JPH0711008B2 - Magnetic powder for electromagnetic clutch - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a magnetic powder for electromagnetic clutches. More specifically, the present invention relates to magnetic powder by magnetizing the magnetic powder with an exciting coil. The present invention relates to a magnetic powder for an electromagnetic clutch, which is suitable for use in a so-called electromagnetic clutch, which transmits a rotational force using a magnetic coupling force acting between particles.

[Prior Art] Magnetic powders for electromagnetic clutches are required to have various characteristics. Among them, magnetic properties such as magnetic permeability and saturation magnetic flux density, and mechanical properties such as oxidation resistance and wear resistance are important.

If fine powder is generated due to oxidation or wear during the use of the electromagnetic clutch, the torque will decrease. Therefore, in order to obtain a stable torque characteristic for a long period of time, it is necessary to use a magnetic powder that is excellent in oxidation resistance and abrasion resistance with less generation of fine powder.

In recent years, there has been a strong demand for miniaturization of electromagnetic clutches, and the amount of magnetic powder used has also decreased. Therefore, magnetic powder with a higher saturation magnetic flux density, that is, higher torque when the same current is applied, is obtained. There is a demand for magnetic powders that can be used.

In addition, with the downsizing of electromagnetic clutches, the operating conditions tend to become more severe, and in particular, the use under conditions where the temperature of the magnetic powder rises to around 500 ° C, which was previously unthinkable with regard to temperature, has been studied. There is.

Conventionally, powders such as Fe-Al-Cr alloys (Japanese Patent Publication No. 38-23558) or Fe-Cr stainless steels have been mainly used for electromagnetic clutches.

[Problems to be Solved by the Invention] However, these conventional powders are generally considered to have a composition of powder on the assumption that the powder is used up to about 200 ° C, and oxidation at a high temperature near 500 ° C causes remarkable oxidation. It often progresses and produces a large amount of fine powder, which often cannot be used.

[Means for Solving the Problems] In order to achieve such an object, the present inventor has conducted various studies, and as a result, the use of Fe—Al—Cr—Co alloy powder improves the oxidation resistance at high temperature. It has been found that it is possible to achieve both a remarkable improvement and a sufficient saturation magnetic flux density.

That is, the first invention according to the present application is Al: 2 to 8% by weight, Cr: 8
It is a magnetic powder for an electromagnetic clutch, which comprises -20% by weight, Co: 5-35% by weight, the balance Fe and inevitable impurities.

The second invention according to the present application is Al: 2 to 8% by weight, Cr: 8
-20% by weight, Co: 5-35% by weight, further REM (rare earth metal): 0.1-1.5% by weight, Ti: 0.2-2.0% by weight, Zr: at least 1 selected from the group consisting of 1.5% by weight or less A magnetic powder for an electromagnetic clutch, which contains seeds and the balance Fe and unavoidable impurities.

(Reason for limiting components) Al: 2 to 8% by weight Al is an important element that contributes to the increase in hardness and increases the oxidation resistance together with Cr. Hardness and oxidation resistance are greatly improved by the addition of Al: 2% by weight, but the effect is saturated even if it is added in excess of 8% by weight, and the powder becomes brittle and cracking is observed.

Cr: 8 to 20 wt% Cr is the most effective element for improving the high temperature oxidation resistance.
However, if the addition amount is less than 8% by weight, the effect is insufficient. Further, if it is added in an amount of more than 20% by weight, the saturation magnetic flux density is lowered and the torque characteristics are adversely affected, which is not preferable.

Co: 5 to 35 wt% Co is the most effective element for improving the saturation magnetic flux density, and in the pure Fe-Co system, Co can achieve the highest saturation magnetic flux density in metal materials at about 30 atomic weight%. Is generally known. Even in the case of the Fe-Al-Si-Cr-Co alloy of the present invention, the same effect as that of the Fe-Co alloy is required. When Co: 5 wt% or less, no improvement in saturation magnetic flux density is observed, and when it exceeds 35 wt%, the saturation magnetic flux density tends to decrease.

The range of Al: 2 to 5% by weight, Cr: 8 to 15% by weight, Co: 15 to 35% by weight is particularly preferable because the balance between torque characteristics and oxidation resistance is good.

Further, in the second invention, in addition to the components of the first invention,
REM (rare earth metal): 0.1 to 1.5% by weight, Ti: 0.2 to 2.0% by weight, Zr: at least one selected from the group consisting of 1.5% by weight or less.

By including such an element, the oxidation resistance at high temperature can be remarkably improved.

As REM (rare earth metal), for example, misch metal, Y, Ce or the like may be used. REM is a useful element that significantly improves the oxidation resistance when added in a trace amount. This effect is particularly large when a large amount of Cr is contained, and in the case of this composition, a significant improvement in the oxidation resistance is recognized by adding 0.1% by weight or more. Further, even if added in an amount of more than 1.5% by weight, the effect is saturated and it is economically useless.

Further, in the case of Ti, the addition of 0.2 wt% or more and in the case of Zr, 1.5 wt% or less significantly improves the oxidation resistance at high temperatures. However, the effect is saturated even if it is added in an amount of more than 2.0% by weight in the case of Ti and more than 1.5% by weight in the case of Zr.

