PVC Pipe Extrusion Start-up Procedure
http://www.plastics.com/content/articles/17/1/PVC-Pipe-Extrusion-Start-up-Procedure/Page1.html
Skip Thacker
BIOGRAPHIC BACKGROUND
EDUCATION:B. A. in Chemistry,Wabash College, 1956
MBA Program, Xavier University, 1960-61
TECHNICAL ORGANIZATIONS: Society of Plastic Engineers, Fellow Emeritus Grade Member; Vinyl Division, The Chlorophiles.
PROFESSIONAL EXPERIENCES:Over 35 years in research, development, technical services, sales and marketing activities centered primarily on polymer additives to improve processing and end-use properties of plastics. Currently retired, but available for PVC help.
By Skip Thacker
Published on 04/8/2007
Rigid PVC Pipe: Start-Up
Although this procedure describes CM-80 twin screw pipe extrusion start-up using pressure sizing, many of the same steps are also necessary for any extrusion process, regardless of end product or extruder type.
pg 1
Rigid PVC Pipe: Start-Up
Although this procedure describes CM-80 twin screw pipe extrusion start-up using pressure sizing, many of the same steps are also necessary for any extrusion process, regardless of end product or extruder type.
A. Assuming die is on machine properly, double check all electrical hookups,
match each heat zone with proper controls on panel.
B. Heat controls should be set at 300 F, 150 C across the board. Arrange to
have heats turned on a couple of hours prior to start-up, so as to give the
head and die a good "heat soak" period. This a good time to check heater
bands and controllers to make sure all work properly.
C. Turn up heats to roughly the following profile:
BARREL ZONES
____1____ ____2____ ____3_____ ____4_____
350-360 F 340-350 F 320-340 F 300-320 F
175-180 C 170-175 C 160-170 C 150-160 C
ADAPTER SPIDER- DIE VARIAC for MANDREL(pin) SCREW OIL
350-360 F 370-380 F 20-40% 300-320 F
175-180 C 185-195 C 150-160 C
Give the die at least an hour or two to arrive at final temperatures before
putting powder in machine. And give the die bolts a final tightening down!
Meanwhile, make sure powder blend is ready, and vacuum or pneumatic
system to the hopper is in operating order.
D. Put powder inhopper and follow this sequence:
1. Turn on extruder - slow speed (500-750 drive RPM).
2. Turn on feeder screw - slow speed (1.5 set) and feed just a little powder into screw flights (1/3 to1/2 full).
3. Watching at vent (no vacuum yet), and watching amps and back pressure, let material start coming out of die. (This may take 10-15 minutes at slow speed).
4. Gradually increase extruder speed to 1000, then 1500 RPM - watching amps. And after each increase in screw speed, increase feed rate to keep screws partially (1/3-1/2 ) filled.
5. After the purge compound is all pushed out, the initial pipe material will look cold out of die - but this should improve as RPM and feed are gradually raised. Look for a stock temperature (needle pyrometer) of about 370-380 F (185-195 C). Once at a reasonable production (1700 RPM to 2000 RPM) speed, gradually increase feed rate so screws are full - again watching amps. AMP readings in the 35-60 range are probably okay - start to worry above 60 amps. Remember to always increase screw RPM before increasing feed!
E. Once this speed is obtained with full screws, look at material in vent. It
should be a slightly damp to "cheesy" powder so that a vacuum can be
pulled without pulling a lot of powder (a little "snow" is okay). If not fused
enough, increase zones 1 and 2 by 10-20 F each. If too fused, decrease
zones 1 and 2 by 10-20 F each (5-10 C)
Although this procedure describes CM-80 twin screw pipe extrusion start-up using pressure sizing, many of the same steps are also necessary for any extrusion process, regardless of end product or extruder type.
A. Assuming die is on machine properly, double check all electrical hookups,
match each heat zone with proper controls on panel.
B. Heat controls should be set at 300 F, 150 C across the board. Arrange to
have heats turned on a couple of hours prior to start-up, so as to give the
head and die a good "heat soak" period. This a good time to check heater
bands and controllers to make sure all work properly.
