Sealing elements and / or support rings manufactured from compressed carbon fiber reinforced composite materials

Abstract

The present invention relates to a sealing element and / or support ring, particularly for a reciprocating compressor, manufactured by compression molding of chips of a carbon fiber reinforced composite material, wherein at least a portion of the chips contains carbon fibers having a length of 3 to 20 mm, and the carbon fibers in the sealing element and / or support ring have a random fiber orientation.

Description

Technology Field

[0001] The present invention relates to a sealing element and / or support ring, particularly for a reciprocating compressor, manufactured by compression molding of a mixture of chips of a carbon fiber reinforced composite material, a method for manufacturing such sealing element and / or support ring, and a reciprocating compressor comprising at least one such sealing element and / or support ring. Background Technology

[0002] Sealing elements such as pistons or packing rings, guide rings such as piston guide rings, and guide seals such as piston guide rings must meet a wide range of requirements to fulfill their roles. In particular, they must possess appropriate hardness, sufficiently high tensile strength, sufficiently high elongation at break, good fit, high aging resistance, low pressure creep and cold flow tendencies, excellent chemical resistance, excellent heat resistance, and—depending on the application—high ozone resistance in some cases. For example, good fit is required to ensure that the sealing element functions reliably even when in motion. Furthermore, it is essential to have low pressure creep and cold flow tendencies to prevent irreversible plastic deformation under load in cold conditions even after long-term operation.

[0003] Due to its excellent properties, sealing elements are often made from compositions based on polytetrafluoroethylene (PTFE). PTFE is characterized, for example, by a very wide thermal coverage, almost universal chemical resistance, and excellent light resistance, weather resistance, and resistance to hydrothermal vapors. Additionally, PTFE is characterized by excellent sliding properties, excellent anti-adhesion behavior, excellent electrical properties, and excellent dielectric properties. However, to reduce cold flow and improve mechanical properties, PTFE is generally not used in its pure form but is reinforced with fillers. For example, carbon, graphite, molybdenum disulfide, or bronze particles are used as fillers. More recently, fiber-reinforced composites containing PTFE embedded with fibers such as glass fibers, carbon fibers, or aramid fibers have been increasingly used for this purpose. However, these PTFE-based materials are limited to applications as sealing elements or support rings in lower pressure ranges due to their limited mechanical stability. For applications at higher pressures, corresponding materials based on high-performance polymers such as polyimide, polyaryletherketone, polyphenylene sulfide, or polyetheretherketone (PEEK) are used. For example, carbon fiber reinforced plastics (CFRP), such as those having a matrix of PEEK with 10 weight percent carbon fibers embedded therein, are used for this purpose.

[0004] Typically, these carbon fiber reinforced plastic sealing elements and support rings are manufactured by injection molding using carbon staple fibers with a maximum length of 1 mm. These staple fibers have the advantage of aligning themselves to the contour of the part being manufactured and not protruding from the surface of the manufactured part. It is also known that these parts are manufactured by sintering from particles using staple fibers with a fiber length of typically about 0.1 mm. The granules are sintered with the fibers within the manufactured part under pressure. However, the disadvantages of sealing elements and support rings manufactured in this manner are strength requiring improvement, relatively low airtightness, and excessively high and non-uniform thermal expansion. The problem to be solved

[0005] Based on this, the present invention is based on the purpose of providing a sealing element or support ring that is characterized by increased strength and higher airtightness, improved to have low thermal expansion and particularly uniform, and is particularly suitable for use in reciprocating compressors. Specific details for implementing the invention

[0006] According to the present invention, this objective is achieved by a sealing element and / or support ring, particularly for a reciprocating compressor, manufactured by compression molding of a mixture of chips of a carbon fiber reinforced composite material, wherein at least a portion of the chips contains carbon fibers having a length of 3 to 20 mm, and preferably, the carbon fibers within the sealing element and / or support ring have a random fiber orientation.

