Que Xuandong (Xi'an Dajin Qing'an Compressor Co., Ltd.), such as "death" and "uneven air gap", seriously reduced the performance of the product, conducted a theoretical analysis, studied its production rules, and combined production practice, proposed reduction and prevention Measures and suggestions for the adverse effects of welding center stress and deformation, such as center deviation and key dimension changes: Among them, the formation process of three-point plug welding and upper girth welding residual stress and deformation and the harm to the compressor are analyzed. And experience in reducing and preventing welding residual stress and deformation and improving product performance.
1 Introduction to the welding process of air-conditioning compressors Rotor compressors and scroll compressors are two products with very different structures. Although the welding processes used by the two are not very different, it is because of their structural differences that they are in the same The welding deformation produced under the welding method and its effect on product quality and performance are obviously different.
Lifting ring C02 welding: upper cover MAG welding electrical box, sealed plug; seat projection welding: lower bearing, body TIG welding exhaust pipe 丨 silver brazing, bracket projection welding I suction pipe> 诲 brazing 丨 reservoir furnace Welding fc liquid cylinder under silver brazing; the structure and welding method of MAG rotor compressor and scroll compressor. All welding methods (welding) are marked in the figure 140. From the structure, it can be seen that the rotor compressor Three-point plug welding is to weld the cylinder and the cylinder together, three-point plug welding of the scroll compressor is to weld the cylinder and the lower bearing body, and four-point plug welding is to weld the cylinder and the bracket together. In addition, there are no key parts on the outer and inner parts of the rotor compressor, and there is a disc-shaped part in the upper casing of the scroll compressor-the partition, which is "hot pressed" by high-frequency heating and formed between it and the upper casing The surplus is connected and integrated.
According to the judgment of the compressor failure on the production line, the relevant processes of the main failures "incapable", "not started", and "stuck" are three (four) spot plug welding and upper casing girth welding (hereinafter referred to as upper girth welding), All are fusion welding processes. Among all three types of welding methods, only welding has the largest welding stress and deformation. Therefore, it is necessary to conduct a specific analysis to discuss the mechanism of the problem and the countermeasures and preventive measures that should be taken to continuously reduce the product defect rate, reduce production losses, and improve product quality and performance.
2 Welding stress and deformation generation mechanism In the process of compressor plug welding and girth welding, the welded parts (base material) have been restricted by other parts in the overall size, which has formed constraints; at the same time, welding The temperature is sufficient to cause the base material to undergo intense thermal expansion and reach the yield limit. In addition, the hot liquid metal produced by fusion welding largely offsets the expansion tendency of the base material when heated, which also relatively reduces the amount of elastic deformation, so that after the base material cools, most of the expansion trend is converted into shortened The trend eventually exacerbates the influence of residual stress and deformation. Therefore, the compressor plug welding and girth welding not only have the above two conditions for forming residual stress and deformation, but also the absorption of the expansion tendency of the liquid metal increases the degree of residual stress and deformation.
Shown is the typical welding residual deformation of the butt joint under unconstrained conditions after the welding thermal strain cycle. Therefore, it can be inferred that if under restraint conditions, the welding warpage deformation tendency will be transformed into a downward deformation tendency or downward thrust stress.
3 Analysis of the welding deformation law of the compressor. The residual stress and deformation of the plug welding point and the girth weld of the compressor follow the above deformation law from a microscopic point of view, but the macroscopic phenomena are not the same.
First, take the plug welding point of the three-point plug welding of the rotor compressor as an example. The welding point is triangular in shape. After the above welding thermal strain cycle, the internal residual large tensile stress, the welded base material-the cylinder and the cylinder are both Pulled towards the center of the solder joint; at the same time, the shrinkage stress of the two "sides" of the triangular solder joint is constrained by the base material (compressor barrel), but on the outside "side"
Since there is no restraint and shrinkage deformation occurs, there is also warpage deformation. Observed from the compressor as a whole, because the compressor barrel (base material) is barrel-shaped and the cross-section is circular, the transverse shrinkage of the solder joints makes the circumference shorter and radius smaller, and because of the warpage deformation, the The welding spot moves toward the center of the compressor relative to the original position, and is accompanied by thrust stress directed toward the compressor axis. The thrust stress on the compressor axis caused by the shrinkage and tensile stress of the three plug welding points and the deformation in the same direction will all act on the cylinder of the rotor compressor.
The shape of the rotor compressor cylinder and the position of the three-point plug welding welding points are not symmetrically distributed on the circumference, so that the cylinder will deviate from the original center position under the action of the residual thrust stress (deformation) of the three plug welding points. This causes the crankshaft motor rotor assembly connected to the cylinder to be offset from the original center. If the rotor of the motor deviates from the center based on the stator of the motor, the air gap of the motor will be uneven. The uneven air gap of the motor will reduce the efficiency of the motor and increase the loss. Not only will the energy efficiency ratio be reduced, the start will be difficult, and the noise will be increased. The bad phenomenon will cause the compressor to fail to start normally or even burn the motor. In addition, the unqualified air gap is a failure that cannot be repaired. Once it is generated, it can only be discarded.
