The additive feeding systems in the plastics industry have at least two separate control programs, one for injection molding – for dosing precise amounts in part of the production cycle, and another for extrusion – for continuous feeding. In this post we’ll discuss a third program for extrusion blow molding that’s present in a number of leading feeders in the field, among them the ColorSave 1000.
Extrusion blow molding (EBM) can be viewed as a hybrid of injection and extrusion. On the one hand, it produces individual products, one each cycle, using a mold, like injection. On the other hand, the feed is continuous, like in regular extrusion. Accordingly, the EBM program is also a hybrid between injection and extrusion. It feeds the additive continuously and yet allows the treatment of production cycles individually. We’d like to show that it’s preferable to use an EBM feeder for an EBM system.
Since the feed is continuous, it’s possible in principle to use a feeder with an extrusion program (continuous feed) with an EBM system. This feeder would do the job well, however for the machine operator a feeder with a specific EBM program is easier to operate and generally preferable.
A feeder that speaks the operator’s language
In a feeder with an extrusion program, the operator can enter a constant additive throughput in kg/hour, or if the feeder is synchronized with an extruder the operator can enter the extruder’s maximum throughput in kg/hour and the desired percentage of the additive. In each of these options, the operator must enter data in terms of throughput in kg/hour. These terms are the “language” spoken in classic extrusion factories, such as those that produce pipes, profiles, films, etc., however in a factory with extrusion blow molding machines, the machine operators’ terms are not throughput in kg/hour, but rather product weight.
The product weight is a given that the operator knows or can easily find out by weighing the final product and adding the weight of the material from that cycle that was not used and is to be recycled. As soon as the product weight value is known, it can be entered along with the desired additive percentage and that’s it, you can start working.
Always synchronized with the production machine
When working with a feeder with an EBM program that’s synchronized with the production machine, one can always enter the desired percentage for the production process. As a rule, working with synchronization with the production machine, which allows the operator to enter the desired additive percentage, is always preferable to working without synchronization, in which case constant throughput must be entered.
So how can the feeder work with a percentage of the system’s throughput? How does the feeder know what the extruder’s throughput is at any given moment? In order to know the extruder’s momentary throughput, you need a synchronization value and a reference point, and then the extruder’s momentary throughput can be calculated with simple math. The mathematical calculation is usually multiplication or division of two values – the synchronization value, which is variable, and the reference point, which is constant.
So far we have shown that for an EBM system operator working with an EBM feeder is preferable to working with an extrusion feeder, since the EBM feeder “speaks his language” and is always in sync with the production machine.
The illustration below shows the main screen of the ColorSave 1000 with an EBM program. You can see that the set point is product weight and desired percentage.
In the next section we’ll see that with a feeder specific to EBM the synchronization is not only constant, but also easier than the synchronization of an extrusion feeder, and it’s also easier to calculate the reference point in a feeder with an EBM-specific program.