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SEALING FOR HIRTH COUPLING

IP.com Disclosure Number: IPCOM000229404D
Publication Date: 2013-Jul-26
Document File: 4 page(s) / 301K

Publishing Venue

The IP.com Prior Art Database

Abstract

ABSTRACT This invention pertains to couplings for compressors. In a conventional compressor, load transfer capability from shaft to the impeller can be improved by providing the Hirth joint which is a mechanical connection, with teeth machined on the abutting surfaces of the hollow shafts. The problem with the existing Hirth coupling is gas leakage through the joint. The invention is a modified Hirth coupling with a step on either side with seal ring. The ring has two extending rims on the underside that fit into corresponding recesses in the shafts. On either side of the joint at the seal ring legs, metal to metal sealing can be achieved by utilizing the shaft preload, available pressure difference and centrifugal force due to rotation of the components. During assembly, the seal ring is shrink-fitted on to one side shaft of the coupling, allowing for easy assembly. All segments of the shafts are preloaded by tightening the tie rod, which generates the metal to metal contact pressure and in turn provides sealing against gas leakage, while the metal to metal sealing is reliable and robust.

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SEALING FOR HIRTH COUPLING

BACKGROUND

This invention pertains to couplings for compressors. In a conventional compressor, impellers are attached to the shaft by interference fit. At higher speed this kind of attachment does not provide sufficient load transfer capability from shaft to the impeller because of more centrifugal force, since the amount of interference reduces. Load transfer capability from shaft to the impeller can be improved by providing the Hirth joint (Fig. 1) which is a mechanical connection, with teeth machined on the abutting surfaces of the hollow shafts. A tie rod which passes through the hollow shaft, which transfers load to a series of hollow shaft segments assembled in tandem.

FIG. 1: Hirth shaft coupling

The problem with the existing Hirth coupling is that, when there is pressure difference between the inner and outer surfaces of the shaft, gas leaks through the joint. The invention proposes a new joint sealing device for compressor couplings.

BRIEF DESCRIPTION OF DRAWINGS

Sealing for Hirth coupling is disclosed with reference to the following drawings.

Figure 1: Hirth shaft coupling

Figure 2: Location for the proposed ‘metal to metal seal

Figure 3: Proposed metal to metal seal design with seal ring shown on the right

Figure 4: Different conceptual designs for seal ring

DETAILED DESCRIPTION

The present invention proposes metal to metal seal to avoid gas leakage through the joint. The stator and rotor assembly in a centrifugal compressor along with the locations for the proposed ‘metal to metal sealing’ joints are shown in Fig. 2.

FIG. 2: Location for the proposed ‘metal to metal seal

The concept requires modifying the Hirth coupling with a step on either side with seal ring as shown in Fig. 3. The ring has two extending rims on the underside that fit into corresponding recesses in the shafts. On either side of the joint at the seal ring legs, metal to metal sealing can be achieved by utilizing the shaft preload, available pressure difference and centrifugal force due to rotation of the components.

 

FIG. 3: Proposed metal to metal seal design with seal ring shown on the right

During assembly, the seal ring is shrink-fitted on to one side shaft of the coupling, allowing for easy assembly. All segments of the shafts are preloaded by tightening the...