WO1993005521A1 - Cable isole par un mineral a base de silice et procede de production de ce cable - Google Patents

Cable isole par un mineral a base de silice et procede de production de ce cable Download PDF

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Publication number
WO1993005521A1
WO1993005521A1 PCT/US1992/007664 US9207664W WO9305521A1 WO 1993005521 A1 WO1993005521 A1 WO 1993005521A1 US 9207664 W US9207664 W US 9207664W WO 9305521 A1 WO9305521 A1 WO 9305521A1
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WO
WIPO (PCT)
Prior art keywords
paste
set forth
fused silica
insulator
binder solution
Prior art date
Application number
PCT/US1992/007664
Other languages
English (en)
Inventor
Williams J. Koch
Collins P. Cannon
Original Assignee
American Technology, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by American Technology, Inc. filed Critical American Technology, Inc.
Publication of WO1993005521A1 publication Critical patent/WO1993005521A1/fr

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Classifications

    • 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
    • C04B35/14—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 silica
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B19/00—Apparatus or processes specially adapted for manufacturing insulators or insulating bodies
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
    • H01B3/02—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of inorganic substances
    • H01B3/10—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of inorganic substances metallic oxides
    • H01B3/105—Wires with oxides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
    • H01B3/02—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of inorganic substances
    • H01B3/12—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of inorganic substances ceramics
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B7/00—Insulated conductors or cables characterised by their form
    • H01B7/16—Rigid-tube cables
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B7/00—Insulated conductors or cables characterised by their form
    • H01B7/17—Protection against damage caused by external factors, e.g. sheaths or armouring
    • H01B7/28—Protection against damage caused by moisture, corrosion, chemical attack or weather
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B7/00—Insulated conductors or cables characterised by their form
    • H01B7/17—Protection against damage caused by external factors, e.g. sheaths or armouring
    • H01B7/29—Protection against damage caused by extremes of temperature or by flame
    • H01B7/292—Protection against damage caused by extremes of temperature or by flame using material resistant to heat

