XINHAI NEWS
Defect in Cast Aluminum Casting Solve and Analysis
Defects in cast aluminum and Analysis
An oxide slag
Defect features: multi- oxide slag distributed over the surface of the casting , the mold without ventilation corner site. Fracture mostly white or yellow , x-ray fluoroscopy or found during machining can also be found in the caustic , acid or anodized
Reason:
1 . Burden dirty , excessive usage charge back
2 bad gating system design
3 . Alloy liquid slag is not cleaned
4 . Improper casting operation , into the slag
5 After the standing time is not enough refining modification
Prevention methods:
1 . After blowing sand should charge , the amount of the charge due to lower back
2 . Improved gating system design, to improve their ability slag
3 using the appropriate flux to slag
4 . It should be smooth and should pay attention to slag pouring
5. After refining before pouring the liquid alloy should stand for some time
Two holes bubble
Defect feature : three inner wall of the casting hole is circular or elliptical in general , have a smooth surface , the oxide scale is generally shiny , sometimes yellow oil . Surface porosity , air bubbles can be found by sandblasting , air bubbles can be internal porosity by X -ray or machined holes bubbles found in the X -ray film was black
Reason:
1 . Casting alloy is not stable, involved gas
2 . (Core ) sand mixed with organic impurities ( such as litter , grass-roots horse manure , etc.)
3 . Sand core mold and poor ventilation
4 . Cold iron surface shrinkage
5. Adverse gating system design
Prevention methods:
1 . Proper understanding of casting speed , avoid getting gas .
2 . (Core ) must not be mixed with sand to reduce fat organic impurities in the gas modeling materials
3 . Improve exhaust capability ( core ) sand
4 . Correct selection and processing of cold iron
5. Improved gating system design
Three shrinkage
Defect features: aluminum casting shrinkage generally produce including runner near the roots Heavy fly riser parts of the wall thickness of the adapter and the thin-walled office with a big plane. When cast fracture is gray, pale yellow after heat treatment is yellowish gray or gray-black was cloudy on the x-ray film showed a filamentous severe shrinkage can be found by X- ray fluorescence method for low magnification fracture and other tests <br>
Reason:
1 . Riser feeding poor role
2 . Charge too much gas content
3 . The runner near overheating
4 . Sand too much water , not dry sand core
5. Alloy coarse grains
6. Cast in the mold of improper position
7 . Pouring temperature is too high, too fast casting
Prevention methods:
1 . Pouring molten metal from the riser up , riser design improvements
2 . Charge should be clean and free of corrosion
3 . Casting shrinkage of the set riser , put cold iron or iron and riser combined with cold
4 . Moisture control sand and sand core drying
5. Take measures to refine the product Reap
6. Improved casting position in the mold and the pouring temperature of the casting speed to reduce
Four cracks
Defect characteristics:
1 . Casting cracks. Development along the grain boundary , often accompanied by segregation , a crack is formed at higher temperatures in the alloy and a large volume shrinkage of more complex shape castings prone
2 . Heat treatment cracks : Because burning or overheating caused by heat-treated , often transgranular cracks. Often produces stress and thermal expansion coefficient larger alloy cooled drama. Or when there are other metallurgical defects arising
Reason:
1 . Casting structure design is unreasonable, sharp corners , changes in wall thickness is too poor
2 . Sand ( core ) poor yield of
3 . Mold local overheating
4 . Pouring temperature is too high
5. Remove the casting from the mold prematurely
6. Hot or burning heat treatment , cooling rate excesses
Prevention methods:
1 . Improved casting structure designed to avoid sharp corners, and strive uniform wall thickness , smooth transition
2 . Take measures to increase the sand ( core ) yield of
3 . Ensure that each part of the casting solidification or solidification while improving gating system design
4 . Appropriate to reduce the pouring temperature
5. Control the type of mold cooling time
6. When casting thermal distortion correction method
7 . Proper control of the heat treatment temperature, decreasing the quench rate
Porosity analysis
Casting defects , there is a maximum of stomata .
Stomatal characteristics . Has a smooth surface , a circular or elliptical shape . In the form of the casting surface can , pinholes or subcutaneously , in the casting may also be internal .
( 1 ) the source of gas
1 ) alloy liquid precipitation of gas -a and b related to raw materials related to the melting process
2 ) die casting process involved in gas - a and b casting process parameters and die structure of
3 ) release agent decomposition gases - a and b are related to inherent characteristics of the paint spraying process related
( 2 ) to produce raw materials and smelting process gas analysis
Liquid aluminum is mainly hydrogen gas , accounting for about 85% of the total gas .
