patented binder based on polypropylene (10-15 vol %) by kneading to produce feedstock in pellet form. The pellets arc fed into the hopper of a 40 ton standard injection moulding machine where compacts arc moulded in cycle times ranging from 40 to 60 seconds. buring our visit to the plant we saw a robot remove the moulded parts from the die area, separate the parts from the runners· in this case small IC packages each weighing only 0.8 g, and deposit them into a sintering tray. When the tray reaches a predetermined weight, the system signals to a Starboy robot to come and collect the tray for transfer to one of the sintering furnaces sitpated in the adjacent room. The Starboy robot runs along magnetic tracks (see Fig,7) and can work untiringly for 24 hours a day, 7 days per week even in the dark. There are currently four 40 ton moulding machines in the MIM plant, and one of the other lines was seen producing the soft magnetic yokes for printer heads. Debinding ofthe MIM compacts is first done in one of four microprocess controlled air furnaces operating at 400 - 600C with the debinding cycle taking from less than a day to 2 days depending on the part's shape and weight. The 'brown' parts with densities of 50 to 60% are then transferred for sintering at temperatures of 1200 - 1500C in one of two vacuum furnaces (Fig.l1) to achieve densities typically greater than 95% of theoretical. A new pusher type furnace capable of continuous sintering of MlM parts at temperatures up to 1500C was in the process of being installed during our visit. Shrinkage during sintering was said to be a uniform 18% and is three dimensional and homogeneous. The dimensional precision of sintered MIM parts is within +/-0.3%. A small development facility in the MIM plant houses a Yokokagawa digital oscilloscope to test the magnetic properties of printer heads, two shadowgraphs are used to check part dimensions, and a thermal coeffiency tester is used for measurement of thermal expansion coefficients of semiconductor devices. The small powder metallurgy team at PAMCD led by Akira Kimura (Fig.12) has done an impressive job both with its powder production plant and the new MlM facility where modern PM technology pays homage to a small Buddha shrine perched above Mr Kimura's desk.
FIG. 12 Mr Akira Kimura, direclarand deputy general manager of the PAMCD Hachinohe Works
MPR June 1990
capacity. i.e. 13,000 tonnes/month, but that this would be increased during 1990 to around 20,000 tonnes/month with the construction of a new continuous casting plant. 60% of stainless steel output at Hachinohe is in the form of blooms, slabs, billets and ingots, which are further worked into sheet and bar. 30% is in the form of wire rod, and the remaining 10% in round bars and stainless steel powders.
POWDER PRODUCfION PAMCO first began to investigate the water atomization of 300 series stainless steel powders in the mid-1970s, starting at the outset with a facility developed in-house and based essentially on large scale atomization by using charges of 30 tons of refined ferro nickel and pig iron from one of the three ASEA-SKF furnaces which are transferred in a ladle to the two water atomization stations. Mr Yoshiyaki Kato, manager ofPAMCO's powder metallurgy section, told MPR that water atomization technology developed in-house allowed for
FIG. 1 ASEA-SKF furnace at Pacific Metals Co Ltd
the complete control of particle shape and size, thereby allOWing grades to be produced for PM 'parts, filters, and for usc as a refining additive in the company's own ferronickcl and ferrochrome production. Total powder production was said to be running at 150 tonnes/month of conventional stainless steel grades and a further 30 tonnes/month of other types of powders. One of the important advantages in operating an atomization plant on this scale is consistency and high productivity, but another major advantage is the source of the molten raw material, said Yoshiyaki Kato. He further stated that because no scrap is used at any stage in the smelting and refining process, purity of the water atomized stainless steel powders is guaranteed giving the powder superior compressibility, machinability and weldability, and corrosion resistance. PAMCO was one of the first companies to introduce high pressure water atomization into the mass production of powders in 1982 by incorporating a specially developed nozzle system and water pumps capable ofgenerating pressures up to 1000 kgf/cm z compared with conventional atomization pressures of 100 200 kgf/cm z. This allowed the company to produce bulk quantities of ultra-fine high alloy steel and stainless steel powders with an average particle size of less than 10 micron. The process has been further refined to allow pressures of up to 1500 kgf/cm z to be used for atomization of 30 tonne melts. Even at this high pressure the company states that it has complete control of particle shape
