U.S. patent application number 14/414469 was filed with the patent office on 2015-06-18 for shot sleeve assembly with materials of different coefficients of thermal expansion.
This patent application is currently assigned to Pratt & Whitney Services PTE LTD.. The applicant listed for this patent is Pratt & Whitney Services PTE LTD.. Invention is credited to Wai Tuck Chow, Yee Ling Kwan.
Application Number | 20150165521 14/414469 |
Document ID | / |
Family ID | 54782377 |
Filed Date | 2015-06-18 |
United States Patent
Application |
20150165521 |
Kind Code |
A1 |
Chow; Wai Tuck ; et
al. |
June 18, 2015 |
SHOT SLEEVE ASSEMBLY WITH MATERIALS OF DIFFERENT COEFFICIENTS OF
THERMAL EXPANSION
Abstract
A shot sleeve assembly for a die casting process includes a
housing defining a bore open at both a front end and a rear end and
a pour opening for receiving molten material, the housing includes
a first coefficient of thermal expansion. A core is received within
the bore and includes a second coefficient of thermal expansion
lower than the first coefficient of thermal expansion. Front and
rear covers attached to the housing hold the core in place within
the bore and accommodate differences in thermal expansion between
the housing and core.
Inventors: |
Chow; Wai Tuck; (Singapore,
SG) ; Kwan; Yee Ling; (Singapore, SG) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Pratt & Whitney Services PTE LTD. |
Singapore |
|
SG |
|
|
Assignee: |
Pratt & Whitney Services PTE
LTD.
singapore
SG
|
Family ID: |
54782377 |
Appl. No.: |
14/414469 |
Filed: |
July 26, 2013 |
PCT Filed: |
July 26, 2013 |
PCT NO: |
PCT/SG2013/000310 |
371 Date: |
January 13, 2015 |
Current U.S.
Class: |
164/113 ;
164/312 |
Current CPC
Class: |
B22D 17/04 20130101;
B22D 17/10 20130101; B22D 17/2023 20130101; B22D 17/22
20130101 |
International
Class: |
B22D 17/20 20060101
B22D017/20; B22D 17/22 20060101 B22D017/22; B22D 17/04 20060101
B22D017/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 27, 2012 |
SG |
201205636-2 |
Claims
1. A shot sleeve assembly for a die casting process comprising: a
housing defining a bore open at both a front end and a rear end and
a pour opening for receiving molten material, the housing
comprising a material of a first coefficient of thermal expansion;
a core received within the bore and extending from the front end to
the rear end including a core opening aligned with the pour
opening, the core comprising a material of a second coefficient of
thermal expansion lower than the first coefficient of thermal
expansion; a front cover attached to the front end of the housing;
and a rear cover attached to the rear end of the housing, the rear
cover forcing the core against the front cover holding the core
within the bore of the housing.
2. The shot sleeve assembly as recited in claim 1, wherein the rear
cover comprises a nut threadingly received within the bore and
rotatable to force the core against the front cover.
3. The shot sleeve assembly as recited in claim 1, wherein the
housing includes flats for holding rotation of the housing
responsive to rotation of the rear cover.
4. The shot sleeve assembly as recited in claim 1, wherein the
front cover includes a shoulder against which the core abuts for
holding the core within the bore.
5. The shot sleeve assembly as recited in claim 1, including a
plurality of fasteners extending through the front cover for
securing the front cover to the front end of the housing.
6. The shot sleeve assembly as recited in claim 1, wherein the
front cover includes a plurality of threaded openings for receiving
corresponding threaded fasteners for forcing the front cover from
the housing.
7. The shot sleeve assembly as recited in claim 1, including a key
member disposed between the housing and the core for holding a
position of the core relative to the housing.
8. The shot Sleeve assembly as recited in claim I, wherein the core
is fabricated from a refractory metal material.
9. The shot sleeve assembly as recited in claim 1, wherein the core
is fabricated form a ceramic material.
10. A method of casting a cast article comprising: defining a mold
cavity between at least two mold parts; mounting a shot sleeve
heating a shot sleeve to a pre-heat temperature; tightening a rear
cover threadingly received within a housing to force a core
disposed within the housing into a front cover; pouring a quantity
of molten material into the core through a pour opening in the
housing; forcing the molten material into the mold cavity; and
curing the molten material within the mold cavity.
