Foam under control
Foam Extrusion. A thorough control theory links the individual components of contemporary foam extrusion systems. Adjustments in throughput together with startup and shutdown of the entire system happen largely automatically, reproducibly and in a user-friendly method.
Typical raw material formulations for foam extrusion consist of up to 8 components that must be processed under described conditions. Machines manufacturers face the challenge of growing control and technologies concepts that ensure reproducible development of semi-finished foam goods.
The twin-screw extruder is fed with the polymeric raw materials by means of a gravimetric unit(loss-in-weight feeder) and this determines the machine throughput. The physical blowing agent in liquid shape is fed into the barrel with the aid of high pressure pumps.
The twin-screw extruder is starve-fed. The acceleration of the twin screws can be varied within selected limits. The partnership between polymer throughput [kg/h] and screw swiftness [rpm] is defined as the precise throughput: (1) A reduction in screw swiftness for a set throughput results in an increase in specific throughput. Gleam minimum speed below that your feeding capacity of the extruder is not any longer satisfactory. If the maximum certain throughput .m spez,ZE,max is exceeded, the feed zone becomes filled. Raising the screw swiftness reduces the specific throughput. Normally, this leads to a rise in melt heat and a shortening of the back-up length. Since the backup length is critical to give sealing and prevent reverse circulation of the blowing agent in this technique, the specific throughput includes a lower limit. The screw speed cannot be increased to any value.
The specific throughput of the singlescrew extruder can also be established in a manner similar to which used for the melting extruder. Here, too, the specific throughput can be varied within limitations and therefore have some influence on the melt temperatures along with the pressure level in the complete system.
With the aid of the specific throughputs, the control of the extruder speeds can be from the polymer throughput. A transformation in the throughput specified automatically results in a change in speed.
A typical raw material formulation for foam extrusion includes up to eight elements: the virgin polymer, additives and reclaim for cell size control, colorants and flame retardants. The amounts of the substances are specified in terms of percent, for example, for component. A comprehensive control theory links the individual components of contemporary foam extrusion systems. Alterations in throughput and also startup and shutdown of the entire system happen largely instantly, reproducibly and in a user-friendly manner.
For certain foam goods, up to three blowing agents are added. Injection takes place into the polymer melt directly, i. e. in to the barrel of the twin-screw extruder.
Maintaining constant task parameters is crucial for consistent top quality of the ultimate end 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 could be from the polymer throughput also. This does mean a noticeable transform in the absolute move rate of blowing agent with a adjust in throughput. Knowing the individual proportions of the polymeric elements and the blowing agents, the formulation clearly is specified. Knowledge of the polymer throughput, the proportions of all materials and the precise throughputs of the two extruders, means that the essential parameters of an functioning point are defined.
Regular changes of the operating point, such as 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 complete throughput of each specific component in [kg/h] is calculated with regards to the full total polymer throughput. To maintain proportions exactly, all factors gravimetrically are fed. Likewise, the specified sums for the blowing agents are likewise stated in percent with regards to the full total polymer throughput. The absolute ideals of blowing agents throughput are as well calculated with regards to the total polymer throughput and entered as setpoints on the metering pump controls.
Measurement of the stream rate is founded on the theory of the Coriolis drive. The total throughput of a foam tandem line is calculated because the sum total of the polymer and blowing agent throughputs, that is, the blowing agent is going to be incorporated into 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 at which changes should be made can be preselected with the aid of a ramp function.
It is defined at the change found 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 thus reproducible. The operator can focus on observing the product quality and adjusting the brand speed. If you loved this short article and you would like to obtain even more facts concerning plastic extruder kindly see our own webpage. Any necessary temperature improvements for individual zones happen to be either entered manually or transmitted to the machine with the previously stored formulation. All equipment parameters are recorded continuously, stored and will be shown graphically in pattern diagrams.Using these diagrams, the behavior of the processes over time could be observed and analyzed. In this way, changes in the required operating points could be monitored perfectly by the operator.
