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vacuum impregnation - correction of defects in cast parts

impregnation process and its principle

Machined parts can have micro fissures or similar defects, which are causing cast part leak. It is necessary to fix these defects, in order to prevent the necessary scrap of cast parts, which are marked as rejects. The main aim of the impregnation process is to fill in porosity cavities, micro fissures and other defects and to secure required leak tightness of the cast part. Another advantage of this method is a prevention of corrosion of cast parts thanks to the sealing by an impregnation liquid. Other reason why use the impregnation is its ability to remove acid and alkaline salts in pores, which were removed during galvanic modification of parts. The impregnation can be performed on a majority of cast parts, but it is use mostly at cast parts manufactured by pressure or gravity die casting. 

Porosity

In spite of careful production techniques, castings made of iron, copper, aluminium and magnesium alloys often turn out to be porous and thus unsuitable for their intended use, e.g. as motor parts, oil pans, brake cylinders, pump casings, filter parts or valves. Furthermore, cast parts, which were originally pressure tight may start leaking. This is a typical after-effect of disruption of already existing pores. 

How does porosity appear?

Porosity appears mainly because of their contours, which solidify as the first part during the cooling stage after previous casting. When further cooling of the castings takes place, the metal shrinks and porosity can form inside the castings. In spite of advances in processing, porosity cannot always be avoided. Other factors like melting temperature, alloy composition and mould design additionally influence casting quality.

How can be pores impregnated?

Cast components with the wall thickness of 3-5 mm can have impregnated pores with the diameter of 0,2 mm. If the wall is thicker, it is possible to impregnate pores with the diameter of 0,5 mm. 
Double impregnation can seal even bigger deficiency. The smaller possibly impregnated pore in which the impregnation material is still polymerized is appx. 0,5 um. 

Our solution - Impregnation

Expensive porous work pieces do not need to be scrapped. The products are actually enhanced with our metal impregnation process. The impregnation costs are only a fraction of the part value. It would be costly and time consuming to replace these parts. The risk of replacement parts leaking is also avoided. Impregnation is 98 Shore A after solidification. 

Three forms of porosity in the casting

Impregnation process

The following schematic shows how the sealant fills the pores and thus warrants permanent sealing.