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GRIP couplings are mechanical components used to connect two shafts (driving shaft and driven shaft) in different mechanisms, enabling them to rotate together to transmit torque. In high-speed, heavy-load power transmission systems, some couplings also provide buffering, vibration damping, and improved dynamic performance of the shaft system. A coupling consists of two halves, each connected to the driving shaft and the driven shaft respectively. Generally, prime movers are connected to working machines via couplings.

GRIP Coupling Introduction

It consists of two hubs and a thin-walled metal tube, joined by either welding or bonding. Although many other materials are available, stainless steel and nickel are the most commonly used materials for the metal tube. Nickel tubes are produced using electrodeposition. This method first involves machining a solid mandrel into a corrugated shape, electroplating nickel onto the mandrel, and then chemically dissolving the mandrel to obtain a nickel bellows. This method allows precise control over the wall thickness of the bellows and can achieve thinner walls than those produced by other methods. These thin-walled bellows give the coupling high sensitivity and rapid response, making it ideal for applications in extremely small and precision instruments.

GRIP Coupling Structure Composition

Coupling structure: The input end features a clamping collar structure, where preload is generated by tightening screws to securely join the power input shaft with the clamping collar. The output end features a taper-lock structure, where tightening screws preloads a cone, causing the expansion sleeve to expand and fit into the inner bore of the power output shaft, forming a unified connection. The middle section features a bellows structure, with both ends of the bellows adhesively bonded to the input and output ends.

GRIP Coupling Troubleshooting

Based on the coupling structure, the coupling transmits power to the power output shaft (gearbox shaft) via a taper-lock expansion fit, and to the power input shaft via a clamping collar. Power is transmitted between the clamping end and the taper-lock end through the bellows, which is adhesively bonded to both the taper-lock end and the clamping collar. The fault location is at the interface between the clamping collar and the bellows. Two pre-deformation slots are machined radially into the clamping collar. The slot width is approximately 2mm, and the slot on the side with the clamping screw is a through-slot in the diametrical direction but does not penetrate completely in the depth direction at the junction with the bellows, featuring a beveled cross-section. The other slot does not extend fully in the radial direction, but its longitudinal section at the junction with the bellows also does not penetrate completely, featuring a beveled cross-section. During clamping, the clamping screws are tightened to the specified torque using a torque wrench. The deformation of the clamping collar eliminates the clearance between the bore and the shaft, achieving a secure clamp. As seen from the cross-sectional view, due to the presence of the two pre-deformation slots, the cross-section at this location is weaker, and deformation primarily occurs at these slots. The pre-deformation slot on the side with the clamping screw has the smallest cross-sectional area and is the weakest point. Permanent V-shaped deformation marks at its end indicate that the stress in this area during clamping is significant, exceeding the yield limit of the super-hard aluminum. According to the stress distribution diagram, once the bevel gear box and main gearbox are assembled and clamped, the stress value at the adhesive interface of the pre-deformation slot on the clamping screw side is 164Mpa, with a deformation magnitude of 0.027mm. During launcher operation, the coupling is subjected to alternating composite stresses, resulting in even greater stress and deformation at this location. If minor defects such as voids, inclusions, or blemishes exist at the adhesive interface during manufacturing, micro-cracks will first form at the defect sites within the region of maximum stress on the coupling's adhesive surface when the alternating stress exceeds the bond strength, creating a fatigue source. Due to stress concentration at the crack tip, the crack gradually propagates as the number of stress cycles increases and the duration of constant stress extends. As the crack spreads, the adhesive interface is progressively weakened. When the crack reaches a certain size, fatigue failure occurs. The coupling functioned normally during initial tests, but as usage time increased, the cracks gradually propagated. Even under low loads, the coupling eventually failed. The presence of stress at the adhesive joint is a potential hidden cause of failure. To avoid generating excessive stress when the coupling clamping collar is tightened, annular grooves are typically machined into the clamping collar for stress relief.

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