JP4125826B2 - Glow plug - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
  The present invention relates to a glow plastic used for diesel engine preheating and the like.ToRelated.
[0002]
[Prior art]
In general, the glow plug as described above has a resistance heating heater disposed on the inner side of a metal shell having a mounting thread portion formed on the outer peripheral surface thereof so that a heat generating portion at the tip protrudes from one end surface of the metal shell. It has a structure. And it uses by attaching to an engine head with the said screw part.
[0003]
By the way, the metal shell is generally made of an iron-based material such as carbon steel, and the surface thereof is often galvanized for corrosion protection. Although the galvanized layer has an excellent anticorrosive effect against iron, as is well known, the galvanized layer on iron is easily consumed by sacrificial corrosion, and the appearance is changed to white due to the generated zinc oxide. There are also disadvantages that are easily damaged. Therefore, in many glow plugs, the surface of the galvanized layer is further covered with a chromate film to prevent corrosion of the plated layer.
[0004]
By the way, a so-called yellow chromate film has been used as a chromate film applied to the metal shell of the glow plug. Since this yellow chromate film has good anticorrosion performance, it has been widely used in fields other than glow plugs, such as canned inner surface coating. However, in recent years when interest in environmental protection has been increasing on a global scale due to the fact that some of the chromium component is contained in the form of hexavalent chromium, it has gradually been shunned. For example, in the automotive industry in which glow plugs are used in large quantities, considering the influence of waste glow plugs on the environment, the use of chromate coatings containing hexavalent chromium has been studied to be eliminated in the future. In addition, since the treatment bath for the yellow chromate film treatment contains a relatively high concentration of hexavalent chromium, there is a problem that the waste liquid treatment is very expensive.
[0005]
[Problems to be solved by the invention]
In response to this trend, the development of a chromate film that does not contain hexavalent chromium, that is, a film in which substantially all of the chromium component is contained in the form of trivalent chromium has been underway relatively early. The treatment bath generally has a low hexavalent chromium concentration, and a bath containing no hexavalent chromium has been developed, and the problem of waste liquid treatment has been reduced. However, the trivalent chromium-based chromate film has a major disadvantage that the anticorrosion performance is inferior to that of the yellow chromate film, and has not been widely used as a coating film for the glow plug metal shell. In addition, the chromate film, including the yellow chromate film, has a common drawback that it has poor heat resistance.
[0006]
  An object of the present invention is to provide a glow plug that has a low hexavalent chromium content in the chromate film covering the surface of the metal shell and is superior in anticorrosion performance and heat resistance as compared with conventional chromate films.GIt is to provide.
[0007]
[Means for solving the problems and actions / effects]
  In order to solve the above-mentioned problem, the glow plug of the present invention has a structure in which a resistance heating heater is disposed in the metal shell so that the tip portion projects from one end face of the metal shell,The main component of the cationic component is a chromium component, and 90% by weight or more of the chromium component is composed of trivalent chromium and a trivalent chromium-based chromate layer mainly composed of silicon oxide. The surface of the metallic shell is covered with a silicon composite chromate film including at least two layers of a silica-based layer having a film thickness of 0.2 to 0.8 μm that directly or indirectly covers the other through another layer. M in the silica-based layer of the coating ₂ The content of alkali metal M in terms of O is μ1, and SiO ₂ The value of μ2 / μ1 is 2 to 4 when the content of the silicon component converted into is μ2.It is characterized by that.
[0008]
The “cationic component” means that the ion valence is positive at the binding energy peak of the component of interest in the photoelectron spectrum obtained when the film is analyzed by X-ray photoelectron spectroscopy (XPS or ESCA). It is a component in which a chemical shift in the direction occurs.
[0009]
In the above configuration, a silicon composite chromate film containing a silicon component as a main component of the cationic component is formed on the surface of the metal shell, and 90% by weight or more of the chromium component becomes trivalent chromium. ing. That is, in the normal yellow chromate film, about 25 to 35% by weight of the chromium component is hexavalent chromium, whereas in the film of the present invention, the content of hexavalent chromium with respect to the chromium component is as low as 10% by weight or less. Therefore, it is possible to enhance the effect on environmental measures to reduce hexavalent chromium. In addition, the chromate treatment liquid used does not contain any hexavalent chromium component, or even if it contains it, the amount can be greatly reduced compared to the treatment liquid such as yellow chromate coating. Hard to occur.
