Within the plastics processing industry, having a quality screen changer to filter debris from the plastic melt can make or break the finished plastic material, as an unfiltered thermoplastic material is often unsuitable to be used in the production of the final product. The areas in which this plastic melt is used cover a wide range of markets, including sheet and film, blow molding, pipe and profile, compounding, resin production, nonwovens, and other similar specialty industries. Suppose the plastic melt used in these manufacturing facilities is contaminated. In that case, this could affect the finished product's reliability, posing a genuine threat within these markets. Therefore, melt filtration is not just an option but a vital necessity for the quality of the production process.

In the world of screen changers, there are many choices depending on the needs of how companies wish to filter out contaminants. However, not all screen changers are created equal. For example, discontinuous melt filtration systems such as those using manual screen packs are more straightforward and less expensive, but the production line must be stopped when changing the screen. Semi-continuous models like slide plates and dual bolts are suitable for almost any thermoplastics but also require line disruptions. Continuous machines such as rotary disc and scraper methods are a good choice but these can be substantially greater in both physical size and capital investment. However, one style of continuous screen changer is ideally suited for most melt filtration applications, known as the belt type, which offers many desirable benefits.

What is a continuous belt screen changer?

A continuous belt screen changer (also known as a continuous melt filter) is a device that allows for continuous filtration of contaminants in a polymer processing system by enabling a filter screen to be changed while the process is still in operation and under full process conditions. It consists of a moving belt that acts as the filter screen and it continuously introduces clean filter material as the belt moves across the melt flow while the used filter material exits the machine at the same rate and in the same sequence.  This is the only mechanical filtration approach that prevents interruption to the smooth flow of the plastic melt. While a discontinuous screen-changing mechanism requires an operator to be involved in the process, a continuous belt system can automatically maintain constant, uniform extrusion pressure without any operator involvement.

What are the many benefits of a continuous belt screen changer?

1. Continuous Operation: The first and most widely recognized benefit of using a continuous belt screen changer is the continuous operation itself, as this continuous belt design permits the filter screen to be easily indexed so that impurities are removed without ever disrupting the flow of the melt. In melt filtration processes, stray debris can clog up screens quickly, and these process disruptions rapidly become costly. As a result, the continuous melt filter reacts to these disruptions allowing a more uniform process.
2. Improved Production Rates: When there is continuous filtration in the plastic extruding process, this continuity will inevitably lead to improved production rates and higher overall output resulting in uniform pressure. This maximized efficiency results in not only a better quality of the resulting product but also more of the end product to work within a shorter span of time.
3. Better Quality Products: As previously mentioned, maintaining a consistent flow of filtered material will naturally produce a higher quality product with a much lower chance of any stray debris caught in the extruded plastic. In addition, because the continuity of the belt maintains a uniform extrusion pressure, and this pressure determines the level of heat, there is also a uniform melt temperature which causes a clean production of the extruded plastic without any deformities due to temperature degradation.
4. Lower Maintenance Costs: Because continuous belt filtration is an entirely automated operation, the frequency of maintenance to the operation is reduced. This maintenance reduction results in lower maintenance costs, saving money in the upstream process of the extrusion and further downstream where the plastic is produced.
5. Increased Safety: Since there is little need for any manual intervention with the continuous belt, there is a significantly reduced risk of injury to operators when this machinery is running. In addition, operations or maintenance are not required to handle hot molten parts. These safety benefits alone make the continuous melt filter machine a worthwhile investment.
6. Ease of Use: Finally, the overall design of the continuous belt allows for easy and convenient screen roll changes that do not require personnel with highly specialized training or expertise. Roll changes can occur in as little as five minutes on the scene while the production line continues at full output without interruption.

At Parkinson Technologies' Key Filters brand, our engineers and technicians have a wealth of knowledge about the many benefits a continuous belt melt filter offers to a plastic extrusion operation. We look forward to answering any further questions you may have about how a continuous belt can benefit your company's process. In addition, we have a series of other articles about screen changers and their specific functions, linked below for your convenience.

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