U.S. patent application number 10/447812 was filed with the patent office on 2004-12-02 for mold release agent and method of application for die casting.
Invention is credited to Brown, Mark D..
Application Number | 20040238147 10/447812 |
Document ID | / |
Family ID | 33451336 |
Filed Date | 2004-12-02 |
United States Patent
Application |
20040238147 |
Kind Code |
A1 |
Brown, Mark D. |
December 2, 2004 |
Mold release agent and method of application for die casting
Abstract
A die cast mold release agent comprises a lubricant selected
from at least one of the group of silicones, olefins, vegetable
oils, waxes and organic esters of fatty acids preferably very
little water. A method is of application of The pressure die cast
mold release agent is disclosed where a die casting machine has a
mold with mold halves forming a mold cavity when the mold halves
abut against one another, a shot sleeve and a plunger which pushes
molten material through the shot sleeve and into the mold cavity.
The mold release agent is placed into the pressure die casting
machine remote from the mold halves, molten material is introduced
into the shot sleeve, and the molten material and the mold release
agent are forced into the mold cavity by movement of the plunger
into the shot sleeve.
Inventors: |
Brown, Mark D.; (Dexter,
MI) |
Correspondence
Address: |
Miller, Canfield, Paddock and Stone P.L.C.
c/o Robert Kelley Roth
Suite 2500
150 West Jefferson Ave
Detroit
MI
48226
US
|
Family ID: |
33451336 |
Appl. No.: |
10/447812 |
Filed: |
May 29, 2003 |
Current U.S.
Class: |
164/72 ; 164/113;
508/208; 508/214; 508/491 |
Current CPC
Class: |
C10M 2205/16 20130101;
C10M 2207/125 20130101; C10M 2207/40 20130101; C10M 129/40
20130101; B22D 17/2007 20130101; C10M 2229/02 20130101; C10M 155/02
20130101; C10M 159/08 20130101; C10M 2203/022 20130101; C10N
2050/12 20200501; B22D 17/2038 20130101; C10M 159/06 20130101; C10N
2040/36 20130101; C10M 2205/14 20130101 |
Class at
Publication: |
164/072 ;
164/113; 508/208; 508/214; 508/491 |
International
Class: |
B22C 003/00; B22D
017/10; C10M 101/00 |
Claims
What is claimed is:
1. A pressure die cast mold release agent comprising, in
combination: a lubricant selected from at least one of the group of
silicones, olefins, vegetable oils, waxes and organic esters of
fatty acids.
2. The die cast mold release agent of claim 1 wherein the lubricant
comprises at least 71 percent by weight of at least one of the
group of silicones, olefins, vegetable oils, waxes and organic
esters of fatty acids.
3. The pressure die cast mold release agent of claim 1 wherein the
lubricant comprises greater than 80% by weight silicone.
4. The pressure die cast mold release agent of claim 1 wherein the
mold release agent comprises less than 5% by weight of water.
5. The pressure die cast mold release agent of claim 1 wherein the
lubricant comprises one of a liquid, a solid, and an encapsulated
liquid having a solid exterior.
6. A die cast mold release agent comprising, in combination: a
lubricant selected from at least one of the group of silicones,
olefins, vegetable oils and organic esters of fatty acids; wherein
the mold release agent comprises less than 19 percent by weight of
water.
7. A die cast mold release agent comprising, in combination:
greater than 40% by weight of a lubricant selected from at least
one of the group of olefins, vegetable oils, organic esters of
fatty acids and waxes; and greater than 5% by weight of a
silicone.
8. The pressure die cast mold release agent of claim 7 further
comprising less than 19% water.
9. A die cast mold release agent comprising, in combination: an
encapsulated lubricant comprising a plurality of beads, wherein
each bead has a solid exterior and a liquid interior.
10. The pressure die cast mold release agent of claim 9 wherein the
encapsulated lubricant is selected from at least one of the group
of silicones, olefins, vegetable oils, waxes and organic esters of
fatty acids.
