The degree of supersaturation reached before the formation of hydrogen bubbles is a function of the number of hydrogen bubbles nucleating, while oxides and other inclusions are contributing to the bubbling effect.
The hydrogen bubbles formed by the separation of supersaturated hydrogen have no time to float up and discharge, and the tiny and scattered pores formed during the condensation process are commonly referred to as pinholes. 2. The more hydrogen dissolved in copper castings, its solubility increases with the increase of the temperature of the alloy liquid, and decreases with the decrease of the temperature. The solubility of hydrogen in the copper alloy decreases when the liquid is transformed into a solid state. The copper alloy can absorb a lot of hydrogen during smelting and pouring, and it is continuously separated due to the decrease of solubility during cooling.
Therefore, during the cooling and condensation process of the copper alloy liquid, the hydrogen content exceeds its solubility at a certain time, Aluminum alloy sand casting that is, it is separated in the form of bubbles.
3. If the crystallization temperature is larger, the probability of mesh pinholes is much larger. In the late stage of condensation, the residual copper solution in the dendritic voids may be isolated from each other and exist in small spaces that are approximately closed. Under normal casting production conditions, copper castings have a wide range of solidification temperatures, allowing copper alloys to easily form strong dendrites. Because they are less affected by the external atmospheric pressure and the static pressure of the alloy liquid, when the residual copper liquid is further cooled and shortened, a certain degree of vacuum is formed to separate the supersaturated hydrogen in the alloy to form pinholes.
During the daily inspection process, be sure to check the copper sleeve. The main content of the inspection is to use the listening needle tool to check whether the copper casting is stuck, noise and smooth operation. The temperature can be measured with a thermometer, or the shell temperature of the copper sleeve bearing can be manually touched to see if it is within the numerical requirements of the controllable measurement range specification.
2. The purpose of the copper casting bearing seal is to prevent dust. Moisture and the like enter the bearing to prevent the loss of lubricating oil. Before installing the bearing with the shaft, measure the outer diameter of the shaft and the inner diameter of the bearing to prevent over-tightening and over-loosening. Over-tight installation makes the oil gap smaller and the bearing temperature higher. If the assembly is too loose, the bearing will enter the inner or outer sleeve, causing damage to the shaft and bearing. The above is the inspection and protection of copper castings, but it is recommended that when installing the bearing, it is strictly forbidden to directly strike with a hammer to avoid damage to the copper sleeve. The method of copper rod or casing transition can be used.
Tags: aluminum alloy engine part, Aluminum alloy sand casting, gravity casting parts
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