Rotary moulding

Biscuits can be shaped by cutting, either rotating or vertical, wire cutting or rotary moulding. These processes are covered in Chapter 8 (Section 8.4 on biscuits). 

Very soft doughs that are not suitable for rotary moulding are extruded onto a belt to produce strips of dough. These dough strips can then be guillotined before or after baking. 

Multi-colour moulding. This concept was devised for the automotive industry, specifically for rear light lens clusters in PMMA (polymethyl methacrylate). It involves a rotary mould assembly, with the different colours being injected sequentially from separate cylinders as the mould rotates. 

Special rotary curing units are designed for continuous vulcanisation of V-belts. This method eliminates any areas of overcure and moulded in stresses, which result from methods using presses vulcanising belts in sections. Belt and tension roller pressure release mechanisms allow for easy unloading and loading of the belts. 

Fig. 9a-h. Different design patterns for superimposition of rotation, reciprocating-rotary and oscillating vibrations on the main flow of molten polymer under extrusion (a-d) and pressurized moulding (e-h). Explanation of flow diagrams is given in the text,... 

It may be dried before or after moulding in fluidized-bed continuous-belt or rotary-tube driers. 

The gas mixtures are usually manufactured by grinding and blending the raw materials, which after a pre-compacting step are pressed into pellets or disks on (rotary table) presses, after which they are weighed out. Gas mixtures containing -> Nitrocellulose are moulded after gelatinising in the usual way. 

Note that a portable tester based on the same principle as the compression tackiness tester is defined by a British Standard for testing of soils16. It uses a split mould 38 mm in diameter and 76 mm long (note the 2 1 ratio), with the sample of soil extruded into it from a sampling tube. The load is applied manually by a rotary handle and a lead screw, through a calibrated spring. 

Although the above are the major moulding processes for thermosets, injection moulding can now be used for the selected thermoset moulding operations. The major use of thermosets still remains with screw closures. These are made on either a multicavity platen tool (up to 96 cavities) or a rotary type press which resembles a rotary tableting machine. 

Thermosetting caps are compression moulded on either platen or rotary-type equipment. Pressure, dwell time and temperature are critical to the curing operation, otherwise brittle or soft caps may be produced. 

Foundries utilise mechanisation and automation depending on the need for reproductivity and on the series sizes. The most flexible installation is typically the jobbing foundry. This produces a variety of products in small numbers (<100). In general, this type of foundry applies manual moulding techniques with resin-bonded sand moulds. The melting furnace works batch wise to allow an easy change of alloy. This implies the use of induction or rotary furnaces. 

Developed in the early 1980s as a revolutionary tool for the production of foamed refrigerator doors, the well-known concept of the rotary polymerisation system is now being proposed as a compact and simple mould-carrying system for the production of automotive seats (see Figure 3.12). 

Three-station rotary machine for tslow moulding (after Modem Plastics Encydopedia). 

The plasma treatment is carried out downstream from the PET blow-moulding machine, and is of a design based on the company s own well-proven rotary high-output technology. The first model, ACTIS 20, has 20 stations and can treat 10 000 PET bottles up to 0.61 litre size an hour. According to Sidel calculations, the cost price of 33 and 50 cl size containers is, in fact, less than competitive packages. 

An innovative development concerned with engine management of twin camshaft engines has been introduced by Brampton Renold in France a key feature is the use of PES for the linear-to-rotary piston. The requirements are the ability to be moulded to close tolerances, with good creep and abrasion resistance in the presence of hot lubricants. 

Two general types of machine are used for ingot casting - the rotary wheel caster and the straight line chain mould machine. The casting wheel uses a rotary table with water-cooled moulds arranged around the outer periphery of the wheel. Molten metal is poured into the moulds at a fixed station. The mould... 

Fig. 7.41. Three-Station rotary machine for blow moulding (after Modern Plastics Encyclopedia). ...

One example of this type of application is a rotary switch for military radios. Here LCPs were chosen to replace a diallyl phthalate (DAP) thermoset for the stator to solve the problem of high reject rates. Close tolerances down to 0.025 mm must be held on critical areas of the moulding, and the ability to mould thin-walled sections is essential. 

Versions and adaptations of the above press types may be seen, such as the sliding table or shuttle press which uses two tools and allows one tool to be loaded, for instance, with inserts, whilst the other tool is moulding (Fig. 5). Rotary presses may be used for moulding high production quantities but require multiple tools and are not in great demand for thermosetting plastics materials. 

To the above list, which is not complete, it may be worth adding that swarf from metal inserts may contaminate moulded items and be a potential hazard on electrical equipment. All inserts should, therefore, be degreased, rotary tumbled to remove swarf and carefully handled at all stages. 

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