US3805378A

US3805378A - Manufacture of remanent reed switch

Info

Publication number: US3805378A
Application number: US00227762A
Authority: US
Inventors: W Archer; K Olsen; P Renaut
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1972-02-22
Filing date: 1972-02-22
Publication date: 1974-04-23
Anticipated expiration: 1991-04-23
Also published as: ATA158973A; NO136323B; BR7301238D0; DK143072C; JPS5642093B2; CA987892A; FR2173038B1; JPS4897044A; IL41586A; DE2307970A1; AR193572A1; SE393218B; AU5225873A; NO136323C; FR2173038A1; ZA731216B; NL160109B; NL160109C; AT337819B; CH567790A5

Abstract

A technique for the fabrication of a sealed remanent reed, selflatching magnetic switch is described. Appropriate magnetic properties are developed through a series of processing steps terminating first in a strand anneal of round wire; secondly a stamping operation which results in some mechanical working and, consequently, physical hardening of the magnetic alloy; and, finally, in a terminal phase-precipitation anneal.

Description

United States Patent [19] Archer et al.

[ 1 MANUFACTURE OF REMANENT REED SWITCH Inventors: Wendel Edward Archer, Gahanna,

Ohio; Karl Martin Olsen, Madison, N.J.; Paul William Renaut, Columbus, Ohio Bell Telephone Laboratories, Incorporated, Murray Hill, NJ.

Filed: Feb. 22, 1972 Appl. No.: 227,762

[73] Assignee:

U.S. Cl. 29/622, 200/166 CM, 335/153 Int. Cl. H0lh 11/00 Field of Search 29/622, 630C; 200/166 C,

References Cited UNITED STATES PATENTS 1/1968 Gould 335/153 Apr. 23, 1974 3,251,121 5/1966 Prival 29/622 3,369,291 2/1968 Shaffer 29/622 3,443,312 5/1969 Morigama 29/622 Primary Examiner-Charles W. Lanham Assistant ExaminerR0bert M. Rogers Attorney, Agent, or FirmG. S. lndig 5 7] ABSTRACT 12 Claims, 1 Drawing Figure BACKGROUND OF THE INVENTION 1. Field of the Invention Theinvention is concerned with the fabrication of a particular type of magnetic self-latching switch-generically known as ferreed." The particular type of concern utilizes the remanent magnetic material responsible for latching as a part of the reed structure which supports the contacting regions of the switch (in contrast to the more usual type in which the remanent member is external to the switch).

2. Description of the Prior Art The Bell System Technical Journal for January 1960 at page 1 et seq. describes a class of switching devices designated as ferreeds. These devices are characterized by sealed metallic contacts which are included within a magnetic circuit which also includes at least one remanent magnetic member. The remanent member/s which are switched, generally by means of an encircling wire coil, has sufficient remanent magnetization so that the contacts may be retained in either the opened or closed condition without continuous expenditure of energy.

At this time ferreed structures are in prevalent use throughout the world. They are of particular significance in modern telephony and many millions of these devices are in use in telephone electronic switching systerns.

The usual ferreed structure in use at this time involves a pair of magnetically soft reed members supporting contacting regions, with these reed members magnetically coupled to one or more remanent members generally external to the switch itself. Design variations suggested at about the time of the development of the prototype device include a simplified structure in which the reed members themselves include or are constructed of a remanent magnetic material (see Bell System Technical Journal, supra, and US. Pat. No. 3,059,075).

The inherent advantages of the remanent reed structure are manifold. Elimination of external remanent magnetic members inherently leads to fabrication economy as well as to size reduction. Under many circumstances, the internal remanent reed structure may be operated with some saving in power as well.

