Mould acceptance

From the purchaser s point of view, checking of the mould carried out on his own injection moulding machine is best. If mould inspection takes place at the manufacturers, however, a few basic principles which are of particular importance for HR moulds need to be applied to avoid problems later on  

When inspecting a mould, a check should be made that the plugs and sockets match the connections present in the heat-regulation cabinets, and whether they have the right number of control modules. 

When used moulds are undergoing trials, it is necessary to make a more thorough analysis of the HR system, especially as the relevant documentation rarely still exists. 

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In all cases a mould accepted for storage must be one in working condition that is ready for use at any time. 

The largest outlet for polystyrene is in packaging applications. Specific uses include bottle caps, small jars and other injection moulded containers, blown containers (a somewhat recent development but which has found rapid acceptance for talcum powder), vacuum formed toughened polystyrene as liners for boxed goods and oriented polystyrene film for foodstuffs such as creamed... 

Sterilisable mouldings have found application in medicine and pharmacy. Because of their durability, nylon hair combs have found wide acceptance in spite of their higher cost. 

Whilst the injection moulding process has now been widely accepted for phenolics the transition from compression moulding has been less extensive with U-F materials. The basic reason for this is that the U-F materials are more difficult to mould. This has been associated with filler orientation during moulding, which can lead to stress peaks in the finished product which the somewhat brittle resin in less able to withstand than can a phenolic resin. 

Fortunately the situation in practice is not quite as complex as it might seem. In general, very acceptable designs are achieved by using impact data obtained under conditions which relate as closely as possible to the service conditions. Impact strength values available in the literature may be used for the initial selection of a material on the basis of a desired level of toughness. Then, wherever possible this should be backed up by tests on the plastic article, or a specimen cut from it, to ensure that the material, as moulded, is in a satisfactory state to perform its function. 

Autoclaves can be specifically designed to accept moulds for tyre retreading. 

The analysis shows that the minimal filling time at maximal temperature of a hot mould Tm is attained at maximal acceptable injection pressure P0. Since the value of Tw is also limited by safety considerations (thermal decomposition), the optimal value of injection pressure must be chosen on the basis of this limitation on the value of T. ... 

Notwithstanding this fact, high pressures are required to transport the fluid mass through the transport channels or into the mould of a processing machine with an acceptable speed. Pressure levels of 50 to 150 MPa (500 to 1500 bar) are normal, so that the machines have to be very robust. 

This process offers a route for the manufacture of complex shapes and, in the traditional pottery industry, is the accepted method for the production of teapots, milk jugs, figurines and large articles such as wash-hand basins. It may be necessary for the mould to be made up of a number of pieces so that the cast article can be removed. 

To improve the notched impact strength and to prevent hydrolysis induced embrittlement of PBT, PBT-styrenic blends have been thoroughly investigated. In comparison with ASA-PC, blends of ASA and PBT generally have to be compa-tibilized in order to yield acceptable mechanical properties. In the case of glass fibre reinforced PBT-ASA blends, an added and important bonus is reduced warpage properties on injection moulding in comparison with reinforced PBT. 

In blends of polyamide with styrenics, compatibilization of the phases is generally a prerequisite for acceptable mechanical properties. This can be accomplished by having reactive groups in the PSAN phase that react with the amino groups of the polyamide phase. Blending is used to improve the main weaknesses of the polyamide, namely moisture sensitivity, toughness and warp-age on injection moulding. 

Considerable work went into modification of the strain (through the use of X-rays or UV light to induce mutations) and improvements were made in the technology of isolation and purification. However, the mould was much more difficult to handle and would not accept alternative side-chain precursors as did Penicillium chrysogenum hence, it was impossible to prepare semi-synthetic cephalosporins by this route. In addition, the discovery of methicillin with its resistance to penicillinases negated the advantages of cephalosporin C, and for a while it appeared that this new class of antibiotics was doomed. 

Once all departmental activities are satisfied, with redesign and resamples if necessary, metal should be cut for the full production tool, but on the understanding that further purchaser evaluations must be completed before tool acceptance (or, for example, before a mould is finally plated or hardened). 

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