Basic knowledge of couplings
A coupling that enables two shafts to be connected at all times during operation.
First: Function
Couplings are usually used to connect two axes and transfer motion and torque between them. It has the ability of absorbing vibration and mitigating impact; Can be used as a safety device to prevent the connected parts from bearing too much load, play the role of overload protection; When the shaft is connected by coupling, the two shafts can only be separated after disassembly when the machine stops running.
Fixed rigid couplings: the center line of the two shafts to be connected is strictly aligned;
Movable coupling: allows a certain amount of installation error between the two shafts.
Elastic jaw coupling: the elastic component materials are different, can compensate the displacement between two axes in a certain range, and the role of buffer shock absorption.Jaw flexible coupling main used in stainless steel gear pumps and water pump, fans....
Due to the influence of manufacturing and installation error, bearing deformation, bearing wear, unbalance of rotary parts and temperature change, the axis of the two shafts connected by the coupling often has some degree of relative displacement and deflection;
Coupling from the structure to take a variety of different measures, so that the coupling has the performance of compensation for various offsets, otherwise it will cause additional load in the shaft, coupling, bearing design, resulting in the deterioration of the working situation.
The types of displacement between two axes are: axial displacement, radial displacement, angular displacement and comprehensive displacement.
Two: Fixed rigid couplings
Structural features
A. Simple structure, convenient maintenance, can transfer large torque;
B. However, it lacks the ability to compensate the relative displacement between the two connected axes;
C. The neutral requirements of the two axes are very high. If the relative displacement of the two axes occurs, additional loads and serious wear will be caused on the shaft, coupling and bearing, seriously affecting the normal operation of the shaft and bearing; In addition, shock and vibration absorption cannot be mitigated during load transfer.
Application scenarios
Low speed, large torque, stable load, short and rigid shaft connection.
Type
Flange coupling and sleeve coupling two kinds.
Structural characteristics of flange couplings
A. Composition: two semi-couplings with flanges and A set of bolts;
B. Working principle: two flanged semi-couplings are connected at two shafts respectively by keys, and then the two semi-couplings are connected together by bolts to transfer motion and torque.
C. Centering method: 1. Centering is carried out by the mutual chiming of the two half couplings with convex shoulders and grooves respectively, and the half couplings are connected by ordinary bolts; (The torque is transferred by the friction generated by the pretightening of the ordinary bolt on the flange edge contact surface; Centering with reamed hole bolts and relying on screw to bear extrusion and shear transfer torque. 2. The two half couplings are made of convex shoulders, which are matched with a split ring to achieve alignment.
D. Applicable: low speed, large torque, stable load, short and good rigidity shaft connection.
E. Simple structure, large transmission torque; Reliable force transmission, good to neutral; Easy to disassemble and assemble, widely used; But it has no displacement compensation function; According to the standard selection.
Structural characteristics of sleeve couplings
A. Composition: the two shafts are connected by keys or pins through A common sleeve.
B. Advantages: simple structure, convenient manufacturing, low cost, small radial size.
C. Disadvantages: Axial movement is required when assembling and disassembling.
D. Application occasions: small diameter of two axes, high accuracy of two axes to neutral, smooth operation occasions, used for small torque transfer occasions.
Flexible couplings
Types of rigid movable coupling (inelastic element coupling) : cross slider coupling, universal coupling and drum type gear coupling.
1.Gear couplings
A. Composition: two outer sleeves with inner teeth and flange, two inner sleeves with outer teeth;
B. Working principle: the two inner sleeves are connected with the two shafts respectively by keys, and the two outer sleeves are connected by bolts. Torque and motion are transmitted through the meshing of the inner and outer teeth.
C. Features: In order to compensate the relative displacement of the two axes, the tooth of the outer tooth ring is made into a drum tooth, and the tooth tip is made into a sphere on the axis with the center line, and a large gap is left between the tooth tip and tooth side.
Through the top clearance and side clearance between the meshing teeth, it has the function of allowing radial, axial and angular comprehensive displacement compensation between the two axes. High speed (up to 3500r/min), can transfer a large torque (up to 106N·m), and can compensate for a large comprehensive displacement, high work, the installation accuracy is not high, to lubrication;
D. Disadvantages: large quality, difficult manufacturing, high cost.
E. Application: Widely used in automobiles and other large heavy machinery equipment.
2.Oldham couplings
A. Structure features: it is connected by half shaft coupling device 1, 3 (left and right sleeve) and floating disk 2 (cross slider), and the two shafts rotate together; The tenon of the floating disk can slide in the groove of the semi-coupling; The friction is large and should be lubricated.
B. Advantages: small radial size, simple structure
C. Disadvantages: but poor impact resistance, easy friction damage between the slider and the groove, need lubrication; Because of the radial displacement of the cross slider, a large centrifugal inertia force will be generated, which will bring additional loads to the shaft and bearing.
D. Application: usually used for large rigidity, low speed, small impact occasions.
3.Universal coupling
A. Structure: composed of A cross shaft, two universal joint forks and four needle bearings; The center of rotation (axis) of all rotation pairs intersects at a point O, and the Angle between the two axes is α. It is a device (coupling) used to transfer the motion between two intersecting axes of variable Angle.
B. Working principle: When axis I rotates once, axis II will also rotate once, that is, the average transmission ratio of the two axes is 1; However, the instantaneous transmission ratio of the two axes is not constant 1, but changes periodically. This characteristic of universal joint is called instantaneous transmission ratio nonuniformity;
For a single universal joint, when there is an included Angle between the input axis and the output axis, the angular velocity of the two axes is not equal, that is, the universal joint has unequal velocity. The larger the included Angle α between the two axes, the more obvious the velocity fluctuation of the driven axis. Therefore, α should be between 35° and 45°. In order to prevent the main and driven axis angular velocity is not equal; In order to completely eliminate the shortcomings of the driven shaft variable speed transmission in the universal joint, it is often used in pairs.
C. Advantages: With large angular compensation capacity, compact structure, high transmission efficiency;
D. Disadvantages: Additional dynamic load will be generated in the transmission, the speed should not be too high;
Commonly used elastic couplings has two kinds
- Elastic sleeve pin bush coupling (Standard No. Gb423-2002)
A. Structure: similar to flange coupling in structure, except that the connecting bolt is replaced by A cancellation covered with rubber elastic sleeve;
B. Principle: using the elastic deformation of the elastic sleeve to compensate the relative displacement of the two axes;
C. Features: the elastic sleeve pin coupling is easy to manufacture, convenient assembly and disassembly, low cost, but the elastic sleeve is easy to wear, short life.
D. Suitable for: steady load, positive and negative rotation or start frequently, high speed transmission of small and medium torque of the two axis connection.
- 2.Elastic pin coupling
- A. Structure: A number of non-metallic material pin, placed in the flange hole of the two half coupling, and realize the connection of the two half coupling; The pin material is usually nylon, and other non-metallic materials with elasticity are also available.
- B. Principle: The elastic deformation of the elastic pin is used to compensate the axial displacement of the two axes;
- C. Features: Elastic pin coupling can allow large axial movement, but the compensation of radial displacement and angular displacement is small. Its structure is simple, easy to manufacture and easy to maintain.