Despite the apparent advantages inherent in the internal remanentfreed structure it has not found prevalent commercial use. In general, continued manufacture of the more costly, larger structure using the external remanent circuitry is ascribed to certain manufacturing difficulties associated with the remanent reed device. Theprimary difficulty involves the actual formation of the reed. This operation desirably takes the form of a simple stamping (involving flattening of a round wire form )Qlt has been found that this operation, as carried out on material of appropriate magnetic properties, frequently results in sufficient embrittlement to cause fracture.-

The foregoing assumes use of an alloy composition generally known as Remendur. This material is nominally 50-50 cobalt-iron alloy with small vanadium addition. Development of the appropriate remanence (of the order of at least 10,000 gauss) involves one or more hardening operations.

SUMMARY OF THE INVENTION A series of critical processing steps-permits expedient fabrication of a sealed remanent reed, self-latching magnetic switch structure. Processing terminates in a sequence of a wire strand anneal (sometimes supplemented by slight mechanical working), followed by a stamping operation and, finally, by a phaseprecipitation anneal. Detailed parameters for these three procedures as well as for preliminary procedural steps are described in the Detailed Description.

The composition utilized for the remanent portion of the reed (and the entirety of one or more reeds may be of such material) is the usual Remendur composition, i.e., 40 to parts by weight cobalt, 25 to 60 parts by weight iron, and l to 5- parts by weight vanadium. Preferred compositions as well as possible minor additives are specified under Section 2' of the Detailed Description.

The nature of the fabricated Remendur reed, particularly its surface characteristics, have, in the past, given rise to an additional problem, i.e., formation of a durable hermetic seal where the reed emerges from the capsule. A preferred embodiment of the invention is directed to the materials and procedure for overcoming this difficulty.

BRIEF DESCRIPTION OF THE DRAWING The FIGURE is a front elevational view of a ferreed structure fabricated in accordance with the invention.

DETAILED DESCRIPTION 1. The FIGURE The FIGURE depicts a prototype remanent reed structure illustrative of those contemplated for fabrication in accordance with the invention. A detailed description of this device as well as a number of variations is contained in the aforementioned US. Pat. No. 3,059,075. The FIGURE depicts a glass envelope 1 containing two reeds, 2 and 3, each of which is provided with contacting

regions

4 and 5, respectively. The larger part of each of

reeds

2 and 3 is flattened from a round wire of the cross-sectional configuration retained by unflattened projecting portions 6 and 7. Such portions, 6 and 7, enter the envelope 1 through glass seal regions 8 and 9. While a variety of circuit arrangements are possible and variations are in actual use, the device depicted entails two separate windings, 10 and 11, the first of which, when suitably energized by means not shown, results in polarization of reed 2 in either of the two permitted directions while the second, coil 11, also when suitably energized by means not shown, results in polarization of reed 3. This particular arrangement, which, in more sophisticated variations, may involve overlapping coils, permits separate control of each of the reeds and is, therefore, adaptable to use in a cross-point array.

Operation of the device is simple. Polarization of

reeds

2 and 3 in the same direction (e.g., north-south from left to right) accomplishes closure while magnetization of

reeds

2 and 3 in opposite directions (e.g., north-south for reed 2 and south-north for reed 3, both from left to right) results in open circuit. As described above, the nature of the remanent material, of which at least a portion of at least one of

reeds

2 and 3 is constructed, is such that either closed circuit or open circuit may be maintainedwithout expenditure of energy, i.e., the remanent magnetization is sufficient to overcome the natural restoring forces of the structure and maintain closure.

Variations on the structure involve possible use of permanent bias of one'reed, for example, by constructing it of a permanent magnetic material which is not switched during operation or by use of a separate magnetic biasing element, incorporation of any number of additional reeds and/or contacts, and, as indicated, a variety of circuit arrangements.

