1 The surface of the cast ingot is not even, and there are many honeycomb holes and cracks
2 The molten pool is thick, the fluidity is poor, it is hard to be cast, and if it is heated more, it is easy to go far.
3 There are too many bottom sediments in the molten pool, which makes the molten pool be thick and pasty. According spectroscopic analysis, the contents of Fe and Mn are often over 2%
4 It is easy to be stricken on the mold, and mold release is not smooth
5 There are included slags at the section of aluminum ingot, continuous golden scum and black scum of suspended particles are produced in the molten pool
6 Gas cannot be removed from the molten pool after going through the strict degassing steps
7 In gravity casting, a lot of pores appear near the casting head for the finished piston
8 After the finished product of die casting is stripped from the casting head, overflowing occurs for the product at the casting head, resulting in the increase of defect rate
9 Pouring nozzle cracks during mold opening
10 The casting is easy to break because of the embrittlement during polishing, finish machining and drilling
11 The castings cannot be completely fused at the confluence and obvious boundary marks remain there
12 The product cannot be formed during die casting
13 There are irregular black stripes and water ripples on the surface of casting
14 The surface of the casting is dark and black, with oxidation and sometimes white hairs
15 "Lack of flesh" or "rough surface" occurs on the surface of the casting. The causes of surface depression (the academic term "depression" is also called "shrinkage depression" and "suffocation") are as follows
16 There are bubbles on the surface of the casting, which are formed by gas accumulation under the surface of the casting, and the cause is as follows
17 There are small pinholes on the surface or section of the casting
18 There are a lot of pores and sometimes large cavities in the section of the casting, which is called "shrinkage cavity" academically. The causes are as follows
19 There are sand hole in the casting blank
20 The casting has shrinkage
21 The finished casting is deformed or its dimensional accuracy is poor
22 There are hard spots, sometimes black particles, sometimes shiny crystals in the casting, and they obstruct the cutting tool in finish machining
23 The surface of the casting is apt to be warped during sandblasting
24 After anodizing, the color of the casting is not uniform
25 After casting of the finished piston, its expansion coefficient is too large, resulting in wear of cylinder wall
1 The surface of the cast ingot is not even, there are many honeycomb holes and cracks
A. When silicon content in the alloy reaches about 12%, the crystallization temperature interval of the alloy gets narrower, and shrinkage cavity and shrinkage porosity occur at the top of the cast ingot in the course of solidification, which is due to the inherent nature of alloy, and it is the characteristic of eutectic silicon alumina, in particular for ADC-12 alloy. When silicon alloy is smaller than 10.5%, cracking does not occur.
B. The shaking (vibration) of the conveyor belt accelerates the solidification of the alloy liquid, resulting in the increase of depth of shrinkage cavity and porosity, and the formation of honeycomb holes, which is caused by external factors and has no effect on the internal quality.
C. It is closely related to mixing ratio of raw and mature materials.
2 The molten pool is thick, the fluidity is poor, it is hard to be cast, and if it is heated more, it is easy to go far.
After any metal is melted into liquid, bottom materials (sediments) will be produced. For high grade metal and low grade metal, the difference is only more or less bottom materials. This is closely related to the purity of raw materials. After being mixed into alloy, about 10% silicon should be added to Al-Si alloy. Raw metal silicon will bring in impurities such as calcium (Ca), iron (Fe), and increase the impurities such as calcium oxide and iron oxide. The bottom materials are mainly attached impurities of metal compounds and non-metal compounds. Increase of temperature does not work. It is found by spectroscopic analysis that the components are completely different from they should be, and it can no longer be used for casting parts. Therefore, the following should be noted in operation:
A. When the aluminum alloy ingot is to be produced out of the pool after melting, the bottom material must be separated from the pool and shall not be mixed with it;
B. In the process of die casting, the user shall remove the bottom sediments and clean the crucible when a certain amount is remained after each crucible of aluminum soup is poured and cast. It is not allowed to continuously add materials onto casting head and add waste castings and flash aluminum chips in the pouring process, so that the bottom sediments gradually accumulate and finally form a pot of thick and pasty aluminum soup, which not only makes the soup lose its fluidity, but it's also hard to clean the pot. This often happens to many domestic users.
3 There are too many bottom sediments in the molten pool, which makes the molten pool thick and pasty. According spectroscopic analysis, the contents of Fe and Mn are often over 2%
Refer to the answer of the above point 2.
There are too many sediments in the molten pool, and the components of the alloy are different from they should be according to the spectroscopic analysis of the sediments (bottom materials). Mn and Fe have been formed into (Fe.Mn) compound, and the bottom materials have been deposited again and again. The user is required to correct his melting method in time, and handle it in accordance with the correct technical process in point 2.
