Demoulding temperature

It can now be seen why semi-plasticized (12i%) PVC is a suitable choice for the bristle holder. At its demould temperature it is in its rubbery state, above Tg, and can be easily deformed to accommodate the other parts. It is an elastomer and will thus recover its shape after the deformation. When cool, it is below its Tg, and hence has the rigid properties of a glassy material. 

Cure Heat-up (maximum heat-up rate) dwell (time, pressure, temperature) cure (minimum time, pressure, temperature) cool-down (max. cool down rate) tolerances maximum demoulding temperature... 

The demoulding temperature requirements of various materials are given in Table 4.1. 

Table 4.1 Recommended values for the demoulding temperature of different plastics ...

Thermosets unlike thermoplastics require heating in the mould and not cooling. The demoulding temperature is therefore the temperature the mould is set at for crosslinking. More details on controlling the cooling or heating systems can be found in Chapter 8. 

An accelerator which permits processing of rubber compounds to be carried out with less risk of scorching but which does not slow down the rate of cure at normal vulcanisation temperatures. Demoulding... 

Nucleating agents in PET also allow faster demoulding times, that is, the injection moulded part can be ejected from the mould more quickly or at a higher temperature. 

Massive chocolate products are deposited at 30-31°C into pre-heated (30-32°C) metal or plastic moulds. The moulds are then conveyed through a cooling tunnel where the temperature of the product is reduced to 8-9°C. The volume of the cocoa butter and chocolate shrinks during cooling and a contraction takes place which eases demoulding. 

The resistance of the concrete against chloride penetration was mainly tested by use of the Rapid Chloride Migration (RCM) method [6] and electrical resistivity measurements based on the two-electrode method [7], The testing was carried out on 50 mm cut slices from 0100 x 200 mm concrete cylinders, and the concrete samples were mainly cured in water with a temperature of 20 2 C and tested at regular intervals of up to 90 days. In addition, some samples from two of the concrete mixtures (PO O and Pl. O) were wrapped in plastic sheeting after demoulding and stored in air with a temperature of 20 2°C until time of testing. 

All foams to be tested in each catalyst set were mechanically crushed 1 minute after demoulding using a Black Brothers Roller crusher set to a gap of 2.54 cm. Crushing was carried out three times on each part, rotating the foam 90 degrees after each pass through the roller. All parts produced for physical testing were allowed to condition for at least seven days in a constant temperature and humidity room (23 2 °C, 50 2% relative humidity). 

After mixing, the material is poured into closed moulds at a controlled temperature. The expansion is complete in about 20 s and the product can be demoulded in about 5 min. The skin thickness is controlled by variation in mould temperature which is generally below the temperature of the material. 

Demoulding Especially for large components, demoulding necessitates well-designed tools. The adhesion between the cured part and the mould surface can be considerable. Therefore, moulding must always take place at sufficiently low temperature, when the material has reached its final strength and stiffness (so usually at least below its Tg). 

At the time of the release of the component from the mould, adhesion is at its weakest level. Therefore, in the case of self-adhesive or primer technology, it is essential to demould cautiously as, once silicone and substrate are separated, no adhesion will form again. In the case of self-adhesive LR, upon cooling and after sufficient storage and/or further heat treatment, adhesion will develop to its utmost extent. This will be explained further in Section 11.11.1. It is essential that the plastic material used for the moulding of the hard substrate solidifies quickly at a high mould temperature. 

The FRE test specimens were hardened at room temperature (22 C) for 24 hours before demoulding. 

Typical hot ruimer systems for a thermoplastic have a heated manifold. A hot mnner system will have a temperature which is in the range of melt temperature of the thermoplastic and therefore significantly higher than the standard rurmer system. This ensures that the material does not freeze off prematurely in the ranner. Less raw material is required because the runner content does not need to be demoulded and is available for the next shot. 

Mould temperatmes 40-100 °C Upper range temperatures improve the flow behaviour of the mass and reduce the formation of internal stresses. Higher temperatures can make demoulding more difficult. 

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