System and method for molding amorphous polyether ether ketone

A method for molding amorphous polyether ether ketone including steps of preparing a molten mass including polyether ether ketone, cooling a mold assembly to a temperature of at most about 200° F., and injecting the molten mass into the cooled mold assembly.

FIELD

This application relates to polyether ether ketone and, more particularly, to amorphous polyether ether ketone and, even more particularly, to molding amorphous polyether ether ketone.

BACKGROUND

Aircraft experience electromagnetic effects (EME) from a variety of sources, such as lightning strikes and precipitation static. Metallic aircraft structures are readily conductive and, therefore, are relatively less susceptible to electromagnetic effects. Basic epoxy-based composite aircraft structures, however, do not readily conduct away the significant electrical currents and electromagnetic forces stemming from electromagnetic effects. Therefore, when composites are used on an aircraft, steps are often taken to protect against electromagnetic effects, such as by incorporating conductive materials into the composites.

Fasteners with integral dielectric layers have been developed in an attempt to provide protection against electromagnetic effects. For example, U.S. Pat. Pub. No. 2013/0259604 discloses a fastener having a fastener head and a layer of dielectric material mechanically attached to the fastener head. The layer of dielectric material may include a polymeric material, such as polyether ether ketone.

Polyether ether ketone is commonly used in the aerospace industry due to its dielectric properties, its ability to maintain strength at elevated temperatures, and its chemical resistance. However, the limited toughness of polyether ether ketone has curtailed its application as a dielectric material in connection with electromagnetic effects-protective fasteners.

Accordingly, those skilled in the art continue with research and development efforts in the field of electromagnetic effects protection.

SUMMARY

In one embodiment, the disclosed method for molding amorphous polyether ether ketone may include the steps of: (1) preparing a molten mass including polyether ether ketone; (2) cooling a mold assembly to a temperature of at most about 200° F.; and (3) injecting the molten mass into the cooled mold assembly. The cooling and injecting steps may be performed in series (e.g., cooling then injecting) or simultaneously (cooling while injecting).

In another embodiment, the disclosed system for molding amorphous polyether ether ketone may include a mold assembly defining a cavity and a fluid channel, a cooling system in fluid communication with the fluid channel, the cooling system supplying a cooling fluid to the fluid channel, wherein the cooling fluid cools the mold assembly to at most about 200° F., and a polymer injection subsystem in fluid communication with the cavity, the polymer injection subsystem supplying a molten mass to the cavity, wherein the molten mass includes polyether ether ketone.

In another embodiment, disclosed is part (e.g., a mechanical part for an aircraft) formed from the disclosed method for molding amorphous polyether ether ketone and/or the disclosed system for molding amorphous polyether ether ketone.

In yet another embodiment, disclosed is a fastener that includes a fastener body and a portion of polyether ether ketone connected to the fastener body, wherein the polyether ether ketone has a crystallinity of at most about 15 percent. For example, the fastener body may include a shaft and a head, and the polyether ether ketone may be connected to the head.

Other embodiments of the disclosed system and method for molding amorphous polyether ether ketone will become apparent from the following detailed description, the accompanying drawings and the appended claims.

DETAILED DESCRIPTION

Referring toFIG. 1, one embodiment of the disclosed electromagnetic effects-protective fastener, generally designated100, may include a fastener body102having a shaft104and a head106connected to the shaft104. A portion108of amorphous polyether ether ketone may be molded onto the fastener body102. For example, the portion108of amorphous polyether ether ketone may be molded onto the head106of the fastener body102, thereby forming a layer110on the head106, such as on the top of the head106(as shown inFIG. 1) and/or on the side of the head106.

The fastener body102may be formed from various materials. As one general, non-limiting example, the fastener body102may be formed from a metallic material. As one specific, non-limiting example, the fastener body102may be formed from titanium or titanium alloy. As another specific, non-limiting example, the fastener body102may be formed from aluminum or aluminum alloy. Furthermore, while a threaded bolt-type fastener is shown in the drawings, those skilled in the art will appreciate that various mechanical fasteners may be used without departing from the scope of the present disclosure.

