JP2000249340A - Glow plug and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glow plug having a chromate coating covering the surface of a main metal containing small quantity of hexavalent chromium and excellent in corrosion resistance and heat resistance as compared with a conventional one, and a manufacturing method thereof. SOLUTION: Surface of a main metal is covered with a chromate coating of 0.2-0.5 μm thick where trivalent chromium occupies 95 wt.% or more of chromium component. Since the chromate coating is made thick as compared with conventional trivalent chromium based chromate coating of about 0.1 μm thick, corrosion resistance is enhanced significantly and a sufficient durability against corrosion can be imparted to the main metal. Furthermore, corrosion resistance of the main metal can be sustained sufficiently even in the inherent environment of glow plug susceptible to easy temperature rise and acid attack. Chromate treating bath where a trivalent chromium salt is mixed with a complexing agent for trivalent chromium is preferably employed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glow plug used for preheating diesel engines and the like, and a method for manufacturing the same.

[0002]

2. Description of the Related Art A glow plug as described above is generally provided inside a metal shell having a threaded portion formed on an outer peripheral surface thereof.
It has a structure in which a resistance heating heater is arranged in such a manner that a heat generating portion at the tip projects from one end face of the metal shell. And it is used by being attached to the engine head by the above-mentioned screw portion.

The metallic shell is generally made of an iron-based material such as carbon steel, and its surface is often plated with zinc for corrosion protection. The galvanized layer has an excellent anticorrosion effect on iron, but as is well known, the galvanized layer on iron is easily consumed by sacrificial corrosion,
There is a disadvantage that the generated zinc oxide discolors white and the appearance is easily impaired. 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.

A so-called yellow chromate film has been used as a chromate film applied to a metallic shell of a glow plug. Since this yellow chromate film has good anticorrosion performance, it has been widely used in fields other than glow plugs, such as, for example, inner can coating. However, the concern that some of the chromium components are contained in the form of hexavalent chromium has led to a growing concern on environmental protection in recent years that has been increasingly avoided. For example, in the automotive industry where a large amount of glow plugs are used, studies are underway to eliminate the use of chromate films containing hexavalent chromium in the future in consideration of the environmental impact of waste glow plugs. Further, since a treatment bath containing a relatively high concentration of hexavalent chromium is used as a treatment bath for the yellow chromate film treatment, there is a problem that a large cost is required for waste liquid treatment.

[0005]

In response to this trend, the development of chromate coatings that do not contain hexavalent chromium, ie, coatings in which substantially all of the chromium component is contained in the form of trivalent chromium, has been relatively developed. It has been advanced from an early stage.
The treatment bath generally has a low hexavalent chromium concentration, and some baths containing no hexavalent chromium have been developed, and the problem of waste liquid treatment has been reduced. However, the trivalent chromium-based chromate coating has a major drawback in that the anticorrosion performance is inferior to that of the yellow chromate coating, and has not been widely used for coating a metal shell of a glow plug.

SUMMARY OF THE INVENTION An object of the present invention is to provide a glow plug which has a low hexavalent chromium content in a chromate film covering the surface of a metal shell and has excellent anticorrosion performance and heat resistance as compared with a conventional chromate film, and a method of manufacturing the same. Is to provide.

[0007]

In order to solve the above-mentioned problems, a glow plug according to the present invention has a resistance heating heater inside a metal shell, and a tip of the glow plug projects from one end face of the metal shell. In addition, the surface of the metal shell is formed by a chromate film having a chromium content of at least 95% by weight of trivalent chromium and a film thickness of 0.2 to 0.5 μm. Is coated.

[0008] In the above structure, the chromium component contained on the surface of the metal shell is trivalent chromium in an amount of 95% by weight or more and has a thickness of 0.2 to 0.5 µm.
m is a chromate film. That is, in the ordinary yellow chromate coating, hexavalent chromium accounts for about 25 to 35% by weight of the chromium component, whereas in the coating of the present invention, the content of hexavalent chromium with respect to the chromium component is as low as 5% by weight or less. Therefore, the effect on environmental measures for reducing hexavalent chromium can be enhanced. In addition, the chromate treatment solution used does not contain any hexavalent chromium component as described later, or even if it does, the amount can be significantly reduced as compared with a treatment solution such as a yellow chromate film. Processing problems are less likely to occur.

