Extrusion guide SX HFFR
This guide applies to the following grades:
CT06-30, SX545, SX407, SX538, SX559, CT09-03, CT09-38, CT09-05, CT09-13
| Equipment | ||
| Extruder | Ideally 20 to 24 L/D ratio. | |
| Extruder head | Ideally with as small a volume as possible and with deep flow channels. A head assembly with a diverter valve is beneficial. | |
| Screw | Low compression ideally 1.2:1. | |
| Extension piece | If there is an extension piece connecting the end of the extruder and head then this needs to be heated to 160oC by heater bands or similar. When using SX538 or SX559 heating to 180oC is recommended. | |
| Tooling Pressure | Short land length; no longer than 3mm. The flow path should be as gentle as possible with the adequate separation of the core and ring die. | |
| Tubing | Double taper designs are preferred. Draw down ratios of no greater than 1.5:1 is recommended. | |
| Processing conditions | ||
| Drying | The graft should not be dried. The catalyst can be dried in a dehumidifying drier. | |
| Temperature profile |
Ranging from 130 to 160oC from the feed to the end of the extruder with 165oC on the head and 170 on the die. Melt temperatures should be kept below 170oC. CT09-03 and CT09-05 will tolerate melt temperatures up to 190oC. |
|
| Extrusion speed | The aim is always to keep the residence time in the extruder to a minimum. On initial start up screw speed should be at a minimum of 5 rpm and during production at a minimum of 20 to 30 rpm. When changing tooling or during other stoppages every attempt should be made to keep material moving through the extruder. |
|
| Trial procedure | It is suggested that when conducting a first trial, the graft is run first without catalyst and a satsifactory extrusion is achieved. Initially catalyst should be used at 3% and if it runs well then it can be increase to 5%. A rough finish may be exerienced at extruder speeds below 10 rpm but this shoud disappear above screw speeds of 20 rpm. |
|
| Colour masterbatches | Those from PW Hall are recommended. | |
Troubleshooting guide
|
Problem |
Cause |
Solution |
| Poor surface finish | Temperature low | Increase barrel and head temperatures |
| Use higher shear screw | ||
| Melt fracture |
Increase barrel and head temperatures |
|
| Use lower draw-down ratio | ||
| Reduce extrusion rate | ||
| Extrusion O/D too low | Reduce haul off speed | |
| Change to smaller die (run with slight die swell) | ||
| Material pre-cured | See reactive material below | |
|
Material reactive on start up |
Compound shelf life expired | Replace material |
| Compound wet | Vacuum dry at ambient temperature | |
| Replace material | ||
| Catalayst masterbatch too strong or overdosed | Vacuum dry at high temperature | |
| Reduce amount used | ||
| Replace with weaker catalyst masterbatch | ||
| Long residence time in extruder | Maintain a minimum extruder speed of 6rpm during start-up phase. | |
| Material reactive during production |
Stagnation in extruder or head | Use process aid |
| Check screw and head design | ||
| Melt temperature too high | Check extruder heating and cooling for faults | |
| Reduce temperature profile | ||
| Catalyst overdosed | Check dosing unit calibaration | |
| Die drool | Low moecular wieght material exuding during extrusion | Use highly polished die/ point |
| Add 1-2% process aid | ||
| High motor amps | Is motor rating sufficient? | Upgrade motor |
| Incorrect screw design | Use lower shear/ compression design | |
| Material crosslinking | See reactive material above | |
| Gauze pack too harsh | Remove some/ all gauzes | |
| Head design restrictive | Change head design | |
| Material too stiff | Increase temperature profile | |
| Check heater bands/thermocouples | ||
| Use higher MFI material | ||
| Gels in extrudate | Stagnation | Use process aid |
| Use highly polished die and point | ||
| Check screw and head design | ||
| Gels in extrudate | See reactive section above | |
| Fails hot set test | Shear breaks (locked-in stresses too high) | Reduce draw down ratio |
| Reduce vacuum | ||
| Adjust die separation | ||
| High elongation (low cure level) | Increase cure time | |
| Check calibration of catalyst dosing unit | ||
| Use stronger or more catalyst |
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