11. The method of casting a cast article as recited in claim 10,
including loosening the rear cover prior to cooling the shot sleeve
to room temperature that is less than the pre-heat temperature.
12. The method of casting a cast article as recited in claim 10,
comprising removing the front cover by inserting at least one
threaded fastener through a threaded opening and threading the at
least one fastener through the front cover and into engagement with
a front end of the housing and forcing the front cover away from
the housing by extending the threaded fastener from the front
cover.
13. The method of casting a cast article as recited in claim 10,
wherein the core has a lower coefficient of thermal expansion than
the housing.
14. The method of casting a cast article as recited in claim 10,
including extending a key through the housing against the core for
preventing relative rotation between the core and the housing.
15. A casting assembly comprising: a mold including at least one
cavity for receiving molten material; a shot sleeve mounted to the
mold for injecting molten material into the cavity, the shot sleeve
including a housing defining a bore open at both a front end and a
rear end and a pour opening for receiving molten material, the
housing comprising a material of a first coefficient of thermal
expansion, a core received within the bore and extending from the
front end to the rear end including a core opening aligned with the
pour opening, the core comprising a material of a second
coefficient of thermal expansion lower than the first coefficient
of thermal expansion, a front cover attached to the front end of
the housing, and a rear cover attached to the rear end of the
housing, the rear cover forcing the core against the front cover
holding the core within the bore of the housing; and a plunger
movable through the bore of the shot sleeve for forcing molten
material through the core and into the at least one cavity.
16. The casting assembly as recited in claim 15, wherein the rear
cover comprises a nut threadingly received within the bore and
rotatable to force the core against the front cover.
17. The casting assembly as recited in claim 15, wherein the front
cover includes a shoulder against which the core abuts for holding
the core within the bore.
18. The casting assembly as recited in claim 15, including a key
member disposed between the housing and the core for holding a
position of the core relative to the housing.
Description
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0001] This subject of this disclosure was made with support from
the Singapore government.
BACKGROUND
[0002] This disclosure is generally directed to a shot sleeve for a
die casting process. More specifically, this disclosure is
generally directed to a shot sleeve formed of different
materials.
[0003] A die casting process utilizes a mold cavity defined between
mold parts. Molten metal material is feed in to the cavity and held
under pressure until the metal hardens. The mold parts are then
separated and the cast part removed. In some processes a shot
sleeve is utilized to hold molten material and introduce that
material to the cavity. The shot sleeve includes an opening for
introducing molten material into a bore that leads to the cavity. A
plunger moves within the bore to inject the molten material into
the cavity. The plunger is subsequently withdrawn and additional
material-is-introduced into the plunger for fabricating another
part within the same cavity.
[0004] The shot sleeve experiences the very high temperatures of
the molten metal material and therefore is fabricated of materials
compatible with those high temperatures. However, materials that
are compatible with the high temperatures encountered during the
die casting process can be costly and difficult to machine.
Accordingly, it is desirable to design and develop shot sleeves
that can withstand the high temperatures while reducing cost and
easing manufacturing.
SUMMARY
[0005] A shot sleeve assembly for a die casting process according
to an exemplary embodiment of this disclosure, among other possible
things includes a housing defining a bore open at both a front end
and a rear end and a pour opening for receiving molten material.
The housing includes a material of a first coefficient of thermal
expansion, a core received within the bore and extending from the
front end to the rear end including a core opening aligned with the
pour opening. The core including a material of a second coefficient
of thermal expansion lower than the first coefficient of thermal
expansion, a front cover attached to the front end of the housing,
and a rear cover attached to the rear end of the housing, the rear
cover forcing the core against the front cover holding the core
within the bore of the housing.
[0006] In a further embodiment of the foregoing shot sleeve
assembly, the rear cover includes a nut threadingly received within
the bore and rotatable to force the core against the front
cover.
[0007] In a further embodiment of any of the foregoing shot sleeve
assemblies, the housing includes flats for holding rotation of the
housing responsive to rotation of the rear cover.
