Patent Description:
Silicone is a polymeric organic silicon compound. Silicone rubber is an elastomer (rubber-like material) composed of silicone. Throughout this disclosure, the term silicone will refer to the elastomer form (e.g., silicone rubber). Silicone may be used for water-resistant and heat-resistant components of electrical power systems, such as voltage line insulators, vacuum interrupters, or the like. For example, vacuum interrupters may be encapsulated within an outer silicone layer for additional protection. Silicone is an ideal material for cast molding due its pliable properties above its melting temperature (approximately <NUM>) and its relatively low curing rate. Likewise, silicone may be cast with a two-part addition curing process at room temperatures. However, silicone castings have added challenges during the removal (e.g., ejection) of the casting from the mold.

Ejecting straight-wall, seamless tall silicone castings from a poured cast mold is difficult for many elastic materials, such as silicone rubber, that may exhibit high friction against the interior surface of the mold. High forces are required to retrieve silicone castings from common molds due to the adhesive forces between the exterior surface of the silicone casting and the interior surface of the mold. Typically a taper is used to facilitate ejection of the silicone casting, but in some instances a tapered final product is not usable in electrical applications. Alternatively, a clamshell mold process may be used, but in some instances the seam parting lines (e.g., flash) from the clamshell mold also make the casting unusable in electrical applications. Any protrusion of material on the exterior surface of an insulated electrical component, such as the excess material along the parting line, will cause undesired gaps between the insulated electrical component and an adjacent solid insulation layer. During operation of the electrical component, these gaps may lead to dangerous high voltage breakdowns between the solid insulation layers.

For example, a vacuum interrupter being assembled into a preformed cylindrical straight wall rigid shell (e.g. covering) should not have a parting line as such a line would serve as a fault path, and it should not have a tapered outer form as it would create an air gap that may cause a dielectric breakdown in the primary circuit under certain conditions.

In <CIT> there is disclosed a mold for encapsulating an electrical component as it is defined in the pre-characterizing portion of claim <NUM> and a cast molding process for encapsulating an electrical component as it is defined in the pre-characterizing portion of claim <NUM>. Further such molds are described in <CIT> and <CIT>.

This document describes a novel solution that addresses at least some of the issues described above.

The present invention is a mold for encapsulating an electrical component as it is defined in claim <NUM> and a cast molding process for encapsulating an electrical component as it is defined in claim <NUM>. The mold for encapsulating an electrical component includes an encapsulation chamber and an air inlet. The encapsulation chamber is defined by a housing, an open top, and a solid bottom. The bottom is removable. The housing includes a solid outer wall, a permeable inner wall, and an air chamber between the solid outer wall and the inner wall. Optionally, each of the solid outer wall, the permeable inner wall, and the air chamber may be cylindrical in shape. The air inlet is configured to introduce a gas into the air chamber. The encapsulation chamber is sized and shaped to receive the electrical component while leaving a gap for the introduction of encapsulant around the electrical component. In accordance with the invention, the solid bottom comprises at least one ring positioned between the solid outer wall and the permeable inner wall to maintain a gap that forms the air chamber between the solid outer wall and the permeable inner wall. Optionally, the encapsulant may be silicone rubber. Optionally, the gap may be about <NUM> to about <NUM>.

Optionally, the open top includes a planar disc having a central opening and the planar disc includes at least one second ring positioned between the solid outer wall and the permeable inner wall to further maintain the gap that forms the air chamber between the solid outer wall and the permeable inner wall.

As an example, in another embodiment, the air chamber includes a plurality of plenum chambers positioned between the solid outer wall and the permeable inner wall. Optionally, the air inlet may include a plurality of apertures, each of which leads to one of the plenum chambers. Optionally, the housing may include a plurality of plenum sidewall members that extend from the solid outer wall to the permeable inner wall and form the plenum chambers.

The inventive cast molding process for encapsulating an electrical component includes providing a mold, positioning an electrical component within the mold, introducing an encapsulant into the mold between the electrical component and the permeable inner wall, curing the encapsulant around at least a portion of the electrical component within the mold forming a combination casting, introducing pressurized gas into the air chamber to pass through the permeable inner wall separating the contact surface of the encapsulant from the mold, and ejecting the combination casting from the mold. Optionally, the electrical component may be a vacuum interrupter.

