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The extrusion equipment
process begins with pellets or powder and ends with medical-grade tubing. In
between is the multistep, multicomponent process of extrusion. Despite
extrusion equipment manufacturers' continued reliance on conventional
processes, new technologies are being implemented more frequently up and
down the extrusion line. Among other things, this new equipment is intended
to boost extrusion accuracy and repeatability, reduce scrap and downtime,
improve cooling processes, and enhance product quality. Related words are
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A key extrusion equipment element
Extrusion equipment system designs vary, but the screw is a key component in
each of them. Screw design was a major focus of engineers at Davis-Standard
Corp. (Pawcatuck, CT) during the
extrusion equipment development of the
company's Corporate extruder line. The engineers acquired two patents for
the design of the extruder's barrier screw. "As far as I know, it's the
first new thing to happen to barrier screws in 10 years.
Screw design was a principal focus of the extrusion equipment corporate
extruder line.
The
extrusion equipment function of the barrier screw is to separate melted
from solid material inside the extruder. In typical systems, this process
has little effect on the material in the solid pool. To address this, the
standard added a second flight to the barrier screw—locating it in the solid
pool. The new flight configuration, according to them, mixes material in the
solid pool more thoroughly and reduces the time needed for the melting
process, which can decrease the generation of imperfections in the extruded
product.
Pumping up the extrusion equipment process
As extrusion equipment pushes material through the system, gear or melt
pumps are often used to perform a metering function. What's the advantage of
this arrangement? "Everybody in the medical field talks about accuracy and
repeatability rather than speed, "everything has to be accurate." To meet
the needs of these manufacturers, gear pumps must be capable of metering
material volume with 1% accuracy. They explain that his company's gear pumps
have pressure sensors at both ends to stabilize pressure changes along the
length of the system, which boosts metering accuracy to 0.1%. Related words
are cost of foam profile, killion sheet, calendaring, plastic taper, used
twin screw, down stream, ice cream, price of new when starting a business,
used twin screw compounding, air filters for all.
Extrusion equipment Alternate Polymer extruder enables seamless changes in
polymer composition.
Increasing the accuracy of new extrusion equipment systems, however, can
also boost both equipment and operating costs. "When you have a small
machine like a medical tubing extruder, the gear pump costs almost as much
as the whole extruder system," note extrusion equipment editors. More over,
the pumps must be cleaned thoroughly whenever extrusion materials are
changed. The cleaning process can take hours and often can fail to remove
all of the residual material from the pump.
An extrusion equipment engineer explains that after he took over the
extrusion process for a former employer, he immediately removed the gear
pump from the line. As a result, "I was extruding better product." He
reasons that his employers "weren't getting the pump cleaned very well, so
they were getting black specks in a lot of their extrusions."
But what about the need for extrusion equipment accuracy?
Extrusion
equipment precision can be achieved without the use of a melt pump,
according to extrusion equipment product manager. "A melt pump is a Band-Aid
for an improperly designed screw," quoting a colleague. "It's a great device
if you're trying to use a general-purpose extrusion screw to move various
materials. But a general-purpose screw isn't a great screw for any one
material."
Bessemer believes that a screw designed for a specific material will perform
well in most instances. "Some extruder manufacturers will tell you that when
they're putting a line together, they try their best to use a screw designed
for a particular material—and only use a melt pump as a last resort."
DRIVE FOR ACCURACY
Twelve Welex 21/2-in. extruder lines equipped with Conair Gatto vacuum
sizers.
In addition to the screw and melt pump, the drive is another component that
affects extrusion accuracy. Because they offer greater precision, ac drives
have replaced dc drives in most extrusion systems. are more accurate because
they give you full torque across the whole speed range. A dc drive has to
attain a certain speed before you get full torque out of it." He adds that
advanced ac drives have become so accurate that some users have been able to
eliminate the use of melt pumps in their systems.
Use of ac drives offers other advantages over their dc counterparts. The
ventilation systems required for dc motors can blow carbon dust and other
pollutants into the atmosphere. In contrast, ac drives are enclosed, which
can promote cleaner operationadds that ac drives require less maintenance
than dc drives and are less expensive in smaller size ranges.
To manage the extrusion process company now offers a microprocessor-based
control system. The system's Windows-based software facilitates the
recordkeeping process. "Users can take all the machine's operating
parameters, analyze them in many different ways, and make spreadsheets,.
"And they can store the data forever."
To satisfy FDA requirements, tubing manufacturers must keep detailed records
of their extrusion process. Small manufacturers, unable to afford expensive
process controllers, often keep records by hand. For these manufacturers,
Davis-Standard developed midrange process controllers that are less
expensive than the company's Epic controllers. Unlike the Epic, the firm's
Mesa controllers do not communicate with every piece of equipment in the
extrusion process; however, communication can be maintained with important
equipment, such as the extruder, melt pump, and downstream puller.
Mesa controllers also provide limited levels of reporting. "You'll have to
depend on something other than the Mesa to do all the reporting you need.
"But if you have a gauge in the line, you can get reports out of it for
dimensional control."
Process control can be especially challenging during extrusion of multilayer
products. In multilayer extrusion, each separate material requires its own
extruder. With several extruders around a single die, an operator would have
difficulty adjusting the individual drive speeds during the extrusion
process. Instead, separate drives are often linked to a master in a
configuration called a coordinated drive system.
Process controllers of extrusion equipment are linked to equipment that
monitors the dimensions of extruded tubing. To ensure that the cross section
is round, the
extrusion equipment system uses x-y lasers that take outside
diameter (OD) measurements in two directions. In previous versions,
individual measurements were generated on displays in such rapid succession
that operators had difficulty reading the numbers from extrusion equipment.
Now, almost all laser measuring devices display only the average value of
every 100 extrusion equipment measurements taken. Related words are cost of
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screw compounding, air filters for extrusion equipment
.
While the extrusion equipment system uses lasers to check the OD, ultrasound
equipment measures wall thickness. These dimensions are then communicated to
the process controller. If the product is out of tolerance, the control
equipment makes the necessary correction. Although this control process is
not new, the system is faster than previous versions,
extrusion equipment
results reports. With signals traveling more quickly to and from control
equipment, extrusion systems produce a smaller amount of flawed tubing than
in the past of extrusion equipment.
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