Definitions

  • This invention is generally directed to mineral insulated cables and, more particularly, to a silica insulated cable, the preform used as the mineral insulation in such cables, and a. method for producing the silica preform.
  • Soft cables typically include an inner conductive wire surrounded by an organic insulator, such as rubber or plastic.
  • organic cables have the advantages of being relatively inexpensive to manufacture, flexible and therefore inexpensive to install, and good multi- frequency conductors, owing to the relatively low dielectric constant of the organic insulator. That is, soft cables are typically capable of transmitting electrical signals within a broad spectrum of frequencies, which is commonly referred to as having a broad bandwidth. In particular, soft cables are relatively good at transmitting high frequency signals.
  • Hard cables typically have less of the electrical transmission advantages possessed by soft cables, but are advantageously resistant to damage and disruption from environmental stresses, such as nuclear radiation, temperature, or pressure, which is not true of soft cables.
  • a hard cable typically includes an inner conductive wire surrounded by a mineral insulator, such as a ceramic, and placed within a metallic sheath.
  • the mineral insulator resists the invasive effects of environmental stress, such as radiation, owing to its crystal structure with its very strong covalent or ionic type atomic bonds.
  • the insulation in soft cables on the other hand r has low strength organic chemical bonds holding the structure together. Thus, any stress, such as nuclear radiation or heat, can disturb the bonding of the atoms in the insulation and severely deteriorate its insulative properties.
  • hard cables are advantageously resistant to environmental stress because of the structure of the inorganic mineral insulator, they are correspondingly disadvantaged by this same inorganic structure. That is, hard cables typically do not have good electrical characteristics at high frequency, owing to the relatively high dielectric constant of a typical mineral insulator. Rather, hard cables are generally limited to the transmission of low frequency and D.C. signals. Hard cables typically do not have a high bandwidth.
  • the amorphous silica or ground quartz For example, during the construction of silica-based hard cables, the amorphous silica or ground quartz,
  • silica is generally very stable, reaction between the sheath and the impure silica is sometimes observed. This reaction can also result in the metal conductors being corroded and ultimately failing.
  • the present invention is directed to overcoming one or more of the problems discussed above by providing a hard cable that is both resistant to environmental stresses and is capable of transmitting relatively high- frequency signals.
  • This invention eliminates effects of residual moisture and other impurities, and gives electrical and dielectric properties not possible with organic insulation or all other forms of presently used silica as amorphous silica, ground quartz, ground cristobalite or ground tridimite.
  • a ceramic preform for use as an insulator in a mineral insulated cable is provided. The ceramic preform is formed primarily from fused silica.
  • a paste suitable for firing into a ceramic preform for use as an insulator in a mineral insulated cable is provided.
  • the paste is formed from a mixture of fused silica and a binder solution.
  • a method for forming a ceramic preform to be used as a insulator in a mineral insulated cable includes the steps of: preparing a binder solution; combining fused silica and the binder solution into an extrudable paste; extruding the paste into a preselected geometric configuration; and firing the extruded paste.
  • a mineral insulated cable in another aspect of the invention, includes at least one conductive wire, a sheath positioned about and spaced from the conductive wire, and an insulator positioned between the conductive wire and the sheath, the insulator being comprised of fused silica.
  • Fig. 1 illustrates a perspective cut-away view of a coaxial mineral insulated cable
  • Fig. 2 illustrates a perspective cut-away view of a triaxial mineral insulated cable. While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that this specification is not intended to limit the invention to the particular forms disclosed herein, but on the contrary, the intention is to cover all modification, equivalents, and alternatives falling within the spirit and scope of the invention, as defined by the appended claims.
  • Fig. 1 shows a cut ⁇ away perspective view of a ceramic preform 10, a center conductor electrical wire 12 and a metallic sheath 16, which, when assembled, form a hard cable 18.
  • the metallic sheath 16 is preferably formed from a nickel iron chrome alloy, but can be constructed from a more refractory metal, if desired.
  • the electrical wire 12 is formed from any suitable conductive material, however, copper is preferred.
  • the ceramic preform 10 is preferably formed from a compound that includes a significant amount of silica. The specific compound and method used in constructing the preforms 10 is discussed in greater detail below. However, for a proper understanding of the instant invention, it is useful to first appreciate the construction and assembly process of a hard cable.
  • the wire 12 is manually threaded through a series of relatively short preforms 10 (i.e., two inches each) until a desired length is reached (i.e. forty feet) . Thereafter, the wire 12 and preforms 10 are inserted into a sheath 16 to form the hard cable 18.
  • a series of relatively short preforms 10 i.e., two inches each
  • a desired length i.e. forty feet
