One of the leading places among diseases caused by viruses of the family Herpesviridae, is occupied by cytomegalovirus infection (CMVI), an increase in the prevalence of which is currently observed in all countries of the world. Over the past decade, the list of diseases, one of the causes of which is also cytomegalovirus (CMV), has expanded significantly. The concept of CMV infection covers the problems of intrauterine infection, seronegative mononucleosis, hepatitis, gastrointestinal diseases, post-transfusion syndrome, organ and tissue transplantation, oncogenesis, HIV infection, since CMV infection is defined by WHO experts as an AIDS indicator disease. The most successful definition of this disease seems to be: “Cytomegalovirus infection is a widespread viral disease mainly in children early age, characterized by a wide variety of clinical manifestations and a standard two-component morphological picture, including peculiar owl-eye-like cytomegalic cells and lymphohistiocytic infiltrates.”
Etiology
CMV was first described in 1881 by the German pathologist M. Ribbert, who discovered cytomegalic cells (CMC) in kidney tissue in congenital syphilis. E. Goodpasture and F. Talbot in 1921 proposed the name “infantile cytomegaly,” which is still used today. CMV was isolated from cell culture by M. Smith in 1956.
The diameter of CMV virions is 120-150 nm. The virion is covered with a glycoproteinolipid envelope. The CMV virus has the shape of an ixahedron, the protein shell of which (capsid) consists of 162 symmetrically arranged capsomers. The CMV genome is represented by double-stranded DNA. CMV is thermolabile, inactivated at a temperature of +56°C, its optimal pH is 7.2-8.0. Currently, three strains of CMV have been isolated: Davis, AD 169, Kerr.
Epidemiology
The only reservoir of CMV in nature is humans. The virus is released from an infected body in urine, saliva and tear fluid. Transmission factors for CMV can be maternal blood, cervical and vaginal secretions, breast milk and sperm. The prevalence of CMV depends on the socio-economic and hygienic living conditions of people. Screening studies using enzyme-linked immunosorbent assay (ELISA) revealed antibodies to CMV in 33% of children under 2 years of age and in 50% of adults in countries with high level life. In developing countries, 69% of children and 100% of adults have specific antibodies.
The main source of infection in children are mothers who are carriers of CMV. Intrauterine infection of the fetus can occur at any stage of antenatal development. Transplacental hematogenous infection of the fetus is facilitated by reactivation of CMV infection in pregnant women and insufficient barrier function of the placenta. The risk of infection penetrating the placental barrier increases with prolonged viremia and the chronic nature of the infection. In cervical secretions, CMV is detected in the first trimester of pregnancy in 2% of women, in the second - in 7%, in the third - in 12%. The fetus can aspirate CMV-infected amniotic fluid; damage to the external integument of the fetus can also serve as an entry point for CMV. 5% of newborns are infected intranatally. Infection of the fetus in the early stages of intrauterine development poses the greatest danger and is often accompanied by spontaneous abortion or disorders of organ and histogenesis. In those infected with CMV, more late dates after birth, cytomegaly syndrome, transient jaundice, and hepatosplenomegaly are observed. Subsequently, from 10 to 30% of such children suffer from brain damage, expressed in microcephaly with ventricular calcification, atrophy of the auditory nerve and mental retardation.
Infants can become infected through breastfeeding milk. However, with mother's milk, the child receives secretory IgA, which does not penetrate the placenta and is not produced in the child in the first months of postnatal life. Secretory IgA increases the newborn's resistance to viral and bacterial infections, so children infected through breast milk suffer only from the latent form of CMV.
If there is close contact between mother and child, saliva can become a factor in transmitting the virus to the child. There is evidence that half of children under 3 years of age attending kindergartens are infected with CMV from their peers and then infect their mothers.
The source of CMV for adults and children can be the urine of a patient or a virus carrier.
A common route of infection is sexual, since the virus is contained in sperm in high concentrations for a long time.
There is also an airborne route of infection. In patients with a severe form of acute respiratory viral infection, which is often caused by CMV, cytomegalovirus is detected in nasopharyngeal swabs.
Blood transfusions, infusion therapy, and organ and tissue transplantation are also dangerous, since biological drugs or tissue from CMV-infected donors are often introduced into the recipient’s body. There is a lot of information in the literature about infection of recipients after these manipulations. The use of immunosuppressants and cytostatics in patients after organ transplantation not only promotes the reactivation of previously acquired latent infection, but also increases their susceptibility to primary CMV infection.
The presence of antigenically different strains of CMV explains the possibility of reinfection with the development of the manifest form of the disease at any age.
Pathogenesis
CMV has a pronounced tropism for the tissues of the salivary glands. In the latent form of the virus, the virus is detected only in the epithelium of the salivary tubes, which is why sometimes CMV is rightly called the “kissing disease.”
CMV causes significant dysregulation of the immune response, which is based on damage to the interleukin system. As a rule, the ability of infected immunocompetent cells to synthesize interleukins is suppressed due to excessive production of prostaglandins, and the responses of target cells to IL-1 and IL-2 are also changed. Virus-induced immunosuppression develops with a sharp inhibition of natural killer cell function.
Once CMV enters the blood, it reproduces in leukocytes and the mononuclear phagocyte system or persists in lymphoid organs. CMV virions are adsorbed on cell membranes, penetrate the cytoplasm and induce cytomegalic cell metamorphosis. Viral RNA is detected in T-helper and T-suppressor cells even in long-term periods of convalescence.
