There are many advantages to using a rotational molder when manufacturing various plastic products that are in high demand today. When making plastic products, the ability to move a mold can be very helpful, and it makes for a myriad of available plastic fabrication possibilities. Rotational molders also reduce production costs by controlling cycle times and increasing the efficiency of the thermoplastic casting process. Rotationally molded plastic products can be customized to many different thicknesses, material compositions, configurations, and product specifications. Additionally, there are a multitude of temperature, melt flow, and shrink rate issues that can be solved using rotational thermoplastic molding. This industry is continuously experiencing innovations and becoming increasingly efficient.
Being that roto casting uses centrifugal force and gravity to fill a mold, rotational molds have lower costs upfront. This is especially true when compared to other molding processes such as injection molding and blow molding.
Quick links to Rotational Molders Information
Resins and Materials
Resins and plastics used in rotational molding can be composed of a few different materials. Each type of polymer or resin has different properties that different products may require. For instance, not all plastic materials are FDA approved, so where one type of polymer would be perfect for a product that requires strength, it may not work in an application where it will come in contact with food.
Polyethylene is one of the main materials used in this roto casting process. Some types of polyethylene products include:
- Low-Density Polyethylene (LDPE)
- Linear Low-Density Polyethylene (LLDPE)
- Cross-Linked Polyethylene (HDPE)
- Regrind from Internally Recycled Polyethylene Scraps
Polyethylene isn't the sole material that can be used in the rotomolding process. There are a few other materials that can also be used. Some other types of these roto-molded plastic materials are:
Benefits and Drawbacks of Rotational Molding
Using rotational molding has a few benefits that would be difficult to achieve using other plastic forming processes.
- Shorter lead-time from concept development to production.
- Can be made with a one-piece hollow construction.
- Unparalleled design flexibility.
- This can be said about both small plastic parts to large industrial-style products.
- Economical for short production runs.
- Helpful in the areas of prototype research and volume production.
- The plastic roto casting process creates excellent load-bearing products.
- This type of thermoplastic casting makes it simple to produce multi-walled parts.
- Product thicknesses can be varied without making modifications to the mold.
- Cooling costs are lower and more economical.
- Rotationally molded products are more resistant to cracking and corrosion.
- Complex contours, flanges, and molded graphics can be created with this type of molding.
- Colors in plastics are so evenly distributed that they never crack or chip.
- There are many FDA-approved products, materials, and designs that can be created and used with this type of molding process.
The main disadvantages of rotational molding are the slowness of the process compared to other formation methods like injection molding as well as the high cost of rotational molding equipment.
The Rotational Molding Process
Rotational molding (otherwise known as rotomolding) is a casting process commonly used in the plastic fabrication industry. The molding process is done in four steps.
- The mold is filled with a polymer.
- A heating tool is used with an oven to melt the materials.
- A cooling tool solidifies the part.
- The part is removed from the tools.
Hollow parts are produced by pouring powder or liquid types of resin in a hollow mold or tank. Molds are rotated bi-axially using a tool within an oven. Rotation continues until the resin melts and coats the inner cavity of the mold. Parts are then cooled and removed from the mold. A wide range of parts and plastic products and parts are created using this unique form of thermocasting.
Rotational molders, in some ways, are very similar to plastic extruders, injection molders, and vacuum formers. Each machine involves the heating of raw plastic material beyond its melting point in order to form the plastic into a usable product. The major difference between rotational molders and other plastic formation tools is that roto molders involve a movable mold. The rotational molding process begins with a collection of raw plastic material in a partially open mold. Once filled, the mold is sealed and heated. Once the plastic within the mold is heated beyond its melting point, the mold is rotated in order to distribute the plastic throughout the mold. When the plastic has coated the mold's interior, the mold is cooled by water jets or other cooling methods. The newly rotationally molded plastic product is then ejected from the mold and either prepared for shipment to customers or sent for additional processing like cutting and surface treatment. Many parts can be produced simultaneously during rotational molding, resulting in very little scrap and reduced assembly costs. The main disadvantages of rotational molding are the slowness of the process compared to other formation methods like injection molding as well as the high cost of rotational molding equipment.
Rotational Mold Machines
There are a few types of molding machines. Each operates differently, and it can be helpful to understand the basics of how they work. Some molding machines include clamshell machines, rock and roll machines, and shuttle machines.
- Clamshell Machines
- Have a singular arm. It is usually supported by other arms on either end. This machine uses the same chamber to heat and cool the mold. Considering the size of the product it makes, this machine is economically friendly. Clamshell machines are commonly used in schools for prototyping.
