JPH02101138A - Spark plug electrode material - Google Patents

Abstract

PURPOSE:To obtain the title material having excellent consumption resistance, improved workability and reliability by forming Cr or Cr alloy into high relative density and limiting the contents of Al, Si, O, N and C therein. CONSTITUTION:The spark plug electrode material is formed with chips constituted substantially of Cr or Cr alloy and having >=95% relative density thereof. At this time, in the above chips, the contents of <=50ppm Si, <=500ppm O, <=100ppm N and <=500ppm C (zero is not included in either element) are regulated and, if required, one or more kinds among 0.1 to 10wt.% Fe, Co and Ni are furthermore added for the purpose of preventing cracks and chippings at the time of working. At least either of a center electrode and an earth electrode is formed with the above chips, by which the workability and consumption resistance of the electrode can drastically be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION (Industrial Field of Application) The present invention relates to spark plugs used in internal combustion engines, and more particularly to spark plug electrode materials having improved wear resistance.

(Prior Art) A combustion chamber of a gasoline engine is equipped with an ignition plug for igniting and exploding the deflagration gas compressed within the cylinder. An electrode is embedded in the axis of the spark plug, and its tip protrudes from the spark plug into the combustion chamber, and a spark discharge is generated by applying a high voltage generated by the ignition coil to this electrode.

Therefore, the material of the spark plug electrode is required to have excellent heat resistance and also excellent wear resistance such that it will not be corroded by corrosive components in the deflagration gas.

Conventionally, such electrode materials include ■-Cr 5 star%
Below, Ni-based low alloys consisting of 5% by weight or less of Mn, 5% by weight or less of Si, and the remainder substantially Ni have been frequently used.

As another example, ■: Ni-based alloys such as Inconel 600 containing a relatively large amount of Cr, which is an effective component for corrosion resistance, are also used.

In addition, as another attempt, (2): A material made of almost pure Cr with a further increased amount of Cr has been studied.

(Problem to be solved by the invention) However, in recent years, the environment in which spark plug electrodes are used has become harsher due to demands for lower fuel consumption, higher performance, use of various types of oil, etc. It's getting to the point where I can't stand it anymore.

For example, the alloy materials listed in ■ and ■ above satisfy the characteristics required for spark plug electrodes, but
There are still many points that need to be improved in order to meet the recent demands for longer life and lower cost I for spark plugs.

In addition, although the electrode material described in (1) above also satisfies the characteristics required for spark plug electrodes, it is difficult to ignite due to the secondary properties of spark plugs (highly correlated with cost reduction). If the plug electrode is subjected to severe processing, problems such as cracks, cracks, and chips may occur in the electrode.

Furthermore, the workability referred to here includes not only the processing into a predetermined shape for the plug electrode tip described above, but also the bondability with the base metal (for example, silver soldering properties, pressure bondability, etc.), but conventional materials There is also room for improvement in these processability.

An object of the present invention is to provide a reliable electrode material for a spark plug that has excellent wear resistance and improved workability.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the present inventors investigated the influence of each component on the spark plug electrode characteristics in the Ni-based alloy based on Inconel 60-0 mentioned above. When I investigated, I found that high C
It has been found that the Ni-based alloys shown in the above have lower hardness and improved workability without compromising the required wear resistance.

Based on this, the present inventors further conducted improvement research on high Cr materials, and as a result, they developed the spark plug electrode of the present invention.

That is, the spark plug electrode material of the present invention is an electrode material constituted by a tip having a relative density (relative to theoretical density ratio) of 9596 or more and consisting essentially of Cr or a Cr alloy, wherein Al in the tip And as for the content of Sl, Al is 50 ppm or less (not including zero) 1. S
l satisfies the condition of 50 ppm or less (not including zero),
Furthermore, the content of oxygen, nitrogen, and carbon in the Cr is as follows: oxygen is 500 ppm or less (not including zero), nitrogen is 100 ppm or less (not including zero), and carbon is 500 ppm or less.
It is characterized by satisfying the condition of less than or equal to ffl (not including zero).

FIG. 1 is a partial sectional view of an embodiment of a spark plug equipped with the spark plug electrode material of the present invention, and FIG. 2 is a partially enlarged view.

