US3919682A - Electrical resistor with a polycrystalline ceramic cover and a process for its manufacture - Google Patents

Electrical resistor with a polycrystalline ceramic cover and a process for its manufacture Download PDF

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Publication number
US3919682A
US3919682A US393998A US39399873A US3919682A US 3919682 A US3919682 A US 3919682A US 393998 A US393998 A US 393998A US 39399873 A US39399873 A US 39399873A US 3919682 A US3919682 A US 3919682A
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United States
Prior art keywords
vitreous
ceramic
covering
electrically resistive
resistor
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Expired - Lifetime
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US393998A
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English (en)
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Ubaldo Costa
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S E C I SOC ELETTROTECNICA CHIMICA ITALIANA SpA
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Seci
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C1/00—Details
    • H01C1/02—Housing; Enclosing; Embedding; Filling the housing or enclosure
    • H01C1/034—Housing; Enclosing; Embedding; Filling the housing or enclosure the housing or enclosure being formed as coating or mould without outer sheath
    • H01C1/036—Housing; Enclosing; Embedding; Filling the housing or enclosure the housing or enclosure being formed as coating or mould without outer sheath on wound resistive element
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T29/00—Metal working
    • Y10T29/49—Method of mechanical manufacture
    • Y10T29/49002—Electrical device making
    • Y10T29/49082—Resistor making
    • Y10T29/49087—Resistor making with envelope or housing