4 It is easy to be stricken on the mold, and mold release is not smooth
A. The selected mold release agent is of poor quality, such as water-based graphite mold release agent, which causes the casting hard to slide out of the cavity smoothly
B. The content of impurities in the alloy exceeds the limit
C. The mold release slope in the mold is too small, which makes mold release unsmooth
D. There are too many cracks in the old mold, which causes mold sticking
E. The content of iron in the alloy is too low, lower than the standard range of technical requirements for casting, which also causes mold sticking
5 There are included slags at the section of aluminum ingot, and continuous golden yellow scum and black scum of suspended particles are produced in the molten pool
In the melting process of aluminum alloy, fluxes such as slag remover, modifier and magnesium remover are commonly used. The raw materials of these additives are mainly composed of fluoride, nitrate and chloride. These halo alkali compounds will cause golden scum when they volatilize. The formation of scum of black suspended particles is mainly because the melting point of silicon is as high as 1,412℃. In the melting process of aluminum alloy, if silicon is not completely melted into solid solution according to the operating procedures, the primary silicon will float on the liquid surface in the aluminum soup in black suspended form. Therefore, the slag removal process must not be sloppy, but it shall be done in strict accordance with the technical procedure, and the fluxes mixed with carbonate, sulfate and nitrate shall be used so that the chemical reaction products form dry slag easy to be separated from liquid aluminum.
6 Gas cannot be removed from the molten pool after going through the strict degassing steps
The degassing process of aluminum alloy has been improved, including inert gas degassing method and solid flux degassing method. The gases to be degassed include chlorine, argon and nitrogen. And there is a three-gas degassing method. Solid flux degassing agents include non-toxic degassing agents such as hexachloroethane (C2C16), carbon tetrachloride and sodium nitrate. As long as the operation is reasonable, the gas (H2) in liquid aluminum can be removed. The primary condition of degassing flux is that it shall not contain gas. The gas here refers to the hydrogen gas (H2) from water (H2O), so the degassing agent itself has very strict requirements for gas content, and dehydration is required in production. Sometimes the gas cannot be removed even after degassing operation, which is often caused by the poor quality of degassing agent. For example, the water content of degassing agent is too high, the degassing agent is placed for a long time, and it is degraded and not fresh due to exposure to moisture. The user shall observe the specific use and operation process of the manufacturer of the other party on the spot and solve the problem together.
7 In gravity casting, a lot of pores appear near the casting head for the finished piston
This is caused by improper casting process and mold design: a complete set of design (Jingren method) has been formed for piston casting process, namely goose-neck gate system. A single or two casting heads (lateral casting head) are set at one side or both sides according to the diameter and wall thickness of the piston. Some manufacturers only design small sprues and small casting heads in order to save liquid aluminum, hence, casting head is too small, shrinkage supplementation is poor and pores occur.
8 After the finished product of die casting is stripped from the casting head, overflowing occurs for the product at the casting head, resulting in the increase of defect rate
A. It is mainly related to unreasonable design of casting mold, and too thick sprue will result in too much flesh remaining around the sprue.
B. The position of sprue set at the thin wall of the casting will also result in too much flesh upon cleaning
C. The material cake (*) is too thin, and there are shrinkage holes and occluded foreign substances at the breaking part
*<The pouring system of the casting is composed of inner sprue, overflow groove and material cake, and a casting head is not set there. Here, “casting head” is wrong, it should be material block (cake)>.
9 Pouring nozzle cracks during mold opening
A. The mold is not designed and made reasonably, and the ejector pins do not coordinate (do not synchronize) with each other at mold opening due to their length
B. The ejection position is not designed reasonably
C.The raw materials are too brittle and not tough enough. Analyze with samples and the cause can be found. Moreover, specific casting part should be observed to decide what the cause is.
10 The casting is easy to break because of the embrittlement during polishing, finish machining and drilling
A.Silicon content in alusil alloy is slightly higher, the material is brittle and is easy to break
B.The too long temperature retaining and laying time for the aluminum alloy liquid and too hot alloy liquid also causes the casting to be brittle and easy to break
11 The castings cannot be completely fused at the confluence and obvious boundary marks remain there
A. The temperature of alloy liquid is low or the temperature of mold is on the low side, as well as fluidity of alloy liquid is poor, and they result in this defect, the cause is that the two liquid flows cannot fused together
B. The filling speed is low
C. The mold is not designed reasonably and the distribution position of overflow groove is not proper
D. Specific pressure is on the low side. The structure and size of each casting is different, and a correct casting process shall be designed according to actual object.
12 The product cannot be formed during die casting
The whole set of casting technology is not grasped. It is suggested that the casting plant of the other party strengthen its technical strength.
13 There are irregular black stripes and water ripples on the surface of casting
A. The dosage of paint is too much (water-based graphite paint is used)
B. Mold temperature is too low (flow mark is to occur in case of lower than 180℃)
C. Water ripples occur when the filling speed is too high
14 The surface of the casting is dark and black, with oxidation and sometimes white hairs
A. The castings are not stored properly. They are stacked in the open air, exposed to rain and sunshine, or the place where castings are stacked is near electroplating and thermal treatment workshop, etc.
B. The operation environment is too poor, there is humidity in the air, where there’s too much acid and alkali, which cause surface of aluminum castings to be oxidized
C.Mold release agent is degraded
15 . "Lack of flesh" or "rough surface" occurs on the surface of the casting. The causes of surface depression (the academic term "depression" is also called "shrinkage depression" and "suffocation") are as follows
A. The overflow groove is too small, there are too few of them, or no overflow groove is set at the place which is thick
B. Mold temperature is too high
C. Specific pressure is too low
