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Tag Archive: Seal Casting Porosity

1. How to Seal Die Casting Porosity?

   May 23, 2025 7:44 am Leave a Comment

   Die casting is a metal casting process that involves injecting molten metal into a die using high pressure. Die casting facilitates the production of hundreds or thousands of pieces with high dimensional accuracy and a good surface finish, making it highly economical; however, maintaining quality and consistency at such high volumes comes with its own challenges. Manufacturers need to account for porosity, or the tendency for die castings to have voids or holes that cause surface-level flaws. Read on to learn more about die casting porosity, problems it can cause, and how vacuum impregnation seals die casting porosity.

   

   What Is Die Casting Porosity?

   Die casting porosity refers to specific defects found within the casting. Two of the most common types of porosity in completed metal goods are gas porosity and shrinkage porosity. Gas porosity is often caused by trapped air or other gases during solidification. It is always buoyant, meaning the resulting bubbles are typically found near the top of the casting (as seen below).

   

   Shrinkage porosity, on the other hand, refers to internal voids that can form as the metal cools. This is because the solid metal volume is less than the volume of liquid metal at higher temperatures. Shrinkage porosity has a linear or jagged appearance and tends to occur in either the drag or cope portion of the casting (below the surface).

   

   In addition to the above, having too much die lube can also contribute to porosity in die casting. While die lube is essential for removing cooled goods from the molds, too much can interfere with solid formation and create surface-level flaws. 

   Why Is Porosity a Problem?

   While porosity is inherent in die casting manufacturing, it can impact part performance, especially in applications where pressure integrity is a vital characteristic. Far from just being an aesthetic or durability problem, die-cast porosity can lead to early breakdowns or even failures. Consider the following examples: 

   Blind Porosity

   Blind porosity creates gaps that sit along the surface, pushing slightly into the interior but not creating uninterrupted passages for liquid to seep in. Manufacturers can expose blind porosity during the finishing stages. While it doesn’t make goods mechanically weaker, it does increase the risk of corrosion. The pores can also hold onto cleaning chemicals from powder coating or anodizing pre-treatments and then leach out after treatment, causing blemishes on the surface.

   Through Porosity

   Through porosity creates a leak path that runs through casting walls, or can be exposed after machining. This can weaken the metal and make it unsuitable for applications that require excellent pressure tightness, such as automotive and marine applications. Through porosity may make components weaker, create failure points, and prevent parts from reliably holding fluids.

   Fully Enclosed Porosity

   These pores are completely enclosed and don’t create leak paths. However, fully enclosed pores can become problematic if they’re exposed during surface finishing.

   

   How to Fix Die Casting Porosity

   Manufacturers can significantly reduce or completely eliminate failures due to die casting porosity with the right equipment and processes. One of the most effective methods is vacuum impregnation. With this controlled method, manufacturers use vacuuming and pressure to introduce the impregnating material into the voids, sealing the voids to make the casting fit for pressure-sensitive applications. 

   Benefits of using die casting vacuum impregnation include: 

   • A fast, cost-effective seal that doesn’t impact the component’s physical properties or functionality
   • No residual contamination or leaching

   Manufacturers can use vacuum impregnation for castings of any size, creating a permanent seal as well as a more consistent look, feel, and functionality in finished products.

   Why Godfrey & Wing Is the Trusted Solution for Die Casting Porosity

   At Godfrey & Wing, we specialize in closing the gaps left by die casting processes. Our equipment can provide fast, cost-efficient, and thorough vacuum impregnation processes to address porosity in die casting manufacturing. We’re committed to building systems that create effective, reliable seals that meet or exceed OEM requirements, and our team has decades of experience researching and improving solutions for die cast porosity. 

   Contact us today to learn more about our products and services.

2. Useful Lessons from Henry Ford on Modernizing Equipment

   January 31, 2022 2:29 pm Leave a Comment

   As manufacturing equipment ages, the maintenance and repair (MRO) of the equipment increases while the Overall Equipment Effectiveness (OEE) decreases. Given this, companies must decide while bidding on new projects: “Use the aged equipment and invest in MRO while accepting a lower OEE” or “Invest in new equipment using the latest technology and generate a higher OEE.”

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3. Video: When Should I Impregnate a Casting

   June 20, 2019 12:50 pm Leave a Comment

   The goal of a foundry is to produce high quality die castings that meet or exceed the customer’s specifications at a competitive cost.  In some die casting cases, those specifications require that the part must hold pressurized fluid or gasses. Companies use vacuum impregnation when the part must hold fluids or gasses under pressure. A common question asked about vacuum impregnation is “When Should I Impregnate a Casting?” This video addresses this question by answering if vacuum impregnation should be done before or after machining and finishing. 