The present inventors have found that, in the case of a conventional trivalent chromium-based chromate coating such as a glossy chromate coating commonly called Unichrome or a blue chromate coating, the formed film thickness is about 0.1 μm at the maximum. And thin,
We thought that sufficient corrosion resistance and heat resistance could not be secured for the metal shell in the main use environment of the glow plug, and as a result of intensive studies on film thickness, we found a film thickness range particularly suitable for glow plugs. The invention was completed. That is, by ensuring that the thickness of the chromate film is 0.2 μm or more, the anticorrosion performance of the chromate film mainly composed of trivalent chromium is significantly improved, and the metal shell can be sufficiently imparted with corrosion resistance. Become like In addition, the corrosion resistance of the metal shell can be sufficiently maintained even in a usage environment peculiar to a glow plug, in which the temperature easily rises and an acid attack due to an exhaust gas component (CO ₂ or NOx) or the like is liable to occur.

An energizing terminal shaft for energizing the resistance heating heater is disposed on the glow plug so that its rear end protrudes from the other end surface of the metallic shell, and is formed at the rear end of the energizing terminal shaft. Many have a structure in which a nut for fixing an energizing cable to the energizing terminal shaft is screwed to the male screw portion. In this case, at least a part of the surface of the nut can be covered with the chromate film. This makes it possible to sufficiently impart corrosion resistance and heat resistance to the nut together with the metal shell.

The thickness of the chromate film is 0.2 μm.
If it is less than 1, the anticorrosion performance and heat resistance cannot be sufficiently secured. On the other hand, if the film thickness exceeds 0.5 μm, cracks may occur in the coating or the coating may easily fall off, which may lead to impairment of the anticorrosion performance. The thickness of the chromate film is desirably 0.3 to 0.5 μm. In addition, it is desirable that the chromate film does not substantially contain hexavalent chromium.

The chromate treatment is a kind of chemical conversion treatment in which a chromium component is replacedly deposited while oxidizing and eluting a base metal. Therefore, in an electroless chromate treatment in which power is not supplied from the outside, the base metal needs to be a metal that can be eluted into the chromate treatment bath. In a glow plug, the metal shell or nut is generally made of an iron-based material such as carbon steel, and a zinc-based plating layer mainly made of zinc is formed on the surface of the metal shell or nut to prevent corrosion. can do. This zinc-based plating layer is advantageous as a base metal for forming a chromate film in the above sense. 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 zinc plating or hot-dip galvanizing. 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.

A zinc plating layer is used as the base metal layer, and a chromate film having the above-mentioned thickness range is formed on the zinc plating layer, so that the plating corrosion resistance test method stipulated in JIS 8502 defines “5. Neutral salt spray test”. When 可能 is performed, it is possible to secure a durable time of 40 hours or more until white rust resulting from corrosion of the galvanized layer appears on about 20% or more of the entire surface. The level of corrosion resistance that metal fittings should have is sufficient.

Further, by forming the chromate film having the above-mentioned film thickness by using a zinc plating layer as the base metal layer, good durability performance can be obtained even in the following test assuming a use environment in which the temperature of the glow plug rises. Is obtained. That is, after heating in air at 200 ° C. for 30 minutes,
When "5. Neutral salt spray test method" in the corrosion resistance test method for plating specified in 8502 was performed, the durability time until white rust resulting from corrosion of the galvanized layer appeared about 20% or more of the entire surface. For more than 40 hours.

Also, in the following test assuming a use environment in which the glow plug receives an acid attack, good durability performance can be obtained. That is, when the “7. Cass test method” in the plating corrosion resistance test method specified in JIS H8502 was performed, the durability time until white rust resulting from corrosion of the galvanized layer appeared about 20% or more of the entire surface. , 20 hours or more.