2. Remanent Reed Composition It has been indicated that the remanent material utilized is a member of the class of materials sometimes referred to as Remendur. It has been indicated that the full range of this compositional class is from 40 to 75 parts by weight cobalt, 25 to 60 parts by weight iron, and l to parts by weight vanadium. Compositional variations as well as preferred ranges are set forth in U.S. Pat. No. 3,364,449. As there indicated, the nominal (and preferred) composition contains approximately equal amounts of cobalt and iron with a preferred range for the major ingredients being specified as from 45 to 65 parts cobalt, remainder iron. The preferred range of vanadium, included to control coercivity, is from 2 to 4 parts by weight based on 100 parts by weight of the three ingredients, cobalt, iron, and vanadium. Additional ingredients may include manganese contained to minimize the deleterious effect of any sulfur inclusion (ordinarily up to about one part by weight on the above basis) and possibly minor amounts of silicon and aluminum (either in amount of less than one part by weight on the above basis). These last two ingredients serve to bind oxygen which may also be deleterious in processing. In addition to the intentional ingredients set forth, there are tolerable amounts of ordinarily encountered impurities. Such impurities, the total amount of which does not exceed one part by weight on the above basis, may include nickel, carbon, copper, and sulfur.

3. Processing A. The Remanent Magnetic Material 7 The composition designated is known as Remendur only when possessed of such intermediate hardness as to result in a remanent magnetization of the order of at least 10,000 gauss. In a soft magnetic state, the composition is sometimes known as Permendur, while in its hardened state, it is sometimes known as Vicalloy. Development of the requisite degree of magnetic hardness necessarily entails both cold working and phase precipitation hardening. The invention is, in large part, based on the particular manner in which these procedural steps are carried out. While the most significant processing steps from the inventive standpoint are the terminal three steps (numbered 5 (or 5 plus 5A), 6 and 7), the following description specifies appropriate preliminary steps starting with the formation of the alloy composition itself.

Step I. A melt is prepared of initial ingredients. Suitable ingredients areelectrolytic cobalt, electrolytic iron, ferrovanadium (an alloy of vanadium and iron) and electrolytic manganese. The ingredients are melted (melt temperature about I550C). Temperature is maintained for a minute or two to ensure thorough mixing and an ingot is formed by cooling.

Step 2. The ingot is hot worked at a temperature between 900C and 1250C. Working may take the form of rolling, swaging, or extrusion. Hot working is continued to an expedient dimension, e.g., to a diameter of about one-fourth inch. This step ordinarily involves many passes.

Step 3. The hot worked body is softened by heating to a temperature of at least 750C and quenching at a rate sufficient to avoid significant phase precipitation. This is ordinarily accomplished by rapid immersion in ice brine. Room temperature is attained in a period of substantially less than 1 minute.

Step 4. The quenched rod is cold worked to the desired final dimension (cold drawing to a round wire diameter of from 50 to 10 mils is common).

Step 5. The first of the special procedures considered responsible for expedient device fabrication in accordance with the invention involves a strand anneal. in accordance with this step, the wire is softened by heat treatment to result in a tensile strength of a maximum of about 200,000 p.s.i. and an elongation of a minimum of about 10 percent. An illustrative treatment entails maintenance at a temperature over a range of from about 850C to l050C. Maintenance at this temperature should be for a minimum of at least about 5 seconds with the upper time limit being noncritical and determined on the basis of expedience. In accordance with one procedure found satisfactory, the wire is passed through a 3 foot hot zone at a rate of about 6 feet per minute thereby resulting in maintenance at a temperature approaching that of the zone for a period of about fifteen seconds. Immediately following this heating the wire is passed through a water cooled chamber to chill it at a rate fast enough to prevent phase precipitation and associated hardening. For a variety of reasons, this step is carried out in a reducing atmosphere, e.g., hydrogen or cracked ammonia. While in principle inert atmosphere is permissible, from a practical standpoint, it is more expedient to operate with a reducing atmosphere than to use that degree of care necessary to exclude minor quantities of oxidizing ingredients from commercial inert gases. The purpose of the reducing atmosphere or, more generally, of the non-oxidizing atmosphere, is to avoid formation of surface oxide, primarily vanadium dioxide, which, due to its abrasive qualities, results in rapid die wear during step 6. Use of such a non-oxidizing atmosphere is also desirable to provide a relatively clean surface for subsequent plating for contact formation as per B below.