The mold includes an encapsulation chamber defined by a housing, an open top, a bottom and an air inlet. The housing includes a solid outer wall, a permeable inner wall, and an air chamber between the solid outer wall and inner wall. The air inlet is configured to introduce a gas into the air chamber.

In accordance with the invention, the bottom of the mold is openable and closable, a step of enclosing the bottom end of the mold precedes the step of introducing the encapsulant, a step of opening the bottom of the mold precedes the step of introducing the pressurized gas into the air chamber, and the step of ejecting the combination casting includes pressing the combination casting from the bottom through the open top end after the bottom is opened. Optionally, the encapsulant may be silicone rubber. The step of curing the encapsulant may include forming the combination casting of the silicone rubber at a thickness of about <NUM> to about <NUM>.

As an example, in an embodiment, the electrical component includes a top, a bottom, a cylindrical wall, a first post, and a second post, wherein the first post extends from the top and be positioned within the open top end of the mold, and the second post extends from the bottom and is positioned within the bottom end of the mold. Optionally, the steps of introducing the encapsulant and curing the encapsulant may at least partially encapsulate the electrical component in the encapsulant with the top of the electrical component remaining exposed, the bottom of the electrical component remaining exposed, or both the top and bottom of the electrical component remaining exposed.

As an example, in another embodiment, the air chamber includes a plurality of plenum chambers positioned between the solid outer wall and the permeable inner wall, wherein the air inlet includes a plurality of apertures, each of which leads to one of the plenum chambers, and the step of introducing the pressurized gas into the air chamber includes substantially equalizing pressure in the air chamber by introducing pressurized gas into each of the plenum chambers.

Terminology that is relevant to this disclosure is provided at the end of this detailed description. The illustrations are not to scale.

<FIG> is a sectional view of an example mold <NUM> for encapsulating a workpiece such as an electrical component <NUM>. The mold <NUM> employs a permeable inner wall <NUM> during a mold process. The mold <NUM> includes an encapsulation chamber <NUM> for receiving the electrical component <NUM>, and an air inlet <NUM> that provides a path by which air from outside of the mold <NUM> may be forced into the mold <NUM>.

The encapsulation chamber <NUM> may be defined by an interior volume of a housing <NUM>. The housing <NUM> includes an outer wall <NUM>, an inner wall <NUM>, a top wall <NUM>, and a bottom wall <NUM>. An air chamber <NUM> is defined by the volume between the outer wall <NUM> and the inner wall <NUM>, optionally from the top wall <NUM> to the bottom wall <NUM> or between any points between the top and bottom walls. The bottom wall <NUM>, and optionally the top wall <NUM>, is/are removable, and the inner wall <NUM> may be separated from the outer wall <NUM>. Alternatively, the outer wall <NUM>, inner wall <NUM>, top wall <NUM>, and bottom wall <NUM> may be integral.

The top wall <NUM> includes an upper opening <NUM> and the bottom wall <NUM> includes a lower opening <NUM> (see <FIG>). A removable plate <NUM> may be positioned within the lower opening <NUM>. For example, the encapsulation chamber <NUM> may be defined as the volume within the inner wall <NUM> from the upper opening <NUM> to the plate <NUM> filling the lower opening <NUM>.

The outer wall <NUM>, top wall <NUM>, and bottom wall <NUM> may be solid in that they have a porosity value (i.e., the measurement of voids within a solid) small enough to prevent gas from passing through the outer wall <NUM>, top wall <NUM>, and bottom wall <NUM> from the air chamber <NUM> to the exterior of the housing <NUM>, as will be described in more detail below. (Note: the term "solid", when used in this document to refer to a wall, does not mean that the wall must be fully solid. Instead, it means that either the inner surface or the outer surface of the wall must be substantially impermeable to air as described above. ) The outer wall <NUM> may also include an aperture <NUM> configured to receive the air inlet <NUM> and to be a conduit for the gas to enter the air chamber <NUM>. The inner wall <NUM> is permeable and may have a porosity value large enough to allow gas to pass through the inner wall <NUM> from the air chamber <NUM> to the interior of the encapsulation chamber <NUM>, but not so porous as to allow encapsulation material to pass through the inner wall <NUM>, as will be described in more detail below. For example, the inner wall <NUM> may be made from stainless steel, bronze, aluminum, or any material having suitable controlled porosity. The air inlet <NUM> may be configured to introduce a gas into the air chamber <NUM>. The gas may be a pressurized gas, as will be described in more detail below.