Definitions

  • ABSTRACT A new covering material for electrical resistors and the related process for the manufacturing of these resistors are disclosed, according to which an insulating and protective vitreous polycrystalline ceramic is obtained by controlled in-situ crystallisation of vitreous material so as to .form microcrystals uniformly dispersed in the vitreous mass, the above mentioned crystallisation being carried out in the vitreous starting material prepared by powdering mixtures adapted for producing vitreous substances, already covering the ceramic support of the resistor already fitted with the resistive winding and the rheophores, by baking the assembly at a temperature of 600 850C for 5 120 minutes.
  • the invention relates also to the new class of insulated resistors thus obtained.
  • ELECTRICAL REslsToR WITH A POLYCRYSTALLINE CERAMIC COVER AND A PROCESS FOR ITS MANUFACTURE NiCr, constantan-etc. is wound on a ceramic supportv generally of cylindrical, flat or tubular shape and is coveredvvith a number of layersof a vitreous enamel which is baked at temperatures greater than 850C.
  • the vitreous enamel of these resistors must have a coefticient of thermal expansion which issuitable for the cerami e support so that the individual materials (ceramic support enamel and metal materials) are coupled withoutir nechanical-tension and the formation of cracks in the ,vitreouser amel-is avoided even if the resistor is :subjectedtoalternate variable, repeated cycles off heating olr cooling, As stated, during the various stages of manufacture .the resistors undergo various. baking cycles at hightemperatures usually greater than Under these conditions the NiCr alloy, of which the resistive element is usuallymade, becomes subjected a number of times to temperatures at whichthe crystals of the alloy undergo coarsening.
  • vitre'ous enamels which are substantially amorphous glasses to which some colouring pigment 's'uch”as "Cr O C00 etc. have been added, i
  • vitreous enamels of low baking temperature have a poor mechanical strength, a low viscosity at the baking temperature of the resistor and a higher chemical reactivity.
  • the geometrical shapeof the enamelled resistor precisely because the vitreous enamel behaves as a liquied at the baking temperature of the resistor, is not always perfectly uniform so that on the resistor there are points having different thicknessesof enamel with consequent different values of insulation resistance and dielectric strength.
  • vitreous enamels having a low softening temperature v I Furthermore the high chemical reactivity of the vitreous enamel more easily gives rise to reaction with metal .materialsof which the resistor is constituted (wires, rheophores etc.) and this leads to the formation of spongy zones. It is consequently practically impossible with vitreous enamels of low softening point known up to the present time toobtain a enamelled wire resistor of good quality and with a high level of reliability.
  • the objectof the present invention is to provide a covering for electrical wire resistors which enables the aforementioned disadvantages to be obviated.
  • I A further object is to' provide a new material for covering resistors which has excellent characteristics of uniformity of s gagture,.mechanical, strength, insulating resistance and dielectric strength, and moreover having a coefficient of expansion which makes it particularly suited to covering resistors.
  • a further object is to provide a method for preparing the resistors covered with the new covering.
  • a resistor consisting of a ceramic support of any type or shape, with a resistive element of wire or suitable metal alloy strip (such as Ni- Cr, constantan etc.) and provided with rheophores of suitable material (for example 42 alloy, Fe-Cr alloy etc.) is covered with an insulating and protective inorganic material namely vitreous ceramic and defined as a polycrystalline ceramic obtained by controlled in-situ crystallisation of a vitreous material in such a manner the vitreous mass; this vitreous ceramic, after applicavitreous substances, which consist mainly of SiO,, 8
  • nucleants and/or crystallisation promoters in the form of powders such as titanium dioxide -of the rutile type, chromium oxide etc.
  • a so-called frit is obtained, i.e., a substance consisting essentially of a vitreous material. Crystallisation can be controlled in-situ during the annealing of the material so obtained by adopting a suitable. baking cycle, and depending on thequantity and type of nucleant used.
  • FIG. 1 shows a typical differential thermal analysis diagram for a vitreous ceramic.
  • the amorphous vitreous phase can represent up to 95% of the vitreous ceramic, or the polycrystalline phase may represent 95% of the product.
  • the vitreous ceramics may also be prepared by adding nucleants and/or crystallisation promoters to powdered glass and then baking the mixture obtained under suitable thermal cycles.
  • micro-crystals uniformly distributed in the mass of the vitreous ceramic material creates a new type of protective material which has different characteristics than the original glass.
  • this new material defined as vitreous ceramic which is formed during the baking of the resistor has a high uniformity and a structure practically free from internal pores, high mechanical strength, high insulation resistance and high dielectric strength.
  • vitreous ceramic materials When conventional vitreous enamels exceed the softening temperature they rapidly become fluid for small temperature increases, whereas vitreous ceramic materials have the interesting and very useful characteristic of maintaining their viscosity practically constant even at temperatures very much higher than the softening temperature.
  • the coefficient of expansion of a vitreous ceramic is lower than that of the vitreous phase present in it because the crystals which form have a lower coefficientof expansion than that of the glass in which they are immersed, and hence as the process of formation of the crystals can be controlled, it is possible to reduce this coefficient.
  • vitreous ceramic materials are distinguished from the well known amorphous vitreous enamels and divitrifiable glasses mainly because they have a microcrystalline structure finely and uniformly distributed in a vitreous matrix.
  • Changes of structure from amorphous to crystalline can be revealed by different thermal analysis in that they are accompanied by the development or absorption of energy in the form of heat.
  • FIG. 2 The same diagram for a vitreous enamel (as shown in FIG. 2) only shows the softening point ofthe single vitreous phase present.
  • vitreous ceramics adhere very well to the ceramic supports and metal materials constituting the resistor.
  • Wire resistors of any shape and size protected by the vitreous ceramic covering materials of the present invention constitute a new class of resistors capable of supporting the most severe conditions of use, such as those which no other wire resistor protected by the normal amorphous vitreous enamels known today can support.
  • this comprises in substance the operations of applying a layer of the initial vitreous material already containing the nucleants and/or crystallisation promoters to the ceramic support previously fitted with the resistive winding and present invention, the variouscomponents of the final vitreous ceramic, i.e. vitreous components, nucleants and/or crystallisation promoters in the form of fine powder uniformly mixed, are brought to a temperature of l,200l ,300C and the fused material is poured into water. The product of fusion is wet ground until at least 60% of the particles have a diameter less than 50. mi
  • an aqueous suspension is prepared from the wet ground product of fusion, with the possible addition of filling materials, and the already fittedsupport is covered by immersing it, then proceeding to the baking ,cycle in order to obtain the vitreous ceramic covering in-situ.