Next, in the method for producing a glow plug of the present invention, a metal shell (or a nut) is immersed in a chromate treatment bath containing a trivalent chromium salt and a complexing agent for trivalent chromium. A chromate film as described above is formed on the surface of a metal shell (or a nut).

By using a bath containing a trivalent chromium salt and a complexing agent for trivalent chromium as a chromate treatment bath, a dense and thick trivalent chromium-based chromate film, which is difficult with a general chromate treatment method, can be formed. Thus, a trivalent chromium-based chromate film having a thickness of 0.2 to 0.5 μm, which is the gist of the glow plug of the present invention, can be easily formed. The method for forming such a chromate film is disclosed in detail in DE 19638176 A1. The outline will be described below.

As described above, in the process of forming the chromate film, the underlying metal (eg, zinc) is first oxidized and eluted in the treatment bath, and the eluted underlying metal component reacts with the solution containing chromate ions. It has been theorized that the main mechanism is that trivalent chromium forms a polymer complex by a hydroxyl group or an oxygen bridge and precipitates and deposits on the surface of the underlying metal in a gel state. In this case, in order for the chromate film to grow, the elution of the base metal and the reaction and deposition of the eluted base metal with the chromate ions in the bath must proceed in parallel. However, when the chromate film is deposited to some extent, the elution reaction of the underlying metal layer, which is a heterogeneous reaction via the interface with the bath solution, is prevented, and the film growth stagnates.

According to the disclosure of the above-mentioned German published patent application, in order to increase the thickness of the coating, dissolution of the base metal and
It is important that the rate of reverse dissolution of the deposited chromate film be as small as possible while increasing the rate of film deposition by the reaction between the dissolved base metal component and trivalent chromium. Then, in the above method, it is considered that by adding an appropriate complexing agent to the bath and complexing trivalent chromium, the precipitation of the film is promoted and the film can be made thicker.

As complexing agents, various chelating agents (dicarboxylic acid, tricarboxylic acid, oxyacid hydroxyl dicarboxylic acid or hydroxyl tricarboxylic acid, etc .: for example, oxalic acid,
It is effective to use malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, coric acid, aseleic acid, sebacic acid, maleic acid, phthalic acid, terephthalic acid, tartaric acid, citric acid, malic acid, ascorbic acid, etc. However, other complexing agents may be used. The complexing agents that can be used are as described in the aforementioned German patent publication.

In order to increase the film thickness, it is also effective to raise the temperature of the chromate treatment bath to about 20 to 80 ° C. If the bath temperature is lower than 20 ° C., the effect of increasing the coating thickness by raising the temperature is hardly expected. If the bath temperature is higher than 80 ° C., the evaporation of water from the bath is so severe that it is difficult to control the bath conditions. Also, the immersion time of the object to be treated (metal shell, nut, etc.) in the chromate bath is preferably 20 to 80 seconds. If the immersion time is less than 20 seconds, the thickness of the formed chromate film may not be sufficiently secured. On the other hand, if the immersion time exceeds 80 seconds, the formed chromate film becomes too thick, causing cracks in the film (for example, at the time of processing in assembling or the like) or easily falling off of the film, and on the contrary, the anticorrosion performance May be impaired.

On the other hand, in order to promote the dissolution of the underlying metal, the re-dissolution of the deposited film should not be severe,
It is effective to lower the pH of the chromate treatment solution. A desirable pH range is, for example, about 1.5 to 3. Further, in order to suppress the re-dissolution of the deposited film, it is effective to incorporate a hardly re-dissolved hydroxide such as nickel, cobalt or copper into the film. For this purpose, the above metal compound can be dissolved and blended in the chromate treatment bath.