The encapsulation chamber <NUM> may be sized to substantially conform to the size and shape of the electrical component <NUM> or other workpiece while leaving a gap G for the introduction of encapsulant <NUM> (see <FIG>). For example, the encapsulation chamber <NUM> may be cylindrical, cubical, or the like.

As illustrated in <FIG>, the electrical component <NUM> (or other workpiece) may be positioned within the encapsulation chamber <NUM> to provide an even gap G between the sidewalls <NUM> of the electrical component <NUM> and the inner wall <NUM> of the housing <NUM>. The electrical component <NUM> may be any device that can benefit from electrical insulation. For example, the electrical component <NUM> may be a circuit breaker, switch, motor, generator, battery, resistor, transistor, capacitor, inductor, transformer, relay, integrated circuit, microprocessor, or the like. An example circuit breaker component requiring electrical insulation may be a vacuum interrupter, such as vacuum interrupter <NUM> shown in <FIG>.

<FIG> is a sectional view of the mold <NUM> in <FIG> during an encapsulation process. The encapsulant <NUM> is a material for encapsulating the electrical component <NUM> or other workpiece forming a combination casting. For example, the encapsulant <NUM> may be silicone rubber, Ethylene Propylene Diene Monomer (EPDM) rubber, polyurethane rubber, or the like. The thickness of the encapsulant <NUM> may be any thickness providing proper electrical insulation. For example, an encapsulant <NUM> thickness may be from about <NUM> to about <NUM>, from about <NUM> to about <NUM>, from about <NUM> to about <NUM>, or from about <NUM> to about <NUM>. During the encapsulating process, liquid encapsulant <NUM> is poured from a source through a controllable valve <NUM> into the gap G between the electrical component <NUM> and the encapsulation chamber <NUM>. Once the electrical component <NUM> is encapsulated with encapsulant <NUM> to the desired height, the valve <NUM> is closed and the source of liquid encapsulant <NUM> is removed. The sidewalls <NUM> of the electrical component <NUM> may be at least partially encapsulated in encapsulant <NUM> or alternatively the liquid encapsulant may be allowed to also cover the upper surface <NUM> of the electrical component <NUM>. The electrical component <NUM> may rest directly on the plate <NUM> of the housing <NUM> or alternatively may be spaced from the plate <NUM> to allow for encapsulant <NUM> to also encapsulate the lower surface <NUM> of the electrical component <NUM>.

<FIG> is a sectional view of the mold <NUM> in <FIG> during an ejection process. After the liquid encapsulant <NUM> is allowed to cure (i.e. allowed for the encapsulant <NUM> to cool to a temperature below the melting point and return to a solid state) the plate <NUM> of the encapsulation chamber <NUM> may be removed. The contact surface <NUM> of the encapsulant <NUM> is the surface of the encapsulant <NUM> in direct contact with the housing <NUM>, especially the inner wall <NUM>. The adhesive forces between the contact surface <NUM> of the encapsulant <NUM> and the housing <NUM> require additional forces to eject the combination casting without damage to the electrical component <NUM> and/or the encapsulant <NUM>. Gas is introduced into the air chamber <NUM> of the housing <NUM> from the air inlet <NUM> through the aperture <NUM> in the outer wall <NUM> of the housing <NUM>. As the pressure of the gas within the air chamber <NUM> increases, the pressurized gas is forced through the voids of the permeable inner wall <NUM> of the housing <NUM> and against the contact surface <NUM> of the encapsulant <NUM> to push uniformly against the encapsulant <NUM>, thus providing the additional force to counteract the adhesive forces. As the gas exits the permeable inner wall <NUM> into the encapsulation chamber <NUM>, a thin layer of gas separates the contact surface <NUM> of the encapsulant <NUM> from the encapsulation chamber <NUM>. This thin layer of gas allows the ejection of the combination casting from the encapsulation chamber <NUM> with significantly reduced push-out force F or damage to the electrical component <NUM> and/or encapsulant <NUM>.