11. A die casting method for a die casting machine having a mold
with mold halves forming a mold cavity when the mold halves abut
against one another, a shot sleeve with a pour hole to receive
molten material, and a plunger which pushes molten material through
the shot sleeve and into the mold cavity comprising, in
combination, the steps of: placing a mold release agent into the
pressure die casting machine remote from the mold halves and remote
from the pour hole; introducing molten material into the shot
sleeve; and forcing the molten material and the mold release agent
into the mold cavity by movement of the plunger into the shot
sleeve.
12. The method of claim 11 further comprising the step of applying
the mold release agent to a runner connecting the mold cavity to
the shot sleeve.
13. The method of claim 11 further comprising the step of applying
the mold release agent to a gate inlet connected to the mold
cavity.
14. The method of claim 11 further comprising the step of applying
the mold release agent at the shot sleeve.
15. The method of claim 11 wherein the mold release agent is
applied into the die casting machine in the presence of air.
16. The method of claim 11 wherein the mold release agent comprises
a lubricant selected from at least one of the group of silicones,
olefins, vegetable oils, waxes and organic esters of fatty
acids.
17. The method of claim 11 wherein the mold release agent comprises
one of a liquid, a solid, and a bead having a solid exterior and
liquid interior.
18. The method of claim 11 further comprising a runner connecting
the mold cavity to the shot sleeve; wherein the molten material is
introduced adjacent the runner.
Description
FIELD OF THE INVENTION
[0001] This invention relates to improvements to pressure die
casting mold release agents, and to an improved method of
application of the mold release agent in the pressure die casting
process.
BACKGROUND OF THE INVENTION
[0002] Pressure die casting is a well known process in which molten
metal is forced under pressure and heat into a mold cavity of a
mold of a die casting machine. The molten metal is introduced in a
shot sleeve, and a plunger forces the metal into the mold cavity
through a shot sleeve. While in the mold cavity the molten metal
solidifies resulting in a molded part having a geometry conforming
to that of the mold cavity. After the part is formed, it is then
ejected from the mold cavity. Molded parts so produced have
excellent dimensional tolerances, structural integrity and
cosmetics.
[0003] There are at least two distinct classes of lubricants used
in pressure die casting, each applied to a different area of the
pressure die casting machine. One is a plunger lubricant, used for
the "shot end" of the die casting machine; the other is a mold
release lubricant, used for the mold cavity and adjacent area of
the die casting machine. At the shot end of the die cast machine
there are tight tolerances between the plunger tip and the shot
sleeve. Friction may interfere with the efficient movement of the
plunger through the shot sleeve. The plunger lubricant is applied
to the plunger tip or immediately adjacent the plunger to provide
hydrodynamic and boundary lubrication between the plunger and the
shot sleeve and thereby enhance smooth travel and acceleration of
the plunger through the shot sleeve. Plunger lubricants also
provide a barrier film between the molten metal and the plunger to
help prevent adhesion of the metal to the plunger and to help
reduce washout of the shot sleeve.
[0004] While solidifying in the mold cavity, the molten metal will
have an affinity for the surfaces of the steel mold halves. This
can result in stuck castings, soldering or other damage to the
molded parts. To help avoid these problems, the second class of
lubricants, mold release lubricants, have been used to help ensure
proper removal of the cast part from the mold cavity, and to
lubricate parts in the mold cavity as well as any runner and gate
areas of the mold. Mold release agents should be thermally stable
at high temperatures (as they are routinely exposed to molten
metal), should have good wetting properties, should provide a
barrier release between the cast part and the mold cavity, and
should enhance molten metal flow.
[0005] Therefore, in all known pressure die casting processes the
mold release agent is required to lubricate the mold halves for
proper release of the cast part, and the plunger lubricant is
required to lubricate the plunger as it travels in the shot sleeve.
Known plunger lubricants have been liquids comprised largely of a
mineral oil and other organic or inorganic materials added to
enhance hydrodynamics and/or boundary lubrication and to reduce
friction between sliding surfaces. Materials used in plunger
lubricants are noted for providing lubrication between moving
surfaces, and have not been noted for providing the thermally
stable function required of mold release agents.
