Mandrel for extruding heat exchanger tubes - has radial grooves on tapered mandrel to provide inwardly facing ribs af taper section

摘要

The mandrel has a cylindrical section (4), over which the bore of a piece of raw material (A) fits in the extruding press (8). The mandrel next has a short conical section with smooth surface over which the dia. of the mandrel reduces. The next section of the mandrel protrudes through the extruding die. This section tapers again, with a gradually increasing dia. till the mandrel dia. is equal to the bore of the tube to be extruded. The conical end section of the mandrel has grooves which form the fins in the bore of the tube. The smallest dia. of the conical end section is slightly smaller than the radial distance between the fin tips.