Valve casting, ductile iron butterfly valve, cast iron ball, 4 cast iron check valve body flange position is prone to air holes, the core reason is that this 'thick and heavy' structure so that the iron solidification process The core reason why the flange is prone to porosity is that this 'thick and bulky' structure makes the iron solidify in the process of 'gas retention dilemma'.
1. Slow iron flow and gas retention
The thick walled structure of the flange results in a slower flow of iron. Its metal thickness is usually 20% to 30% more than other areas of the valve body, when the high temperature iron from the thin-walled area into the flange, the flow rate will drop dramatically, the dissolved gases in the iron water (such as hydrogen, nitrogen) can not come up to the surface on the 'frozen' in the valve castings within the metal, the formation of bubbles, similar to the pouring of beer when the foam is not completely overflow by the Subsequent liquid pressure.
2. Influence of sand structure and exhaust dead space
There are also flanges around the sand package by the iron, the gas can only be discharged through the sand particles between the tiny gaps, complex structure of the flange sand there may be exhaust dead space, resulting in the gas in the iron solidification 'bulging' in the valve casting flange surface or the formation of internal air holes, such as suction pipe is partially blocked when the air is difficult to discharge smoothly.
3. Slow heat dissipation and gas precipitation
Because the flange of the thick structure of the slower heat dissipation, molten iron for a long time to maintain a liquid state, dissolved gases (especially hydrogen) with the temperature drop continue to precipitate, if not in time to float to the mouth of the vent, it will be in the valve casting(like ductile iron butterfly valve) flange internal aggregation of dense air holes.
4. Unreasonable riser design
Improperly designed of risers may 'help'. If the risers opened in the flange side rather than the top, fill shrinkage of the direction of flow of iron will be originally gathered at the top of the bubble 'squeeze' to the root, in the ductile iron butterfly valve to form a more hidden air holes, similar to the middle of the toothpaste from the extrusion of the two ends of the bulge, the air bubbles are forced to be pressed into the weak area.