1)Internal Pipe: Because of homogeneous of a billet, center of the billet moves faster than periphery. As a result of depth metal zone extend along the outer surface of billet. After 2/3rd of billet extruded, outer surface of billet moves towards the center. Since, the surface of billet after contain of oxidized layer (skin), this type of flow results in internal oxide stringers. This defect is known as internal pipe. Section of the extruded metal, it will appear as a ring. High friction between billet and container increase the probability of this defect.
2)Axial Hole: While extrusion is carried out to the point at which the length of the billet remaining in the container is about 1/4th its diameter, the rapid radial flow into the die results in the creation of an axial hole/funnel in the back end of extrusion. This region must be discarded. The length of this defect can be reduced by inclining the face of ram of an angle to the ram axis.
3)Fir Tree Cracking: When ram speed is too high for the extrusion , surface of the billet becomes badly rough. Repeat ting transverse cracking is called fir tree cracking.
It is also called chevron cracking. It can decure at low extrusion ratio. High frictional resistance at the tool and billet interface produces a sound product while center burst occur while the friction is low
5)Surface Crack and Lamination: The lubricant film must be complete and continuous between the billet and container wall during extrusion. Gapes in the film will cause to initiate shear zones which can developed into surface cracks. Lamination of oxide can be created in the same way.
2)Axial Hole: While extrusion is carried out to the point at which the length of the billet remaining in the container is about 1/4th its diameter, the rapid radial flow into the die results in the creation of an axial hole/funnel in the back end of extrusion. This region must be discarded. The length of this defect can be reduced by inclining the face of ram of an angle to the ram axis.
3)Fir Tree Cracking: When ram speed is too high for the extrusion , surface of the billet becomes badly rough. Repeat ting transverse cracking is called fir tree cracking.
It is also called chevron cracking. It can decure at low extrusion ratio. High frictional resistance at the tool and billet interface produces a sound product while center burst occur while the friction is low
5)Surface Crack and Lamination: The lubricant film must be complete and continuous between the billet and container wall during extrusion. Gapes in the film will cause to initiate shear zones which can developed into surface cracks. Lamination of oxide can be created in the same way.
No comments:
Post a Comment