Abstract: In insulator including alumina as a main component, a Na component in the insulator is set in the range of 0.07 to 0.5 wt % as Na2O. While the Na component content is as high as to have conventionally been regarded to be beyond the common sense, with this range of the Na component content, insulation resistance, mechanical strength and the like at high temperature are unexpectedly not reduced and an insulator with performances comparable to those of an insulator from conventional low soda alumina lower in Na component content than the above described range can be obtained. As a result, medium soda alumina and regular soda alumina that are much lower in cost than conventionally used low soda alumina can be used instead of the low soda alumina, so that dramatic reduction in production costs of insulator 2 for a spark plug 100 and in addition, of the spark plug 100 using the insulator 2 are realized.

Abstract: A spark plug comprising: a center electrode; a metal shell; and an alumina ceramic insulator disposed between the center electrode and the metal shell, wherein at least part of the surface of the insulator is covered with a glaze layer comprising oxides, wherein the glaze layer comprises: 1 mol % or less of a Pb component in terms of PbO; 30 to 60 mol % of a Si component in terms of SiO2; 20 to 50 mol % of a B component in terms of B2O3; 0.5 to 25 mol % of a Zn component in terms of ZnO; 0.5 to 15 mol % in total of at least one of Ba and Sr components in terms of BaO and SrO, respectively; 2 to 12 mol % in total of at least two alkaline metal components of Na, K and Li, in terms of Na2O, K2O, and Li2O, respectively, wherein K and Li is essential; and 0.1 to 10 mol % of a F component in terms of F2.

Abstract: A glaze layer 2d of the spark plug has the composition comprising 1 mol % or less of a Pb component in terms of PbO; 25 to 45 mol % of a Si component in terms of SiO2; 20 to 40 mol % of a B component in terms of B2O3; 5 to 25 mol % of a Zn component in terms of ZnO; 0.5 to 15 mol % of Ba and/or Sr components in terms of BaO or SrO; 5 to 10 mol % in total of at least one alkaline metal component of of Na, K and Li in terms of Na2O, K2O, and Li2, respectively, where K is essential; and further, 0.5 to 5 mol % in total of one or two kinds or more of Mo, W, Ni, Co, Fe and Mn in terms of MoO3, WO3, Ni3O4, Co3O4, Fe2O3, and MnO2, respectively.

Abstract: A spark plug having a glaze layer on the insulator thereof, wherein the glaze layer has a reduced Pb content, is capable of being fired at a relatively low temperature, exhibits excellent insulation properties, and can have a smooth surface.

Abstract: A spark plug comprising: a center electrode; a metal shell; and an alumina ceramic insulator disposed between the center electrode and the metal shell, wherein at least part of the surface of the insulator is covered with a glaze layer comprising oxides, the glaze layer comprising: 1 mol % or less of a Pb component in terms of PbO; 40 to 60 mol % of a Si component in terms of SiO2; 20 to 40 mol % of a B component in terms of B2O3; 0.5 to 25 mol % of a Zn component in terms of ZnO; 0.5 to 15 mol % in total of at least one of Ba and Sr components in terms of BaO and SrO, respectively; 2 to 12 mol % in total of at least one alkaline metal component of Na, K and Li, in terms of Na2O, K2O, and Li2O, respectively, wherein K is essential; and 0.

Abstract: In a spark plug of the invention, as the top end edge of a terminal 13 is located within a middle trunk portion 2g of the insulator 2 with a longer reach of the screw portion 7, it acts as a support against fracture, more likely causing the problem of strength. Thus, the wall thickness of the middle trunk portion 2g at a position corresponding to the top end edge of the terminal 13 is sufficiently secured to be 0.42 or larger, based on the value of (D−d)/D, whereby it is possible to prevent the inconvenience such as fracture of the insulator, particularly, the middle trunk portion 2g from occurring owing to some strong force of bending, impact or torque applied on the insulator 2, when the spark plug is attached.

Abstract: An insulator for spark plug comprises an alumina-based sintered body comprising: Al2O3 as a main component; and at least one component (hereinafter referred to as “&bgr; component”) selected from the group consisting of Ca component, Sr component and Ba component, wherein the alumina-based sintered body comprises particles comprising a compound comprising the &bgr; component and Al component, the compound having a molar ratio of the Al component to the &bgr; component of 4.5 to 6.7 as calculated in terms of oxides thereof, and has a relative density of 90% or more.

