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The basic knowledge of aluminum casting ingots(D)
Dec 01, 2017


Causes of Common Defects in Aluminum Alloy Castings and Preventive Measures


Defect type (a): owe cast and cold compartment


1. Cause: pouring temperature and shell temperature is low

Prevention: Properly increase the pouring and shell basin

2. Causes: liquid aluminum gas content, serious oxidation resulting in decreased mobility

Prevention method: The correct smelting process to reduce the gas content of liquid aluminum

3 reasons: casting wall too thin

Prevention methods: pay attention to the design of pouring system to reduce the flow resistance and flow, increase the sprue height

4 reasons: inadequate shell melting or poor shell permeability

Prevention methods: roasting fully or increase the shell permeability

5. Reason: casting speed is too slow or pouring molten aluminum flow or pouring insufficient

Prevention method: to ensure the necessary pouring amount, the appropriate increase in casting speed and to avoid breaking


Defect type (two): scarring (sand)


1. Causes: too much sand or sanding sand dust, sand and more, resulting in sand layered between layers;

Prevent methods: Sand and sand should not be too thin and should be uniform, less dust, humidity should not be too high.

2. Causes: paint viscosity, local accumulation, hardening sufficient, layered between the paint;

Prevention methods: strict control of paint viscosity, paint should be uniform and reasonable selection of hardening process parameters;

3 reasons: high temperature or sand and sand and paint a long time interval, when the removal of sand coating surface has become hard skin, paint and sand layering between;

Prevent methods: shorten the coating time and sand spraying interval;

4. Reason: The second layer or reinforcement coating viscosity, poor fluidity, the coating can not penetrate fine metal fine sand gap, in the rear layer of paint and the sand layer between the former;

Prevention methods: appropriate to reduce the viscosity of the second layer or reinforcement coating, the use of low viscosity transition coating;

5 reasons: shell front layer of excessive hardener too much, the back layer of paint can not penetrate well into the gap of the sand layer before, in the back of the coating layer and the front layer of sand produce stratification;

To prevent: strictly control the drying time, add a small amount of active agent in the reinforcement coating, if necessary, rinse the outer surface with water after drying, wash away residual hardener;

6. Causes: hardening temperature is much higher than the studio temperature, quenching and shrinking caused by hardening after the shell partial cracking, peeling;

Prevention methods: Choose the appropriate hardening and studio temperature;

7. Causes: fusible and wet coating of the first layer is poor, forming a gap between the shell and fusible mold;

Prevent methods: fusible mold surface degreasing treatment, the surface Xu Xu added surfactant to improve the fusible mold and the surface coating wettability;

8. Causes: shell roasting, pouring expansion and contraction changes, resulting in cracking the inner layer, peeling off:

Prevent methods: Choose a small change in the amount of fire-resistant materials, to prevent the roasting shell cooling too much:

9. Causes: paint viscosity, material is too thin or sprinkle sand insufficient, resulting in over-hardening shell, cracking, peeling;

Prevention method: control paint cat degree. Sand should be sprinkled sand evenly spread in the paint layer;

10. Causes: surface layer and reinforcement refractory material is too large, inconsistent expansion and contraction, the surface layering, delamination

Prevention methods: try to avoid the use of the surface layer and reinforcement layer expansion coefficient of contraction difference between the fire-resistant materials.


Defect type (c): shrinkage


1. Causes: Castings unreasonable structure, there is difficult to make up the Heat Festival;

Preventive measures: Improve casting structure. Minimize heat section;

2 reasons: Riser system design is unreasonable;

Prevention methods: Rational design of Riser system, the formation of the order of solidification;

3 reasons: pouring temperature is too high, aluminum liquid shrinkage rate;

Prevention method: choose the right pouring temperature;

4 reasons: liquid aluminum contains more gas and oxidation slag, so that the ability to reduce mobility and shrinkage:

Prevention methods: Improve the smelting process, reduce the gas content of liquid aluminum and oxides;

5. Causes: unreasonable module assembly, type shell partial cooling conditions are poor;

Prevention methods: reasonable assembly, to improve the cooling conditions;

6 reasons: pouring riser, pouring cup is not full

Prevention method: Pouring should be guaranteed riser and pour cup filled with liquid aluminum


Defect type (D): concentrated pores


1. Causes: shell permeability is poor, pouring cavity gas out of time;

Prevention methods: to improve the permeability of the shell, if necessary, can be set in the shell vent;

2 reasons: shell roasting is not sufficient, not fully rule out the mold remnants and shell material in the gas-generating substances;

Prevent methods: fully baked shell;

3 causes: cold shell casting, shell damp;

Prevent methods: hot shell casting, the shell shall not be damp;

4 causes: aluminum gas content is too high, bad deoxy;

Prevention methods: to improve the deoxy method;

5 reasons: pouring system design is unreasonable, pouring into the gas

Prevention methods: Improve the structure of the casting system


Defect type (E): porous stoma and pinholes


1. Causes: aluminum liquid gas refining is not sufficient;

Prevention method: to improve the refining of aluminum degassing method;

2. Cause: ladle baking is not sufficient;

Prevent methods: ladle should be fully baked;

