JPS61121276A - Ceramic heater - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a ceramic heater suitable for use in glow plugs for preheating diesel engines and the like.

[Prior art]

A glow plug is used in the Daze μ engine as a starting component at low temperatures, and a glow plug equipped with a quick-heating heater is required to improve engine startability.

In order to meet this demand, the inventors first added molybdenum silicide (Mo5iz) and silicon nitride (SLN4) to the tip of a support member made of an electrically insulating ceramic sintered body.
Patent application 1983-'FO6 for the purpose of developing a ceramic heater in which a heating element made of a ceramic sintered body made of
No. 70, Japanese Patent Application No. 59-410109).

This ceramic heater has excellent high-temperature oxidation resistance and high-temperature strength, and can be used exposed inside the combustion chamber of an engine, so it has excellent heat-up properties.

[Problems to be solved by the present invention]

In the above ceramic heater, the supporting member is made of 5isNa or Si, 3N4, and alumina (A
rgon).

By the way, one problem with this ceramic heater is that when used as a glow plug, if cold and hot temperatures are repeated over a long period of time, cracks will occur in the support member, especially near the part that contacts the lead wire buried therein. It is.

Therefore, the object of the present invention is to prevent the above-mentioned cracks from occurring and improve the durability of the ceramic heater.

[Means for solving problems]

The above-mentioned cracks occur mainly because the coefficients of thermal expansion of the support member and the +7- wire are different, and thermal stress is repeatedly generated in the support member due to repeated heat generation during startup, leading to fatigue failure.

In order to solve this problem, the inventors conducted repeated research experiments and developed a sintered body of a mixture of Sialon and AlhOx, a sintered body of a mixture of 81sN and AgxOs, and a sintered body of a mixture of Sialon and AlhOx as supporting members.
and a sintered body of a mixture of SLa N4, Sialon, and Ag2Os, and the coefficient of thermal expansion of the supporting member is set to the coefficient of thermal expansion of the tungsten lead wire (4XIO
degree), that is, the range of 20 articles above and below, i.e. 3.6
It was confirmed that when the adjustment is made within the range of Odeg to 5.2'X10 αeg, the occurrence of cracking is significantly lower than when it is outside the above range, and durability can be improved.

Adjustment of the coefficient of thermal expansion of the support member is achieved by selecting the proportions of the constituent materials. In order to keep the coefficient of thermal expansion of the support member within the above range, the constituent materials must be Sialon and Alto.
For s, Sialon 387μ% ~ 80mo/L/*
, S'LsN< and Ag5Os, the total ffi of Si, iNa, and Sialon is 35 mol, 96 to 8o, and in the case of Si, aN4, Sialon, and Alto@, It may be set to MoA/96.

Including sialon in the support member is effective in increasing the high temperature strength of the support member.

〔Example〕

Hereinafter, an embodiment in which the present invention is applied to a glow plug for an engine will be described.

In the glow plug shown in FIG.
A heating element 1 having a U-shaped cross section is connected to the tip of the heating element 1. A pair of tungsten lead wires 3a, 31) are embedded in the supporting member 2 in the axial direction, and their tips are connected to the heating element 1.

A metal sleeve 4 is attached to the outer periphery of the support member 2, and a metal body 5 is attached to the outer periphery.

The rear end of the lead wire 3a extends to the base end of the support member 2, is connected to a metal cap 6 fitted to the base end, and is connected to a power source (not shown) via the cap 6 and a nickel wire 7. . On the other hand, the rear end of the lead wire 3b is connected to the metal body 5 through the metal sleeve number V! Continued. This glow plug is fixed to the engine combustion chamber wall (not shown) by a screw 51 formed on the metal body 5.

Heating element 1 is made of conductive MO8L and insulating SL N4.
It is a sintered body of mixed powder. MO8iz is heating element 1
5LN4, which has a low coefficient of thermal expansion, provides heat shock resistance.

The particle size of Mo5i, is also smaller than that of 51sN4, and the small-diameter MOSj-x particles are Si, sN,
MOS1. The structure is such that the x particles are in contact with each other.

The support member 2 in which the leads g3a and 3b are embedded is a sintered body of Sialon and Ag*OjO mixed powder, S'LsNa.
A sintered body of mixed powder of and Sialon also Id S1s L
The heating element 1 and the support member 2 are integrally sintered.

FIG. 2 shows a method of manufacturing a ceramic heater, in which a ceramic sheet 1 to form a heating element 1 and a ceramic sheet 2 to form a support member 2 are combined and laminated as shown, and lead wires 3a , 31) as a whole'
11600'c.

A ceramic heater is manufactured by hot pressing under conditions of about 500114.

The first method using the ceramic heater obtained in this way
In the glow plug shown in the figure, current passes through the nickel/L' wire 7, the metal cap 6, and the lead wire 3a to the heating element 1t.
- It flows and generates heat, and is grounded through the lead wire 3b1 metal sleeve 4 and metal pod 5t.

Next, by changing the composition of the support member 2, a ceramic heater was produced by the above method, and a durability test was conducted on the glow plug to which this heater was attached. The composition of the heating element is M
O8ix-70mo/L'U'OLs ~4.

The room temperature resistance of this heating element is 0.18Ω.