On the other hand, as a result of further studies by the present inventors, a predetermined amount of a sodium salt (for example, sodium nitrate, etc.) is set so that the content of the sodium component in the chromate-treated film is 2 to 7% by weight. Has been found to be more easily formed into a thick chromate film by blending in a chromate treatment bath. Although the detailed mechanism is unknown, it is presumed that if sodium ions are taken into the chromate film, the chromate film is less likely to be redissolved in the treatment bath. If the content of the sodium component in the chromate-treated film is out of the range of 2 to 7% by weight, it may be difficult to secure a thick film of the chromate film to 0.2 μm or more. The content of the sodium component in the chromate-treated film is more desirably 2 to 6% by weight.

When a film is formed on the nut, it goes without saying that the same method can be applied by replacing the metallic shell with the nut in the above process.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Some embodiments of the present invention will be described below 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 outside the sheathed heater. As shown in FIG. 1B, the sheathed heater 2 has two resistance wire coils, that is, a heating coil 21 arranged on the front end side, and a rear end welded to the inside of a sheath tube 11 having a closed front end side. The control coil 23 connected in series is sealed together with an insulating material such as magnesia powder. The main body 11 a of the sheath tube 11, which houses the heating coil 21 and the control coil 23, protrudes from the metal shell 3 at the tip end to form a protruding portion. The heat generating coil 21 is electrically connected to the sheath tube 11 at the end thereof, but the outer peripheral surfaces of the heat coil 21 and the control coil 23 and the inner peripheral surface of the sheath tube 11 are insulated by the interposition of magnesia powder. I have. 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 projects a predetermined length from one open end. Have been. A hexagonal cross-section tool engaging portion 9 for engaging a tool such as a torque wrench when attaching the glow plug 1 to a diesel engine is formed on the outer peripheral surface of the metal shell 3. The thread part 7 for mounting is formed.

The base end of the sheath tube 11 is pressed into the through hole 4 of the metal shell 3 and fixed. On the other hand, a counterbore portion 3 a is formed in the opening opposite to the through hole 4, and a rubber O-ring 1
5 and an insulating bush (for example, made of nylon) 16 are fitted. Further, a pressing ring 17 for preventing the insulating bush 16 from dropping is mounted on the energizing terminal shaft 13 on the further rear side. The pressing ring 17 is fixed to the energizing terminal shaft 13 by a caulking portion 17a formed on the outer peripheral surface, and
A knurl portion 13b is formed on the corresponding surface of No. 3 to increase the crimping coupling force. A female screw portion 13a is formed at the rear end of the energizing terminal shaft 13, and a nut 1 for fixing the energizing cable to the energizing terminal shaft 13 is provided.
9 is screwed.

The glow plug 1 has a screw portion 7 of the metal shell 3.
In the cylinder block of a diesel engine. Thereby, the tip of the sheath tube 11 in which the heating coil 21 and the control coil 23 are accommodated is positioned in the combustion chamber (or the auxiliary combustion chamber) of the engine. In this state, when a voltage is applied to the energizing terminal shaft 13 using a vehicle-mounted battery as a power source, the energizing terminal shaft 13 → the control coil 23 → the heat generating coil 21 → the sheath tube 11 → the metal shell 3 → (grounded via the engine block). It is energized by the route. This energization causes the sheath heater 2 to generate resistance heat and ignite the fuel injected into the engine block.
In the sheath heater 2, since the temperature of the control coil 23 is low and the electric resistance value is small at the beginning of energization, a relatively large current flows through the heating coil 21 to rapidly raise the temperature. Then, when the temperature of the heating coil 21 rises, the control coil 23 is heated by the heat generation, the electric resistance value increases, and the value of the current supplied to the heating coil 21 decreases. As a result, the temperature rise characteristic of the heater is such that after the temperature rises rapidly in the initial stage of energization, the energizing current is suppressed by the operation of the control coil and the temperature is saturated thereafter.

