Adjustable air gap ferrite structures and methods of manufacture

• US 4,523,170 A
• Filed: 11/05/1982
• Issued: 06/11/1985
• Est. Priority Date: 11/05/1982
• Status: Expired due to Fees

• Current Assignee: Spang & Company
• Original Assignee: Spang & Company
• Inventors: Huth, Joseph F. III
• Primary Examiner(s): Kozma, Thomas J.
• Application Number:
  US06/439,370
• Time in Patent Office: 949 Days
• Field of Search: 29/602 R, 29/607, 29/608, 29/606, 264/67, 264/DIG. 58, 336/83, 336/130, 336/132, 336/134, 336/135, 336/136, 336/233, 336/200, 338/87
• US Class Current: 336/83
• CPC Class Codes: H01F 21/06 by movement of core or part of core relative to the windings as a whole
• CPC Class Codes: H01F 41/0246 Manufacturing of magnetic circuits by moulding or by pressing powder magnetic cores made by moulding or by pressing powder H01F27/255; soft magnetic particles H01F1/20, H01F1/36
• CPC Class Codes: Y10T 29/49076 From comminuted material

Abstract

New fabricating methods and products are disclosed for manufacture and assembly of tunable-inductance magnetically-soft ferrite core assemblies. Pot core type elements are pressure molded from ferrimagnetic particles having residual reactivity; unitary helical threads are tapped in central openings of compacted core elements while in the green state; subsequent heat treatment converts the green compact to a ceramic. Use of a shrink tap provides compatibility of the unitary threads with the pre-threaded male adjustment members of the prior practice. A new assembly enables use of identical core half sections; provision is made for support at one or both longitudinal ends of the male tuning member.

Claims

1. Method for manufacturing a magnetically-soft ferrite core part to provide unitary means for accurately adjusting the inductance of an electrical inductance device which includes such core part, comprising

providing a substantially homogeneous mass of particulate ferrimagnetic material which is reactive when treated at elevated temperatures to form a magnetically-soft ceramic ferrite,

molding such ferrimagnetic material at elevated pressure to form a unitary greem compact, such green compact including

an elongated center post symmetrically distributed about a centrally located longitudinal axis,

a web portion extending in transverse relationship to such axis contiguous to one longitudinal end of such center post, and

a skirt portion extending from such web in spaced relationship from such center post and extending in an axial direction to define a space for receiving coil windings between such center post and such skirt portion,

such center post defining a central opening extending longitudinally with and substantially symmetrically about such longitudinal axis,

such central opening presenting interior wall surface means of circular cross section in a plane transverse to such longitudinal axis,

such interior wall surface means including a wall surface portion of reduced diameter with respect to the remainder of such interior wall surface means,

such reduced diameter wall surface portion being established during pressure compaction and being contiguous to such one longitudinal end of the center post from which such web portion extends,

forming unitary helical threads solely in such reduced diameter portion of the central opening interior wall surface means,

such helical threads being formed in such reduced diameter portion of such interior wall surface means of such pressure molded unitary green compact, and thereafter

sintering such green compact at elevated temperature to form a ceramic core part with unitary helical threads established along at least a predetermined portion of its central wall surface means extending longitudinally along its central opening within its center post for receiving an externally-threaded nonmagnetic portion of an elongated male tuning member when such tuning member is inserted axially into such central opening,

such externally-threaded nonmagnetic portion of such male tuning member presenting threads of predetermined specifications,

the unitary helical threads in such portion of the central opening wall surface means of the pressure molded unitary green compact being formed with predetermined specifications to compensate for shrinkage of such unitary green compact during sintering so as to accommodate such threads of predetermined specifications presented by such externally-threaded nonmagnetic portions of such male tuning member.

2. A magnetically-soft ferrite pot core part produced in accordance with the method of claim 1.

3. A magnetically-soft ferrite pot core assembly with adjustable air gap comprising, in combination,

a pair of unitary core elements adapted to be assembled in contacting relationship, each such core element being formed from a single substantially homogeneous mass of ferrite material and including a center post symmetrical about a centrally located axis, a web extending from one end of the center post in transverse relation to such axis, and a skirt extending from the web in spaced relation to the center post defining a space for coil windings between the center post and the skirt,

each skirt terminating in a mating surface for contacting the corresponding mating surface on the other core element skirt,

the center post of each core element terminating in a distal surface with such distal surfaces being spaced axially from one another to define an air gap when the mating surfaces on the skirts of the pair of core elements are in contacting relationship,

each center post defining a central opening, symmetical about its centrally located axis, extending through the center post and presenting wall surface means,

such central openings being in axial alignment when the pair of core elements are assembled,

the central opening in the center post of one of the pair of core elements including

two axially aligned cylindrical sections of unequal diameter with the cylindrical section of larger diameter being located contiguous to the longitudinal end of such center post terminating in such distal surface,

unitary helical threads located in the remaining cylindrical section wall surface of smaller diameter which is located contiguous to the remaining longitudinal end of the center post from which such web portion extends, and

an elongated male tuning member including magnetic material and nonmagnetic material,

such male member being insertable axially within such axially alinged central openings to permit rotation about its central axis to adjust the magnetic characteristics of such air gap,

the elongated male tuning member including

a nonmagnetic head portion of circular cross section in a plane transverse to its longitudinal axis,

such head portion being located at one longitudinal end of such male tuning member,

a nonmagnetic shaft portion of circular cross section in a plane transverse to its longitudinal axis,

such shaft portion being of smaller diameter than such head portion and being located at the remaining longitudinal end of such male tuning member,

such shaft portion including helical threads of predetermined specifications on its exterior periphery contiguous to such remaining longitudinal end of such male tuning member,

the magnetic material of the elongated male tuning member comprising

a ferrite tuning slug having a cylindrical exterior configuration,

such tuning slug being axially aligned with and held between such head portion and such remaining longitudinal end of the elongated male tuning member,

thecentral opening in the remaining core element of such pair of core elements presenting throughout its axial length a thread-free cylindrical wall surface having a uniform diameter corresponding dimensionally to the diameter of the head portion of the elongated tuning member to provide frictional contact between such head portion and such thread-free cylindrical surface of such remaining core element, such that

the elongated male tuning member is held at one of its longitudinal ends by such head portions contacting such thread-free cylindrical surface of such remaining core element and is held at its opposite longitudinal end upon rotation of such male tuning member by cooperative engagement of such helical threads on such shaft portion of the elongated male tuning member with such unitary helical threads in such smaller diameter cylindrical wall surface of the core element having two cylindrical central opening sections of unequal diameter.