Extruder Heater Materials
PTFE Breaks down at 230C, so replacement marterials are required in order to safely process plastics with high melting points such as PLA and HDPE.
Several high-heat areas are present in the nozzle, with different requirements:
- The heater barrel - Low thermal resistance needed.
- The heater cladding - High thermal resistance, some "give".
- Nozzle holder - High thermal resistance, rigid.
The proposed approach is to use ceramic-filled BBQ paint to insulate the heater barrel from the nichrome heating coil. BBQ paint is good for up to 600C but does outgass on its first heating.
To protect and enclose the heater element, I am proposing a fibreglass wrap saturated in plaster of paris, much in the same way a plaster cast is made. The fibreglass can be arrnaged to make sure the thermistor and all protruding wires do not rip through the plaster jacket if tugged.
To attach the barrel to the extrusion mechanism, a rigid block of insulating concrete is proposed. This need be no more than 30mm in dameter and 60mm high. A standard cement mix with added perlite and vermiculite should suffice. Due to the small size of the component, a fairly damp mix may be needed to ensure the concrete cures before it dries out.
A 3mm knitting needle through the centre of the block will maintain the central cavity, and hold the heater barrel in allignment. The needle will be removed before the concrete fully hardens.
One end of the block will have threaded rods embedded in it to facilitate attachment to the extrusion mechnism; washers or nuts may be embedded to improve adhesion. The other end will hold the heater barrel by means of a cluster of nuts and washers. The nuts and washers will be embedded, allowing the barrel to be unscrewed for maintenance or replacement.
A removable nozzle will be installed to ensure that the barrel and central cavity can be properly cleaned of debris before extrusion commences.
-- Main.VikOlliver - 04 Feb 2006