Step 5a. While from the standpoint of device properties, a strand anneal, as described, is adequate to prepare the material for the cold working of Step 6, certain practical considerations may dictate a variation. For example, it has been observed that the final reed evidences differing magnetic properties as between the flattened portion which carried the contact and the still round portion desirably retained for sealing purposes. From the standpoint of manufacturing expedience, it may be desirable to so treat the reed as to make these properties more nearly equal. While this will have no significant effect on device operating characteristics, it may, for example, be expeditious by reason of such practical considerations as the specification of wire properties for the intermediate product which is about to undergo the processing specified in Step 6. A possible approach in this connection is to use a slightly hardened wire at this stage. This may result, for example, from a cold working following the strand anneal already specified at Step 5. This cold working, which would be sufficiently slight so as to permit the wire to be within the maximum allowable tensile strength values, might take the form of an area reduction of as little as 20 percent or possibly as great as 50 percent. This procedure is to be considered optional.

Step 6. This is a stamping operation. During this step, the round wire resulting from Step 5 or Step 5 and Step 5a is flattened to produce the enclosed region of the reed (while retaining the round crosssectional configuration of that portion of the member which is hermetically sealed to the envelope). This stamping operation may also include chopping the reed to desired length. Properties developed during Step 6 or processing advantages gained during Step 6 involve the flattening action only. Properties developed by the stamping operation include a coercivity of about 30 to 60 oersteds and remanent magnetization values of 7,000 to 10,000 gauss. Further improvement in properties are obtained by a phase precipitation treatment as described in Step 7.

Since the wire produced by the series of procedures terminating with Step 5 or Step 5a ordinarily evidence some curvature, it is usual to straighten the wire at this time. Ordinarily the wire leaving Step 5 or 5a is first straightened, then flattened, and finally chopped into the desired length, in that order. The effect of straightening on mechanical or magnetic properties is slight.

An additional minor mechanical treatment which may be carried out at this time involves barrel tumbling in liquids containing abrasive particles and/or other means for removing any burring or other surface irregularities produced ,by the mechanical stamping operation.

It has been observed in general that the degree of cold working during the stamping operation is of relatively small consequence with regard to the final developed characteristics. For example, starting with a round diameter of 21 mils, flattening to a 5 mil specimen on theone hand and 8or 9 rnils on the other resulted in no significant variation in final magnetic properties. in general, a thickness reduction of at least about 40 percent (representing the fraction of the least final cross-sectional dimension divided by the unflattened wire diameter) is-sufficient at this stage to result in properties adequate for device operation.

Step 7. The final processing step involves phase precipitation carried out at such temperature and for such time'as to develop the desired values of remanent magnetization and coercivity. For devices to which the invention is directed, it is generally desired that remanent magnetization lie within the range of from 10,000 gauss to 20,000 gauss, and that the coercivity lie within the range of from 10 oersteds to 50 oersteds. These values are a measure of the properties for both the round flattened portions of the reed. It has been determined that both magnetic characteristics result from heat treatment of the reed at temperatures within the range of from 550C to 670C for a period of from one-half to 6 hours. Extensive experimentation has indicated that excessively longer times and/or higher temperatures will result in a lowering of both the remanent magnetization and coercivity to values below the specified level. Shorter time and/or lower temperature results in retention of higher values of coercivity but does not cause development of desired remanent magnetization.

It has been indicated that a preferred embodiment involves the manner in which the protruding portion of the reed is hermetically sealed to the envelope. it has been indicated that use of a non-oxidizing or, preferably, a reducing atmosphere in Step 5, in avoiding formation of surface oxide, is of benefit in reed stamping and plating operations. In addition, it has been found that superior hermetic seals are produced by other processing steps. These steps, inclusion of which with Steps 1 through 7 above constitutes this preferred embodiment, are now described.

Step 2a. Following hot working, the surface oxide layer is removed either mechanically or chemically. While ordinary pickling with strong acid solution is of benefit, it has been found most desirable to resort to mechanical processing such as grinding or milling. Concern here is primarily with surface smoothness thereby obtaining surface conditions on the rod which will permit its processing into wire free from surface defects. Such wire is essential for hermetic sealing since the wire-to-glass seal appears to be primarily compressive (essentially nonchemical).

