US3733171A - Apparatus and method for firing magnetic cores - Google Patents

Apparatus and method for firing magnetic cores Download PDF

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Publication number
US3733171A
US3733171A US00135980A US3733171DA US3733171A US 3733171 A US3733171 A US 3733171A US 00135980 A US00135980 A US 00135980A US 3733171D A US3733171D A US 3733171DA US 3733171 A US3733171 A US 3733171A
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tube
parts
gas
cores
heating
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US00135980A
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English (en)
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R Sisolak
J Bryant
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Electronic Memories and Magnetics Corp
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Electronic Memories and Magnetics Corp
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    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/64—Burning or sintering processes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J6/00—Heat treatments such as Calcining; Fusing ; Pyrolysis
    • B01J6/001—Calcining
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/26—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on ferrites

Definitions

  • Another method which has been used for heat treating the cores involves the use of a platinum belt that extends through a furnace to carry individual cores thereon. While this apparatus enables a more rapid cycle time such as one or two minutes, it still has many disadvantages. A cycle time of l or 2 minutes still means that a large number of cores may be improperly sintered before the furnace settings are altered, even where samples are quickly tested at the output end of the belt. Another disadvantage is that uncontrolled amounts of air can leak into the furnace through the openings where the belt enters and exits, and that cores lying near the center of the belt may be heat treated differently than those near the edge of the belt, so that close control of sintering is difficult. A further problem is that the platinum belt wears and ages, and its cost of replacement is high.
  • cores may occasionally stick to the belt or fall off the belt inside the kiln and, when they finally drop off into the collecting box after undergoing numerous heat treat cycles, they may be misshapen and tend to clog the testing apparatus in addition to having unsatisfactory electrical properties.
  • An object of the invention is to provide-heat treating apparatus for small parts, that can be constructed, operated, and maintained at relatively low cost.
  • Another object is to provide heat treating apparatus for small parts that'enables very close control of the heating cycle even atvery high production rates.
  • Yet another object is to provide a method for the heat treating of small parts, which is rapid and economical, and which enables very close control.
  • an apparatus and method for the economical and high precision heat treating of small parts, and particularly for the sintering of magnetic cores.
  • the apparatus includes a tube of platinum or other high temperature-resistant material that extends substantially vertically through a furnace. Parts are dropped into a portion of the tube above the furnace and collected as they emerge from a location below the furnace.
  • a pressured gas is applied to the upper end of the tube, and is regulated to flow at a controlled rate through the tube. The flow rate is adjusted so that the cores fall through the tube at a controlled rate, to thereby control the period during which each core is maintained in the heated region of the tube.
  • Another gas inlet is provided near the bottom of the tube, below the central heated portion but above the exit where heat treated parts emerge. A cooling gas is admitted into this inlet to provide a controlled atmosphere for cooling the cores before they drop into the collecting box.
  • the heat treating apparatus can be constructed at relatively low cost, inasmuch as there are no moving parts in the high temperature zone of the furnace, except for the parts being heat treated.
  • the magnetic cores can be sintered in a short time, such as several seconds, so that high production and close control can be achieved.
  • the atmosphere in the tube can be closely controlled to provide highly uniform results.
  • FIG. 1 is a sectional side view of heat treating apparatus constructed in accordance with one embodiment of the present invention
  • FIG. 2 is a view taken on the line 2-2 of FIG. 1;
  • FIG. 3 is an enlarged view of the region 3-3 of FIG.
  • FIG. 4 is an enlarged view of the region 44 of FIG. 2;
  • FIG. 5 is an enlarged section view of a portion of the tube of FIG. 1, showing the manner in which magnetic cores fall therethrough.
  • FIG. 1 illustrates heat treating apparatus, including a kiln 12, a parts feeder 14 for feeding small magnetic cores or other small parts into the kiln, and a box 16 for collecting the cores after they pass through the kiln.
  • the kiln includes a vertically-extending carry tube 18, a vertically-extending shroud tube disposed about the carry tube, and numerous heating elements 22 disposed along most of the length of the tubes.
  • a firebrick insulation column 24 surrounds the tubes and the center portions of the heating elements, and a steel frame 26 encases the firebrick column.
  • the parts feeder 14 is normally filled with green, or unsintered, magnetic cores, and it drops them into an upper portion 28 of the carry tube for free fall through the tube. During such free fall, the cores are exposed to intense heat, inasmuch as a long center portion of the carry tube 18 is heated. When the cores emerge at a lowerportion 30 of the tube, they have been fully heat treated and are ready to be tested and thereafter installed in electronic equipment.
  • the cores would not fall through the tube. This is because the intensly heated carry tube 18 acts like a chimney to create a strong updraft therethrough.
  • gas from a pressured gas source 32 is connected through a volume flow regulator 34 to the upper portion 28 of the carry tube 18 to pump gas downwardly through the tube. This allows cores fed into the tube by the parts feeder 14 to fall therethrough and exit at the lower end 30 into the box 16.