   

    

   Video Transcript

   Hey, everyone. Welcome to “Casting Call” with Johnny Impreg. This is a premiere episode of a video blog series where we hope to answer all your compelling questions of everything impregnation. We’re going to start with the question I think I hear most often from folks is, “When should I impregnate a casting?”

   Spoiler Alert!

   Now, spoiler alert, I’m going to give you the answer now in case you’re short on time. But you want to do the impregnation after machining and prior to any kind of finishing like plating or painting. 

   Types of Porosity

   Now, here’s why. Let’s consider the three different types of porosity you see in a raw casting—blind porosity, through porosity, wall to wall, and fully enclosed. If you impregnate a casting in this condition, you’ll get sealant in the blind. You’ll get it here, but you won’t get any sealant in this area. That becomes important when you do the machining, because when you machined from here, you’re going to have a leak path.

   

   Now, if you do the impregnation after machining, you’ll still fill this and now you’ll fill this leak path as well. The reason you want to do it prior to finishing is you want to fill up all the porosity before you do the plating or painting. Otherwise, you could end up with out gassing or other blemishes that really don’t look so nice.

   

   Real World Example

   Let’s look at a real-world example on a cylinder block. Now, in this region here, we had a case where there was blind porosity going from here into the casting. It didn’t cause a problem until this machining cut was made. We have some other areas where we had enclosed porosity that was connected through two different machining passes. So, this is a real-world example of why you should do impregnation after machining. 

   

   So, I hope this little tutorial helped you. If you have any questions, please feel free to leave comments below and hit me up on WhatsApp or LinkedIn.

4. What Size of Porosity Can Vacuum Impregnation Seal?

   June 4, 2018 12:45 pm Leave a Comment

   A commonly asked question is “What size of porosity can vacuum impregnation seal?” What seems like a simple, straightforward question is actually a complicated one. This blog will address the topic by describing the basics of die casting porosity, and what vacuum impregnation will seal.

   

   Porosity

   While some refer to porosity as a defect, it occurs naturally and is found in most materials, both man-made and in nature. In metal castings, porosity is typically considered any void found in the casting. Casting porosity can be caused by gas formation or solidification while the metal is being moved from a liquid state to a solid state. This porosity can range in size, from sub-micron to voids greater than 10 mm, depending on the casting.

   Metal casting porosity can affect the part’s structural integrity, creating a failure point. Porosity can also prevent the part from being pressure tight. This will impact performance if the part is designed to hold gases or fluids.

   What Does Vacuum Impregnation Seal?

   Vacuum Impregnation is a process that seals metal casting porosity. Specifically, it seals the internal, interconnecting path of porosity, which breaches the casting wall. The process is not a surface treatment, so it does not seal open pores found on the casting surface. Nor is it intended to seal casting structural defects such as cracks or open knit lines.

   Understanding Die Casting Porosity

   It’s difficult to pinpoint a generic porosity range that vacuum impregnation seals because, generally speaking, one pore does not cause a leak path. A leak path is created through a series of interconnected pores. For example, a breach caused by a 5mm pore interconnected with a series of smaller pores will be easily sealed (Figure 1).

   

   Figure 1: This sectioned casting shows a 5 mm pore that is interconnected to a series of smaller pores. Vacuum impregnation can seal this leak path.

   Conversely, if the same 5mm pore breaches a 5mm wall it will be difficult, if not impossible, to seal as there is little casting material for the sealant to adhere (Figure 2). A pore of that nature has characteristics similar to surface porosity which is not a candidate for sealing through vacuum impregnation. The large open pore breaches the both casting walls and is sometimes called “see through” porosity. One needs to view the porosity in three dimensions to see how it is interconnected, not simply analyze individual pores.

   

   Figure 2: Vacuum impregnation will not seal this surface porosity. There is not enough casting material for the sealant to adhere.

   In Summary

   The wide range of casting parameters creates a limitless array of shapes and sizes of porosity possibilities. Despite this, vacuum impregnation can seal porosity of any size. While vacuum impregnation can seal porosity of any size, it is important to realize that the leak path is the key characteristic to evaluate and not pore size. A leak path is created through a series of interconnect pores, and not a single pore. Instead of asking “What size of porosity can vacuum impregnation seal?” one should ask “Can vacuum impregnation seal the leak path?”

   A future blog will discuss the topic of leak rates.

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5. Understanding the Vacuum Impregnation Process

   July 19, 2017 12:10 pm Leave a Comment

   Vacuum impregnation  seals porosity and leak paths in metal castings and powdered metal parts that form during the casting or molding process. The process is done by filling the pores with a sealant under pressure to stop fluids or gases from leaking under pressure. Vacuum impregnation stops casting porosity and allows manufacturers to use parts that would otherwise be scrapped.

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