Not only that, the welding residual stress and deformation of the three-point plug welding will also harm other parts. It is the result of measuring the inner diameter profile of the cylinder before and after three-point plug welding. It can be clearly seen from the figure that the depression deformation generated under the thrust stress of the plug welding point, and the size of the slider groove is therefore significantly reduced.
The size of the sliding vane slot is one of the most critical assembly dimensions of the rotor compressor. Each compressor must be strictly measured and assembled in groups of several microns, which shows the importance of this size. After the width of the slider groove is narrowed under the action of welding residual stress and deformation, the slider will not be able to move normally and flexibly within the narrow gap, and leakage will occur between the high and low pressure chambers, that is, internal leakage. Generally, the energy efficiency ratio of the compressor is low, and the exhaust temperature rises, which greatly reduces the performance of the compressor: when the pressure is serious, it will cause the compressor pressure to rise, that is, a "incapable" failure, or the slider is stuck and compressed The machine can't rotate, causing "stuck" failure.
For the scroll compressor, although the welding residual stress and deformation generated by the plug welding point always exist, because the plug welding points on the plug welding parts are symmetrically distributed on the circumference, there will be no center deviation, and there will be no " The "air gap is not uniform" failure; and the plug-welded parts-the bracket and the lower bearing body also have no gaps such as sliding grooves in the structure, which will also not cause "inability" and "stuck" failures. It is especially pointed out that the cross-section of the plug welding point of the scroll compressor is oval, and the thrust stress generated mainly comes from the shrinkage of the plug welding point in the circumferential direction. The welding residual stress and deformation tend to be much smaller than that of the rotor compressor. Then analyze in detail.
The above is the law of the welding residual stress and deformation of the plug welding on the quality and performance of the compressor. Let us look at the law of the welding residual stress and deformation of the girth welding on the quality and performance of the compressor.
The upper girth welding of the compressor refers to the method of connecting the upper cover and the cylinder body by the method of C02 or MAG.
For the welding residual stress and deformation trend, see (Welding Deformation of Lap Joints under Unconstrained Conditions).
According to the deformation trend of the welding deformation process of the girth welding on the scroll compressor, combined with the previous analysis of the deformation trend of the plug welding point, it can be easily concluded that the girth welding seam will also occur under the constraint of the cylinder and the upper cover The thrust stress directed to the compressor axis is accompanied by deflation in the circumferential direction. At the same time, because the girth welds are not welded at the same time, the first welded part first produces thrust stress and deformation, which causes the center of the upper cover to shift relative to the cylinder. The final welded part is based on the center that has been shifted from the center. The welding process is completed on the top, so the residual stress and deformation hazards of the upper girth welding are mainly manifested in the center offset of the upper cover.
(Structure of the rotor compressor) It can be seen that the upper casing of the rotor compressor and the running parts of the compressor are not rigidly connected, and the residual stress and deformation generated by the above-mentioned upper girth welding will not have much effect on the performance of the rotor compressor Adverse effects. From (the structure of the scroll compressor), we can find that there are many parts in the upper casing, among which the partition is the most important. Because the diaphragm of the scroll compressor is not only interference-connected with the upper casing, but also elastically connected with the key part of the scroll compressor-the static disk (static scroll). In this way, the residual stress and deformation of the upper girth welding will be transmitted to the static plate through the partition plate, causing the center of the static plate to shift.
For scroll compressors, the dynamic and static disks are the most precise and critical parts, and the motion gap between the two is only 10 microns, see. The displacement of the center of the static plate caused by welding deformation will inevitably reduce the gap between the dynamic and static plates, causing friction and collision between the two, and increasing the running resistance of the compressor. Therefore, similar to the consequences of reducing the size of the rotor compressor vane groove, generally it will cause the compressor energy efficiency ratio to be low and the compressor noise to increase, which greatly reduces the performance of the compressor; It can't be turned, and the failure of "not starting" or even "stuck" occurs.
It can also be seen that the involute of the scroll compressor has two and a half turns, which means that the welding residual stress and deformation generated by the girth welding in any direction will have the above serious consequences. Therefore, reducing and eliminating the welding residual stress and deformation generated by the upper girth welding is very important to ensure the performance of the scroll compressor, and effective elimination and preventive measures must be taken.
4 Countermeasures to reduce welding stress and deformation According to the above analysis, it can be seen that the welding residual stress and deformation that are harmful to the compressor mainly come from the three-point plug welding of the rotor compressor and the ring welding process of the scroll compressor. According to the mechanism and law of its production, it can reduce or prevent its adverse impact on the quality and performance of the compressor. The measures in this area can be summarized as two countermeasures in the process and design.
