CS212142B1 - A method for reducing internal residual stresses - Google Patents

Abstract

The invention relates to methods for reducing internal residual stresses in components and solves the problem of removing deformations, buckling of components and increasing the resistance of the material to cracks, possibly brittle and fatigue fracture and corrosion. A component with at least atmospheric temperature, preferably with a temperature of 30 to 550 ° C, is subjected to vibration with a frequency of up to 500 Hz. The vibration occurs in repeated, consecutive cycles with a delay of no more than 2 seconds, with a duration of 5 seconds to 20 minutes, with the total duration of cyclic vibrations being 3 to 120 minutes.

Description

The invention relates to a method for reducing the internal residual stresses of parts and machine structures of ferrous and non-ferrous materials.

As a result of manufacturing processes, ie machining, heat treatment, casting, forming and welding, internal residual stresses, namely first-order and macro-stresses, and microscopic stresses, arise in machine components.

Macroscopic and especially microscopic stresses are superimposed in the workpiece and cause undesirable deformation and deformation of the workpiece and increase the tendency of the material to fracture, cracks, possibly brittle and fatigue fracture and corrosion.

While macroscopic stresses can be greatly reduced by a properly selected design and manufacturing technology, microscopic stresses are virtually unaffected during component manufacturing.

If it is not possible to produce a component without internal residual stresses or with minimal stress, it is necessary to relieve the internal stress component or redistribute the internal stress so that an equilibrium condition is achieved which eliminates the occurrence of the mentioned defects.

A number of methods are known to reduce the internal residual stresses of components and structures.

The original and most widespread method, natural aging, has been replaced by artificial aging, i.e. annealing at a temperature range of 500 to 650 ° C, for several hours followed by gradual cooling in the annealing furnace.

There are also known other methods of heat and mechanical treatment components, such as heat shock, thermocycling aging, static and dynamic loads, which shall act to remove ^one not napělových peaks and stress redistribution, while reinforcement of the metal matrix, thereby increasing the relaxation resistance.

In these methods, the main drawback is, on the one hand, a too long annealing cycle, and on the other hand, in the case of thermal shocks, there is a risk of failure of a component subject to rapid temperature changes.

In the case of vibration at a constant oscillation frequency, the internal stress is reduced only at the oscillation amplitude above the material creep limit. At lower amplitudes, the effect is small. Achieving material vibration load levels above the creep limit is technically difficult and is associated with the risk of component failure in their weakened cross-sections.

Another way is to use harmonic vibration. Both the vibrator and the acceleration sensor are clamped on the component that vibrates at gradually increasing oscillation frequencies. The component is allowed to vibrate for some time at the resonant spikes. The effect of vibration is monitored either by measuring the power of the vibrator or by monitoring the displacement of the resonant peaks or by measuring the logarithmic decrement of the attenuation. The process is terminated when the monitored quantity reaches constant values. The disadvantage of this method is that the resonant peaks are determined only at the clamping point of the acceleration sensor, while other component locations can resonate at completely different frequencies. Therefore, it is necessary to move the acceleration sensor gradually and repeat the vibration cycle throughout the components. However, this procedure is complex and such an apparatus is very difficult to carry out.

These drawbacks are largely eliminated by the method of reducing internal residual stresses according to the invention, which consists in subjecting the machine part to repeated vibrations with a delay of a maximum of 2 seconds in successive cycles ranging from 5 seconds to 20 minutes, the total cycle time vibration is 3 to 120 minutes.

The whole cycle of vibration is very simple and does not require professional service. It can be fully automated using timers to set the vibration cycle time, repeat it, and the total cycle vibration time. In cyclic vibration it is possible to use a vibrator with constant and variable oscillation frequency without acceleration sensors. If a vibrator with a constant oscillation frequency is used, the vibrated part is subjected to a oscillation range at the time of acceleration but mainly at the time of deceleration, the inertia of the vibrator and the weight of the component, the maximum frequency of which is given by the selected vibrator frequency. by re-impulsing the vibrator for the next vibration cycle.

In this way, the frequency of the oscillations throughout the component changes periodically. In a short period of time, which is given by the length of one vibration cycle, resonant peaks arise and disappear and the vibration efficiency is multiplied by repeating the vibration cycles. The vibration cycle is correctly performed when the power consumption of the vibrator drops by 5 to 15% of the original value and remains constant during longer vibration.

The component is placed on a resilient, eg rubber, mat or suspended on resilient ropes on a stand or crane. Shaped parts can be bundled together. A vibrator is attached to them. The small parts may be individually, bundled or packaged, fixed to a table on which the vibrator is mounted.

Example 1

A constant frequency oscillator controlled by a timer system is clamped onto the machine component. The first controls the duration of one vibration cycle and is set to 30 seconds. The second controls the delay between cycles and is set to two seconds. The third switch controls the total vibration time and is set to 20 minutes. Closing the first switch also turns on the third. After 30 seconds, the first switch will turn off and the second switch will operate, which will activate the first switch after two seconds. The whole cycle is repeated. After 20 minutes, the third switch disables the first and second switches, and the cyclic vibration is complete.

Example 2

The vibrator is clamped to the component with a variable frequency. The component is subjected to a vibration of 1 to 2 minutes at each frequency, e.g., 40, 80, 120, 80 and 40 Hz. The cycle is repeated for 15 to 20 minutes.

Example 3

A vibrator with a continuously variable oscillation frequency with a maximum of 100 Hz is mounted on the component. The part vibrates with continuously increasing frequency of oscillations to maximum and with continuously decreasing frequency to zero. The cycle is repeated periodically for 15 minutes.

Example 4

The small parts are placed tightly in the package or bundled, or individually attached to a vibrator-controlled vibrating table. Cyclic vibration occurs in some of the ways described above.

Claims (1)

Method for reducing the internal residual stresses of parts and machine structures of ferrous and non-ferrous materials having a temperature of at least atmospheric up to 550 ° C by vibrations with a frequency of up to 500 Hz, characterized in that the machine component is subjected to vibration a delay of a maximum of 2 seconds in successive cycles, ranging from 5 seconds to 20 minutes, with a total cycle time of 3 to 120 minutes.