Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – To produce composite – plural part or multilayered article
Reexamination Certificate
1999-12-28
2001-10-30
Ortiz, Angela (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
To produce composite, plural part or multilayered article
Reexamination Certificate
active
06309579
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and an apparatus for forming a casting (a molding) which includes an insert. Examples of such a casting are electric coils or inductors, IC's, and thermistors which have inserts sealed in resin.
2. Description of the Prior Art
Some of known electric coils (electric inductors) and IC's have coatings of potting material or sealing plugs for providing waterproofness. It is known to seal electric parts in resin. Sealing electric parts in resin is advantageous in cost and recycling. Generally, sealing electric parts in resin uses an insert molding process which is good in cost and mass-productivity.
Japanese published unexamined patent application 55-91642 discloses an apparatus for forming a casting which includes an insert. In the apparatus of Japanese application 55-91642, dies have a cavity in which an insert is located, and the insert can be supported by hold pins capable of moving relative to the dies. During the formation of the casting, the insert is located at a given place within the cavity while being supported by the hold pins. Under these conditions, the cavity is charged with molten resin. Then, the hold pins are moved back from the cavity before the cavity is further charged with molten resin. The final casting contains the insert entirely sealed in the resin.
During the formation of the casting by the apparatus of Japanese application 55-91642, if the hold pins are moved back from the cavity before charging the cavity with molten resin is completed, the insert tends to be displaced by a motion of the molten resin. The displacement of the insert causes an unevenness in thickness of the final casting.
It is conceivable that the hold pins are moved back from the cavity after charging the cavity with molten resin is completed. In this conceivable case, solidified layers of resin have already been formed around the hold pins immediately before the hold pins are moved back from the cavity. As the hold pins are moved back from the cavity, molten resin enters and occupies the spaces resulting from the backward movement of the hold pins. The molten resin, which enters and occupies the spaces, tends to insufficiently fuse with the solidified layers. The insufficient fusion causes minute holes in the resin of the final casting which allow the introduction of water or others toward the insert. The minute holes correspond to unfused portions of the resin in the final casting.
SUMMARY OF THE INVENTION
It is a first object of this invention to provide an improved method of forming a casting (a molding) which includes an insert.
It is a second object of this invention to provide an improved apparatus for forming a casting (a molding) which includes an insert.
A first aspect of this invention provides a method of forming an insert-containing casting which comprises the steps of holding an insert in a cavity within a die set by a movable hold member; injecting molten resin into the cavity when the insert is held by the hold member; separating the hold member from the insert at a given timing; and heating a surface of the hold member to a temperature higher than a temperature of an inner surface of the die set, the hold-member surface contacting the molten resin, the die-set inner surface being exposed in the cavity.
A second aspect of this invention is based on the first aspect thereof, and provides a method wherein the heating step comprises heating the hold member to a temperature equal to or higher than a melting point of the injected resin.
A third aspect of this invention is based on the first aspect thereof, and provides a method wherein the separating step comprises separating the hold member from the insert after the injection of the molten resin into the cavity is completed.
A fourth aspect of this invention is based on the first aspect thereof, and provides a method further comprising the step of cooling a first region of the molten resin in the cavity at a rate greater than a rate of cooling of a second region of the molten resin in the cavity, the second region adjoining the hold member, the first region being more distant from the hold member than the second region is.
A fifth aspect of this invention is based on the fourth aspect thereof, and provides a method wherein the first region is thinner than the second region.
A sixth aspect of this invention provides a method of forming an insert-containing casting which comprises the steps of holding an insert in a cavity within a die set by a movable hold member; injecting molten resin into the cavity when the insert is held by the hold member; separating the hold member from the insert at a given timing; and cooling a first region of the molten resin in the cavity at a rate greater than a rate of cooling of a second region of the molten resin in the cavity, the second region adjoining the hold member, the first region being more distant from the hold member than the second region is.
A seventh aspect of this invention is based on the sixth aspect thereof, and provides a method wherein the first region is thinner than the second region.
An eighth aspect of this invention is based on the first aspect thereof, and provides a method wherein the holding step comprises simultaneously holding an inner portion and an outer portion of the insert by the hold member, the inner portion being inserted into the outer portion.
A ninth aspect of this invention provides an apparatus for forming an insert-containing casting which comprises a die set having a cavity; a hold member movably provided on the die set for holding an insert in the cavity; means for injecting molten resin into the cavity when the insert is held by the hold member; means for separating the hold member from the insert at a given timing; and means for heating a surface of the hold member to a temperature higher than a temperature of an inner surface of the die set, the hold-member surface contacting the molten resin, the die-set inner surface being exposed in the cavity.
A tenth aspect of this invention provides an apparatus for forming an insert-containing casting which comprises a die set having a cavity; means for controlling a temperature of the die set; a hold member movably provided on the die set for holding an insert in the cavity; means for injecting molten resin into the cavity when the insert is held by the hold member; means for separating the hold member from the insert at a given timing; and means for heating the hold member.
An eleventh aspect of this invention is based on the ninth aspect thereof, and provides an apparatus wherein the hold member comprises a heat feeding portion and a body covering the heat feeding portion.
A twelfth aspect of this invention is based on the eleventh aspect thereof, and provides an apparatus wherein the heat feeding portion comprising a heating member which generates heat when being supplied with an electric current.
A thirteenth aspect of this invention is based on the ninth aspect thereof, and provides an apparatus wherein the hold member comprises a heat generating member and a body, the heat generating member being made of an electrically-conductive ceramic, the body surrounding the heat generating member, the body being made of an insulating ceramic.
A fourteenth aspect of this invention is based on the ninth aspect thereof, and provides an apparatus wherein an inner surface of the die set comprises means for facilitating cooling of a first region of the molten resin in the cavity relative to cooling of a second region of the molten resin in the cavity, the die-set inner surface being exposed in the cavity, the second region adjoining the hold member, the first region being more distant from the hold member than the first region is.
A fifteenth aspect of this invention is based on the fourteenth aspect thereof, and provides an apparatus wherein the first region is thinner than the second region.
A sixteenth aspect of this invention is based on the ninth aspect thereof, and provides an apparatus wherein the heating mean
Asano Keigo
Koyama Hiroshi
Nakamura Tadatsugu
Onoue Tsutomu
Shoji Izuru
Nippondenso Co. Ltd.
Ortiz Angela
Pillsbury & Winthrop LLP
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