[0010]
The silicon composite chromate film used in the present invention is characterized in that it contains a silicon component as a cationic component. By including a silicon component in the composite chromate film, the anti-corrosion performance is greatly improved as compared with a normal trivalent chromium-based chromate film, and the metal shell can be sufficiently provided with durability against corrosion. Become. Further, by combining the silicon component, the heat resistance of the coating is dramatically improved, and the corrosion resistance of the metal shell can be sufficiently maintained even in an environment where the temperature of the glow plug is likely to rise.
[0011]
In the glow plug, an energizing terminal shaft for energizing the resistance heating heater is arranged with its rear end protruding from the other end face of the metal shell, and a male screw formed at the rear end of the energizing terminal shaft Many parts have a structure in which a nut for fixing an energizing cable to the energizing terminal shaft is screwed to the portion. In this case, at least a part of the surface of the nut can be covered with the silicon composite chromate film. Accordingly, corrosion resistance and heat resistance can be sufficiently imparted to the nut as well as the metal shell.
[0012]
The silicon component can be contained, for example, in a form combined with oxygen, that is, in the form of a silicon oxide such as silica. In the present specification, if the silicon peak having a valence of +4 or close to it and the peak of oxygen having a valence of -2 or close to it are detected simultaneously in the above-mentioned XPS photoelectron spectrum, the silicon component is oxygen. It is thought that it is contained in a combined form.
[0013]
On the other hand, the chromate film is formed by the reaction between the base metal and a solution containing chromate ions, but this film formation reaction involves the formation of a polymer complex by trivalent chromium by a bridge of hydroxyl and oxygen. By doing so, it is said that the mechanism of precipitating and depositing in the form of a gel on the surface of the underlying metal is the main component. When a hydroxyl group is bonded to trivalent chromium, the valence of chromium is apparently shifted to +4 due to the influence of protons contained in the hydroxyl group. In the present specification, if a peak component chemically shifted from a trivalent chromium peak position to a position corresponding to a valence of approximately +4 is observed in the XPS photoelectron spectrum, the chromium component is regarded as a component of the chromate film. I think that it has become.
[0014]
The chromate treatment is a kind of chemical conversion treatment in which the chromium component is replaced and deposited while the base metal is oxidized and eluted. Therefore, in the electroless chromate treatment in which power is not supplied from the outside, the base metal needs to be a metal that can be eluted in the chromate treatment bath. In glow plugs, the main metal fittings or nuts are generally made of an iron-based material such as carbon steel, and a zinc-based plating layer consisting mainly of zinc is formed on the surface to prevent corrosion. can do. In this sense, this zinc-based plating layer is convenient as a base metal for forming a chromate film. In this case, the eluted zinc component is often taken into the chromate film. The zinc-based plating layer can be formed by known electrolytic galvanization or hot dip galvanization.
[0015]
On the other hand, if the electrolytic chromate treatment method is employed, a chromate film can be formed even if the metal component is mainly a nickel-based plating layer made of nickel.
[0016]
Next, in the method of forming the chromate film to be formed into a silicon composite chromate film that is a feature of the present invention, for example, a water-soluble silica-based compound, for example, an alkali silicate such as water glass is blended in a chromate treatment bath. Then, there is a method of incorporating silica components in the formed chromate film. However, from the viewpoint of further improving the anticorrosion performance (particularly durability against the salt spray test) and heat resistance, the silicon composite chromate film should have the following structure. That is, the silicon composite chromate film is mainly composed of a trivalent chromium-based chromate layer in which the main component of the cationic component is a chromium component and 90% or more of the chromium component is composed of trivalent chromium, and an oxide of silicon. In addition, at least two layers including a silica-based layer that directly or indirectly covers a trivalent chromium-based chromate layer via another layer are included.
[0017]
In the trivalent chromium-based chromate layer, the total weight of the chromium component may be 50% by weight or more with respect to the total weight of the cationic component, and the balance is other cationic components such as silicon or zinc, It may be a component such as nickel. On the other hand, in the silica-based layer, the total weight of the silicon component may be 50% by weight or more with respect to the total weight of the cationic component, and the remainder is other cationic components such as chromium, zinc, nickel, etc. It may be a component of.
[0018]
Such film formation can be realized, for example, by the glow plug manufacturing method of the present invention including the following steps.
