What are the defects of aluminum casting, including the defects of low pressure cast aluminum and di
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發布日期:2014-10-15
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What are the defects of aluminum casting, including the defects of low pressure cast aluminum and die cast aluminum?1. Under-casting (under-filling, unclear outline, corner defects):Reason f..........
What are the defects of aluminum casting, including the defects of low pressure cast aluminum and die cast aluminum?

1. Under-casting (under-filling, unclear outline, corner defects):

Reason for formation:

(1) The fluidity of the aluminum liquid is not strong, the gas content in the liquid is high, and the scale is large.

(2) The cause of the casting system is bad. The inner gate section is too small.

(3) Reasons for poor exhaust conditions. The exhaust gas is not smooth, the coating is too much, and the mold temperature is too high, so that the gas pressure in the cavity is high, so that the gas is not easily discharged.

Prevention method:

(1) Improve the fluidity of aluminum liquid, especially refining and slag. Appropriately increase the temperature and mold temperature. Increase the casting speed. Improve the structure of the casting, adjust the thickness allowance, and set the auxiliary rib channel.

(2) Increase the cross-sectional area of the ingate.

(3) Improve the exhaust condition, add a liquid flow tank and an exhaust line, and open a vent plug at the deep concave cavity. Make the coating thin and uniform, and then mold it after drying.

2, crack:

Characteristics: The blank is broken or broken, forming slender cracks, which are irregularly lined, with two types of penetration and non-penetration, which develop under the action of external force. The difference between cold and hot crack: the metal in the cold crack is not oxidized, and the hot crack is oxidized.

Reason for formation:

(1) The casting structure is unreasonable, and the shrinkage resistance is too small.

(2) The ejector device is deflected and the force is uneven. -

(3) The mold temperature is too low or too high, and it is severely strained and cracked.

(4) The harmful elements in the alloy exceed the standard and the elongation decreases.

Prevention method:

(1) Improve the structure of the casting, reduce the difference in wall thickness, increase the roundness and the arc R, and set the process ribs to make the section change smoothly.

(2) Correct the mold.

(3) Adjust the mold temperature to the working temperature to remove the slope and unevenness and avoid cracking.

(4) Control the composition of the aluminum coating to make it a harmful element.

3, cold separation:

 Characteristics: There are traces at the docking or lap joint of the liquid flow, and the intersection edge is smooth, and the development trend continues under the action of external force.

Reason for formation:

(1) The flowability of the liquid flow is poor.

(2) The liquid flow splitting is poorly integrated or the process is too long.

(3) The filling temperature is too low or the exhaust is poor.

(4) Insufficient filling pressure.

Prevention method:

(1) Appropriately increase the temperature of the aluminum liquid and the temperature of the mold, and check and adjust the alloy composition.

(2) Make the filling filling points and arrange the overflow tank reasonably.

(3) Improve the casting speed and improve the exhaust.

(4) Increase the filling pressure.

4, hollow:

Feature: A concave portion that appears on a smooth surface.

Reason for formation:

(1) The structure of the casting is unreasonable, and a hot section is generated in the local thick portion.

(2) The alloy has a large shrinkage rate.

(3) The gate cross-sectional area is too small.

(4) The mold temperature is too high.

Prevention method:

(1) Improve the structure of the casting, the wall thickness should be as uniform as possible, and the transitional connection should be used. The thick part can be used to eliminate the heat knot.

(2) Reduce the alloy shrinkage.

(3) Appropriately increase the cross-sectional area of the ingate.

(4) Reduce the temperature of the aluminum liquid and the temperature of the mold, use a temperature control and cooling device to improve the heat balance condition of the mold, improve the exhaust condition of the mold, and use a paint with a small amount of gas.

5, bubbles

Features: Under the skin of the casting, the bubbles formed by the accumulation of gas bulge.

Reason for formation:

(1) The mold temperature is too high.

(2) The filling speed is too fast, and the metal liquid is drawn into the gas.

(3) The paint has a large amount of gas and a large amount of water. It is not volatilized before casting, and the gas is wrapped on the surface of the casting.

(4) The exhaust is not smooth.

(5) It is too early to open the mold.

(6) The temperature of the aluminum liquid is high.

Prevention method:

(1) Cool the mold to the working temperature.

(2) Reduce the filling speed and avoid eddy entrainment.

(3) Select a paint with a small amount of gas, the amount is thin and uniform, and the mold is completely volatilized.

(4) Clean and add exhaust slots.

(5) Correct the mold opening time.

(6) Correct the smelting process.

6, air holes (gas, slag holes)

Features: The shape of the gas formed inside the casting is regular, and the surface is smooth.

Reason for formation:

(1) The aluminum liquid enters the cavity to generate a frontal impact, creating a vortex.

(2) The filling speed is too fast, causing turbulence.

(3) The exhaust is not smooth.

(4) The mold cavity position is too deep.

(5) Too much coating, not evaporated before filling.

