 How are polymers molded? Before we begin, let's just go back a little and know a bit about what polymers actually are. A polymer is a large molecule composed of many repeated subunits. Based on the mechanical response at high temperatures, polymers are classified into two major categories. First are thermoplastic polymers which soften when heated and harden when cooled down. These polymers are usually soft and can be repeatedly molded into required shapes. Second are thermosetting polymers. These polymers become soft during first heating and then permanently harden when cooled. They are more hard, brittle and heat resistant when compared with thermoplastic polymers. Coming back to molding, the first step in molding of polymers is processing of polymers. Which due to the very nature of polymers is similar to those used to form and shape metals. Hence, we will look at it under two main subheadings. First, molding of thermosetting polymers which is done by using two main methods. One being compression molding in which a measured amount of polymer powder is placed in a female cavity that is preheated to about 125 to 250 degree Celsius. The upper part of the die compresses the material with a pressure of 0.5 to 50 megapascals. This pushes the material into the mold cavity where it solidifies and is removed with the help of ejector pins. Disadvantages include low residual stress, low setting time and good surface finish. Disadvantages include increased overall cycle time and low production rate. Compression molding is used for making gears, buttons, knobs, handles, dishes and fittings. Another type of thermosetting polymer processing is transfer molding, which is an advanced method of compression molding. The material is generally preheated and placed in the lower half of the mold. The upper part of the die applies a pressure of 20 to 100 megapascals and once cured the material part is ejected. One of the main advantages of transfer molding is the ability to insert different inserts like semiconductor chips, ceramics, etc. before introducing the material but is limited by its high equipment cost and wastage of material. Transfer molding is used to manufacture electronic components with molded terminals, pins, etc. Then comes molding of thermoplastic polymers which can be studied under three main parts. One being injection molding. One being injection molding here. The material is fed from a hopper to the rotating screw which discharges the material in front of the extruder. Heat is developed from the electric band heaters and friction from the rotating screw. Advantages of injection molding include faster production rate, production of complicated shapes with high accuracy and is limited by high initial cost. Advantages are productions of cups, chairs, toys, car parts, etc. Second in line is blow molding which is a process in which air pressure is used to inflate soft plastic into a mold cavity. The soft plastic is usually called a paracin which is grid between a two piece mold. The air pressure is about 400 to 800 kilopascals. As the form component cools the mold is open and the part is removed. Advantages include low initial cost of molds, high flexibility in production. Advantages are high cooling times. Blow molding is used for making foot packaging, water bottles, pipes, floats and doll bodies. Third and last type of thermosetting molding is thermoforming. Here with the help of clamps a polymer sheet is gripped around the mold. Heat is used to bring the polymer up to 90 degree Celsius. Vacuum is applied using small holes in the lower die. This gives the polymer sheet a perfect shape. Advantages of thermoforming include low thermal stresses, quick setup, low production cost with a lack of ability to manufacture components with holes. Thermoforming is used for producing luggage bags in a panels of refrigerators etc. That's it. But mechanically how do you produce sheets and pipes? Or how are cables coated with polymers to provide insulation you may ask? Well, there is one last process which is common between both thermoplastic and thermosetting polymers. It is called extrusion. Sounds familiar? It might be because it is used in the forming of metals. Link in the description below. Extrusion of films is done by the combination of extrusion and blowing. The tube is first excluded then drawn upward by using rollers and air is blowed uniformly using a tube. The guide rolls and restrain the blown tube and form a flat tube which is the film. Sheets of polymers are formed using calendaring process which is similar to rolling process. Here the first roller serves as a feeder, the second as a metering device and the third one serves as the gauge length of the sheet. Extrusion of pipes is similar to film formation only here they are held in position by a mandrel. The coating of wire and cable for insulation purpose is one of the most important polymer extrusion process. Here the polymer melt is applied to the bare wire as it is pulled through a die at high speed. For adhesion of coating a slight vacuum is drawn before the polymer and wire. Here comes the quick revision of molding of polymers. Finally it's time for this episode's question how are glass tubes shaped? Also it's time to answer our last episode's question. What is atomization? In powder metallurgy atomization is accomplished by forcing a molten metal stream through an orifice at moderate pressure. A gas is introduced into the metal stream helping in splitting the powder into small components.