US3726713A - Methods of treating electrical heating elements - Google Patents

Methods of treating electrical heating elements Download PDF

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Publication number
US3726713A
US3726713A US00009887A US3726713DA US3726713A US 3726713 A US3726713 A US 3726713A US 00009887 A US00009887 A US 00009887A US 3726713D A US3726713D A US 3726713DA US 3726713 A US3726713 A US 3726713A
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United States
Prior art keywords
fluid
sheath
heating element
methods
moisture
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Expired - Lifetime
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US00009887A
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English (en)
Inventor
G Hawk
F Martin
T Poulson
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Hoover Co
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Hoover Co
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B3/00—Ohmic-resistance heating
    • H05B3/40—Heating elements having the shape of rods or tubes
    • H05B3/42—Heating elements having the shape of rods or tubes non-flexible
    • H05B3/48—Heating elements having the shape of rods or tubes non-flexible heating conductor embedded in insulating material
    • H05B3/52—Apparatus or processes for filling or compressing insulating material in tubes

Definitions

  • the present invention relates to heating elements of the type comprising an outer metallic sheath within which extends an electrical conductor with an insulating material packed between it and the sheath and the principal object of the invention is to provide new and improved methods of an apparatus for reducing electrical leakage between such conductor and sheath.
  • this type of sheathed tubular heating element is used to a great extent in die-cast or molded electric domestic appliances such as smoothing irons or frying pans Where the sheath is in electrical conducting relationship with the body of the appliance, it will be appreciated that consistent maintenance of this insulation is essential and the present invention is concerned particularly with methods of reducing the risk of current leakage due to the presence of moisture in the insulating material and also to apparatus for carrying out such methods.
  • 200 microamperes is the desirable goal for the maximum acceptable leakage current.
  • the 200 microampere minimum level has been set as a desirable goal in a number of publications and in particular or after their incorporation by molding or die-casting in an appliance.
  • this fluid apparently does not form a barrier preventing moisture from entering the element, it appears that it does prevent the moisture from altering the resistance of the magnesium oxide where it is present.
  • the difficulty with soaking is that unless the soaking period is extensive, only the ends of the element become impregnated with the silicone. For example, a few drops of silicone fluid added to the open ends of a dry untreated element may reduce leakage current to some extent.
  • the leakage current can rise to 50 microamperes after one day, about microamperes after five days and to over 1,000 microamperes after seventy-five days.
  • a further difliculty which is experienced is that al though the presence of moisture in the element on a given occasion may be relatively low, energization of the heating element and a consequent rise in temperature thereof drives the contained moisture outwardly toward the relatively cold terminal ends resulting in an accumulation of moisture in the vicinity of such ends which temporarily increases the leakage current to an undesirable degree.
  • a method of at least partially impregnating a packing insulator in a sheathed heating element with a protective fluid includes the introduction of such fluid into the sheath under pressure.
  • the process is of particular application to elements which have already been incorporated in cast or molded appliances so that the fluid is not subjected to the molding temperatures
  • the scope of the invention does not preclude its use on heating elements which have not yet been integrated with the appliance but which will be so integrated by a process which does not raise the temperature of the fluid to above a critical temperature.
  • the fluid is a silicone fluid
  • this critical temperature is around 550 F. since eventual decomposition of the silicone fluid will result if it is subjected to temperatures above this for prolonged periods.
