Metal founding – Means to shape metallic material – Including means to assemble mold parts
Reexamination Certificate
2002-02-26
2004-06-08
Stoner, Kiley (Department: 1725)
Metal founding
Means to shape metallic material
Including means to assemble mold parts
C164S312000, C164S348000
Reexamination Certificate
active
06745821
ABSTRACT:
TECHNICAL FIELD
This invention relates to high-pressure diecasting methods and apparatus, and more particularly, to hot sprue systems for use with hot-chamber, high-pressure diecasting.
BACKGROUND TO THE INVENTION
There is a very large installed base of hot-chamber, high-pressure, diecasting machines dedicated to the production of small die-cast products of zinc, lead, tin magnesium, aluminum and their alloys.
FIG. 1
shows a typical machine
10
of this type. A pool of molten metal
12
is held in a heated pot
14
from which ‘shots’ of melt are forced, by a plunger
16
working in a submerged cylinder
18
, through a gooseneck
20
and an externally flame-heated connecting nozzle
22
, into a cavity
24
formed between a fixed die
26
and a moving die
28
. Fixed die
26
is mounted on a fixed platen
30
and moving die
28
is mounted on a moving platen
32
that is pressed toward the fixed platen by the piston
34
of a hydraulic or pneumatic ram, the clamping force being taken by tie-rods
36
. When dies
26
and
28
are closed, plunger
16
is driven downwards into cylinder
18
by the piston
38
of a pneumatic ram
40
to force a shot of melt into cavity
24
and to hold the pressure until it has frozen. After which, plunger
16
is raised to suck the remaining liquid melt from nozzle
22
and gooseneck
20
back into melt pool
12
. To assist the flowback of melt at the end of a shot, nozzle
22
normally slopes upward to fixed die
26
. Indeed, for the same purpose, the whole press portion of the machine (comprising the dies and platens) can be tilted slightly downward towards nozzle
22
.
At the commencement of a shot, the melt is conveyed from heated nozzle
22
through a sprue bush
42
fitted in the back of fixed die
26
and through a sprue channel
44
, formed in the fixed die
26
, to the interface or parting-line
46
of dies
26
and
28
. It is then conveyed along the interface
46
by one or more runner channels
48
, through a gate orifice
49
, into cavity
24
. As the injection pressure in such machines is commonly between 10 and 30 mPa, nozzle
22
must be pressed hard against sprue bush
42
and gooseneck
20
to avoid leakage. The use of sprue bush
42
assists in forming the seal at the die end of nozzle
22
and it has the advantage that it can be easily replaced should a freeze-plug form therein after a shot.
Sprue channel
44
is strongly tapered so that it widens toward die interface
46
from sprue bush
42
in the direction of melt flow. It is of such a volume that the freeze-point will occur in sprue channel
44
inwards or down-stream of bush
42
at the end of a shot. On the other hand, the runner channel(s) generally narrow(s) in the direction of melt flow (i.e., towards gate
49
) so that the melt is accelerated and enters the cavity at high velocity. This common arrangement of sprue and runner channels allows the cast sprue and runner(s) to be easily removed from the dies, together with the attached products, as one piece after the dies have opened. Each runner channel
48
is normally connected to its respective cavity
24
via narrow slot-like gate
49
so as to form a thin and easily broken connection between the product casting and it's attached runner and sprue castings.
It will be appreciated from the above that, in this specification, the sprue and runner channels form a melt path within the dies that conveys the melt to the cavity gate(s). The sprue channel conveys the melt from the exterior (normally the back) of the fixed die to the front face—or parting-line—of the fixed-die, while each runner conveys the melt from the sprue channel to the respective cavity gate along the interface between the fixed and moving dies. The sprue and runner castings are the die-cast metal that solidifies in the sprue and runner channels (respectively) at the end of a shot.
Though hot-chamber diecasting is very common, relatively trouble-free and can produce high quality product at high production rates, a major disadvantage of the technique is the large amount of metal contained in the sprue and runner castings compared with the metal in the product. After detachment from the products, the sprue and runner castings are generally remelted and reused, but this represents high-energy losses and causes melt contamination. Another significant disadvantage of conventional hot-chamber diecasting is the abrupt discontinuity in both section and direction in the melt path between the wide and widening sprue channel and the narrow and narrowing runner channel(s); a discontinuity which leads to turbulent and inefficient melt flow.
It will be appreciated that hot-chamber diecasting is a similar process to the injection moulding of plastics materials. While both can pump shots of melt into cavities via sprue and runner systems, losses associated with the sprue and runner castings are much less with injection moulding. In injection moulding, it is common to employ electrically heated sprue-channels (often called ‘nozzles’ in the injection moulding context), or electrically heated cores (called ‘hot-tips’) within the sprue-channels, to eliminate the generation of sprues. Indeed, if such a device is used to inject molten plastic directly into a cavity, both runners and sprues can be eliminated. It is even possible to use a mechanical valve in the sprue nozzle or hot-tip to close the channel at the entrance to the cavity so that the molten plastic feed-line can be kept pressurized between shots, allowing very high production rates.
While it has been suggested from time to time (see for example U.S. Pat. Nos. 4,304,544 and 4,795,126 to Crandell) that heated nozzles and hot-tips designed for injection moulding can be used for direct-injection diecasting, this has proved impractical. The much higher melting point, thermal conductivity and electrical conductivity of metals relative to plastics have made direct-injection diecasting problematic.
The most notable attempt at direct-injection in hot-chamber diecasting known to the applicant is that undertaken by the Battelle Columbus Laboratories for the International Lead Zinc Research Organization [ILZRO] during most of the 1980s. A large number of progress reports were prepared and published on this work by ILZRO or Battelle. An early such report was published in a paper (No. G-T83-066) entitled “Heated Manifold, Direct-Injection System for Zinc Diecasting” by Groeneveld and Kaiser of Battelle and Herrschaft of ILZRO at the International Diecasting Congress and Exposition, Minneapolis, Oct. 31 to Nov. 3, 1983. A further progress report, entitled “Commercial Application of the Heated-Manifold Direct-Injection System of Zinc Diecasting” was published in a paper at the Exposition of Jun. 3-6 1985 in Milwaukee, Wiss., with Groeneveld of Battelle as primary author. A further progress report (No. 30) on the ILZRO direct-injection project (authored by Groeneveld) was published by in March 1988, noting that “several million castings have been made by direct injection”. Production rates and product quality were reported to be at least equal to conventional diecasting using runners and sprues.
Despite the obvious and great benefits offered by direct-injection diecasting, the technique disclosed in the above publications (particularly, the Battelle work) has not been widely applied by the diecasting industry. The principal reason for this appears to be that die and ‘nozzle’ design methods for direct injection have not been developed to anywhere near the same facility and reliability as die, runner and sprue design techniques for conventional hot-chamber diecasting. Consequently, a great deal of highly-expert and highly-expensive experimentation must be undertaken before any given product, cavity, die, machine and ‘nozzle’ combination can be made to work satisfactorily. Furthermore, direct-injection in multi-cavity dies involves major changes to existing diecasting machines with respect to metal flow and control, making machine set-up and tool-changing lengthy processes. In short, implementation of direct-injectio
Hotflo Diecasting Pty Ltd.
Kerns Kevin P.
Sidley Austin Brown & Wood LLP
Stoner Kiley
LandOfFree
Hot sprue system for diecasting does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Hot sprue system for diecasting, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Hot sprue system for diecasting will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3337124