Compressed air plays an important role in the spraying process. It can not only drive the piston of the booster pump and pressurize the paint tank, but also the power of the air Spray Gun to atomize the paint. It not only plays an important role in the spraying process, but also is widely used in various pneumatic equipment and air control equipment. It can control the pneumatic water supply system, fire extinguishing system and instrument system, and is used for liquid and solid transportation, stirring and other operations. It can even be used for anti-corrosion treatment. Therefore, it is important to understand the preparation and performance of compressed air.
Within an average height of 300km above the earth's surface, there is a layer of atmosphere, the air we breathe. Air is a gas mixture consisting of about 78% nitrogen and 21% oxygen, which also contains a small amount of water vapor, carbon dioxide and inert gases. Although air is very light, it still has weight, so it will exert pressure on the earth's surface. The pressure generated by the weight of air on the earth's surface is called atmospheric pressure. The maximum atmospheric pressure at sea level on the earth is 101.325kPa. As the altitude increases, the air density decreases and the atmospheric pressure gradually decreases.
Air, like other gaseous substances, is compressible. When the pressure increases, the volume will decrease, and the relationship is inversely proportional. When the pressure increases by 10 times, the volume will shrink to 1/10 of the original.
Since the volume and density of air often change with the change of temperature and pressure, in order to facilitate mutual comparison, the air with a temperature of 20°C, a relative humidity of 36%, and an atmospheric pressure of 101.325kPa is called the standard state of air. , the density of the air at this time is about 1.29g/L.
当常压下的空气在机械力的作用下被压缩到储气罐中时,它的体积缩小,压力上升就成为压缩空气。压缩空气具有相当大的能量,当它向外释放时能对外做功。把制备压缩空气的机械称为空气压缩机,把利用压缩空气为动力的机械称为气动设备。空气压缩机的工作能力通常是用它的产气能力来表示的,在单位时间内产生具有_定压力的压缩空气的数量越多,空气压缩机的工作能力越强。由于压缩空气的体积是随压力变化的,为便于相互比较,在表示体积时需要标明它的压力。同样气动设备的工作能力可用压缩空气的耗气量来表示,把在单位时问内消耗一定压力的压缩气体的数量称为耗气量。所以表示压缩机和气动设备的工作能力时都用到两个指标:体积流量和气体压力。如某台气动设备的耗气量为气体压力等于689.5kPa时,气体流量为0.283m3/min。它的意义是当表压为689.5kPa时,该设备的耗气量为0.283m3/min。
由于空气压缩机的理论工作能力都是折算成标准状态下空气体积表不的。所以只有在压缩机人口处吸入的是标准状况下的空气时,它才有这种工作效率,而实际状况往往会有偏差,主要表现在以下几种情况。
(1)海拔高度变化由于大气压力和空气密度都是随海拔高度降低的,所以在高海拔地区使用同一台压缩机产生的压缩空气要比低海拔地区少。这是由于空气压缩机入口处的空气压力要比标准状态值低的缘故,一般海拔高度每上升305m,空气压缩机的产气能力就会下降3%。
(2)环境温度的变化当空气压缩机在环境温度高于标准状态的20℃的条件下工作时,由于压缩机入口处吸入的空气密度要比标准状态时低,所以空气压缩机的实际产气能力会下降。当环境温度高于20℃时,每升高4.6℃,压缩机的产气能力就会下降2%。而在37℃的条件下工作,它的产气能力要下降6%左右,所以夏天应把压缩机放在阴凉通风的地方工作。
(3) Error caused by compression heat generation Since the air is compressed, it will generate heat, so the compressed air discharged from the compression outlet is hot. According to the type of compressor and the working pressure, the temperature of the compressed air can be between 65 and Change within the range of 260 ℃, the higher the working pressure, the more heat generated, and the higher the temperature of the compressed air. When the hot compressed air enters the gas storage tank, since the volume of the gas is fixed at this time, its pressure will also increase as the temperature rises, so the pressure gauge reading on the gas storage tank will be higher, but this is not gas storage. The pressure at which the tank works. When the heat is dissipated, the temperature of the gas drops. Although the gas is not used, the air pressure in the container will also drop. This is because the pressure is proportional to the temperature when the volume is constant. In order to know the actual pressure of the air tank, the air pressure should be measured when the temperature of the compressed air is equal to the room temperature (or ambient temperature). In order to avoid measurement errors, an aftercooler is generally connected between the compressor outlet and the air storage tank to cool down the compressed air as soon as possible.