Next, a galvanized layer 41 for corrosion protection is formed on the entire outer surface of the base layer (for example, carbon steel) 40 of the metal shell 3.
(A zinc-based plating layer) is formed, and further outside thereof is covered with a chromate film 42. Similarly, on the outer surface of the nut 19, a zinc plating layer 45 and a chromate coating 46 are formed.
Are formed. These galvanized layers and chromate coatings are both formed by the same method, and will be described below on behalf of the metal shell 3 as an example.

The galvanized layer 41 is formed by a known electrolytic galvanizing method.
It is about 20 μm. If the thickness is less than 3 μm, it may not be possible to secure sufficient corrosion resistance.
If the film thickness exceeds the above range, the specification is excessive in terms of ensuring corrosion resistance, and the piece time during production may be reduced, leading to an increase in cost. Specifically, the metal shell 3
The thickness of the zinc plating layer 41 of the nut 19 is preferably 12 to 20 μm, and the thickness of the zinc plating layer 45 of the nut 19 is 3 to 8 μm.
m.

On the other hand, in the chromate film 42, 95% by weight or more of the chromium component contained is trivalent chromium, and the thickness thereof is 0.2 to 0.5 μm. The chromium component preferably has a trivalent chromium component as much as possible, more preferably substantially all of the chromium component is a trivalent chromium component.

FIG. 2 schematically shows an example of a method for forming the chromate film 42. That is, the metal shell 3 on which a zinc plating layer having a predetermined thickness is formed by a known electrolytic zinc plating method or the like is immersed in the chromate treatment bath 50. The type of the chromate treatment bath 50 to be used has already been described. As a result, FIG.
As shown in (a), a chromate film 42 is formed on the surface of the zinc plating layer 41 of the metal shell 3. FIG. 2 is an explanatory view showing a conceptual process, in which the metal shell 3 is simply immersed in the chromate treatment bath 50. However, in order to improve the treatment efficiency, a known barrel treatment method ( (A process in which metal shells are piled up and inserted in a liquid-permeable container, and the container is rotated in the processing bath 50).

After being subjected to the chromate treatment, the metal shell 3 is washed and dried, then incorporated in the glow plug 1 shown in FIG. 1, and attached to a diesel engine for use. The metal shell 3 or the nut 19 is such that the chromate film formed on the galvanized layer has significantly higher anticorrosion performance and heat resistance than a conventional trivalent chromium-based chromate film and furthermore a yellow chromate film. It becomes possible to sufficiently impart corrosion resistance to the plating layer. The present invention can be similarly applied to a metal shell or a nut of a glow plug using a ceramic heater instead of a sheathed heater.

[0033]

The results of experiments conducted to confirm the effects of the present invention will be described below. (Example 1) STKM specified in JIS G3445
Using 13CE as a raw material, a metal shell 3 having a shape shown in FIG. 1 was manufactured by cold forging. In addition, the nominal size of the thread part 7 of the metal shell 3 is 10 mm, and the axial length is about 51.5.
mm. Next, a zinc plating layer having a film thickness of about 16 μm was formed by subjecting this to electrolytic zinc plating using a known alkaline cyanide bath.

Next, a chromate treatment bath 50 shown in FIG.
With chromium chloride (II
_{I) (CrCl 3 · 6H 2} O) of 50 g, cobalt nitrate (I
I) 3 g of (Co (NO ₃ ) ₂ ), sodium nitrate (Na
A bath was prepared by dissolving 100 g of NO ₃ ) and 31.2 g of malonic acid, and the temperature of the bath was maintained at 60 ° C. by a heater, and the pH of the bath was adjusted to 2.0 by adding an aqueous solution of caustic soda. Then, the zinc-plated metallic shell 3 was immersed in the chromate treatment liquid 50 for 60 seconds, washed with water, dried, and dried with warm air at 80 ° C. to form a chromate film (test sample: Example).