Pathanatomy
A characteristic pathomorphological sign of CMV is giant cells detected in tissues, saliva, sputum, urine sediment and cerebrospinal fluid. The cells have intranuclear and cytoplasmic inclusions and contain a multiplying virus. Changes in the nucleus of the cell give it a resemblance to an owl's eye. Giant cells are localized primarily in the epithelium of the excretory ducts of the salivary glands, in the epithelium of the distal parts of the nephron in the kidneys, in the epithelium of the bile ducts in the liver, and in the epithelium of the ependyma of the ventricles of the brain.
In response to the effects of CMV, lymphohistiocytic infiltrates appear in the surrounding interstitial tissue, sometimes having the character of nodules. In the generalized form, damage to the lungs, kidneys and intestines is more common, and less often to the liver and other organs. Along with giant cells and lymphohistiocytic infiltrates, a picture of interstitial pneumonia is found in the lungs, interstitial nephritis in the kidneys, ulcerative enterocolitis in the intestines, and cholestatic hepatitis in the liver.
Congenital generalized CMV infection is also characterized by hemorrhagic rashes on the skin and mucous membranes, hemorrhages in internal organs and the brain, significant anemia, and the development of foci of myelo-erythroblastosis in the liver, spleen and kidneys. Eye damage is also noted - uveitis, clouding of the lens and subatrophy of the iris.
Classification of CMVI (A.P. Kazantsev, N.I. Popova, 1980):
- congenital CMV infection - acute form, chronic form;
- acquired CMV - latent form, acute mononucleosis-like form, generalized form.
Clinic for CMVI in children
Acute form of congenital CMV. The clinical picture of the acute form of CMV infection is characterized by the most severe course with pronounced signs of toxicosis, enlarged liver and spleen, thrombocytopenia, hemorrhagic syndrome, changes in the blood count and damage to the central nervous system. This form of the disease is often called fetal cytomegalovirus syndrome. Children are born prematurely, with low body weight, reflexes are depressed, and sometimes there are disorders of the acts of sucking and swallowing. In 60% of cases, jaundice occurs, possible causes of which may be CMV hepatitis or increased hemolysis of red blood cells. Jaundice resembles physiological jaundice, but the intensity of the disease gradually increases, and it persists for 1-2 months. In 90% of children, the liver is enlarged and protrudes 3-5 cm below the edge of the costal arch. The spleen is enlarged in 42% of cases, it is dense and painless. In the blood of 70% of children there is thrombocytopenia, increased bilirubin content, as well as an increase in the activity of transaminases - up to 150 IU / l and alkaline phosphatase - up to 28 IU.
The acute form of CMV occurs under the guise of hemolytic disease of the newborn. Gastrointestinal lesions are also common; dyspeptic syndrome and progressive dystrophy predominate.
In the acute form of congenital CMV, the death of children occurs in the first weeks or months of life, most often from associated bacterial infections.
Chronic form of congenital CMV. Children who have had an acute form of the disease experience an undulating course of the chronic form of CMV infection. Congenital malformations of the central nervous system often form, in particular microcephaly - in 40% of cases. Chronic hepatitis may develop, in rare cases turning into cirrhosis. Changes in the lungs in 25% of children are characterized by the development of pneumosclerosis and fibrosis.
Differential diagnosis of congenital CMV infection is carried out with rubella, listeriosis, toxoplasmosis, as well as hemolytic disease of newborns, congenital syphilis and sepsis.
Latent form of acquired CMV infection. The latent form does not manifest itself clinically and is detected only during a virological examination.
Acute mononucleosis-like form of acquired CMV infection. The acute form, in clinical manifestations in older children, resembles infectious mononucleosis and often occurs after blood transfusions. The disease is characterized by an acute onset with a rise in temperature and the appearance of symptoms of intoxication. Lymphadenopathy, pain on palpation of the parotid region, symptoms of acute respiratory infections, and hepatomegaly are recorded. Characterized by leukocytosis, an increase in the number of neutrophilic granulocytes and atypical mononuclear cells. It is recommended to perform the Paul-Bunnel and Hoff-Bauer reactions, which are positive in the case of infectious mononucleosis and negative in the case of cytomegalovirus mononucleosis-like syndrome.
Generalized form of acquired CMV infection. The generalized form is characterized by lymphadenopathy, intoxication, and increased body temperature. The earliest symptoms of respiratory damage are detected: a dry, painful cough, mixed shortness of breath. Auscultation reveals dry and moist rales in the lungs. Developing pneumonia is characterized by a protracted course, which determines the severity of the underlying disease. Due to the layering of bacterial and fungal infections, it can be difficult to distinguish the symptoms of generalized CMV infection.
CMV often occurs in association with other diseases of viral or bacterial etiology. The combination of CMV and ARVI is especially common, in which cytomegalovirus is isolated in 30% of sick children. This type of flu occurs in a more severe form and promotes the activation of CMV infection by suppressing immune reactions.
CMV clinic in adults
CMV infection in adults occurs in latent (localized) and generalized forms. The latent form usually does not manifest itself with clear clinical symptoms. Sometimes mild flu-like illnesses and vague low-grade fever are observed. Diagnosis of this form of CMV is based on the results of laboratory tests.
The generalized form of acquired CMV infection in adults is rarely observed. As a rule, its clinical signs are detected against the background of some other disease that sharply reduces immunity: after severe surgical operations, against the background of leukemia or neoplasms. In these cases, the use of various immunosuppressants in the treatment of patients is of pathogenetic importance. Generalized CMV in adults is manifested by sluggish pneumonia or a peculiar acute infectious disease characterized by fever, enlarged and painful liver, an increase in the number of mononuclear cells in the blood (mononucleosis caused by CMV), and damage to the gastrointestinal tract. Lymphadenopathy and tonsillitis are absent.
Diagnosing the disease is difficult. In women, latent CMV infection can be suspected with repeated miscarriages and stillbirths. The diagnosis is based on data from cytological and virological studies.
