Boron nitride sealing element

Details Boron nitride sealing element Boron nitride sealing element

1999-07-09

2001-10-09

Tentoni, Leo B. (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

Recycling of reclaimed or purified process material

Of excess solid particulate

C264S109000, C264S233000, C277S627000, C277S650000, C277S935000, C277S936000, C277S939000, C277S940000, C423S290000

Reexamination Certificate

active

06299805

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to boron nitride sealing members which are particularly suitable for sealing off an oxygen reference chamber with respect to a lambda-probe space containing exhaust gas, as well as a method for its manufacture.
Boron nitride (BN) gaskets, formed by machining from hot-pressed BN blocks made of hexagonal boron nitride material, fulfill the necessary resistance to gasoline, but are too expensive as a mass production product because of the costly manufacture.
The attached
FIG. 1
shows schematically a lambda probe, known illustratively from the U.S. Pat. No. 5,571,379, which is situated in an exhaust-gas path of an internal combustion engine. The probe, designated generally by
10
, is located within a housing
12
that is screwed into a flange
14
of an exhaust pipe
11
leading from the engine
13
. Situated within a cylindrical zirconium-dioxide probe substrate
5
is an oxygen (O
2
) reference chamber
3
which projects into a porous part of housing
12
seated in exhaust pipe
11
. So that the measuring results are not invalidated, a peripheral flange
4
of substrate
5
is sealed off with respect to housing
12
by gaskets
1
,
2
made of boron nitride, so that no exhaust gas
15
can reach oxygen reference chamber
3
. As already mentioned, in the U.S. Patent indicated above, the BN gaskets are machined from hot-pressed boron nitride blocks, and thus have the disadvantage of the high production costs already described. It should be mentioned that the design of the oxygen sensor or of lambda probe
10
, selected in
FIG. 1
for the related art, can be implemented just the same with boron-nitride sealing members formed according to the invention, i.e., that the construction shown in
FIG. 1
can also be used in conjunction with the invention.
SUMMARY OF THE INVENTION
In light of what has been said above, the object of the present invention is to make possible boron nitride sealing members which are less expensive to produce and are particularly suitable for sealing off an oxygen reference chamber with respect to a space of a lambda probe containing exhaust gas, as well as a cost-effective method for manufacturing them.
According to one essential aspect of the invention, this objective is achieved in that the sealing member has form-pressed boron nitride powder, obtained by comminution from hot-pressed hexagonal boron nitride material, and an added binding agent. Such boron nitride powder, falling off during the production of boron nitride members that are machined from hot-pressed boron nitride blocks made of hexagonal boron nitride material, can be fractionated according to particle categories. The particles have good flowability, and are made of hot-pressed hexagonal boron nitride which has a relatively high density (about 2.2 g/cm
3
). According to the invention, this powder is pressed, while adding a binding agent, to form a sealing member.
DETAILED DESCRIPTION OF THE INVENTION
The selected particle size of the boron nitride powder is preferably in the range of approximately 5 to 30 &mgr;m particle diameter. A suitable organic binding agent is wax which can be easily evaporated, and the amount of binding agent is a function of the selected particle size of the boron nitride powder. For example, organic binding agent in an amount of 0.1% by weight is mixed with the boron nitride powder.
An inorganic binding agent, like the familiar fire-resistant binding agents such as aluminum phosphate which is likewise admixed to the boron nitride powder in a very small quantity, can also be used as an additive for consolidating the pressed object.
The use of boron nitride powder from which free boron oxide has been washed out, e.g., the type HSS of ESK Elektroschmelzwerk Kempten, is advantageous.
According to another essential aspect of the present invention, the objective stated above is fulfilled by a method for manufacturing boron nitride sealing members, in particular for sealing off an oxygen reference chamber with respect to a lambda-probe space containing exhaust gas, which is characterized by the following steps:
make available a powdery waste material which falls off during the production of boron nitride components made by machining from hot-pressed boron nitride blocks composed of hexagonal boron nitride material;
fractionate the powdery waste material according to particle size;
separate a particle-size range desired for producing the boron nitride sealing member;
mix the powder of the separated particle-size range with a small amount of an organic or inorganic binding agent;
form-press the mixture to form a sealing member having a desired shape; and
dry, while evaporating the volatile matter contained in the binding agent.
The method of the present invention can be used particularly advantageously for the cost-effective production of boron nitride sealing devices in planar oxygen sensors, especially in a sandwich type of construction as an intermediate layer between two steatite packets.


REFERENCES:
patent: 4205858 (1980-06-01), Shimazaki et al.
patent: 5571379 (1996-11-01), Derrick
patent: 21 22 621 (1972-11-01), None
patent: 1321033 (1973-06-01), None
patent: 63-46287 (1988-02-01), None
Database WPI Week 8626, Derwent Publications, Ltd., London, GB; AN 86-167200 XP002095656, “Sealing Resin Composition with High Coefficient of Thermal Conductivity”.

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