C. Turn up heats to roughly the following profile:
BARREL ZONES
____1____ ____2____ ____3_____ ____4_____
350-360 F 340-350 F 320-340 F 300-320 F
175-180 C 170-175 C 160-170 C 150-160 C
ADAPTER SPIDER- DIE VARIAC for MANDREL(pin) SCREW OIL
350-360 F 370-380 F 20-40% 300-320 F
175-180 C 185-195 C 150-160 C
Give the die at least an hour or two to arrive at final temperatures before
putting powder in machine. And give the die bolts a final tightening down!
Meanwhile, make sure powder blend is ready, and vacuum or pneumatic
system to the hopper is in operating order.
D. Put powder inhopper and follow this sequence:
1. Turn on extruder - slow speed (500-750 drive RPM).
2. Turn on feeder screw - slow speed (1.5 set) and feed just a little powder into screw flights (1/3 to1/2 full).
3. Watching at vent (no vacuum yet), and watching amps and back pressure, let material start coming out of die. (This may take 10-15 minutes at slow speed).
4. Gradually increase extruder speed to 1000, then 1500 RPM - watching amps. And after each increase in screw speed, increase feed rate to keep screws partially (1/3-1/2 ) filled.
5. After the purge compound is all pushed out, the initial pipe material will look cold out of die - but this should improve as RPM and feed are gradually raised. Look for a stock temperature (needle pyrometer) of about 370-380 F (185-195 C). Once at a reasonable production (1700 RPM to 2000 RPM) speed, gradually increase feed rate so screws are full - again watching amps. AMP readings in the 35-60 range are probably okay - start to worry above 60 amps. Remember to always increase screw RPM before increasing feed!
E. Once this speed is obtained with full screws, look at material in vent. It
should be a slightly damp to "cheesy" powder so that a vacuum can be
pulled without pulling a lot of powder (a little "snow" is okay). If not fused
enough, increase zones 1 and 2 by 10-20 F each. If too fused, decrease
zones 1 and 2 by 10-20 F each (5-10 C)
pg 2
F. If material out of die looks smooth (both O.D. and I. D.) and has some rea-
sonable hot strength, it is ready to be strung up through the line. First, check
flow out of die - is it even all the way around? If not, die bolt adjustments
should be made at this time.
G. If material is too cold outof die (also too powdery at vent) go up 10 degrees F
or so in barrel. If material looks okay at vent, but is either hot, or cold out of
die, temperature changes in metering zone and screw oil temperature will
have greatest effect.
H. Do not change spider temperatures - 350-360 F, 175-185 C should be
sufficient as temperatures above 360 F or 185 C may cause spider burn.
Possibly the die may be increased to 380-385 F or 193-198 C and mandrel
increased to 30-40% for I.D., but try screw oil and zone 4 first.
I. On string-ups, the extruder and feeder are stopped, and the following opera-
tions take place quickly (this requires two people - one stationed on each
side of die):
1. Cut material flush to die opening.
2. Put sizing sleeve(water off) on die.
3. Insert anchor ring for chain and plug (screws into center of mandrel).
4. Roll cooling tank up to sizing sleeve so the sleeve protrudes into tank
slightly.
5. Start up extruder (slowly again - around 1200 RPM) and feeder. As
hot pipe comes out, cut a hole to insert hook which also hooks into
string-up pipe extending through haul-off.
sonable hot strength, it is ready to be strung up through the line. First, check
flow out of die - is it even all the way around? If not, die bolt adjustments
should be made at this time.
G. If material is too cold outof die (also too powdery at vent) go up 10 degrees F
or so in barrel. If material looks okay at vent, but is either hot, or cold out of
die, temperature changes in metering zone and screw oil temperature will
have greatest effect.
H. Do not change spider temperatures - 350-360 F, 175-185 C should be
sufficient as temperatures above 360 F or 185 C may cause spider burn.