Liver pathology occupies a special place in CMV disease. Cytomegalovirus hepatitis, developing in response to the introduction of CMV, is characterized by degeneration of the epithelium of the biliary tract and hepatocytes, stellate endothelial cells and vascular endothelium. They form cytomegalic cells, surrounded by inflammatory mononuclear infiltrates. The combination of these changes leads to intrahepatic cholestasis. Cytomegalic cells desquamate and fill the lumens of the bile ducts, causing the mechanical component of jaundice. At the same time, degenerated CMV hepatocytes are destructively altered, up to necrosis, which causes the development of cytolysis syndrome. It should be noted that in CMV hepatitis, which has a prolonged, subacute or chronic course, the leading role belongs to cholestasis syndrome.
In the diagnosis of CMV hepatitis, the results of a puncture biopsy of the liver are of great importance (detection in the puncture of giant, 25-40 μm in diameter, cytomegalic cells in the form of an owl's eye with a huge nucleus and a narrow border of cytoplasm), as well as cytological (detection of cytomegalic cells in the urine sediment) and serological (detection of IgM antibodies to CMV) methods. Differential diagnosis of CMV hepatitis is carried out with other viral hepatitis: B, Epstein-Barr, herpetic hepatitis.
With CMV, the salivary glands are usually affected. Mononuclear infiltrates are found in them. Sialadenitis is chronic. Simultaneously with damage to the salivary glands, degeneration of the epithelium of the stomach and intestines is observed with the development of erosions and ulcers and lymphohistiocytic infiltrates in the thickness of the intestinal wall.
Damage to the lymph nodes is characteristic of CMV infection. At the same time, all the typical signs of this infection remain. It is the pathology of the lymphatic system that aggravates the organ and systemic manifestations of CMV infection.
Damage to the respiratory system with CMV infection is characterized by the development of interstitial pneumonia, bronchitis, and bronchiolitis. In this case, the epithelium of the alveoli, bronchi, bronchioles and surrounding lymph nodes undergoes specific changes. Infiltrates of mononuclear cells, macrophages and plasma cells are formed in the peribronchial tissue. CMV pneumonia often occurs with a staphylococcal layer, accompanied by purulent bronchiolitis and abscess formation. The presence of CMV is confirmed by the detection of cytomegalic cells. Often CMV pneumonia is combined with pneumocystis with an extremely severe course of the disease.
Kidney damage with CMV infection is also common. In this case, the cells of the epithelium of the convoluted tubules, the epithelium of the glomerular capsules, as well as the ureters and bladder undergo specific (“giant cell”) changes. This explains the detection of cytomegalic cells in urine sediment.
Damage to the central nervous system in adults is rare and occurs in the form of subacute encephalitis.
Eye lesions with CMV infection are characterized by the development of chorioretinitis. Chorioretinitis is very often combined with CMV encephalitis.
Laboratory diagnostics
Currently, there are several reliable methods for determining CMV.
- Traditional isolation of the virus on a culture of embryonic fibroblasts and a culture of human diploid cells in which CMV exhibits its cytopathic effect. The method is the most reliable and sensitive (determination period is 2-3 weeks).
- An accelerated method of culturing the virus for 6 hours using monoclonal antibodies to indicate early antigens.
- The method of cytoscopy of sediments of urine and saliva, as well as light and electron microscopy of histological preparations, in particular liver biopsy, allows identifying giant CMV cells in the form of an owl's eye, with a narrow border of cytoplasm and a large nucleus.
Various methods are used to detect antibodies to CMV.
- Complement fixation reaction (CFR). The most common way to study specific humoral immunity in CMV infection. The method is not sensitive enough, since only total antibodies are detected. RSC with a titer of 1:4 is negative, 1:8 is weakly positive, 1:16 is positive, 1:32 is strongly positive.
- Immunofluorescence analysis. Determines an increase in the titer of Ig antibodies of classes M and G to CMV. This method is more sensitive compared to RSC.
- Enzyme immunosorbent (peroxidase) analysis.
- Solid-phase radioimmunoassay. It also allows you to determine Ig classes M and G.
- Immunoblotting. Using polyacrylamide gel electrophoresis, he evaluates antibodies to CMV of various classes. This is the most modern method specific diagnostics, it can be used to determine the entire spectrum of antibodies to CMV.
Treatment
There is no reliable antiviral therapy for CMV infection yet. In particular, this is due to the fact that CMV uses the metabolic apparatus of the host cell for its own reproduction. Treatment tactics for patients should take into account the possibility of primary, latent stages and recurrent diseases. For congenital CMV infection, complex pathogenetic treatment is carried out, depending on the severity of certain clinical manifestations. For jaundice and liver damage, follow general principles therapy for viral hepatitis. For pneumonia, which is often of a mixed viral-bacterial nature, antibiotics are prescribed as usual. A number of drugs with varying activity against CMV have been proposed in our country and abroad. These are ribavirin (Virazol, Rebetol), acyclovir (Lovir, Ciclovir, Zovirax, Herperax), interferon (Viferon, Interal, Infagel), etc. The principle of their action is that they prevent the inclusion of nucleotides in synthesized viral DNA.
Two purine nucleosides, cytarabine and vidarabine, are also effective inhibitors of viral DNA replication. They completely inhibit viral DNA polymerase and are also included in cellular and viral DNA. Because these drugs are nonspecific, they have some cytotoxicity.
The action of Zovirax is more specific. Zovirax is low-toxic and easily penetrates virus-infected cells. It is more effective in the treatment of CMV infection than cytarabine and vidarabine.
