Plastic Rotational Molding
Plastic rotational molding is a type of forming method that is used to create hollow thermoplastic products. Using a revolving metal mold, roto molding machines produce products that are uniform in wall thickness, seamless and of a single construction. They are valued for these qualities and for the savings they offer via the elimination of the costs of additional fabrication processes and replacement parts.
Quick links to Plastic Rotational Molding Information
Plastic Rotational Molding Process
Before doing anything else in the rotomolding process, manufacturers must fabricate a mold that fits the dimension specifications of the part to be created. Typically, they use stainless steel or aluminum. To create a non-uniform wall thickness, they can use a combination of both metal materials. For complex designs and constructions, they will do so using the die casting process. For less complex designs, on the other hand, they can simply weld the mold. Either way, once a mold is created, manufacturers mount it onto a rotating spindle, which revolves on either one or two axes. When the mold and spindles are assembled, manufacturers pour powdered, raw metal stock onto the mold. From here, the mold is transferred into an oven chamber, where it continuously revolves as the metal powder melts and evenly coats the mold walls. Once the metal has completely covered the mold, the mold is transferred to a cooling chamber, where a combination of air and cold water cool and cure the molten plastic. This portion of the molding process generally takes around 20 minutes to complete. After the plastic has dried completely, it is removed from the mold. This is typically done manually, and can sometimes prove difficult, as the plastic can shrink during the process. Either way, once off the mold, the new hollow plastic part can either be sent on for shipping or sent on for further processing. Common processing procedures they undergo include cutting to size, welding with small components, painting, polishing and cleaning.
Types of Machines to Plastic Rotational Mold
There are a lot of different machines that can be used to perform plastic rotational molding. These include: rock and roll machines, clamshell machines, shuttle machines, vertical or up and over machines, carousel machines and swing arm machines.
- Rock and Roll Machines
- Specially designed with small heating chambers to create long, narrow parts.
- Clamshell Machines
- A type of rock and roll machine, though they distinguish themselves by their use of a single primary rotational arm (not counting the usual support arms they have on their ends). Most other plastic rotational molding machines use at least two arms.
- Shuttle Machines
- Typically have two arms that work independently, moving the mold back and forth in between the heater and the cooler as it turns biaxially. Some shuttle machines do, however, have only one arm. In this case, the arm moves the mold horizontally from the heater to the cooler as it spins.
- Vertical Rotational Machines
- Smaller than most other rotomolding machines; they are considered small to medium in size. They are valued for their energy efficiency, which is born out of their compact heating and cooling chambers.
- Carousel Machines
- One of the most commonly used rotational molding machines. Carousel machines may have up to four arms and six stations, and they come as either fixed or independent equipment. Typically, fixed arm carousel machines consist of three arms that are required to move together, while independent arm carousel machines have between three and four arms, all which move separately from one another. Both types of carousel machines are available in a wide variety of sizes.
- Swing Arm Machines
- Can have up to four arms, all of which move bi-axially. The arms, which do not all have to be engaged at the same, are mounted on the respective corners of the machine, where they swing in and out of the oven.
Applications of Plastic Rotational Molding
Plastic rotational molding is used to make all sorts of products used in diverse industries, such as agriculture, chemical processing, construction, food and beverage processing, furniture, marine manufacturing, material handling, packaging and assembly, pharmaceuticals, plumbing, recreation and sporting goods, toy manufacturing and waste water management. Some examples of the plastic products that can be fabricated via rotomolding include footballs, helmets, kayaks, outdoor planters, plastic tanks, playground slides, pipe fittings and safety cones.
Things to Consider When Choosing Plastic Rotational Molding
Plastic rotational molding tends to be engaged less commonly than forming methods like thermoforming, blow molding, or injection molding because the machinery needed is somewhat large and initially expensive. However, it does offer many benefits that make it a viable option. For example, it creates seamless products. It also creates products with highly uniform wall thicknesses. Furthermore, their products can be imbued with enhanced qualities through the inclusion of additives in the thermoplastic material. Find out more by contacting an experienced manufacturer today.