(1) Chromate treatment step: By immersing the metallic shell in a chromate treatment bath, a trivalent chromium-based chromate layer in which 90% by weight or more of the chromium component is composed of trivalent chromium is formed on the surface of the metallic shell.
(2) Silica-based layer forming step: After applying a silicate solution in which an alkali silicate is dissolved in a predetermined solvent to the metal shell on which the trivalent chromium-based chromate layer is formed, the solvent is added. By evaporating, a silica-based layer mainly composed of silicon oxide is formed on the trivalent chromium-based chromate layer.
In this case, the silica-based layer is mainly composed of an oxide composed mainly of an alkali metal element and silicon.
[0019]
Needless to say, the same method can be applied to the formation of a coating film on the nut by replacing the metal shell with the nut in the above process.
[0020]
As described above, the anticorrosion performance of the coating can be further greatly improved by previously forming the trivalent chromium-based chromate layer on the surface of the metal shell and covering the surface with the silica-based layer. Further, the heat resistance of the coating can be achieved at a level that surpasses that of the conventional trivalent chromium-based chromate coating as well as the yellow chromate coating containing hexavalent chromium.
[0021]
In addition, for the formation of the silica-based layer, a vapor phase film forming method such as high-frequency sputtering, reactive sputtering, ion plating, or chemical vapor deposition (CVD) may be used. However, according to the above method by application of the silicate solution, the metal shell (or nut) after the chromate treatment is immersed in the silicate solution, or after the silicate solution is applied by spraying or the like, A silica-based layer can be easily formed simply by drying the coating film.
[0022]
In addition, a trivalent chromium-silicon mixed layer is formed between the trivalent chromium-based chromate layer and the silica-based layer, in which the trivalent chromium component and the silicon component are mixed at an intermediate content ratio between the two layers. It may be. Thereby, the anticorrosion performance or heat resistance of the silicon composite chromate film may be further improved. For example, the formation of the trivalent chromium-silicon mixed layer as described above means that a kind of composition gradient structure is formed between the trivalent chromium-based chromate layer and the silica-based layer. Improved coating performance as described above has been achieved by improving the adhesion between the trivalent chromium-based chromate layer and the silica-based layer and reducing stress based on the difference in shrinkage between the chromate layer and the silica-based layer during heating. it can.
[0023]
It is said that the anti-corrosion performance of yellow chromate coatings, etc., is due to the fact that the trivalent chromium network is restored by the action of the hexavalent chromium contained even when the coating is destroyed in a corrosive environment. ing. However, in the trivalent chromium-based chromate layer, since such a repair effect due to hexavalent chromium cannot be expected, if defects such as pinholes occur in the coating, the influence of corrosion directly affects the base such as the zinc-based plating layer, It is thought that corrosion progresses rapidly. However, in the silicon composite chromate film having the above-described structure, the trivalent chromium-based chromate layer is overcoated with a silica-based layer, and the influence of corrosion is less likely to reach the surface of the trivalent chromium-based chromate layer and the underlying layer. It is considered that the anticorrosion performance is improved.
[0024]
On the other hand, it is considered that the conventional chromate film is inferior in heat resistance because the chromate film is contracted by heating and defects such as cracks are likely to occur. However, in the above configuration, even if the above-mentioned defects occur in the chromate layer, the surface is overcoated with a silica-based layer having good heat resistance, so that the anticorrosion performance is hardly deteriorated. Conceivable.
[0025]
In order to form a uniform silica-based layer, it is also important to improve the wettability between the silicate solution and the underlying trivalent chromium-based chromate layer. For example, if a trivalent chromium-based chromate layer has defects such as pinholes or cracks (in this case, including those that have inherited defects in the ground due to scratches or adhesion of foreign matter), the wettability is poor. When a silicate solution is used, bubbles and the like are likely to remain in the defect. In this case, it is also effective to mix an appropriate amount of a surfactant in the aqueous silicate solution.
[0026]
On the other hand, after completion of the chromate treatment step, there is also a method of performing a silica-based layer forming step by immersing the surface of the metal shell in a silicate solution in an undried or semi-dried state. That is, after the chromate treatment is finished, a trivalent chromium-based chromate layer is formed on the surface of the metal shell in an undried or semi-dried state with a slight amount of moisture, The familiarity is also good. As a result, even if defects are formed in the trivalent chromium-based chromate layer, the aqueous solution of silicate sufficiently penetrates into the defects, and it is difficult for bubbles and the like to remain, resulting in good anticorrosion performance of the coating. can do.