[0006] U.S. Pat. No. 5,076,339 to Smith discloses a plunger
lubricant formed as a solid, wherein the plunger lubricant
comprises at least 40% wax. The solid wax lubricant is applied
through the pour hole into a shot sleeve at the plunger. This solid
plunger lubricant has found some commercial success for lubrication
of the shot sleeve and plunger tip. However, a mold release
lubricant is still required to be applied to the mold halves, just
as with all other heretofore known plunger lubricants.
[0007] U.S. Pat. No. 5,039,435 to Hanano discloses a pressure
die-cast mold release agent formed as a powder, essentially a solid
lubricant. It comprises three elements: a lubricant, an organic
polymer, and a metal soap. The lubricant can be one from the group
of boron nitride, silicon nitride, molybdenum disulfide, graphite,
mica and metal oxides (inorganic materials). The organic polymer
can be one of eight different materials: polyethylene, silicon
resin, polypropylene, phenol resin, polystyrene, acrylate resin,
epoxy resin and alkyd resin. The lubricant is coated with the
organic polymer or the metal soap. The powdery mold release agent
is applied to the mold cavity halves electrostatically and in a
vacuum, requiring incorporation of expensive capital equipment.
[0008] The September-October 1972 issue of Die-Casting Engineer
discloses an article by Radtke which teaches a pore-free die
casting technique. Here, air is drawn out of the mold cavity and
replaced with oxygen. A solid lubricant is applied to not only the
mold cavity, but also the plunger tip and to the shot sleeve. The
composition of the lubricant is not defined, but it does state that
"oily type lubricants cannot be used in the process." Petroleum oil
based mold release lubricants (i.e., "oily type lubricants") have
been used in the past, but have fell out of favor due to safety and
environmental concerns.
[0009] Currently, almost all mold release agents for pressure die
cast manufacturing are liquids. More specifically, conventional
mold release agents are water-based emulsions which may contain
waxes, oils, silicones, surfactants, anti-foams, extreme pressure
additives, rust inhibitors, and biocides. The mold release agent is
combined with air under high pressure and then directly applied
onto the mold cavity through spray nozzles. Typically water
comprises about 45-90% by weight of the composition of conventional
concentrated mold release agents. In turn, the concentrated mold
release agent is then diluted with additional water immediately
prior to application to the mold halves. These water-based mold
release agents have the advantage of good heat extraction and
lubrication properties. However, the large amount of water creates
enormous amounts of waste effluent which must be cleaned from the
machine and which must be removed and treated at additional
expense. Also, large amounts of water cause thermal cycling of the
mold halves, significantly shortening mold life. In addition,
uneven application of mold release agent can result in uneven
temperatures across the mold, which may deleteriously affect part
quality. It would be desirable to have a mold release agent with
little or no water while still maintaining good heat extraction and
lubrication properties.
SUMMARY OF THE INVENTION
[0010] In accordance with a first aspect, a pressure die cast mold
release agent comprises a lubricant selected from at least one of
the group of silicones, olefins, vegetable oils, waxes and organic
esters of fatty acids preferably very little water. In accordance
with another aspect, the pressure die cast mold release agent can
comprise a combination of a lubricant selected from at least one of
the group of olefins, vegetable oils, organic esters of fatty acids
and waxes; and a significant percentage of a silicone. In
accordance with another aspect, the pressure die cast mold release
agent comprises an encapsulated lubricant comprising a plurality of
beads, wherein each bead has a solid exterior and a liquid
interior. In accordance with another aspect, a method is provided
where a pressure die casting machine has a mold with mold halves
forming a mold cavity when the mold halves abut against one
another, a shot sleeve and a plunger which pushes molten material
through the shot sleeve and into the mold cavity. A mold release
agent is placed into the die casting machine remote from the mold
halves and remote from the pour hole, molten material is introduced
into the shot sleeve, and the molten material and the mold release
agent is forced into the mold cavity by movement of the plunger
into the shot sleeve.