[0007] This solution is based on the surprising discovery that such sealing elements and / or support rings, manufactured by compression molding of chips of carbon fiber reinforced composite material (at least some of which contain carbon fibers with a length of 3 to 20 mm), not only exhibit improved strength but also possess characteristics of higher airtightness, improved low thermal expansion, and particularly uniform thermal expansion. In compression molding, chips of carbon fiber reinforced composite material are introduced into a cavity of a mold, which is then heated and closed using a plunger, and as a result, the composite for molding is pressed into a shape defined by the cavity. When small chips are injected into the cavity, they are arranged randomly, and consequently, a random fiber orientation is obtained within the finished part. That is, carbon fibers oriented in all directions are contained within the finished part. As a result, sealing elements and support rings having at least generally isotropic characteristics are obtained. In particular, the sealing element and support ring according to the present invention are characterized by relatively uniform thermal expansion, with the thermal expansion in the compression direction being slightly higher than the thermal expansion in the direction transversing it. Furthermore, the sealing element and support ring according to the present invention are characterized by very low thermal expansion, particularly in the transverse direction relative to the pressing direction, which is within the range of steel. In the pressing direction, the thermal expansion corresponds to the thermal expansion of the plastic forming the matrix of the carbon fiber reinforced composite. Due to the low thermal expansion, only a small gap is required between the sealing element or support ring and the parts to be sealed or supported, such as between the piston rod and the support ring, and as a result, a constant narrow gap is obtained. This reduces the risk of localized heating during operation and, consequently, the risk of jamming. This material expands less when heated, whereas conventional support rings expand when heated and, as a result, come into contact with the piston rod, causing friction and mutual heating between the support ring and the piston rod. In addition, the mechanical properties of the sealing element and support ring according to the present invention are relatively uniform.Furthermore, the sealing element and support ring according to the present invention are characterized by higher airtightness. Thus, it is possible to lap a properly manufactured valve plate, thereby obtaining a very fine surface. This plate is highly impact-resistant, highly heat-resistant, has a low temperature coefficient, and is lightweight. Finally, despite its relatively long length of 3 to 20 mm, the carbon fiber does not protrude from the sealing element or support ring, and consequently, friction with other parts such as the piston rod is not expected. Rather, from the perspective of the present invention, it was observed that the ends of the carbon fiber would be crushed when it protruded from the part. For all these reasons, the sealing element or support ring according to the present invention is particularly suitable for use in piston compressors.

[0008] According to the present invention, carbon fibers within a sealing element and / or a support ring have a random fiber orientation in at least two dimensions, preferably in all three dimensions. That is, the properties imparted by the fibers are isotropic or mostly isotropic in at least two dimensions, preferably in all three dimensions.

[0009] According to the present invention, a sealing element or support ring is manufactured from chips of a carbon fiber reinforced composite material, at least a portion of which contains carbon fibers having a length of 3 to 20 mm. If the length of the carbon fibers is less than 3 mm, the benefits of the present invention, such as improved strength and low and uniform thermal expansion, are no longer obtained to a desired degree. If the carbon fibers are longer than 20 mm, sufficiently high random fiber orientation within the part is no longer obtained by compression molding, and thus homogeneity of properties is not achieved to a desired degree.

[0010] According to the present invention, at least some of the chips contain carbon fibers having a length of 3 to 20 mm. In order to achieve the above-mentioned advantages of the present invention to a high degree, in further development of the present invention, it is proposed that at least 50%, more preferably at least 60% or 70%, particularly preferably at least 80%, and very particularly preferably at least 90% of the chips used in compression molding have carbon fibers having a length of 3 to 20 mm.

[0011] Most preferably, all chips used in compression molding contain carbon fibers having a length of 3 to 20 mm.

[0012] In addition to carbon fibers having a length of 3 to 20 mm, the chip may also contain carbon fibers having different lengths. However, it is preferable that at least 50%, more preferably at least 60% or 70%, particularly preferably at least 80%, and very preferably at least 90% of the carbon fibers contained in each chip containing carbon fibers having a length of 3 to 20 mm have a length of 3 to 20 mm. More preferably, all carbon fibers in each chip containing carbon fibers having a length of 3 to 20 mm have a length of 3 to 20 mm.

