Basic HTML Version
-11-
THE EXTRUDER TIMES / ISSUE 10 / AUGUST 2010
1. HMI
2. Motor
3. Torque Coupling
4. Gearbox
5. GB / SS coupling
6. EPZ
(
Screw Elements,
Shafts & Barrels
)
7. Devolatilizing system
8. Die Assembly
2
3
4
5
6
7
8
1
Extruder Care and Maintenance
TO BE CONTINUED
The Art of Extruder Care and Maintenance
Remaining part of this article will be covered in ET 11 & 12
This article was possible with the contribution from
Mr. Prasanna Kumar, Sr.
STEER India
Manager Technical Services,
E-mail: prasannakumar@steerworld.com,
Screwdismantling procedures
Twin-screw extruders are equipped with screws that are segmented;
and intermeshed with each other; operators to pull them out of the
machine in one piece and have both come out together. The screws
are usually not difficult to remove if you first run a purge material
through the extruder first. If your usual resin is a polymer which is
going to stick to the screws and be difficult to clean off, try to find a
good purge resin to flush it out and that is easier to get off the screws.
Ÿ
Move the die, screen changer, gear pump and whatever else
is bolted on the end of the extruder out of the way.
Ÿ
For larger machines have a table or hoist set up to support the
screws as they are pulled from the barrels. If using supports
from underneath, wood blocks are a good choice. If using an
overhead hoist, web slings are easier to work with than chains.
Ÿ
With the feeder off, run the drive at 60 RPM for 2 or 3 minutes, or
until all the purge resin is flushed out of the machine. Now, stop
the drive, but leave the heat zones on.
Ÿ
Clean the screw tips with a brass scraper or wire brush. Break
loose the front screw tips, but do not remove the back screw
tips.
Ÿ
Both the tips have a left-hand thread, hence you need to turn
the tip wrench clockwise to loosen them. It’s not unusual for
them to be fairly tight, so you might have to whack the tip
wrench handle with a hammer a couple of times to break them
loose.
Ÿ
Remove the side covers from the gearbox coupling area, and
check to see if your couplings have setscrews or coupler holding
the screw shafts in place. Normally you want to leave the
setscrews which hold the couplings onto the gearbox output
shafts tightened. This way the couplings stay attached to the
gearbox output shafts.
Ÿ
Remove front screw tip and thread in the screw removal fixture
provided with the extruder.
The screws should pull right out without having to apply a lot of force.
Start brushing the polymer off them as they come out. Use either a
SS or carbon steel wire brush, or copper gauze. The screw elements
have a very hard surface, so you don’t have to worry about scratching
them.
Ÿ
When you get the screws all the way out, and you've cleaned
them, set them on wooden blocks to cool. (note: it’s easy to
make some screw shaft rests. Just take some 4” x 4” lumber
and cut 2 “V”-notches into one side. This will keep the screws
from rolling off the blocks)
Ÿ
While the barrels are still hot this is a good time to clean them
also. Use a round wire brush the correct diameter for the barrel
bores, on a long extension handle. (note: you can make a nice
tool for this by attaching a round wire brush to a long piece of
3/8” or 1/2” galvanized pipe. You can then use an electric drill
at low RPM to do a thorough job of cleaning the barrels) When
you get all the polymer out, take a look inside the barrels with a
flashlight and inspect for galling and wear.