Plastics cover a broad field of organic synthetic resin and may be divided into two main classifications - aerospace thermoplastics _ and aerospace thermosetting plastics. Thermoplastics may be softened by heat and can be dissolved in various organic solvents.
Thermoplastics may be softened by heat and can be dissolved in various organic solvents. Two kinds of transparent thermoplastic materials are commonly employed in windows, canopies, etc. These are known as acrylic plastics and cellulose acetate plastics. Cellulose acetate was used in the past but since it is dimensionally unstable and turns yellow after it has been installed for a time, it has just about passed from the scene and is not considered an acceptable substitute for acrylic. Acrylic plastics are known by the trade names of Lucite or Plexiglas and by the British as Perspex and meet the military specifications of MIL-P-5425 for regular acrylic, MIL-P-8184 -~ 184 for craze-resistant acrylic.
Aerospace Thermosetting Plastics.
Thermosetting plastics do not soften appreciably under heat but may char and blister at temperatures of 240 to 260 'C (400 to 500 °F). Most of the moulded products of synthetic resin composition, such as phenolic, urea-formaldehyde, and melamine formaldehyde resins, belong to the thermosetting group. Once the plastic becomes hard, additional heat will not change it back into a liquid as it would with a thermoplastic.
Storage and handling.
Because transparent thermoplastic sheets soften and deform when they are heated, they must be where the temperature will never be excessive.
Transparent acrylic plastics get soft and pliable when they are heated to their forming temperatures and can be formed to almost any shape. When they cool, they retain the shape to which they were formed. Acrylic plastic may be cold-bent into a single curvature if the material is thin and the bending radius is at least 180 times the thickness of the sheet. Cold bending beyond these limits will impose so much stress on the surface of the plastic that tiny fissures or cracks, called crazing, will form.
Simple Curve Forming. Heat the plastic material to the recommended temperature, remove it from the heat source, and carefully drape it over the prepared form. Carefully press the hot plastic to the form and either hold or clamp the sheet in place until it cools. This process may take from ten minutes to one-half hour. Do not force-cool it.
This type of forming is normally used for such parts as canopies or complex wingtip light covers, and it requires a great deal of specialized equipment. There are four commonly used methods, each having its advantages and disadvantages.
Stretch forming. Preheated acrylic sheets are stretched mechanically over the form in much the same way as is done with the simple curved piece. Special care must be taken to preserve uniform thickness of the material, since some parts will have to stretch more than others.
Male And Female Die Forming. This requires expensive matching male and female dies. The heated plastic sheet is placed between the dies which are then mated. When the plastic cools, the dies are opened.
Aerospace Vacuum Forming Without Forms. Many aircraft canopies are formed by this method. In this process a clamp with an opening of the desired shape is placed over a vacuum box and the heated sheet of plastic is clamped in place. When the air in the box is evacuated, the outside air pressure will force the hot plastic through the opening and form the concave canopy. It is the surface tension of the plastic that shapes the canopy.
Aerospace Vacuum Forming With A Female Form. If the shape needed is other than that which would be formed by surface tension, a female mould, or form must be used. It is placed below the plastic sheet and the vacuum pump is connected. When air from the form is evacuated, the outside air pressure will force the hot plastic sheet into the mould and fill it.
Teflon is the trade name for PTFE (polytetrafluoroethylene), a polymer consisting of carbon and fluorine. Teflon was developed back in 1938 by a DuPont researcher named Dr. Roy Plunkett. The development changed the plastic industry forever.
Plunkett and his DuPont team created one of the most slippery substances that exist. PTFE is not only beneficial for its nonstick property; it offers many other great qualities as well. The polymer is resistant to high temperatures, chemical reaction, corrosion, and stress cracking. These traits allow PTFE to be used for many different purposes.
One common household use for Teflon or PTFE is cooking. Many kitchen supply brands market their Teflon pots, pans, and utensils. These products are safe and make cooking a lot easier. The non stick PTFE component guarantees your food will slide right off the pot or pans surface. Cooking sprays and grease are no longer needed when you cook and bake with a Teflon coded product.
Another at home use for PTFE is with beauty products. Nail Polish is commonly infused with Teflon to create a strong, crack free product. Once applied, the Nail polish will stick to your nails longer with chipping. Many hair styling products, like curling irons and flat irons are also made with PTFE. The non stick coating helps the tools glide smoothly through hair, unaffected by the high heat temperatures.
PTFE is also significant in the automotive industry. One frequent use is with windshield wiper blades. Manufacturers coat their wiper blades with Teflon so the well known "squeaky blade situation" does not occur.
A fourth public use of PTFE is as protection for carpets and fabrics. Carpets and fabrics that include Teflon are less susceptible to stains. The PTFE acts as a repellant to liquids so spills can be easily wiped off.
Besides household and personal use, PTFE is widely used in a variety of business industries. The Steel and Chemical Processing Industries are two prime examples. These industries need strong and reliable hoses and tubing to transfer highly caustic and corrosive chemicals. They work with high temperatures to produce their products or services and they have to have a means for withstanding the heat. Teflon is great since it is carries the heat resistant and corrosion or stress free characteristics. PTFE tubing and hoses deteriorates less rapidly than metal piping. Manufacturers are catching on to this cost saving technique.
As you can see, PTFE properties are endless. They assist us with day to day tasks like cooking, cleaning, and driving. They contribute to our beauty prepping. And, PTFE's play a major role in the processes of industries like the Steel and the Chemical Processing Industry. Plunkett and DuPont might not have realized just how far their development would go. They created a product that remains essential to many functions in society today.