In these figures, the center electrode 1 and the ground electrode 2 are conventional alloys for plug electrodes, such as Ni-based, Fe-based, or Co-based alloys containing pure Ni and Cr. At the tips of the center electrode 1 and the ground electrode 2, the Cr chips of the present invention of IB and 2B, i.e., with Al and Si contents of 50 ppm or less, respectively, are applied via thermal stress buffer materials IA and 2A, depending on the case.
Suppression of oxygen, nitrogen, and carbon by 500 pI each; 1.
A Cr chip made of Cr controlled to OOppm s500 ppa+ or less is bonded.

In FIG. 1, numeral 3 is an insulator covering the center electrode 1, 4 is a center terminal, 5 is a low antibody, and 6 is a screw portion for attachment to the cylinder head of an internal combustion engine.

In some cases, either the center electrode 1 or the ground electrode 2 does not need to use a C chip or a thermal stress buffer. In other words, usually, at least one of the center electrode and the ground electrode is made of a Cr chip. By configuring the spark plug as described above, the wear resistance of the picture electrode can be greatly improved.

In the spark plug electrode of the present invention, it is important to use Cr for at least one of the center electrode and the ground electrode, and moreover, Cr
The key point is to limit the amounts of Al5Si, oxygen, nitrogen, and carbon within a predetermined range. Limiting these elements to the above ranges is not only important for improving the abrasion resistance of the plug electrode material of the present invention, but also for maintaining processability in order to stably and economically obtain the CR main electrode. It is also important for improvement.

Furthermore, in the spark plug electrode of the present invention, at least one of the center electrode and the ground electrode contains Fe or C.

and at least one type of Ni, Q, 1 to 10 vt%
A Cr alloy containing Cr may also be used.

In other words, regarding workability, it is necessary to suppress cracks, splits, and chips that occur on the surface or especially at the corners of the Cr chip when processing it into an electrode shape. The density of the Cr chip abrasive is important, and if the density is less than 95% of the theoretical density, cracks and the like will tend to appear on the surface, so it must be avoided.

In such a case, the wear resistance as a plug electrode is significantly inferior. Therefore, the number of voids is as small as possible (in order to control C
In the sintering process when obtaining r-chip material, the above Fe5
Addition of the auxiliary component CoSNi is more effective in preventing cracking and chipping during processing, and is advantageous in obtaining a smoother processed surface.

A smooth machined surface also has the effect of obtaining a stable and consistent spark voltage.

(Example) The Cr chip of the present invention was attached to the center electrode and ground electrode of a spark plug as shown in FIG. 1, and a wear resistance test was conducted using the method and conditions described below.

A microscopic observation of the arc damage on the electrode after the abrasion resistance test of the Cr chip used in the test revealed that cracks and tears appeared from the tip of the Cr electrode, or they grew along the grain boundaries of the chip. In particular, tears and cracks can cause parts to separate from the chip depending on the conditions, affecting material consumption. In addition, the growth of the above-mentioned splits and cracks is caused by A IOS i O2, Cr2 with a grain size of about several μm in the grain boundaries.
It has been found that the presence of inclusions such as 0323゜ causes selective concentration of discharge, resulting in significant material consumption.

These inclusions are generally scattered at grain boundaries, so the cracks and
Cracks grow along grain boundaries.

Therefore, the above findings suggest that removal of inclusions such as Al2O3 is important for improving the wear resistance of Cr electrodes.

Foreign substances such as oxides that are in the form of oxides from the beginning and are simply mixed into the raw material powder are removed by a sedimentation method that takes advantage of the difference in specific gravity with the raw material powder, or by using the difference in particle size. It can be removed in advance using a sieve. By giving these tasks, good results were shown in reducing wear and tear.

However, the problem is impurities that exist as a solid solution or precipitate in the raw materials. It was thought that these could not be removed by sieving and the difference in specific gravity was one of the factors that increased the consumption. However, as a means of solving this problem, it was recognized that by carefully examining the raw material powder (Cr powder) and selecting a raw material powder with fewer impurities, the occurrence of abnormal consumption phenomena tends to be further reduced. .

