German OPTIBELT coupling OPTIBELT model OPTIBELT price

OPTIBELT couplings connect two flanged half-couplings to their respective shafts using standard parallel keys, and then bolt the two half-couplings together into a single unit to transmit motion and torque. This type of coupling has two main structural forms: (1) alignment of the two shafts is achieved by bolts in reamed holes, with torque transmitted through compression and shear on the bolt shanks; (2) alignment is achieved by the fit between a spigot on one half-coupling and a recess on the other. The bolts connecting the two half-couplings can be standard bolts of grade A and grade B, with torque transmitted through the friction torque at the interface of the two half-couplings.

OPTIBELT coupling introduction

It consists of two hubs and a thin-walled metal tube, connected 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 by electroforming. 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 the nickel bellows. This method allows precise control of the bellows wall thickness and can produce thinner walls than other manufacturing methods. These thin-walled bellows give the coupling high sensitivity and rapid response, making it ideal for applications in extremely small and precision instruments.

OPTIBELT coupling structure composition

The input end of the coupling features a clamping hub structure, where clamping screws generate preload to rigidly connect the power input shaft to the clamping hub. The output end features a taper-lock structure, where tightening screws preload a cone, causing the locking sleeve to expand and fit into the bore of the power output shaft, forming a single unit. The center section features a bellows structure, with both ends of the bellows adhesively bonded to the input and output ends.

OPTIBELT coupling troubleshooting

Based on the coupling structure, power is transmitted from the coupling to the power output shaft (gearbox shaft) via a taper-lock fit, and to the power input shaft via a clamping hub. Power is transmitted between the clamping end and the taper-lock end of the coupling through the bellows, which is adhesively bonded to both the taper-lock end and the clamping hub. The failure location is at the clamping hub and the bellows. Two pre-deformation slots are machined radially into the clamping hub, with a slot width of approximately 2mm. On the side with the clamping screw, the slot is through in the diametrical direction but does not penetrate fully in the depth direction at the junction with the bellows, resulting in an angled cross-section. The other slot does not extend fully in the radial direction, but also does not penetrate fully at the longitudinal junction with the bellows, also resulting in an angled cross-section. During clamping, the clamping screws are tightened to the specified value using a torque wrench, eliminating the clearance between the bore and the shaft through deformation of the clamping hub to achieve a secure fit. As shown in the cross-sectional view, due to the presence of the two pre-deformation slots, the cross-section at this location is weaker, and deformation occurs primarily 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 gearbox 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, causing even greater stress and deformation at this location. If minor defects such as voids, inclusions, or flaws exist at the adhesive interface during manufacturing, micro-cracks will first form at defective areas within the region of highest stress on the 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, leading to fatigue failure once the crack reaches a certain size. The coupling functioned normally during initial testing, but as service time increased, the cracks gradually propagated, causing the coupling to fail even under low loads. The presence of stress at the adhesive joint is a potential hidden cause of failure. To avoid generating high stress in the clamping hub during clamping, annular grooves are typically machined into the clamping hub for stress relief.

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