[0027]
Further, as another effect, the chromate treatment liquid remaining on the surface layer portion of the formed trivalent chromium-based chromate layer is mixed with a part of the applied silicate aqueous solution, and the aforementioned trivalent chromium-silicon mixture is mixed. There is an advantage that a layer is easily formed. The effect of forming the trivalent chromium-silicon mixed layer has already been described.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, some embodiments of the present invention will be described with reference to the drawings.
A glow plug 1 as an example of the present invention shown in FIG. 1A includes a sheathed heater 2 and a metal shell 3 arranged on the outside thereof. As shown in FIG. 1B, the sheathed heater 2 has two resistance wire coils, that is, a heating coil 21 disposed on the distal end side, and a rear end thereof welded to the inside of the sheath tube 11 whose distal end is closed. A control coil 23 connected in series is enclosed together with an insulating material such as magnesia powder. The body portion 11 a of the sheath tube 11 that accommodates the heat generating coil 21 and the control coil 23 protrudes from the metal shell 3 to form a protruding portion. Although the heat generating coil 21 is electrically connected to the sheath tube 11 at the tip thereof, the outer peripheral surface of the heat generating coil 21 and the control coil 23 and the inner peripheral surface of the sheath tube 11 are insulated by the intervention of magnesia powder. Yes. The metal shell 3 is formed in a cylindrical shape having an axial through-hole 4, and the sheathed heater 2 is inserted and fixed in a state where the distal end side of the sheathed tube 11 protrudes a predetermined length from one opening end. Has been. A tool engaging portion 9 having a hexagonal cross section for engaging a tool such as a torque wrench when the glow plug 1 is attached to the diesel engine is formed on the outer peripheral surface of the metal shell 3. A screw part 7 for attachment is formed.
[0029]
The base end side of the sheath tube 11 is press-fitted and fixed in the through hole 4 of the metal shell 3. On the other hand, a counterbore 3a is formed in the opening on the opposite side of the through hole 4, and here, a rubber O-ring 15 and an insulating bush (for example, nylon) 16 which are sheathed on the energizing terminal shaft 13; Is inserted. On the further rear side, the energizing terminal shaft 13 is provided with a pressing ring 17 for preventing the insulation bush 16 from falling off. The holding ring 17 is fixed to the energizing terminal shaft 13 by a caulking portion formed on the outer peripheral surface, and a knurled portion 13b for increasing the caulking coupling force is formed on a corresponding surface of the energizing terminal shaft 13. Has been. Further, a female screw portion 13 a is formed at the rear end portion of the energizing terminal shaft 13, and a nut 19 for fixing the energizing cable to the energizing terminal shaft 13 is screwed.
[0030]
The glow plug 1 is attached to a cylinder block of a diesel engine at a threaded portion 7 of the metal shell 3. Thereby, the front-end | tip part of the sheath tube 11 in which the heat generating coil 21 and the control coil 23 were accommodated is positioned in the combustion chamber (or auxiliary combustion chamber) of the engine. In this state, when a voltage is applied to the energizing terminal shaft 13 using an in-vehicle battery as a power source, the energizing terminal shaft 13 → the control coil 23 → the heating coil 21 → the sheath tube 11 → the metal shell 3 → (grounded through the engine block). Energized along the route. This energization causes the sheathed heater 2 to generate resistance heat and ignite the fuel injected into the engine block. In the sheathed heater 2, since the temperature of the control coil 23 is low and the electrical resistance value is small in the initial stage of energization, a relatively large current flows through the heating coil 21 to rapidly raise the temperature. When the temperature of the heat generating coil 21 rises, the control coil 23 is heated by the heat generation, the electric resistance value increases, and the current value supplied to the heat generating coil 21 decreases. As a result, the temperature rise characteristic of the heater is such that after the temperature is rapidly raised in the initial stage of energization, the energization current is suppressed by the action of the control coil and the temperature is saturated.
[0031]
Next, a zinc plating layer 41 (zinc-based plating layer) for corrosion prevention is formed on the entire outer surface of the metal shell 3, and the outer side thereof is covered with a silicon composite chromate film 42. Similarly, a galvanized layer 45 and a silicon composite chromate film 46 are also formed on the outer surface of the nut 19. The galvanized layer and the silicon composite chromate film are both formed by the same method, and will be described below on behalf of the metal shell 3 side.
