Injection moulding runner

Injection moulding and extrusion may be carried out at temperatures in the range of 300-380°C. The polymer has a high melt viscosity and melt fracture occurs at a lower shear rate (about 10 s ) than with low-density polyethylene (about 10 s ) or nylon 66 (about 10 s ). Extruders should thus be designed to operate at low shear rates whilst large runners and gates are employed in injection moulds. 

An injection moulding is in the form of a flat sheet 100 mm square and 4 nun thick. The melt temperature is 230°C, the mould temperature is 30°C and the plastic may be ejected from the mould at a centre-line temperature of %°C. If the runner design criterion is that it should be ejectable at the same instant as the moulding, eshmate the required runner diameter. The thermal diffusivity of the melt is 1 x 10 m /s. 

This process uses the plasticising and heat advantages of the injection unit to impart good flow properties to the rubber mix. It also offers the advantages of the flexibility of the transfer layout without the sprue and runners of the balanced runner system required by injection moulding. The space used by runners in other systems can be profitably used by more mould cavities. 

High heat bushings, valve seats, ball valve seats, contact seals, insulator bushings. .. Thermal isolators, high heat insulator bushings for hot runner plastic injection moulds... Guide rollers. .. 

As in Sect. 6.1, let us consider the injection moulding of a long thin plate through a slit runner, neglecting the resistance of the runner. Then Eqs. (4.12), (5.11), (5.12) for pressure distribution P(z, t), the motion of the averaged flow front h(t), and filling time will have the form ... 

Information gained by methods such as these is of value in establishing conditions both for injection moulding and extrusion. It can help in ensuring, as examples, that the diameter of a runner system or the size of a die is suitable for a good flow of material, satisfactory cycling, and obtaining the finish required. 

Injection Molten polymer flows into the injection cavity via the hot runner block, to produce the desired shape of the preform with a mandrel (the core pin) producing the inner diameter and the injection cavity the outer. After a set time the injection moulds and core pins part and the preform held in a neck carrier is rotated 90°. 

Injection moulding Mater-Bi can be injection moulded using normal injection presses, with cold runners or hot chamber injection systems. The maximum injection temperature is less than 200 °C. Novamont claims that about 10% of the scraps can be reused in injection moulding, which is about the same as traditional plastics. Mater-Bi can be coloured using the Mater-Bi-based, biodegradable masterbatches. 

Frenkel, D. Zawistowski, H., Hot Runners in Injection Moulds, Rapra, Shawbury, 2001. 

The Lost Foam process (Figure 2.36) starts with the 3D-CAD design and production of a precision moulded foam pattern, made from expanded polystyrene (EPS) or PMMA, produced by automated injection moulding machines. These patterns can be made from one piece or by assembling a number of parts by adhesives. Here usually, a number of patterns, dependent on size, are fixed to a runner-down gating system, made from the same material as the pattern, thereby generating a cluster. 

In injection moulding processors often use multi-cavity moulds to make several products in one cycle. The runners required to supply material to each cavity contain a considerable amount of material which, if the product itself is small, may be of the same mass as the parts themselves. This is evidently quite uneconomic. Hot rurmer systems solve this problem by keeping the material in the runners from solidifying between moulding cycles. 

In RIM, as in injection moulding, whether thermoplastic or thermoset, there is a transition zone between the nozzle (mix head) and the mould. In injection moulding, this transition zone includes the sprue/runner/gate system, and, in special cases, can also include a static mixer. The analogy to RIM is very apt. The transition zone for the RIM process also includes a sprue/runner/gate system, as well as an after mixer. One function of the RIM transition zone is to convert the mixing head liquid stream from a turbulent state to one which is in a laminar flow mode. If this does not occur, air traps (i.e. large subsurface voids in the finished part) can become a problem. 

Fig. 6.9. RIM runner design. (Courtesy of W. E. Becker (1979). Reaction Injection Moulding, Van Nostrand Reinhold, New York).

The process is injection moulding, using an eight-impression tool, with hot runners to minimize scrap. No reground material is permitted. 

The acetal spring is manufactured by injection moulding. A two-impression tool is used. Although hot runners are often used for acetal, the extra tooling cost is not warrented in this case, and the approximately 20% sprue scrap is re-used. 

For the injection moulding of the plastic parts, hot runners allow a waste free production. The plastic is injection moulded as in a conventional process. When sufficient solidification is reached, the mould opens, and an index plate (this is a rotating platen which takes the plastic parts from the first cavity and puts them into the liquid rubber cavity by rotating them through 180 degrees), robot, etc., extracts the plastic moulding and transfers it into the silicone cavity. 

In the meagre selection of works on the subject of the design of injection moulds, comparatively little space is devoted to hot runner systems. There is only one book exclusively addressing this subject, and that was published in 1960 [E. Moslo, Runnerless Moulding, Reinhold Publishing Corporation, I960]. 

---