[Examples of the Invention] Al, Cr and Co all have the effect of improving the oxidation resistance.
Moreover, the magnetic properties of the powder change intricately depending on the combination of Al, Cr, and Co. Therefore, atomized powders of various components shown in Table 1 were prepared, and actually mounted in an electromagnetic clutch to measure torque characteristics, and a ball mill was used to perform heating at 500 ° C. for a long time, and an oxidation resistance test was performed. .

Table 2 shows the characteristic values of the manufactured powder and the test results.

The oxidation resistance was evaluated by X-ray diffraction, and the ratio between the intensity of the X-ray diffraction peak of the oxide and the intensity of the X-ray diffraction peak of the iron matrix was measured. The smaller this value, the lower the degree of oxidation.

Also, the hardness, which has a great influence on the wear resistance, is measured. The suitability as a magnetic powder for an electromagnetic clutch was comprehensively examined.

Regarding the torque measurement, it is required that a rated current or more be applied with a certain amount of magnetic powder incorporated to obtain a torque equal to or higher than the rated torque. The larger this value, the higher the torque efficiency, and it is possible to transmit a certain amount of torque with a smaller amount of magnetic powder or with a smaller current.

From the viewpoint of wear resistance, the higher the hardness, the more preferable. At least Hv180 or higher is required.

In Tables 1 and 2, NoA1 to A5 are examples of the first invention,
NoA6 to A11 are examples of the second invention. NoB1 and B2 are conventional examples, B1 is a Fe-Al-Cr alloy, and B2 is a 12Cr stainless steel.

In Table 1, spherical magnetic powders were obtained from the alloys of the component systems A2 and A6 by the gas atomizing method. The particle structure of the magnetic powder A2 before use is shown in FIG.

As shown in Fig. 1, some spherical powders adhered to each other during the cooling process in the spherical powders obtained by the gas atomization method. In other words, the existence of a kind of indeterminate powder in which spherical powder particles stick together is unavoidable. However, the presence of these irregularly shaped powders does not impair the characteristics of the electromagnetic clutch at all and poses no practical problem at all.

Further, in the case of the spherical powder produced by the gas atomizing method, the fluidity and the space factor are excellent, so that the response of the electromagnetic clutch and the stability of the torque are improved, and there are many contact points between the powders and the transmission torque is appropriately dispersed and excessive. In order to avoid the generation of frictional force, it exhibits good durability in combination with the oxidation resistance and wear resistance of the powder itself.

When both A2 and A6 magnetic powders are used in the electromagnetic clutch, the magnetic characteristics are excellent and the torque characteristics are good. The results of measuring the current-torque characteristic of the A6 powder are shown in FIG. FIG. 2 also shows the result of B1 which has been conventionally used for comparison. The electromagnetic clutch subjected to this test has a rated torque of 10 kg · m at a rated current of 1.5 A, and the B1 powder shows a torque of 10.8 kg · m at the rated current. On the other hand, A6 shows a torque of 16.3 kgm at the rated current, and shows a higher torque than the B1 powder over the entire current range.

Both the A2 and A6 magnetic powders have excellent resistance to oxidation at high temperatures, and show stable torque over a long period of time even under conditions in which the magnetic powders reach a temperature near 500 ° C. Table 3 shows the rate of decrease in torque after the 1000-hour high temperature durability test. Table 3 shows B1 and B2 of 1000
The results of the time high temperature durability test are also shown. B1 and B2 show a remarkable decrease in torque at high temperatures so that they are almost unusable, but A2 and A6 both have a low rate of decrease in torque and can withstand sufficient use.

[Effects of the Invention] According to the first invention of the present application, there is an effect that it is possible to provide a magnetic powder that is small in size and can be used for an electromagnetic clutch used at high temperatures.

Further, according to the second invention of the present application, in addition to the effect of the first invention, there is an effect that it is possible to provide a magnetic powder having more excellent oxidation resistance.

[Brief description of drawings]

FIG. 1 is a micrograph showing the particle structure of spherical powder obtained by the gas atomizing method. FIG. 2 is a graph showing current torque characteristics.

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display area H01F 1/20

Claims (6)

[Claims] 1. Al: 2 to 8% by weight, Cr: 8 to 20% by weight, Co: 5 to
Magnetic powder for electromagnetic clutches, consisting of 35% by weight, balance Fe and unavoidable impurities. 2. Al: 2 to 8% by weight, Cr: 8 to 20% by weight, Co: 5 to
35% by weight, and further REM (rare earth metal): 0.1-1.5% by weight,
A magnetic powder for an electromagnetic clutch, which contains at least one selected from the group consisting of Ti: 0.2 to 2.0% by weight and Zr: 1.5% by weight or less, and the balance Fe and inevitable impurities. 3. The magnetic powder for an electromagnetic clutch according to claim 1, wherein the powder is spherical. 4. The magnetic powder for an electromagnetic clutch according to claim 2, wherein the powder is spherical. 5. The magnetic powder for an electromagnetic clutch according to claim 1 or 3, wherein the powder is a powder obtained by a gas atomizing method. 6. The magnetic powder for an electromagnetic clutch according to claim 2 or 4, wherein the powder is a powder obtained by a gas atomizing method.