Glossary of industry terms M to O
Material reservoir - An excess cavity in a mould to permit enough material to be placed in the mould in the bulk form to complete the moulding to the desired wall thickness. The term may also be used to describe a feature used to make loading a narrow mould tool easier.
Maximum swing - The diameter of the largest imaginary sphere, with its centre located at the intersection of the minor and major axes that could be placed in both the oven and cooling chamber, individually.
Maximum weight per arm - The maximum total weight which can be safely supported and set in motion on a single machine arm. This weight includes mould spider or mould frames, moulds, counterweights, and material.
MFI - Melt flow index. A measure of how easily a material flows when molten.
Micro-grinding (pulverising) - The process of reducing polymer in pellet form down to a powder.
Micropellet (Gala pellet) - A form of pelletised polymer suitable for using directly in rotational moulding without the need to reduce it to powder.
Mismatch - Parts of a mould which do not align accurately are said to be mismatched. Normally refers to split lines.
Mixer (Blender, high speed blender, high speed mixer) - A machine used to mix additives with powder polymer (usually pigment).
Model - 1. Physical representation of the moulding normally made from resin or wood (or both) used for manufacturing cast tooling and made at a calculated size to allow for moulding shrinkage and casting contraction.
2. Physical representation of the moulding normally made from resin or wood (or both) used for evaluation of the shape, styling etc. and made at size or sometimes scaled (1/2 full-size).
3. Electronic data defining the geometry of the moulding - 3D cad model.
Mould - A tool in which material is placed and then acted upon by pressure or heat to form a part which conforms to the shape of the mould. In the case of rotational moulding, material is placed in the mould, heated, and rotated, so the material collects on the inside surface of the mould. Once the total material has collected and "cured" on the mould, the mould is cooled until the material has "set-up". The mould is then opened and the part removed. Rotational moulds are usually produced by casting using aluminium, machining out of solid material, or fabricating out of sheet stock. The term normally includes all of the components flanges, clamps, mounting plates, etc. that are required to run the mould on a machine. That which forms the cavity, along with cast-in parts such as flanges and posts. Tool is the "package" mould, clamping, mounting plate, frame etc. Verb: The act of forming parts by using a mould.
Moulded-in Graphic (in mould graphic) - A graphic which is applied to the tool and moulds into the moulding to provide an attractive and durable result.
Moulded-on Graphic - A graphic which is applied to the moulding to provide an attractive and reasonably durable result.
Mould enhancer - A chemical system applied to the mould tool to improve the surface finish of the moulding.
Mould pressurisation (pressurisation, air injection) - The use of low pressure air pumped through the arm of the moulding machine and into the mould tool to control the distortion and shrinkage of a moulding. A variation of this process using higher pressures can improve the surface finish of mouldings.
Mould tool (mould, tool) - Term used to describe the mould that the polymer powder is placed in to produce the moulding.
Mould wall thickness - The thickness of the mould tool. This must be relatively uniform or in some cases deliberately adjusted to ensure that the resultant moulding is of uniform wall thickness or in some cases deliberately varies, as required for the application.
Multi layer - Term used to describe a moulding that has more than one layer within the wall section. These layers may be the same basic polymer but with different properties i.e. an outer layer of high density polyethylene of one colour, and an inner layer of medium density polyethylene of another colour. They can also be different basic polymers i.e. an outer layer of medium density polyethylene, and an inner layer of nylon. Sometimes a further layer (tie layer) is required to join them.
Multi layer one shot - Term used to describe moulding materials that form more than one layer within the wall section of the moulding although they are introduced into the mould tool in a single shot.
Nest (fixture) - Term used for an item which holds the moulding during CNC or manual machining of post moulding trim details.
Neutral axis - Term used to describe the intersection zone of the two axes on the rotational moulding machine where the linear velocity is effectively zero. Placing a mould tool incorrectly with some sections of the tool entering this area can lead to significant reduction in the wall section of the moulding.
Offset arm - A machine arm whose mould mounting plate is offset to one side of the actual spherical mould area.
Oven - The part of the moulding machine where the tools are heated to form the moulding.
Oven time (oven cycle) - the amount of time the mould tool is in the oven melting the polymer.
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