Various engagement features112(e.g., undercut protrusions; a roughed surface; etc.) may optionally be present on the head106to enhance the connection between the top layer110and the head106of the fastener body102. Additionally or alternatively, an optional tie layer (e.g., an adhesive) may be positioned between the top layer110and the head106to enhance the connection therebetween.

While the fastener100is shown and described as having a portion108of amorphous polyether ether ketone molded onto a fastener body102, fasteners may be formed entirely of amorphous polyether ether ketone without departing from the scope of the present disclosure. Furthermore, those skilled in the art will appreciate that fasteners are only one specific example of parts that may be formed from amorphous polyether ether ketone, in accordance with the present disclosure. Various other parts, such as mechanical aircraft parts, may be molded from amorphous polyether ether ketone using the disclosed system200and method300.

As used herein, an “amorphous” polyether ether ketone refers to polyether ether ketone have a crystallinity that is substantially less than the crystallinity achieved using traditional polyether ether molding techniques. In one expression, the amorphous polyether ether ketone may have a crystallinity of at most about 15 percent. In another expression, the amorphous polyether ether ketone may have a crystallinity of at most about 10 percent. In another expression, the amorphous polyether ether ketone may have a crystallinity of at most about 5 percent. In another expression, the amorphous polyether ether ketone may have a crystallinity of at most about 2 percent. In another expression, the amorphous polyether ether ketone may have a crystallinity of at most about 1 percent. In yet another expression, the amorphous polyether ether ketone may have a crystallinity of about 0 percent.

Without being limited to any particular theory, it is presently believed that molding an amorphous polyether ether ketone, as disclosed herein, results in the layer110of the electromagnetic effects-protective fastener100having a greater toughness, as compared to a layer formed by molding crystalline (e.g., 30 to 35 percent crystallinity) polyether ether ketone using traditional molding techniques. The tougher amorphous polyether ether ketone may result in the electromagnetic effects-protective fastener100being more suitable for use in aerospace applications, such as on an aircraft wing.

Referring toFIG. 2, one embodiment of the disclosed system for molding amorphous polyether ether ketone, generally designated200, may include a mold assembly202, a polymer injection subsystem204, and a cooling subsystem206. As is described in greater detail herein, the polymer injection subsystem204may inject a molten mass of polyether ether ketone (or a polyether ether ketone blend) into the mold assembly202while the cooling subsystem206may cool the mold assembly202, thereby yielding an amorphous polyether ether ketone.

The mold assembly202may include a first mold plate208and a second mold plate210. The first mold plate208may be sealingly, yet releasably, mated with the second mold plate210to define a cavity212therebetween. The first mold plate208may define a channel214, and the channel214may fluidly couple the cavity212with the polymer injection subsystem204. While an axial configuration is shown, various mold configurations may be used without departing from the scope of the present disclosure.

A fastener body102(or other component) may be positioned in the mold assembly202to receive thereon the molded polyether ether ketone. For example, the second mold plate210may define a seat215, and the head106of the fastener body102may be seated in the seat215of the second mold plate210. Therefore, the head106of the fastener body102may at least partially define the cavity212of the mold assembly202.

The first mold plate208, the second mold plate210or both the first and second mold plates208,210may define fluid channels216. The cooling subsystem206may direct a cooling fluid through the fluid channels216to cool the mold assembly202to the desired temperature (e.g., prior to introduction of the molten mass). Cooling the mold assembly202may include cooling the entire mold assembly202or only a portion of the mold assembly202(e.g., only one of the first and second mold plates208,210).

Without being limited to any particular theory, it is believed that cooling the mold assembly202to a temperature of at most about 200° F.—which is a significant departure from standard polyether ether ketone molding practices—may yield an amorphous (rather than crystalline) polyether ether ketone. In one realization, the mold assembly202may be cooled to a temperature of at most about 150° F. In another realization, the mold assembly202may be cooled to a temperature of at most about 100° F. In another realization, the mold assembly202may be cooled to a temperature ranging from about 50° F. to about 120° F. In yet another realization, the mold assembly202may be cooled to a temperature ranging from about 80° F. to about 100° F.