In this way, although the selection of raw material powder with few impurities (mainly oxides here) is effective in reducing the remarkable consumption phenomenon, rigorous experiments revealed that there is still room for improvement. they admitted.

That is, a lot in which impurities in the Cr powder are not substantially recognized is selected, and this is used as a Cr raw material to produce Cr powder for spark plugs.
Despite manufacturing electrodes, we obtained two types: one with the presence of precipitates in Cr and one with no precipitates, and when we compared the wear resistance properties of these, we found that the former alloy with precipitates It was found that more wear and tear occurred on the spark plugs that were used.

It is assumed that such precipitates are impurities generated by a reaction between certain elements dissolved in the Cr powder and the atmosphere during sintering. Therefore, in order to further improve the wear resistance, it is necessary to not only contain impurities such as oxides that are simply mixed in the raw materials, but also to contain certain elements that are dissolved in the raw materials (because they are in a solid solution state, they cannot be seen microscopically). This suggests that there is a need to pay attention to (generally, detection cannot be confirmed). In other words, this suggests the necessity of controlling through a series of processes, especially in the production of Cr electrodes for spark plugs. What is the series of processes?
This refers to the selection of raw materials that meet predetermined conditions in the process of manufacturing Cr electrodes for spark plugs by sintering, and refers to techniques for controlling sintering conditions and manufacturing Cr plates.

In implementing the method of the present invention, the type and amount of impurities in the Cr powder are extremely important as they also affect other processes. As already mentioned, the oxide (AlO5102)23' that causes significant consumption or the metal (AlSSi) dissolved in Cr powder,
Newly formed oxides due to reaction with the atmosphere during sintering or processing are particularly problematic. As mentioned earlier, the C electrode for spark plugs, which frequently suffers from significant wear and tear, is
The amounts of these in r were large and a correlation was obtained.

When considering the frequency of occurrence in relation to other processes, Al s
The content of Si is preferably 50 ppm or less, respectively, and the content of oxygen and nitrogen in Cr is preferably at least 500 ppm and 100 ppm or less, respectively. When Al5Si etc. exceeds the above-mentioned value of 50 ppIll, a large amount of products are generated due to reaction with the atmospheric gas in the sintering process in the subsequent process and reaction with the combustion chamber atmospheric gas, resulting in poor wear resistance. Unfavorable for improving properties.

Further, the influence of carbon on workability is similar to that of oxygen and nitrogen. In other words, chromium to the grain boundaries of C
Precipitation of carbides significantly impairs workability, and the thickness
Considering workability as a plug electrode material that requires thinning of +1 or less, the carbon in Cr is 5
It is desirable to suppress it to 0.00 ppm or less. Wear resistance decreases due to selective dropout of Cr carbides precipitated at grain boundaries.

Preparation of raw material C Currently, the scouring method for metal Cr currently supplied industrially is F.
24゜C such as eCr OMgCr2O4 ore is reduced with other metals such as Al or Si to produce metal C.
There are two main methods: a method for obtaining r (reduction method), and a method for dissolving the Cr ore, separating undissolved non-metallic impurities, and electrolyzing this using an electrolyte to obtain metal Cr (electrolytic method). be.

However, Cr obtained by the former reduction method has a gas amount (oxygen, nitrogen) of about 1,000 ppm, Al, Si
, impurities such as Fe, number 1,000 ppI11~1
0. Contains approximately OOOppIm. On the other hand, when producing Cr using the latter electrolytic method, the amount of gas (oxygen, nitrogen) is 1,000
It is extremely high, ranging from 0 ppm to 10,000 ppm, and contains relatively little impurities such as Al, for example, generally about several 100 ppm or less.

As described above, it is common that either impurities such as Al s Si or gas such as oxygen are present in large amounts.

When several Cr chips were processed and subjected to a wear resistance test, it was observed that the wear resistance exhibited large variations. That is, mainly the amount of oxygen is 7 x 10. p
Cr containing pm and Cr containing 7X102ppm are more likely to be the former (the spread of scum during the wear test is large,
Moreover, the amount of gas consumption tends to be large, and we obtained findings suggesting that the amount of gas is also related to the consumption resistance.