On the other hand, as a yellow chromate treatment bath, 7 g / liter of chromic anhydride and 3 g of sulfuric acid were used with respect to deionized water.
Per liter and nitric acid at a rate of 3 g / liter were prepared and maintained at a liquid temperature of 20 ° C. Then, a metal shell was immersed in this for about 15 seconds, pulled up, and dried to produce a test piece (test product: comparative example). As a luster chromate treatment bath, chromium potassium sulfate 3 against deionized water is used.
g / L, 4 g / L nitric acid and 2 g / L hydrofluoric acid were prepared and maintained at a liquid temperature of 20 ° C. Then, a metal shell was immersed in this for about 15 seconds, pulled up, and dried to produce a test piece (test product: comparative example).
When the thickness of the chromate film of each of the above test products was measured by actual measurement from a cross section by SEM, the test products were 0.33 μm, 0.31 μm, and 0.07 μm. The cross-sectional SEM image used for the film thickness measurement is shown in FIG.
3 is shown. (A) of the test product, (b) of the test product,
(C) is each SEM image of a test article. In order to facilitate observation of the chromate film, an Au thin film is formed on the surface of the film by a sputtering method. In the SEM image, the underlying zinc plating layer having high conductivity and the Au coating layer
Since the chromate film layer having a low conductivity appears dark, the image of the chromate film can be easily confirmed from the contrast. In each SEM image, a white line is displayed at a position corresponding to each boundary between the chromate coating layer confirmed from the contrast, the galvanized layer and the Au coating layer, and the film is determined from the distance between the white lines. Identify the thickness.

On the other hand, the presence of chromium in each of the formed chromate films was examined by X-ray photoelectron spectroscopy (XPS). FIG. 3 shows a peak portion of chromium (2p _2/3 ) in a photoelectron spectrum with the test sample. In the test sample (solid line), no peak appears at the position corresponding to hexavalent chromium, and it can be confirmed that almost all of the chromium component is trivalent chromium. On the other hand, in the test sample, the peak of trivalent chromium overlaps with the peak of hexavalent chromium, and a bump-like bulge appears on the shoulder on the high energy side of the peak.

FIG. 4 shows the shape of each peak assuming that the intensity of the photoelectron X-ray is I (vertical axis in the figure: cps) and the binding energy value is x (horizontal axis in the figure: eV). -(X-μ) ² / 2σ ² ｝ ‥‥ (1) (where μ represents the x-coordinate of the peak and σ represents the half-width of the peak curve), and the result of the peak separation analysis. It is. According to this, the peak height of trivalent chromium is defined as I1, and the peak height of hexavalent chromium is defined as I2.
/ (I1 + I2) is about 0.2 (in terms of hexavalent chromium reduction, I2 / (I1 + I2) is desirably 0.05 or less). A calibration curve was prepared using a standard sample of dichromium trioxide, and the weight content of hexavalent chromium in the total amount of chromium components was calculated based on the calibration curve. About 15% by weight was hexavalent chromium and the balance was trivalent chromium. It turned out to be chrome. The same analysis was performed on the sample and the sample, but substantially all of the chromium component was trivalent chromium.

For the above test items, JIS85
Perform the “5. Neutral salt spray test method” in the corrosion resistance test method of plating specified in No. 02, and evaluate the durability by the time until white rust resulting from corrosion of the galvanized coating appears about 20% or more of the entire surface. went. In this specification, the metal shell is used as a sample as it is, and one surface of the tool engaging portion (hexagonal portion) is used as a sample surface. FIG. 5 shows the results. In other words, the metal shell satisfying the requirements of the glow plug of the present invention showed a very good endurance time of 240 hours. This is substantially the same as the test product using the yellow chromate treatment, and is about eight times as large as the test product using the conventional thin glossy chromate film.

