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Home > Industry Information > Aluminum alloy extrusion defect analysis and quality control method (2)

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Aluminum alloy extrusion defect analysis and quality control method (2)

2018-07-26 02:28:34

Aluminum alloy extrusion defect analysis and quality control method (2)

【China Aluminum Network】

First, metal pressure

During the extrusion process, metal chips are pressed into the surface of the product, which is called metal pressing.

The main causes of metal intrusion:

1. Wool ends have defects;

2. The inner surface of the wool is covered with metal or the oil contains metal debris and other dirt;

3, squeeze barrel is not clean, there are other metal debris;

4, ingot into other metal foreign body;

5, slag inclusions in the wool.

Prevent method:

1, remove the burr on the wool;

2, to ensure the wool surface and lubricating oil clean and dry;

3, clean out the metal debris in the mold and squeeze tube;

4, use high quality wool.

Second, non-metallic press

Extruded products inside and outside surface pressed into foreign bodies such as black, called non-metallic press. After the foreign material is scraped off, the inner surface of the product exhibits unequal depressions, which will destroy the continuity of the surface of the product.

The main causes of non-metal press-in:

1, graphite particle size is large or clumping, containing water or oil stirring uneven;

2. The flash point of cylinder oil is low;

3, cylinder oil and graphite ratio improper, too much graphite.

Prevent method:

1, using qualified graphite, keep dry;

2, filter and use qualified lubricants;

3, control the ratio of lubricating oil and graphite.

Third, the surface corrosion

Surface-treated products that have not been surface-treated are chemically or electrochemically reacted with external media and cause local defects in the surface. This is known as surface corrosion. The surface of the corroded product loses its metallic luster, and when it is severe, it produces grayish white corrosion products.

The main cause of surface corrosion:

1. The product is exposed to corrosive media such as water, acids, alkalis, salts, etc. during production, storage and transportation, or parked in a humid atmosphere for a long period of time;

2, the alloy into the distribution ratio is not appropriate.

Prevent method:

1. Keep the surface and production and storage environment clean and dry;

2. Control the content of elements in the alloy.

Fourth, orange peel

On the surface of the extruded product, wrinkles like unevenness on the surface of orange peel appear, also called surface wrinkles. It is caused by coarse grains during extrusion. The coarser the crystal grains, the more obvious the wrinkles.

The main causes of orange peel:

1. Inhomogeneous ingot structure and insufficient homogenization;

2. The extruding conditions are unreasonable and the finished products are coarse;

3, stretch straightening amount is too large.

Prevent method:

1. Reasonably control the homogenization process;

2, the deformation is as uniform as possible (control extrusion temperature, speed, etc.)

3, control the pull correction should not be too large.

Fifth, uneven

After the extrusion, the thickness of the product in the plane of the area changes in the appearance of depression or bulge, generally not visible with the naked eye, through the surface treatment shows a detailed shadow or bone shadow.

The main causes of uneven:

1. Improper design of mold work belt, repair mode is not in place;

2. The size of the shunt hole or pre-chamber is unsuitable, and the force of drawing or expansion of the cross-section profile causes slight changes in the plane;

3, the cooling process is not uniform, the cooling rate of the thick-walled part or the cross-section is slow, causing the plane to shrink in varying degrees of deformation during cooling;

4, due to the great difference in thickness, thick-walled parts or transition area tissue and other parts of the organization increased.

Prevent method:

1. Improve mold design, manufacture and mold repairing level;

2, to ensure uniform cooling speed.

Six, vibration pattern

This is a periodic stripe defect in the M direction of the extruded product surface. The feature is that the surface of the product exhibits a continuous periodic stripe from the M direction, and the stripe curve coincides with the shape of the mold working belt. In severe cases, there is a noticeable bumpy feel.

The main cause of vibration pattern:

1, due to equipment caused by the extrusion shaft forward jitter, causing the metal out of the hole jitter;

2, due to mold caused by the metal out of the die hole jitter;

3, mold support pad is not suitable, mold stiffness is not good, jitter occurs when the extrusion force fluctuations.

Prevent method:

1, using qualified molds;

2, the use of a suitable support pad to install the mold;

3, adjust the equipment.

Seven, inclusion

The main cause of inclusions:

Due to the presence of metal or non-metallic inclusions in the inclusions, they are not found in the previous process and remain on the surface or inside of the product after extrusion.

Prevent method:

Strengthen the inspection of the blanks (including ultrasonic inspection) to prevent the blanks containing metal or non-metallic inclusions from entering the extrusion process.

Eight, water marks

The light white or light black irregular water marks on the surface of the product are called water marks.

The main cause of water marks:

1, after the cleaning is not good, the surface of the product residual moisture;

2. The residual moisture on the surface of the products caused by rain, etc. is not treated in time;

3. The fuel of the aging furnace contains water, and the moisture condenses on the surface of the product during cooling after the aging of the product;

4. The fuel of the aging furnace is not clean, and the surface of the product is corroded by sulfur dioxide after combustion or is contaminated by dust;

5. Quenching media are contaminated.

Prevent method:

1. Keep the surface of the product dry and clean;

2, control the water content and cleanliness of the aging material;

3, strengthen the management of quenching media.