3 reasons: shell roasting is not full or roasted shell re-damp

Prevent the method from fully baking the shell and prevent the shell from damp


Defect type (six): slag


1 reasons: poor smelting metal slag, slag is not clean;

Precautionary approach: Aluminum liquid should have sufficient tapping temperature, and appropriate sedation to facilitate slag floating;

2. Cause: There is no net ladle in the residue;

Prevent methods: ladle clean up before use;

3 reasons: not good slag when pouring;

Prevention methods: If necessary, use teapot-style or bottom-pouring ladle;

4 causes: pouring system set unreasonable, slag the role of poor

Prevention method: reasonable design pouring system


Defect type (seven): sticky sand


1. Causes: surface coating viscosity is low, sand particles too coarse;

Prevent methods: to improve the viscosity of the paint, the use of finer sand particles;

2 reasons: surface coatings on the fusible mold coating is poor, uneven coating, reinforcement coating and sanding sand and aluminum tuck direct contact;

Prevent methods: fusible mold for degreasing;

3. Reason: aluminum melt quality is not high, there are more mixed oxide;

Prevention methods: improve the smelting process, to reduce oxidation inclusions;

4 reasons: casting structure or casting system design unreasonable, resulting in shell overheating

Prevent methods: Improve the design of casting system, improve shell cooling conditions, to prevent local overheating


Defect type (eight): hot cracking


1. Causes: casting structure is unreasonable, the wall thickness difference between the corner of the fillet R is too small

Prevention methods: Improve the structure of castings, such as; to reduce the wall thickness difference. Increase the fillet radius, set the process ribs

2 reasons: pouring system design is unreasonable, increasing the thickness of the casting temperature difference or blocked castings blocked

Prevention method: reasonable design pouring system

3 reasons: shell high temperature strength, poor concession

Prevention method: appropriate to reduce the high temperature strength of the shell

4 causes: metal solidification range, high content of harmful impurities, thermal cracking tendency

Prevention methods: Improve the smelting process, reduce the content of harmful impurities and oxide inclusions;

5 reasons: casting shell temperature is low, pouring temperature is too high

Prevention methods: appropriate increase shell temperature, lower pouring temperature;

6. Reason: Shell shell cooling conditions are poor

Prevention methods: to improve the cooling conditions of the casting easy to crack sites


Defect type (9): Roughness too coarse


1. Causes: rough surface or clean pressure type cavity is not clean

Prevention method: The pressure cavity should have a suitable surface roughness and clean the pressure type

2. Causes: uneven preparation of the mold. The old material is too much filtration inadequate treatment

Prevent methods: uniform ingredients, control the use of old materials and filtration

3 reasons: low pressure molding, mold injection temperature is low, injection pressure is small;

Prevention methods: appropriate increase in pressure temperature, mold injection temperature and pressure

4 causes: sand size coarse;

Prevent methods: use a smaller particle size sand surface

5 reasons: surface coating and fusible mold wetting poor;

Prevent methods: to ensure that the fusible surface degreasing treatment, to determine a reasonable surface paint formula, to improve the wettability between the surface coating and fusible mold

6 causes: shell roasting is not sufficient;

Prevent methods: fully baked shell

7. Causes: casting of unreasonable cleaning process

Prevent methods: Choose a reasonable cleaning methods and processes


Defect type (ten): deformation


1. Causes: irrational casting structure or casting system design is unreasonable, causing emery mold and casting deformation in different stages of the process;

Prevention methods: improve the structure of castings and improve the design of casting system;

2 reasons: the poor thermal stability of the mold or mold studio temperature is too high;

Preventing methods: improve the mold or reduce the molding studio temperature;

3 reasons: pressure-type structure is not reasonable, pressure-type assembly is not correct, the active part is not tight;

Prevent methods: improve the pressure design, check the pressure type and carefully assembled pressure type;

4 reasons: pressure-type temperature is too high, dwell time insufficient;

Prevention methods: to prevent the appropriate method to reduce the pressure type temperature, increase dwell time;

5 reasons: improper mold or mold premature;

Methods to prevent: to improve the method of taking the mold or to extend the mold taking time;

6 reasons: improper storage of fusible mold or storage time is too long;

Prevention methods: to improve the storage conditions, shorten the storage time;

7. Causes: shell process unreasonable, resulting in deforming shell delamination;

Prevent methods: Strict shell technology to prevent shell deformation delamination;

8. Causes: refractories refractories or low strength high temperature shell;

Prevention method: Refractory refractory materials used to try to improve the high temperature strength of the shell;

9. Causes: shell roasting temperature is too high;

Prevent methods: strictly control the roasting temperature;

10. Causes: pouring temperature is too high or metal pressure is too large;

Prevent methods: strict control pouring depression, using the appropriate metal pressure;

11. Causes: casting out of the box, shelling premature;

Prevention methods: to determine a reasonable ratio of boxes, shelling time;

12. Reason: casting improper cleaning

Prevention methods: improve the method of casting cleaning;

13 causes: casting heat treatment process unreasonable

Prevent methods: improve the heat treatment process

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