Due to the special nature of its manufacturing process, hot-extruded aluminum profiles may exhibit the following surface defects during the hot extrusion process, caused directly or indirectly by the mold polishing quality or process conditions: coarse texture, color separation, dark bands, bright bands, scratches, ribbing, and poor smoothness.
Causes of Rough Surface Defects in Extruded Aluminum Profiles: In the extrusion production of aluminum profiles, common defects are quite intuitive, such as bending, twisting, deformation, and slag inclusion.
Aluminum profiles that come off the extrusion production line are referred to as base material, billet, or raw material.
The preliminary assessment of surface quality is generally conducted after 2-3 pieces are extruded following die setup. Initial samples are taken to make a preliminary judgment on whether the surface quality is acceptable. Once the surface is deemed acceptable, other inspections are carried out.
5 Methods to Quickly Assess Surface Quality Defects of Aluminum Extrusion Billets
1. Tactile touch: Use your hand to touch the surface of the substrate, or scratch with your fingernail to feel the grooves or raised areas, and determine whether there is an obvious tactile sensation. Applicable for judging various surface treatments.
2. Pencil scratches: During the extrusion of aluminum profiles, use a pencil to scratch the surface of the aluminum profile. By feeling and observing the continuity of the pencil scratches, determine whether there are coarse patterns or grooves. Suitable for judging the surface of anodized materials.
3. Spray paint test: For the first inspection sample, use automatic spraying to coat the surface of the substrate, simulating painting effects. After 1-2 minutes, when the surface is dry, observe and judge whether there are scratches, grooves, raised areas, or other defects. Suitable for judging painted surfaces.
4. Alkali Washing Test: During the initial inspection sampling, take a 300mm sample from the 3rd rod, and immerse it in the mold tank for 30-40 seconds. (Note: consider the alkali solution concentration and tank temperature; if the concentration or tank temperature is too low, appropriately extend the soaking time, generally not exceeding 60 seconds.) After alkali washing, the surface of the substrate can be checked for defects such as color separation, scoring, or mold weld lines. This is suitable for oxide materials with high surface requirements.
5. Surface Grinding: During the initial inspection sampling, take a 300mm sample section and use an industrial white clean cloth to grind the substrate surface transversely. After grinding, it is easier to observe finer defects on the substrate surface. This is used to identify surface defects such as fine scratches, (not easily picked off with a fingernail) concave bulges, convex bulges, and surface defects that are difficult to judge using the above four methods. It is applicable for surface inspection of coatings, anodized materials, and fluorocarbon materials.
The first step is a rapid inspection to determine whether the surface quality is acceptable. Even if the first piece is qualified, abnormal situations may still occur during the extrusion process. Therefore, in actual production, it is necessary to formulate a reasonable inspection frequency based on the severity of the base material defects, the type of surface treatment, and in combination with the order and customer quality requirements, according to the requirements of the operation instructions. The appropriate methods should be chosen for assessment, making timely and accurate judgments, with the principle of avoiding misjudgment or missed judgment.