Step 3a. Following quenching, it is observed that a very light oxide has again formed, and this too is removed, for example, by grit blasting. An alternative procedure involves pickling. It may be possible to eliminate Step 2a and perform the entire surface removal at this stage. Attempts to carry out the entire grinding or milling operation at this stage have however, resulted in some fracture during the cold working of Step 4. It is possible that the entire surface removal may be performed on smaller diameter rods, whether obtained by additional hot rolling as in Step 2 or by cold working quenched rods as in Step 4.

Step 3b. Past experience has indicated that Remendur treated in accordance with Step 3 is amenable to the requisite cold drawing or other cold reduction without use of a metallic plating. Less expensive lubricating techniques using oils or dry lubricants have generally been considered sufficient. In accordance with the preferred embodiment of this invention, however, it is found that use of a copper or other soft metal, e.g., silver or tin, coating usually applied electrochemically or, alternatively, of other chemical coating materials such as zinc phosphate, borax, or inorganic oxalates, not only aids in lubrication action but also provides a protective layer which facilitates fabrication of wire with a more perfect surface, desirable for hermetic sealing. Consistent with prior practice, any such coating material may be removed, generally by chemical etching, prior to final drawing through diamond dies (as distinguished from carbide dies). This generally corresponds with a diameter of the order of mils. A permissible alternative at this stage is to retain the copper of other permissible soft metal plating (organic coating as well as tin or other lowmelting metals must be removed-the final configuration must be capable of withstanding the hermetic sealing temperature of between 600 and l400C).

Still with a view to maintaining a high degree of surface perfection to optimize hermetic sealing, one or more additional strand anneals starting at a diameter of about 60 mils is introduced to avoid surface scoring. Such anneal may take the form of 3 feet per minute passage through a 3 foot hot zone to reach temperatures of 850C to l050C for a period ofabout one-half minute followed by passage through a water-cooled chamber to reduce rapid cooling.

B. Contact Formation The contacting portions of the reeds are provided with suitable platings in the usual manner. In general, a simple single layer of hard gold (e.g., cobalt-hardened gold produced from citrate-buffered cyanide bath) is adequate. Plating thickness, again not unusual, is not critical and may be within the range of from 0.5 to microns. Due, however, to the usually small dimensions, particularly the gap dimension of the structure, it is ordinarily desirable to maintain thickness uniformity within 1 50 percent.

C. Hermetic Sealing The other operation which deserves discussion here involves the hermetic seal of the protruding reed portion to the envelope material. The requirements are common to glass-to-metal seals in other arts. Appropriate temperature coefficient of expansion to closely match that of Remendur may be accomplished by use of lead base glass compositions or other appropriate materials. It has been indicated that under general circumstances thebond is considered to be primarily compressive. Accordingly, the glass envelope material softened by heating flows around the protruding reed. On cooling, compressive stresses are set up in the seal area by deliberate design due to the very slight mismatch of the coefficient of expansion of the glass and the reed material. The best hermetic seals have been prepared in accordance with the preferred embodiment of this invention, i.e., by use of Steps 2a, 3a, and 3b.

The temperature-sensitive nature of the desired device properties of the Remendur reeds imposes a further requirement on the sealing operation. It has been found that maintenance of the reed at temperatures above about 800C even for the brief periods of about 6 seconds resulting during sealing may result in a reduction of as much as 20 percent in coercivity.

