Basic performance of spring
A spring is a mechanical part that uses the elasticity and structural characteristics of the material to deform during operation, convert mechanical or kinetic energy into deformable energy (bit energy), or transform deformable energy (bit energy) into mechanical or kinetic energy. .
Spring application occasions:
Buffering or damping, such as the support spring of the crusher and the suspension spring of the vehicle;
Mechanical energy storage, such as clocks, gauges, and springs on automatic control mechanisms;
Control movements such as valves, clutches, brakes, and springs on various regulators;
Force measuring devices, such as springs and springs on a power meter.
Spring characteristic line: The relationship between load and deformation is called the spring's characteristic line.
There are roughly three types of characteristic lines for springs: 1) linear type 2) gradually increasing type 3) decreasing type
The stiffness of the spring: The ratio of the increment of load to the increment of deformation, ie the load required to produce a unit deformation, called the stiffness of the spring.
The stiffness of compression and tension springs is K=(P2-P1)/(H1-H2)
The stiffness of the torsion spring is K = (T2-T1)/(torque angle 2 - twist angle 1)
The characteristic line is a gradually increasing spring, and the stiffness increases with the increase of the load;
Decreasing type of spring, stiffness decreases with increasing load;
Linear springs, whose stiffness does not change with load, are also called spring constants.
Deformation energy of spring
The deformation energy of the spring is inversely proportional to the shear modulus G and the elastic modulus E of the spring material. Therefore, the low modulus is advantageous for the large deformation energy required; the size of the deformation energy is proportional to the square of the maximum working stress and increases. Stress means that the material has a high elastic limit, and a high elastic limit also corresponds to a high modulus (stress plays a decisive role).
To obtain large deformation energy, the volume or stress of the spring material can be increased, or both can be increased at the same time.
Spring fatigue strength
In mechanical equipment, there are roughly two kinds of stress that are produced when a component composes a work: static stress and variable stress.
Destruction of parts or materials subject to static stress is plastic deformation or brittle fracture, so their strength is measured by the elastic limit of the material or the yield strength and the limit of displacement. The failure of parts or materials subject to stress is fatigue fracture, so their strength is measured by the fatigue strength.
The fatigue strength is lower than the static stress strength such as elastic limit or yield strength.
Types of stress change: stability cyclic stress, unstable cyclic stress, and random stress.
Factors affecting fatigue strength: yield strength, surface condition, size effect, metallurgical defects, corrosion media, temperature
Factors influencing the spring fatigue test: internal factors such as chemical composition, metallographic structure, etc.;
External factors such as surface conditions, shape dimensions, temperature, and surrounding media.
Cylindrical helical compression spring
When the winding ratio is between 3 and 10, the spring end surface is preferably flattened; between 10 and 15, the end surface may or may not be worn; when it is larger than 15 o'clock, it may not be ground.
In order to avoid excessive force due to load eccentricity, the minimum number of operating cycles is 2, but generally not less than 3.
Convolution ratio C = spring diameter / wire diameter
Convolute ratio C is too small, the material bending deformation is severe, the required coiling power is large, sometimes the mandrel shaft end is too thin and easy to break; the coiling ratio C is too large, after the coil spring, the spring ring is easy to loosen, the diameter of the spring Difficult to control; In addition due to the weight of the spring itself, causing the coil springs constantly vibrate. The ideal convolution ratio is 4~9.
Spring stiffness F"=Gd4 / 8D3n (N/mm)
The effective number of springs required for general loads is ≥ 2.5. For springs with relatively strict load requirements, the effective number of turns is greater than 4; the number of effective turns is small, and the load requirements are high, and it is difficult to manufacture.
For springs with small material diameters and severe load requirements, it is recommended to use a support ring ≥2.
When there is a specified load at two or more points below the specified height, the free height shall not have tolerance requirements. The inner and outer diameters of springs cannot be dimensioned at the same time.
Cylindrical spiral tension spring
Early tension: When the tension spring is formed into a roll, the spring rings generate a compressive force between them. When the external load is applied to the spring, if the tensile force generated by the load does not reach this force, the spring will not be deformed. When the compressive force is reached or exceeded, the deformation begins to occur. The tensile load corresponding to this compressive force is the initial tensile force F0.
Springs with initial tension have much higher load capacity than springs without primary tension.
For tension springs that do not require initial tension, there will be more or less clearance between the rings. When the number of turns of the spring is large, these gaps will affect the theoretical value of the free length of the spring and need to be negotiated with the customer.
Convolution ratio, stiffness formula is the same as compression spring.
The total amount of deformation of the tension spring is the sum of the amount of deformation caused by the effective number of turns and the amount of deformation generated by the hooks at both ends. For a semicircular shackle, it is equivalent to 0.1 turns; a full shackle is equivalent to 0.25 to 0.5 turns.
Springs with initial tension must be made of hardened steel wire.
A spring with a small diameter, a large number of effective turns, and a large spring winding makes it difficult to ensure quality during electroplating.
Cylindrical spiral torsion spring
Spring type: normal torsion spring, parallel double torsion spring, in-line double torsion spring; no spacing and spacing.
Generally, the effective working circle of the spring is not less than 3 revolutions;
The direction of rotation of the torsion spring must be clear, and the direction of rotation must be consistent with the direction of the torque, so that when the spring is working, it is tightened.
The mandrel of the torsion spring must be 10% smaller than the inner diameter of the spring under maximum operating torque.
The radius of each excessive arc of the twist arm should not be less than 2 times the material diameter to avoid excessive stress concentration.
In order to make the torsion spring not lose stability during operation, its maximum twist angle must not exceed the allowable value.
φ Allow = 123.1* The number of effective turns of the free state is the fourth power.
The high accuracy of the torsion spring tempering temperature should not be too high;
For the torsion springs to be electroplated, the radius of curvature of the torsion arms should be as large as possible to prevent them from becoming crispy.
Spring manufacturing process
Coil Springs - (Calibration) - Elimination of Stress Tempering - Rough Grinding of End Faces - Internal and External Burrs - (Blasting) - Standing Treatment (or Heavy Pressure Processing) - Grinding End Face - Inspection - Prevention Rust treatment - packaging
Shot peening: improving spring fatigue life
Set or strong pressure treatment: the height of the spring is pressed to the working height limit or each round and tight several times or stay for a period of time, in order to achieve a stable size and improve the bearing capacity.