[0013] Most preferably, all chips used in compression molding exclusively have carbon fibers having a length of 3 to 20 mm. For the purposes of the present invention, it is understood that each carbon fiber contained in the chip has a length of 3 to 20 mm, but the lengths of all fibers do not necessarily have to be the same as long as each carbon fiber has a length of 3 to 20 mm. Accordingly, a chip containing a first carbon fiber each with a length of 5 mm, a second carbon fiber each with a length of 10 mm, and a third carbon fiber each with a length of 15 mm is a chip containing carbon fibers having a length of 3 to 20 mm exclusively.

[0014] In all of the above embodiments, chips containing carbon fibers having a length of 3 to 20 mm are particularly preferred when they contain carbon fibers having a length of 3 to 10 mm.

[0015] To obtain excellent random orientation when filling a mold used for compression molding, and to further advance the idea of ​​the present invention, it is proposed to use chips that are not excessively large. In particular, excellent results are obtained from chips that are at least substantially plate-shaped, having at least a substantially square or rectangular cross-section, with a length of 3 to 20 mm, a width of 1 to 10 mm, and a thickness of 1 to 5 mm. Consequently, it is desirable that at least 50%, more preferably at least 60% or 70%, particularly preferably at least 80%, most preferably at least 90%, and most preferably all of the chips used in compression molding have a length of 3 to 20 mm, a width of 1 to 10 mm, and a thickness of 1 to 0.5 mm. In particular, it is desirable that the chips have a length of 3 to 10 mm.

[0016] Preferably, the carbon fibers within an individual chip are arranged at least substantially parallel to one another. For the purposes of this patent application, the arrangement of carbon fibers within an individual chip at least substantially parallel means that the longitudinal fiber axes of at least 80% of the carbon fibers are offset from all other longitudinal fiber axes of at least 80% of the carbon fibers in the chip by 20° or less. Preferably, this applies to at least 90%, more preferably at least 95%, and most preferably all carbon fibers in the chip. Most preferably, the longitudinal axes of the fibers are offset from each other by 10° or less, more preferably 5° or less, particularly preferably 2° or less, and most preferably 1° or less. Most preferably, all carbon fibers in the chip are parallel to each other.

[0017] The parallel arrangement of carbon fibers within these individual chips, or at least substantially parallel arrangement, can preferably be achieved by first providing at least one tape of carbon fiber reinforced composite material, wherein the carbon fibers within the at least one tape are arranged parallel or at least substantially parallel before the at least one tape is cut into chips each having a length of 3 to 20 mm in a direction transversing the carbon fiber direction. Thus, the parallelism of the carbon fibers in the tape is maintained in the chips produced therefrom.

[0018] A sealing element or support ring having excellent properties is obtained, in particular, when a chip containing carbon fibers having a length of 3 to 20 mm contains 20 to 70 weight% of carbon fibers, preferably 40 to 70 weight% of carbon fibers, particularly preferably 60 to 70 weight% of carbon fibers, for example, about 65 weight% of carbon fibers, and the remainder of 100 weight% is at least one thermoplastic material.

[0019] The matrix material is selected according to the desired precise properties. Suitable examples of the matrix material for chips, particularly chips containing carbon fibers having a length of 3 to 20 mm, are thermoplastic materials selected from the group consisting of polyphenylene sulfide, perfluoroalkoxy polymer, polyetheretherketone, polytetrafluoroethylene, polyimide, polyamide, and any mixture of two or more of the aforementioned thermoplastic materials.

[0020] According to a very particularly preferred embodiment, a chip containing carbon fibers having a length of at least 3 to 20 mm contains one or more polyetheretherketones as a thermoplastic material.

[0021] Particularly excellent results are obtained using a chip containing carbon fibers having a length of 3 to 20 mm, containing 20 to 70 weight% of carbon fibers, preferably 40 to 70 weight% of carbon fibers, particularly preferably 60 to 70 weight% of carbon fibers, for example, about 65 weight% of carbon fibers, and the remainder of 100 weight% being one or more polyetheretherketones.

