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Quality Considerations in Plastic Fittings and Connectors
By Jason Cain, Quality Manager, Value Plastics Mark Rosneck, Market Development
Manager, Value Plastics
Plastic fittings are ubiquitous in pharmaceutical operations performing the simple
role of connecting pieces of flexible tubing together. But there’s an awful lot
of flexible tubing used in pharmaceutical processing! Have you ever thought about
how the “quality” of that barbed fitting or luer might affect your process? Is
there a different quality standard for a fitting that connects plastic lines in
a car’s vacuum system from one that connects two pieces of silicone tubing to
a laboratory instrument? It seems that there probably is a difference but what
is it? What is “quality” and what isn’t “quality” in fittings and connectors?
That’s the question we’ll answer and it’s one of those instances where what you
don’t know can hurt you.
Surface Contamination – Is That String Cheese?
Surface contamination
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Surface contamination on the exterior of a part is both an appearance issue as
well as a potential cross-contamination issue and a potential leak path. Contamination
on the interior surface is a crucial issue since it presents an immediate contamination
concern. Since any surface contamination is primarily related to machinery and
tooling “housekeeping” issues, the solutions involve both people and process management.
People are often the primary source of contamination on the surface of a part.
Proper handling of products intended for the pharmaceutical industry is all-important
and involves following the Good Manufacturing Practices (GMP) as described in
the 21 CFR 211.28 (a) guidelines for proper attire including static free gowns,
hairnets, beard nets, and gloves as well as manufacturing room cleanliness. There
is a trend in the fittings and connector industry toward meeting the ISO14644-1
cleanroom standard for products sold into the pharmaceutical industry.
Another source of contamination is often the output storage tub. Keeping these
tubs clean is important since contamination can easily attach themselves to parts
as they leave the molding machine.
The rigorous application of machine startup guidelines will also significantly
reduce surface contamination. This includes wiping down key areas where contaminants
such as grease can exist as well as cleaning the molds prior to production. This
cleaning should also be done periodically during the production run. The use of
work in process (WIP) inspections that include well defined AQL (acceptable quality
level) visual inspections is critical. An additional mechanical cleaning step
is often employed to aspirate away any remaining exterior surface contamination.
These cleaners may also employ static reduction techniques to loosen the contamination
from the part.
 Stringer
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Another type of surface contamination can come from “stringers.” Stringers occur
in the same way that mozzarella cheese can “string” as you take a bite of pizza.
In a molding process, stringers can occur when the two halves of the mold separate
and the part is removed. Adequate process control will minimize stringer production.
However, occasionally a stringer is produced and can attach itself to the surface
of a part and create a contamination should it blow into the finished parts bin.
Reducing stringers involves careful control of the mold temperature as well as
the time needed to properly dry the raw material.
Embedded contamination
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Embedded contamination is of a concern since it presents an unknown risk. There
is something clearly within the part but what is it? However, unlike surface contamination,
the clarity of the part affects how easy these defects are to detect. If you are
concerned about embedded contamination, you should take this into account when
purchasing colored parts.
Contamination within a part can come from numerous sources that are often very
difficult to identify. A common source is from inadequate cleaning of the barrel
or screw in the molding machine. Improper cleaning of the part cavity within the
mold is another common source. Cross contamination is a problem particularly when
companies do not utilize an automated material handling system. When the molder
switches from one plastic resin to another, some of the previous resin may still
be present and can appear within the current parts. A robust injection molding
purging process coupled with material system cleaning and purging is absolutely
necessary to reduce cross contamination.
Short Shots
Short
Shot
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Short shots or non-fills are often caused by unstable process conditions and can
result in an impact on the functionality of the part. In general, this is a defect
rather than a nonconformance. At a minimum, short shots create an appearance issue
that brings into question the repeatability of the injection molding process.
There are a number of possible situations that can cause short shorts including
entrapped gasses that prevent the resin from completely filling the part cavity.
The path where the resin flows into the part cavity within the mold is called
the gate. The channel that is machined into the mold that directs resin to the
gate is known as a runner. A poor gate design can also promote the formation of
short shots. Failure to properly monitor and control melt temperatures and mold
temperatures is another common source of short shots.
Within recent years a number of excellent software packages have become available
for real time machine monitoring as well as offline analysis. This has led to
tremendous improvements in process repeatability. However, just as for most other
issues, maintenance of the molding machine and the mold is pivotal to reducing
short shots.
