Mould Needle

Malic acid crystallizes in colourless needles m.p. lOO C. It o- curs in many acid fruits, such as grapes, apples and gooseberries. It can be prepared by microbiological processes using various moulds or from ( + )-bromosuccinic acid by the action of NaOH. 

There are several types of nozzle. The simplest is an open nozzle as shown in Fig. 4.34(a). This is used whenever possible because pressure drops can be minimised and there are no hold up points where the melt can stagnate and decompose. However, if the melt viscosity is low then leakage will occur from this type of nozzle particularly if the barrel/nozzle assembly retracts from the mould each cycle. The solution is to use a shut-off nozzle of which there are many types. Fig. 4.34(b) shows a nozzle which is shut off by external means. Fig. 4.34(c) shows a nozzle with a spring loaded needle valve which opens when the melt pressure exceeds a certain value or alternatively when the nozzle is pressed up against the mould. Most of the shut-off nozzles have the disadvantage that they restrict the flow of the material and provide undersirable stagnation sites. For this reason they should not be used with heat sensitive materials such as PVC. 

A manufacturing method predominately used by the thermoplastic industry for the manufacture of hollow components, also used for thermosetting rubber. The polymer is forced against the inside of the mould surface by gas pressure applied either by a hollow needle or by the decomposition of a blowing agent. 

Casein was versatile in that it could take any colour, or could be moulded in a combination of colours, which made it a very attractive plastic. Its most common uses were as knitting needles and fountain pen barrels. The latter often displayed a pearly lustre. Casein is still in use today for button manufacture. It was also made into brightly coloured jewellery, such as linked bangles. It made a good imitation for ivory as it has a very similar fluorescence under ultraviolet light - the only plastic to display this. 

Figure 5.8 Scanning electron microscopy image showing needle fibre cement developed in a root mould, Campo de Tiro, Mallorca. Scale bar is 50 pm in length.

The method for the determination of the cone penetration of petrolatum (ASTM D937, IP 179) is used for soft wax and petrolatum. It is similar to the method for determining the needle penetration (ASTM D-1321) except that a much larger sample mould is used and a cone replaces the needle. The method requires that a 150-g load be applied for 5 s at the desired temperature. 

Prefdled syringes can also be made from tubular glass or by moulding in plastic (e.g. polypropylene). These units may consist of either a single or double (bi) compartmental type. The latter then involve three seals, as a seal must be achieved between the two compartments. Syringes are further complicated at the end seal by the presence of a fitment for a needle (e.g. Luer) or by having a needle already moulded or fitted. These protrusions may then demand a further cover or seal, e.g. to protect the needle and prevent microbial contamination. 

The ultimate microstructure of a solid will depend on how quickly different crystal faces develop. This controls the overall shape of the crystallites, which may be needle-like, blocky or one of many other shapes. The shapes will also be subject to the constraint of other nearby crystals. The product will be a solid consisting of a set of interlocking grains. The size distribution of the crystallites will reflect the rate of cooling of the solid. Liquid in contact with the cold outer wall of a mould may cool quickly and give rise to many small crystals. Liquid within the centre of the sample may crystallise slowly and produce large crystals. Finally, it is important to mention that the microstructure will depend sensitively on impurities present. This aspect is discussed in Chapters 4 and 8. 

Overlay with 25-30 pL of gelling collagen (Note 13) prepared in the same way as the bottom cushion, position explants using an electtophoretically sharpened tungsten needle (Note 14) (with blunted tip), and allow to set for 30-60 min at room temperature (see Fig. 1). Cover collagen moulds with approximately 0.4-0.5 mL medium (Note 15), and transfer to incubator for the desired time of incubation (Note 16). 

The gauged cement is put into a split brass cylinder 30 mm i.d., to which are attached two needles 156 mm long from the centre-line of the mould, one needle on each side of the split in the mould. 

The cement is allowed to set for 24 h immersed in water at 15-18 C the distance between the ends of the needles is then measured. The mould is immersed in water and boiled for 1 h. When it has cooled, the distance between the ends of the needles is again measured. The difference between the first and second readings should not exceed 10 mm. The test is included in B.S. 12. 

State-of-the-art technology allows the manufacture of such composites in 32 cavity moulds with modern cold runner technology using needle shut off valves. 

From experimental beginnings, radiation therapy soon developed into a separate branch of medicine, with its own specialists, practices, and standards. X-rays had to be applied from an external machine, but radium could be introduced right into the patient. This approach, known as brachytherapy, was pioneered early in the century. The radium was put in gold needles that were inserted into cancerous tissue, in tubes that were placed in body cavities, or in moulds applied to the outside of the body. During tumour surgery, doctors permanently implanted gold capsules, or seeds, filled with short-lived radon to help kill residual cancerous cells. 

It was this commercial market that made the filling operation at Port Hope necessary. To serve private-sector customers, Eldorado had to offer them radium in a form that they could use. The filling lab prepared radium for its primary medical market by packing it in needles, moulds, or tubes in precise quantities. Gradually Errington developed an extensive line of other radium products to serve a wide variety of customer needs. One example was radium-beryllium sources for well-lo ng in the oil business. Companies servicing the mining sector used this technique to determine if there were oil reserves in the vicinity of a dry drill hole. Radium combined with beryllium in the proper ratio produces millions of neutrons a second. This neutron source could be lowered down... 

Tenowo s needle-punched materials provide enhanced elongation values during moulding processes, although their surface abrasion resistance is lower than chemically bonded products but can be improved by chemical treatments. Repellency, adhesive coatings, and flame retardant (FR) treatments are standard to meet OEM specifications and standard weights range from 50 to 250 gsm. 

Thermoplastic resins are generally reinforced with short fibres (for use with injection moulding and not considered in this book), with long fibres (thermoplastic sheet compound, Chapter 5) or with glass mat (i.e. glass mat thermoplastics or GMT). Polypropylene is the resin most used as the matrix for GMT and the reinforcement is usually a random mat, primarily chopped strand but it may be continuous filament or needled mat. 

Cold runner systems that are ready to use are offered as standard in the marketplace. These fimction especially well with needle sealing nozzles that are controlled hydraulically or pneumatically. In order to allow integration with the process sequence of the injection moulding machine, interfaces were developed for control of this type of cold runner. The machine control unit also monitors the position of the needles. 

The simple cold runner nozzle with hydraulic needle sealing system, as shown in Figure 7.11 makes possible either direct or indirect injection of silicone parts. Advantages in the application of this system are good thermal separation between the cold nozzle and the heated mould and the flat gate location on the moulded part. 

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