[0032]
The galvanized layer 41 is formed by a known electrolytic galvanizing method, and has a thickness of about 5 to 20 μm, for example. If this thickness is less than 5 μm, corrosion resistance may not be sufficiently secured. Conversely, a film thickness exceeding 20 μm is excessive in terms of securing corrosion resistance, leading to an increase in cost.
[0033]
On the other hand, as schematically shown in FIG. 2, the silicon composite chromate film 42 is a trivalent chromium chromate in which the main component of the cationic component is a chromium component and 90% by weight or more of the chromium component is composed of trivalent chromium. A layer (hereinafter referred to as a chromate (III) layer) 42a and a silica-based layer 42c mainly composed of an oxide of silicon and covering the chromate (III) layer 42a, and between these layers 42a and 42c. Is formed with a trivalent chromium-silicon mixed layer 42b in which a trivalent chromium component and a silicon component are mixed at an intermediate content ratio between the two layers. It should be noted that as much of the chromium component as possible should be a trivalent chromium component, and it is desirable that substantially all of the chromium component is a trivalent chromium component.
[0034]
The total thickness of the silicon composite chromate film 42 is, for example, 0.8 to 1.5 μm. When the total thickness is less than 0.8 μm, the anticorrosion performance and heat resistance imparting effect on the galvanized layer 41 may be insufficient. On the other hand, a film thickness exceeding 1.5 μm is excessive in terms of ensuring corrosion resistance, leading to an increase in cost. In addition, the silicon composite chromate film may be peeled off.
[0035]
The thickness of the chromate (III) layer 42a is preferably 0.2 to 0.3 μm. If the thickness is less than 0.2 μm, the anticorrosion performance of the silicon composite chromate film 42 may be insufficient. On the other hand, a film thickness exceeding 0.3 μm is excessive in terms of ensuring corrosion resistance, leading to an increase in cost. On the other hand, the thickness of the silica-based layer 42c is preferably 0.2 to 0.8 μm. If the thickness is less than 0.2 μm, the anticorrosion performance and heat resistance of the silicon composite chromate film 42 may be insufficient. On the other hand, a film thickness exceeding 0.8 μm is an excessive specification, which not only leads to an increase in cost, but may be peeled off.
[0036]
FIG. 3 schematically shows an example of a method for forming the silicon composite chromate film 42. First, a metal shell 3 ″ having a galvanized layer having a predetermined thickness formed by a known electrolytic galvanizing method or the like is immersed in the chromate treatment solution 50. As a result, as shown in FIG. On the surface of the galvanized layer 41 formed on the 3 ″ base layer 40, a chromate (III) layer 42a is formed.
[0037]
Examples of usable chromate treatment liquid include those containing the following components (so-called colorless or blue chromate treatment liquid).
Chromic anhydride: 0.1-2 g / liter
Sulfuric acid: 0.3-5 g / liter
Nitric acid: 0.5 to 10 g / liter
Phosphoric acid: Add to about 2 g / liter if necessary
Hydrofluoric acid: Add to about 2 g / liter if necessary
In this treatment liquid, the amount of chromic anhydride used as a hexavalent chromium source is reduced to less than half that of the so-called yellow chromate treatment liquid of 4 to 10 g / liter. Sulfuric acid functions as a reaction accelerator, and nitric acid functions as an oxidizing agent for elution of the base metal. On the other hand, phosphoric acid has the role of improving the adhesion of the chromate film to the underlying metal, and hydrofluoric acid is incorporated into the film as an anion, strengthening the bridge bond in the polymer complex structure, and improving the film strength and thus the anticorrosion performance. Play a role to improve.
[0038]
In addition, it is also possible to use the following liquid that does not use a solute serving as a hexavalent chromium source (so-called chromium (III) chromate treatment liquid).
Potassium chromium sulfate (so-called chromium alum): 2.5 to 3.5 g / liter
Nitric acid: 3.5-4.5 g / liter
Hydrofluoric acid: 1.5-2.5 g / liter
However, the chromate treatment solution is not limited to the above as long as the content ratio of trivalent chromium to the chromium component in the chromate film can be 90% by weight or more.
