MOULD CLOSING

Demonstrations (a) Give four injection-moulded close-packed planes to each student to allow personal building of f.c.c. and c.p.h. (b) Atomix atomic model on overhead projector to show atom packing (Emotion Productions Inc., 4825 Sainte Catherine O, Montreal 215PQ, Canada) or ball bearings on overhead projector. 

Solution Although this runner system is symmetrical, it is not balanced. If the runner had the same diameter throughout all sections, then the mouldings close to the sprue would fill first and would be over-packed before the outermost... 

Impact-resistant foam liners used in helmets and other protective gear are usually not breathable unless air passages are fabricated in them. Brock USA has developed a process for moulding closed-cell foam that permits three-dimensional air flow and moisture evaporation... 

Details are given of the change in cell structure of a closecell foam due to multiple impacts and the range of application of cushion curves as they relate to reusable packaging. Cushion curves and stress-strain curves for up to 15 compressions were generated for three different moulded closed-cell PE foams. 

The whole length of the pipe is not pierced at onoe, an inch being left unbored, and the unfinished pipe with the wire is placed in the half of the copper mould, , b—Pig. 484kk—previously brushed with oil to give smoothness to the stem upon removal. The two halves of tlio mould, closed accurately together by means of pins, are then placed in a frame—Pig. 484m— and the edges kept in contact by the screw vice, a. 

Plastic closures can be made by injection moulding, where the mould has two parts - a core which has the inside features of the closure and a cavity which has the features of the outside of the closure. Molten plastic is injected into the mould, which is water-cooled. The plastic solidifies, and the mould opens and the completed closure is ejected. If the closure is a two-piece design (i.e. fitted with a loose or flowed in-liner), then this is added later. Another technology for moulding plastic closures for the beverage market is compression moulding. A hot pellet of PP is positioned in a mould, similar to the cavity of an injection mould. As the mould closes, the pellet is squashed and defoimed into the shape... 

A special type of injection moulding is the manufacture of foamed articles. The foaming process takes place in the mould, so that mould filling requires considerably lower injection pressures and mould closing forces. Very large mouldings can be made in this way. 

Blowing Once the preform is within the blow mould area the moulds close, a stretch rod is introduced to stretch the preform longitudinally and using two levels of air pressure, the preform is blown circumferentially. 

Injection moulding A plastic processing technique to produce solid parts with a high degree of precision. The material is injected into a mould by a plunger, and a press keeps the mould closed while the material cools. At the end of the process, the mould is released and the part ejected. 

Blow-fill technology is an aseptic process whereby the container is formed from thermoplastic granules, filled with sterile solution and sealed, all within one automatic operation. The bulk solution should have a low bioburden and is delivered to the machine through a filling system that has been previously sanitized and steam sterilized in situ. Concern has been expressed that the machine itself may generate particles. The plastic granules are composed usually of polyethylene, polypropylene or one of their copolymers and are heat extruded at 200°C into a tube. The two halves of a mould close around this tube and seal the base. The required quantity of sterile fluid is filled into the container, which is then sealed. Products packed in this way include intravenous solutions, and small volume parenteral, ophthalmic and nebulizer solutions. The... 

If B 1, there is marked temperature gradient, but if B 1, there is not. For a sheet of polymer of thickness >1 mm cooled by water or by contact with a steel mould, B 3> 1. When B > 10, it is a good approximation to say that the polymer surface temperature is immediately reduced to that of the cooling medium. For a blow-moulded parison (Section 5.5.2) of thickness L = 0.002 mm, cooled in still air on the outside, B = 2. If the lower end of the parison cools for 150 s before the mould closes, it is a reasonable approximation to ignore the temperature gradient through the wall, and calculate the average temperature drop at the end of the parison. 

Figure 5.23 An injection-moulding machine with hydraulic mould closing, showing the cycle of operations.

CIRTM This process allows two or more resins to be simultaneously injected into the mould. Advantages include the ability to create multi-layer and multi-resin structures. CRTM Also known as injection compression moulding, the process involves a gap between the mould surface and the fibre perform (Figure 3.10). Resin is injected into the gap and the mould closed to compress the resin into the fibre preform. This reduces the injection pressure and fill time required in RTM. 

Unrolling and cutting plastic film to required length 2. Infrared (IR) heating of film on holding frame 3. Thermoforming the film in the mould cavity 4. The same process (1-3) is carried out in the other half of the mould at the same time 5. Robotised foam deposition in mould 6. Mould closed for expansion/polymerisation. Parts are removed... 

In extrusion-blow moulding (see Figure 7.44(A)), the extruder extrudes a parison into the open mould. (The extruder ceases to extrude whilst the test of the ( cle takes place.) The mould closes and the parison is inflated (B). When the parison has taken up the shape of the mould (C) the mould is cooled and finaUy the mould opens, and the bottle is removed (D). The extruder then extrudes another parison (A) and the < le is repeated. 

Although UPR show considerable utility in the composite industries, expansion into potentially high-volume applications has been restricted by a number of problems, including a poor surface appearance, fibre pattern showing at the surface, warpage of moulded parts, inability to mould close tolerances, and internal cracks and voids, particularly in thick sections such as reinforcing ribs and bosses [72]. 

Mould open with preform in place Mould closed with flash forced out... 

Mould sealing arrangements are more complex. Sealing must contain resin and maintain pressure levels within the mould, as the mould pieces move together during the secondary mould-closing phase. 

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