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The audi sedan logo is four circles representing four companies before the merger. These companies used to be manufacturers of bicycles, motorcycles and buses. Since the company was originally a merger of four companies, each ring is a symbol of one of the companies.
The rapid development of air filters is closely related to the development of military industry and electronic industry. In the first world war, the use of various chemical agents, asbestos fibre filter paper as the smoke filter layer of military gas masks came into being. The glass fiber filter medium is used in air filtration to obtain a patent in the United States in October 1940. In the 1950s, the United States studied the production process of glass fiber filter paper, and the air filter was improved and developed. In the 1960s, HEPA filters came out; In the 1970s, the filter paper of fine glass fiber was used as the HEPA filter of filter medium, and the filtration efficiency of particle size of 013 micron particle diameter was 99.9998%. Since the eighty s, with the emergence of new test method, use evaluation to improve and to improve the filtering performance requirements, found the HEPA filter there is a serious problem, and he had a higher ULPA filter performance. Countries are still working on it and expect more advanced air filters soon
The underground metal detector is made of advanced technology. It has the characteristics of wide detection, accurate positioning, strong resolution and easy operation. Metal detectors are mainly used to detect and identify metal objects buried underground. In addition to military applications, it is widely used in security inspection, archaeology and prospecting, and the search for scrap metal, which is also known as "iron probe", which is a good helper for waste recycling.
Note that the epoxy adhesive curing speed varies depending on temperature. At higher temperatures it dries faster, but has less resistance and firmness. During the winter you might also leave a few minutes in double boiler pots, and try to take certain temperature (never to be more than 30 degrees at all), like too cold, the information becomes more complicated, thus a viscous mix.
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