  • the invention is also manifestly applicable to elements which will be used in such manner that they will be neither cast nor molded into an appliance or device.
  • the fluid which is introduced does not necessarily prevent moisture from entering an element. It is believed that the beneficial effect, for example of silicone fluid, is obtained because it coats the minute particles of the magnesium oxide used as the packing insulator so that when moisture does extend into the element, no electrical continuity is obtained between the electrical conductor and the outer sheath of the element which will convey dangerous leakage currents.
  • heating element impregnation apparatus comprises clamping means for holding a heating element, or a part into which said element has been cast or molded, and coupling means for disposition in sealing relation with the open end of the heating element and in communication with a source of pressurized, moisture-protective fluid to provide for injection of such fluid into the sheath open end and through the compacted material thereat.
  • the coupling -means may, for example, be biased toward the heating element-open end by force-applying means which may comprise a fluid pressure cylinder acting through a lever mechanism.
  • a lost-motion connection may be interposed between the fluid cylinder and the coupling means and may include a spring which normally exerts a light sealing pressure between the coupling means and the element open end, prior to application of full sealing pressure by the fluid cylinder. During such application of full sealing pressure, the lost motion is taken up and the spring is compressed.
  • FIG. 1 is a fragmentary side elevational view, partially in section, of an electric frying pan produced in accordance with the present invention
  • FIG. 2 is a fragmentary, partially in section, bottom plan view of the portion of the pan adjacent the terminal ends of its heating element
  • FIG. 3 is a generally diagrammatic illustration of apparatus in which a frying pan of the type shown in FIGS. 1 and 2 is clamped and by means of which silicone fluid is introduced under pressure into the heating element.
  • FIG. 1 shows a conventional cast aluminum alloy frying pan having a base and an upstanding peripheral wall 11.
  • Cast into the base 10 is a metal sheathed heating element, the terminal ends of which are shown in FIGS. 1 and 2.
  • the element includes an elongated, tubular metalhe sheath 12 formed to a suitable configuration with its terminal ends in side-by-side relation.
  • a resistor conductor Disposed within the sheath 12 and in spaced relation with its inner periphery is a resistor conductor having terminal pins 13 at respective ends thereof protruding axially outwardly of respective sheath ends.
  • the sheath 12 is filled with a highly compacted, electric-insulating, heat-conductive material 14 (such as magnesium oxide) in which the resistor conductor is embedded.
  • a highly compacted, electric-insulating, heat-conductive material 14 such as magnesium oxide
  • the form of sheathed heating element is manufactured according to conventional practice as a suitably looped or otherwise configurated element which is integrated with the frying pan during the manufacture of the pan proper by means of a gravity feed die-casting process.
  • the temperatures reached in the region of the heating element during such a die-casting process are higher than pressure injection die-casting and are too high for silicone fluid to be introduced as a protective fluid into the element prior to casting since the high temperature would cause boiling off or decomposition of the fluid and render it ineffective. Accordingly, the impregnation of the heating element with the protective silicone fluid according to this specific embodiment takes place after the heating element has been integrated into a cast frying pan.
  • the sheath ends may be trimmed flush with the adjacent surface of the cast pan to expose the terminal pins 13 and the compacted magnesium oxide 14, whereafter the frying pan is heated for 15 minutes at 400 F.
  • This may be done by connection of the terminal pins 13 to a source of electrical energy through either a proportional input timer having a thirty second cycle and set at 50% or, alternatively, through a thermostat set at approximately 400 F. in the 15 minute period.
