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.
Plastic is one of the most versatile materials in the market that you can use in a wide variety of applications. The use of plastic ranges from making of children's toys to medical applications. Plastic sheets are one of the most common types of plastics that you will come across. Just like the other plastic materials, they have a wide range of applications. When buying them you need to consider a number of factors such as:
Different sizes of PVC have different uses. When making the purchase you should note that the thicker the plastic, the more expensive it is. The different thicknesses that you have to choose from include:
Light duty: These are 86 micron units that you use in protecting your paintings, furniture, and small home appliances.
Medium duty: They are 125-micron units you use to protect furniture. You can also use the plastic to store and transit furniture. Experts have also shown that they are highly effective in ground warming.
Heavy duty: Heavy duty plastics are 250 microns in size and ideal for weatherproofing, ground warming, wall covers, lawn care, and duty transit.
To get the most from your PVC sheet, you need to get the right thickness. If you will be using the unit outdoors, especially on the ground, you should go for one that is at least medium duty.
In addition to the color being a matter of personal preference, different colors are ideal for different applications. Clear polyethylene sheets are a great choice when you are interested in natural lighting. These sheets have great applications during home repairs and construction. You can also use them in creating walls and roots in greenhouses.
Black sheets are opaque and block most of the light. Just like their clear counterparts, they have wide applications in covering furniture and floor. There are some people that buy them in order to block light from reaching unwanted areas. Black sheets are heavily used in the agricultural setting where they are used to retain ground and keep weeds out.
These are two of the main factors that you should consider when buying PVC sheets. When making the purchase, consider the size of the sheet that you want. This should be informed by the area you want to use them. Also, pay close attention to the quality of the sheets. Just like when buying any other material, go for the highest quality of PVC that you can afford.