Design concept

Structure of the basic geometry

The mould is made from wood, steel, aluminum, PVC, silicone, polyamide or a combination of these materials. The main criteria for the selection of the suitable form material are:

•  the estimated number of castings to be produced by a mould,
• the required accuracy and surface quality of the mineral casting components,
• size, weight,
• planned variants in the casting,
• costs and time

The design of the mould, the calculation of the mould and the construction of the mould all run parallel to the construction of the part. The design criteria of the mould must be considered in order to ensure the geometrical accuracy and high static and dynamic rigidity:

• The design of the main functional surfaces the mold are critical , in order to ensure the accuracy.
• Moulds are mostly made from plates. Basic geometry is design from simple elements.

Integration of mechanical components

Threaded inserts, steel plates, transportation anchors, cables and trunking, s and hollow cells can be cast directly in the mineral casting component as it is a cold casting process.

In order to ensure that it is in optimal working order later on, all mechanical components must be fastened securely as their position can no longer be corrected later on and substantial lift forces develop during the casting procedure, which could change the position if the fastening is not secure enough. It must be ensured when the component is being sesigned and more importantly later with the construction of the mould, that this insert does not obstruct the flow of material or the venting of the mold.

If the threaded holes are too close to the edge or if the mineral casting component has hole pattern with mating holes, special cast parts are moulded in. These special cast parts (mouldings, plates) are anchored to the mineral casting component with hexagonal screws.

Operational surfaces

As described in the chapter on accuracy, a maximum accuracy of approximately +/- 0.1 mm/m can be attained with good moulds. Many components however, have a mating surface for other parts, which clearly require a greater accuracy, for example for the attachment of linear guide systems, sliding or mounting surfaces. It is therefore imperative to integrate these functional surfaces in order to attain the specified tolerances. Today SCHNEEBERGER essentially uses four procedures as below, in order to create the necessary surfaces:

• Machining of mineral casting - with this procedure the mineral casting is poured with an excess and afterwards machined to the exact size by milling or grinding.
• Machining of cast parts - with this procedure, metal parts, such as steel or cast iron plates, are cast into the mineral casting and machined after the casting has hardened.
• Replication - with this procedure the mineral casting is poured approximate 2 mm undersize. After removing the mould there is a second casting stage where very fine material is cast with a precise setting jig.
• Subsequent casting in of metal parts - With this procedure high-precision cast parts are precisely cast in after removal of the mould using positioning gauges.

Transport and set-up

Transport

The mineral casting components must be securely fixed during transport. A crane, fork-lift truck and truck are used for transport. In addition suitable anchors and rails are to be provided.

Set-up

In principle similar rules for bases made from steel or gray cast iron also apply to the set-up of mineral casting racks. Special foundations are very important particularly with large machines because, in their typical suitable construction as an engine foundation with 70-90% of the total mass of a machine, they guarantee a high overall torsional stiffness with the high inertial mass and they can attain the necessary accuracy thanks to the smooth running of the machine.

A correspondingly substantial dimensioning of the machine foundation is of great importance particularly with extremely heavy component parts and/or a correspondingly large workforce or with sudden impact loads, because otherwise it results inevitably in the partial sinking of the machine and so the geometrical accuracies typical of today are no longer attained over the entire working space. Machines with a three-point set-up are an exception to this rule, because their accuracy does not depend on the foundation.