  • the fryin pan is cooled to 300 F. during a 15 minute period either by connection to a constant, below normal operating voltage or by connection to normal operating voltage through a thermostat adapted to cycle at 300 F.
  • the frying pan is assembled in the apparatus shown in FIG. 3 (operation of which will later be described) and silicone fluid, or oil (for example, that sold by General Electric Company under the number SF-99), is introduced under a pressure of 4000 psi on both element ends for a minimum of 10 minutes. During this period, the pan is allowed to cool normally, such cooling, it is believed, assisting flow of fluid into the element sheath. According to present practice, the amount of fluid introduced into each element to provide satisfactory results is in the order of 0.5 gram.
  • the pan After disconnecting the pan from the apparatus, the pan is suitably heated and maintained at 300 F. for approximately 15 minutes, the elfect of which is to continue to distribute the silicone fluid through the compacted magnesium oxide 14.
  • pan is allowed to cool and it may thereafter be completed by attachment of suitable terminals to the projecting terminal pins 13 and by attachment of suitable legs, handles and the like which form no part of the present invention and thus are not herein shown or described.
  • silicone fluid is satisfactorily introduced into substantially all the interstices of the compacted magnesium oxide and tests have shown that an element in a frying pan subjected to a moisture test of RH. and 85 F. for up to 75 days does not produce a leakage current exceeding 16 microamperes.
  • the apparatus shown in FIG. 3 includes a base or support 20 having upstanding portions 21 and 22 between which a frying pan P is introduced and clamped by means of a toggle clamping mechanism 24 which bears against an internal surface of the side wall 11 of the pan and forces the latter against an adjustable clamping block 25 supported on the upstanding portion 22.
  • a toggle clamping mechanism 24 which bears against an internal surface of the side wall 11 of the pan and forces the latter against an adjustable clamping block 25 supported on the upstanding portion 22.
  • the axially outwardly projecting terminal pins 13 of the heating element each extend vertically downwardly and are loosely received within respective bores 27 of individual sleeves 28 which are screw threaded at their lower ends into a manifold block 29 having a lateral inlet 30 for the silicone fluid.
  • the upper ends of the sleeves 28 have annular recesses in their bores 27 which receive flexible sealing collars 32 projecting upwardly beyond the ends of the sleeves so that when the parts are in the position shown in FIG. 1, the free ends of the collars 32 abut the element sheath ends and/or the face of the metal base part of the frying pan around the two projecting terminal pins.
  • the manifold block 29 and its associated parts thus form coupling means by which the magnesium oxide 14 at the element terminal ends is placed into sealed communication with the source of silicone fluid by means of a face seal.
  • seal manifold block 29 is biased upwardly by an end 39 of a seal clamp lever 40 pivoted at 41 to the upstanding portion 21 of the base 20.
  • the opposite end 42 of the lever is biased downwardly by a hydraulic cylinder assembly 44 mounted vertically on the upstanding portion 21.
  • a spring 48 Extending between recesses formed respectively in the upwardly and downwardly facing surfaces of the lever 40 and the seal manifold block 29 is a spring 48.
  • the purpose of this spring is to resiliently bias the seal manifold block 29 upwardly to engage the seal collars 32 against the ends of the element sheath and/or the adjoining face of the fry pan when the latter is initially placed in position and prior to full application of force by the cylinder assembly 44.
  • I. The method of reducing electrical leakage between the current conductor of an electric resistance heating element embedded in compacted, electric-insulating, heatconductive material, and an enclosing metallic sheath having an open end through which a current conductor por tion extends for connection to an electrical power circuit, the improved method which comprises heating said element and driving off any moisture contained within said element sheath, placing the open end of said element sheath and the exposed, compacted material thereat in communication with a source of moisture protective fluid while the temperature of said element is elevated,

