Cast Metal & Diecasting Times July/ August 2016 July/August 2016 | Page 30

28 | IMPREGNATION

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The evolution of casting impregnation
Ultraseal International’s Stephen Hynes discusses the solution to porosity in cast metal parts.

Top loading impregnation equipment.

Porosity in cast metal parts is a problem
that diecasters the world over cannot readily
avoid; the microscopic holes that comprise
porosity form during the diecasting process
itself, making the phenomenon almost
impossible to eliminate.
Given that porosity can cause leak paths to
form in cast metal parts, it is a serious defect
for parts that have to remain pressure-tight in
operation. To counteract this problem, many
manufacturers rely on a post-casting process
that is a reliable and permanent solution to
porosity, called casting impregnation with
porosity sealants, sometimes referred to as
vacuum impregnation.
Essentially, the process involves
introducing a liquid sealant into the
microscopic holes, then curing it into
a solid, flexible plastic that seals the
porosity but does not affect the external
dimensions or appearance of the
component. It is a sub-surface process.
“Traditionally, casting impregnation was
commonly carried out off-line and then
only on parts that were deemed to have
failed a pressure test” explained Stephen
Hynes, Marketing Director of Ultraseal
International, a global leader in the design
and manufacture of casting impregnation
equipment and porosity sealants.
“Many manufacturers now insist on
casting impregnation being carried
out as a routine quality enhancement
because they do not want to face costly
compensation claims under extended
warranties if parts are sub-standard. “The
process has evolved over the years and has

recently been transformed into a highly
efficient, two-stage, fully automated
process that is cost-effective and easy
to integrate into a just-in-time (JIT)
production line.”
Casting impregnation evolution
For many years, top loading casting
impregnation equipment was the most
commonly used process technology.
From the early batch plants, top loading
technology has developed into a highly
efficient process and provides users with

great flexibility in terms of capacity and
the component mix. Ultraseal evolved top
loading technology with the introduction
of process enhancing features such as
rotational drain and cascade washing.
The top loading impregnation process
consists of three stages. Firstly, parts
would be placed in an autoclave and a
vacuum applied to remove air from any
porosity before the liquid sealant was
introduced. Secondly, any excess sealant
would be drained off and the parts
thoroughly washed in the cold wash stage.
Finally, they would be transferred to a
tank of hot water at around 95°C, where
the sealant would be ‘cured’ into a solid,
flexible plastic.
The introduction of recycling
impregnation sealants reduced the wastage
of chemicals. Up to 95% of the recycling
sealants can be recovered from the cold
wash stage and returned directly to the
autoclave for immediate re-use. Water
from the cold wash stage is also recycling
in this process. Recycling impregnation
technology has led to a more cost-effective
process and greater environmental benefits
Another step forward was the advent
of front loading machines. Although top
loading machines can be fully automated,
they usually require operators to manually
load and unload the baskets containing
parts and they often require a gantry
overhead. Top loaders are rarely fully
incorporated into production cells.
In contrast, front loading machines are
far easier to automate and can be readily
incorporated into a modern production
line. They are particularly suited to single
part processing of components such as
engine blocks.
When selecting casting impregnation

Ultraseal semi-automatic front loading machine.

C a s t M e t a l & D i e c a s t i n g Ti m e s J u l y / A u g u s t 2 0 1 6