Metal treatment – Process of modifying or maintaining internal physical... – Carburizing or nitriding using externally supplied carbon or...
Reexamination Certificate
1994-04-14
2001-01-30
Ip, Sikyin (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Carburizing or nitriding using externally supplied carbon or...
C148S228000, C148S230000, C148S231000, C148S212000
Reexamination Certificate
active
06179932
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a motor rotary shaft which comprises a journal portion of a hard nitride layer to have remarkably improved properties, such as durability, and also to a manufacturing method of the motor rotary shaft.
BACKGROUND OF THE INVENTION
DC (direct current) or AC (alternate current) servo motors used for an actuator in industrial robots and the like are generally required to have quick response for controlling positions of the robots quickly with high accuracy, and also sufficient durability to bear frequently repeated operation of startup, stoppage, and change of normal and reverse rotation.
FIG. 4
exemplifies a DC servo motor including a general construction of the servo motor. The servo motor
20
has a motor casing
21
with left and right side walls each having bearing metal
23
with which rotatably supported are journal portions
22
a
of a motor rotary shaft (rotary)
22
made of steel. The motor rotary shaft
22
comprises an armature
24
, an armature coil
25
, a commutator
26
and the like. A permanent magnet
27
is fixed on the casing
21
at a position to face the armature
24
, and the rotary shaft
22
is connected at its one end with a position/speed detector
30
and at an output portion
22
b
of the another end is connected with a speed reducer
29
, such as gears. The servo motor
20
constructed with the above structure is required to have high durability at the journal portions
22
a
thereof in association with the bearing metals
23
in order to meet the aforesaid requirement.
Hence, specific kinds of steel material having high durability are selected for the motor rotary shaft
22
to improve the durability at its journal portions
22
a
. This, however, leads to problems such as increases in cost of material and weight.
Accordingly, an object of the invention is to improve the durability of the journal portions of the motor rotary shaft without increases in cost of material and weight.
SUMMARY OF THE INVENTION
To accomplish the above object, a first aspect of the invention is directed to a motor rotary shaft having a journal portion whose surface layer is formed into a hard nitride layer, and a second aspect of the invention is directed to a manufacturing method of a motor rotary shaft wherein a journal portion of the motor rotary shaft is held in fluorine- or fluoride-containing gas atmosphere under a heated condition for forming a fluoride layer on the surface of the journal portion, and thereafter further held in nitride atmosphere under a heated condition for forming a hard nitride layer on the surface of the journal portion.
In detail, the motor rotary shaft of the present invention is constructed at the surface layer of the journal portion with a hard nitride layer but does not employ a hard material for the whole motor rotary shaft, thereby enabling provision of the motor rotary shaft which is obtainable at a low cost, not so heavy and excellent in durability. Furthermore, in the manufacturing method of the motor rotary shaft according to the present invention, the journal portion of the shaft is first held in fluorine- or fluoride-containing gas atmosphere under a heated condition to form a fluoride layer on the surface of the journal portion, and further held in nitride atmosphere under heated condition to remove the formed fluoride layer from the journal portion and simultaneously form a hard nitride layer on the part removed (on the surface layer of journal portion). In the course of the method, formation of fluoride layer on the surface of journal portion is carried out before nitriding to purify and at the same time activate the surface of the journal portion, so that the nitride layer can be uniformly and rather deeply formed on the surfaces of the journal portion, whereby the hard nitride layer can be uniform and thick in forms of thickness.
Next, details of the present invention are described below.
Fluorine- and fluoride-containing gas to be used for fluorinating in the present invention is an inactive gas, such as N
2
containing at least one of the fluorine source components, such as NF
3
, BF
3
, CF
4
, HF, SF
6
, and F
2
. NF
3
is most preferable and useful in respect of reactivity, handling properties, and the like for the purposes of the present invent.
Upon nitriding in the manufacturing method according to the present invention, the journal portion of the motor rotary shaft (made of steel, such as stainless steel, and with the other portion than the journal portion being masked by coating a known anti-hardening agent) is held, as aforementioned, in the fluorine- or fluoride-containing gas atmosphere under a heated condition at 250 to 400° C. when NF
3
is used, for example, to form a fluoride layer on the surface of the journal portion, followed by nitriding (or carbon nitriding) using a known nitriding gas, such as ammonia. The concentration of the fluorine source components such as NF
3
in the fluoride gas is, for example, 1000 to 100000 ppm, preferably 20000 to 70000 ppm and most preferably 30000 to 50000 ppm. The time for holding in the fluorine- or fluoride-containing gas may be selectively set corresponding to kinds of steel materials, sizes of the motor rotary shaft, heating temperatures or the like and it is generally a few minutes or scores of minutes.
The manufacturing method of the present invention will be further detailed. A journal portion
22
a
of a motor rotary shaft
22
shown in
FIG. 4
which is made of steel and masked at portions other than the journal portion may be cleaned so as to be degreased and then placed in a heat treatment furnace
1
as shown in FIG.
1
. The heating furnace
1
is a pit furnace comprising an outer shell
2
, a heater
3
provided therein and an inner container
4
disposed inside the heater
3
. A gas guide line
5
and an exhaust pipe
6
are inserted into the pit furnace. Gas is fed to the gas guide line
5
from cylinders
15
,
16
through a flow meter
17
and a valve
18
and the like. Atmosphere inside the pit furnace is agitated by a fan
8
which is rotated by a motor
7
. The motor rotary shaft
22
is held in a metallic container
11
to be placed in the furnace. In the drawing, reference numeral
13
denotes a vacuum pump and
14
a noxious substance eliminator. Fluorine- or fluoride-containing gas, for example a mixed gas of NF
3
and N
2
is injected into the furnace and heated to a predetermined reaction temperature. NF
3
generates active fluorine at 250 to 400° C., so that organic and inorganic contaminant on the surfaces of the journal portion
22
a
are removed and the generated fluorine simultaneously is reacted with Fe, chrome substrate or oxides such as FeO, Fe
3
O
2
, and Cr
2
O
3
on the surface of the journal portion
22
a
as represented in the following formula, thereby forming on the surface of the journal portion
22
a
a quite thin fluoride layer containing therein such compounds as FeF
2
, FeF
3
, CrF
2
, and CrF
4
.
FeO+2F→FeF
2
+1/2O
2
Cr
2
O
3
+4F→2CrF
2
+3/2O
2
The reaction changes the oxide layer on the surfaces of journal portion
22
a
to a fluoride layer and removes O
2
adsorbed on the same surface. The fluoride layer is stable at temperatures below 600° C. when there exists no O
2
, H
2
, nor H
2
O, to thereby prevent forming oxide layer and adsorption of O
2
on and by the metallic substrates. Also, according to the fluorinating process, the fluoride layer is formed on the surface of the furnace material at the initial stage, so that the fluoride layer thereafter prevents a possible damage to the surfaces of furnace material due to application of fluorine- or fluoride-containing gas. The journal portion
22
a
duly treated with fluorine- or fluoride-containing gas is further heated to a nitriding temperature 480 of to 700° C. and applied in this state with NH
3
gas or a mixed gas of NH
3
and a gas containing carbon sources (such as RX gas), whereby the aforesaid fluoride layer is reduced or broken by H
2
or trace amount of water as represented by the followin
Armstrong, Westerman Hattori, McLeland & Naughton
Daidousanso Co. Ltd.
Ip Sikyin
LandOfFree
Motor rotary shaft and manufacturing method thereof does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Motor rotary shaft and manufacturing method thereof, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Motor rotary shaft and manufacturing method thereof will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2488213