Product category:
Handling and automation equipment
News Release from: Krauss-Maffei (UK) | Subject: PUR mixing heads
Edited by the Manufacturingtalk Editorial
Team on 28 November 2007
Plastics pouring rates precisely
controlled
Mixing heads can be used in plastics moulding production with maximum flexibility allowing their output can be varied from one shot to the next.
Krauss-Maffei said that PUR mixing heads can be used in production with maximum flexibility if their output can be varied from one shot to the next The production of vehicle seat squabs from PUR foam is a good example, because in producing the different hardness zones to specifications, the PUR pour rate is changed from shot to shot
This article was originally published on Manufacturingtalk on 11 Jun 2001 at 8.00am (UK)
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To achieve this, while keeping the mixing quality consistently excellent, it is necessary to change the nozzle gaps in the mixing head in line with the pour rate.
The nozzle gap is changed by means of movable pin.
KraussMaffei has now developed a system for moving the nozzle pins characterized by flexibility and precision.
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The great gain with the new system, said a report to manufacturingtalk.com, is an extended working range for the mixing head.
In conventional nozzle designs, the nozzle gap is altered by means of the spring-loaded nozzle pin.
The operating range of the nozzle is limited as soon as component pressure exceeds the permissible limit.
Another problem is the possibility of the spring/ nozzle pin system starting to oscillate under certain conditions.
* A balance of forces - Krauss-Maffei engineers have now developed a system for changing the position of the nozzle pin that eliminates these drawbacks.
The new development will pay off especially in applications where flexibility and precision are of overriding importance.
In the new design, an electric motor moves the nozzle pin.
Special design measures were necessary to keep the force required to move the pin as small as possible.
Moving the pin against the pressure of the component flow normally requires very high forces and correspondingly powerful drives.
The new nozzle design successfully neutralizes component pressure, so that the forces acting on the nozzle pin are balanced.
It is therefore ipossible to move the pin using a relatively small stepper motor.
The electrically adjustable nozzle has the same dimensions as a spring-loaded nozzle, so that existing KraussMaffei multicomponent mixing heads can be retrofitted with the new nozzles.
The nozzle pin is adjusted in such a way that component pressure remains constant for any desired output rate.
The electrically adjustable nozzle pin thus extends the bandwidth of output rates that a single mixing head is capable of covering.
Precise pressure control requires a preliminary calibration process.
In this process, the system's characteristic curve is mapped as the basis for determining the correct pin position for every desired output rate.
The time required for a pin position change is well under half a second.
With the smallest increment for pin movement 2.5 micron, the output rate can be set very precisely, while the components continue to be mixed uniformly.
* About Krauss-Maffei - Krauss-Maffei is the only supplier worldwide of the three key machine technologies for the plastics and rubber compounding and processing industries.
The KraussMaffei brand stands for comprehensive systems for injection and reaction moulding, while the KraussMaffei Berstorff brand covers the whole spectrum of extrusion systems, including complete extrusion lines.
KraussMaffei has a unique wealth of know-how across the whole range of processing methods.
As a technology partner, it links this know-how with innovative engineering to deliver application-specific and integrated solutions.
KraussMaffei operates a network of 70 subsidiaries and sales agencies close to customers worldwide.
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