What is claimed is:

1. Process for fabrication of a hermetically sealed remanent reed, self-latching magnetic switch comprising a sealed envelope containing at least two protruding reed members, each of said members including an electrically contacting surface, in which at least a portion of at least one of the said reeds consists essentially of an alloy containing from 40 to 75 parts by weight cobalt, 25 to 60 parts by weight iron, and l to 5 parts by weight vanadium, in which said body portion is produced by a series of processing steps including hot working, heat treatment, quenching, cold working, and phase precipitation hardening, so resulting in a remanent magnetization of at least 10,000 gauss and a coercivity of at least 10 oersteds, characterized in that the said series of processing steps concludes with operations in which a round wire body portion of the said alloy is strand annealed so as to give the said body portion a heat treatment equivalent to maintenance at a temperature of 850C to 1050C for a period of from 10 seconds to 15 minutes and is chilled so as to result in an elongation of at least 10 percent and a maximum tensile strength of 200,000 psi, is flattened to a thickness reduction of at least 40 percent, said figure being the fraction of the least thickness dimension after flattening divided by the wire diameter before flattening, the said wire prior to flattening having the said elongation and maximum tensile strength followed by precipitation hardening resulting from annealing in a nonoxidizing atmosphere at a temperature from 550C to 670C for a period of from one-half to 6 hours.

2. Process of claim 1 in which the said values of elongation and tensile strength result from specified processing including strand anneal in which the said round wire is produced by cold working a quenched body.

3. Process of claim 2 in which the said round wire is produced by cold working a hot worked body which is softened by heating to a temperature of at least 750C.

4. Process of claim 2 in which said specified processing terminates with a cold working procedure in which the area of the wire is reduced by from 20 percent to 50 percent.

5. Process of claim 1 in which said alloy consists essentially of from 45 to 65 parts cobalt, iron to total parts cobalt plus iron, and 2 to 4 parts vanadium.

6. Process of claim 5 in which the cobalt and iron content of the said alloy are approximately equal.

7. Process of claim 1 in which a surface layer is mechanically removed following hot working.

8. Process of claim 7 in which a surface layer of said wire is chemically removed subsequent to quenching.

9. Process of claim 8 in which the said wire is coated subsequent to said chemical removal of the said surface layer.

10. Process of claim 9 in which the said coating consists essentially of copper produced by electroplating.

11. Process of claim 10 in which the copper coating is removed prior to the termination of cold working.

12. Process of claim 1 in which the envelope consists essentially of a lead base glass and in which hermetic sealing to the protruding portion of the said reeds is accomplished by heating at least the encompassing portion of the envelope to a temperature of from 600C to 1400C and cooling to solidify the envelope.

Claims

1. Process for fabrication of a hermetically sealed remanent reed, self-latching magnetic switch comprising a sealed envelope containing at least two protruding reed members, each of said members including an electrically contacting surface, in which at least a portion of at least one of the said reeds consists essentially of an alloy containing from 40 to 75 parts by weight cobalt, 25 to 60 parts by weight iron, and 1 to 5 parts by weight vanadium, in which said body portion is produced by a series of processing steps including hot working, heat treatment, quenching, cold working, and phase precipitation hardening, so resulting in a remanent magnetization of at least 10,000 gauss and a coercivity of at least 10 oersteds, characterized in that the said series of processing steps concludes with operations in which a round wire body portion of the said alloy is strand annealed so as to give the said body portion a heat treatment equivalent to maintenance at a temperature of 850*C to 1050*C for a period of from 10 seconds to 15 minutes and is chilled so as to result in an elongation of at least 10 percent and a maximum tensile strength of 200,000 psi, is flattened to a thickness reduction of at least 40 percent, said figure being the fraction of the least thickness dimension after flattening divided by the wire diameter before flattening, the said wire prior to flattening having the said elongation and maximum tensile strength followed by precipitation hardening resulting from annealing in a non-oxidizing atmosphere at a temperature from 550*C to 670*C for a period of from one-half to 6 hours.

3. Process of claim 2 in which the said round wire is produced by cold working a hot worked body which is softened by heating to a temperature of at least 750*C.

5. Process of claim 1 in which said alloy consists essentially of from 45 to 65 parts cobalt, iron to total 100 parts cobalt plus iron, and 2 to 4 parts vanadium.

12. Process of claim 1 in which the envelope consists essentially of a lead base glass and in which hermetic sealing to the protruding portion of the said reeds is accomplished by heating at least the encompassing portion of the envelope to a temperature of from 600*C to 1400*C and cooling to solidify the envelope.