Rotomolding

Index

1. What are the applications of Rotational Molding?
2. What is Rotational Molding?
3. What is the Rotational Molding process?
4. The advantages of Rotational Molding
5. The advantages over injection molding
6. What plastic resins are available and what are their properties

What are the applications of Rotational Molding?

What is Rotational Molding?

Rotational molding is a cost effective way of producing both large and small plastic parts. By using a variety of materials such as, linear low density polyethylene (LLDPE), cross linked polyethylene (PE) and high density polyethylene (HDPE), allows rotational molding to cater to a variety of structural requirements; these individual properties will be discussed later.

What is the Rotational Molding process?
-The five main stages of rotational molding:
It is essential to have a good quality mold, either cast or fabricated. The mold is mounted on the machine, which has 3 different stations; loading, heating and cooling.

1. A pre weighted amount of plastic resin powder is loaded into the mold cavity (tool) and the mold is securely closed at the loading station.
2. The mold then moves from the loading station to the heating station for a pre-set optimized time period where it is rotated on both the horizontal and vertical axis. The plastic resin powder fuses together lining the inside of the mold and evenly covers all surfaces inside the mold with uniform thickness (uniformity is an option).
3. Once the heating stage is complete the mold moves to the cooling station where the parts are cured for a pre-set time.
4. Once cooling is complete the mold moves back to the loading station for the parts to be released from the mold and the process repeats. There are usually multiple molds operating within one cycle.
5. Following the molding cycle, parts are trimmed, routed and processed in order to obtain the finished part; additional secondary operations may be required depending on the part produced.

The advantages of Rotational Molding
Cost Advantage:

• Tooling for rotational molding is less expensive  when compared to injection and blow molding
• Rotational molding  lends itself to short runs of 15+ parts.
• Existing part designs e.g. Cold Air Intake systems can be converted from a costly metal design to a cheaper high quality plastic part.
• Recycled material can be used in some applications making the product cheaper and greener.

Time Advantage:

• The time taken to manufacture a mold is short.
• Short production runs can be carried out and rotationally molded part can be shipped out virtually the same day.

Design Advantage:

• Inserts are easy to mold in.
• Under cuts are easy to mold into a part.
• Special Graphics can be molded in.
• Depending on the design, the final product is relatively stress free.
• Different types of resins in different colors, and glow properties.

Advantages over injection molding:
Cost Advantage

• Rotational molding is a more cost effective process than injection molding because tooling is less expensive to design, create and operate. Injection molding requires pressurizing the plastic resin into the tool however; rotational molding does not require a pressure-sustained environment.
• The rotational mold making process is cost efficient and simpler to alter /make revisions to designs with a quicker turn-around time.
• Injection mold tooling is relatively expensive due to complex pressured plastic pathways.
• Cost effective prototyping is feasible in rotomolding because short runs are possible.

Design Advantage

• There are also design advantages in rotational molding over injection molding; in injection molding, some parts require several stages of production to complete one assembly. Rotomolding can produce these in a single mold; this reduces the need for additional costs in the mold making process.
• Design strengths are an advantage in rotomolding because there is always uniform wall consistency (when required) and strong corners can be made stress free.
• Inserts threads, handles and undercut are easy to mold in.

What plastic resins are available and what are their properties:

• Low density polyethylene (LDPE): Has flexible properties and is less stiff than HDPE.
• Linear low-density polyethylene (LLDPE): Can be used for an array of desired applications. LLDPE also has good ductile strength and impact resistance.
• High Density polyethylene (HDPE): HDPE is a stiff resin used for applications requiring strength and rigidity.
• Cross linked polyethylene (XLPE) : Is a resin which works well in low temperature conditions. Parts are sustainable under cold temperatures and have excellent ductile strength/impact resistance.
• Recycled Polyethylene: Is a cost effective material used for various applications.