The higher melting temperature , the higher the solubility of hydrogen in liquid aluminum , but the solubility in solid aluminum is very low , so the solidification process , the evolution of hydrogen to form pores .
The source of hydrogen :
1 ) atmospheric water vapor, liquid hydrogen-absorbing metal from the humid air.
2 ) hydrogen content of raw material itself , the alloy ingot surface wet, charge back dirty oil.
3 ) tools, flux wet.
( 3 ) die casting process produces gas analysis
As the pressure chamber , the gating system , cavity are vented to the atmosphere , while the liquid metal is high pressure , high speed filling, if you can not achieve an orderly , smooth flow state , swirl the liquid metal , will roll into the gas .
Casting process developed to consider the following questions:
1 ) pouring the molten metal in the system can clean, smooth flow , no separation and vortex .
2 ) there are no sharp corners or dead zone area exist?
3 ) Are there changes in the gating system sectional area ?
4 ) exhaust ducts , overflow tank location is correct ? Is big enough? Whether it will be blocked ? Gas will be effective and smooth discharge ?
A computer simulation of filling process is to analyze these phenomena , in order to make a reasonable judgment to select process parameters .
( 4 ) Analysis of the coating gas is generated
Coatings : If hair has a direct impact on large gas casting porosity .
Spraying process : excessive use , causing a large amount of volatile gases , lubricants much punch , or charred , are the source of the gas.
( 5 ) The way to solve the casting porosity
First analyze what causes the stomata , again take the appropriate measures.
1 ) dry, clean alloy material .
2 ) control of the melting temperature to avoid overheating, degassing treatment .
3 ) a reasonable choice of casting process parameters, especially the injection speed . Adjust speed switching starting point.
Fill 4 ) a gas discharge cavity beneficial sequence , the sprue and runner is of sufficient length (> 50mm), to facilitate the smooth flow of the liquid alloy and the gas discharge opportunity . The thickness of the gate can be changed , the direction of the gate , an overflow tank , the exhaust hole is formed at the position of the groove . The sum of the cross-sectional area of overflow goods not less than 60% of the total cross-sectional area of the gate , otherwise slagging poor results.
5 ) Choose good performance coatings and spray volume control .
Address deficiencies ideas
Because the cause of every defect from a number of different factors , and therefore actual production to solve the problem , because in the end face of many merits and demerits of the first transfer machine ? Or the first refueling ? Or modify the mold ? Recommended by the degree of difficulty , the first Jane complicated to deal with, their order :
1 ) Clean the parting surface , cleaning the cavity , cleaning plunger ; improve paint spraying process improvement ; increases clamping force , increasing the amount of metal casting . These operations can be implemented by simple measures .
2 ) adjusting the process parameters , injection pressure , injection speed , filling time , mold time , pouring temperature , mold temperature.
3 ) refueling , select high quality aluminum ingots, new material and change back to charge ratio improved smelting process .
4 ) modify the mold , modify gating system , increasing the gate , additional overflow tank , exhaust ducts.
Casting a reason such burrs are generated :
1 ) die casting machine problem : clamping force adjustment wrong.
2 ) process issues : injection speed is too high, too high a pressure shock peak .
3 ) Mold Problem: deformation parting surface debris, inserts, wear is not flush with the slider , templates strength is not enough . Burrs order solutions : clean up parting surface → improved clamping force adjusting the process parameters → → → improved wear parts to repair mold mold stiffness. From easy to difficult , to do every step of improvement , the first test of its effect , no further step two.
Common factors casting defects
Factors common pitfalls
Less sticky residue die casting bubble deformation abrasions factors shrinkage porosity crack root causes cold shut clip category
√ √ √ B than the pressure die casting machine
Injection speed √ √ B
Time pressure built √ √ B
Pressure chamber fullness √ √ √ B
1-2 speed intersection √ √ √ B
Coagulation time √ √ B
Mold temperature √ √ √ √ √ C mold
Die exhaust √ √ √ √ A
Gating system incorrectly √ √ A
Mold surface treatment bad √ √ A
Casting slope enough √ √ √ √ A
Casting hardness enough √ √ A
√ √ √ C pouring temperature field operations
Pouring metal content √ √ C
Metal -containing impurities √ C
Paint √ √ √ √ √ √ √ √ C
Note : A class of factors: depending on mold design and manufacturing.
Class B factors: performance largely depends on the die casting and die casting machine paramete selection.
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