In addition, even if the amount of gas is relatively small, if there is a large amount of Al5Si, etc., stable wear resistance is shown at the beginning of the wear test, but as the discharge progresses, there are cases where wear increases suddenly at a certain point. , Al SS i in Cr is oxidized by a small amount of oxygen in the discharge atmosphere, and A I 203,
It is thought that because SiO2 was formed, the wear rate changed from the time of its formation.

Therefore, Al, Si, etc. are originally Al2O3, SiO
This suggests that even Al5Si dissolved in Cr that does not have a form such as 2 needs to be suppressed to a small extent.

On the other hand, the tearing and cracking of the Cr chip is caused by the aforementioned □Cr
The cause is not only inclusions such as A I 203, S io 2, and C 203, gases such as oxygen, but also poor workability due to the brittleness of Cr itself.

In other words, C" caused by shock during machining and pressure
It has also been observed that microscopic cracks on the surface become a trigger and develop into larger cracks or tears. Therefore, Cr
This suggests that ensuring chip processability is also an important factor in ensuring wear resistance. That is, as mentioned above, if there are many voids (incompletely sintered state) remaining in the C chip, it will trigger cracks and the wear resistance will be poor.

According to observations, when the aforementioned cracks and fissures progress along grain boundaries, in Cr chips containing Fe, Co, and Ni, the grain boundaries become healthy due to improved sinterability. Falling off due to the cracks and the like was reduced. Fe
It was also found that when the total amount of at least one of 5Co and Ni is 10 vt% or more, it does not exhibit the same corrosion resistance as Cr, which is disadvantageous.

Evaluation conditions: Abrasion resistance: 12,000 arc discharges per minute are generated between the center and ground electrodes in a high-pressure atmosphere (5 kg/cm) via a normal ignition system, and the volume loss is measured after a 100-hour test. did.

Workability: Expressed by the workability when a given Cr plate material is rolled up to the first order. Represent something with a symbol.

Examples 1-31. Comparative Examples 1 and 2 Various types of Cr chips with a diameter of about 3 mrms and a thickness of 1 mrms were glued to the tip of the center electrode, and the size was 2 mrms in length x width x thickness.
A 5×2

In addition, among each Cr chip, those that are difficult to manufacture by rolling method (X mark and Δ mark in Tables 1 and 2)
A test piece was obtained by cutting a thick plate and polishing it.

Table 1 shows the evaluation results of workability and wear resistance.

As is clear from Table 1, Al in the Cr chip is 300
1) I) 111 or more, 310. ppm (Comparative Example 1.2)
In the case of 1, it is difficult to process into thin plates, especially in the former case.
The latter was also found to be undesirable, as cracks and crazing occurred from the surface to deep inside, as well as large wear and dispersion. On the other hand, when the amount of Al in the Cr chip was 50 ppm or less (Example 1°2.3), it was possible to process the board to a predetermined thickness, and the wear resistance was also good.

Macro and microscopic observation of the surface and interior of each of these Cr chips after the bench test revealed that Comparative Example 1.2, which contains a large amount of Al, had many fissures on the surface and also had A at the grain boundaries.
12O3 was present, concentrated traces of discharge, and falling off, and it is thought that these impeded the wear resistance.

On the other hand, in Examples 1 and 2.3 with a small amount of Al, there were very few inclusions at the grain boundaries of the chip after the bench test, and there were especially few traces of discharge concentration, which was a favorable situation. there were. The results are shown in Table-1.

As described above, the amount of Al in the Cr chip has an important influence on workability and wear resistance, and it is preferable to suppress the amount to 50 ppm or less. In addition, 5 ppIll (Example-
3) Although it is thought that these properties can naturally be improved even if the amount of Al is smaller, it has been difficult to suppress the amount to less than this in practical industrial terms.

Comparative Examples 3-4, Examples 4-6 A bench test was conducted in the same manner as in Examples 1-3 and Comparative Examples 1-2. Incidentally, a sample Cr chip was also produced under the same conditions and process. As is clear from the workability and wear resistance test results shown in Table 1, the amount of Si in the Cr chip is 200%.
0 ppI 11 or more and 290 ppm (Comparative Example 3.
In the case of 4), it is particularly difficult to process the former into a thin plate, and the latter is also undesirable because cracks occur on the surface and deep inside, and wear and tear are also seen in large variations. found.

