Glossary of industry terms P to R
Particle size distribution - Term used to describe the distribution of the various particle sizes within a moulding powder. Performance of a powder is not solely determined by the sieve size, it is also determined by the size of smaller particles and the proportion of the overall that they represent.
Permanent mould release - a release which is sprayed onto the mould tool and then baked and provides multiple releases for months or even years of production. Typically the release agent is PTFE (Teflon) based, and provides a gloss or lustre finish to the tool and therefore the moulding.
Pinholes (pinholing) - Small voids visible on the surface of a moulding.
Photo-etching - A method for applying a range of textures to the internal surface of the mould tool which transfer to the moulding to provide an attractive surface finish.
Plaster casting (ceramic casting) - an alternative to sand casting for the production of cast aluminium mould tools. Instead of using sand to form the cavity into which molten aluminium is poured, a form of plaster is used. This creates a higher definition tool 'as cast', and through the use of flexible patterns allows the production of undercuts.
Plastisol - The liquid form of PVC (Poly Vinyl Chloride) used in rotational moulding.
PlusNut - A commonly used insert for secondary finishing operations which gives good torque resistance and pull out resistance and offers a robust thread.
Pock mark - A blemish on the surface of a cross linked polyethylene moulding caused by out gassing from the cross-linking agent.
Porosity - 1. Term used to describe voids in a mould. This is undesirable because it can adversely effect the surface finish of the moulding by reproducing the void as a small bump on the moulding and it may also lead to blow holes in the moulding if the porosity in the tool contains trapped air. Porosity may be present in the base material of cast aluminium moulds and in welded joints.
2. Term used to describe some types of voids in mouldings.
Powder - The form in which most polymers are used in rotational moulding.
Preheat (preheating) - The manual or automatic heating of a static tool prior to rotation in the oven.
Prototype mould - A preliminary mould, usually made as inexpensively or as quickly as possible, to prove out the design concept for a moulding. Methods of manufacture are:
a. GRP fabrication using high temperature epoxy reinforced with carbon fibre.
b. Flame spraying of molten metal onto a master until a shell of predetermined thickness is achieved.
c. Direct CNC machining of aluminium stock. Only in the case of CNC machining can the tool give a normal production life.
Ratio - The interrelationship of the speeds of the primary and secondary rotation on the moulding machine.
Receiver - Threaded sleeve mounted in receiver tube to allow closure by tightening a receiver bolt through the top spider.
Reverse draft - draft on a moulding which runs against the draw and relies on shrinkage for the feature to de-mould successfully.
Ripple - Term used to describe the surface finish on the inside of a moulding when it is only just fully fused or when made from certain materials and correctly fused.
Rock and roll - The rotation taking place in the moulding process where the tool is rotated through approximately 45° either side of horizontal in one axis (Rock) and 360° in the other (Roll).
Release (release coat, mould release, release agent) - a chemical system applied to the mould tool to facilitate easy removal of the moulding from the tool, may be semi-permanent or permanent.
Ring (plate) - A circular steel fabrication which is attached to end of the mould machine arm to provide a location for fixing tools.
Rotational mold, rotational molding - US spellings of rotational mould, rotational moulding.
Rotational moulding (rotomoulding, rotamoulding, rotational casting) - A process used to mould hollow parts. The material is placed in the cavity of a mould that rotates on two axes. The mould is subjected to heating and then cooling while rotating. The material melts and adheres to the cavity walls to form the shape desired, and is then cooled to solidify it.
Rotational mould - A mould tool specifically designed for the rotational moulding process.
Rotation - The motion of the machine and the tool which forms the moulding.
Rotation speed - The speed at which the primary and secondary axes of the moulding machine rotate.
Routing - The term used to describe the secondary operation of machining which is used to create apertures and edge profiles on mouldings.
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