U.S. patent application number 12/073471 was filed with the patent office on 2008-09-25 for aluminum alloy in mold for tire and tire mold.
This patent application is currently assigned to BRIDGESTONE CORPORATION. Invention is credited to Masashi Yano.
Application Number | 20080233000 12/073471 |
Document ID | / |
Family ID | 39529657 |
Filed Date | 2008-09-25 |
United States Patent
Application |
20080233000 |
Kind Code |
A1 |
Yano; Masashi |
September 25, 2008 |
Aluminum alloy in mold for tire and tire mold
Abstract
An aluminum alloy for a tire mold comprises Mg: 3.0-6.0 mass %,
Si: 0.2-4.5 mass % and the balance being Al and inevitable
impurities.
Inventors: |
Yano; Masashi; (Saitama-shi,
JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 320850
ALEXANDRIA
VA
22320-4850
US
|
Assignee: |
BRIDGESTONE CORPORATION
TOKYO
JP
|
Family ID: |
39529657 |
Appl. No.: |
12/073471 |
Filed: |
March 5, 2008 |
Current U.S.
Class: |
420/530 ;
420/546 |
Current CPC
Class: |
B29L 2030/00 20130101;
C22C 21/08 20130101; B29C 33/38 20130101 |
Class at
Publication: |
420/530 ;
420/546 |
International
Class: |
C22C 21/08 20060101
C22C021/08; C22C 21/02 20060101 C22C021/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 23, 2007 |
JP |
2007-77512 |
Claims
1. An aluminum alloy for a tire mold comprising Mg: 3.0-6.0 mass %,
Si: 0.2-4.5 mass % and the balance being Al and inevitable
impurities.
2. An aluminum alloy for a tire mold according to claim 1, which
further contains at least one of Cu: not more than 0.10 mass %, Zn:
not more than 0.10 mass %, Fe: not more than 0.10 mass %, Mn: not
more than 0.10 mass %, Ni: not more than 0.05 mass %, Ti: 0.01-0.30
mass %, Sn: not more than 0.05 mass %, Cr: not more than 0.10 mass
%, B: not more than 0.10 mass %, Ag: not more than 0.10 mass % and
Ca: not more than 0.10 mass %.
3. A tire mold for use in vulcanization building of a tire, which
comprises an aluminum alloy as claimed in claim 1.
4. A tire mold for use in vulcanization building of a tire, which
comprises an aluminum alloy as claimed in claim 2.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to an aluminum alloy suitable as a
starting material of a tire mold used in the vulcanization building
of tires, and more particularly to a casting aluminum alloy and a
tire mold comprising such an aluminum alloy.
[0003] 2. Description of the Related Art
[0004] A tire mold (hereinafter referred to as "mold" simply),
particularly a so-called split mold consisting of plural mold
segments is commonly made from an aluminum alloy from a viewpoint
of the casting property. As a typical example of the casting
aluminum alloy used in the tire mold are known AC2B, AC4C and AC7A
defined in JIS H5202 (1992), which is disclosed in Non-Ferrous
Metals of JIS HANDBOOK. These aluminum alloys are easy in the
plastic deformation because an elastic limit strain .sigma..sub.e
is as small as 0.04% in AC2B system, 0.10% in AC4C system and 0.12%
in AC7A system.
[0005] In the mold made of the aluminum alloy, therefore, local
deformation is easily caused because the elastic limit strain
.sigma..sub.e is small as compared with that of steel material as a
typical example of a mold material.
[0006] In the mold for the tire building, since the opening-closing
of the mold is carried out every the vulcanization building, the
local deformation of the mold is caused in the repeated
opening-closing operations, particularly in the fitting of the mold
segments. The local deformation results in the deformation of the
inner face form of the mold, which brings about the deterioration
of RR in the tire or the poor fitting among the mutual mold
segments in the split mold and hence disadvantageously produces a
rubber-protruded tire.
[0007] Such a local deformation of the mold is usually generated in
about one year starting from the use in the vulcanization building
of the tires, so that it is obliged to conduct the repairing of the
mold at a cycle of one year.
SUMMARY OF THE INVENTION
[0008] It is, therefore, an object of the invention to propose a
way for enhancing an elastic limit strain of a casting aluminum
alloy in order to suppress the local deformation of the mold made
of the aluminum alloy.
[0009] The construction of the invention is as follows.
[0010] (1) An aluminum alloy for a tire mold comprising Mg: 3.0-6.0
mass %, Si: 0.2-4.5 mass % and the balance being Al and inevitable
impurities.