With the acquired latent form of CMV in pregnant women, the main task is to prevent the generalization of infection and intrauterine infection of the fetus. For this purpose, desensitizing and restorative therapy is carried out, vitamins are prescribed (adaptovit, aquadetrim, alvitil, alphaVIT, benfogamma, biovital, vikasol, vitabalance 2000, vitrum prenatal, gendevit, geriavit, gerimax, dodex, doppelgerz vitamin E, complivit, macrovit, nicodin, revivona, tocopher-200, triovit, cebion, evitol, enduracin). Normal human immunoglobulin containing specific antibodies against CMV is used as a specific agent. The drug is administered intramuscularly in 6-12 ml doses at intervals of 2-3 weeks in the first trimester of pregnancy. Levamisole (Decaris, Levamisole) is prescribed 50 mg twice a day after meals for 3 months. If there is no effect, switch to T-activin 100 mcg subcutaneously 2 times a week. The number of stillbirths with this treatment tactic is reduced by 5 times.
Patients with a transplanted heart have had positive experience in treating CMV infection with ganciclovir at a dose of 1 mg/kg/day for 2-3 weeks. In addition, ganciclovir (Cemeven) is effective in 70-90% of HIV patients treated for CMV retinitis and colitis. The initial dose of the drug was 5 mg/kg 2 times a day intravenously for 2-3 weeks, the maintenance dose was 5 mg/kg/day intravenously. Neutropenia, a major toxic effect, can be reduced by the use of colony-stimulating factors. In bone marrow recipients, the use of ganciclovir and CMV immune globulin resulted in a positive result in 50-70% of patients with CMV pneumonitis.
For varieties of CMV resistant to ganciclovir, foscarnet (foscarnet sodium, gefin) is effective (in the treatment of patients with CMV retinitis due to HIV infection). The initial dose of foscarnet is 60 mg/kg every 8 hours for 2-3 weeks, then it is administered infusionally at a dose of 90-120 mg/kg every day. In patients after bone marrow transplantation, foscarnet is used at an average daily dose of 100 mg/kg for 3 weeks. In 70% of patients, recovery from CMV infection was observed, the temperature normalized, and laboratory parameters improved.
Currently, new promising chemotherapy drugs against CMV are being developed and tested.
With congenital CMV with damage to the central nervous system, the prognosis is unfavorable, while with acquired generalized CMV it is determined by the underlying disease. With the latent form of acquired CMV, the prognosis is favorable.
Prevention
It is necessary to exclude contact between pregnant women and children with congenital CMV infection. If a woman gives birth to a child with congenital CMV, the next pregnancy may be recommended no earlier than 2 years later (the period of virus persistence for localized acquired CMV).
Currently, an active search for vaccines against CMV is underway. Live vaccines have already been created in the USA and Great Britain, which are currently undergoing clinical trials.
It is important to remember that CMV infection requires doctors to be knowledgeable in a variety of areas of medicine and creative search for the effective use of proven methods of diagnosis, treatment and prevention. Early detection of CMV infection helps to increase the effectiveness of care for this category of patients, as well as timely recognition of cases of HIV infection and AIDS. n
Literature
- . Rakhmanova A. G., Isakov V. A., Chaika N. A. Cytomegalovirus infection and AIDS. - L.: Research Institute of Epidemiology and Microbiology named after. Pasteur, 1990.
- Demidova S. A., Semenova E. I., Zhdanov V. M., Gavrilov V. I. Human cytomegalovirus infection. - M.: Medicine, 1976.
- Farber N.A. Cytomegalovirus infection in clinical medicine // Ter. Archive, 1989. - No. 11.
- Farber N. A. Cytomegalovirus infection and pregnancy // Obstetrics and gynecology. - 1989. - No. 12.
- Samokhin P. A. Cytomegalovirus infection in children. - M.: Medicine, 1987.
- Kazantsev A.P., Popova N.I. Intrauterine infectious diseases and their prevention. - L.: Medicine, 1980.
- Report of the WHO scientific group “Immunological deficiency”. - M.: Medicine, 1980.
- Kozlova S. I., Semanova E., Demikova N. S., Blinnikova O. E. Hereditary syndromes and medical genetic counseling. - L.: Medicine, 1987.
- Harrison J. Guide to internal medicine: In 10 volumes - 1998. - Vol. 5.
- Lawlor Jr. G., Fisher T., Adelman D. Clinical immunology and allergology. - M.: Praktika, 2000.
V. V. Skvortsov,Candidate of Medical Sciences
R. G. Myazin
D. N. Emelyanov, Candidate of Medical Sciences
Volgograd State Medical University, Volgograd
IntroductionWelding equipment and technology occupy one of the leading places in modern production. The hulls of giant supertankers and the retina are welded together human eye, miniature parts of semiconductor devices and human bones during surgical operations. Many designs of modern machines and structures, for example space rockets, submarines, gas and oil pipelines, it is impossible to manufacture without welding. The development of technology places new demands on production methods and, in particular, on welding technology. Today, materials are welded that until relatively recently were considered exotic. These are titanium, niobium and beryllium alloys, molybdenum, tungsten, high-strength composite materials, ceramics, as well as all kinds of combinations of dissimilar materials. Electronic parts several microns thick and heavy equipment parts several meters thick are welded. The conditions in which welding work is carried out are constantly becoming more complicated: welding has to be done under water, at high temperatures, in a deep vacuum, with increased radiation, in zero gravity.
All this places increased demands on the qualifications of specialists in the field of welding, especially welding workers, since they are the ones who directly master new methods and techniques of welding, new welding machines. Today, it is not enough for a working welder to be able to perform several, even complex, operations of the welding method he has mastered. He must understand the physical essence of the main processes occurring during welding, know the features of welding of various structural materials, as well as the meaning and technological capabilities of other, both traditional and new, promising welding methods.