[0039]
The reaction during the chromate treatment is considered to be as follows. That is, when the metal shell 3 ″ having a galvanized layer is immersed in the liquid, the gel-like film mainly composed of chromium (III) hydroxide is replaced by the dissolution of zinc by replacing the chromium ions in the liquid. A part of the dissolved zinc is taken into the film in the form of, for example, zinc chromate, etc. The structure of the formed chromate film is, for example, in the form as shown in FIG. That is, a polymer complex of trivalent chromium formed in a network by a hydroxyl group or oxygen bridge is formed, and a part of the network is made of chromate, dichromate, sulfuric acid, chloride, fluoride, etc. The anion (the kind of anion varies depending on the composition of the chromate treatment solution to be used) is substituted with one or more of the anions (of the chromate (III) layer 42a). Adjustment of NaruAtsu is can be performed, for example, by the immersion time and the adjustment of the liquid temperature to the chromating solution of the metal shell 3 ".
[0040]
Next, as shown in FIG. 3B, the metal shell 3 ′ after the formation of the chromate (III) layer 42a is in an undried or semi-dried state in an aqueous silicate solution 51 (silicate solution). Then, this is dried to form a trivalent chromium-silicon mixed layer 42b and a silica-based layer 42c, as shown in FIG. 4 (c).
[0041]
As the silicate aqueous solution 51, a so-called aqueous solution of water glass can be used. Water glass has the general formula M₂O · nSiO₂(Wherein M is an alkali metal element such as sodium or potassium), and silicon dioxide is deposited by drying and hardened into a gel. The resulting silica-based layer 42c is composed of an oxide mainly composed of an alkali metal element and silicon (for example, a gel-like cured product mainly composed of alkali silicate and silicon dioxide). .
[0042]
As water glass, n is about 2-4. When n is 2 or less, gelation hardly occurs and the obtained silica-based layer 42c becomes water-soluble, so that a stable film cannot be obtained. On the other hand, if n exceeds 4, hydrolysis of the alkali silicate proceeds excessively in the solution 51, and silicon dioxide gel precipitates and precipitates, so that the coating process cannot be carried out stably. Note that n is more preferably in the range of 3-4. In this case, M in the entire silicon composite chromate coating 42₂The content of alkali metal M in terms of O is μ1, also SiO₂If the content of the silicon component converted into is μ 2, it is desirable to adjust the value of μ 2 / μ 1 in the range of 2 to 4, preferably 3 to 4.
[0043]
In order to form the silica-based layer 42c as uniformly as possible on the chromate (III) layer 42a, the silicate aqueous solution 51 is desirably adjusted to a concentration of alkali silicate of 30 to 200 g / liter. When the concentration is less than 30 g / liter, the formation thickness of the silica-based layer 42c becomes insufficient, and the anticorrosion performance or heat resistance performance of the silicon composite chromate film 42 may not be ensured. On the other hand, if the concentration exceeds 200 g / liter, the viscosity of the aqueous silicic acid solution 51 becomes too high, and it becomes difficult to form a uniform silica-based layer 42c due to the occurrence of coating unevenness and the like.
[0044]
As shown in FIG. 4A, the chromate treatment liquid 50 remains on the surface portion of the chromate (III) layer 42a immediately after being pulled up from the chromate treatment liquid 50. In this state, the chromate treatment liquid 50 is in the silicate aqueous solution 51. When immersed, as shown in FIG. 4B, for example, a part of the applied aqueous silicate solution 51 is mixed to form a mixed layer 42b ′. When this is dried, as shown in FIG. 4C, a trivalent chromium-silicon mixed layer 42b derived from the mixed layer 42b ′ is formed between the chromate (III) layer 42a and the silica-based layer 42c. It is formed. The trivalent chromium-silicon mixed layer 42b is formed by mixing the chromate treatment solution 50 and the silicate aqueous solution 51 (or the penetration of the silicate aqueous solution 51 into the chromate (III) layer 42a). A trivalent chromium component and a silicon component are mixed at an intermediate content ratio between 42a and 42c. This means that a kind of composition gradient structure is formed between the chromate (III) layer 42a and the silica-based layer 42c via the trivalent chromium-silicon mixed layer 42b. Effects such as improved adhesion and stress reduction based on the difference in thermal shrinkage can be achieved.
[0045]
Note that the chromate (III) layer 42a is formed in a wet state on the surface of the metal shell 3 'in an undried or semi-dried state after the chromate treatment is completed, and the familiarity with the silicate aqueous solution 51 is improved. . Accordingly, as shown in FIG. 5 (a), even if a defect def such as pinholes is formed in the chromate (III) layer 42a, the silicate aqueous solution 51 is sufficiently easily penetrated here, and the formed silica. It is possible to make it difficult for bubbles and the like to remain in the system layer 42c (FIG. 5B).