  • the assembled hard cable 18 is passed through conventional metal drawing dies.
  • the drawing dies forcibly reduced the diameter of the sheath 16, and thereby lengthen the cable by a small amount.
  • the cable 18 is consecutively reduced in diameter and increased in length until a desired diameter and/or length is reached. It is preferable to heat treat (anneal) the cable between successive draws to remove work hardening from the metal sheath.
  • the ceramic preforms 10 positioned within the cable 18 are relatively hard, but are crushed lightly during the drawing operation. This crushing action, however, advantageously allows the ceramic to fill any voids within the cable 18 and thereby improve the cable's electrical properties.
  • the instant invention also finds beneficial application in multi-conductor cables, i.e. cables where the number of electrical conductor wires present within the interior of the ceramic insulation varies from one to upwards of 200. In cable geometries of this type, it is generally preferable to position the wires so that insulation thickness between adjacent wires and between wires and the sheath are equal.
  • Triaxial-type hard cables are substantially similar to that shown in Fig. 1, but include an additional metallic sheath 20 positioned between the wire 12, and the sheath 16 (see Fig. 2) .
  • Insulation 22, 24 is provided between the sheaths 16, 20 and also between the additional sheath 20 and the wire 12.
  • the insulation 24 placed between the wire 12 and additional sheath 20 is preferably fused silica
  • the insulation 22 placed between the sheaths can take any of a variety of forms, including, but not limited to, mineral insulators, such as fused silica.
  • Fused silica (Si0 2 ) in contrast to soft organic insulation or amorphous silica, ground quartz, cristobalite or tridimite insulation, strongly resists environmental stresses, such as nuclear radiation, temperature, etc. , and yet has excellent electrical properties in addition to its low dielectric constant (approximately 3.8). Further, fused Si0 2 is very chemically stable and does not tend to react with the sheath or wire of the hard cable. Fused silica possesses a lower dielectric constant and considerably higher voltage breakdown resistance than any of the other four forms of silica (i.e., amorphous silica, quartz, cristobalite or tridimite) . The thermal conductivity is very low and uniform across a temperature range from room temperature to its melting point at about 1732°C. The coefficient of thermal expansion has similar uniformly low values.
  • fused silica has a resistance to voltage breakdown of about 500 volts per mill, in a 1/8 inch thick test sample. This is second only to Boron Nitride in voltage breakdown resistance.
  • the first step in manufacturing a fused silica preform involves the preparation of a swageable ceramic powder, consisting of pure ground fused silica.
  • Fused silica is a chemically fabricated material.
  • the process for manufacturing fused silica involves heating high purity alpha quartz to a temperature above the melting point of silica, 1732°C. This temperature causes the alpha quartz grains to fuse together and form a molten high viscosity liquid.
  • the liquid is quenched by pouring the white hot material into distilled water. Quenching, of course, causes the liquid material to solidify, but in a shattered form.
  • the resultant shattered material is then ball milled using silica balls in a silica lined mill to an average particle size of 8 to 10 microns.
  • This resulting ball milled silica is very fine, with a powder like consistency.
  • fused silica powder is available from, for example, C-E Minerals, Greeneville, Tennessee as electronic grade 44B.
  • a binder solution is combined with the ground fused silica powder to form a paste that is suitable for extruding and will substantially maintain the extruded shape. Accordingly, the next step involves the preparation of the binder solution.
  • a variety of well known binders could be readily used, but preferably, an ash free binder is employed. One example of such an ash free binder is discussed below. The following list of items should be combined in the order listed and then heated to approximately 85°C. Substantial stirring is preferred during the heating process.
  • Triple Distilled Water 3001 grams
  • the solution When the solution reaches 85°C, it should be removed from the heat, and 567.5 grams of Methocel #A4C is stirred into the solution slowly. After approximately two minutes of stirring, the solution will appear milky in color. Thereafter, 1800 grams of triple distilled water is stirred into the milky solution.
  • the triple distilled water is approximately room temperature. This entire solution is preferably covered and aged overnight. Shelf life of the solution is estimated to be approximately six to eight weeks if kept cool (i.e. 7 to 10°C) .
  • binder solution and ceramic powder prepared may be combined to form an extrusion paste.
  • Approximately 530 grams of the fused silica powder and 389 grams of the binder solution are added to a sigma blade type stainless steel mixer, such as is available from Paul 0. Abbe', Inc., of Little Falls, New Jersey.
  • the total working chamber, including all moving parts, of the mixer are coated with titanium nitride.
  • a titanium nitride coated cover plate of the mixer should be locked in place to prevent spillage.
  • the mixer is first operated until the contents appear uniform (approximately three minutes) . Approximately 190 grams of triple distilled water are added and mixed for an additional three minute period. Thereafter, any additional distilled water is added using a 10% binder 90% triple distilled water solution mixture, up to 80 grams maximum. The resulting mixture should be sufficiently stiff to have no deformation of the hole or outer diameter of the preform 10 after extrusion or drying.
