HighTemperatureMaterials
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.
Promising materials are:
- BBQ Paint, or other "high heat" paint.
- Plaster of Paris
- Fibreglass insulation
- Perlite/vermiculite (possibly pummice)
- Cement or concrete
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 arranged to make sure the thermistor and all protruding wires do not rip through the plaster jacket if tugged. It should be resilient enough to cope with thermal expansion and contaction of the heating element.
To attach the barrel to the extrusion mechanism, a rigid block of insulating concrete is proposed. This need be no more than 30mm in diameter 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. This, of course, weakens the concrete so a happy medium needs to be found.
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 mechanism; 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. Some smoothing of the finish and washing will be necessary for the concrete component, to keep debris to a minimum.
A removable nozzle will be installed to ensure that the barrel and central cavity can be properly cleaned of debris before extrusion commences.
Purchasing notes
For small quantities of premixed cement, ask your DIY store for a cement "patch pack", used for small repairs.
Check out several brands of black "high heat" paints. Prices vary by a factor of 2. Automotive stores also sell this paint for spraying engines and exhaust systems.
White cement varies from ordinary grey cement only in terms of colour and additional cost.
Test Articles
A test cylinder was made from 5 parts cement premix and 3 parts damp greenhouse vermiculite/perlite mix together with just enough water (quantity not measured). A woodscrew and 3mm knitting needle were placed in the concrete.
The concrete was kept in place by a thick cardboard tube 37mm I/D and blocked at one end with gaffer (duct) tape The tube was dampened before use to avoid drying out the concrete. The components were taped in place to stop them sinking, and the whole assemblage left in shady surroundings. All cats were dissuaded from entering the experimental zone.
Time started, 4:30pm. Ambient temp 21.5C, gentle breeze, some cat hair.
After 1 hour the needle was removed by pulling upwards. This resulted in some damage to the upper surface of the block and the coating on the tip of the needle. Pushing downward may have been a better idea, or perhaps a more comprehensive mould is required.
10am next day, the concrete is just starting to show small grey patches on the upper surface. Initial curing is expected to be complete within an hour or so, but the test article will be left alone for at least 24 hours.
It is already becoming apparent that the hole left by the needle is substantially larger than 3mm.
-- Main.VikOlliver - 04 Feb 2006