[0046]
The metal shell 3 or nut 19 treated in this way has a silicon composite chromate film formed on the galvanized layer, which is significantly higher in corrosion protection than the conventional trivalent chromium-based chromate film or yellow chromate film. It has performance and heat resistance, and can sufficiently impart durability against corrosion to the galvanized layer.
[0047]
In addition, after the chromate treatment, the surface of the metal shell 3 ′ may be sufficiently dried and then immersed in the silicic acid aqueous solution 51. In this case, since the chromate (III) layer 42a is once dried, the mixed layer 42b 'of the chromate treatment solution 50 and the silicate aqueous solution 51 is hardly formed. Therefore, as shown in FIG. 2B, a clear trivalent chromium-silicon mixed layer 42b may not be formed between the chromate (III) layer 42a and the silica-based layer 42c.
[0049]
The present invention can be similarly applied to a glow plug metal shell or a nut using a ceramic heater instead of a sheathed heater.
[0050]
【Example】
In order to confirm the effect of the present invention, the following experiment was conducted. First, the metal shell 3 having the shape shown in FIG. 1 was manufactured by cold forging using STKM13CE as a material. The nominal diameter of the threaded portion 7 of the metal shell 3 was 10 mm, and the axial length was about 51.5 mm. Next, an electrolytic galvanizing treatment using a known alkali cyanide bath was performed on the galvanized layer to give a galvanized layer having a thickness of about 16 μm.
[0051]
Next, as the chromate treatment solution 50 shown in FIG. 3, a solution prepared by dissolving 3 g / liter of potassium chromium sulfate, 4 g / liter of nitric acid, and 2 g / liter of hydrofluoric acid in deionized water was prepared, and the liquid temperature was set to 20 ° C. Retained. On the other hand, Na₂O ・ 3.5SiO₂A silicate aqueous solution 51 was prepared by dissolving sodium silicate (water glass) having the following composition in deionized water at a concentration of 100 g / liter. Then, the galvanized metal shell is dipped in the chromate treatment solution 50 for 15 seconds, and then immediately immersed in the silicate aqueous solution 51 without being dried by performing only draining, and further at 80 ° C. The silicon composite chromate film was formed by sufficiently drying with warm air (test product (3): product of the present invention).
[0052]
The result of measuring the photoelectron spectrum of XPS while etching this silicon composite chromate film in the thickness direction is shown in FIG. From the spectral peak intensity of each component at each etching depth to about 0.5 μm from the surface, chromium (2p_2/3) Is hardly observed, indicating that the silica-based layer is mainly composed of silicon oxide. Note that, when examined in more detail by fluorescent X-ray analysis, the silica-based layer is composed of silicon and SiO.₂About 77% by weight in terms of converted value, sodium as Na₂It was found that the content was about 22% by weight in terms of O.
[0053]
On the other hand, although a slight silicon peak was observed at a depth of 0.7 to 1 μm from the surface, the cationic component was mainly chromium, and then a large amount of zinc was detected. The chromium (2p_2/3As a result of examining the peak of) in more detail, 99% by weight or more of the chromium component was trivalent chromium. That is, it was found that the approximately 0.3 μm portion in the depth range was a trivalent chromium-based chromate layer.
[0054]
The portion of about 0.3 μm in thickness located between the two layers is a trivalent chromium-silicon mixed layer containing a chromium component and a silicon component in the middle of both layers from the spectral peak intensity of each component of XPS. I found out that
[0055]
In addition, after being immersed in the chromate treatment liquid 50 for 15 seconds, not immersed in the silicate aqueous solution 51 but dried as it is (test product {circle over (2)}: comparative example), conversely, not immersed in the chromate treatment liquid 50, What was immersed and dried only in the silicate aqueous solution 51 (test product (4): comparative example) was also prepared. When the formed coatings of the test products (2) and (4) were analyzed by XPS and X-ray fluorescence analysis, the former had a weight content ratio of trivalent chromium in the chromium component of about 99% or more and a thickness of about 0. .5μm chromate film, the latter is silicon with SiO₂77% by weight in terms of converted value, sodium as Na₂It was found that the oxide-based film contained 22% by weight in terms of O.