<FIG> is an isometric view of another example mold <NUM> for encapsulating a workpiece such as a vacuum interrupter <NUM> or other electrical component employing a silicone encapsulant <NUM>. <FIG> is an expanded view of the mold <NUM> in <FIG>. <FIG> is a sectional view of the mold <NUM> in <FIG>. Mold <NUM> is similar in operation to the mold <NUM> described above, but with additional features.

Referring to <FIG> together, mold <NUM> may include an encapsulation chamber <NUM> for receiving the vacuum interrupter or other workpiece. The encapsulation chamber <NUM> may be defined by an interior volume of a housing <NUM>. The housing <NUM> includes an outer wall <NUM>, an inner wall <NUM>, a top <NUM>, and a bottom <NUM>. The outer wall <NUM> may have a cylindrical shape. The outer wall <NUM> may also have one or more apertures <NUM> for receiving an air inlet <NUM>. The inner wall <NUM> may also have a cylindrical shape having an outer diameter smaller than the inner diameter of the outer wall <NUM>. The inner wall <NUM> is positioned within the outer wall <NUM> creating a gap G between the inner wall <NUM> and outer wall <NUM>. The top <NUM> may be a planar disc having a plurality of locking notches <NUM> along the perimeter for receiving locking bolts <NUM> or other locking members. The top <NUM> may have a central opening <NUM> for receiving the workpiece and the liquid encapsulant <NUM>. The top <NUM> may also have a pair of nested rings <NUM>, <NUM> on the lower surface for maintaining a gap G between the outer wall <NUM> and inner wall <NUM>. The bottom <NUM> may also be a planar disc having a plurality of locking notches <NUM> along the perimeter and aligned with the locking notches <NUM> of the top <NUM> for receiving the locking bolts <NUM>. If the workpiece is a vacuum interrupter, an upper terminal post <NUM> of the vacuum interrupter <NUM> may extend through the central opening <NUM> in the top <NUM> while the bottom <NUM> may also have a central opening <NUM> for receiving a lower terminal post <NUM> of the vacuum interrupter <NUM> and one or more annular apertures <NUM> for filling the encapsulation chamber <NUM> with liquid encapsulant <NUM> from below. The bottom <NUM> may have a matching pair of nested rings <NUM>, <NUM> on the upper surface similar in size and shape as the nested rings <NUM>, <NUM> of the top <NUM>. The top and bottom nested rings <NUM>, <NUM>, <NUM>, <NUM> maintain the spacing of the outer wall <NUM> from the inner wall <NUM> and, combined with the lower surface of the top <NUM>, the inner surfaces of the outer wall <NUM> and inner wall <NUM>, and the upper surface of the bottom <NUM> form a sealed air chamber <NUM>. For example, an inner ring <NUM> on the top <NUM> may be positioned between the outer wall <NUM> and the inner wall <NUM> to further maintain the gap G that forms the air chamber <NUM> between the outer wall <NUM> and the inner wall <NUM>. Likewise, an inner ring <NUM> on the bottom <NUM> may be positioned between the outer wall <NUM> and the inner wall <NUM> to further maintain the gap G that forms the air chamber <NUM> between the outer wall <NUM> and the inner wall <NUM>. The locking bolts <NUM> may be removed from the top <NUM> and bottom <NUM> allowing the mold <NUM> to be disassembled (see <FIG>) for repair and/or replacement of parts. For example, the mold <NUM> may include a selection of inner walls having various inner diameters. An inner wall <NUM> may be selected for each different vacuum interrupter <NUM> or for each desired encapsulant <NUM> thickness. Likewise, the mold <NUM> may include a selection of paired outer and inner walls having various heights. A pair of matching outer and inner walls <NUM>, <NUM> may be selected for vacuum interrupters having different heights.