[0008] In a further embodiment of any of the foregoing shot sleeve
assemblies, the front cover includes a shoulder against which the
core abuts for holding the core within the bore.
[0009] In a further embodiment of any of the foregoing shot sleeve
assemblies, includes a plurality of fasteners extending through the
front cover for securing the front cover to the front end of the
housing.
[0010] In a further embodiment of any of the foregoing shot sleeve
assemblies, the front cover includes a plurality of threaded
openings for receiving corresponding threaded fasteners for forcing
the front cover from the housing.
[0011] In a further embodiment of any of the foregoing shot sleeve
assemblies, includes a key member disposed between the housing and
the core for holding a position of the core relative to the
housing.
[0012] In a further embodiment of any of the foregoing shot sleeve
assemblies, the core is fabricated from a refractory metal
material.
[0013] In a further embodiment of any of the foregoing shot sleeve
assemblies, the core is fabricated form a ceramic material.
[0014] A method of casting a cast article according to an exemplary
embodiment of this disclosure, among other possible things includes
defining a mold cavity between at least two mold parts, mounting a
shot sleeve, heating a shot sleeve to a pre-heat temperature,
tightening a rear cover threadingly received within a housing to
force a core disposed within the housing into a front cover,
pouring a quantity of molten material into the core through a pour
opening in the housing, forcing the molten material into the mold
cavity, and curing the molten material within the mold cavity.
[0015] In a further embodiment of the foregoing method of casting a
cast article as recited in claim 10, includes loosening the rear
cover prior to cooling the shot sleeve to room temperature that is
less than the pre-heat temperature.
[0016] In a further embodiment of any of the foregoing methods of
casting a cast article, includes removing the front cover by
inserting at least one threaded fastener through a threaded opening
and threading the at least one fastener through the front cover and
into engagement with a front end of the housing and forcing the
front cover away from the housing by extending the threaded
fastener from the front cover.
[0017] In a further embodiment of any of the foregoing methods of
casting a cast article, the core has a lower coefficient of thermal
expansion than the housing.
[0018] In a further embodiment of any of the foregoing methods of
casting a cast article, includes extending a key through the
housing against the core for preventing relative rotation between
the core and the housing.
[0019] A casting assembly according to an exemplary embodiment of
this disclosure, among other possible things includes a mold
includes at least one cavity for receiving molten material, and a
shot sleeve mounted to the mold for injecting molten material into
the cavity. The shot sleeve includes a housing defining a bore open
at both a front end and a rear end and a pour opening for receiving
molten material. The housing includes a material of a first
coefficient of thermal expansion. A core received within the bore
and extending from the front end to the rear end includes a core
opening aligned with the pour opening. The core includes a material
of a second coefficient of thermal expansion lower than the first
coefficient of thermal expansion. A front cover attached to the
front end of the housing, and a rear cover attached to the rear end
of the housing. The rear cover forces the core against the front
cover holding the core within the bore of the housing, and a
plunger movable through the bore of the shot sleeve for forcing
molten material through the core and into the at least one
cavity.
[0020] In a further embodiment of the foregoing casting assembly,
the rear cover includes a nut threadingly received within the bore
and rotatable to force the core against the front cover.
[0021] In a further embodiment of any of the foregoing casting
assemblies, the front cover includes a shoulder against which the
core abuts for holding the core within the bore.
[0022] In a further embodiment of any of the foregoing casting
assemblies, includes a key member disposed between the housing and
the core for holding a position of the core relative to the
housing.
[0023] Although the different examples have the specific components
shown in the illustrations, embodiments of this disclosure are not
limited to those particular combinations. It is possible to use
some of the components or features from one of the examples in
combination with features or components from another one of the
examples.
[0024] These and other features disclosed herein can be best
understood from the following specification and drawings, the
following of which is a brief description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a schematic view an example mold assembly.
[0026] FIG. 2 is a cross-section of an example shot sleeve.
[0027] FIG. 3 is a perspective view of the example shot sleeve.
[0028] FIG. 4 is a rear perspective view of the example shot
sleeve.
[0029] FIG. 5 is a schematic view of a method of utilizing the
example shot sleeve.