  • the covering of the ceramic support prior to the thermal cycle is made in the form of a drawn tube which is mounted over the support carrying the resistive elements and rheophores, after which the thermal baking cycle is carried out.
  • the covering operation and subsequent thermal treatment may be repeated a number of times, according to the required covering thickness and for ensuring homogeneity.
  • the nucleisation and formation of crystals and their consequent coarsening begins as soon as a temperature of 700C is reached and proceeds more or less swiftly according to the temperature chosen between 600 and 850C. Crystallisation may be interrupted by cooling to below 600C.
  • the contents and size of the microcrystals may be dosed at will simply be acting on the temperature and/or on the baking time, and by suitably metering the quantity of nucleants and/or crystallisation promoters in the original glass formula.
  • the wire resistors protected by vitreous ceramic materials may be manufactured at a lower cost than those protected by normal well known vitreous enamels, because the baking temperatures of the vitreous ceramic material may be considerably lower which reduces the percentage of rejects during manufacture and also the time required for baking the resistors may be much shorter.
  • FIG. 3 is a partially sectional view of a resistor according to the present inventin, comprising a support of ceramic material 1, on which a resistive" element 2 is wound.
  • the resistor is completed by the rheophores 3 connected to the ends of the resistive element 2, and the finished vitreous ceramic insulating covering is indicated by the reference numeral 4.
  • the wire resistors protected by vitreous ceramic have a greater reliability of operation over longperiods of time than resistors protected by'normal vitreous enamels because of the greater resistance to thermal shock, higher mechanical strength, lower thermal stress of the resistive elements during manufacture, higher chemical resistance, excellent adherence of the protective vitreous ceramic covering to the parts constituting the resistor (and particularly to the metal parts) and the absence of cracks.
  • a mixture is prepared consisting of the following powders (the percentages being expressed in weight in the total mixture):
  • the material so formed may be defined as vitreous ceramic and has a coefficient of expansion measured between C and 370C of 510-.
  • a vitreous ceramic material consists of a ceramic supporting body 1 of steatite, foe example the type 22lK produced by Rosenthal Stemag Technische Keramik G.m.b.H.
  • the rheophores 3 of iron-nickelmetal alloy and the rersistive element 2 were applied to this support by known methods.
  • the protective covering for the resistor is prepared starting from the following composition:
  • the resistor so protected was brought to a temperature of 650C for 30 minutes and the external geometrical shape remained nearly unchanged.
  • the finished resistor comprises a covering of a vitreous ceramic material obtained in-situ, consisting of microcrystals uniformly dispersed in the vitreous mass.
  • EXAMPLE 3 An electrical resistor constructed with a vitreous ceramic material was made principally starting from a ceramic supporting body of steatite, for example the type 221K- of Rosenthal Stemag Technische Keramik G.m.b.I-I. The rheophores of iron-nickel metal alloy and the resistive element were applied to this support using known methods.
  • a protective covering with the composition referred to in example I was applied to the thus assembled resistor.
  • the aqueous suspension of the material described in Example 1 has the following composition: fine 50 micron powder of material described in Example 1, 70 g; clay 2 g; water 28 g.
  • the resistor is immersed in the described suspension so as to obtain a uniform covering. After drying, the therrrialtreatment according to the cycle shown in FIG. 6 is carried out. The application of the described aqueouss'uspension with consequent baking was repeated three times.
  • the finished resistor comprised a covering of a vitreous ceramic material obtained in-situ, consisting of microcrystals uniformly dispersed in the vitreous mass.
  • EXAMPLE 4 An electrical resistor is constructed from a vitreous ceramic material as described in examples 1 and 2.
  • the protective covering of the resistor is prepared starting from the following composition:
  • the described composition was brought to a temperature of l200-l 300C so as to melt it.
  • the fused material was poured into water and was reduced to grains and then wet ground in a ball mill until the particles of the material so obtained had a diameter of less than 10 micron.
  • the powder obtained was dried and made into a paste with a solution of 10% of methylcellulose in water.
  • the paste obtained was drawn in order to form tubes of suitable dimensions.
  • the tubes of suitable length were mounted over the resistors, the resistor was then baked first at a temperature of 400C for one hour in order to eliminate the methylcellulose, then at 780C for 30 minutes in order to produce the controlled crystallisation of the vitreous I port, a resistive element on said support, and conductors connected to said resistance element and extending from said support, and an inorganic insulating and protective cover chemically and physically bonded to all the parts constituting the resistor including those portions of said conductors adjacent said support, said cover comprising a polycrystalline ceramic obtained by controlled in situ crystallization of a vitreous material in such a manner as to obtain microcrystals uniformly dispensed and distributed in the vitreous mass.
  • vitreous ceramic insulating and protective cover consists for of a vitreous phase and for 5% of a crystalline phase.
  • vitreous ceramic insulating and protective cover consists for 95% of a crystalline phase and for 5% of a vitreous phase.
  • vitreous ceramic insulating and protective cover has a coefficient of expansion lying between 1.10 and 8.10 and a softening point lying between 600 and 800C. 7
  • step (b) providing said covering in the form of a vitreous ceramic frit which consists essentially of a mixture of ceramic oxides having a softening point and at least one crystalline phase within the temperature range of 600-850C, and wherein said baking is carried out in the temperature range of 600-850C for a time sufficient to convert at least 5% of saidfrit to crystalline phase.
  • vitreous ceramiccovering is applied to the electrically resistive metal by pulversing it and then mechanically pressing the powder, possibly in the presence of known organic or inorganic binders such as methylcellulose, clay or the like and baking the covered electrically resistive metal at 600800C for a time of l minutes, so as to form in-situ the vitreous ceramic covering which constitutes the electrical insulation and protection of the electrically resistive metal.
  • vitreous ceramic covering is provided in the form of powder which and the assembly is baked at said temperatures of 600-850C for 1-120 minutes so as to form in-situ the vitreous ceramic covering which constitutes the electrical insulation and protection for the electrically resistive metal.
  • the original electrically resistive material is in the form of a wire which is sprayed with an aqueous suspension of a fine powder consisting of the vitreous ceramic covering material containing nucleants and/or crystallisation promoters and is baked at said temperatures between 600 and 850C for 1-120 minutes so as to obtain the vitreous ceramic covering in-situ on the wire, the thermal cycle and spray application of the aqueous suspension on the wire being repeated at least twice so as to form a uniform thickness of vitreous ceramic covering on the wire.
  • the chromium and titanium oxides being mutually exclusive.
  • said frit consists essentially of the following:
  • said frit consists essentially of the following:

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  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Apparatuses And Processes For Manufacturing Resistors (AREA)
  • Glass Compositions (AREA)
US393998A 1972-09-08 1973-09-04 Electrical resistor with a polycrystalline ceramic cover and a process for its manufacture Expired - Lifetime US3919682A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
IT28983/72A IT967290B (it) 1972-09-08 1972-09-08 Resistore elettrico e procedimento di fabbricazione

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US (1) US3919682A (fr)
CA (1) CA1011837A (fr)
DE (1) DE2345102A1 (fr)
ES (1) ES418549A1 (fr)
FR (1) FR2209182B1 (fr)
GB (1) GB1402384A (fr)
IT (1) IT967290B (fr)
NL (1) NL7312346A (fr)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0059006A1 (fr) * 1981-02-19 1982-09-01 Koninklijke Philips Electronics N.V. Résistance en fil bobiné
US4672358A (en) * 1986-05-19 1987-06-09 North American Philips Corp. Surface-mounted power resistors
US4825535A (en) * 1987-02-10 1989-05-02 Sony Corporation Method of manufacturing a resistor element
US4926542A (en) * 1988-08-26 1990-05-22 Dale Electronic, Inc. Method of making a surface mount wirewound resistor
USRE33541E (en) * 1986-05-19 1991-02-19 Surface-mounted power resistors
US20020167391A1 (en) * 2001-05-09 2002-11-14 Gunther Wedeking Electrical resistor and method for its manufacture
US20030062399A1 (en) * 2001-10-01 2003-04-03 Masami Kimura Metal/ceramic bonding article and method for producing same

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2118928A (en) * 1982-04-21 1983-11-09 Geoffrey Cooke Enamelling process
JP3093601B2 (ja) * 1994-09-28 2000-10-03 株式会社住友金属エレクトロデバイス セラミック回路基板
DE102005022927A1 (de) † 2005-05-13 2006-11-16 Würth Elektronik iBE GmbH Elektronisches Bauteil und Verfahren zu seiner Befestigung

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3229237A (en) * 1962-02-09 1966-01-11 Cons Electronics Ind Small electrical unit with molded ceramic coating
US3392312A (en) * 1963-11-06 1968-07-09 Carman Lab Inc Glass encapsulated electronic devices

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3229237A (en) * 1962-02-09 1966-01-11 Cons Electronics Ind Small electrical unit with molded ceramic coating
US3392312A (en) * 1963-11-06 1968-07-09 Carman Lab Inc Glass encapsulated electronic devices

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0059006A1 (fr) * 1981-02-19 1982-09-01 Koninklijke Philips Electronics N.V. Résistance en fil bobiné
US4406994A (en) * 1981-02-19 1983-09-27 U.S. Philips Corporation Wire-wound resistor
US4672358A (en) * 1986-05-19 1987-06-09 North American Philips Corp. Surface-mounted power resistors
USRE33541E (en) * 1986-05-19 1991-02-19 Surface-mounted power resistors
US4825535A (en) * 1987-02-10 1989-05-02 Sony Corporation Method of manufacturing a resistor element
US4926542A (en) * 1988-08-26 1990-05-22 Dale Electronic, Inc. Method of making a surface mount wirewound resistor
US20020167391A1 (en) * 2001-05-09 2002-11-14 Gunther Wedeking Electrical resistor and method for its manufacture
US20030062399A1 (en) * 2001-10-01 2003-04-03 Masami Kimura Metal/ceramic bonding article and method for producing same
US6935554B2 (en) * 2001-10-01 2005-08-30 Dowa Mining, Co. Ltd. Metal/ceramic bonding article and method for producing same

Also Published As

Publication number Publication date
FR2209182A1 (fr) 1974-06-28
CA1011837A (en) 1977-06-07
NL7312346A (fr) 1974-03-12
GB1402384A (en) 1975-08-06
IT967290B (it) 1974-02-28
FR2209182B1 (fr) 1975-04-11
DE2345102A1 (de) 1974-03-21
ES418549A1 (es) 1976-03-16

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