Possibly the die may be increased to 380-385 F or 193-198 C and mandrel
increased to 30-40% for I.D., but try screw oil and zone 4 first.
I. On string-ups, the extruder and feeder are stopped, and the following opera-
tions take place quickly (this requires two people - one stationed on each
side of die):
1. Cut material flush to die opening.
2. Put sizing sleeve(water off) on die.
3. Insert anchor ring for chain and plug (screws into center of mandrel).
4. Roll cooling tank up to sizing sleeve so the sleeve protrudes into tank
slightly.
5. Start up extruder (slowly again - around 1200 RPM) and feeder. As
hot pipe comes out, cut a hole to insert hook which also hooks into
string-up pipe extending through haul-off.
pg 3
J. Start haul-off, carefully watching speed to match speed of hot pipe. Use a
hose with cold water playing on hook area to prevent tearing. As pipe is
slowly pulled through tank, start cooling water one zone at a time behind
the hook - first the sizing sleeve, then the water spray. Try not to let water
inside pipe!
Once pipe is through haul-off, get plug and chain ready to insert. Turn off
water on sizing sleeve and first part of cooling tank to make about a one foot
longitudinal cut in the pipe, hook chain on to eyebolt, and feed chain into
hole. Insert plug into hole and force it as much as possible into pipe, toward
the extruder. (Very little air pressure should be on plug - otherwise it will
blow out.)
As the hole travels down cooling tank, turn off water - turning water back on
immediately after plug passes. (A rag over the hole will keep out much of
the spray.) Turn on water in sizing sleeve again. Use just enough air to
keep pipe from collapsing, so plug can drag against inside without jamming.
Once plug has reached the end of its chain, a little more air pressure (5-10
psi) to keep pipe against sizing sleeve should give a nice glossy O.D. All
cooling zones behind plug hole should be on for full cooling with final plug
air pressure at 4-10 psi.
K. Once all this start-up pipe is through the haul-off and saw, watch that opened
area or any ballooned area of pipe can clear the saw opening - otherwise
the line will go down and string-up starts all over again! In fact all during the
hectic period of item J above, do not forget to check hopper for powder,
which is another common cause for a line to break requiring a repeat string-
up! At 1000+ pounds per hour,it does not take long to empty the hopper, and
2-3 empty screw flights will cause the line to break unless the haul-off is
slowed temporarily.
L. Once strung-up, and running smoothly, gradually increase screw RPM (and
corresponding feeder speed and haul-off speed) to maximum output - 2000-
2500 RPM. It is best to calculate the RPM ratio of extruder and haul-off so an
exact haul-off setting can be reached quickly.
M. At this point, the vacuum should be turned on (slowly) until at least 15-25
inches is obtained to remove volatiles.
N. Upon checking wall thickness, minor adjustments in die bolts and haul-off
speed may be required. Examination of I.D. should tell if pipe is too hot or
too cold. Wavy I.D. with high gloss is too hot. A fairly smooth I.D. with "semi-
gloss" is just right. One will normally see what looks like concentric rings
when looking down a length of twin screw pipe. These are screw marks
typical of twin screw extruders known affectionately as "Anger Rings". Screw
oil and zone four temperature should control the I.D.
O. Anytime a change is made in extrusion conditions - especially a temperature
setting - sufficient time must be given to see the effect of the change. For a
small extruder - up to 300 pounds/hour - allow at least 20-30 minutes. For a
medium extruder - up to 800+ pounds/hour - allow at least 45-60 minutes.
For a large extruder - up to 1000+ pounds/hour - allow at least 60-75 minutes.
If changes in conditions are made too quickly, it will be impossible to tell
which one caused any change in the product appearance.
P. At the end of the run, turn down all temperatures to 300-330 F, 150-165 C,
slow down extruder and haul-off to let machine begin to cool and allow the
hopper to run out. Break the line, swing hopper away, and begin feeding
purge compound to the throat of the extruder (vacuum off). Continue with
purge until the head and die are completely free of pipe compound, and
finally until screws are empty, at which point all power can be turned off.
