Mold-Rubber System

2 Effect of the Position of the Heating System 4.1.2.1 Mold-Rubber System 

Comparison between these two heating systems is thus possible. 

At the same time, the effect of the thickness of the rubber sheet is considered, whereas the thickness of the slabs of the mold is kept constant. 

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The scheme of the mold-rubber system is described in Figure 4.1. The mid-plane of the rubber sheet is a plane of synunetry. Two systems of heating are considered for the mold in order to maintain the temperature of the mold at a constant the one where the heating system is on the external surface of the mold in contact with the surrounding, and the other where this heating system is on the surface in contact with the rubber. 

FIGURE 4.1 Scheme of the mold-rubber system, the mid-plane of the rubber being a plane of symmetry for the system (vertical dotted line). 

The results are expressed in terms of profiles of temperature developed through the thickness of the mold-rubber system, and of profiles of the state of cure, obtained at various times. The thickness of the rubber sheet is varied within the 1-4 cm range, whereas the thickness of each slab of the mold is 1 cm. The initial temperature is 20°C for the rubber and 180°C for the slabs of the mold. The system of heating is different for the mold on the one hand, it is on the external surface in contact with the surroundings (Figures 4.2-4.4), and on the other hand, it is on the surface in contact with the rubber (Figures 4.5-4.7). 

For most rubber systems the network is formed after the polymer is compounded and molded into the desired final shape. Once cross-linked, the material no longer can be processed. If cross-linking occurs prior to compounding or molding, the material is referred to as gelled, and it cannot be used. Most rubber is used in a compounded and cured form. There is an optimum cross-link density for many failure properties such as tensile strength and tear which will be discussed in the next section. 

Low modulus elastomers are materials that have found wide use in the automobile industry for fascia, bumper covers, and trim parts. Other applications include integral window seals and a wide variety of applications where it is replacing molded rubber. Most of these materials are not pure polyurethane, but polyurethane/polyurea hybrids with improved processing and properties when compared with the earlier allurethane systems. 

Mono-Coat . [Chem-Trend Chem-Trend A/S] Solvent-based mold release system for use on laminates, composite molding, rubber molding, mold conditioning. 

FIGURE 4.3 Profiles of temperature either in the mold (extreme right) or in the rubber (right) and of state of cure (left) with a thickness of the rubber of 2 cm with the thickness of 1 cm for each slab of the mold, whereas the initial temperature is 20°C for the rubber and 180°C for the mold. Heating system on the external surface of each slab. Thermal and kinetic parameters in Table 4.1 with enthalpy of 14.3 J/g. Because of the symmetry, only half the thickness of the rubber-mold is shown, with the plane of syrtunetry at position 0. 

The effect of the kinetic parameters on the cure is evaluated in this subsection by using the values collected in Table 4.1, which are the basis values around which they are varied. The mold-rubber is considered with the heating system placed on the mold surface in contact with the rubber sheet. The results are expressed in terms of temperature-time histories and of state of cure-time histories calculated either at the rubber surface or at the mid-plane of this rubber sheet. The rubber thickness is 2 cm, and the mold temperature is 170°C. The cure enthalpy is 14.3 J/g associated with sulfur at 2%. 

Uses Slip agent for polyethylene films lubricant and mold release for inj. molding applies., processing thermoplastic resins, thermoplastic elastomers, and thermoset rubber systems dispersant food-pkg. adhesives, coatings, paper, polymers, films... 

The rubber compound is fed into the machine and the screw loads a known volume of rubber into the cylinder. When the cylinder is completely filled, the screw then acts as a ram to force the rubber compound into the runner system and the mold. 

In certain processes (such as rubber tire manufacture and plastic injection molding operations), it is common for a valve sequencing system to first provide hot steam followed by cold cooling water and thus for cross-contamination to occur. The result may be the stripping of passivated cooling system surfaces by steam and for the condensate to be infiltrated by cooling water. 

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