Compressor with highly corrosion-resistant screws and its assembly method

Abstract

A compressor having an airtight sealing screw, the airtight sealing screw comprising a layer of pre-coated plastic material deposited on the outer surface of the portion of the screw shank that contacts the head and on the surface below the head; and an assembly process for the compressor wherein, during screw tightening, the pre-coated plastic layer fills the gap between the region below the head and the underlying metal surface, while mixing and inducing a stage of polymerization and hardening.

Description

Technical Field

[0001] This invention relates to the field of corrosion protection for mechanical devices including hermetically sealed screws extending beyond the device itself, such as screws tightened on the head of a compressor. Background Technology

[0002] As is well known, in many mechanical devices—such as semi-hermetic compressors, and more broadly, such as the various types of compressors shown in DE2131237A1—there are multiple components made of iron alloys and assembled together by screws that can be operated directly from the outside, making it easy to operate these components to facilitate the assembly or disassembly of the device.

[0003] For compressors, a critical aspect involves oxidation, as these units are often exposed to highly corrosive environments, typically when used in marine or saline atmospheres, or, for example, in the rail sector, during regular cleaning operations of locomotives and rolling stock.

[0004] The tests that must be passed without causing corrosion include: a salt spray exposure test according to technical standard UNI EN ISO 9227, in which no signs of oxidation are observed in the area below the screw head for 500 hours, and a test for 1000 hours.

[0005] To achieve effective corrosion protection, the known practice is to apply a special protective coating to the entire device after it has been fully assembled; however, even if the entire device has been coated, there are still parts of the device that cannot be effectively protected.

[0006] These portions are in particular the gaps formed in the undercut, which is defined between the underside of the screw head and the metal surface of the underlying component—such as a compressor head, cover, or other element; industrial spraying cannot effectively penetrate these gaps because at least one side of the screw head is often located near protrusions that hinder the proper deposition of the coating during industrial coating, for example, in a location adjacent to a compressor head, where the presence of the compressor head makes it difficult for the spray to reach the underside of the screw head.

[0007] It must also be considered that after the compressor's functional testing and before the entire unit is painted, an external phosphating and degreasing treatment is required as a preparation step for the subsequent painting stage. This preparation step includes a cleaning stage, and if necessary, a rinsing stage.

[0008] Improvements in oxidation resistance have been achieved by replacing blued steel screws with hot-dip galvanized screws; however, galvanizing is still insufficient to guarantee the high performance required in certain situations, especially due to the persistent presence of corrosive substances in the gaps.

[0009] Due to the manual nature of this process and the large number of screws on each compressor, additional solutions—such as applying a sealant around the underside of the screw heads after cleaning and before coating, once the compressor has been assembled—would create bottlenecks in the production process. Furthermore, these known solutions still have drawbacks, primarily in terms of associated costs, the expense of disposing of various chemicals, and the inability to restore corrosion resistance after screw removal and reassembly.

[0010] Manually filling gaps with suitable sealant has proven to be a slow and costly process, unsuitable for industrial production. Summary of the Invention

[0011] Therefore, the object of this invention is to provide a solution to the problem of protecting the gap between the underside of the head of a sealing screw and the metal surface of an underlying component—such as a compressor head, cover, etc.—from corrosion, a solution that is effective, economical, and industrially feasible. This invention is applicable to compressors, or more broadly, to connections involving unpainted metal-to-metal contact tightened by screws. This technical solution is applicable to all situations requiring improved corrosion resistance at the connection between two metal components first assembled by tightening one or more screws or bolts and subsequently coated, and is also applicable in highly corrosive environments.

[0012] According to the present invention, these and other objectives are achieved by using a special galvanized screw and applying a coating of plastic material—for example, based on nylon 11 or polyamide 11, or alternatively based on a polyolefin material—under the head of the screw.

[0013] Preferably, the present invention provides the use of galvanized screws with hexagonal heads or internal hexagonal heads; such as Figure 1 As shown, the coating (1) is applied to the surface of the area (4) below the head and to the outer surface (2) of the part of the rod (5) that is in contact with the head (3).

[0014] The thickness of the coating is typically between 0.2 mm and 2 mm.

[0015] According to a preferred embodiment, good results can be obtained by applying a coating of a pre-coated material based on a microencapsulated epoxy resin—this type of resin is used as a thread-locking compound—which remains inert on the fastener until the tightening caused by the threaded engagement causes the resin to mix, then fill the gaps below the head, subsequently polymerize and harden to seal these gaps, thereby eliminating the risk of oxidation.