Various cooling fluids may be used to cool the mold assembly202without departing from the scope of the present disclosure. In one variation, the cooling fluid flowing through the fluid channels216of the mold assembly202may be a liquid. Examples of suitable liquid cooling fluids include, but are not limited to, water, alcohol and glycol. In another variation, the cooling fluid flowing through the fluid channels216of the mold assembly202may be a gas. Air (e.g., ambient air) is one non-limiting example of a suitable gaseous cooling fluid.

Optionally, the mold assembly202(or select portions of the mold assembly202) may be formed from (or may include) a highly thermally conductive material, such as a highly thermally conductive metal (e.g., copper). The highly thermally conductive material may aid in heat transfer.

The cooling subsystem206may be any apparatus or system capable of supplying a cooling fluid to the fluid channels216of the mold assembly202. For example, the cooling subsystem206may include a cooling fluid source220and a pump222configured to pump the cooling fluid through the fluid channels216of the mold assembly202, such as by way of fluid supply lines224. The cooling fluid may make a single pass through the fluid channels216of the mold assembly202or, alternatively, may be recirculated through the fluid channels216.

In one particular implementation, a temperature sensor226may be connected to the mold assembly202(e.g., to the second mold plate210). Multiple temperature sensors, while not shown, may be used. The temperature sensor226may be in communication with the cooling subsystem206(e.g., with a controller228associated with the cooling subsystem206). Therefore, the cooling subsystem206may actively control the temperature of the mold assembly202, such as by controlling the temperature of the cooling fluid being supplied to the mold assembly202(e.g., by way of a heat exchanger) and/or by controlling the flow rate of the cooling fluid being supplied to the mold assembly202to minimize a difference between a target mold assembly temperature and the actual temperature of the mold assembly202.

The polymer injection subsystem204may be any apparatus or system capable of supplying a molten mass of polyether ether ketone (or a polyether ether ketone blend) to the mold assembly202. The polymer injection subsystem204may form the molten mass by heating the polyether ether ketone to a temperature ranging from about 650° F. to about 750° F., such as from about 670° F. to about 720° F. (e.g., about 710° F.). Therefore, the molten mass of polyether ether ketone may be flowable as it passes to the mold assembly202and, ultimately, into the cavity212.

In one construction, the polymer injection subsystem204may be configured as an injection molding machine, and may include a barrel230, a screw232, a nozzle234, a motor236, one or more heaters238, and a hopper240containing a quantity242of polyether ether ketone (e.g., pellets of polyether ether ketone). The screw232may be received in the barrel230and may be driven by the motor236. Rotation of the screw232within the barrel230may urge polyether ether ketone deposited (from the hopper240) proximate (at or near) the aft end244of the barrel230to the forward end246of the barrel230and, ultimately, through the nozzle234. As the polyether ether ketone moves toward the forward end246of the barrel230, the heaters238may heat the polyether ether ketone to form a molten mass. The polymer injection subsystem204may inject the molten mass of polyether ether ketone into the mold assembly202.

The molten polyether ether ketone injected into the mold assembly202by the polymer injection subsystem204may enter the cavity212of the mold assembly202where it may be rapidly cooled to form the portion108of amorphous polyether ether ketone on the head106of the fastener body102, as shown inFIG. 1. Because the mold assembly202is cooled, the rate at which the molten polyether ether ketone is injected into the mold assembly202(the injection rate) may be sufficiently high to ensure the cavity212is properly and fully filled prior to solidification of the polyether ether ketone. Those skilled in the art will appreciate that the injection rate will depend on various factors, including the temperature of the mold assembly202, the temperature of the molten mass of polyether ether ketone, the size of the cavity212and the shape of the cavity212.