  • the flow regulator 34 not only allows the cores to fall down through the tube, but enables a relatively close control of the rate at which gas flows through the carry tube 18.
  • a control of the flow rate of gas results in control of the rate at which the cores fall through the tube. This is because the cores are amall, so that they have a high air resistance-to-weight ratio. Accordingly, their free fall speed can be readily controlled by controlling the rate of movement of the atmosphere through which they fall.
  • Another gas source 36 is coupled to the lower portion 30 of the carry tube below the heated central portion thereof, to introduce a cooling gas. The cooling gas helps to cool the cores prior to their emergence at the extreme lower end of the carry tube into the box 16.
  • the gas sources 32 and 36 that are coupled to the carry tube 18 not only serve to control the rate of descent of cores through the tube and to cool the cores, but also enable close control of the atmosphere during the process. That is, these gas sources enable a selection of the type of atmosphere that surrounds the cores during heating and cooling.
  • Magnetic cores may be constructed of a variety of materials, and each may require a different atmosphere during heat treating. For example, magnesium-manganese-ferrite cores require an oxidizing atmosphere during firing, but a neutralizing atmosphere during cooling.
  • the pressured gas source 32 that is connected to the upper end of the carry tube may supply oxygen mixed in a predetermined ratio with other gas components, while the gas source 36 connected to the lower end of the tube may be nitrogen. In many cases, the gases may be air, so that the pressured gas source 32 is a pump and the lower gas source 36 is merely an opening into the ambient atmosphere.
  • FIG. 4 illustrates the region where the lower portion 30 of the carry tube 18 is connected to a cooling feed tube 38 that carries the cooling gas from the gas source 36.
  • the cooling feed tube 38 is coupled to the carry tube 18 to extend with a downstream directional component, so that a partial pressure is created in the feed tube 38. This allows air from the ambient atmosphere to be sucked into the feed tube 38 where the feed tube is merely open to the atmosphere instead of being connected to a pressurized gas source.
  • the carry tube 18 It is generally necessary that the carry tube 18 extend in a primarily vertical direction. Tests have been conducted using a carry tube oriented horizontally and with air pressure applied to one end to blow small parts therethrough. However, it was found to be extremely difficult to closely control the rate at which the parts move through the tube, particularly if it is desired to move them slowly through the tube. It is desirable to orient the carry tube so that it extends primarily in a vertical direction rather than a horizontal direction, at least along the center portion that is heated. Satisfactory kilns have been constructed where the carry tube extends within several degrees of the vertical.
  • the tendency to a strong updraft through the carry tube 18 can be prevented by blocking the lower portion 30 of the carry tube to the ambient atmosphere, as by connecting the lower portion 30 to a sealed box 16.
  • Cores have been dropped into such apparatus, and they can fall through the carry tube in that case.
  • the atmosphere in the carry tube quickly becomes unsatisfactory, largely due to the depletion of oxygen by the cores.
  • the process becomes unsatisfactory, even in the case of cores that can be fired and cooled in air.
  • some air can leak into the upper end of the carry tube through a parts feed tube 40 that connects the parts feeder 14 to the carry tube 18. Where such leakage is considered a problem, the parts feeder 14 can be enclosed in an airtight case to prevent air leakage.
  • a vibratory parts feeder may be employed which is of small size, so that such encasing is easily accomplished.
  • the kiln 12 is constructed to define four different heating zones 41, 42, 43, and 44 along the central length of the carry and shroud tubes 18, 20.
  • Three baffles 48 between the firebrick column 24 and shroud tube 20 seal the heating zones from one another.
  • Four thermocouples 50 connected to meters (not shown) measure the temperature of the shroud tube 20 near the top of each heating zone.
  • the heating elements 22 can be silicon carbide rods of the type which have a high electrical resistance at the center portions thereof which lie near the shroud tube 20.
  • the temperature of each zone can be closely controlled by regulating the current delivered to the heating elements within the zone. The provision of several heating zones enables more complex heat treating processes to be carried out.
  • the shroud tube 20 is constructed of a high heatresistant material such as alumina.
  • the carry tube 18 is preferably constructed of a heat-resistant material which is highly resistant to corrosion, such as platinum. The cost of a platinum tube is minimized because the carry tube 18 is of small diameter.
  • the heat treating of the magnetic cores is typically carried out at temperatures such as 2,300 to 2,400 F, and sometimes at a temperature several hundred degrees higher. At these temperatures, large amounts of heat can be transferred by radiation. Accordingly, the heating elements 22 heat the shroud tube 20, the shroud tube 20 heats the carry tube 18, and the carry tube 18 heats the cores passing therethrough, all largely by radiation.
  • FIG. 5 illustrates the manner in which magnetic cores 54 fall through the carry tube 18.
  • the great heating of the atmosphere flowing through the carry tube creates air currents and these plus the variable air resistance of the tumbling cores causes the cores to move in a random manner to different positions within the tube, sometimes bouncing gently ofi the walls of the tube.
  • all surfaces of the cores are exposed to heat, both by radiation from the heated tube 18, and by conduction from the heated atmosphere surrounding the cores.
