Demoulding

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... 

To decrease demoulding time (i.e. decrease cycle time for the part). 

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. 

Inserts can be incorporated into the mould before injection or placed after demoulding into a moulded hole. For neat resins, the first solution is generally avoided because of the big difference between the coefficients of thermal expansion of metals and plastics. In both cases, inserts and embossing must obey some general rules. Among these, some, but not all, are recalled below ... 

When the thermoplastic is softened and shaped, the mould is cooled to solidify the material and allow demoulding. 

This process is only used for special cases because of the long time needed to heat and then cool the thermoplastic parts before demoulding. 

The contact with the hot mould plasticizes the material, which, by the pressure applied, takes the form of the cavity. The cooling of the mould leads to part solidification and lows demoulding. 

A solution of the polymer is sprayed onto a former that has roughly the shape of the article to be moulded. After drying the polymer is demoulded. 

Under pressure in a closed mould during gelation. After cooling and demoulding, the expanded parts are re-heated (post-expansion) to obtain closed-cell foams such as life jackets. 

Design parts to ease demoulding by including sufficient draft if the material does not support stretching. 

Draw sufficient draft angles to be able to demould. 

In-mould decoration (IMD) with films reduces finishing operations. If the process and its operating conditions are suitable, the demoulded parts are finished. 

This method is normally followed for plastic products. However the same with modifications of equipment is adopted for manufacture of small rubber components. By careful control of the feed stock the rubber products can be vulcanized in less than several minutes. This method can be completely controlled by proper feed, injection and demoulding cycles resulting in low rejection rates and lower finishing costs. 

The key practical problems for the chocolate maker and for the process engineer are that the thermodynamically stable form (Form VI) is not the one that the consumer finds attractive, and that the lower forms will not effectively demould, causing problems in manufacture. Making commercial chocolate thus involves ensuring that the final product is in form V, the right form to be sold and eaten. Figure 22.1 shows... 

As noted above solidification is critical in manufacture as it determines whether the chocolate will demould successfully. During solidification, the material changes shape. It is not possible to follow the shape of the surface of chocolate using conventional tribological techniques, which involve physical contact between the surface and a stylus of some sort. One technique which can be used to follow the surface morphology of chocolate is to use an infrared laser to measure the sample height. 

A. Carnot, I. Frateur, S. Zanna, B. Tribollet, I. Dubois-Brugger, and P. Marcus, "Corrosion Mechanisms of Steel Concrete Moulds in Contact with a Demoulding Agent Studied by EIS and XPS," Corrosion Science, 45 (2003) 2513-2524. 

Moulding is similar to that for the fondants, i. e. the mixture is deposited into starch moulds. The deposited jelly or gum achieves its final consistency and water content within 4-24 hours. When modified starch is used as the gelling agent, the products are set 24-48 hours in the so-called drying chamber at 30-50°C before demoulding. 

The demoulded products need protective coating which can be made of sugar, oil or wax and also chocolate. 

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. 

Accelerators are used primarily to increase the rate of early strength gain and allow earlier demoulding. 

By using superplasticizers to reduce water content and lower the water/cement ratio, it is possible to increase early strength and allow earlier demoulding. 

At the end of each experiment, the material was demoulded from the apparatus and cut into a number of slices to evaluate the removal/accumulation of species as... 

Furthermore, the high pressure makes the cast pieces very dry and so demoulding can be done immediately and a new casting cycle started... 

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