Product Description
The intended product is intended for use as a support for the installation and installation of load-bearing columns in the construction of industrial buildings.
The support is a welded box-type structure.
platform
30
shell
spacer
edge
640
Fig.1. Product design
All parts of this design are made of steel grade 09G2S.
Steel 09G2S belongs to low-carbon, low-alloy steels.
Steels of this class have good weldability with all types of arc welding and are widely used for the manufacture of welded structures used in the construction industry.
Table 1
Chemical composition of steel 09G2S
table 2
Mechanical properties of steel 09G2S
| Rolled thickness, mm | Tensile strength σ V, MPa | Yield strength σ T, MPa | Relative elongation δ5,% | Impact strength KSU, J/cm², at temperature, |
||
| +20 | -40 | -70 |
||||
| 10-20 | 470 | 325 | 21 | 59 | 29 |
|
Welded structures used as load-bearing elements during the construction of buildings and structures belong to group II of responsibility, since their destruction during operation can lead to large material costs.
Responsibility group II requires increased attention to the quality of work performed in total production cycle(from material procurement to the scope of final product control).
Taking into account the design features of the product, the material of the incoming parts, as well as the annual production program (2000 pieces), the most optimal manufacturing method will be semi-automatic welding in a carbon dioxide environment.
Welding method
Gas shielded welding is one of the arc welding methods. With this method, shielding gas is supplied to the arc zone, the stream of which, flowing around the electric arc and the weld pool, protects the molten metal from exposure to atmospheric air, oxidation and nitriding. Welding in shielding gases has the following advantages: high productivity (2...3 times higher than conventional arc welding), the ability to weld in any spatial position, good protection of the welding zone from oxygen and nitrogen of the atmosphere, no need to clean the seam from slag and strip the seam for multilayer welding; small heat affected zone; relatively small deformations of products; the ability to monitor the seam formation process; availability of mechanization and automation. The disadvantages of this welding method are the need to take measures to prevent the blowing off of the shielding gas jet during the welding process, the use of gas equipment, and in some cases the use of relatively expensive shielding gases.
The following types of welding in shielding gas are known: in inert monoatomic gases (argon, helium), in neutral diatomic gases (nitrogen, hydrogen), in carbon dioxide. In practice, argon arc welding and carbon dioxide welding are most widely used. The inert gas helium is used very rarely due to its high cost. For welding critical structures, welding in a mixture of argon and carbon dioxide gases in a ratio of 85% argon and 15% CO 2 is widely used. The quality of this steel welding is very high. The arc is powered by direct current sources with a rigid characteristic. In recent years, welded rectifiers of the VDU series with universal external characteristic, i.e. hard, or steeply falling by simply switching the packet.
Alternating current is not used due to the low stability of the arc burning process, poor formation and poor quality of the weld. The arc voltage when welding in CO2 should be no more than 30 V, since spatter and oxidation increase with increasing voltage and arc length. Typically, the arc voltage is 22-28 V, the welding speed is 20-80 m/h, the gas flow is 7-20 l/min. Welding in CO2 with wire gives deeper penetration than electrodes, therefore, when switching from manual welding, it is considered justified to reduce the legs by about 10%. This is explained by the increased current density per 1 mm 2 of electrode wire. The main elements of the welding mode in CO 2 are in Table 1.
Table 3
Typical parameters of welding mode in C0 2
| Wire diameter, m | Welding current, A | Speed wire feeding | Arc voltage, V | Consumption l/min | Wire extension, mm |
| 0,8 | 50-110 | installed selection for the mode | 18-20 | 5-7 | 6-12 |
| 1,0 | 70-150 | 19-21 | 7-9 | 7-13 |
|
| 1,2 | 90-230 | 21-25 | 12-15 | 8-15 |
|
| 1,6 | 150-300 | 23-28 | 12-17 | 13-20 |
Welding in carbon dioxide is carried out in almost all spatial positions, which is very important during construction and installation work. Welding is carried out by feeding the arc with direct current of reverse polarity. When welding with direct current of straight polarity, the stability of the arc decreases, the formation of the seam worsens and losses increase electrode metal for fumes and splashing. However, the deposition rate is 1.6...1.8 times higher than with reverse polarity. This quality is used in surfacing operations. Sheet material from carbon and low-alloy steels is successfully welded in carbon dioxide; sheets with a thickness of 0.6... 1.0 mm are welded with flanged edges. Welding without flanging is also allowed, but with a gap between the edges of no more than 0.3...0.5 mm. Sheets with a thickness of 1.0...8.0 mm are welded without cutting edges; in this case, the gap between the welded edges should be no more than 1 mm. Sheets with a thickness of 8... 12 mm are welded with a V-shaped seam, and for larger thicknesses - with an X-shaped seam. Before welding, the edges of the product must be thoroughly cleaned of dirt, paint, oxides and scale. Welding current and welding speed largely depend on the size of the groove being welded, i.e., on the amount of deposited metal. The voltage is set so as to obtain a stable welding process with the shortest possible arc (1.5...4.0 mm). With a longer arc length, the welding process is unstable, metal spatter increases, and the possibility of oxidation and nitriding of the deposited metal increases.
Rice. 2. Movement of the electrode during welding in carbon dioxide when performing a multi-layer seam
The figure shows the movements of the electrode during welding in carbon dioxide when making a multi-layer weld. To reduce the risk of cracking, it is recommended to weld the first layer at low welding current. The seam should be completed by filling the crater with metal. Then the supply of the electrode wire stops and the current is turned off. The supply of gas to the welded crater continues until the metal has completely solidified.