[0011] From the foregoing disclosure and the following more
detailed description of various preferred embodiments it will be
apparent to those skilled in the art that the present invention
provides a significant advance in the technology and mold release
agents for die casting. Particularly significant in this regard is
the potential the invention affords for providing a high quality
mold release agent which is environmentally friendly. Additional
features and advantages of various preferred embodiments will be
better understood in view of the detailed description provided
below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a schematic sectional view of a pressure die
casting machine in which a mold release agent is used according to
a preferred embodiment.
[0013] FIG. 2 is a schematic view of a pair of mold halves, showing
the mold cavity, runners and inlet gate.
[0014] It should be understood that the appended drawings are not
necessarily to scale, presenting a somewhat simplified
representation of various preferred features illustrative of the
basic principles of the invention. The specific design features of
the method of application of as disclosed here, including, for
example, the specific dimensions of the mold halves, will be
determined in part by the particular intended application and use
environment. Certain features of the illustrated embodiments have
been enlarged or distorted relative to others to facilitate
visualization and clear understanding. In particular, thin features
may be thickened, for example, for clarity of illustration. All
references to direction and position, unless otherwise indicated,
refer to the orientation illustrated in the drawings.
DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS
[0015] It will be apparent to those skilled in the art, that is, to
those who have knowledge or experience in this area of technology,
that many uses and design variations are possible for the mold
release agent and method of application of the mold release agent
disclosed here. The following detailed discussion of various
alternative and preferred features and embodiments will illustrate
the general principles of the invention with reference to a
lubricant suitable for use with die-cast pressure molding of metal
parts. Other embodiments suitable for other applications will be
apparent to those skilled in the art given the benefit of this
disclosure.
[0016] Referring now to the drawings, FIGS. 1 & 2 show part of
a pressure die casting machine 8 suitable for forcing molten metal
under some pressure and heat into a mold cavity 16 of a mold 10.
The mold cavity is formed when a pair of mold halves 12, 14 abut
against one another, and cooperate to form the shape of the part to
be made from the molten metal. The molten metal is introduced in a
shot sleeve 22 through, for example, pour hole 28, and a plunger 24
forces the metal into the mold cavity 16 through a shot sleeve. The
molten metal may travel through a runner 18 and/or a gate inlet 20,
as shown in FIG. 2, or in some preferred embodiments, the runner
may not be used. The gate inlet 20, shot sleeve 22, plunger 24 and
any runner(s) 20 are positioned outside of the mold cavity 16, and
do not define the geometry of the part. Typically for the die
casting process disclosed herein no vacuum is drawn and the mold
cavity is not pressurized prior to introduction of the molten
metal. Vents 30 may be provided to allow atmospheric air and
entrapped gases to escape from the mold cavity 16.
[0017] Heretofore it has been thought by those in the art of
pressure die casting that for die casting machines to operate
properly, a plunger lubricant needed to be applied (either at pour
hole 28 or immediately behind the plunger 29), and a mold release
lubricant must be applied directly onto the surface to be
lubricated. However, in accordance with a highly advantageous
feature, the inventors have determined that a mold release agent of
some compositions may be applied to the gate, the runner, or to the
shot sleeve, or to any combination therewith, (i.e., remote from
the mold halves) and yet still function properly to lubricate the
mold halves and permit release of the cast part from the mold
cavity. Essentially, the metal pushes the mold release agent in
front of it, forming a lubrication front that coats the mold halves
as it travels through the mold cavity. This method of application
advantageously can reduce the total amount of mold release agent
that needs to be applied, reducing costs for the die caster.
Additional savings may be realized by reducing waste effluent.
Further cost reductions may be obtained through shorter cycle times
since less lubricant needs to be applied and the mold release of
the present invention may be applied more rapidly than known mold
release agents.
