Rotational moulding is a process that is mainly used to create hollow one-piece plastic items. Also called "rotomoulding", it is a low pressure, high temperature manufacturing method that combines heat and bi-axial rotation. Typical moulded parts can include parts such as
bulk fluid containers, compartment liners, spill trays, pallets, pipe supports, etc.
The Process of Rotational Moulding
The rotational moulding process consists of 4 parts:
- Preparing the mould
- Heating and fusion
- Cooling the mould
- Unloading / demoulding
Types of Moulds & Polymers
Moulds used in the rotational moulding process are typically manufactured from either stainless steel or aluminum. Although thicker than equivalent stainless steel moulds, Aluminum's thermal conductivity is many times greater than that of steel and thus the rotational moulding cycle time is not significantly affected.
Aluminum moulds are the most common used in the rotational moulding industry. With cast aluminum moulds manufacturers can produce complex shapes with intricate detailing in a wide range of sizes - from very small products (such as ear bulb syringes) to large industrial items (such as waste water holding tanks). A cast aluminum mold is preferred for its heat transfer, malleability, strength, design flexibility, and how it faithfully reproduces the product appearance.
According to recent reports 80% - 90% of all material used in the rotational moulding industry is polyethylene (HDPE, LPDE and LLPDE). Although PVC, nylons, and polypropylene compounds are also used. Most manufacturers decide upon polyethylene as the resin of choice because of its availability, ease of use, and suitable properties.
A paper written by J.D. Ratzlaff of Chevron Phillips Chemical Company LP in 2004 entitled "Polyethylene: Process Sensitivity in Rotational Moulding" presents the results of a study of the impact sensitivity of polyethylene to processing conditions and discusses methods to maintain high impact standards.
Request a Quote!