Part of the equipment
The composition of the technological equipment necessary to perform welding work during mechanized arc welding in shielding gases includes:
power supply;
assembly and welding devices;
gas equipment;
gas main devices;
welding machine (semi-automatic).
3.1 Power supply
Power supply
(IP) of a welding arc is a device that provides the necessary type and strength of the arc current.
The power source and the welding arc form an interconnected energy system in which the power supply performs the following main functions: it provides the conditions for the initial excitation (ignition) of the arc, its stable combustion during the welding process and the ability to configure (regulate) the mode parameters.
An important technical characteristic of the IP, which determines the possibility of its operation with one or another type of arc, is the dependence of the voltage at the “welding” clamps (terminals) of the IP on the welding current. This dependence is called the external current-voltage characteristic (volt-ampere characteristic) of the IP. The most characteristic current-voltage characteristics for known IPs: steeply dipping, gently dipping and rigid .
Based on the type of current in the welding circuit, there are:
alternating current sources - single-phase and three-phase welding transformers, specialized installations for welding aluminum alloys;
DC sources - welding rectifiers and generators with drives of various types.
IN in this case We use a modern, powerful 400-amp inverter power supply for semi-automatic welding and surfacing in shielding or active gases of the DC 400.33 brand.
This IP has:
Remote control of welding voltage.
Digital indicator of welding current and voltage.
Function >.
Power supply from both a stationary network and a diesel generator.
Table 4
Technical characteristics of the DC 400.33 inverter
| Supply voltage, V | 3 80,+10% -15 % |
| | 20 |
| Source voltage (pressure-regulated), V | 16-36 |
| Welding current (smoothly adjustable), A | _ |
| Nominal operating mode PN, % (at +40 C) | 60 |
| Maximum current at PN = 100%, A | 300 |
| Operating temperature range, C | From - 40 to + 40 |
| Weight, kg | 44 |
| Overall dimensions, mm | 610x280x535 |
For IP brand DC 400.33, we selected a feed mechanism of brand PM-4.33. It is designed for solid steel, aluminum and flux-cored wire from 0.6 to 2.4 mm when working with the device DS400.33, DS400.33UKP or any other source with a current-voltage characteristic.
This PM has:
Version with “open” and “closed coil”
Digital display of wire feed speed, welding current and voltage
Smooth adjustment of welding wire feed speed and arc voltage
Digital setting of all welding parameters
smooth ignition of the arc, thanks to the setting of the wire retardation at the beginning of welding
setting the blowing time at the beginning of welding and gas blowing after its completion
smooth extinguishing of the arc, thanks to the setting of the wire slowdown at the end of welding
Four-roller wire feeder from COOPTIM Ltd. (roller profile depends on the diameter and type of welding wire)
Gearing of feed and pressure rollers
Adjustable clamping force
Can be used at a distance of up to 50m from the welding source
Shielding gas cut-off device
"Gas test" and "wire test" on the front panel
Remote control of wire feed speed
Table 5
Technical characteristics of PM-4.33
| Supply voltage, V | ~36V |
| Power consumption, kVA, no more | 0,2 |
| Wire feed speed, m/sec | 1-17 |
| Wire diameter, mm |
|
| -Solid | 0.6-1.6 |
| - Aluminum | 1.0-2.4 |
| - Powder | 0.9-2.4 |
| Operating temperature range, °C | -40 to +40 |
| Weight, kg | 14 |
| Overall dimensions, mm | 580x202x423 |
On the afternoon of May 24, 2012, His Beatitude Archbishop Jerome of Athens and All Greece took part in the official opening ceremony of the Day of Slavic Literature and Culture in Moscow.
Your Holiness, Patriarch of Moscow and All Rus' and beloved brother in Christ Kirill, Eminence archpastors, respected representatives of the authorities, venerable fathers, beloved Christians!
It is with deep emotion and gratitude that I am called to remember the greatness Slavic culture, reviving in his memory the bountiful harvest that the vineyard of Saints Cyril and Methodius produced in these blessed lands. It was here that Archpastor Christ placed them to confess the faith and teach people. The result of their teachings was a multifaceted culture, in every manifestation connected with the faith of our Church.
Being on this sacred land of glorious Russia, I reflect on and admire its long and very diverse tradition, its history. I admire her art, sporting achievements and culture: literature, philosophy, classical music, folk and classical dances, architecture, painting, cinema, serious developments in the field of technology and space science, but above all, church art and tradition as they were formed and found expression in music, icon painting and church chants.
The centuries-old path of Russian culture was outlined and determined by our common Byzantine roots, the development of Western philosophy and, to a large extent, two centuries of cultural flourishing, starting with the era of Peter the Great.
Today Russian cultural heritage occupies one of the highest positions in the world, spreading its spiritual influence everywhere. Numerous talented Russian artists and scientists have made enormous contributions to the field of culture, decisively contributing to the significant increase in modern scientific achievements in medicine, genetics, biotechnology, space science and many other fields.
Russian literature is one of the richest and most beloved in the whole world. Its strong foundations were laid in the 10th century, and in the 18th century it received significant impetus thanks to the works of such prominent literary figures as M.V. Lomonosov and D.I. Fonvizin. The 19th century gave us writers whose names are inscribed in golden letters in the fund of world literature. This is A.S. Pushkin, who is considered the Russian Shakespeare, M.Yu. Lermontov and A.P. Chekhov, considered fathers literary drama, L.N. Tolstoy, F.M. Dostoevsky, N.S. Leskov and many others. In particular, Tolstoy and Dostoevsky were such outstanding personalities that literary critics all over the world they are unanimously considered to be greatest writers of all times. This tradition was continued in subsequent years by the great writers I.A. Bunin, V.V. Khabokov, I.E. Babel, Yu.K. Olesha and many others who do your country a great honor.
