Practical Guide to Rotational Moulding by R. J. Crawford
By R. J. Crawford
Rotational moulding is a truly aggressive replacement to blow moulding, thermoforming and injection moulding for the manufacture of hole plastic components. It deals designers the opportunity to provide relaxing articles, with uniform wall thickness and intricate shapes. Rapra's useful advisor to Rotational Moulding describes the elemental points of the method and the newest cutting-edge advancements within the undefined.
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Extra info for Practical Guide to Rotational Moulding
11 Mould Clamps As indicated earlier, the purpose of the mould clamps is to keep the mould tightly closed during the heating and cooling of the rotomoulded part. Poor or ineffective clamping will result in a variety of problems. These include: • Visual and structural imperfections such as ‘blow holes’ at the parting line. • ‘Flash’ at the parting line which will probably necessitate trimming of the final part. This introduces extra costs and may result in visual imperfections or stress concentrations due to knife slits in the moulded part.
51 there is a practical demonstration of the faster moulding cycles achieved with blackened and rough moulds. 48 ‘Profit pins’ on external mould surfaces. 49 ‘Profit pins’ on internal mould surfaces. 50 ‘Profit pins’ detail. 51 Blackened ‘profit pins’ on external mould surface with two venturis. 18 Mould Shielding (Internal) It is often desirable to mould in ‘holes’ or create ‘blank’ areas on moulded parts. This overcomes the need for post-moulding trimming, cutting or drilling, which is time consuming and prone to inconsistencies particularly if performed manually.
The method of holding the insert depends to a great degree on the size, number, and function of the insert. There are two general classes of moulded-in inserts. Plastic inserts are used where the dimensional tolerance of a rotationally moulded region is unacceptable, or where rotational moulding is impractical due to wall thickness or mould dimensions. Care must be taken during the rotational moulding process to minimise thermal damage and heat distortion to the insert while ensuring that there is sufficient fusion of the molten plastic to the insert to provide integrity in the moulded part.