Many clients throughout the Wellington area have heard the term vacuum forming, but they do not know what it really means, and they don’t know what it does or how it can help them in their business. Vacuum forming is a procedure that can shape performance plastic sheet materials into many different forms, and it is one of the best ways to make a host of different plastic products.
How Does it Work?
A type of thermoforming, vacuum forming, is a process by which a plastic sheet or thin sheet of plastic, such as a PVC sheet, is heated up so that it becomes malleable. The heating process includes the use of aluminum plates and infrared heaters. The heat application will come from the top and the bottom so that it is uniform and will provide the best results.
Once the heat finally reaches the proper temperature (which can differ based on the thickness of the sheets in use) the vacuum will mold the sheets to form the product. The vacuum is able to provide an airtight environment, which is going to be better for the overall molding process.
Products from Vacuum Forming
With this type of thermoforming, one could create countless types of products, and you may find that your company could benefit greatly from the process. One of the most common products using vacuum forming today are children’s plastic toys, but that’s just one of the possibilities. Product packaging is another option, and it is one most companies that create, manufacture, package and sell products could use. Most of the plastic items that you see around the home and office have gone through some type of thermoforming, and it’s often the vacuum process.
Wellington Best Plastic Sheet Supplier
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.
What Plastic Materials Are UV Stable?
Some of our most popular questions are "Is this material UV stable?", or "How long will this last in direct sunlight?", or some similar themed question. These are great questions. Just look at the 'cheap' backyard furniture you bought last season, yep, it is faded and cracking or broken. Why is that?
The quick answer is the material had either no UV (Ultra Violet Light) stabilizer or very little - or it was simply the wrong plastic for the part. Most plastic materials are not UV stable to start with, other than Acrylic which is invisible to UV. All other materials need a little something (an additive) to give it the protection it may need from the sun. Many plastic materials, if given the proper UV resistant additives, can be used in direct sunlight for 10 - 15 years, or more, providing excellent performance in harsh environments.
The first factor in picking such a material is the intended use. Not all materials are good choices for all applications. While some materials will perform exceptionally well, others plastic materials under the same conditions will fail. Many plastic materials are not well suited to: high temperatures, chemical exposure, UV light, high impact, or electrical applications. Please contact us for details on a material that may meet your needs.
HDPE sheet is one of the best materials for long term outdoor use, if given the proper additives (without UV inhibitors it will fade and crack quickly). Next time you drive by a children's playground in your local city, look at the brightly colored panels used to make the play equipment. This is a HDPE sheet with heavy UV additives, and this makes an excellent application. Available in a rainbow of colors and able to be fabricated easily, this material is excellent for many outdoor applications.
If your application is more mechanical, other materials that might be used would be: Polycarbonate, UHMW, ABS (especially with Korad - Acrylic cover), Acetal, Noryl and many more.
Our standard Makrolon Polycarbonate is a UV stable material in sheet, and is frequently used in replacement glazing applications. The remaining materials on the list are available in Black (a carbon black pigment) which extends outdoor usage. While still not recommended for direct sunlight, they can be used with a good possibility of success - depending on design. Plastics can become brittle or lose properties over time if material does not have UV stabilization, with the proper material and the proper additives, you can get years of trouble free service.
Additionally, many materials will work well if they are painted to cover the plastic surface. Many spray paints, especially Acrylic paints, last many years in the sun. Please check with us, as some material do not accept paints or coatings.
Take some time to review your requirements, and the properties of the plastic you intend to use. The right material will provide the best performance. Contact any of our Plasticologists for assistance, call 866-832-9315 or email us. You can always do research on plastic materials at Industrial Plastic Supply.