DETAILED DESCRIPTION
[0030] FIG. 1 schematically illustrates an example mold assembly 10
that includes a mold 12 having a first part 14 and a second part 16
that defines a cavity 18. The example mold 12 includes an opening
20 that receives a shot sleeve 22. The example shot sleeve 22
defines a bore 34 through which molten material 26 is injected into
the cavity 18. A plunger 24 is movable within the bore 34 to inject
the molten material 26 into the cavity 18. The molten material 26
is of a temperature in excess of 2000.degree. F. (1093.degree. C.).
Accordingly, the material comprising the shot sleeve 22 must be
compatible with the excessive temperatures of the molten material
26.
[0031] Referring to FIGS. 2, 3 and 4, the example shot sleeve 22
includes a housing 28 with a front end 30 and a rear end 32. The
bore 34 is disposed about a longitudinal axis 15 and extends from
the front end 30 to the rear end 32. The bore 34 is opened at both
the front and rear ends 30, 32. The housing 28 is comprised of
common steel and/or alloys of steel with a coefficient of thermal
expansion that causes significant thermal growth during operation.
Moreover, it is not desirable to provide direct contact between the
housing 28 and the molten material 26 within the bore 34.
[0032] A core 42 fabricated from a material with a much lower
coefficient of thermal expansion than steel is provided to define
the internal surfaces in direct contact with the molten material
26. The core 42 is received within the bore 34 and provides an
interior surface capable of withstanding the temperatures of the
molten material 26 that can exceed 2000.degree. F. (1093.degree.
C.).
[0033] The example core 42 is comprised of a refractory metal
material such as Anviloy or TZM. The core 42 may also be comprised
of a ceramic material such as silicon nitride or silicon carbide
that have low coefficients of thermal expansion. As appreciated,
other high temperature compatible materials may be used and are
within the contemplation of this disclosure.
[0034] Although a low coefficient of thermal expansion is
desirable, the shot sleeve assembly 22 must also be of a sufficient
strength and thickness to withstand and prevent the shot sleeve 22
from bending upwards due to encountering the temperatures of the
molten material. Molten material is poured (FIG. 1) through an
opening 36 defined in the housing 44 that is aligned with an
opening 52 within the core 42. Molten material therefore sits on a
bottom surface 66 of the core 42 prior to being injected into the
cavity 18. Because the molten material 26 sits on the bottom
surface 66 of the core 42, the bottom portion of the housing 28 and
the core 42 are heated more than the top surface and will expand
more than the top portion causing the shot sleeve 22 to bend
upwardly. The example housing 28 is of a sufficient thickness to
overcome the upward bending caused by the differential temperatures
between the bottom and top surfaces while also including the
thinner core 42 that withstands the higher temperatures.
[0035] The example shot sleeve 22 includes a front cover 44 that is
attached to the housing 28 with a plurality of fasteners 56. The
example fasteners 56 are machine screws that extend through
openings in the front cover 44 into threaded holes defined in the
front end 30 of the housing 28. The front cover 44 is fabricated
from a material determined to withstand the impact and wear
encountered due to interaction with the mold assembly 10.
[0036] The front cover 44 is a separate piece from the housing 28
and thereby may be removed and replaced without having to replace
the entire housing 28. The core 42 is fit within the bore 34 of the
housing 28 such that it may be removed and replaced due to wear and
if damaged without replacing the entire shot assembly 22.
[0037] The front cover 44 further includes threaded openings 58
that receive fasteners that extend through to engage the front
surface 30 of the housing 28. As appreciated, the fasteners 56
extend through clearance openings within the front cover 44 and are
received within internally threaded openings in the housing 28. In
contrast, the openings 58 are threaded such that a fastener
extending through the openings will abut the end surface 30 and
upon further tightening, drive the front cover 44 away from the
front end 30 of the housing 28. In this way, the front cover 44 can
be removed even if expansion or residual molten material makes it
difficult to remove. The example front cover 44 also includes a
shoulder 68 against which the core 42 abuts.
