Rotational moulding is more environmentally friendly in several ways:

• All the raw material is used up in each moulding: there is almost no waste
• The majority of the material used in rotomoulding plastic is polyethylene which by comparison with other polymers is ‘clean’ to manufacture and to process
• Polyethylene can be readily reprocessed to manufacture either new rotational mouldings or mouldings made by other processes; alternatively it can be cleanly incinerated for heat recovery
• Significant percentages of additives cannot be incorporated into rotational mouldings and therefore the amount of segregation needed for successful reprocessing is minimal, thereby making it more economic and therefore more likely.

The answer is yes and no. In most cases tooling for rotational moulding is cheaper than other methods of manufacturing plastic. This is true for two reasons: rotomoulding does not have to withstand the high pressures that are often required for other processes, and rotomoulded components are purely hollow cavities with no core section required.

Mouldings may also be cheaper than GRP hand lay-up, vacuum formings, and vacuum-formed assemblies, RRIM, RIM, and RTM. Injection mouldings, blow mouldings, and extrusions will generally be cheaper.

The design can be specified in many ways, from a basic sketch showing roughly the shape required, through to fully defined 3-D CAD models complete with all assembly data, with practically any form of design data – and practically anywhere between those two extremes. Most commonly designs are specified by:

• 3-D CAD models
• Dimensioned manufacturing drawings
• Physical models.

tecni-form pride themselves on providing very high levels of design support and collaboration, and can work with customers to turn a basic idea into fully production-viable rotational mouldings with all of the supporting documentation being created by tecni-form in-house if required.

Yes, the smallest moulding tecni-form have seen is a 25 mm diameter, 30 mm high cylinder (which was moulded by them), and the largest is an 80,000 litres tank (which was not). tecni-form can currently accommodate moulds that would fit inside a sphere 3m in diameter.

Generally the plastics used are the crystalline thermoplastics such as, polyethylene, polypropylene, nylon and PET. tecni-form can, however, handle some notable exceptions, such as PVC and polycarbonate which are amorphous thermoplastics, and polyurethane which is a thermoset.

The full answer to this question can be found on the Why tecni-form? page. In brief:

• tecni-form‘s service encompasses a broader range than other rotomoulders
• tecni-form pride theirselves on an exceptional design expertise which they share with their customers
• tecni-form continually innovate
• tecni-form‘s clients, from all over the globe, come back for more
• tecni-form work to time and budget
• tecni-form really care that quality should be right.

Rotomoulding’s inherent ability to manufacture hollow parts means it is particularly suited to the manufacture of all types of console, especially those used as ducts to provide heating and cooling air.

Open hollow shapes like console covers can be cost effectively made by producing two mouldings ‘back to back’ in the same tool and then machining the moulding to produce two identical parts.

The process inherently produces hollow parts which is ideal for the manufacture of tanks. Combining this with polyethylene’s resistance to a wide range of chemicals including acids and alkalis, and the low levels of inbuilt stress in rotational mouldings, and you have the perfect solution for the creation of storage tanks to contain volumes from less than 1 litre to over 80,000 litres.

As with all other moulding processes, this is very much dependent on the material used. The factors leading to potential part failure are the temperature, the time the part is subjected to the temperature, and the loads being applied. It is therefore not easy to provide a definitive answer, but as a basic guide, polyethylene is suitable up to about 60° C, polypropylene to about 100° C, and nylon 120° C.

The blow moulding process is another method used to manufacture hollow plastic components, and it is generally used to create higher volumes of products than rotational moulding.

One advantage of rotational moulding over blow moulding is the more even wall thickness generally achieved. This regularity means that a rotationally moulded item is less likely to have weak points in its surface. Another advantage is the ease with which metallic and non-metallic inserts can be incorporated into the moulding.

Rotational moulding is actually a very suitable process for the manufacture of fuel tanks of all types – including those for marine applications. Both diesel and petrol tanks are commonly manufactured from either LLDPE (linear low-density polyethylene), or XLPE (cross-linked polyethylene), and for diesel applications no further processing is required.

In the case of petrol, post moulding fluorination is used to provide the barrier properties to meet permeation regulations. However, other materials may be used, either on their own or in conjunction with polyethylene (normally as an inner layer) to provide enhanced performance, such as improved heat resistance or barrier properties.

Tools made by several different methods can be used for rotational moulding as follows:

• Cast aluminium
• CNC machined aluminium
• Sheet steel fabricated
• Electroformed
• Flame sprayed zinc
• Plastic composite (epoxy resin reinforced with carbon fibre or prototype production only).

In all cases the tools are only cavities (no core is required) with interiors that are an exact representation of the external geometry of the moulding, and exteriors which closely follow the internal form.

The lifespan of any rotationally moulded plastic product is very much dependent on the end application: for example, rotational mouldings have been used for single use transportation packaging where the life of the moulding is effectively a few weeks, but there are other examples where mouldings are still in use after 30 to 40 years of continuous service.

This is actually a very difficult question to answer as tecni-form have yet to write off a tool because it is no longer serviceable. Generally tecni-form recommend that it is prudent to assume a life of 10 years in regular volume production, although they do have some tools still running after 15.