MIXER AND INERTING OPERATIONAL RECOMMENDATIONS
The important factor to consider is that the mixer should be inerted prior to commencing
high speed mixing. However, when the powder is loaded into the mixer, it will carry air
trapped in its voids, as much as 50% of the volume in the case of powder. If only the
unfilled headspace of the mixer was inerted, then when mixing starts, this air would be
released and would increase the oxygen level in the bulk of the mixer. However, by
purging underneath via the shaft seal, it is possible to displace this air during the initial
purge cycle provided some gentle agitation was taking place. Without agitation, the
nitrogen may just channel through the powder and not effectively displace the air.
Therefore during the initial purging cycle, it is recommended to operate the mixer tools on
a low speed.
1. Load mixer with powder and aluminium (or other) pigment.
2. Close lid.
3. Operator checks that dust extraction is in place and operational.
(This could be interlocked to sequence if required)
4. Start operational sequence.
· Nitrogen Flow Starts.
· Nitrogen Flow Switch indicates a flow.
· Operator Checks Flow Rate. (Pre-set at regulator?)
· Sequence Pauses.
· Operator Confirms Flow Rate and presses button to ‘continue’.
· Mixer Starts on Slow Speed.
· Nitrogen Flow continues for Pre-Set Time. (Tbc during commissioning)
· Mixer Speed Increases to Required Bonding Speed.
· Bonding Continues until End Point Reached. (Pre-determined by temperature?)
· Mixture Discharged to Cooler. (operator needs to manually check cooling water flow
· Nitrogen Flow Stops.
· End of Sequence.
As the cooler will hold more than one mixer load, then cooler discharge will be better
controlled manually rather than built into the PLC programme sequence.
Some care will be needed when loading the next batch as the mixer will still have some
nitrogen in it. As the mixer is emptied, air will be drawn in to replace the powder, so will
dilute the nitrogen. The residual nitrogen concentration should be checked during
commissioning using oxygen analysis.
The sequence would need to change slightly if it was decided to add aluminium after
the powder was hot via screw feeder.