Abstract: A method for producing a spark plug, the spark plug comprising a center electrode, a metal shell and an alumina ceramic insulator disposed between the center electrode and the metal shell, wherein at least part of the surface of the insulator is covered with a glaze layer comprising oxides, the method comprising the steps of: preparing a coated glaze powder so that a surface of each particle of a glaze powder is covered by an elution-suppressing coating layer, the elution-suppressing coating layer suppressing an elution of water soluble component that is contained in each particle of the glaze powder; preparing a glaze slurry by suspending the glaze powder in a water solvent; applying the glaze slurry to a surface of the insulator so as to form a glaze powder-deposited layer; and baking the glaze powder-deposited layer to the surface of the insulator to form the glaze layer by heating the glaze powder-deposited layer.

Abstract: A method for producing a spark plug, the spark plug comprising a center electrode, a metal shell and an alumina ceramic insulator disposed between the center electrode and the metal shell, wherein at least part of the surface of the insulator is covered with a glaze layer, the method comprising the steps of: preparing a plurality of kinds of element glaze powders wherein each kind of the element glaze powders has a different dilatometric softening point and a different linear expansion coefficient compared to other kinds of element glaze powders; coating a surface of the insulator with the plurality of kinds of element glaze powders so as to form a glaze powder layer; and baking the glaze powder layer to the surface of the insulator so as to form the glaze layer by heating the glaze powder layer.

Abstract: A method for manufacturing a spark plug, the spark plug comprises: a cylindrical metal shell having a portion to be caulked and a tool-engaging portion that is to be attached on an engine; an insulator that is inserted into the metal shell and extends axially; and a caulking metallic mold, the method comprising caulking the portion to be caulked to be fixed to an outer circumferential face of the insulator with the caulking metallic mold, wherein the caulking metallic mold comprises a face, the face comprising a hard carbon film that comprises an amorphous carbon phase, and the face is contact with or sliding to the portion to be caulked.

Abstract: In insulator including alumina as a main component, a Na component in the insulator is set in the range of 0.07 to 0.5 wt % as Na2O. While the Na component content is as high as to have conventionally been regarded to be beyond the common sense, with this range of the Na component content, insulation resistance, mechanical strength and the like at high temperature are unexpectedly not reduced and an insulator with performances comparable to those of an insulator from conventional low soda alumina lower in Na component content than the above described range can be obtained. As a result, medium soda alumina and regular soda alumina that are much lower in cost than conventionally used low soda alumina can be used instead of the low soda alumina, so that dramatic reduction in production costs of insulator 2 for a spark plug 100 and in addition, of the spark plug 100 using the insulator 2 are realized.

Abstract: A resistor-containing spark plug 100 has an alumina insulator 2 coated with a glaze layer 2d, the glaze layer 2d has a lead component content of 1 mol % or lower in terms of PbO and containing a silicon component, a boron component, a zinc and/or alkaline earth metal component, and an alkali metal component. The insulator has, in an axially central position thereof, a projection part protruding from the outer circumferential surface thereof and extending in a circumferential direction. That main body of the insulator which is located adjacent to the projection part on the rear side thereof, which is the side opposite to the front side facing the center electrode in the axial direction, has a base portion having a cylindrical outer circumference. The outer circumference of the base portion is covered with the glaze layer which, when examined by the method as provided for in JIS B 0601, gives a surface roughness curve having a maximum height Ry of 10 &mgr;m or smaller.

Abstract: A spark plug comprises: a center electrode (3); an insulator (2) provided around the center electrode (3); a metal shell (1)provided around the insulator (2); a ground electrode (4) disposed in opposition to the center electrode (3) so as to form a spark discharge gap; and a sealing-material layer (61) comprising a sealing material, wherein the sealing material comprises talc, and the sealing material is filled in a space between the inner face of the metal shell (1) and the outer face of the insulator (2), so as to seal the space, wherein the sealing material has a filling density of 1.5 g/cm3 to 3.0 g/cm3, or the sealing-material layer (61) comprises at least one of an inorganic material and a silicone binder in an amount of 2 to 7 wt %.