[0016] A microencapsulated epoxy resin composition that has achieved good results includes: - 30% to 40% polyoxymethylene melamine urea; - 30% to 40% epoxy resin; - 10% to 20% of 4,4'-methylenebis(cyclohexylamine); - 5% to 10% adhesive.

[0017] The compressor's production cycle then continues with functional and leak testing, followed by degreasing or phosphating, cleaning, and rinsing if necessary, before spraying; spraying typically includes a first primer coating, followed by a finishing enamel coating. Attached Figure Description

[0018] Figure 1 A longitudinal section of the screw is shown, wherein a pre-coated plastic coating (1) is shown on the outer surface (2) of the portion of the shank (5) that contacts the head (3) and on the surface of the region (4) below the head.

[0019] Figure 2 A perspective view of a compressor is shown, comprising a housing, suction and discharge valves for refrigerant fluid, a compressor head, and other known components, and the compressor is assembled by a plurality of reversible, hermetically sealed connections, particularly by a plurality of screw connections. The figure points out the heads (3) of certain screws that are particularly difficult to protect from corrosion by painting alone. This invention is generally applicable to any screws in a compressor whose heads are exposed to the external environment. Detailed Implementation

[0020] The following detailed description of embodiments of the invention, provided by way of non-limiting example only with reference to the accompanying drawings, highlights additional features and advantages derived from the invention, which form part of the invention.

[0021] According to the present invention, the solution to the technical problem of reducing or eliminating corrosion in the gap between the region defined below the head of the sealing screw and the underlying metal surface lies in using a special screw to which a pre-coated plastic material (1) has been applied. More specifically, the pre-coated plastic material is applied to the surface of the underside of the head (4) and to the outer surface (2) of the portion of the shank (5) that contacts the head (3), such that the plastic material fills the gap during screw tightening.

[0022] Preferably, the pre-coated plastic material comprises a microencapsulated epoxy resin composition comprising the components shown in the following percentages by weight.

[0023] - 30% to 40% polyoxymethylene melamine urea; - 30% to 40% epoxy resin; - 10% to 20% of 4,4'-methylenebis(cyclohexylamine); - 5% to 10% adhesive.

[0024] During screw tightening, the pre-coated plastic material mixes and fills the gaps, simultaneously inducing a polymerization and hardening phase.

[0025] Good results were achieved when the thickness of the pre-coated plastic material was approximately 1 mm.

Claims

1. A compressor comprising a plurality of reversible airtight sealing screw connectors, wherein the heads of some of the airtight sealing screw connectors are exposed outside the compressor, characterized in that, At least one screw in which the head (3) of the screw is exposed to the outside of the compressor includes a coating (1) pre-coated with plastic material, the coating being applied to the surface of the bottom side (4) of the head of the screw and the outer surface of the portion of the shank (5) that contacts the head (3).

2. The compressor according to the preceding claim, characterized in that, The pre-coated plastic material comprises a composition of microencapsulated epoxy resin, which in turn comprises the compounds shown in the following percentages by weight: 30% to 40% polyoxymethylene melamine urea; 30% to 40% epoxy resin; 10% to 20% of 4,4'-methylenebis(cyclohexylamine); 5% to 10% adhesive.

3. The compressor according to claim 1, characterized in that, The coating (1) pre-coated with plastic material includes one or more of the following compounds: nylon 11, polyamide 11, and polyolefin.

4. The compressor according to any one of the foregoing claims, characterized in that, The thickness of the pre-coated plastic material is between 0.2 mm and 2 mm.

5. The compressor according to any one of the foregoing claims, characterized in that, The thickness of the pre-coated plastic material is between 0.5 mm and 1 mm.

6. A method for assembling a compressor according to any one of the preceding claims, characterized in that, The method Includes the following stages: a) depositing a pre-coated plastic coating (1) according to any one of the preceding claims on the outer surface (2) of the portion of the rod (5) that contacts the head (3) and on the surface of the bottom side portion (4) of the head of one or more of the screws; b) Tighten the screw, thereby causing the resin to mix and fill the void below the head; c) Wait until the resin has completed polymerization and has been hardened.

7. The method for assembling a compressor according to the preceding claim, characterized in that, After phase c) where aggregation is awaited to complete, the following additional phases are provided: d) Degreasing (phosphating degreasing); e) Cleaning; f) Painting.

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