  • fused silica powder is added to the mixture. After all of the fused silica powder has been added, and mixed for 3-minutes, the batch is divided in half, and each half batch is mixed for approximately three to four minutes. Each half batch is then placed in a plastic bag and aged for an approximate minimum time of ten hours at a temperature of 7 to 10°C.
  • the moisture content of the paste should be approximately 27 ⁇ 1 percent.
  • the moisture content can be determined either by using a weight loss method or by using a moisture balance, such as a Mettler LP16-M Moisture Determination System available from Fisher Scientific Co. of St. Louis, Missouri, as item number 01-913-93B.
  • the weight loss method of determining moisture content involves accurately weighing the paste before and after drying at about 110°C for about four hours. The difference in weight corresponds to the amount of moisture lost therefrom.
  • the paste should preferably be extruded within one week after preparation.
  • the paste should be kneaded by hand on a clean plexiglass sheet for approximately two minute to give it uniform plasticity and to form it into a shape for loading into a tungsten carbide extrusion chamber.
  • the extrusion process may begin using, for example, a 40-ton extruder having an extrusion chamber and plunger or ram head formed from tungsten carbide. Such an extruder is available from Loomis Products, Co. of Levittown, Pennsylvania.
  • the extruder includes a pin used to form the opening in the preform 10 so that the wire 12 may be threaded therethrough.
  • This pin is adjustable and should preferably be properly positioned or centered prior to actually extruding the paste.
  • the extrusions are formed in approximately 30-inch lengths using tungsten carbide tooling.
  • Extrusion pressure should be three to four tons, as registered on the pressure gauge.
  • the extrusions are preferably placed on 1/4" wide V shaped grooves in a plaster board (6" wide x 30" long x 3/4" total thickness) that has been previously dusted with GP- 38 graphite powder, available from Union Carbide Coatings Corp. , of Danbury, Connecticut.
  • the damp extrusions should preferably be placed in a drying chamber.
  • the extrusions should be dried on the graphite dusted plaster boards at approximately 100°F maximum in a closed chamber (minimum of approximately 25 hours) . Thereafter, this initial drying period is followed by overnight drying in an air circulating dryer at a temperature range of about 125 to 150°C.
  • the extrusions After drying, the extrusions have a wood-like consistency and can be readily cut to a desired length for firing.
  • the extrusions can be cut to a desired firing tile length using a back and top block, straight edge, and a safety-type stainless steel razor blade or Ex-actoTM knife.
  • the cut extrusions should be loaded onto a mullite grain bonded hi-alumina type V-grooved setter tray, such as is available from Applied Ceramics, Inc., of Atlanta, Georgia as part number TAC 218.
  • the V- grooves should be filled to approximately 1/8 inch over their depth, with a plurality of the extrusions stacked therein.
  • the setter trays are stacked four high and two wide into a periodic furnace, such as a 3000 series furnace with Kanthal Super 33 heating elements, available from CM Furnaces, Inc. of Bloo field, N.J.
  • a periodic furnace such as a 3000 series furnace with Kanthal Super 33 heating elements, available from CM Furnaces, Inc. of Bloo field, N.J.
  • the fused silica extrusions are fired in the furnace in an air atmosphere.
  • the furnace is heated to about 400°C over a three hour period, and then held at this temperature for one hour.
  • the temperature of the furnace is raised to about 1275°C at a rate of about 150°C per hour. From this temperature, the rate of increase is slowed to about 100°C per hour until a peak temperature of about 1400°C is reached. This peak temperature is held for an additional two hours.
  • the furnace is then turned off, and the fired extrusions are allowed to cool overnight (minimum) in the closed furnace.
  • the ceramic preforms 10 are now ready to be cut to specified length, usually two inches.
  • the preforms 10 are preferably cut to a flat end cut using a back and top block straight edge and a four inch diameter diamond impregnated 1/32" wide cutting wheel. Physical Tests
  • the modulus of rupture (MOR) is measured using a Chatillon model DFGHS- 100 digital compressive force gauge on a model LTCM-4 mechanical test stand.
  • the test stand is preferably equipped with a controlled motorized lifting table and a tungsten carbide base block having its knife-edge force- points positioned one-inch apart and its tungsten carbide chisel edge tip positioned on the bottom of the digital force gauge.
  • the MOR of the preforms 10 should be approximately 1000 ⁇ 200 PSI.
  • the outer diameter of the preforms 10 should be measured with, for example, a spring loaded electronic digital read-out micrometer accurate to ⁇ 0.0001" min.
  • the outer diameter of the preforms 10 is approximately 0.125 ⁇ 0.002 inch.
  • the inner diameter of the openings should be measured using, for example, spring steel gauge pins accurate to ⁇ 0.0001 inch.
  • the gauge pins are available in intervals of 0.001 inch.
  • camber is measured and preferably should be within a tolerance of about 0.005 inch/inch or mm/mm.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Ceramic Engineering (AREA)
  • Inorganic Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Structural Engineering (AREA)
  • Organic Chemistry (AREA)
  • Compositions Of Oxide Ceramics (AREA)