[0018] The lubricant used in the mold release agents disclosed
herein can advantageously be one of many types of low friction
materials providing good thermal stability endurance and having
either solid, liquid or wax-like properties and good wetting and
adhesion properties. Lubricants suitable for use herein can
comprise, for example, silicones, polyolefins, organic esters, and
waxes. Synthetic oils made of one or more of these materials may be
used. Also, some natural oils may be used as all or part of the
lubricant, such as vegetable oils including rapeseed oil, castor
oil and soybean oil. Such suitable materials may be used
individually, or mixed together with other materials to form the
lubricant suitable for use as a mold release agent. The die cast
mold release agents may also optionally be formed as a solid or
flexible gelatin-like material encapsulating a liquid and applied
as a series of beads.
[0019] Silicones comprise a wide variety of polymers that have
alternating silicon and oxygen atoms in repeating diorganosiloxy
groups. Such silicones may also incorporate one or more
organofunctional groups. Examples of suitable materials are Dow
Corning's DC-203 and 230 fluids, DC-2503 silicone and DC-2-5088
wax. Olefins generally comprise any unsaturated aliphatic
hydrocarbon with one or more double bonds, and two hydrogens for
every carbon (e.g., polymerized ethylene or butene). Olefins can
comprise polyalphaolefins, alpha olefins and normal alphaolefins
and polybutenes. Polyolefins are often a large component of
synthetic oils. Examples of suitable materials are Petro-Canada API
Group III and IV Oils; Durasyn 162 supplied by Amoco; Synton PAO
100 supplied by Crompton Corporation; Indopol H-100 by BP Amoco.
Organic esters suitable for use as a lubricant here can comprise,
for example, sucrose esters of fatty acids such as Sefose.RTM. by
Proctor & Gamble, carboxylic acid esters, methyl esters such as
Keil's Base ML, methyl canola esters and methyl tallowate esters.
Waxes can comprise a wide variety of materials including natural
waxes such as paraffin and other petroleum waxes, lignite, peat and
montan waxes, animal waxes, and vegetable waxes, or synthetic or
partially synthetic waxes such as polyolefin waxes, polar synthetic
waxes, and Firscher-Tropsch waxes. Suitable waxes often at least
partially comprise carboxylic acid esters, oxidized polyethylenes,
ethylene acrylic acid copolymers, bis-stearamide wax or
microcrystalline wax. Other lubricants suitable for use as all or
part of a mold release agent will be readily apparent to those
skilled in the art given the benefit of this disclosure.
[0020] As there is no need to spray this mold release agent over
the mold halves 14, 16, the mold release agent can comprise a
significantly small amount of water compared with current known
mold release agents. Preferably the mold release agent comprises
less than 20% water by weight, and most preferably no water. For
example, the mold release agent can be comprised of essentially
entirely silicone with no water, formed either as a solid or as a
liquid, advantageously eliminating the need to add water to a
lubricant. Alternatively, the mold release agent could comprise a
high percentage of wax (e.g., greater than 40% by weight) or one of
the other suitable lubricant materials mentioned above and a small
percentage of silicone, such as 5-10 percent by weight.
[0021] Preferably the mold release agent would be applied remote
from the pour hole in the area of the shot sleeve 35 shown in FIG.
2, and most preferably immediately adjacent the runner 18 as shown
by arrow 36 in FIGS. 1-2. It has been found that such application
positions are most effective in lubricating the mold halves 12, 14
so that the part created can be properly released from the mold
cavity 16. Depending on the intended application, the mold release
agent application location can be the shot sleeve, pour hole,
and/or any runner and gate inlet connecting the shot sleeve to the
mold cavity that is remote from the plunger.
[0022] From the foregoing disclosure and detailed description of
certain preferred embodiments, it will be apparent that various
modifications, additions and other alternative embodiments are
possible without departing from the true scope and spirit of the
invention. The embodiments discussed were chosen and described to
provide the best illustration of the principles of the invention
and its practical application to thereby enable one of ordinary
skill in the art to utilize the invention in various embodiments
and with various modifications as are suited to the particular use
contemplated. All such modifications and variations are within the
scope of the invention as determined by the appended claims when
interpreted in accordance with the breadth to which they are
fairly, legally, and equitably entitled.
* * * * *