  • all cores are heat treated nearly identically, and the heat treatment is applied to all regions of the cores.
  • the inside diameter D, of the tube is much larger than the diameter D, of the cores. This allows the cores to tumble freely and to bounce off the walls of the tube 18 only occasionally. It is generally desirable that the diameter D, of the tube be at least four times as great as the largest linear dimension of the parts passing therethrough.
  • Heat treating apparatus has been constructed utilizing a kiln having a length L of about eight feet and employing a platinum carry tube 18 with an inside diameter of about one-fourth inch. Cores of a diameter such as one-fifieth inch were heat treated by passing them through the kiln. The rate of gas flow through the carry tube was regulated so that it required about three seconds for the cores to pass through the heated portion, of about 7 feet in length, of the carry tube. This is about four times as long as it would require for an object to fall the same distance in a vacuum. Thus, a kiln of moderate length can be employed to heat treat free falling parts, even where the heat treating is to be carried out over a period of a few seconds.
  • Core testing equipment can be provided to test samples of cores soon after they emerge from the lower portion 30 of the carry tube.
  • the results of the sample test can be utilized to alter the temperatures in the kiln, the flow rate through the flow regulator 34, or other conditions.
  • the fact that the cycle time during which the cores are heated is short, often being only a few seconds, means that corrections can be made rapidly and before too many additional cores have been heat treated, for a given production rate.
  • the small size of the apparatus also enables conditions to be changed rapidly.
  • the heat treating apparatus of this invention has numerous advantages over the apparatus heretofor conventionally used in the heat treatment of small parts, and particularly magnetic cores, wherein the cores were carried on belts or saggers through a furance.
  • the short cycle term enables very high production rates, such as. several million cores per hour, even with the relatively small kiln described above.
  • Samples of the cores can be cycled and tested, and adjustments can be quickly made in the apparatus.
  • Closely uniform heat treating is applied to all of the cores and to the different parts of each core. This may be compared with apparatus wherein cores are carried on belts or the like, and wherein cores near the edges of the belt may be heated differently from those near the middle, and where the lower part of the core that rests on the belt may not be heated in the same manner as the opposite side which is directly exposed to the heat.
  • the apparatus of this invention enables close control in a simple manner, of the atmospheres in which the cores are heated and cooled.
  • the apparatus has no parts moving within the high temperature portion of the kiln, except for the cores themselves, so that construction and upkeep is minimized.
  • the invention provides a relatively simple apparatusand method for the heat treating of parts, and particularly the sintering of magnetic cores, by the use of a tube with a heated central portion for carrying the cores in substantially free fall.
  • the rate of fall of the cores as well as the atmosphere in which they are heated, is controlled by controlling the admittance of a pressurized gas into an upper end portion of the tube. Cooling of the cores prior to their falling into a collecting box or the like is encouraged by coupling a tube to the lower portion of the carry tube at a location above the core exit, to admit cooling gases.
  • the cooling tube may be exposed to the ambient atmosphere, or may be coupled to a supply of a desired gas, and the pressure or flow rate of cooling gas can also be controlled.
  • Apparatus for heat treating small parts comprising: an elongated tube having first and second end portions and having a parts inlet and a parts outlet at said first and second end portions, respectively; means for heating a center portion of said tube; means for supporting said tube to extend in a primarily vertical direction, with said first end portion above said second end portion; and means coupled to said first end portion of said tube for supplying pressured gas to flow through at least said center portion of said tube, including a source of pressured gas and a volume flow regulator coupling said source to said tube to control the volume rate at which gas flows into said tube, whereby to control the time of passage of said parts through said heated center portion.
  • a method for heat treating small parts comprising: dropping said parts into a primarily vertically extending tube; heating at least a predetermined portion of said tube;
  • a method for heat treating small parts comprising: dropping said parts into a primarily vertically extend ing tube; heating at least a predetermined portion of said tube;
  • Apparatus for heat treating small parts comprising:
  • parts feeding means for feeding parts individually into said first end portion of said tube, so that they fall through said tube spaced from one another;
  • Apparatus for heat treating small parts comprising:
  • a method for sintering green cores comprising:
  • Apparatus for heat treating small parts comprising:
  • said outer and inner tubes extend substantially vertically; and including means coupled to the upper end of said inner tube for forcing a gas downwardly therethrough.
  • said means for heating includes a plurality of separately controllable heating means spaced along said center portion of said outer tube, to create a plurality of separate heating zones.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Ceramic Engineering (AREA)
  • Organic Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Structural Engineering (AREA)
  • Materials Engineering (AREA)
  • Inorganic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Furnace Details (AREA)
  • Tunnel Furnaces (AREA)
US00135980A 1971-04-21 1971-04-21 Apparatus and method for firing magnetic cores Expired - Lifetime US3733171A (en)