[0011] (2) An aluminum alloy for a tire mold according to the item
(1), which further contains at least one of Cu: not more than 0.10
mass %, Zn: not more than 0.10 mass %, Fe: not more than 0.10 mass
%, Mn: not more than 0.10 mass %, Ni: not more than 0.05 mass %,
Ti: 0.01-0.30 mass %, Sn: not more than 0.05 mass %, Cr: not more
than 0.10 mass %, B: not more than 0.10 mass %, Ag: not more than
0.10 mass % and Ca: not more than 0.10 mass %.
[0012] (3) A tire mold for use in vulcanization building of a tire,
which comprises an aluminum alloy as described in the item (1) or
(2).
[0013] According to the invention, the design for enhancing the
elastic limit strain can be given to the casting aluminum alloy.
Therefore, by using such an aluminum alloy can be improved
mechanical properties of a cast mold made of the aluminum alloy,
and particularly the local deformation is suppressed during the
vulcanization building, and hence it is possible to prolong the
service life of the mold.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] As to the composition of the aluminum alloy according to the
invention, the reason of the limitation on the each component is
described in detail below.
[0015] Mg: 3.0-6.0 mass %
[0016] Mg is a solid-solution strengthening element and is included
for strengthening the grain boundary with Al--Mg precipitates.
Also, Mg having an atomic radius larger than that of Al is
inhabited in the crystal grain to form Guinier-Preston zone (GP
zone), and the elasticity can be maintained by the GP zone. That
is, the GP zone is a stacking fault due to aggregation of
solid-solution elements. The solid-solution strengthening by the GP
zone appearingly serves as a dispersion strengthening to trap
dislocation causing loss of elasticity, and hence the elastic limit
increases and the strength rises. For this end, it is required to
include nor less than 3.0 mass % of Mg. On the other hand, when the
content of Mg exceeds 6.0 mass %, the stable GP zone is not formed
and the scattering of the properties inclusive of elastic limit
becomes large every the cast lot and further the castability is
considerably deteriorated and the precision casting is
difficult.
[0017] Si: 0.2-4.5 mass %
[0018] Si contributes to strengthen the grain boundary by an
eutectic system with Al. Since Al--Si eutectic is easily peeled off
from Al matrix, it is required that Al--Mg--Si based inclusion is
produced at the solidification stage of the casting and bonded to
the Al--Si eutectic to prevent the crystal slippage at the grain
boundary. For this end, it is required to include not less than 0.2
mass % of Si. Particularly, in order to produce the Al--Mg--Si
based inclusion at the solidification stage of the casting, the
aforementioned inclusion of not less than 3.0 mass % of Mg is
required in addition to not less than 0.2 mass % of Si. That is,
the Al--Mg--Si based inclusion produces Al--Mg.sub.2Si fine
precipitates, and the Al--Mg.sub.2Si also forms the GP zone to
bring about the improvement of the elastic limit likewise the above
case. On the other hand, when it exceeds 4.5 mass %, the
Al--Mg.sub.2Si is preferentially precipitated in the grain boundary
to easily cause embrittlement, so that Si is required to be not
more than 4.5 mass %.
[0019] The balance other than Mg and Si is Al and inevitable
impurities. In the aluminum alloy according to the invention, one
or more of Cu, Zn, Fe, Mn, Ni, Ti, Sn, Cr, B, Ag and Ca may be
included in addition to the above components, if necessary. Among
them, Sn, B, Ca and Cr are existent as an inevitable impurity. A
preferable content range of each of these components is as
follows.
[0020] Cu: not more than 0.10 mass %
[0021] Cu is preferably added in an amount of not less than 0.05
mass % in order to stably produce the Al--Mg based GP zone and
Al--Mg.sub.2Si based GP zone, but when the addition amount of Cu
exceeds 0.10 mass %, the above GP zones are segregated to make the
scattering of the properties large, so that the upper limit is 0.10
mass %.
[0022] Zn: not more than 0.10 mass %
[0023] Zn is is preferably added in an amount of not less than 0.05
mass % in order to stably produce the Al--Mg based GP zone and
Al--Mg.sub.2Si based GP zone, but when the addition amount of Zn
exceeds 0.10 mass %, there is a fear that Al--Mg.sub.2Si is
preferentially precipitated in the grain boundary to induce the
intergranular cracking, so that the upper limit is 0.10 mass %.
[0024] Fe: not more than 0.10 mass %
[0025] A slight amount of Fe added leads to the improvement of
elastic limit, so that Fe is preferably added in an amount of not
less than 0.05 mass %. However, when the addition amount exceeds
0.10 mass %, the castability is obstructed, so that the upper limit
is 0.10 mass %.
