Valve protective cover has excellent chemical stability, corrosion resistance, sealing, high lubrication non-stick, electrical insulation and good anti-aging endurance. Widely used in papermaking, cement, chemical processing, oil refinery. Can be used for concentrated sulfuric acid, nitric acid, hydrochloric acid, alkali and other acid and alkali pipe flange protection valve protection, easy installation, long service life. Valve Shields Valve Shields,Valve Spray Shields,Valve Protectors,Safety Shields For Valves Zhejiang Amin Environmental Protection Technology Co., Ltd. , http://www.safetysprayshields.com
From this time on, human beings have gradually recognized the role of the blade in production practice. It can be said that an original cutting process is formed. Basically, there are basic conditions for cutting: tools (stones with cutting edges), objects to be processed (production and household goods), and cutting motion.
China's metal cutting process began to sprout from the Bronze Age and gradually formed and developed. From the Yin Shang to the Spring and Autumn Period, there have been quite a variety of bronze tools in the bronze smelting industry, such as bronze knives, bronze gongs, bronze saws and so on. At the same time, there are unearthed cultural relics and Oracle records showing that the bronze tools and living tools produced during this period are mostly processed or ground during the manufacturing process. China's smelting and casting technology is more than a thousand years earlier than Western Europe. The invention of carburizing, quenching, and steelmaking techniques provides convenient conditions for the manufacture of hard and sharp tools. The emergence of iron tools indicates that metal cutting has entered a new stage. It has been recorded that the Shang Dynasty, which was more than 3,000 years ago, has a rotating jade tool, which is the predecessor of metal cutting machine tools. In the 1970s, the five-dollar money unearthed at the Han Tomb No. 1 in Mancheng, Hebei Province, had traces of turning on the outer circle, the knife flower was even, the cutting vibration was clear, and the ovality was small. It is possible to put five cents on a square shaft and then clamp it on a wooden lathe and use a tool to cut it.
In the eighth century, China had a metal cutting lathe. In the Ming Dynasty, the handicraft industry had a great development, and various cutting methods had a fine division of labor. Such as: car, milling, drilling, grinding, etc. It can be seen from the astronomical instruments on the Beijing Ancient Observatory that similar processing methods were used at the time. This means that there are higher precision grinding, turning, milling, drilling and so on. Its power is animal power and water power.
At the end of the Qing Dynasty, due to government corruption and foreign aggression, China's science and technology development stagnated, and metal processing was also in a backward state.
Before the liberation, China's industry was already very backward, and there was no machine tool or tool manufacturing industry. Even tool materials such as high-speed steel cannot be manufactured by ordinary tools such as twist drills.
After the liberation, China's machine tools have also made great progress. Machine tool and tool manufacturing has also grown from scratch to small.
In the 1970s and 1980s, tool materials were further developed, and the specifications and varieties of cemented carbide and high-speed steel continued to increase. Such as: coated cemented carbide, cubic boron carbide, ceramics and so on. In the 1980s, digital and digital display devices began to develop. Due to the influence of electronic equipment, microcomputer, transmission, etc. at that time, there is not much room for development. With the rapid development of electronic devices, microcomputers, and transmission rates, digital control and digital display devices have also developed rapidly.
Valve Shields can be made according to the use of different materials, the valve jacket (PVC Spray Shields, PTFE Spray Shields, PP Spray Shields)
The development history of cutting and tool materials in China
China has a long history in metal cutting. Ancient processing of stone, wood, bone and other non-metallic objects is the prelude to today's metal processing. In the Paleolithic era, there were stone chopping devices. In the Neolithic Age, people's production tools in the struggle with nature have been continuously improved, such as: stone axe, stone knife, stone scorpion and so on. And to be able to drill holes in the stone. Even the hard stone blade is inlaid or bonded to the bone handle to make a clamped stone blade.