In the casting process, liquid PVC plastisol is poured at room temperature into a suitably shaped, open mould. Unlike injection moulding, the material is not injected under high pressure into a closed mould cavity. Instead, the plastisol is poured into the mould and, following heat treatment in an oven, gels to form a solid, rubber-elastic PVC plastic part.
Depending on the type of Covytec® used, a plastisol with the appropriate formulation is processed. On the Overview page for Covytec® models You can view the available material types and download the relevant material data sheet directly.
When the filled mould is heated, the heat passes through the mould wall and the exposed surface of the casting compound into the PVC plastisol. The PVC particles absorb the liquid plasticiser and form a cohesive PVC structure.
As the temperature rises, this process continues until the plastisol has completely set in the mould. The required duration of the heat treatment depends on the temperature of the mould and, in particular, on the thickest part of the moulded component.
Following heat treatment and subsequent cooling, the mould is dismantled and the finished component is removed. Depending on the requirements, it can then undergo further processing.
The casting process allows for the production of comparatively thick walls and also significant variations in wall thickness within a single component. Heat can penetrate the material both via the mould wall and via the exposed surface of the casting compound. This means that even with greater wall thicknesses, sufficient heat treatment of the plastisol can be achieved without thinner areas being damaged by the necessary heat treatment.
The required duration of the heat treatment depends, in particular, on the thickest part of the component. This means that even components with significantly varying wall thicknesses can be produced in a single mould.
This distinctive feature makes the casting process particularly suitable for components that require large wall thicknesses or significant variations in wall thickness.
The casting process offers a wide range of design options, even for components with complex geometries. The open mould can be adapted to the desired contour, meaning that, in addition to simple shapes, contours featuring steps, recesses, curves and varying cross-sections can also be produced.
The possibilities offered by geometry are largely determined by the design and demouldability of the mould. Undercuts and other complex mould features can also be accommodated if the mould can be constructed in such a way that the finished component can subsequently be removed.
As the PVC plastisol is introduced into the open mould without pressure during the casting process, air bubbles may form against the mould wall during filling. They are not necessarily dislodged from the surface by the pressure-free filling process. This can affect the finish of the surface, particularly in undercuts and areas that are difficult to access.
The exposed surface of the casting may also exhibit a more irregular structure following heat treatment, due to air bubbles that have risen to the surface. These characteristics are inherent to the process and do not pose a problem for many technical applications, particularly where appearance is not a decisive factor.
Material shrinkage must also be taken into account when designing the moulding tool and determining the plastisol dosage. The quantity of material required for the finished component is therefore calculated with an appropriate allowance added.
Through subsequent machining, the dimensions and fits achievable during casting can be specifically adapted to the component’s requirements. It is also possible to refine the surface finish. Depending on the geometry and requirements, a belt grinding machine, for example, can be used for this purpose.
You now know how the PVC casting process works and for which specific component geometries it may be of interest. However, the key factor is whether the process is actually suitable for your particular component.
On our services page Castings Find out what solutions HAMCO can deliver using the casting process and how we assess the manufacturability of your component.
Large and small quantity requirements Direct processing
Large and small quantity requirements
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