Further, for a test specimen prepared in the same manner as above, which was prepared separately, the “7. Cas test method” in the corrosion resistance test method for plating specified in JIS H8502 was performed.
The evaluation was made based on the durability time until white rust resulting from corrosion of the galvanized coating appeared on about 20% or more of the entire surface. Further, a durability test using sulfuric acid and nitric acid was performed as follows. First, a sulfuric acid solution or a nitric acid solution having a pH of 2 is placed in a desiccator, and the test article is sealed in the desiccator so that the test article and the acid solution do not come into direct contact with each other but can come into contact with the solution vapor. Then, the desiccator was held in a thermostat at a temperature of 90 ° C., and evaluated according to the same criteria as in the above-mentioned Cass test. The above results are shown in FIG.
And FIG. In each of the tests, the test specimens using the yellow chromate treatment or the gloss chromate treatment showed only a short durability time, whereas the test specimens according to the examples of the present invention showed good durability results. It turns out that it shows.

Next, the above metal shell was heat-treated at 200 ° C. for 30 minutes in the air, and the same salt spray test was conducted. The results are shown in FIG. Using yellow chromate treatment,
Or 20 specimens using gloss chromate treatment
While the test piece according to the example of the present invention showed only a short durability time around the time, the durability time was 200 hours even after the heat durability test, showing a good result.

(Embodiment 2) A metal shell similar to that of Embodiment 1
Was manufactured under the same conditions until the zinc plating treatment. Next
Then, as a chromate treatment bath, add 1 l to deionized water.
Chromium (III) chloride (CrCl₃・ 6H
₂O) and 50 g of cobalt (II) nitrate (Co (N
O ₃)₂) And sodium nitrate (NaNO₃) To 5
0-150 g, dissolve in the ratio of malonic acid 31.2 g
The bath temperature is kept at 60 ° C by the heater.
At the same time, the pH of the bath is adjusted by adding an aqueous solution of caustic soda.
Adjusted to 2.0. And the metal shell after galvanizing
Immerse in the above chromate treatment liquid 50 for 60 seconds, then wash with water
・ After drying, dry with warm air at 80 ° C to
A chromate film was formed. And the obtained chromate
The thickness of the film was measured by SEM cross-section observation,
The amount was measured by ESCA. The above results are shown in FIG.
You. That is, the Na content in the coating is 2 to 7% by weight,
Large film thickness in a relatively short time when 2-6% by weight
It can be seen that a chromate film of No. was obtained.

(Embodiment 3) A metal shell similar to that of Embodiment 1
Was manufactured under the same conditions until the zinc plating treatment. Next
Then, as a chromate treatment bath, add 1 l to deionized water.
Chromium (III) chloride (CrCl₃・ 6H
₂O) and 50 g of cobalt (II) nitrate (Co (N
O ₃)₂) And sodium nitrate (NaNO₃) To 5
0-150 g, dissolve in the ratio of malonic acid 31.2 g
The bath temperature is kept at 60 ° C by the heater.
At the same time, the pH of the bath is adjusted by adding an aqueous solution of caustic soda.
Adjusted to 2.0. And the metal shell after galvanizing
Immerse in the above chromate treatment solution for 40-80 seconds, and then
After washing and drying, dry with warm air at 80 ° C
A chromate film was formed. Each after chromate film formation
Neutral salt spray test similar to Example 1 was performed on the metal shell.
Was evaluated. The results are shown in FIG. Coating thickness
Is 0.2 to 0.5 μm, especially 0.3 to 0.5 μm
It can be seen that good durability results have been obtained.

[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.

FIG. 2 is an explanatory view of a chromate treatment step.

FIG. 3 is a view showing the results of X-ray photoelectron spectroscopy analysis of the chromate films of the test samples of Example 1 and (the peak portion of chromium (2p _2/3 ) in the photoelectron spectrum).

FIG. 4 is a view showing a result of performing peak separation analysis on a chromium (2p _2/3 ) peak portion of a photoelectron spectrum of the same test sample.

FIG. 5 is a graph showing the results of a neutral salt spray test performed on each test sample of Example 1.

FIG. 6 is a graph showing the results of the same Cass test.

FIG. 7 is a graph showing the results of the same acid durability test.

FIG. 8 is a graph showing the results of a neutral salt spray test after heat durability.

FIG. 9 shows Na in the chromate film of the test sample of Example 2.
5 is a graph showing the relationship between the amount and the coating thickness.

