When and Why Vacuum Impregnation of Casting is Needed?

Vacuum impregnation, porosity sealing, or metal impregnation technique is used to seal pores in different components such as casting metal or graphite parts. It is an effective way to deal with the porosity to reduce waste during production.

There are several reasons why casting parts need vacuum impregnation, for example:

• Vacuum impregnation is necessary to seal pores in a component so that the fluids inside don’t leak.
• Pores can cause cracks on the parts and porosity sealing can fix this problem.
• By using this method, manufacturers can fix ruined parts to save production time and cost.
• Metal impregnation is necessary in order to avoid faster degradation of metal components.

When Vacuum Impregnation of Casting Is Performed?

The right time to perform vacuum impregnation on a casting part is after machining the part. To understand why you have to know some facts.

First of all, casting parts have three types of porosities such as blind porosity, through porosity, and fully enclosed porosity. Secondly, when a series of different types of porosities connect together they create a leak path.

The leak paths created by blind and through porosities are fixable with vacuum impregnation before machining. But fully enclosed porosity has no connection to the leak path. So the sealant of vacuum impregnation cannot reach it. Therefore, it is not fixable before machining.

But after the machining of a part, sometimes a fully enclosed pore can open up and make a leak path. So then it becomes fixable with the metal impregnation technique. For this reason, it is better to perform vacuum impregnation on a casting part after machining or surface finishing so that all pores can be sealed at once.

What Type of Parts Are Suitable for Vacuum Impregnation?

A variety of casting metal parts are suitable for vacuum impregnation, for example:

• Die casting parts such as aluminum die cast impregnation or other metal impregnation parts.
• Permanent or semi-permanent mold casting parts such as lever handles, valves, nozzles, etc.
• Lost-foam and sand-casting parts such as metal pipe joints and pumps.
• Powdered metal parts such as con rods and different types of gears.
• Over-molded electronics, graphite, composite materials, 3D printed parts, etc.

What Are the Types of Sealants for Vacuum Impregnation?

The available sealants for vacuum impregnation are of 3 types such as anaerobic, thermosetting recoverable, and thermosetting recyclable sealant.

Anaerobic Sealant

Manufacturers use this sealant to mostly repair over-molded cable and powdered-metal components. A catalytic reaction occurs between the sealant and the metal ion while impregnation occurs.

This type of sealant is recoverable with the help of a centrifuge. It takes about 48 hours of curing for this sealant in order to seal the pores in a metal part.

Thermosetting Recoverable Sealant

Die-cast manufacturers use this sealant on different types of metal casting parts. It is also suitable for graphite parts and cables. However, heat makes this sealant react with the metal parts’ pores and fill them. Manufacturers can recover this sealant after use from the aluminum die cast impregnation chamber.

Thermosetting Recyclable Sealant

Unlike the thermosetting recoverable sealant, manufacturers cannot reuse the thermosetting recyclable sealant for vacuum impregnation after the first time. However, they can recycle this sealant and use it for other purposes. This type of sealant is also suitable for casting metal parts.

What Are the Common Misconceptions Regarding Vacuum Impregnation?

Many people have some common misconceptions regarding vacuum impregnation. These are:

The Dimensions of the Part Changes After Vacuum Impregnation

Vacuum impregnation simply fixes the porosity defects in a part. It doesn’t change the dimension of the part at all. In fact, you don’t need to have any dimensional allowance for the part to go through the vacuum impregnation process.

Vacuum Impregnation Plugs the Pores

Vacuum Impregnation “doesn’t plug the pores”. If it did, then empty spaces be left within the internal structure of the metal. It will spread throughout the leak path and seal it from within.

Vacuum Impregnation Is a Type of Coating

This is one of the most common misconceptions that people have about vacuum impregnation. Though you immerse a part is in the sealant, that doesn’t mean that the sealant coats the part.

After rinsing, the surface of the part will be free of the sealant. So, it is illogical to think that vacuum impregnation is a type of coating.