[0022] To enhance the present invention, it is suggested that a sealing element and / or a support ring can or is obtained by a method comprising the following steps:

[0023] i) a step of providing at least one tape of carbon fiber reinforced composite material - carbon fibers are arranged at least substantially parallel within at least one tape -,

[0024] ii) a step of cutting at least one tape into chips having a length of 3 to 20 mm each in the transverse direction with respect to the carbon fiber direction,

[0025] iii) Step of introducing the chip into the mold,

[0026] iv) a step of heating the chip within the mold, and

[0027] v) Step of compressing the chip within the mold.

[0028] Preferably, in step ii), at least one tape is cut into chips each having a width of 1 to 10 mm, and the width of the chips is smaller than its length.

[0029] In particular, to obtain a sealing element or support ring having uniform characteristics, it is desirable to introduce the chip into the mold in a random orientation in step iii).

[0030] Depending on the plastic used, in step iii), the chip is preferably heated to a temperature of 120 to 450°C, particularly preferably to a temperature of 320 to 450°C.

[0031] Excellent results, particularly in terms of thermal expansion and airtightness, are obtained especially when the chip is compressed at a pressure of 0.1 to 30 MPa in step iv).

[0032] The sealing element and support ring according to the present invention are particularly suitable as a sealing packing, a sealing ring, a valve ring, a valve plate, or a support ring for a poppet of a poppet valve.

[0033] Another object of the present invention is a reciprocating compressor comprising a sealing element as described above and / or a support ring as described above.

Claims

Claim 1 A support ring manufactured by compression molding of a mixture of chips of a carbon fiber reinforced composite material, wherein at least a portion of the chips contains carbon fibers having a length of 3 to 20 mm, and the carbon fibers within the support ring have a random fiber orientation throughout three dimensions. Claim 2 In claim 1, the chip containing carbon fibers having a length of 3 to 20 mm does not contain fibers of any other length other than carbon fibers having a length of 3 to 20 mm, a support ring. Claim 3 A support ring according to claim 1 or 2, wherein at least 50% of the chips are carbon fibers having a length of 3 to 20 mm. Claim 4 In claim 1 or 2, the carbon fibers within each individual chip are at least substantially parallel to each other, forming a support ring. Claim 5 A support ring according to claim 1 or 2, wherein the chip containing carbon fibers having a length of 3 to 20 mm comprises 20 to 70 weight% of carbon fibers, and the remainder being 100 weight% of at least one thermoplastic material. Claim 6 In claim 1 or 2, the chip containing carbon fibers having a length of 3 to 20 mm is a support ring containing carbon fibers having a length of 3 to 10 mm. Claim 7 A supporting ring according to claim 1 or 2, wherein the chip containing carbon fibers having a length of 3 to 20 mm comprises at least one thermoplastic material selected from the group consisting of polyphenylene sulfide, perfluoroalkoxy polymer, polyetheretherketone, polytetrafluoroethylene, polyimide, polyamide, and any mixture of two or more of the aforementioned thermoplastic materials. Claim 8 In claim 1 or 2, the chip containing carbon fibers having a length of 3 to 20 mm is a supporting ring containing one or more polyetheretherketones as a thermoplastic material. Claim 9 A support ring obtained by a method comprising: i) providing at least one tape of a carbon fiber reinforced composite material, wherein the carbon fibers are arranged at least substantially parallel within the at least one tape; ii) cutting the at least one tape into chips each having a length of 3 to 20 mm in a transverse direction with respect to the carbon fiber direction; iii) introducing the chips into a mold; iv) heating the chips within the mold; and v) compressing the chips within the mold. Claim 10 In claim 9, the at least one tape is cut into chips having a width of 1 to 10 mm each in step ii), and the width of the chips is smaller than the length, a supporting ring. Claim 11 In claim 9, the chip is a support ring introduced in a random orientation within the mold in step iii). Claim 12 In claim 9, the chip is a support ring heated to a temperature of 120 to 450 ℃ in step iii). Claim 13 In claim 9, the chip is a support ring that is compressed at a pressure of 0.1 to 30 MPa in step iv). Claim 14 In claim 9, the support ring is a support ring that is a sealing packing, a sealing ring, a valve ring, a valve plate, or a support ring for a poppet of a poppet valve. Claim 15 A piston compressor comprising at least one support ring according to claim 1 or 2.

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