On the other hand, when the amount of Si in the C chip was 50 ppm or less (Examples 4, 5, and 6), it was possible to process the plate to a predetermined thickness and the wear resistance was also good.

After the bench test, macroscopic and microscopic observations of the surface and interior of each of these Cr chips revealed that in Comparative Example 3.4, which has a large amount of Si, there were many cracks on the surface and 8.
102 were scattered, and there were traces of discharge that seemed to be concentrated there, as well as a situation where they had fallen off, and it is thought that these impeded the wear resistance.

On the other hand, in Examples 4, 5 and 6, where 5iffi is small, there is very little oxide intervening at the crystal grain boundaries of the chip after the bench test, and there are especially few traces of discharge concentration, which is a favorable condition. Met. The results are shown in Table-1.

As described above, the Si particles in the Cr chip have an important influence on the workability and wear resistance, and the amount thereof is preferably suppressed to 50 ppm or less. Furthermore, 5ppI11 (Example-
6) Although these characteristics can naturally be considered to be improved even with a smaller Si value, it has been difficult to realistically suppress the Si value to a lower value.

Comparative Example 5, Examples 7 to 9 Workability and wear resistance were evaluated in the same manner as above. C
A I Jil and 5i Jil in the r chip are 10 to 20 ppm for Al and 20 to 30 ppm for Si.
Even if it is suppressed to about I11, which is within the preferable range of stars, the same C
When the amount of oxygen in r is large (Comparative Example-5, 5770p
pm), Cr undergoes oxidation during discharge and becomes chromium oxide (Cr2
03), and Al and Si also undergo selective oxidation, exhibiting abnormal consumption similar to Comparative Examples 1 to 4 described above. Processability as a Cr chip is also inhibited. On the other hand, when the amount of oxygen in Cr is 5001)l)III or less (Example 7
9) have a center electrode, a ground electrode"1, which shows a remarkable improvement in abrasion resistance, has sufficient processability, and has a preferable oxygen content as electrode feed for spark plugs. The results are shown in Table-2.

Comparative Example 6, Examples 10~]2 Similarly, the amount of nitrogen in the Cr chip also has an important influence on the characteristics, and the amount of nitrogen in the Cr chip was 994 ppm (Comparative Example 6).
In this case, it is difficult to reduce the thickness, and the wear resistance is also poor. In contrast, the amount of nitrogen is 1100 pp or less (Example 1.0.11).

12) In □, there is no problem with both characteristics.

Comparative Example 7, Examples 13 to 14 Similarly, the amount of carbon in the Cr chip also had an important influence on the characteristics.As is clear from Table 2, the amount of carbon in the Cr chip was 1500 ppI11 (Comparative Example In 7), the formation of chromium carbide is observed, which reduces the workability and also causes lumps to fall off due to the concentration of arc during discharge, reducing wear resistance.On the other hand, when the amount of carbon is 5'00 p
Below pm, the above-mentioned effects are small (no problems in workability or wear resistance as a Cr chip). The results are shown in Table 2.

As described above in Examples 7 to 14 and Comparative Examples 5 to 7, A
Even if the amounts of 1 and Si are preferable, even if no consideration is given to the amounts of oxygen, nitrogen, and carbon in chips, both processability and wear resistance will be adversely affected.

Examples 15-16 Examples and results of the combined electrodes are shown in Table 3. Example 15
The C tip of Example-6 was used for the center electrode, and the ground electrode was made of Ni-2, 0Cr-3, 0Mn-1, 8S.
This is an example using i. “Both center electrode and ground electrode are C
It appears that the wear resistance was almost the same as in the case of a combination of r chips, and that it was in a good state of use.

Further, in Example 16, pure Ni was used for the center electrode, and the Cr chip of Example-6 was used for the ground electrode. Example-1
Similar to No. 5, the wear resistance of the picture electrode was good, not much different from that of the C chip.

The results are shown in Table-3.

As mentioned above, even if a plug electrode is made of a combination of Cr chips and other alloys, it has the same wear resistance as a plug electrode made of Cr chips) and exhibits good characteristics. confirmed.

