Foam under control

Foam Extrusion. A thorough control notion links the individual the different parts of contemporary foam extrusion systems. Alterations in throughput as well as shutdown and startup of the complete system happen largely automatically, reproducibly and in a user-friendly manner.

Typical raw materials formulations for foam extrusion consist of up to 8 components that must definitely be processed under identified conditions. Machines manufacturers face the task of growing control and technologies concepts that ensure reproducible production of semi-finished foam items.

The twin-screw extruder is fed with the polymeric recycleables through a gravimetric unit(loss-in-weight feeder) which determines the machine throughput. The physical blowing agent in liquid shape is fed in to the barrel using high pressure pumps.

The twin-screw extruder is starve-fed. The rate of the twin screws could be varied within specific limits. The relationship between polymer throughput [kg/h] and screw rate [rpm] is thought as the precise throughput: (1) A decrease in extrusion systems screw quickness for a set throughput results within an upsurge in specific throughput. There is also a minimum speed below which the feeding potential of the extruder is not any longer sufficient. If the maximum particular throughput .m spez,ZE,max is exceeded, the feed area becomes filled. Increasing the screw acceleration reduces the precise throughput. Normally, this results in an increase in melt temp and a shortening of the back-up length. Since the backup length is crucial to present sealing and prevent reverse movement of the blowing agent in this process, the specific throughput has a lower limit. The screw speed cannot be increased to any value.

The precise throughput of the singlescrew extruder can also be motivated in a manner similar to which used for the melting extruder. Here, too, the precise throughput could be varied within restrictions and thus have some effect on the melt heat range plus the pressure level in the complete system.

Using the specific throughputs, the control of the extruder speeds could be linked to the polymer throughput. A modification in the throughput specified results in a transformation in speed automatically.

A typical raw materials formulation for foam extrusion consists of up to eight pieces: the virgin polymer, additives and reclaim for cell size control, flame and colorants retardants. The levels of the substances are specified when it comes to percent, for example, for component. A thorough control principle links the individual the different parts of contemporary foam extrusion systems. Improvements in throughput in addition to startup and shutdown of the complete system take place largely immediately, reproducibly and in a user-friendly manner.

For certain foam items, up to three blowing agents are added. Injection occurs into the polymer melt directly, i. e. into the barrel of the twin-screw extruder.

Maintaining constant approach parameters is crucial for consistent quality of the finish product. In addition to temperature control, this means the proportions of the polymeric components especially, the blowing agents and the specific throughputs of the extruders.

Based on its percentage, control of the blowing agent may also be from the polymer throughput. This does mean a change in the absolute flow pace of blowing agent with a switch in throughput. Knowing the individual proportions of the polymeric materials and the blowing brokers, the formulation clearly is specified. Knowledge of the polymer throughput, the proportions of all materials and the specific throughputs of the two extruders, means that the fundamental parameters of an operating point are defined.

Common changes of the working point, such as changes on throughput or shutdown and startup of the complete line, Schematic layout of a tandem system for foam extrusion. The sum of all polymeric raw elements is normally 100%. The absolute throughput of each individual component in [kg/h] is calculated in relation to the total polymer throughput. To keep up proportions exactly, all components gravimetrically are fed. Likewise, the specified amounts for the blowing agents are stated in percent with regards to the total polymer throughput also. The absolute ideals of blowing agents throughput are also calculated with regards to the full total polymer throughput and entered as setpoints on the metering pump settings.

Measurement of the flow rate is founded on the principle of the Coriolis drive. The total throughput of a foam tandem brand is calculated as the sum total of the polymer and blowing agent throughputs, that's, the blowing agent is without question incorporated in to the total. Startup at the desired line throughput is initiated from a central control panel with the press of a mouse on a keep an eye on. The speed of which changes should be made can be preselected using a ramp function.

It is defined in the change found in polymer throughput [kg/h] per unit of period. The change then occurs on the basis of the links described above. All sequences are reproducible thus. The operator can concentrate on observing the product quality and adjusting the relative line speed. Any necessary temperature changes for individual zones will be either entered manually or transmitted to the machine with the previously stored formulation. All equipment parameters are recorded continuously, stored and may be displayed graphically in tendency diagrams.Using these diagrams, the behavior of the processes as time passes could be analyzed and observed. In this real way, changes in the desired operating points could be monitored perfectly by the operator.

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