Abstract

Câble (18) isolé par un minéral, pourvu d'un isolateur céramique composé principalement de silice fondue. L'isolateur en silice est obtenu à partir d'une ébauche céramique (10) composée principalement de silice fondue essentiellement pure. L'ébauche (10) peut être matricée et permet la fabrication d'un câble (18) isolé par la silice présentant une largeur de bande électrique très importante, une grande résistivité électrique et une grande résistance aux contraintes qu'imposent les conditions ambiantes, telles que les rayonnements, les fortes températures ou pressions, ainsi que les environnements chimiques corrosifs.
PCT/US1992/007664 1991-09-12 1992-09-10 Cable isole par un mineral a base de silice et procede de production de ce cable WO1993005521A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US758,595 1985-07-24
US75859591A 1991-09-12 1991-09-12

Publications (1)

Publication Number Publication Date
WO1993005521A1 true WO1993005521A1 (fr) 1993-03-18

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PCT/US1992/007664 WO1993005521A1 (fr) 1991-09-12 1992-09-10 Cable isole par un mineral a base de silice et procede de production de ce cable

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WO (1) WO1993005521A1 (fr)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1997028418A1 (fr) * 1996-02-02 1997-08-07 Bicc Public Limited Company Dispositif transducteur de capacite et cables
WO1998043254A1 (fr) * 1997-03-26 1998-10-01 Bicc Public Limited Company Cable a isolant mineral
GB2460697A (en) * 2008-06-06 2009-12-09 Weston Aerospace Ltd High temperature mineral insulated sensing coil
EP2640933A2 (fr) * 2010-11-19 2013-09-25 Zenith Oilfield Technology Ltd Système de jauge en fond de trou supportant une température élevée
CN111489850A (zh) * 2020-03-12 2020-08-04 久盛电气股份有限公司 一种堆芯仪表系统用矿物绝缘电缆及其制作方法

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1428788A (en) * 1973-09-18 1976-03-17 Rolls Royce Method of producing a refractory article
US4221596A (en) * 1976-10-04 1980-09-09 General Motors Corporation Method for low pressure forming of fused silica compositions and resultant bodies

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1428788A (en) * 1973-09-18 1976-03-17 Rolls Royce Method of producing a refractory article
US4221596A (en) * 1976-10-04 1980-09-09 General Motors Corporation Method for low pressure forming of fused silica compositions and resultant bodies

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
CHEMICAL ABSTRACTS, vol. 107 Columbus, Ohio, US; TAKEUCHI, YASUHIRO ET AL. 'Manufacture of ceramic burners' *

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1997028418A1 (fr) * 1996-02-02 1997-08-07 Bicc Public Limited Company Dispositif transducteur de capacite et cables
WO1998043254A1 (fr) * 1997-03-26 1998-10-01 Bicc Public Limited Company Cable a isolant mineral
GB2460697A (en) * 2008-06-06 2009-12-09 Weston Aerospace Ltd High temperature mineral insulated sensing coil
GB2460697B (en) * 2008-06-06 2010-09-29 Weston Aerospace Ltd High temperature speed or proximity sensor
EP2640933A2 (fr) * 2010-11-19 2013-09-25 Zenith Oilfield Technology Ltd Système de jauge en fond de trou supportant une température élevée
CN111489850A (zh) * 2020-03-12 2020-08-04 久盛电气股份有限公司 一种堆芯仪表系统用矿物绝缘电缆及其制作方法

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Publication number Publication date
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