Plastic resin must be mixed with plasticizer and other improving additives before compounding. Leaving thermoset plastics aside, thermoplastic resin is mixed in a mixing tank where it is heated with mechanic friction. Above is lay-out of an high-speed mixer or simply "the mixer". Mixer has three main segments : Loading, cylindrical mixing tank, cooling tank.
Loading : Thermoplastic resin, with plasticizer or without and additives must be loaded in correct dosing. Correct and precise dosing is one key element of compounding process. Performance improving additives and some colorants are may have high cost. They have to be added to the resin in right dosage. On the other hand, failing to put enough would result final product failure. In addition, a good quality product can be produced but good production of one time is useless , instead quality must remain same in repeatedly. This is why loading the mixing tank is one important key elements of compounding process. There are various ways of dosing that you could choose from. Choosing the suitable one for your unique product among various types of Gravimetric or Volumetric dosers is an important task which depends of two main criterias. What is the physical properties of the additives you would be using the most, what is the uniformity level of proportions is required.
Keep in mind that, some additives also need to be premixed or blended prior to main action in mixing tank.
Mixing Tank: In Cylindric shape, made of stainless steel inside. With rotating blades at bottom. Temperature sensor is a must. During mixing resin will be heated and moisture will be removed. Thus, mixer tank should have exhaust pipes. Speed, position, size and angle of rotating blades determined by physical properties of the resin and expected final product. The capacity of the mixing tank is called by its' volume but 70-75% of this volume can be used. So if it is Mixer's capacity is 100lt, it is adviced to make a maximum batch of 70 lt. Average compounding time would vary but 8-10 minutes is fair to use when calculating tank capacity and output per hour. Typical high speed mixer starts heating up by friction between blades, material and tank surface. Blades rotating in high speed creates an axial vortex inside the tank. This ensures the homogenous batch. As blades running fast heat increases until the set temperature. Finished batch should be in free-flowing state. Removed to cooling tank.
Cooling tank : Similar to mixing tank. Adviced double sided with coolant fluid circulating. Cooling tank's capacity is must be minimum three times more than mixing tank. Common aim is to use a tank with less in height and larger in diameter to make sure larger surface of the dry blend in conduct with. The heat of the dry blend will be reduced to 45-55 celcius degrees in cooling tank. Fluid circulating tanks are time consuming and more productive in terms of kg per hour output. An heat sensor is not a must but it is good to know the temperature of the dry blend. There are some types of improving agents and additives that must be added into the dry blend in cooling tank. If such additives would be used, a dosing/feeding solution should be considered for cooling tank as well.