[0026] Mn: not more than 0.10 mass %
[0027] Mn is preferably added in an amount of not less than 0.05
mass % for improving the heat resistance, but when the addition
amount exceeds 0.10 mass %, the castability is obstructed, so that
the upper limit is 0.10 mass %.
[0028] Ni: not more than 0.05 mass %
[0029] Ni is preferably added in an amount of not less than 0.03
mass % for improving the heat resistance and elastic limit, but
when the addition amount exceeds 0.05 mass %, the castability is
obstructed, so that the upper limit is 0.05 mass %.
[0030] Ti: 0.01-0.30 mass %
[0031] Ti is added in an amount of not less than 0.01 mass % for
forming fine grain boundary, but when the addition amount exceeds
0.30 mass %, the effect of forming the fine grain boundary is
unchangeable, so that the upper limit is 0.30 mass %.
[0032] Sn: not more than 0.05 mass %
[0033] Sn is incorporated as an inevitable impurity, but when the
content exceeds 0.05 mass %, the castability is obstructed, so that
the content is controlled to not more than 0.05 mass %.
[0034] Cr: not more than 0.10 mass %
[0035] Cr is also incorporated as an inevitable impurity, but when
the content exceeds 0.10 mass %, the properties are obstructed, so
that the content is controlled to not more than 0.10 mass %.
[0036] B: not more than 0.10 mass %
[0037] B is also incorporated as an inevitable impurity, but when
the content exceeds 0.10 mass %, the properties, particularly
elongation are obstructed, so that the content is controlled to not
more than 0.10 mass %.
[0038] Ag: not more than 0.10 mass %
[0039] Ag is preferably added in an amount of not less than 0.01
mass % for making finer the size of the polycrystalline alloy up to
nano-size, but when the content exceeds 0.10 mass %, the effect of
making the size finer is saturated, so that the upper limit is 0.10
mass %.
[0040] Ca: not more than 0.10 mass %
[0041] Ca is incorporated as an inevitable impurity, but when the
content exceeds 0.10 mass %, the castability is obstructed, so that
the content is controlled to not more than 0.10 mass %.
[0042] The aluminum alloy having the aforementioned composition is
first produced as an ingot, which is cast through a melting furnace
and a holding furnace to form a cast slab and then the resulting
cast slab is reshaped through elastic and plastic deformations and
finally subjected to a machine work to form a mold.
[0043] Thus, there can be obtained a mold having an elastic limit
strain .sigma..sub.e of not less than 0.20%. When the vulcanization
building of the tire is carried out by using the split mold formed
by fitting the mold segments, an average fitting strain is
0.04-0.07%, but the end face is locally deformed in the fitting of
the mold segments to generate strain input corresponding to 2-3
times of the average fitting strain. Therefore, in order to attain
the fitting at an elastic zone, the material used for the mold is
required to have an elastic limit strain of 0.08-0.21%, and hence
the elastic fitting is attained when the elastic limit strain as
the mold is not less than 0.20%.
EXAMPLES
[0044] Each of mold segments used for the vulcanization building of
a passenger car tire having a tire size of 225/60 R15 is cast from
an aluminum alloy having a chemical composition shown in Table 1
under conditions shown in Table 2. As regards the castability, the
state of generating cast cavities is examined under a proper
casting design. In this case, the casting design is a gravity
casting with a chill type ring of one sprue.
[0045] Then, the elastic limit strain is measured with respect to
the resulting molds. Furthermore, the vulcanization building of
tires is conducted through the above molds under the following
conditions over a long time of period to measure spue generating
ratio and mold repairing cycle after the use period of one year.
The measured results are shown in Table 3.
[0046] Conditions of tire vulcanization building (gas
vulcanization) [0047] platen/jacket temperature: 180.degree.
C./180.degree. C. [0048] initial stage of vulcanization: steam,
pressure 1.67 MPa (17 kgf/cm.sup.2), 2.5 minutes [0049] middle
stage of vulcanization: inert gas (N.sub.2 gas), pressure 2.06 MPa
(21 kgf/cm.sup.2), 12 minutes [0050] last stage of vulcanization:
evacuation of inert gas up to a pressure of 0.34 MPa (3.5
kgf/cm.sup.2) for 1 minute
[0051] Moreover, the ratio of generating cast cavities under the
proper casting design is evaluated by a man-hour for repairing
cavities, in which a case that the man-hour required for repairing
one set of cavities is less than 4 hours is a small ratio
(.largecircle.), a case that the man-hour is 4-8 hours is a middle
ratio (.DELTA.) and a case that the man-hour exceeds 8 hours is a
large ratio (.times.).