Russian philosophy also had a decisive influence on the world community. Its heyday, which occurred in the 19th century, brought such great names as N.Ya. Danilevsky and K.N. Leontyev. Russian philosophy is distinguished by a deep connection with literature and a spirit of revival in the world of politics, arts and science. It should be noted the large figures of N.A. Berdyaev and V.N. Lossky.
I must also mention Russian architecture with its majestic buildings, both from the period of the influence of Byzantine architecture, and from the subsequent period when it followed in its own unique direction. The 16th century gave us the excellent St. Basil's Cathedral; The 17th century, which coincided with the heyday of the Baroque style and the reforms of Peter the Great, led to the development of the so-called “flaming” Baroque; The 18th century, the Rococo century, the era of Catherine the Second and her grandson Alexander the First, turned the city of St. Petersburg into an open-air museum of neoclassical architecture.
Here are some of the typical examples of buildings - works of art: St. Sophia of Novgorod, Golden Gate in Vladimir, Cathedral of Christ the Savior, Annunciation Cathedral, Archangel Cathedral, St. Basil's Cathedral, Kazan Cathedral, Grand Kremlin Palace, Simonov and Novodevichy Monasteries, Lenin's Mausoleum, The White house and many others.
Classical painting has influenced the entire world, giving us works of historical significance. Creativity of masters I.I. Shishkina, V.D. Polenova, B.M. Kustodiev and others who belonged to the school of realistic painting, determined the direction and set the boundaries in the development of this art.
It would take me more than one hour to talk about the valuable contribution of Russian icon painters, such as Andrei Rublev and many others, who represent vivid examples development Byzantine icon painting. They laid the foundation for entire schools and directions based on the manner of their writing, which is proof of the fruit of the spirit of Philokalia and Orthodox spirituality that adorns your people.
Russian classical music has made its way around the world. She continues to touch us all to this day. Timeless, it is capable of strengthening and ennobling the spirit. I consider it my duty to cite several great names, such as M.I. Glinka, M.P. Mussorgsky, P.I. Tchaikovsky, N.I. Rimsky-Korsakov and S.V. Rachmaninov.
In conclusion short speech dedicated to the world-famous culture of your beautiful country, I would like to talk about the great scientific discoveries that you gave to the world, thereby changing our lives forever. DI. Mendeleev discovered the periodic system of chemical elements, which is the basis of modern chemistry. P.N. Yablochkov and A.N. Lodygin - pioneers in the field of electrical engineering, invented the first electric light bulb. A.S. Popov is one of the inventors of radio. N.G. Basov and A.M. Prokhorov jointly invented the laser. K.E. Tsiolkovsky is the father of theoretical cosmonautics. His works inspired outstanding rocket engineers S.P. Koroleva, V.P. Glushko and many others who contributed successful development Soviet space program in its early stages. In 1957, you were the first to launch an artificial satellite into orbit. On April 12, 1961, Yuri Gagarin successfully completed the first manned flight into space.
The list of your country's achievements cannot be contained in a few lines. I have tried only to describe with praise the fate of your culture and in these few words to express to you our common gratitude for everything you have done for us, and also to inform you that we expect much more from you as a natural continuation and development of your illustrious people for the glory of God .
Patriarchy.ru
Technology has revolutionized the world as rationalization in decision complex tasks quickly broke down barriers between developed and developing cities. Today we will talk about the most technologically advanced cities in the world based on the Pricewaterhouse Coopers Cities of Opportunity 6 Report ranking.
25. Jakarta
Indonesia's capital of 10 million people is the most populous city in Southeast Asia. This city is as big as the whole of Singapore. Thanks to the cross-pollination of several cultures, including Arab, Indian, Malay, Javanese, Chinese and Dutch, Jakarta is a true high-tech oasis in Asia.
24. Johannesburg
The financial hub of sub-Saharan Africa, Johannesburg is now powered by technology. The "City Planning Committee" has placed a major emphasis on the development of high-tech industries, especially in the field of information and communication technologies. Johannesburg police have even installed CCTV cameras on every street corner in the city center to reduce crime.
23. Mumbai
From the list of the most technologically advanced cities in the world, the only Indian city, Bangalore (often called the “Silicon Valley of India”) has supplanted Mumbai. This city specializes in information technology and health technology.
22. Shanghai
The most populous city in China, Shanghai has seen a boom in technology lately. Even several special industrial zones were created, which attracted large corporations such as ExxonMobil and Tesla Motors.
Today, Buenos Aires is considered the best technology center in South America. Argentina's capital is also one of the best examples of a city that uses technology to benefit its citizens. For example, the maintenance of almost 1,500 km of drainage pipes was fully automated.
20. Beijing
Beijing's economy has largely become an industrial city in last decades. Its economy is currently 77% services (mainly finance, retail, as well as information technology). In the northwest of the city lies China's "Silicon Valley" of Zhongguancun, home to a number of startups and branches of tech giants such as Lenovo, Google and Microsoft's new China research headquarters.
19. Moscow
Since the collapse of the USSR, Moscow has succeeded in creating copies of Western companies such as Yandex and VKontakte, and the Russian equivalents of Google and Facebook. These days, the city is becoming a leader in new and less common types of technology, such as nanotechnology.
18. Dubai
Dubai is the de facto Middle East technology hub and is also home to global companies such as Hewlett-Packard, Oracle and IBM. The city is investing heavily in technology, even building solar-powered “smart palm trees” that distribute Wi-Fi and are used to charge phones.
