Impregnation Services Ltd

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Please browse our most frequently asked questions below. If you can’t find what you are looking for we’d love to hear from you. Please call us on 0161 344 1004.

What do I need to do before sending my castings to you?

Please ensure that items are clean and free from debris.

The cleaner the item is the better and more likely it is for the process to be successful. If pores are clear of dirt, oil, swarf etc the resin is able to fill and cure in the leak path, thus enabling the process to succeed.

Dirty castings are more likely to hold excess sealant on the surface and in holes and this in turn may go on to affect the next stage of the casting’s process

It is always advisable to remove anything that you don’t want to remain in place permanently as it may be difficult to remove after impregnation.

What size of porosity can you seal?

This is a very common and a very difficult question to answer.  No one area of porosity is the same as another, some will be easier for the resin to remain in place and some just won’t hold the resin in place.  It is not something that can be assessed just by looking at a casting, the only way of being sure of success is by carrying out vacuum impregnation on the item.

Vacuum impregnation is at its’ best with micro-porosity where the low viscosity resin is enclosed within the leak path of the pore, thus it doesn’t run straight out when the surface is washed prior to curing.   Visible open pores are more difficult to seal as the resin is not able to adhere to the open inclusion.

We often process castings twice (double impregnation) as the resin can build upon itself.   On some occasions we process more than this, building upon the base layer of resin.

What is the process?

Here is a brief summary of the vacuum pressure impregnation process:

Castings arrive and are dehydrated at 150°C for an hour to burn off any excess water or oils that may remain in the pores.  Items are left to cool to air temperature.

Parts are loaded into a process basket and placed into the vacuum chamber; vacuum is applied ensuring air is removed from the pores.  Once the required level of vacuum has been reached the low viscosity methacrylate resin is introduced into the chamber and vacuum is released, the resin is then pulled into the pores of the casting.   A small amount of pressure is then applied within the chamber pushing the resin further into the pores for greater penetration.

The process basket is removed from the chamber and excess resin is drained (and spun in most instances) from the castings.   The basket is then placed in the wash tank and agitated to wash the resin off the surface and threads of the castings

The final stage of the process is to place the basket into a hot bath at around xx°C initiating the  thermosetting methacrylate resin to cure within the pores.

Take a look at our VIDEO here for a simple explanation.

What size of casting can you process?

From 1g up to 2 tonnes, castings with a diameter of xxx will fit in our standard process line and oversize castings may be suitable for internal pressure impregnation (utilising client specific plates).  If you are unsure if we can process your item, please call us.

In some instances, we are able to impregnate at a customer’s premises, please call us if you would like to discuss this further.

What type of metal can be Impregnated?

Any porous material; e.g., ferrous/non-ferrous metals, ceramic, 3d printed, etc.

Can you guarantee that you will seal my casting?

This is not a process that anyone can guarantee, as you can imagine no one area of porosity is ever the same as another in terms of size, shape, complexity of the porosity, etc.  They only way to find out if it will work is to vacuum impregnate it.

What operating temperature can the sealed casting be used in?

Day to day working temperature -50°C to +200°C and flash temperatures of +250°C.

Can you seal cracks?

Porosity is fixed once the casting has solidified and therefore does not expand and contract in day to day use, therefore the resin is held in place by the pores, whereas a crack may open up during operation causing the resin to be dislodged from the crack, preventing sealing.

Please ensure that cracks are welded prior to sending to us, it is common the impregnate welded castings as they are allied processes.

Is it a surface coating?

No vacuum impregnation is a subsurface treatment so it is sealed within the casting and nothing is left on the surface.

Can it improve the surface pores / aesthetics of the casting?

The sealant is very low viscosity and is drawn within the subsurface porosity of the casting, if the casting has open pores on the surface the resin will not be able to adhere to the inclusion and you will therefore not see any visual change to the surface of the casting.

Does the process change the casting?

As the process takes effect within the subsurface of the casting it does not make any dimensional or structural change to the casting.

At what stage should vacuum impregnation be carried out to obtain best results - pre or post machining / before or after finishing?

This really is a client’s preference.

We would advise that to get the best result vacuum impregnation should be carried out post machining as the machining process can expose blind porosity that was previously covered by metal.  However, some castings are highly machined and have a very delicate surface that a customer may prefer to impregnate prior to machining and take the risk that the porosity may be exposed.

We would also advise vacuum impregnation before surface coatings.  The process can help to prevent gas off / bleed out from the pores that can occur in some surface treatments as the air in the pores has been replaced with resin.  If processing takes place after paint in some cases it can react with the paint/degrade the finish or items may get knocked during processing and damage the finished surface.

Do you pressure test castings prior to despatch?

As we are a job shop dealing with hundreds of different types of castings with different testing requirements it is not possible for us to test prior to despatch.

We are able to provide a pressure test service if this is something you require and you can either send us the test plates and drawings or just the drawings and we can organise test plates – just ask us for the costings for this additional service.

What is the material that is used to impregnate castings?

We use a thermal curing methacrylate resin.

Once the resin is within the pores and the item is introduced into the hot bath of between 75-99°C the catalyst within the resin is activated starting the process of a temperature-induced chemical change within the material.   Once activate the resin will solidify within the casting sealing the pores.