Nine, clearance

The ruler M is superimposed on a certain plane of the extruded product, and a certain gap appears between the ruler and the surface, which is called a gap.

The main cause of gaps:

Uneven flow or uneven straightening of the metal during extrusion.

Prevent method:

Reasonably design and manufacture molds, strengthen mold repair, and strictly control extrusion temperature and extrusion speed according to regulations.

Ten, uneven wall thickness

Extruded products have the same thickness or uneven thickness in the same section or longitudinal direction, which is called wall thickness unevenness.

The main causes of wall thickness unevenness:

1, mold design is not reasonable, or improper assembly of tools and molds;

2. The extrusion cylinder and the extrusion needle are not on the same center line, forming an eccentricity;

3. Excessive wear of the inner lining of the barrel, the mold can not be firmly fixed, forming an eccentric;

4. The uneven wall thickness of ingot blank itself cannot be eliminated after primary and secondary extrusion. The wall thickness of wool ingot is not uniform after extrusion and is not removed after rolling and stretching.

5, uneven application of lubricants, so that the metal flow is uneven.

Prevent method:

1. Optimize the design and manufacture of tool and die, and reasonably assemble and adjust;

2. Adjust the center of the extruder and extrusion tool mold;

3, choose qualified blanks;

4, reasonable control of extrusion temperature, extrusion speed and other process parameters.

Eleven, expand (and) mouth

The defects on both sides of extruded profile products, such as channel-shaped and I-shaped extrusions, are called flaring and inward slanting defects, which are called parallel ports.

Expansion (and) port main causes:

1. Metal flow velocities of the two "legs" (or "legs") of a channel or similar channel profile or I-shaped profile;

2. The uneven flow velocity on both sides of the tank floor;

3, improper stretching and straightening machine;

4, after the product out of the mold hole, online solution treatment cooling uneven.

Prevent method:

1, strictly control the extrusion speed and extrusion temperature;

2, to ensure the uniformity of cooling;

3, the correct design and manufacture of molds;

4, strict control of extrusion temperature and speed, the correct installation of mold.

Twelve, straightening marks

The spiral stripe produced when the roller is straightened on the extruded product is called a straightening mark, and any straightening product on the upper roller cannot avoid the straightening mark.

The main cause of straightening marks:

1, Roller roll surface has a rib;

2, the curvature of the product is too large;

3, too much pressure;

4, the leveling roller roller angle is too large

5, product ellipticity is large.

Prevent method:

According to the causes, take corresponding measures to adjust.

Thirteen, stop marks, instant impressions, bite marks

Stop extrusion during extrusion to produce strips on the surface of the product and perpendicular to the extrusion direction, called the stop marks; in the extrusion process produces a linear or striped pattern on the surface of the product and perpendicular to the extruded square south , known as bite marks or instant impressions (commonly known as "false stop marks").

During the extrusion, the adherents that are stably attached to the surface of the working belt are instantly peeled and adhered to the surface of the extruded product to form a pattern. The work belt that appears when the extrusion is stopped is the “M” mark, which is called a stop mark. The “M” pattern that appears during the extrusion process is called a momentary imprint or bite mark and it will make a noise when it is squeezed.

The main causes of stop marks, moment marks, and bite marks:

1. Inconsistent heating temperature of ingot or sudden change in extrusion speed and pressure;

2, the main part of the mold design, manufacturing or uneven assembly, there is a gap;

3, there is an external force perpendicular to the extrusion direction;

4. The extruder runs unsteadily and crawls.

Prevent method:

1, high temperature, slow speed, uniform extrusion, extrusion force remains stable;

2. Prevent the external force in the vertical extrusion direction from acting on the product;

3, rational design tool mold, the correct choice of mold material, size, strength and hardness.

XIV. Internal surface abrasion

The abrasion of the inner surface of the extruded product during the extrusion process is called inner surface abrasion.

The main cause of internal surface abrasions:

1. The extrusion pin has a metal;

2, extrusion needle temperature is low;

3, the surface quality of the extrusion needle is poor, there are blunt trauma;

4, extrusion temperature, speed control is not good;

5. Improper proportion of extrusion lubricant;

6, uneven grease.

Prevent method:

1. Increase the temperature of the extrusion cylinder and the extrusion needle, and control the extrusion temperature and extrusion speed;

2. Strengthen lubricating oil filtration, often check or replace waste oil, grease should be uniform and appropriate;

3, keep the wool surface clean;

4, timely replacement of unqualified mold and extrusion pin, and keep the surface of the extrusion mold clean and smooth.

15. Failed mechanical properties

The mechanical properties of HB, HV, etc. of extruded products do not meet the requirements of the technical standards or are very uneven, and they are called mechanical properties.

The main causes of unqualified mechanical properties:

1. The chemical composition of the alloy exceeds the standard or the ratio is unreasonable;

2, extrusion process or heat treatment process is not reasonable;

3, poor quality of ingot or billet;

4, online quenching did not REACH quenching temperature or cooling rate is not enough;

5, improper artificial aging process.

Prevention and control measures:

1. Strictly control chemical composition according to standards or establish effective internal standards;

2, using high quality ingot or billet;

3, optimize the extrusion process;

4, strictly enforce the quenching process system;

5. Strictly implement the artificial aging system and control the furnace temperature;

6, strict temperature measurement and temperature control.

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