17. Milan
The economic center of Italy, Milan is mainly known for its fashion and banking industries. But Milan is not only glamor and money. Numerous high-tech exhibitions are held here. The city is also a leader in biotechnology.
16. Madrid
Although Barcelona is Spain's main industrial center, Madrid has recently seen a boom in high-tech manufacturing and advanced technology. The combination of a highly educated workforce and the headquarters of many Spanish multinational corporations has made Madrid one of the leading technology hubs in Europe.
15. Kuala Lumpur
Kuala Lumpur is every programmer's dream city. It ranks 9th in the world in development software and multimedia design. The city also has blazing fast Wi-Fi and has become a favorite haven for freelance programmers.
14. Sydney
The largest city in all of Oceania is famous for its biotech and high-tech manufacturing, which accounts for 11% of the city's total output. Sydney also ranks 5th worldwide for internet access in education.
13. Toronto
Although Canada is already known for its high-tech industry, Toronto leads the way in this regard - one of the best technology cities in North America, which ranks fifth behind Washington, Seattle, Silicon Valley and Boston. Globally, the city ranks eighth in terms of digital technology.
12. Berlin
For decades (if not centuries), Berlin has been a major center for medical technology, partly due to Germany's creation of the oldest universal healthcare system in the world. Berlin is particularly focused on clean technology.
11. Paris
Paris has been a world leader in technological progress for decades. Initial innovations such as the use of glass in architecture and gas lighting throughout the city brought the city fame a century ago. The modern achievements of Paris are high-tech manufacturing industries, primarily the optical and aerospace industries.
10. Tokyo
Tokyo is widely recognized as one of the most technologically advanced cities in the world - and not just because of its bullet trains. The city hosts numerous technology executive meetings and is one of the world's leading software development cities.
9. Chicago
Chicago has been running a program for years to teach students at city universities the skills needed to succeed in the high-tech field. In October 2015, the city received a federal grant to equip every classroom with high-speed broadband and Wi-Fi.
8. Singapore
Singapore has long wanted to become the eco-friendly capital of the world. In addition, the city is home to the research centers of many global companies such as Microsoft and Google. Among other things, Singapore provides its citizens with free high-speed Internet access.
7. Los Angeles
The City of Angels is second in the United States in terms of digital economy and third in environmental development. In terms of technological development, it is growing almost 30% faster than Silicon Valley.
6. San Francisco
The Bay Area is a huge tech district in the city that is home to companies such as Apple, eBay and Tesla Motors. This area grew up during the dot-com boom of the 1990s, when thousands of startups were launched in the city. Despite the proximity of Silicon Valley, many companies have moved from it to San Francisco.
5. New York
Most people associate New York with banking and Broadway rather than with high technology. However, the local “Silicon Valley” is one of the most developed in the world; more than $7.3 billion of venture investments are pouring into high-tech here. The city is currently undergoing a global modernization of fiber-optic telecommunications.
With some of the fastest internet speeds in Asia, Hong Kong is one of the easiest places in the world to open a business. The government regularly funds innovation, investing more than $1.8 billion in science and technology development.
3. Stockholm
The fastest growing technology hub in Europe, Stockholm is the start-up capital of Europe. While much of the rest of Europe has been in financial decline since 2008, Sweden has seen growth steadily accelerate, thanks in large part to its stable economy and highly educated workforce.
2. London
The English capital ranks first in the world for multimedia design and technological innovation. London's Silicon Roundabout is the third largest start-up platform in the world. The area attracts some of the world's largest technology companies, many of whom are establishing innovation centers and research laboratories in the Central/East London cluster.
1. Seoul
Seoul is an economic center South Korea, producing 21% of the national GDP, occupying less than 1% of the country's territory. Home to tech giants such as Samsung and LG, Seoul has begun to gradually transform into a "smart city" (a similar initiative was previously launched in Dubai). To start, the city is distributing free used smart devices to low-income families, with the goal of connecting everyone to the city's high-speed wireless networks.
Also, smart CCTV cameras are installed everywhere in the city, which can detect illegal entry and high-tech Street lights, which broadcast audio and distribute wireless Internet access.
One more especially for our readers most interesting rating- GO=https://site/blogs/060216/34920/] 15 countries with the highest life expectancy in the world.
The secret of how and why Japan has taken one of the leading places in the world economy lies in the huge investments in modern technologies, in the incredible hard work of the Japanese and in several other factors. I wondered why private companies invest a significant portion of their income in Scientific research and development? The fact is that the Japanese understand one thing simple thing– people will buy the best (including modern in all respects) products, created using high-tech equipment. Plus, there is also the “competitiveness factor”. According to him, buyers will prefer a product that fully satisfies their needs. And a lot of research helps companies find out what product their consumers need at the moment. You will be surprised, but Japanese manufacturers broke the world record by investing 800% of the same figure 25 years ago in research and new technologies.
Taxes, private business and resources.
Interestingly, the development of private business is another important reason why Japan has taken one of the leading places in the world economy. The state (represented by smart and pragmatic officials) understands that a developed person who is capable of doing business will be much more interested in the prosperity of his own business, compared to “working for an uncle.” Even if you have to pay large taxes. Still, 28-37% of current business taxes on a profit of $1 million is acceptable. Compared to 10% of $20 thousand “per owner.”
Surprisingly, Japan very successfully uses available resources: water, land, human. Moreover, they do not have enough land! She's all busy Agriculture. With this approach, almost any country (if desired) could achieve similar success.
Alien technologies.
The Japanese embodied the saying “a smart person learns from other people’s mistakes” in at its best. Why? They actively use other people's inventions and technologies. But simply "copying" would be too easy for them. The Japanese take the "core" of an idea and then refine it until it produces a great result. We can say that they never tire of developing in this regard.