What is Impregnation?

 

Sealant impregnation fills the voids and microporosity in a wide variety of materials. A micropore is a tiny defect in the component, which has the potential to turn into a large and expensive problem. By cleaning and then sealing the surface of the component in a vacuum, these small defects can be filled, prolonging the lifespan of the treated piece.

 

There are many reasons to use surface impregnation:

 

  • To prevent leaks
  • To reduce moisture entrapment
  • To improve integrity of welds on cast iron and aluminium substrates
  • To reclaim expensive castings and fabrications that would fail due to leakage
  • To prevent "blow-out" of entrapped gases during plating or painting processes

 

What is the process?

During the impregnation process, components are packed carefully into designated baskets. The baskets are then lowered into a vacuum chamber containing Ultraseal resin sealant. The chamber has its pressure lowered to a vacuum greater than 10 mbar. This draws air out of any porosity that has a leak path to the surface of the component. After a suitable vacuum is achieved and held for a specified time, the air is allowed back into the chamber forcing resin sealant into the previously evacuated pores. The components are drained thoroughly and then excess sealant on the external surfaces and in holes is washed off with cold water. The basket is then immersed in hot water to cure the sealant and prevent porosity.

 

The impregnation process involves five key stages:

 

  • Part preparation
  • Impregnation
  • Drain
  • Cold wash
  • Hot cure

 

Part Preparation

Before impregnation, porosity within the component must be completely clean and dry. While this is achievable through a separate pre-process, Ultraseal offers modules for aqueous washing and vacuum drying that can be integrated into the system.

 

Impregnation Equipment

Ultraseal International offers two types of autoclave with top-load equipment:  

 

Vertical Transfer System (VTS)

Here, the workload is suspended in a basket during the vacuum phase before being lowered and immersed in the sealant. The vacuum is then released, forcing the sealant deep into the porosity. VTS-based impregnation machines are simple in design and have a relatively small footprint.  

 

Sealant Transfer System (STS)

Here, the workload is loaded into the autoclave with the sealant in an adjacent tank. After the vacuum has been drawn on the autoclave, a valve is opened and the sealant transfers into the autoclave, immersing the components. The vacuum is then released, forcing the sealant into the porosity, after which unused sealant returns to its original tank under vacuum. STS machines are simpler to automate and benefit from well-conditioned sealant due to the length of time the sealant is held under vacuum. For critical applications, a pressure autoclave can be supplied, enabling a pressure cycle to be incorporated following the vacuum phase.

 

Drain 

The drain cycle involves removing excess sealant from the component after impregnation. Good draining is essential to reduce 'carry-over' to the cold wash tank and limit the amount of sealant lost as effluent. While a static drain is suitable in some applications, sealant may become trapped in pockets or features within more complex components. A rotational drain system physically rotates the components in their basket to maximise sealant removal. This is then collected and automatically returned to the autoclave.

 

Cold Wash

After draining, the components are transferred to the cold wash tank for removal of surface sealant. For more complex components, a rotational system is recommended. The wash solution is pumped from the lower tank into the chamber, passing over and through the rotating workload, before returning to the tank. The workload is not immersed, as if the components were to remain in the water during washing, contamination in the wash solution would adhere to the components and cause potential cleanliness problems during curing. The weight and volume of washing media passing through the components affect a high level of cleanliness and the subsequent rotation drain minimises carry-over to the hot cure module.

 

Hot Cure

This takes place in a separate tank with water controlled at a minimum of 90°C (195°F). For maximum productivity, a rotational system is recommended, where the hot cure solution is pumped from the tank to the manifold at the top of the chamber. The solution fills the chamber to a point where it automatically weirs back to the lower sump while the chamber is continually filled with filtered, reheated solution from the lower storage tank. This method not only cures the sealant within the porosity but provides a very effective final washing action.

 

What does impregnation achieve?

 

  • Outstanding void filling capacity due to low shrinkage during polymerisation
  • Optimised viscosity and capillary action for fast deep penetration of micro porosity
  • Tough and flexible attributes to provide resistance to chemical, temperature and vibration
  • Excellent adhesion to cavity walls ensuring a permanent seal
  • Stability at operating temperatures between -50°C and +220°C (-58°F and +428°F)

 

The Ultraseal impregnation process will treat any size of component using sealant formulations designed to ensure full compatibility with various substrates. These include: Aluminium, Magnesium, Cast Iron & Steel, Carbon Fibre Composites, GRP Mouldings, Plastics and Wood, however can work with customer's materials to diversify a sealant to help them cope with porosity in their components.

 

When the impregnation process is complete, the component can be put to use without further treatment. The process does not damage or distort the impregnated component. Treated parts are resistant to coolants, lubricants, solvents and most corrosive acids. It will continue to function in a wide range of continuous temperatures.