- Rock and Roll Machines
- Designed to produce long and narrow parts. Some machines are of the clamshell type and only have one arm. Each arm rotates the mold 360 degrees in one direction while simultaneously rocking the mold at 45 degrees angles above and then below the horizon. Newer designs use hot air for mold heating. Rock and roll machines are great for large parts. Their smaller chambers are quite cost-effective compared to other bi-axial machines.
- Shuttle Machines
- Tend to have two arms that move the molds between a heating chamber and a cooling station. These arms turn independently and bi-axially. The mold is moved in a linear motion in and out of the chambers.
Rotational Molds That Are Available
The quality of the mold consumers choose is very important. There is no substitute for a good mold. A production rotational molder can help consumers find the best type of mold for a specific project and which type of resin would be most suitable.
- Cast Molds
- One of the most commonly used rotational molds. Cast molds can be used to produce both large and small parts. Cast molds tend to produce parts that have lots of detail and elaborate designs. They can be easily tweaked to integrate design changes. These molds are also great for "pulling" on the textures and shapes of existing objects. Essentially, parks with complicated curving or unique features are well suited to be cast in this way.
- Epoxy Molds
- Work by using a liquid polyester which works with thermosetting and then adding epoxy, which is formed and then cured. Like cast molds, these epoxy molds are fantastic for short runs or concept designs that may need adjustments made to them before their final versions are produced. Epoxy molds are comparatively inexpensive but do not have the same tolerance levels and durability that other molds may have.
- CNC Molds
- Used in situations where extreme precision is required. CNC molds are also good in circumstances that require extended production runs. They tend to be pretty expensive and are usually only used in special circumstances.
Products Made From Rotocasting
Many fantastic products can be produced using roto casting, some of which include tanks and basins.
- Plastic Tanks
- One product that is commonly created using roto-molded plastic. Tanks come in a wide range of sizes and styles. Styles may vary depending on which plastic molding process was used during their fabrication. Some common tank sizes are 300, 230, 130, 100, 65, 135, 220, 330, and 550 gallons. Though it is not a standard size, many tanks are even capable of holding 800 gallons or more. Rotational plastic molding is one of the only casting processes that can produce double-walled products. Double walls are an important component of many plastic tanks. A few things consumers may want to keep an eye out for when shopping for these types of tanks include quality construction, correct sizes, and appropriate thickness.
- Tank Stands
- Used to elevate molding tanks at different levels. These stands can come in many different specifications, strengths, and sizes. Stands are usually compatible with tanks of the same brand, though custom stands can also be made. They are usually made of different types of heavy gauge steel in order to have good strength and corrosion resistance. Some stands are stackable and may even contain storage. Many are finished with chemical-resistant coatings as well. The seller that a consumer chooses to purchase tank stands from will be able to help them find the right tank stand for their operation. A durable and reliable stand is a very important component of a thermoplastic casting unit. Often, manufacturers of plastic tanks will also offer tank stands.
- Containments/Containment Basins
- Large basin-style tubs that go beneath the tank and stand unit. Their purpose is just that, containment. They protect from leakage or accidental spillage of plastic materials. Some containments can also serve to stabilize the tank. These containments come in sizes that are usually compatible with specific brands and tank and stand units. It is important to choose a containment that is durable and of the right size. Containments can be a very useful component of the roto casting process.
Other products include toys and leisure products, industrial products, medical products, marine industry essentials, and many other miscellaneous plastic items.
Accessories for Rotational Molders
Consumers also may be interested in purchasing things like A/C solar mounting brackets, straps, containment basin hardware, plastic bulkheads, quick set-up brackets, stainless steel bulkhead fittings, hardware for tank stands, ball valves, lid replacements, and other solar packages and components from producers who use roto casting and sell roto casting machinery. Rotocasting products and accessories are sold by many vendors who are usually happy to help consumers find what they need for any number of rotomolding-related applications.
Choosing the Right Rotational Molder Manufacturer
It may be helpful for consumers to take time to consider which company they choose to work with when looking for roto casting products and parts.
Understanding all of the concepts related to roto casting can seem like a complicated endeavor, and finding a knowledgeable seller can help consumers find what they are looking for more quickly. A good manufacturer will be able to answer any questions that their clients may have. Sellers should also be able to help with things like service and repairs of molding equipment, and some companies may even be willing to assemble tanks and stands on-site. Companies may even offer to send their clients field service technicians. In addition to selling roto casting parts and related accessories, many companies sell a variety of resins and plastics which can save clients time and money if they choose to purchase products in bulk. A manufacturing company that offers high-quality products is also a must because products created with a good design and premium materials are going to be more reliable and efficient.