German Sealmaster coupling Sealmaster model Sealmaster price

Sealmaster 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 shoulder on one half-coupling and a groove on the other. The bolts connecting the two half-couplings can be standard bolts of grade A and grade B, with torque transmitted by the frictional torque at the mating surfaces of the two half-couplings.

Sealmaster 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 common 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 control over the precision of the bellows wall thickness and can produce thinner walls than other methods. These thin-walled bellows give the coupling high sensitivity and rapid response, making it ideal for applications in extremely small and precise instruments.

Sealmaster coupling structure composition

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

Sealmaster coupling troubleshooting

From the coupling structure, it is known that 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 collar. Power is transmitted between the clamping end and the taper-lock end of the coupling through the bellows, which are adhesively bonded to the taper-lock end and the clamping collar. The fault location is at the clamping collar and the bellows. Two pre-deformation slots are machined radially into the clamping collar, with a slot width of approximately 2mm. On the side with the clamping screw, the slot is through in the diametral direction but does not penetrate completely in the depth direction at the junction with the bellows, having an inclined cross-section; the other slot does not extend through radially, but its longitudinal section at the junction with the bellows also does not penetrate completely, having an inclined 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 collar to achieve clamping. As seen from the cross-sectional view, during clamping, the presence of the two pre-deformation slots creates a weaker cross-section in this area, with deformation occurring mainly 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 in this area. If minor defects such as voids, inclusions, or flaws exist at the adhesive interface during manufacturing, micro-cracks will first form at defective spots within the region of highest stress on the coupling's adhesive interface 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 when the crack reaches a certain size. The coupling functioned normally during initial testing, but as usage 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 collar during clamping, annular grooves are generally cut into the clamping collar for stress relief.

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