In the durability test, the voltage was set so that the equilibrium temperature was 1300°C, and the product was heated at this voltage for 1 minute, then cooled with no current for 1 minute, then energized intermittently until the support member cracked and broke. The number of cycles was investigated.

(1 N Sialon-A608 sintered body The relationship between the blending ratio of Sialon and AJ*Os and the coefficient of thermal expansion of the sintered body is shown in Figure 3. In the figure, the line W
is the coefficient of thermal expansion of tungsten (same in the following figures).

Table 1 shows the results of a durability test of a glow plug in which a sintered body of Sialon-Ag*o was used as a supporting member and a tungsten lead wire was embedded therein. The durability cycle is 600, which is the lifespan of a conventional metal sheath type glove wog.
The investigation was conducted using a truncated test with 20,000 cycles (equivalent to about 10 years), which is approximately three times as many as 0 cycles (equivalent to about 3 years). The coefficient of thermal expansion of the supporting member is 4.4 X I O ± 2096 deg, that is, 5.2
X I Odeg ~3,6 X : L Odeg
(Sialon 38 mo/I/96 to 807% in the supporting member) will withstand 20,000 cycles/I/l/(but in other ranges, the supporting member will not reach 20,000 cycles/I/l/l). occurs, leading to damage.

Table 1 (2) Six ~4 Alh Os sintered body 81
sN< and A I! ! -01 blending ratio,
Figure 4 shows the relationship between the thermal expansion coefficient of the sintered body.

The reason why the coefficient of thermal expansion does not change up to the A41xOs amount of 38 moA/* is due to the formation of β'-sialon in S1s~4-AJxOn. As a result of X-ray diffraction, Ae
xOm Quantity 38moA/* or less”t’ HaA g x
Om -ff, f is consumed in the formation of sialon and the sintered body becomes S'5. ．． Composed of 5N4-Sialon. Thermal expansion of Sialon-1 Rukara All! 01 The coefficient of thermal expansion of the sintered body does not change until the amount reaches 38 m/I/*lC. And for 38Mo/L/96 or higher, α-Agzos
A phase is formed, and the coefficient of thermal expansion changes depending on the amount of phase.

Table 2 shows the durability of the Sis N, -is Ox sintered support member. In this case as well, the coefficient of thermal expansion is 4.4×10
+ 2096 deg (SLsN< 37 MOA
/% to 59% to 59%), it shows outstanding durability.

[Table 2 (3) 5isN+-sialon-AJ*Oa sintered body Si, jNi: β'-"j-i10/'i50aa/L
/*: 50 mo/L/% and AlhOs is used as the raw material for adjustment.
Figure 5 shows the thermal expansion coefficients of sintered bodies with various amounts.

Table 3 shows the durability of the 81sNs-sialon-AIlxOa sintered support member. In this case as well, the coefficient of thermal expansion is 4.
4 X I O+ 2096 +18g (51sN
<+SiAlON 35 mol% to 80 mol%/L/*) Exhibits outstanding durability when closed.

Table 3 As mentioned above, in the support member of a ceramic heater that supports a heating element and has a tungsten lead wire embedded therein, the support member is used as a ceramic heater.
, S'rsNa-ALOx, Sis N, -Sialon-Agx Os sintered bodies were confirmed to exhibit excellent thermal expansion coefficient υ and particularly excellent durability in all cases.

Therefore, the heater of the present invention is extremely effective when applied to parts such as glow plugs that are used under severe conditions where cold and hot cycles are repeated.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a glow plug equipped with a ceramic heater of the present invention, FIG. 2 is a diagram showing a method of manufacturing a ceramic heater of the present invention, and the third factor, FIGS. 4 and 5 are Sialon A (lsos sintered body, Sis, N
FIG. 4 is a diagram showing the relationship between the blending ratio of components and the coefficient of thermal expansion of a 4-Alh Os sintered body and a Sls Nm-Sialon-Arhoz sintered body. 1-...Heating element 2--Support member 3a, 31)...-Lead wire Fig. 1 Fig. 2 Fig. 3 Fig. 5i 3N4 TJ Iron Mol O10→
AL203 Figure 4

Claims (4)

[Claims] (1) A heating element made of a sintered body of a mixture of molybdenum silicide and silicon nitride, a support member made of an electrically insulating ceramic sintered body and having the heating element bonded to one end thereof, and a support member embedded in the support member. A ceramic heater is provided with a lead wire whose tip is connected to the heating element, and the support member is made of a sintered body of a mixture of sialon and alumina, a sintered body of a mixture of silicon nitride and alumina, and silicon nitride. It is composed of either a sintered body of a mixture of Sialon or alumina, and the coefficient of thermal expansion of the support member is 3.6 × 10^-^6 deg.
Ceramic heater with a range of ^-^1 to 5.2 x 10^-^6 deg^-^1. (2) The ceramic heater according to claim 1, wherein the support member is a sintered body of a mixture of 38 mol% to 80 mol% sialon and the balance alumina. (3) The support member contains 37 mol% to 59 mol% of silicon nitride.
2. The ceramic heater according to claim 1, which is a sintered body of a mixture of alumina, the balance being alumina. (4) The total amount of the support member made of silicon nitride and sialon is 35
The ceramic heater according to claim 1, which is a sintered body of a mixture of mol % to 80 mol % and the balance being alumina.