[0038] A rear cover 46 is threadingly received within the bore 34
of the housing 28. The rear cover 46 includes a threaded portion 48
that extends about the circumference of the core 42 and engages a
threaded portion defined within the housing 28. The rear cover 46
also defines an opening 50 through which the plunger 24 may extend
to drive the molten metal material 26 through the shot assembly 22
and out an opening through the front cover 44. The core 42 is
sandwiched between the shoulder 68 of the front cover 44 and the
rear cover 46 within the bore 34. Accordingly, the bore 34 may
comprise a slip fit with the core 42 to ease removal.
[0039] A key 54 extends through the housing 58 and engages a
surface of the core 42 to prevent rotation of the core 42 relative
to the housing 28 and to maintain an alignment between the opening
52 of the core 42 and the opening 36 within the housing 28. The
example key 54 comprises a threaded bolt that extends through the
housing 28 and engages a flat surface 55 defined on the outer
surface of the core 42. The flat surface 55 accommodates some
longitudinal movement of the core 42 relative to the housing 28 as
may occur due to differential thermal expansion during
operation.
[0040] The housing 28 further includes an integral collar portion
38, including flats 40 that are utilized and provide for engagement
of a tool. As appreciated, a tool can be utilized to engage the
surfaces 40 to prevent rotation of the housing and thereby the shot
sleeve 22 during tightening or loosening of the rear cover 46.
Additionally, the example housing 28 does not include a mounting
flange that requires larger starting stock material that is simply
machined away to define a mounting flange.
[0041] Referring to FIG. 5 with continued reference to FIGS. 2-4,
the example shot sleeve 22 is installed within the mold assembly 10
and heated to a preheat temperature. The preheat temperature can
range between 500.degree. F. and 2000.degree. F. (260-1093.degree.
C.) and provides for heating the shot sleeve 22 to a temperature
closer to that of the molten metal material to eliminate
excessively quick rises of temperature.
[0042] The core 42 includes a thermal expansion coefficient
schematically indicated at 64 that is much less than a thermal
expansion coefficient of the housing 28 indicated at 62.
Accordingly, once the shot sleeve 22 is heated to the preheat
temperature; the housing 28 will become longer than the core 42.
Because the housing 28 is longer than the core 42 a gap 60 may form
between an end of housing 28 and the core 42. In this example, the
gap 60 is defined between the shoulder 68 of the front cover 44 and
an end of the core 42. Molten material poured within the bore 34
can become entrapped within the gap 60 and reduce effectiveness of
the shot sleeve assembly 22. Accordingly, the core 42 is movable
longitudinally in response to tightening of the rear cover 46. As
appreciated, once the shot sleeve 22 is at the preheat temperature,
the rear cover 46 is tightened such that it moves inwardly to push
the core 42 forward against the shoulder 68 defined in the front
cover 44. The rear cover 46 is then tightened to a defined torque
to maintain the desired interface between the front end of the core
42 and the shoulder 68 of the front cover 44.
[0043] The molding operation can then proceed as indicated and
described in FIG. 1 where molten material 26 poured through the
opening 36 into the bore 34 defined by the core 42. The plunger 24
is then pushed through the bore 34 to inject the molten material
into the cavity 18.
[0044] Once molding has been completed, the shot sleeve 22 will
cool to a much cooler temperature such as room temperature. At room
temperature, the housing 28 will contract to a much larger degree
than the core 42 thereby inducing stresses on the front cover 44
and the rear cover 46. Therefore, prior to cooling of the shot
sleeve assembly 22, the rear cover 46 is loosened such that it
moves longitudinally outward to provide additional space for the
relative thermal contraction between the housing 28 and the core
42.
[0045] The example shot sleeve assembly 22 therefore includes
modular components that can be replaced upon wear to reduce the
expense of manufacture and accommodate relative thermal expansion
between the core and the housing 28. The allowances provided by the
example modular shot sleeve assembly 22 provide for the use of
temperature compatible materials in locations where it is required
while also providing for the use of cheaper materials for the
housing 28 to reduce costs and assembly. Additionally, the example
shot sleeve assembly 22 provides a modular assembly that has the
capability of preventing gaps between different thermally acting
materials.
[0046] Although an example embodiment has been disclosed, a worker
of ordinary skill in this art would recognize that certain
modifications would come within the scope of this disclosure. For
that reason, the following claims should be studied to determine
the scope and content of this disclosure.
* * * * *