Static molds – Container-type molding device – Including auxiliary port for transmission of fluid – i.e.,...
Reexamination Certificate
1999-09-09
2002-04-09
Nguyen, Nam (Department: 1722)
Static molds
Container-type molding device
Including auxiliary port for transmission of fluid, i.e.,...
C425S546000, C425S571000, C425S130000, C425S812000, C425SDIG001, C264S572000
Reexamination Certificate
active
06367765
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a vent, system and method for a mold and more particularly to a vent insert, method of making the insert, and system and method for controlling vent flow to and from the mold.
BACKGROUND OF THE INVENTION
During molding, the atmosphere inside the mold cavity must somehow be vented from the mold cavity to avoid the air in the mold cavity, along with gases from the mold material, from causing defects in the part being molded. If the trapped air is not vented from the mold cavity quickly enough or not vented at all, the finished part can have defects. For example, trapped air can impart knit lines or poor surface cosmetics in the exterior of the finished part. Even worse, gases from the mold material can migrate into the mold material creating porosity or bubbles in the finished part.
Venting also has an impact on how fast parts can be molded. It stands to reason that the faster air and other gases in the mold cavity can be vented from the cavity, the faster the mold cavity can be filled. Conversely, when defects occur because venting is poor or virtually nonexistent, the rate of injecting the hardenable mold material into the cavity is often significantly reduced rather dramatically slowing production. Thus, not only can venting related problems lead to defective finished parts that must be scrapped, these problems can also significantly reduce production, which is also costly.
The reason that venting-related defects occur so frequently is that venting is not well understood and that venting is neither cheap nor easy. For example, vents typically require rather precise machining to create a vent passage or orifice in the mold cavity and a passageway that leads from the orifice away from the cavity. Machining the orifice particularly requires skill because the orifice must be wide enough to allow gas in the cavity to enter but small enough to stop the mold material from entering the orifice and plugging.
Unfortunately, machined-in-place vents, such as core pin vents, ejector pin vents, perimeter vents, and circumference vents, can have problems. One problem that commonly results from machined vents is that volatile gases from the mold material can condense at the narrowest portion of the vent, typically the orifice or passage, plugging the vent. This usually is because the orifice is too narrow and does not increase in cross-sectional size for a great length until it connects to the passageway. As a result, the pressure of the volatile gases is increased in the orifice while it is simultaneously cooled causing some of the gases to condense and plug the vent. If the condensate doesn't completely plug the vent, it can partially obstruct the vent, rendering the vent effectively useless and requiring the vent to be periodically cleaned. Even if not rendered useless, a partially plugged vent can lead to one or more of the vent-related molding problems previously discussed.
Another problem with machining these vents is that if precise tolerances are not maintained during machining, the resulting vent will not perform properly and may have to be filled and re-machined. For example, if an orifice is off by as little as two one-thousandths of an inch (0.002″), the vent will either be too large and allow mold material to enter the orifice plugging the vent or be too narrow leading to one or more of the above-identified vent-related problem.
In an attempt to overcome these problems, it is known to utilize a one-piece sintered vent insert received in a pocket in the mold that is in gas flow communication with the passage. Unfortunately, the sintering process creates uneven vent surfaces, has pores that are not parallel, and has corners. Any corner or deviation from straight (or smooth) means that the gases being vented do not travel along a straight line causing them to condense.
Another type of vent, a parting line vent, typically suffers from other problems. For example, the flowing molding material can impact against the interior surface adjacent the parting line vent with such force that it can dent or peen the interior surface. This can lead to surface irregularities in the finished part. If the dents extend too far into the vent, the mold material can enter the vent creating unwanted flash that must be trimmed. Of course, any additional operation that must be performed costs money and requires labor, both of which are undesirable. Moreover, because of the peening, that part of the mold must be periodically resurfaced to restore the integrity of the mold surface so future finished parts will have a better surface finish and no flash.
What is needed is an improved vent arrangement.
OBJECTS AND SUMMARY OF THE INVENTION
A mold vent and system that can control flow of a fluid to and from a mold that has a mold cavity into which a hardenable or moldable material is introduced and molded. In one preferred embodiment, the vent of the present invention comprises a plurality of perforations or orifices, each of which preferably is oblong in shape. The vent of the present invention can comprise an insert received in a pocket in the mold cavity or carried by a pin. In another preferred vent embodiment, the vent comprises a reciprocable pin that has clearance between its head and the mold cavity providing a vent passage therebetween. In preferred methods, the system can be used to withdraw atmosphere from the mold cavity, introduce fluid into the mold cavity, or vent atmosphere from the mold cavity before introducing a fluid into the mold cavity.
The fluid can comprise a gas or mixture of gases, such as air, a vapor, such as steam or another vapor, a combination thereof, as well as a liquid. In its preferred embodiment, gas or vapor is directed through the vent. The hardenable or moldable material preferably includes any material, which can be molded or formed in a mold. Examples of such material include plastic, metal, or a metallic material that is introduced into the mold cavity and which is flowable while in the cavity during molding.
Each orifice of a vent is constructed to permit fluid flow of gas or vapor while preventing flow of hardenable material. Each orifice communicates with a vent passage that in turn leads to a vent passageway. So that fluid flowing through an orifice will not condense inside, each orifice has a narrow entrance adjacent the mold cavity that opens in the passage into an expansion chamber downstream. In one preferred embodiment, each orifice is oblong or slot-shaped. As a result of this construction, the venting surface area is increased, which advantageously enables atmosphere within a mold cavity to be more quickly vented permitting faster mold cycle times to be achieved.
The vent can be made as an insert. Such a vent insert communicates with a larger passageway and can be disposed in a pocket or the like. A preferred insert has orifices that are slots. In one preferred embodiment, the insert has at least three slots. Each slot is oblong and narrow in width. Each slot opens in the mold cavity and preferably communicates with a vent passage in the insert that has an enlarged chamber spaced from its opening. This enlarged chamber reduces the pressure of that which is vented from the cavity after it has passed through the narrower opening to prevent condensation at the opening or in the vent passage. In one preferred embodiment, the slot has a width of between 0.005 inches and 0.0005 inches to permit gas and vapor flow while obstructing the hardenable material.
In one preferred insert construction, the insert is a slotted grate. The grate is comprised of two halves, with each grate half having recesses that separate and define fingers. In one preferred assembly, each finger of one grate half is received in a recess in the other grate half and vice versa. At least some adjacent fingers of the assembled vent grate are spaced slightly apart, defining vent slots between them. To help strengthen the vent grate, the end of each finger preferably bears against an adjacent recess endwall that preferably is slant
Boyle Fredrickson Newholm Stein & Gratz S.C.
Del Sole Joseph S
Nguyen Nam
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