"PURGE" FORMULATION
PVC (K-67) --------------------100
CaCO3 (1-2 micron)-------------100
Calcium Stearate------------------- 4.0
165 Paraffin Wax -------------------3.5
Methyl tin or Butyl tin
Mercaptoester stabilizer
(TM 181 or T94C) -----------------10.0
Indicator pigment as desired
hose with cold water playing on hook area to prevent tearing. As pipe is
slowly pulled through tank, start cooling water one zone at a time behind
the hook - first the sizing sleeve, then the water spray. Try not to let water
inside pipe!
Once pipe is through haul-off, get plug and chain ready to insert. Turn off
water on sizing sleeve and first part of cooling tank to make about a one foot
longitudinal cut in the pipe, hook chain on to eyebolt, and feed chain into
hole. Insert plug into hole and force it as much as possible into pipe, toward
the extruder. (Very little air pressure should be on plug - otherwise it will
blow out.)
As the hole travels down cooling tank, turn off water - turning water back on
immediately after plug passes. (A rag over the hole will keep out much of
the spray.) Turn on water in sizing sleeve again. Use just enough air to
keep pipe from collapsing, so plug can drag against inside without jamming.
Once plug has reached the end of its chain, a little more air pressure (5-10
psi) to keep pipe against sizing sleeve should give a nice glossy O.D. All
cooling zones behind plug hole should be on for full cooling with final plug
air pressure at 4-10 psi.
K. Once all this start-up pipe is through the haul-off and saw, watch that opened
area or any ballooned area of pipe can clear the saw opening - otherwise
the line will go down and string-up starts all over again! In fact all during the
hectic period of item J above, do not forget to check hopper for powder,
which is another common cause for a line to break requiring a repeat string-
up! At 1000+ pounds per hour,it does not take long to empty the hopper, and
2-3 empty screw flights will cause the line to break unless the haul-off is
slowed temporarily.
L. Once strung-up, and running smoothly, gradually increase screw RPM (and
corresponding feeder speed and haul-off speed) to maximum output - 2000-
2500 RPM. It is best to calculate the RPM ratio of extruder and haul-off so an
exact haul-off setting can be reached quickly.
M. At this point, the vacuum should be turned on (slowly) until at least 15-25
inches is obtained to remove volatiles.
N. Upon checking wall thickness, minor adjustments in die bolts and haul-off
speed may be required. Examination of I.D. should tell if pipe is too hot or
too cold. Wavy I.D. with high gloss is too hot. A fairly smooth I.D. with "semi-
gloss" is just right. One will normally see what looks like concentric rings
when looking down a length of twin screw pipe. These are screw marks
typical of twin screw extruders known affectionately as "Anger Rings". Screw
oil and zone four temperature should control the I.D.
O. Anytime a change is made in extrusion conditions - especially a temperature
setting - sufficient time must be given to see the effect of the change. For a
small extruder - up to 300 pounds/hour - allow at least 20-30 minutes. For a
medium extruder - up to 800+ pounds/hour - allow at least 45-60 minutes.
For a large extruder - up to 1000+ pounds/hour - allow at least 60-75 minutes.
If changes in conditions are made too quickly, it will be impossible to tell
which one caused any change in the product appearance.
P. At the end of the run, turn down all temperatures to 300-330 F, 150-165 C,
slow down extruder and haul-off to let machine begin to cool and allow the
hopper to run out. Break the line, swing hopper away, and begin feeding
purge compound to the throat of the extruder (vacuum off). Continue with
purge until the head and die are completely free of pipe compound, and
finally until screws are empty, at which point all power can be turned off.
"PURGE" FORMULATION
PVC (K-67) --------------------100
CaCO3 (1-2 micron)-------------100
Calcium Stearate------------------- 4.0
165 Paraffin Wax -------------------3.5
Methyl tin or Butyl tin
Mercaptoester stabilizer
(TM 181 or T94C) -----------------10.0
Indicator pigment as desired