FIG. 2 Argon-oxygen-decarburization (AOD) converter instal/ed in the stainless steel plant
smelting capacity by constructing an Elkem 40,000 KVA closed furnace, which is said to be the largest of its type in the world, and shortly after an ASEA-SKF furnace (Fig.1), degassing unit, ADD converter (Fig.2) together with Mannesmann continuous casting units were added to make Hachinohe unique in its approach to a totally integrated facility for producing austenitic grades of stainless steels. On MPR's recent visit to PAMCO's huge facility, production of all types of stainless steel materials FIG. 3 Steam drying furnaces in PAMCO's modern powder finishing was said to be running at full plant 476
and size distribution. For example, one of the fine powder grades in production - PF20A - uses a special atomization system which provides advanced shape control thereby allowing the production by water atomization of powder particles with tap densities approaching those achieved in gas atomization. One application for such a powder is metal injection moulding. The care taken to produce a consistently pure and uniform water atomized powder in 30 ton batches is not lost in the finishing process such as drying, sieving. blending and packaging. These MPR June 1990
FIG. 4 Sieving station and charging ofpowder into coded 2.5 tonne stainless steel containers
homogenised in the container itself in a recently installed tumbling system (Fig.5). This avoids any risk of contamination with other powders or contact with air which was previously unavoidable. The final stage is also fully automated with the containers being packaged into 25 kg plastic bags or 250 kg drums (Fig.6). The finishing plant has the capacity to handle 300 tonnes/month of metal powders.PAMCO also uses two smaller atomization plants to produce smaller batches of special high alloy steel and other stainless steel grades at a rate of30 tonnes/month. These plants comprise a 1.5 ton vacuum induction melling furnace and a 500 kg induction furnace. Gas atomization is also used for some grades, but is considered too expensive for the fine stainless steel powders. The list of metal powders currently in production at PAMCO is conlinually being expanded. The 304 and 316 stainless steel
FIG. 5 Tumble mixer for homogenising powder mixes in storage containers has replaced the com'entionall0 tonne V-cone blender. The extensive storage area can also be seen operations arc done in a modern, clean (no sign of powder dust anywhere), facility where the moist powder is first dried in screw type steam furnaces (Fig.3) operating under high pressure at around 100C, or in a new type of furnace details of which are confidential but which provides significantly quicker drying. After drying the powder is fed into 2.5 ton capacity coded containers which in turn are automatically lifted above one of four sieving stations (Fig.4) to obtain the desired size fraction of powders, and then stored in racks. Screening of fine powders is done in two special Pulseair air classifiers having 50 kg/hr and 200 kg/hr capacity respectively. PAMCO produced around 250 tonnes of fine powders, mainly 304L stainless steel grade, during 1989. Computers arc used to store the data on each of the coded 2.5 tonne containers and when a particular grade is required an automatic retrieval system operating on rails collects the appropriate container, and delivers it to the blending station for homogenisation. Instead of feeding the powder into a V-cone blender as was previously the case, the powder is MPR June 1990
grades used in PM parts and filters, and flake used in paints, hai'e been supplemented by 400 series powders, 17-4' PH powder, nickel base alloy powders, iron-cobalt. Kovar, and high-speed steels.