Blinded By The Flash
 Flash
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Flash poses a risk to the functionality of the part and can, if it breaks loose,
present a contamination risk. Flash on the interior of a part can actually have
a significant effect on the flow rate capability of the part. Flash on the surface
can also potentially cause leak paths.
Like short shorts, flash is primarily an issue of poor process control. Too hot
of a mold temperature or improper rate of resin injection are common sources of
flash. If many instances of flash are observed, it is often an indication that
the resin is being utilized outside of the manufacturer’s recommendations. Other
sources of flash include tool wear, improper tool workmanship, and improper pack
pressure or transfer point.
Avoid The Void
 Void
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Voids are bubbles within a part. Like embedded contamination, voids are only discernable
on transparent parts and pose an unknown risk for colored parts. Solid color parts
such as nylon often have voids although these voids cannot be detected by a visual
inspection. Parts made from materials such as polycarbonate, polypropylene, or
PVDF are not any more susceptible to voids than nylon but these parts are transparent
and so voids are easily observed.
The location and size of a void creates different concerns. Should a void break
into the interior of a part, there is a possibility that some of the material
flowing through the part could pool creating the potential for contamination.
The creation of turbulent flow within the part is also a possibility.
Very large voids or voids in key areas of the part can create other concerns.
A large void near the grip of the part can make the part susceptible to breakage.
Voids in the part’s barb can reduce the strength of the barb which can result
in leakage.
Voids are generally caused by an incomplete resin fill often on the inner walls
of the tool. As the part cools the resin shrinks creating a bubble. Thick walled
areas of parts are generally more susceptible to the formation of voids. Reducing
these areas during the design of the part as appropriate reduces the possibility
of voids in production. Proper gate design is also important to reducing the possibility
of incomplete fills.
Degating – Manual Or Automatic?
Gate vestige
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“Degating” is separating the gate that was used to fill the part cavity with resin.
If you’ve ever made a plastic model airplane, you’re very familiar with this process.
Degating a part has the potential to leave a small, sharp artifact or vestige
on the part. These degating artifacts create an appearance concern, are sharp
to the touch, and can rip medical gloves under some circumstances.
Proper gate design is fundamental to the reduction of these artifacts. Additionally,
parts should be twisted from the gate rather than pulled as a means to reduce
artifacts. In some circumstances, secondary operations such as filing or clipping
can be used to smooth degating artifacts although this adds extra expense that
can often be eliminated through proper part design.
In addition to manually degating parts, automated degating robots are available
and commonly used. The robot removes parts and runners in one piece from the mold
and then cuts the part from the gate. This is a significant improvement from manually
cutting gates with a hand-held blade or pneumatic cutter and results in more consistent
cuts and reduced operator costs.
The Path To Defect-Free Fittings
Providing quality fittings and connectors is fundamentally related to part design,
the design of the mold, repeatable injection molding process, mold maintenance
and injection molding machine preventative maintenance. An example showing how
these can all come together to affect quality is demonstrated by the threads in
the following photograph. The threads on the left hand part have a poor thread
profile compared to the part on the right. Thin areas in the part are also quite
noticeable. There are many possible causes of a poor thread profile including
poor tool design, inadequate venting, excessive tool wear, and inadequate mold
maintenance. This kind of poor thread profile can present both a functional as
well as a fit issue for the customer.
Another key to quality and reducing defects is maintaining well understood process
parameters. Tracking software has become crucial in monitoring pressure, temperature,
and machine settings so that long term trends are recognized and evaluated. These
tools have the added advantage of tracking production data resulting in improved
productivity and reducing scrap.
Any defects that do appear must be addressed through a rigorous continuous improvement
process. This improvement process may involve improving the performance of a tool
or re-validating the injection molding processes. In some cases, organizations
may need to proceed in generating an Engineering Change Order (ECO) in order to
improve the quality of a product. Maintaining this level of quality is crucial
to consistently producing high volumes of fittings and connectors that fully meet
the needs of pharmaceutical customers, in a cost effective manner.
The authors would like to thank Mr. Bill Magill, Technical Sales Representative, Leeds Precision Instruments, for providing the microscope equipment and expertise for the photographs in this article.
About the author: Mark Rosneck can be reached at mark.rosneck@valueplastics.com or 970-226-8250.
Pharmaceutical Processing
Advantage Business Media
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