Casting plasters

from Wikipedia, the free encyclopedia

In the foundry, the reworking of the castings is referred to as casting cleaning or cleaning for short, i.e. all work on the workpiece that takes place after solidification and before the products are shipped . This includes, in particular, demolding , separating gates and risers , desanding (for molds made from sand), deburring and heat treatment . A distinction is made between rough plastering, which is always carried out by the foundry, and fine plastering,which can also include various further work steps and is agreed between the foundry and the customer. The cleaning work accounts for a large part of the total costs in the foundry, since it can only be partially automated . A plaster-friendly construction of the casting is therefore decisive for the unit costs .


Removing the castings from the molds is called demolding. Some castings cool in the tin at room temperature, which manual unmolding easier, others will be removed from the mold shortly after solidification, which saves time and especially in casting molds is applied (continuous forms) to the shape as possible to drain back. In the case of permanent molds, drafts, ejectors, strippers, slides and inclined ejectors are installed in the molds to remove the cast parts. If sand forms are lost , they are destroyed by shaking or hitting them. The sand, or more generally the molding material , can then be processed and processed into new shapes.

Desanding and coring

In the case of sand molds or cores made of sand, the next step is desanding. Coarser deposits of sand are removed manually by hitting or using pneumatic hammers . The cutting of the gate and the riser can be done at the same time. Automated sanding devices are separating channels , cleaning drums and vibrating grates . The cast parts are also cooled and partially separated from the gate and the feeders. Cleaning drums work in a similar way to systems for drum grinding . There are also special machines for coring that work with impact.

Sandblasting is mostly used for finer layers of sand and also to remove scale . Various metallic and non-metallic substances are used as blasting media; Quartz sand has been banned in Germany since 1973 because of the risk of silicosis (" dust lung "). Instead used hard cast gravel, corundum , cast steel and stainless steel blasting agent.

Separation of gate and riser

The gate is used to feed the melt during the casting process ( casting ). Feeders are used to compensate for the loss in volume caused by the (liquid) shrinkage that the melt passes through from the end of the mold filling until it reaches the melting point. Both are not part of the actual casting and are therefore separated and re-melted as cycle material.

Numerous different processes are used:

Procedure Separable material Maximum separable cross section [cm²]
Knock off with a hand hammer
  • 45
  • 116
  • 70
  • 50
  • 86
  • -
Teeing off with a teeing device
  • 625
  • 4.2
  • -
  • -
  • -
  • -
Knocking off with explosives copper 2000
Cryogenic knocking down (cooling down and knocking off) Cast steel 6.5

Repairing casting defects

Casting defects often occur during casting . If these can be repaired and the costs for doing so are lower than remelting and pouring, this is also done when cleaning. Different manufacturing processes are used depending on the casting defect and material . Soldering , welding , filling , metal spraying and impregnation are of particular importance .