Application Example: High Performance Compounding
PE Resin / Polyolefins / Bulk Polymer Compounding | Wood Plastics | High Performance Compounding | Long Fiber Thermoplastics | BOPP Film Production | Continuous Hot Melt Production | Textile Fiber Production | Gravimetric Extrusion Control
The production of plastics consists of many important process steps, which are needed to generate a homogeneous application-specific plastic compound from a number of different raw materials.
The compounding process is a continuous process. The main steps in the compounding process are:
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conveying
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plasticizing
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melting
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mixing
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homogenizing
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blending
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dispersing
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devolatizing
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reacting
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heating/cooling
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visc-breaking
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cooking
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pressurizing
Main Ingredients
The main ingredients are base polymers such as PP and PE. These must be fed continuously and very accurately.
Typical Additives
Additives can be in the form of powders or masterbatch pellets and include:
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Stabilizers, lubricants, plastifiers, color pigments, fillers, flame retardant, cross linking agents, foam agents, etc.
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Glass or carbon fibers for reinforcement, base polymer pellets for alloying to new compounds
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Recycled material
Key Requirements
One of the key requirements in high speed compounding is to ensure a continuous, uniform infeed with very tight short-term accuracy and repeatability.
Typical Production Output
Twin screw compounders are equipped with different screw diameters from 25 mm up to 150 mm in various steps depending on the manufacturer of the compounder. The typical line rates are from 50kg/h up to 6,000 kg/h.
End-Product Industries
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Automotive, Building and Construction,
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Appliances & Housewares,
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Electronics,
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Furniture,
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Health & Hygiene,
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Leisure & Sport,
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Packaging,
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Pipes,
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Textiles, etc.
Masterbatch
With high performance compounding technology, the timeconsuming step of fine grinding of pellets and premixing in batch quantities can be eliminated. Pigments are fed directly into the melt by means of gravimetric feeders. Pigment concentrations up to 70 percent are possible. Compared with the old premix feeding method, the new process allows formulations with reduced wax content or no wax at all. This means that high performance compounding technology not only benefits productivity and quality but also contributes to reduced raw material costs.
Engineering Plastics
Compounding and pelletizing of engineering plastics (i.e. filling, reinforcing, alloying, coloring and degassing of PA, PP, PET, ABS, PUR, PC or POM) are the specialty of high performance compounders.
Feeding Process
In the illustration above, the main polymer and additive masterbatch are fed very accurately with a single screw feeder, such as K-Tron's K4G, into the main inlet of the compounder. Refill is conducted via a pneumatic conveying system from an octabin station and large storage silos. A K2-ML-T35 feeds the stabilizer in the form of powder into the main extruder inlet.
The chopped fiberglass is fed via K2-ML-KV2F into the side feeder of the second inlet of the extruder. The ratio control is handled via the operator interface KSL which in turn controls the feeders via Smart Control Module, mounted locally at each feeder. The recipe handling and line monitoring are done via the factory DCS-System.
Typical Scope of Supply
The main polymers are normally pellets or powders fed with a single screw feeder such as the K2G or K2-MLS60/S100. Alternatively a K2-MLKV2/3 vibratory feeder can be used.
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The typical feed range for screw feeders is 0.2 - 15,000 l/h
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The typical feed range for vibratory feeders is 2 - 5,000 l/h
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The additives are feed by loss-in-weight screw feeders such as K2-ML-T20/T35 at rates of 0.2 to 200 kg/h, depending on the recipe.
RefillFor free flowing products, Premier loaders can be used to keep the feeders well supplied. For sticky additives, such as Irganox, Tinuvin, or CaCO3, etc. refill hoppers, extracting devices and shut off valves, or bag dumping stations are necessary. Control SystemThe loss-in-weight feeders dose the ingredients in a preset ratio, set in the operator interface or downloaded from the host computer via the K-Tron Smart Line control unit (KSL) to the locally mounted SCM. All the process relevant parameters for each feeder are stored in the appropriate recipe. The on-machine Smart Control Module (SCM) combines the function of motor drive and feeder control in a compact package. In this example the K-Tron Smart Line control unit (KSL) provides a single user interface for up to 8 feeders. The integrated K-Link feature allows for communication with the host DCS system via Modbus (Modicon) RTU, Allen Bradley DF1 or Siemens (3964R). Alternatively, a K-Tron Smart Commander could be used for up to 30 feeders and 8 lines. Environmental ConditionsPlastic compounding systems are typically classified as IP55/NEMA 12. In some processes N2 blanketing is required. This means that the LWF's are equipped with a well-proven pressure compensation system at the inlets and outlets. Depending on the process, gas explosion protection may be required, i.e. Zone 1, Temperature class T3 for Europe and Zone 1, Division 2 for USA. In this case standards K-Tron XP executions must be applied. |
K2G Feeding Station with K-Tron PCS refill System |
Advantages of K-Tron's Smart Weighing Technology
The goal of a compounding plant is economical production! Among other things, this means as little waste as possible and minimum reconfiguration time. The K-Tron feeding system makes this possible. An important factor is the adherence to the recipe during ramping up of the extruder and naturally also during large setpoint changes. The short-term accuracy of a high performance extruder is a key factor for quality of the end product.
In order to even be able to speak of adhering to recipes with changing operating data, one condition must be fulfilled: the mass flow must adapt to the setpoint as quickly as possible. This is only possible with advanced gravimetric control and the high sampling rate and resolution offered by K-Tron's Smart Force Transducer weighing technology.
Massflow during setpoint changeThis image at right shows the requirements of an extruder manufacturer with regard to the desired behavior during a setpoint change in the line. It is nice to show that this challenge could be met in the test lab well beyond any expectations. Instead of overriding the new values first and then working them in, the desired value could be obtained almost directly. This is extremely advantageous for high speed extruder feeding. The next graphs show a comparison of feeding accuracy, which was obtained with different gravimetric control systems. To obtain these results, the following conditions must be given: a high sampling rate (here 112/sec.), efficient digital filtering and a fast control algorithm. In other words: the sampling rate must be higher than the controlled elements can react. Smart SolutionsAdvantages of K2 Modular Feeders with Powersphere
Other Feeder TechnologiesFeeders with flexible walls
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Heavy Duty Screw Feeder
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generally older technology
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lower grade stainless steel with pickled finish is not smooth
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ratiometric weigh sensor with lever system
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large, heavy equipment generally cause more vibrations.
References
Several thousand customers worldwide are successfully using K-Tron Modular Feeders in their compounding processes. Our Sales department will be glad to provide you with a reference list. We will be glad to provide contact information or to help arrange visits to reference sites.
Future Potential
The plastic compounding market is steady growing approximately 3% annually. The auto industry is replacing more and more steel parts with highly reliable plastic parts. New plastic composites will be developed which will lead to the building of new compounding lines.
Retrofitting and debottlenecking of existing compounding lines also offers the opportunity for process improvement.
Typical Applications
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K-Tron feeders with Premier refill system on a compounder |
Testing Facilities
K-Tron has well-equipped testing facilties to test high rates of PE powder and additives. We can handle up to 20 t/hr of PE powder for accuracy testing. Long term testing is also available since material can be recirculated.
Services
Additional services are also available, such as:
Systems Engineering
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Installation Start-up
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Operator and Maintenance Training
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