Referring toFIG. 3, also disclosed is a method for molding amorphous polyether ether ketone. One embodiment of the disclosed method, generally designated300, may begin at Block302with the step of preparing a molten mass of polyether ether ketone (or a polyether ether ketone blend). The molten mass of polyether ether ketone may be at a temperature ranging from about 650° F. to about 750° F., such as from about 670° F. to about 720° F. (e.g., about 710° F.).

At Block304, a mold assembly may be provided. The mold assembly may define a cavity. For example, the mold assembly may include a first mold plate sealingly connected to a second mold plate to define a cavity therebetween. A channel in one of the mold plates may provide fluid access to the cavity.

At Block306, a fastener body may optionally be inserted into the mold assembly. For example, the fastener body may include a head and a shaft, and the head of the fastener body may be seated in a seat defined by one of the mold plates forming the mold assembly. Therefore, together with the first and second mold plates, the fastener body may at least partially define the cavity.

At Block308, the mold assembly (including the fastener body, if present) may be cooled. In one realization, the mold assembly may be cooled to a temperature of at most about 200° F. In another realization, the mold assembly may be cooled to a temperature of at most about 150° F. In another realization, the mold assembly may be cooled to a temperature of at most about 100° F. In another realization, the mold assembly may be cooled to a temperature ranging from about 50° F. to about 120° F. In yet another realization, the mold assembly may be cooled to a temperature ranging from about 80° F. to about 100° F.

At Block310, a sufficient quantity of the molten mass of polyether ether ketone may be injected into the cavity of the cooled mold assembly. For example, a screw rotating in a barrel may urge the molten mass of polyether ether ketone into the cavity of the cooled mold assembly. The injection rate may be sufficiently high to ensure the cavity is quickly and fully filled with the polyether ether ketone prior to solidification of the polyether ether ketone.

Accordingly, by cooling the mold assembly prior to and/or during injection of molten polyether ether ketone, the disclosed system200and method300may yield amorphous (as opposed to crystalline) polyether ether ketone. The amorphous polyether ether ketone may have a higher toughness than crystalline polyether ether ketone and, therefore, may be used in more demanding applications, such as on aircraft.

Examples of the disclosure may be described in the context of an aircraft manufacturing and service method400, as shown inFIG. 4, and an aircraft402, as shown inFIG. 5. During pre-production, the aircraft manufacturing and service method400may include specification and design404of the aircraft402and material procurement406. During production, component/subassembly manufacturing408and system integration410of the aircraft402takes place. Thereafter, the aircraft402may go through certification and delivery412in order to be placed in service414. While in service by a customer, the aircraft402is scheduled for routine maintenance and service416, which may also include modification, reconfiguration, refurbishment and the like.

As shown inFIG. 5, the aircraft402produced by example method400may include an airframe418with a plurality of systems420and an interior422. Examples of the plurality of systems420may include one or more of a propulsion system424, an electrical system426, a hydraulic system428, and an environmental system430. Any number of other systems may be included.

The disclosed system and method for molding amorphous polyether ether ketone may be employed during any one or more of the stages of the aircraft manufacturing and service method400. For example, components or subassemblies corresponding to component/subassembly manufacturing408, system integration410, and or maintenance and service416may be fabricated or manufactured using the disclosed system and method for molding amorphous polyether ether ketone. Also, one or more apparatus examples, method examples, or a combination thereof may be utilized during component/subassembly manufacturing408and/or system integration410, for example, by substantially expediting assembly of or reducing the cost of an aircraft402, such as the airframe418and/or the interior422. Similarly, one or more of system examples, method examples, or a combination thereof may be utilized while the aircraft402is in service, for example and without limitation, to maintenance and service416.

The disclosed system and method are described in the context of an aircraft; however, one of ordinary skill in the art will readily recognize that the disclosed service system may be utilized for a variety of different components for a variety of different types of vehicles. For example, implementations of the embodiments described herein may be implemented in any type of vehicle including, e.g., helicopters, passenger ships, automobiles and the like.

Although various embodiments of the disclosed system and method for molding amorphous polyether ether ketone have been shown and described, modifications may occur to those skilled in the art upon reading the specification. The present application includes such modifications and is limited only by the scope of the claims.