FIG. 10 is a graph showing the relationship between the thickness of a chromate film and the durability time of salt water spray of the test article of Example 3.

FIG. 11 is a cross-sectional SEM of each test sample used in Example 1.
image.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Glow plug 2 Sheath heater 3 Metal shell 7 Screw part 11 Sheath tube 13 Current terminal shaft 19 Nut 50 Chromate treatment bath 41, 45 Zinc plating layer 42, 46 Chromate coating

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) F02P 19/00 F02P 19/00 Z (72) Inventor Tomoaki Kumada 14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi, Japan (72) Inventor Katsunari Ninomiya 14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi F-term (reference) in Japan Special Ceramics Co., Ltd. CA38 DA13 DA16 4K044 AA02 AB03 AB05 BA10 BA15 BB01 BB03 BC02 BC11 CA16 CA18 CA53

Claims (12)

[Claims] 1. A structure in which a resistance heating heater is disposed in a metal shell so that a tip end thereof protrudes from one end surface of the metal shell, and 95% by weight or more of a chromium component contained therein is provided. A glow plug, wherein the surface of the metal shell is coated with a chromate film of trivalent chromium and having a thickness of 0.2 to 0.5 μm. 2. The glow plug according to claim 1, wherein said chromate film does not substantially contain a hexavalent chromium component. 3. An energizing terminal shaft for energizing the resistance heating heater is arranged so that its rear end protrudes from the other end surface of the metal shell, and is formed at the rear end of the energizing terminal shaft. 3. A nut for fixing a current-carrying cable to the current-carrying terminal shaft is screwed to the male screw portion, and at least a part of a surface of the nut is covered with the chromate film. The glow plug according to 1. 4. The glow plug according to claim 1, wherein the content of the sodium component in the chromate film is 2 to 7% by weight. 5. The glow plug according to claim 1, wherein the metal shell, or the metal shell and the nut, are provided with a zinc plating film as a base metal layer of the chromate film. 6. “5. Neutral salt spray test method” in the plating corrosion resistance test method specified in JIS H8502.
6. The glow plug according to claim 5, wherein the durable time until white rust resulting from corrosion of the galvanized coating appears on the surface of the zinc plating film by about 20% or more of the entire surface is 40 hours or more. 7. After heating at 200 ° C. for 30 minutes in the atmosphere, when performing “5. Neutral salt spray test method” in the corrosion resistance test method for plating specified in JIS H8502, corrosion of the galvanized coating film occurs. The glow plug according to claim 5 or 6, wherein a durability time required for white rust derived from the surface to appear by about 20% or more of the entire surface is 40 hours or more. 8. When the “7. Cass test method” in the corrosion resistance test method for plating specified in JIS H8502 is performed, it is required that white rust resulting from corrosion of the galvanized coating film appears at about 20% or more of the entire surface. Endurance time is 20
The glow plug according to any one of claims 5 to 7, which is longer than a time. 9. A method for manufacturing a glow plug having a structure in which a resistance heating heater is disposed in a metal shell so that a tip end thereof protrudes from one end surface of the metal shell, the method comprising the steps of: By immersing in a chromate treatment bath containing a complexing agent for trivalent chromium, 95% by weight or more of the chromium component contained on the surface of the metallic shell is trivalent chromium, and its film thickness is Is 0.2-0.5μ
A method for manufacturing a glow plug, comprising forming a m chromate film. 10. The chromate treatment bath may be 20 to 80
The method for producing a glow plug according to claim 9, wherein the glow plug is used in a state where the bath temperature is adjusted to ° C. 11. The method for producing a glow plug according to claim 9, wherein the immersion time of the metal shell in the chromate treatment bath is 20 to 80 seconds. 12. In the chromate treatment bath, the content of the sodium component in the obtained chromate film is 2 to 7%.
The method for producing a glow plug according to any one of claims 9 to 11, wherein a predetermined amount of a sodium salt is blended so as to be in a percentage by weight.