[0056]
On the other hand, a yellow chromate treatment solution prepared by dissolving chromic anhydride at a rate of 7 g / liter, sulfuric acid 3 g / liter, and nitric acid 3 g / liter in deionized water was prepared and kept at a liquid temperature of 20 ° C. Then, the metal shell was dipped in this for about 15 seconds, pulled up, and dried to prepare a comparative example (test product (1)). When the formed film was analyzed by XPS, it was found that the chromate film had a thickness of about 0.5 μm, in which about 30% by weight of the chromium component was hexavalent chromium and the balance was trivalent chromium.
[0057]
The salt spray test specified in JISZ2371 is performed on the test products (1) to (4) above, until white rust derived from corrosion of the galvanized layer appears about 20% or more of the entire surface, or the underlying iron Durability evaluation was performed based on the time until red rust derived from the corrosion of the layer was visually confirmed. The result is shown in FIG. That is, the test product (3), which is a product of the present invention on which a silicon composite chromate film is formed, has an overwhelmingly superior durability than the test product of any comparative example, including the test product (1) treated with yellow chromate. You can see that Further, from the results of the test products (2) and (4), it is understood that when the trivalent chromium-based chromate layer or the silica-based layer is formed alone, good durability is not obtained.
[0058]
Next, FIG. 8 shows the result of the same salt spray test after heat-treating each test product (1) to (4) in the air at 200 ° C. for 30 minutes. The test product {circle around (1)} treated with yellow chromate has a significantly reduced durability due to heat treatment, while the test product {circle around (3)} of the present invention shows extremely good durability. I understand.
[Brief description of the drawings]
FIG. 1 is a longitudinal half sectional view showing a glow plug according to an embodiment of the present invention and a longitudinal sectional view showing an internal structure of a sheathed heater.
FIG. 2 is a conceptual diagram showing the structure of a silicon composite chromate film together with some modifications.
FIG. 3 is an explanatory diagram of a chromate treatment step and a silica-based layer formation step.
FIG. 4 is a diagram for explaining a formation process of a silicon composite chromate film and an estimated structure of a chromate layer.
FIG. 5 is a diagram for explaining the effect of a method of forming a silica-based layer in an undried state after chromate treatment.
FIG. 6 is a graph showing the XPS analysis results of the silicon composite chromate film formed on the test product (3) of the example.
FIG. 7 is a graph showing the results of a salt spray test on a test product of an example (no heat treatment).
FIG. 8 is a graph showing the results of a salt spray test on a test product of an example (after heat treatment).
[Explanation of symbols]
1 Glow plug
2 Seeds heater
3 metal shell
7 Screw part
11 Seeds tube
13 Current terminal shaft
19 Nut
41, 45 Galvanized layer
42,46 Silicon composite chromate coating
42a Trivalent chromium-based chromate layer
42b Trivalent chromium-silicon mixed layer
42c Silica-based layer

Claims (4)

Having a structure in which a resistance heating heater is disposed in the metal shell such that the tip of the metal heater protrudes from one end surface of the metal shell;
Further, the main component of the cationic component is a chromium component, and 90% by weight or more of the chromium component is mainly composed of a trivalent chromium-based chromate layer composed of trivalent chromium and silicon oxide, and the trivalent chromium The surface of the metal shell is covered with a silicon composite chromate film including at least two layers of a silica-based layer having a film thickness of 0.2 to 0.8 μm that directly covers the system-based chromate layer or indirectly through another layer. ,
When the content of the alkali metal M converted to the form of M ₂ O in the silica-based layer of the silicon composite chromate film is μ1, and the content of the silicon component also converted to SiO ₂ is μ2, μ2 / μ1 A glow plug characterized by a value of 2-4. An energizing terminal shaft for energizing the resistance heating heater is disposed in a form in which a rear end portion protrudes from the other end surface of the metal shell, and a male screw portion formed at the rear end portion of the energizing terminal shaft. On the other hand, a nut for fixing the energizing cable to the energizing terminal shaft is screwed,
The glow plug according to claim 1, wherein at least a part of a surface of the nut is covered with the silicon composite chromate film. Between the trivalent chromium-based chromate layer and the silica-based layer, a trivalent chromium-silicon mixed layer in which a trivalent chromium component and a silicon component are mixed at an intermediate content ratio between the two layers is formed. The glow plug according to claim 1 or claim 2 . The glow plug according to any one of claims 1 to 3, wherein the silica-based layer is mainly composed of an oxide mainly composed of an alkali metal element and silicon .

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