METAL INJECfION MOULDING Two of the major problems associated with the metal injection moulding (MIM) process are (1) the requirement for a fine, spherical powder for the moulding feedstock, and (2) the high cost of fine powder when this is based on gas atomized stainless steel or carbonyl iron grades IIsed for MIM components. PAMCO's success in producing powders of less than 10 microns by its high pressure atomization process led it first to establish a small MIM facility at Hachinohe in 1985 to test its powders under production conditions. The
FIG. 6 Automatic packaging station for atomized pOIl-ders
FIG. 7 PAMCO's modern metal injection moulding facility showing three ofthe four40 ton Nissei moulding machines
477
FIG. 8 Selection of MIM parts
de~'eloped by PAMCD
FIG. 9 MIM parts used in spectacle frames made in Japan
FIG. 10 MIM parts used in watch bracelets and Il'atch cases
FIG. 11 The larger Tokyo Vacuum (lefl) and smaller Shimadzu mcuum furnaces used for MIM sinlering results were sufficiently encouraging for the company to decide to venture further with a mass production facility incorporating four MIM lines which was completed in July 1989 (Fig.7). Production of MIM parts was said to be of the order of 100,000 pieces per month based on a core of ten parts the weight of which varied from 0.2 g to 80 g. Some of the MIM parts in production are shown in Figs,8. 9 and 10 and include stainless steels, Fe. Fe-Ni and Fe-Co alloys and Kovar alloy for IC packages. Some nm'e1 but potentially important commercial applications for PAMCD MIM parts include stainless steel links in spectacle frames, links for watch straps, and watch cases. The company has also succeeded in producing a highly complex soft magnet printer head component for computer printers. 478
Mr Akira Kimura, director and deputy general manager of the Hachinohe works told MPR that the company did not see any conflict of interest between itself as a powder producer entering the field of MIM component production, and the PM parts industry which it supplied. He said that the quantities produced were still 'very small', and that MIM did not compete so much with conventional PM parts as with investment casting and machining. A striking feature of the new MIM plant is the 'cle:]n room' conditions in which parts are produced, and the high level of automation which has been introduced in the moulding operation. Yoshiyaki Kato stated that it was essential to automate production in order to improve productivity and to combat escalating labour costs in Japan. In the metal injection moulding process fine
metal powder is mixed with a patented binder based on polypropylene (10-15 vol %) by kneading to produce feedstock in pellet form. The pellets arc fed into the hopper of a 40 ton standard injection moulding machine where compacts arc moulded in cycle times ranging from 40 to 60 seconds. buring our visit to the plant we saw a robot remove the moulded parts from the die area, separate the parts from the runners· in this case small IC packages each weighing only 0.8 g, and deposit them into a sintering tray. When the tray reaches a predetermined weight, the system signals to a Starboy robot to come and collect the tray for transfer to one of the sintering furnaces sitpated in the adjacent room. The Starboy robot runs along magnetic tracks (see Fig,7) and can work untiringly for 24 hours a day, 7 days per week even in the dark. There are currently four 40 ton moulding machines in the MIM plant, and one of the other lines was seen producing the soft magnetic yokes for printer heads. Debinding ofthe MIM compacts is first done in one of four microprocess controlled air furnaces operating at 400 - 600C with the debinding cycle taking from less than a day to 2 days depending on the part's shape and weight. The 'brown' parts with densities of 50 to 60% are then transferred for sintering at temperatures of 1200 - 1500C in one of two vacuum furnaces (Fig.l1) to achieve densities typically greater than 95% of theoretical. A new pusher type furnace capable of continuous sintering of MlM parts at temperatures up to 1500C was in the process of being installed during our visit. Shrinkage during sintering was said to be a uniform 18% and is three dimensional and homogeneous. The dimensional precision of sintered MIM parts is within +/-0.3%. A small development facility in the MIM plant houses a Yokokagawa digital oscilloscope to test the magnetic properties of printer heads, two shadowgraphs are used to check part dimensions, and a thermal coeffiency tester is used for measurement of thermal expansion coefficients of semiconductor devices. The small powder metallurgy team at PAMCD led by Akira Kimura (Fig.12) has done an impressive job both with its powder production plant and the new MlM facility where modern PM technology pays homage to a small Buddha shrine perched above Mr Kimura's desk.
FIG. 12 Mr Akira Kimura, direclarand deputy general manager of the PAMCD Hachinohe Works
MPR June 1990