Heißkanaldüsen Typ SLT/-DLT Customer information

Heißkanaldüsen Customer information
Typ SLT/-DLT
Stable and Material Saving Processing of Flame Retardant Polyamides with
GÜNTHER Hot Runner Technology
As a world leading supplier, Moeller GmbH (Bonn) pro-
duces components and systems for automation, command
and control devices. Diverse electrical and electronic
components made of plastic are used in these systems.
Fig. 1 Pushbuttons in command and control equipment
(photo: Moeller GmbH)
For a long time now Moeller has been using molds with
hot runners for sprueless production of these parts. The
advantages of hot runner technology over a conventional
gating system include savings in material and a
reduction in cycle time.
When selecting a plastic for electronic components, it is
often necessary to take account not only of the design
requirements but also of statutory provisions and standards.
In the electronics industry, for example, plastic
components that are in direct contact with live parts must
conform to the IEC Standard (International Electrotechnical
Commission) etc. A further requirement is
that the plastic must be capable of extinguishing itself
after catching fire. Here, Standard 94 of the Underwriters
Laboratories has established itself throughout
the world as the authoritative standard for classifying
flame retardance in plastics. The classification in standard
94 of UL depends on the rate of combustion, time
needed for extinction, formation of drops and afterglow
time. Depending on the component's function, the
following criteria must be met:
UL94 V2: Vertical test specimen; self-extinguishing up
to 30s after withdrawal of the flame, drips of flaming
particles allowed; afterglow max. 60s.
UL94 V0: Vertical test specimen; self-extinguishing up
to 10s after withdrawal of flame; no drips of flaming
particles; afterglow max. 30s.
Moeller usually uses PA66 reinforced with 25% fiber
glass with flame retardant for housing of electrical or
electronic components. This type of material complies
with UL94-V2 combustibility grading as well as other
standards.
A lot of devices from Moeller are also used in areas subject
to the ATEX directives (ATEX = Atmospheres Explosibles
= potentially explosive atmospheres). Here the requirements
set for flammability have recently been
tightened so that these components must now meet the
requirements in combustibility class UL94-V0. On
account of this more stringent requirement Moeller has
had to replace the type of plastic it had previously used in
a lot of components by an appropriate one classified in
conformance with UL94-V0.
Depending on the polymer, various flame protection systems
are necessary to make a plastic flame-retardant. In
the case of the PA66 used here, red phosphorus is used
to give flame retardancy. The combustibility class is
usually influenced by the quantity of the flame protection
system used. Depending on the quantity, the red phosphorus
used here reacts more or less strongly to temperature.
Accordingly overheating during processing can
cause thermal damage to the flame retardant. The gases
arising as a result can form deposits on the mold and lead
to corrosion. Occasionally the gases can even inflame.
The PA66 with 25% glass fibers originally used by
Moeller (combustibility class in conformance with UL94-
V2) could be processed easily with the existing hot
runner system. However, after changing to a PA66-GF25
conforming to combustibility class UL-V0, serious problems
arose when processing with this hot-runner system.
In spite of the processing temperatures of 275…295°C
being appropriate for the material, extremely severe deposits
appeared on the molds. The molds had to be
cleaned every 30,000 to 35,000 shots. In addition to
cleaning the mould deposits, the mold inserts had to be
replaced after every 250,000 shots because of
corrosion. The reason for this heavy formation of
deposits and corrosion in the mold was the significantly
excessive rise in temperature in the hot runner nozzles in
connection with the higher quantity of red phosphorus in
the PA66. With a temperature of 290°C set at the control
unit, temperatures of approx. 360°C were sometimes
measured in the nozzles. This caused a reaction in the
flame retardant.
For any questions, please contact our Application Engineering department at +49 (0) 6451 5008-31 or -63.
The information is given in accordance with our present-day knowledge and is meant to provide technical background.
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www.guenther-hotrunner.com
7/12 Subject to technical changes
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