<FIG> is a sectional view of another example mold <NUM>' similar to that of <FIG>. Mold <NUM>' differs from mold <NUM> by a modified housing <NUM>'. The housing <NUM>' includes an outer wall <NUM>', an inner wall <NUM>', a top <NUM>', and a bottom <NUM>'. The outer wall <NUM>' and inner wall <NUM>' each may have a cylindrical shape. Plenum chambers <NUM>' may be formed by plenum sidewall members <NUM>' that extend inwardly from the outer wall <NUM>' to the inner wall <NUM>'. Plenum sidewall members <NUM>' may reinforce the outer wall <NUM>'. The outer wall <NUM>' may also have one or more apertures <NUM>', each of which serves as an air inlet that leads to a plenum chamber <NUM>'. Thus, in this embodiment instead of having one air chamber between the outer and inner walls, multiple plenum chambers <NUM>' provide multiple air chambers between the outer wall <NUM>' and the inner wall <NUM>'. This design may help to avoid all of the pressure being relieved in areas already cleared by an ejecting workpiece, which could reduce the fluid cushion effect and make the workpiece stick on the way out. Also, feeding multiple plenum chambers rather than a single larger chamber can help substantially equalize pressure along the workpiece and help retain a fluidizing layer between outer and inner walls. The inner wall <NUM>' is positioned within the outer wall <NUM>' so that the plenum chambers are positioned within a gap G' between the inner wall <NUM>' and the outer wall <NUM>'. The top <NUM>' may be a planar disc. The top <NUM>' may have a central opening <NUM>' for receiving the workpiece and the liquid encapsulant <NUM>. The top <NUM>' may also have a pair of nested rings <NUM>', <NUM>' on the lower surface for maintaining a gap G' between the outer wall <NUM>' and the inner wall <NUM>'. The bottom <NUM>' may also be a planar disc. If the workpiece is a vacuum interrupter, the bottom <NUM>' may also have a central opening <NUM>' for receiving a lower terminal post <NUM> of the vacuum interrupter <NUM> and one or more annular apertures <NUM>' for filling the encapsulation chamber <NUM>' with liquid encapsulant <NUM> from below. The bottom <NUM>' may have a matching pair of nested rings <NUM>', <NUM>' on the upper surface similar in size and shape as the nested rings <NUM>', <NUM>' of the top <NUM>'. The top and bottom nested rings <NUM>', <NUM>', <NUM>', <NUM>' maintain the spacing of the outer wall <NUM>' from the inner wall <NUM>'.

The gap G' of the modified mold <NUM>' may be larger than the gap G of the mold <NUM> providing for a larger total volume in the plenum chambers <NUM>' compared to the total volume of a single sealed air chamber between the outer and inner walls.

<FIG> is an isometric sectional view of the outer wall <NUM> of the mold housing <NUM> of <FIG>, while <FIG> is an isometric sectional view of the outer wall <NUM>' of the mold housing <NUM>' of <FIG> with plenum sidewall members <NUM>' attached. For example, in comparison of outer wall <NUM> and an outer wall <NUM>' applied to a common inner wall <NUM>, the overall diameter D of the outer wall <NUM> may be smaller than the overall diameter D' of the outer wall <NUM>'.

<FIG> is a sectional view of a mold <NUM> with an example vacuum interrupter <NUM> partially surrounded by silicone encapsulant <NUM> inside the mold <NUM>. The vacuum interrupter <NUM> may have a substantially cylindrical middle section <NUM>. The encapsulant <NUM> may be cured around the cylindrical middle section <NUM> of the vacuum interrupter <NUM> within the encapsulation chamber <NUM>. Gas may be introduced into the air chamber <NUM> via aperture <NUM> releasing the contact surface <NUM> of the encapsulant <NUM> from the inner wall <NUM> as described above. The extending lower terminal post <NUM> may be pressed or the bottom <NUM> may be removed and the underside of the electrical component <NUM> may be pressed to lift the combination casting from the encapsulation chamber <NUM>. During the molding process, the lower terminal post <NUM> may be secured to the bottom of the mold, such as by a locking nut or other securing structure.