Examples 17 to 22, Comparative H8 When the amount of each of aluminum, silicon, oxygen, nitrogen, and carbon in the Cr chip is suppressed within predetermined values, the amount of crack prevention material in the Cr chip becomes o, ]wL%( Example-1
In the case of 7), the effect of suppressing the aforementioned Al etc. is prioritized in terms of properties as a plug electrode material such as wear resistance. . The amount of anti-crack material is 1,,! V! % (Example-18), improvement in the C-filial layer is seen. When the amount of the anti-crack material is 35 wt% (Comparative Example-8), a number of cracks occur on the Cr exclusive surface during processing, which is not preferable, and the upper limit of the amount is 10 wt% (Example-19). In appearance, Co was selected as the crack-preventing material. 9) and Cr chips having relative densities of 85% (Comparative Example 10) were obtained. The sample was placed in the same Bentes I tube as above.
When the sample was subjected to a test, the abrasion resistance was extremely poor due to the falling off of Cr lumps from the sample surface, etc., and it was thought that it would be difficult to put it into practical use. On the other hand, using the same raw materials, 9596 (Example 23),
A similar bench test was performed using a Cr chip with a relative density of 98% (Example 24). As a result, wear resistance properties were shown to be substantially equivalent to or better than those of Examples 1 to 16 described above.

In addition, all of the above-mentioned Examples 1 to 16 and Comparative Examples 1 to 7 have relative densities in the range of 95 to 99.9%.

As a result of the above, the relative density of the Cr chip element for plugs needs to be at least 95%.

Manufacturing of a Cr chip base for plugs An example of manufacturing a Cr chip base according to the present invention will be described below. A raw material Cr that satisfies the conditions described above is prepared. Next, this raw Cr is heated under a vacuum higher than at least 1 x 10' Torr at a preferable temperature of 1300°C to just below the melting point of Cr, which also serves as degassing, to produce briquettes of several to several marks. . The obtained carbon bridgette is made into a Cr powder having a particle size of approximately 10-150 μm in an atmosphere and conditions that suppress oxidation. The amounts are well within the control range, and oxygen, nitrogen and carbon are also within the preferred range.

The obtained Cr powder (mixed with anti-crackling material if necessary) was molded at about 4 tons/cJ, and then placed in a special container and heated at a vacuum level higher than I x 10-5 Torr, for example, at 1
Sintering is performed at 550° C. for 3 hours to obtain a Cr sintered body. When the density is less than 95% of the relative density, if necessary? After densifying the crystalline body by processing it again, forging it, rolling it, etc., it is further sintered at the same temperature and degree of vacuum as necessary.

Finally, mechanical processing is performed to obtain the required dimensions for the chip.

At this time, the presence of a crack-preventing material as an auxiliary material is industrially advantageous because it can reduce the sintering temperature to a certain degree.

The results are shown in Table-5.

FIG. 1 [Effects of the Invention] As is clear from the results of the above examples, the electrode material of the present invention has excellent effects in both wear resistance and workability as a spark plug, and It is extremely useful as an electrode material for plugs and has great industrial value.

[Brief explanation of the drawing]

FIG. 1 is a partial sectional view of an embodiment of the present invention, and FIG. 2 is a partial sectional view of FIG. 1. DESCRIPTION OF SYMBOLS 1... Center electrode, 2... Ground electrode, 3... Insulator, 4... Center terminal, 5... Low antibody, 6... Mounting screw part.

Claims (1)

[Scope of Claims] An electrode material constituted by a chip having a relative density (relative to theoretical density ratio) of 1.95% or more and consisting essentially of Cr or a Cr alloy, wherein Al and Si in the chip The content of Al is 50 ppm or less (not including zero)
, Si satisfies the conditions of 50 ppm or less (not including zero), and the content of oxygen, nitrogen, and carbon in the Cr is such that oxygen is 500 ppm or less (not including zero) and nitrogen is 1
00 ppm or less (not including zero), carbon is 500 ppm or less (not including zero),
Spark plug electrode material. 2. The chip contains at least one anti-crack material selected from the group consisting of Fe, Co and Ni in an amount of 0.1 to 1
The spark plug electrode material of claim 1, containing 0% by weight.