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US00009887A 1969-05-23 1970-02-09 Methods of treating electrical heating elements Expired - Lifetime US3726713A (en)

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Application Number Priority Date Filing Date Title
GB2648169 1969-05-23

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US (1) US3726713A (enrdf_load_stackoverflow)
CA (1) CA927579A (enrdf_load_stackoverflow)
GB (1) GB1303814A (enrdf_load_stackoverflow)

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4101760A (en) * 1975-04-03 1978-07-18 Firma Fritz Eichenauer Refractory granular embedding composition for electric heating coils
US7554064B1 (en) * 2005-02-17 2009-06-30 Gaumer Company, Inc. Method for sealing electrical heating elements
US20090217581A1 (en) * 2007-02-12 2009-09-03 Gaumer Company, Inc. Fuel gas conditioning system
US20100050518A1 (en) * 2007-02-12 2010-03-04 Gaumer Company, Inc. Fuel gas conditioning system with scissor baffles
US20100061710A1 (en) * 2007-02-12 2010-03-11 Gaumer Company, Inc. Fuel gas conditioning system with cross heat exchanger and scissor baffles
US20100059121A1 (en) * 2007-02-12 2010-03-11 Gaumer Company, Inc. Scissor baffles for fuel gas conditioning system
US20100170210A1 (en) * 2007-02-12 2010-07-08 Gaumer Company, Inc. Fuel gas conditioning system with cross heat exchanger
US20110116777A1 (en) * 2009-11-19 2011-05-19 Gaumer Company, Inc. Flow measurement with electric heaters
US20110139765A1 (en) * 2007-02-12 2011-06-16 Gaumer Company, Inc. Fuel gas conditioning system
US8177888B2 (en) 2007-02-12 2012-05-15 Gaumer Company Inc. Fuel gas conditioning system
US8728219B2 (en) 2007-02-12 2014-05-20 Gaumer Company Inc. Heater for vaporizing liquids
US8869880B2 (en) 2007-02-12 2014-10-28 Gaumer Company, Inc. System for subsea extraction of gaseous materials from, and prevention, of hydrates

Cited By (20)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4101760A (en) * 1975-04-03 1978-07-18 Firma Fritz Eichenauer Refractory granular embedding composition for electric heating coils
US7554064B1 (en) * 2005-02-17 2009-06-30 Gaumer Company, Inc. Method for sealing electrical heating elements
US8177888B2 (en) 2007-02-12 2012-05-15 Gaumer Company Inc. Fuel gas conditioning system
US8521014B2 (en) 2007-02-12 2013-08-27 Gaumer Company, Inc. Fuel gas conditioning system with cross heat exchanger and scissor baffles
US20100061710A1 (en) * 2007-02-12 2010-03-11 Gaumer Company, Inc. Fuel gas conditioning system with cross heat exchanger and scissor baffles
US20100059121A1 (en) * 2007-02-12 2010-03-11 Gaumer Company, Inc. Scissor baffles for fuel gas conditioning system
US20100170210A1 (en) * 2007-02-12 2010-07-08 Gaumer Company, Inc. Fuel gas conditioning system with cross heat exchanger
US9222698B2 (en) 2007-02-12 2015-12-29 Gaumer Company, Inc. Heater for vaporizing liquids
US20110139765A1 (en) * 2007-02-12 2011-06-16 Gaumer Company, Inc. Fuel gas conditioning system
US8103156B2 (en) 2007-02-12 2012-01-24 Gaumer Company, Inc. Fuel gas conditioning system
US20090217581A1 (en) * 2007-02-12 2009-09-03 Gaumer Company, Inc. Fuel gas conditioning system
US8182566B2 (en) 2007-02-12 2012-05-22 Gaumer Company, Inc. Fuel gas conditioning system
US8295692B2 (en) 2007-02-12 2012-10-23 Gaumer Company, Inc. Scissor baffles for fuel gas conditioning system
US8391696B2 (en) 2007-02-12 2013-03-05 Gaumer Company, Inc. Fuel gas conditioning system with scissor baffles
US8404013B2 (en) 2007-02-12 2013-03-26 Gaumer Company, Inc. Fuel gas conditioning system with cross heat exchanger
US20100050518A1 (en) * 2007-02-12 2010-03-04 Gaumer Company, Inc. Fuel gas conditioning system with scissor baffles
US8869880B2 (en) 2007-02-12 2014-10-28 Gaumer Company, Inc. System for subsea extraction of gaseous materials from, and prevention, of hydrates
US8728219B2 (en) 2007-02-12 2014-05-20 Gaumer Company Inc. Heater for vaporizing liquids
US8682149B2 (en) 2009-11-19 2014-03-25 Gaumer Company, Inc. Flow measurement with electric heaters
US20110116777A1 (en) * 2009-11-19 2011-05-19 Gaumer Company, Inc. Flow measurement with electric heaters

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Publication number Publication date
GB1303814A (enrdf_load_stackoverflow) 1973-01-24
CA927579A (en) 1973-06-05

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