Abstract: A spark plug comprises: a center electrode (3); an insulator (2) provided around the center electrode (3); a metal shell (1) provided around the insulator (2); a ground electrode (4) disposed in opposition to the center electrode (3) so as to form a spark discharge gap; and a sealing-material layer (61) comprising a sealing material, wherein the sealing material comprises talc, and the sealing material is filled in a space between the inner face of the metal shell (1) and the outer face of the insulator (2), so as to seal the space, wherein the sealing material has a filling density of 1.5 g/cm3 to 3.0 g/cm3, or the sealing-material layer (61) comprises at least one of an inorganic material and a silicone binder in an amount of 2 to 7 wt %.

Abstract: A glaze layer 2d of the spark plug has the composition comprising 1 mol % or less of a Pb component in terms of PbO; 25 to 45 mol % of a Si component in terms of SiO2; 20 to 40 mol % of a B component in terms of B2O3; 5 to 25 mol % of a Zn component in terms of ZnO; 0.5 to 15 mol % of Ba and/or Sr components in terms of BaO or SrO; 5 to 10 mol % in total of at least one alkaline metal component of of Na, K and Li in terms of Na2O, K2O, and Li2, respectively, where K is essential; and further, 0.5 to 5 mol % in total of one or two kinds or more of Mo, W, Ni, Co, Fe and Mn in terms of MoO3, WO3, Ni3O4, Co3O4, Fe2O3, and MnO2, respectively.

Abstract: The present invention provides a spark plug having a glaze layer on the insulator thereof, wherein the glaze layer has a reduced Pb content, is capable of being fired at a relatively low temperature, exhibits excellent insulation properties, and can have a smooth surface.

Abstract: In insulator including alumina as a main component, a Na component in the insulator is set in the range of 0.07 to 0.5 wt % as Na2O. While the Na component content is as high as to have conventionally been regarded to be beyond the common sense, with this range of the Na component content, insulation resistance, mechanical strength and the like at high temperature are unexpectedly not reduced and an insulator with performances comparable to those of an insulator from conventional low soda alumina lower in Na component content than the above described range can be obtained. As a result, medium soda alumina and regular soda alumina that are much lower in cost than conventionally used low soda alumina can be used instead of the low soda alumina, so that dramatic reduction in production costs of insulator 2 for a spark plug 100 and in addition, of the spark plug 100 using the insulator 2 are realized.

Abstract: In a spark plug in which a space between a center electrode at the top end side and a terminal electrode at a rear end side which are arranged to be opposite to each other in an axial hole of an insulator, the glass seal is effected at a temperature within the range of 500 to 1000° C. and under a condition where the concentration of oxygen is 4-12 vol %.

Abstract: In a spark plug (100), the resistor composition constituting a resistor (15) contains semiconductive ceramic particles, offering a superior load life characteristic. Also, the value of (&agr;2−&agr;1)/&agr;1>=−0.30, where a value of electric resistance between a terminal (13) and a center electrode (3) is &agr;1 at 20° C. and &agr;2 at 150° C., so that deterioration of the radio frequency noise prevention performance at high temperatures can be effectively suppressed. The resistor composition contains semiconductive ceramic particles whose temperature coefficient of electric resistance shows a positive value, or a negative value of relatively small absolute value, (e.g., TiO2 particles having a rutile type crystalline structure, titanate or zirconate of alkali earth metal elements, titanium suboxide, etc.), or titanium metal.

Abstract: A glaze layer formed on the surface an alumina-based insulator of a resistor spark plug contains SiO2 (18 to 35% by weight), B2O3 (25 to 40% by weight), ZnO (10 to 25% by weight), BaO (7 to 20% by weight), Na2O (3 to 9% by weight), and K2O (3 to 9% by weight). Since the difference between the coefficients of linear expansion of the glaze and that of the alumina-based insulating material is relatively small, the glaze layer is less susceptible to cracks and the like. Also, since the glaze has a softening point lower than that of conventional lead-silicate-glass-based glaze, the glost-firing temperature can be as low as 800° to 950° C. Therefore, even in the case where glost firing is performed concurrently with a glass sealing step, a center electrode and a terminal metal piece are less susceptible to oxidation. Further, even though the content of the alkali metal component is high, a good insulating performance is obtained so that excellent flashover resistance is attained.