In terms of process methods, reducing welding heat input and scientifically configuring process parameters can achieve the purpose of reducing and eliminating welding residual stress and deformation. For example, adjust the heat input of the three-point plug welding of the rotor compressor, perform multiple welding forming of the plug welding point, and strictly control the current ratio of the three plug welding points to eliminate the cylinder center deviation caused by welding residual stress and deformation. However, this has caused great difficulties in ensuring the tightness of the plug solder joints. The welding process of the compressor must not only ensure the strength of the welding spot, reduce the impact of stress and deformation, but also ensure the airtightness of the compressor; the plug welding holes of the same size should be welded with small and different welding specifications. It is bound to increase the difficulty of ensuring the tightness of the solder joint. A lot of work has been done in this area before, but the results are not very obvious. Therefore, it is the ideal solution to avoid the adverse effects of welding residual stress and deformation on the performance of the compressor from the design.
Taking the cylinder of the rotor compressor as an example, according to the previous analysis of stress and deformation, if it is designed to increase the process hole that absorbs welding deformation near the three plug welding points, the occurrence of uneven air gap can be reduced; if it is slipping Adding process holes around the chip groove to absorb stress and deformation can prevent "incapacitated" and "stuck" failures. These design ideas have been embodied in the new dual-rotor compressor and variable-frequency rotor compressor.
From the above, it can be found that the new type of cylinder fully considers the prevention of welding residual stress and deformation; from the failure rate of the production line, the failure due to welding residual stress and deformation is significantly reduced, which greatly reduces the compressor assembly lower limit rate: at the same time The energy efficiency ratio of the new rotor compressor is also a step higher than the original model.
For the residual stress and deformation of the girth welding on the scroll compressor, referring to the experience of spot welding before welding and prevention of deformation of large structural parts, the spot welding and fixing technology before girth welding (four-point pre-welding) was adopted to solve this problem. Compressor "does not start"
The problem. Specifically, it is opposite to the welding point of the girth welding, spot welding the upper cover in advance, so that it produces a deformation opposite to the girth deformation in advance, to offset the residual stress and deformation produced by the girth welding; then symmetrically in other directions Spot welding three points in order to make the upper cover and the cylinder rigidly fixed, reducing the occurrence of center deviation. After this method is used, the non-starting rate of the scroll compressor is reduced by 90%, and a significant effect is achieved. However, despite the elimination of welding residual deformation, the residual stress is still transmitted to the parts. To completely avoid the influence of welding residual stress and deformation on the dynamic and static disks, it is still necessary to consider from the design.
In terms of design, if the rigid (or elastic) connected components such as dynamic and static plates and baffles are assembled as a whole without contacting the welding base metal (such as the cylinder or the upper cover), the residual stress and the upper girth welding can be avoided Deformation is transferred to key components. In this regard, you can refer to the structural design of other manufacturers. For example, the 500DH-80C1 scroll compressor of Wanbao Compressor Co., Ltd. is not designed with large parts in the upper casing, so the girth deformation is almost not transmitted to the dynamic and static disks; and the ZR series 30 produced by Copeland > K3 series compressors adopt another method, that is, the upper and outer parts and the cylinder are first embedded in the groove of the separator, and then welded, that is, the rigidity of the separator is used to limit the deformation of the girth welding, etc. These are avoided by design. The method of transferring welding deformation to the scroll disk is worthy of our reference.
5 Conclusion In summary, the welding residual stress and deformation are produced regularly. After careful research and production practice, according to the respective structural characteristics of different types of compressors, you can take appropriate measures to target the quality of the products. And the adverse effects of performance are reduced to a minimum. Choosing reasonable welding process parameters and strict control can achieve this goal, but it has not avoided welding residual stress and deformation transmission to the key components of the compressor. The best way to solve this problem still comes from improving the design of the product. It is essential to avoid welding residual stress and deformation from affecting the quality and performance of the compressor. This requires that we must continue to carefully analyze and study various faults, find out their laws, and convert these results into new product design ideas to achieve the effect of preventing accidents.
A pet Strap Dog Harnessis is equipment consisting of straps of webbing that loop nearly around-that fasten together using side release buckles-the torso of an animal.
These strap dog harnesses generally are made to have both a strap on the chest in front of the forelimbs, and a strap around the torso behind the forelimbs, with straps in between connecting these two. Having a D-ring suitable for (pet tags and) a leash to clip to, they are most often used to restrain an animal, but dogs also particularly wear them to assist a person with a disability or haul people and items. There is also the lifting harness for dogs with disabilities, covered in this article.
Some come in different sizes, although many are size-adjustable with tri-glide slides to loosen or shorten the straps` length. The straps may come in a range of different colors, and some have reflective coating.
Strap Harness,Reflective Dog Harness,Premium Dog Harness,Top Product Dog Harness
Yangzhou Pet's Products CO.,LTD , https://www.yzpets.cn