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14 Dec 2015 
Foam Extrusion. A comprehensive control idea links the individual components of contemporary foam extrusion systems. Improvements in throughput and startup and shutdown of the entire system take place largely automatically, reproducibly and in a user-friendly manner.

Typical raw materials formulations for foam extrusion consist of up to eight components that must definitely be processed under described conditions. Machines manufacturers face the challenge of developing technologies and control ideas that ensure reproducible development of semi-finished foam products.

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

The twin-screw extruder is starve-fed. The acceleration of the twin screws could be varied within selected limits. The partnership between polymer throughput [kg/h] and screw velocity [rpm] is defined as the precise throughput: (1) A decrease in screw acceleration for a fixed throughput results within an increase in specific throughput. There is also a minimum speed below which the feeding potential of the extruder is not any longer adequate. If the maximum specific throughput .m spez,ZE,max is exceeded, the feed zone becomes filled. Raising the screw acceleration reduces the specific throughput. Normally, this leads to a rise in melt temperatures and a shortening of the back-up length. Because the backup length is crucial to provide sealing and stop reverse movement of the blowing agent in this technique, the specific throughput also has a lower limit. The screw speed can't be risen to any value.

The precise throughput of the singlescrew extruder can also be decided in a way similar to that used for the melting extruder. Here, too, the precise throughput can be varied within limitations and thus have some influence on the melt temperatures and also the pressure level in the entire system.

Using the specific throughputs, the control of the extruder speeds could be from the polymer throughput. A switch in the throughput specified benefits in a modification in speed automatically.

A typical raw material formulation for foam extrusion consists of up to eight components: the virgin polymer, additives and reclaim for cell size control, flame and colorants retardants. The levels of the components are specified with regards to percent, for example, for component. A thorough control principle links the individual the different parts of modern foam extrusion systems. Alterations in throughput along with startup and shutdown of the complete system take place largely automatically, reproducibly and in a user-friendly manner.

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

Maintaining constant approach parameters is critical for consistent top quality of the ultimate end product. In addition to temperature control, this implies 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 could be linked to the polymer throughput also. This also means a noticeable modify in the absolute stream rate of blowing agent with a alter in throughput. Knowing the individual proportions of the polymeric substances and the blowing agents, the formulation is certainly specified clearly. Knowledge of the polymer throughput, the proportions of all materials and the precise throughputs of both extruders, means that the essential parameters of an operating point are defined.

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

Measurement of the move rate is founded on the basic principle of the Coriolis force. The full total throughput of a foam tandem collection is calculated because the sum total of the polymer and blowing agent throughputs, that's, the blowing agent is definitely incorporated in plastic pellet extruder to the total. Startup at the desired line throughput is initiated from a central control panel with the click of a mouse on a keep an eye on. The speed of which changes should be made can be preselected with the aid of a ramp function.

It is defined in the change in polymer throughput [kg/h] per unit of time. The change then takes place on the basis of the links described above. All sequences are thereby reproducible. The operator can focus on observing the product quality and adjusting the relative line speed. Any necessary temperature alterations for individual zones happen to be either entered manually or transmitted to the machine with the previously kept formulation. All equipment parameters consistently are recorded, stored and can be displayed in trend diagrams graphically.Using these diagrams, the behavior of the processes over time could be analyzed and observed. In this real way, changes in the required operating points can be monitored very well by the operator.
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