persico.com - Rotational Division

Rotational moulding is a simple process, compo-sed of four basic phases:
1) a Pre-weighed amount of powdered or liquid plastic in placed in one half of a thin walled hollow metal mould which is mounted on the arm of a moulding machine. The mould is then closed with clamps or bolts.		3) When the material has melted and has been consolidated, the mould is moved to a cooling station where forced air, water mist or a combination of both is used to bring the part temperature down to a point below the crystallization or solidification point of the material. Biaxial rotation continues to prevent the material from sagging.

2) The mould is then rotated biaxially about perpendicular axes and moved into an oven where heat is applied. The metal mould becomes hot and the power/liquid tumbling inside rises in temperature. Hot material sticks to the mould in successive layers to form the part.		4) Once the part is cool, the mould is moved to the unloading station where the part is removed. The mould is then ready to begin the

ADVANTAGES AND DISADVANTAGES OF ROTATIONAL MOULDING

ADVANTAGES
Economic tooling costs
One-piece construction; virtually stress-free-totally enclosed parts or with openings.
Weight reduction-as compared the most metals.
Uniform wall thickness-no thinning in the extremities.
Variety of finishes and color.
The ability to produce multi-wall mouldings
Design flexibility-from small and intricate to large and complex.
Metal inserts as integral parts.
Economical for short production runs and prototype research as well as volume production.
Minor undercuts are possible-with no draft angles required.
Short lead-time
Resistance to stress-cracking and corrosion.
Excellent load-bearing properties.

DISADVANTAGES
The main disadvantages of rotational moulding can be summarized as follows:
1. The number of materials available for rotational moulding are limited by comparison to other processes.
2. The is not suite to very large production runs of smaller parts - for smaller parts, blow moulding may be more competitive.
3. Material costs are higher due to the need for grinding of pellets to a fine powder for moulding. Developments in micro-pellets may reduce this penalty.
4. Loading of moulds and unloading of parts is labor intensive by comparison to other processes, especially for complex parts.
5. Bosses and ribs for stiffening cannot be easily moulded into parts, designers must use part geometry and design to produce stiff parts.

MOULDS

Rotational moulds are generally consisting of metal shells, coupled in such a manner to realise a closed container, whose internal the resin has been loaded.
The mould also has an external metal structure, called frame, and a closing system.
The mould function consist in defining, through its internal surface, the external surface of the part; furthermore the mould has to conduct the heath for the resin casting, to allow the internal pressure regulation during the heating and the cooling, to be enough stiff not to deform during the process stages, but at the same time its weight has also to be limited.

PRODUCTS

With roto-moulding, parts can be moulded economically in a variety of shapes and sizes, many of them impossible to produce by any other process.
Industrial products: tanks, drums, containers, tote bins, nesting pallets, pump bodies, septic tanks, sewage aerators and lifting units, machine instrument and appliance housings, mannequins, point-of-stage storage and display racks, temporary shelters, utility sheds, salad bars, air ducts, fishnet and navigational floats, portable toilets, grass catchers, and composting containers.
Transportation products: truck-bed boxes, liners, and tool boxes, ventilating ducts, fuel tanks, crash-test dummies; battery cases, motorcycle saddle bags and fairings; go-kart bodies; highway signs; barricades, bumpers;
Consumer products: infant and adult furniture such as tables, chairs, beds, desks, and benches; insulated food and beverage containers: decorative planters, urns, vases, mail boxes; and doghouses.
Recreational products: wading pools; sand boxes; playground equipment, row, motor, and sail boats; kayaks and canoes, playhouses, bowling equipment and furniture, toy storage boxes; carousel and hobby horses, camper tops; exercise equipment; and balls of all types and sizes.
Agricultural products: water tanks; animal feeding and watering troughs; tractor cabs, harvesting-machine panels, and grain bins.