Extruded die caused by extrusion die
[China Aluminum Network] A large cap in extrusion is typically caused by issues with the extrusion die, often resulting from an uneven die surface that leads to a net cut. As aluminum adheres gradually to the die, it can cause a buildup, leading to a large cap. Here are several reasons why an extrusion die may result in a large cap:
1. If the extrusion die surface is not flat or has a defective mouth, there may be gaps on the locking surface, causing aluminum turbulence. Any defects in the die mouth should be repaired through welding, and the mold surface must be kept smooth and even.
2. An oversized feed cavity (with a short modulus) can lead to a small locked area in the mold cylinder. The circumcircle of the feed cavity should maintain a consistent distance from the feed tube wall, with at least 5mm clearance on each side of the 10mm limit. Molds with a high pressure ratio should not be simply adjusted by expanding the manifold. When using such dies, the center points of all sides must be aligned to prevent misalignment and uneven flow.
3. If the extrusion die lacks a milled mouth, and the mold closing surface is too large, the pressure per unit area may fall below the outlet pressure. This can cause aluminum to stick to the mold surface after running, leading to an uneven surface and difficult-to-clean large caps. It's important to properly coat the cylinder surface with aluminum and cut off excess material from the die surface multiple times. Applying oil to the cylinder indentations can help prevent aluminum from sticking to the die surface. Even if small flashes occur occasionally, they can be managed effectively.
4. If the nozzle size of the extrusion die is smaller than the working surface of the cylinder, the closed area of the die will be too small, making it prone to damaging the cylinder’s working surface. When refitting a small machine mold for a larger machine, the die outlet diameter should match the diameter of the large cylinder’s working face.
5. If the thickness of the extrusion die is insufficient, it can cause the tube to be squeezed onto the die set. The mold and mold sleeve must follow the principle where the guide surface protrudes 1mm beyond the sleeve. This ensures that the die set is never directly subjected to extrusion force, which could lead to damage or deformation.
6. If the gap between the mold sets and the die is too large, aluminum can get stuck inside, leading to incomplete shearing and an uneven die surface. This issue is common in molds that have been modified from smaller machines.
7. A high extrusion ratio can create greater resistance at the outlet than the extrusion force itself, causing uneven locking surfaces and aluminum flowing out from these areas. Boring car issues may occur, so it's advisable to increase the rod temperature, mold temperature, and barrel temperature as needed. If necessary, the mold sets and gaskets can be heated on the machine. Shortening the length of the aluminum rod can also help reduce the risk of capping, especially when the rod is too short, as it can be punched without increasing the temperature. However, a high rod temperature can make capping more likely and may restrict speed increases.
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