(6) The charge is not clean and the refining is poor.

(7) There are debris in the cavity, and the filter does not meet the requirements or is improperly placed.

(8) The machining allowance is large.

Prevention method:

(1) Select the shape of the diversion that is conducive to the gas exclusion in the cavity, and avoid the aluminum liquid to first close the drainage system on the parting surface.

(2) Reduce the filling speed.

(3) Open the overflow tank and the exhaust passage at the last filling part of the cavity, and avoid being blocked by the molten metal.

(4) Open the exhaust plug at the deep cavity and increase the exhaust by inserting.

(5) The coating amount is thin and uniform.

(6) The charge must be cleaned and dried, and the smelting process must be strictly observed.

(7) Clean the cavity with a wind gun, and the filter mesh is made in accordance with the process requirements and placed according to the regulations.

(8) Clean the slag in the furnace holding furnace before and after adding the soup.

(9) Adjust the switching points of slow filling and fast filling.

7. Shrinkage characteristics: the irregular shape and the rough surface of the hole caused by insufficient internal compensation during the condensation process.

Reason for formation:

(1) The casting temperature of the aluminum liquid is high.

(2) The wall thickness of the casting structure is not uniform and a hot knot is generated.

(3) The feeding pressure is low.

(4) The gate is small.

(5) The local temperature of the mold is high.

Prevention method:

(1) Obey the operating standards and reduce the casting temperature.

(2) Improve the structure of the casting, eliminate the accumulation of metal, and slowly transition.

(3) Increase the pressure of feeding.

(4) Increase the dark mouth to facilitate the transfer of good pressure.

(5) Adjust the thickness of the paint to control the local temperature of the mold.

8, pattern

Features: The surface of the casting has smooth stripes, which are visible to the naked eye, but can not be felt by hand. The color is different from the metal of the base metal. It can be removed by rubbing with 0# sandpaper.

Reason for formation:

(1) The filling speed is too fast.

(2) Too much coating.

(3) The mold temperature is low.

Prevention aspects:

(1) Reduce the filling speed

(2) The coating amount is thin and uniform.

(3) Increase the mold temperature.

9, deformation

Features: The overall deformation of the casting geometry does not match the design requirements.

Reason for formation:

(1) The casting structure is poorly designed, causing uneven shrinkage.

(2) The mold is prematurely opened and the casting rigidity is insufficient.

(3) The casting inclination is small and the demoulding is difficult.

(4) Improper handling of the casting.

(5) Deformation caused by rapid cooling when the casting is cooled.

Prevention method:

(1) Improve the structure of the casting to make the wall thickness uniform.

(2) Determine the optimum mold opening time and increase the rigidity of the casting.

(3) Amplify the casting pitch.

(4) Care should be taken to pick and place castings.

(5) Place in the air and slowly cool.

10, misplaced

Characteristics: A part of the casting is staggered from the other part on the parting surface, and a relative displacement occurs.

Reason for formation:

(1) Die insert displacement.

(2) The mold guide is worn.

(3) Mold manufacturing and assembly exquisiteness.

Prevention method:

(1) Adjust the insert to tighten it.

(2) Exchange guide parts.

(3) Perform trimming to eliminate errors.

11, shrinkage

Features: Under the X-RAY's exploration, the parts are in the shape of dots, curves, or blocks.

Mainly manifested in the following aspects (with low-pressure casting wheel cooling direction and various parts of the hub):

The solidification sequence of the casting:

A ring - B ring - (C ring, D ring) - spokes - slope - PCD - shunt cone - Tangkou. A, B ring shrinkage:

(1) Appropriately speed up the filling.

(2) Replenishing spray insulation coating.

(3) If the paint is too thick or has poor temperature performance, wipe the paint and then refill it.

(4) Shorten the casting cycle.

C ring shrinkage:

(1) Delay or turn off the air duct at the intersection of the wheel net and the spoke.

(2) The upper mold spokes make up the spray insulation coating, the coating is too thick and clean and re-spray.

(3) The filling speed can be appropriately accelerated.

Spoke root (spoke and wheel net intersection)

(1) Pull the exhaust line at the corresponding position of the upper mold.

(2) Replenish the paint at the spokes of the upper and lower molds.

(3) Properly shorten or delay the cooling parameters of the upper and lower mold slopes and PCD.

(4) The corresponding coating is too thick to clean and re-spray. It is recommended to add 39# paint.

(5) Properly shorten the casting cycle.

Slope shrinkage:

(1) Delay or turn off the split cone cooling parameters.

(3) The cooling time of the upper and lower mold slopes is prolonged, and the expected time is shortened.

(4) Partial water spray cooling.

(5) The paint is too thick to clean and re-spray.

PCD shrinks:

(1) Prolong the holding time and casting cycle.

(2) Properly advance or extend the cooling parameters at the PCD.

(3) The air blow or water spray treatment is applied at the upper mold PCD and the lower mold PCD.


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