[0052] The elastic limit strain is a proportional limit strain
determined from a stress-strain curve obtained by a tensile test of
a JIS No. 4 test piece.
[0053] The spue generating ratio is a ratio of molds generating
spues among 10 molds. In this case, the spue-generated mold is
determined when spues of not less than 1 mm are generated in the
fitted portion between mold segments in the mold.
[0054] Also, the mold repairing cycle means a cycle required for
repairing the spue-generated mold in the continuous use of the
mold, which is evaluated from the mold-repairing result.
TABLE-US-00001 TABLE 1 (mass %) Alloy No. Mg Si Cu Zn Fe Mn Ni Ti
Sn Cr B Ag Ca Remarks A 4.0 1.0 0.1 0.1 0.1 0.1 0.05 0.05 0.05 0.1
0.1 0.1 0.01 Invention Example B 4.0 0.1 0.1 0.1 0.1 0.1 0.05 0.05
0.05 0.1 0.1 0.01 0.01 Comparative Example (corresponding to AC7A)
C 3.0 0.2 0.1 0.1 0.1 0.1 0.05 0.05 0.05 0.1 0.1 0.1 0.01 Invention
Example D 6.0 4.5 0.1 0.1 0.1 0.1 0.05 0.05 0.05 0.1 0.1 0.1 0.01
Invention Example E 3.0 4.5 0.1 0.1 0.1 0.1 0.05 0.05 0.05 0.1 0.1
0.1 0.01 Invention Example F 6.0 0.2 0.1 0.1 0.1 0.1 0.05 0.05 0.05
0.1 0.1 0.1 0.01 Invention Example G 4.0 3.0 0.1 0.1 0.1 0.1 0.05
0.05 0.05 0.1 0.1 0.1 0.1 Invention Example H 2.0 0.2 0.1 0.1 0.1
0.1 0.05 0.05 0.05 0.1 0.1 0.1 0.1 Comparative Example I 6.0 5.0
0.1 0.1 0.1 0.1 0.05 0.05 0.05 0.1 0.1 0.1 0.1 Comparative Example
J 2.0 4.5 0.1 0.1 0.1 0.1 0.05 0.05 0.05 0.1 0.1 0.1 0.1
Comparative Example K 7.0 0.2 0.1 0.1 0.1 0.1 0.05 0.05 0.05 0.1
0.1 0.1 0.1 Comparative Example L 7.0 4.5 0.1 0.1 0.1 0.1 0.05 0.05
0.05 0.1 0.1 0.1 0.1 Comparative Example M 7.0 0.1 0.1 0.1 0.1 0.1
0.05 0.05 0.05 0.1 0.1 0.1 0.1 Comparative Example N 7.0 5.0 0.1
0.1 0.1 0.1 0.05 0.05 0.05 0.1 0.1 0.1 0.1 Comparative Example
TABLE-US-00002 TABLE 2 Sam- Alloy Casting Casting Cover chill ple
symbol temperature rate temperature No. for mold (.degree. C.)
(kgf/min) (.degree. C.) Remarks 1 A 720 100 300 Invention Example 2
B 720 100 300 Comparative Example 3 C 720 100 300 Invention Example
4 D 720 100 300 Invention Example 5 E 720 100 300 Invention Example
6 F 720 100 300 Invention Example 7 G 720 100 300 Invention Example
8 H 720 100 300 Comparative Example 9 I 720 100 300 Comparative
Example 10 J 720 100 300 Comparative Example 11 K 720 100 300
Comparative Example 12 L 720 100 300 Comparative Example 13 M 720
100 300 Comparative Example 14 N 720 100 300 Comparative
Example
TABLE-US-00003 TABLE 3 Castability Evaluation Elastic Spue Mold
Alloy for limit gen- repair- symbol generating strain erating ing
Sample for cast .sigma..sub.e ratio cycle No. mold cavities (%) (%)
(years) Remarks 1 A .largecircle. 0.24 10 5 Invention Example 2 B X
0.08 30 2 Comparative Example 3 C .largecircle. 0.25 12 5 Invention
Example 4 D .largecircle. 0.26 8 5 Invention Example 5 E
.largecircle. 0.25 10 5 Invention Example 6 F .largecircle. 0.28 5
5 Invention Example 7 G .largecircle. 0.27 5 5 Invention Example 8
H X 0.06 40 1 Comparative Example 9 I X 0.25 12 5 Comparative
Example 10 J .DELTA. 0.07 30 2 Comparative Example 11 K X 0.26 8 2
Comparative Example 12 L .DELTA. 0.28 5 5 Comparative Example 13 M
X 0.09 25 1.5 Comparative Example 14 N X 0.27 5 5 Comparative
Example
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