<FIG> presents a flowchart for a method of cast molding. The method of cast molding a workpiece or other electrical component includes: (a) at <NUM>, providing a mold having an air chamber between a solid outer wall and a permeable inner wall; (b) at <NUM>, positioning the workpiece or other electrical component within the mold; (c) at <NUM>, enclosing the workpiece within the mold (although the top may optionally remain open); (d) at <NUM>, introducing an encapsulant into the mold between the workpiece and the permeable inner wall; (e) at <NUM>, curing the encapsulant around at least a portion of the electrical component within the mold forming a combination casting; (f) at <NUM>, optionally opening the bottom end of the mold; (g) at <NUM>, introducing gas into the air chamber to pass through the permeable inner wall separating the contact surface of the encapsulant from the mold; and (h) at <NUM>, removing the combination casting from the mold, such as by pressing the combination casting from the open bottom end to eject the combination casting from the top end of the mold.

The combination casting may be positioned within a cylindrical covering (e.g., rigid outer shell) as a final product. An example encapsulated pole unit teaching may be found in <CIT>. An example pressed-in mechanism with a membrane switch teaching may be found in <CIT>. It is desirable to have no air gaps between the vacuum interrupter and the covering. The encapsulant helps to avoid air gaps between the vacuum interrupter and the covering. This is particularly applicable to vacuum interrupters, where a silicone encapsulation serves as an electrically insulating mechanical interface layer between the vacuum interrupter and the covering as part of an encapsulated pole unit or other switchgear components.

As used in this document, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. As used in this document, the term "comprising" means "including, but not limited to. " When used in this document, the term "exemplary" is intended to mean "by way of example" and is not intended to indicate that a particular exemplary item is preferred or required.

In this document, when terms such "first" and "second" are used to modify a noun, such use is simply intended to distinguish one item from another, and is not intended to require a sequential order unless specifically stated. The terms "about" or "approximately," when used in connection with a numeric value, are intended to include values that are close to, but not exactly, the number. For example, in some embodiments, the terms "about" or "approximately" may include values that are within +/- <NUM> percent of the value.

When used in this document, terms such as "top" and "bottom," "upper" and "lower", or "front" and "rear," are not intended to have absolute orientations but are instead intended to describe relative positions of various components with respect to each other. For example, a first component may be an "upper" component and a second component may be a "lower" component when a device of which the components are a part is oriented in a first direction. The relative orientations of the components may be reversed, or the components may be on the same plane, if the orientation of the structure that contains the components is changed. The claims are intended to include all orientations of a device containing such components.

Claim 1:
A mold (<NUM>; <NUM>; <NUM>') for encapsulating an electrical component (<NUM>), the mold comprising:
an encapsulation chamber (<NUM>; <NUM>; <NUM>') for receiving an electrical component (<NUM>), the encapsulation chamber defined by:
a housing (<NUM>; <NUM>; <NUM>') comprising a solid outer wall (<NUM>; <NUM>; <NUM>'), a permeable inner wall (<NUM>; <NUM>; <NUM>'), and an air chamber (<NUM>; <NUM>) between the solid outer wall and the permeable inner wall,
an open top (<NUM>; <NUM>; <NUM>'),
a lower opening (<NUM>; <NUM>; <NUM>'), and
a solid removable bottom (<NUM>; <NUM>; <NUM>') positioned within the lower opening (<NUM>; <NUM>; <NUM>'); and
an air inlet (<NUM>) configured to introduce a gas into the air chamber (<NUM>; <NUM>);
wherein the encapsulation chamber (<NUM>; <NUM>; <NUM>') is sized and shaped to receive the electrical component (<NUM>) while leaving a gap (G) for the introduction of encapsulant (<NUM>) around the electrical component;
characterized in that the solid bottom comprises at least one ring (<NUM>, <NUM>; <NUM>', <NUM>') positioned between the solid outer wall (<NUM>; <NUM>') and the permeable inner wall (<NUM>; <NUM>') to maintain a gap that forms the air chamber (<NUM>) between the solid outer wall and the permeable inner wall.