Foam Extrusion. A thorough control theory links the individual components of modern foam extrusion systems. Changes in throughput and also startup and shutdown of the complete system happen largely automatically, reproducibly and in a user-friendly method.
Typical raw materials formulations for foam extrusion consist of up to 8 components that must be processed under defined conditions. Accessories manufacturers face the task of developing technologies and control concepts that ensure reproducible development of semi-finished foam goods.
The twin-screw extruder is fed with the polymeric recycleables by means of a gravimetric unit(loss-in-weight feeder) and this determines the system throughput. The physical blowing agent in liquid contact form is fed in to the barrel using high pressure pumps.
The twin-screw extruder is starve-fed. The acceleration of the twin screws can be varied within particular limits. The relationship between polymer throughput [kg/h] and screw quickness [rpm] is thought as the specific throughput: (1) A reduction in screw speed for a set throughput results in an upsurge in specific throughput. There is also a minimum speed below that your feeding capacity of the extruder is no longer adequate. If the maximum specific throughput .m spez,ZE,max is exceeded, the feed area becomes filled. Increasing the screw rate reduces the precise throughput. Normally, this results in a rise in melt temp and a shortening of the back up length. Because the backup length is crucial to provide sealing and stop reverse stream of the blowing agent in this technique, the specific throughput has a lower limit. The screw speed can't be risen to any value.
The precise throughput of the singlescrew extruder can also be established in a manner similar to that used for the melting extruder. Here, too, the precise throughput could be varied within limits and therefore have some influence on the melt heat as well as the pressure level in the entire system.
With the aid of the specific throughputs, the control of the extruder speeds can be linked to the polymer throughput. A transformation in the throughput specified immediately results in a change in speed.
A typical raw material formulation for foam extrusion consists of up to eight parts: the virgin polymer, reclaim and additives for cell size control, colorants and flame retardants. The amounts of the materials are specified in terms of film extrusion percent, for instance, for component. A thorough control strategy links the individual the different parts of modern foam extrusion systems. Changes in throughput in addition to startup and shutdown of the entire system happen largely quickly, reproducibly and in a user-friendly manner.
For certain foam products, up to three blowing agents are added. Injection takes place directly into the polymer melt, i. e. in to the barrel of the twin-screw extruder.
Maintaining constant action parameters is crucial for consistent top quality of the final end product. In addition to temperature control, this means the proportions of the polymeric components especially, the blowing brokers and the specific throughputs of the extruders.
Based on its percentage, control of the blowing agent can be from the polymer throughput also. This does mean a noticeable improve in the absolute flow rate of blowing agent with a transform in throughput. Knowing the average person proportions of the polymeric products and the blowing agents, the formulation is certainly specified clearly. Knowledge of the polymer throughput, the proportions of most materials and the specific throughputs of the two extruders, means that the essential parameters of an functioning point are defined.
Normal changes of the operating point, such as for example changes on throughput or startup and shutdown of the entire line, Schematic layout of a tandem system for foam extrusion. The sum of all polymeric raw components is normally 100%. The absolute throughput of each specific component in [kg/h] is calculated with regards to the total polymer throughput. To keep up proportions exactly, all factors are fed gravimetrically. Likewise, the specified amounts for the blowing agents are stated in percent with regards to the full total polymer throughput also. The absolute values of blowing brokers throughput are likewise calculated with regards to the total polymer throughput and entered as setpoints on the metering pump controls.
Measurement of the circulation rate is based on the theory of the Coriolis power. The total throughput of a foam tandem range is calculated because the sum total of the polymer and blowing agent throughputs, that is, the blowing agent can be incorporated in to the total. Startup at the desired line throughput is set up from a central control panel with the mouse click of a mouse on a keep an eye on. The speed of which changes are to 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 takes place based on the links described above then. All sequences are therefore reproducible. The operator can focus on observing the product quality and adjusting the series speed. Any necessary temperature alterations for individual zones are either entered manually or transmitted to the device with the previously stored formulation. All machine parameters are recorded continuously, stored and will be displayed graphically in development diagrams.Using these diagrams, the behavior of the processes over time can be analyzed and observed. In this way, changes in the required operating points could be monitored perfectly by the operator.