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US (1) US3733171A (cs)
CA (1) CA970965A (cs)
DE (1) DE2219111C3 (cs)
FR (1) FR2133993B1 (cs)
GB (1) GB1391849A (cs)
NL (1) NL7205460A (cs)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000046166A1 (de) * 1999-02-04 2000-08-10 3M Espe Ag Verfahren zum dimensionstreuen sintern von keramik
CN108050844A (zh) * 2018-02-12 2018-05-18 湖北高磁新材料科技有限公司 一种磁芯烧成炉的送料装置
CN119594722A (zh) * 2024-11-28 2025-03-11 湖南艾迪奥电子科技有限公司 一种磁芯排胶烧结系统及烧结方法

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3302679C2 (de) * 1983-01-27 1994-08-11 Egon Koenn Aufklappbarer, elektrisch beheizter Präzisionsofen

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1132738A (en) * 1908-12-12 1915-03-23 Gustave Schwahn Retort and furnace.
US2806783A (en) * 1953-12-21 1957-09-17 Int Nickel Co Method and apparatus for reducing metal oxides
US2994522A (en) * 1960-06-02 1961-08-01 Indiana General Corp Process and apparatus for firing ceramic ferrites

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1132738A (en) * 1908-12-12 1915-03-23 Gustave Schwahn Retort and furnace.
US2806783A (en) * 1953-12-21 1957-09-17 Int Nickel Co Method and apparatus for reducing metal oxides
US2994522A (en) * 1960-06-02 1961-08-01 Indiana General Corp Process and apparatus for firing ceramic ferrites

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000046166A1 (de) * 1999-02-04 2000-08-10 3M Espe Ag Verfahren zum dimensionstreuen sintern von keramik
US20060082033A1 (en) * 1999-02-04 2006-04-20 Holger Hauptmann Process for the dimensionally-true sintering of ceramics
CN108050844A (zh) * 2018-02-12 2018-05-18 湖北高磁新材料科技有限公司 一种磁芯烧成炉的送料装置
CN119594722A (zh) * 2024-11-28 2025-03-11 湖南艾迪奥电子科技有限公司 一种磁芯排胶烧结系统及烧结方法

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DE2219111C3 (de) 1974-06-06
CA970965A (en) 1975-07-15
FR2133993B1 (cs) 1976-08-06
DE2219111B2 (de) 1973-11-08
NL7205460A (cs) 1972-10-24
DE2219111A1 (de) 1973-07-26
FR2133993A1 (cs) 1972-12-01
GB1391849A (en) 1975-04-23

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