Installation Skills and Several Failure Modes of Plum Blossom Coupling

Published: 2018-06-19

Plum couplingDue to the advantages of small radial size and moment of inertia, no gap, good vibration reduction, cushioning effect, axial, radial and angular compensation, etc., it is widely used in metallurgy, petroleum, chemical, lifting and other industries, especially with Medium and high speed working conditions with frequent starting and forward and reverse rotation.Although the plum blossom coupling has good misalignment compensation capabilities, the misalignment of the coupling still produces additional force and torque on the rotor and bearing system, and these additional forces often bring serious consequences.

The quincunx coupling transmits torque mainly through the engagement of the convex teeth of the two halves of the coupling and the quincunx-shaped body.There is no gap between the protruding teeth and the elastic body. When the axes of the two rotors are relatively offset, the elastic element will deform correspondingly, which plays a role of automatic compensation.

There are two main types of plum blossom couplings, one is the traditional straight claw type, and the other is the curved (concave) claw type with zero clearance.The traditional straight-jaw plum blossom coupling is not suitable for use in high-precision servo transmission applications.The zero-backlash claw type plum blossom coupling is evolved on the basis of the straight claw type, but the difference is that its design can be suitable for the application of the servo system, and is often used to connect servo motors, stepping motors and ball screws.The curved surface is to reduce the deformation of the elastic plum spacer and limit the influence of centripetal force on it during high-speed operation.The zero-clearance claw coupling is composed of two metal sleeves (usually made of aluminum alloy, stainless steel can also be provided) and a plum blossom elastic spacer.The plum blossom elastic spacer has multiple leaf branches. Like a slider coupling, it also squeezes the plum blossom elastic spacer and the sleeves on both sides to match, and thus its zero clearance performance.Different from the slider coupling, the plum blossom coupling is driven by squeezing while the slider coupling is driven by shear.When using a zero-clearance claw coupling, users should pay attention not to exceed the tolerance of the elastic element given by the manufacturer (under the premise of zero clearance), otherwise the plum elastic spacer will be squashed and deformed and lose its elasticity. The load disappears, resulting in the loss of zero-gap performance, and the user may only find out after a serious problem occurs.

The advantages of plum coupling:

1. Stable work, with good vibration damping, buffering and electrical insulation properties.

2. Simple structure, small radial size, light weight, small moment of inertia, suitable for medium and high speed occasions.

3. It has large axial, radial and angular compensation capabilities.

4. Polyurethane elastic elements are resistant to oil, have large carrying capacity, and have long service life.

5. The coupling does not need lubrication, the maintenance workload is small, and it can run continuously for a long time.

Plum blossom coupling installation skills:

1. Before installation, check whether the two shafts of the prime mover and the working machine are concentric, whether there are wrapping paper and scratches on the surfaces of the two shafts, whether there are debris in the inner holes of the two half couplings of the plum-shaped coupling, and the edges of the inner holes Whether there are bruises; if any, the shaft and half coupling should be cleaned up, and the bruises should be treated with a fine file.Then check whether the inner hole diameter and length of the two half couplings are consistent with the diameter and shaft elongation of the prime mover and working machine.In general selection, it is better to let the length of the prime mover and the working machine end half coupling be less than the shaft extension of 2-2mm.

2. In order to facilitate the installation, the two half couplings are placed in a 2-120 incubator or oil tank for preheating, so that the inner hole size increases and is easy to install.After installation, the shaft head should not protrude from the section of the half coupling, and it is better to be flush.Detect the distance between the two halves of the coupling:

Measure the readings of 3~4 points along the two inner sides of the flange of the half coupling and take the average value, and the sum of the measured dimensions of the extension section and the two diaphragm sets. The error of the two should be controlled within 0~0.4mm.

3、找正：用百分表检测两半联轴节法兰盘断面和外圆跳动，当法兰盘外圆小于250mm时跳动值应不大于0.O5mm；当法兰盘外圆大于250mm时，跳动值应不大于0.08mm。

4. Install the bolts: insert the bolts from the outside of the small hole of the flange, pass through the outside of the large hole of the other flange, put on the buffer sleeve and elastic washer, screw on the nut, and tighten the nut with a wrench.If the installation is unsuitable or if it is removed and replaced, it will not damage the shaft and the half coupling; after installation, it is better to rotate freely without holding back.

In addition, in actual use, check whether the nut of the plum-shaped coupling is loose or falling off before starting the equipment. If so, tighten the nut with a wrench in time.

Coupling failure form

The failure mode of the coupling is related to the type of the coupling and the working conditions of the coupling. In summary, there are three main failure modes of the coupling.

1. Some components in the coupling are damaged due to insufficient fatigue strength or short-term overload, resulting in the interruption of the connection of the two shafts.For example, the rubber element in the rubber elastic coupling is fatigued and broken or the bonding surface with the metal is torn off under the action of variable stress.

2. The writing element in the coupling is deformed too much or is severely worn during work.Although in this case, the connection of the two shafts is not interrupted, the working performance of the coupling is significantly deteriorated, which greatly increases the additional dynamic load of the transmission system, or generates severe noise, and even causes the shaft system to vibrate.If in this case, continue to operate, it will also cause damage to other components of the transmission system.Therefore, it is generally necessary to stop the machine for inspection, replace the relevant components, and re-adjust.

3. Abnormal operation of some components in the coupling causes failure of other parts adjacent to the coupling.For example, the rubber elements in the tire coupling, such as torsional elastic deformation is too large, or under the action of centrifugal force, due to the shortening of the axial size, a large additional axial load is generated on the two halves of the coupling, making the two shafts The bearing load increases, reducing the service life of the bearing.Just like some couplings due to the relative displacement of the two shafts exceeding the allowable value, the two bearings are subjected to additional bending moments, and finally damaged due to the stress exceeding the allowable value.