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When choosing a vacuum impregnation sealant, you have two sealants choices: thermal-cure, or anaerobic. Choosing one over the other has nothing to do with the quality of the sealant, but it has everything to do with the part material, size of the pore, and leak path.
Curious on what sealant is best for you? The following infographic is a simple snapshot that will help educate and allow you to determine if thermal-cure or anaerobic sealant is best for your needs.
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We posted a blog in May about the common frequently asked questions about vacuum impregnation. With the complexity of the subject, these questions and answers do not fully address all porosity and vacuum impregnation questions. The following are additional answers to commonly asked questions about porosity and vacuum impregnation.
How much does impregnation cost?
This question should read “How much can you save?”. It is important to remember that impregnation costs are a small fraction of remelting, recasting, remachining and overruns. Vacuum impregnation seals the inherent problem of porosity, thus allowing parts once deemed as scrap to be useable. The cost of impregnation depends upon several factors including (but not limited to) the size and complexity of the casting, the amount of castings to be impregnated, and the type of material used to impregnate.
What size porosity can be sealed?
Micro-porosity causing “weepers” is usually easy to seal. For larger micro-porosity and macro-porosity sealing depends on wall thickness and the type of porosity present. Straight through porosity in thin walls is difficult to seal. Sponge like porosity of any type can usually be sealed. 100% solid resin will seal porosity many times larger than other impregnants.
Will impregnated sealant vibrate loose or fall out?
No. When sealing porosity within the wall thickness of a casting, the sealant is locked in and will remain so for the life of the casting.
What temperatures will the impregnant withstand?
For most sealants, 400°F is the highest temperature generally recommended for continuous usage, but will withstand 500°F temperatures for short intermittent periods. Higher surface temperatures, up to 1400°F, can be withstood without resin failure when parts are water-jacked or forced air-cooled. This is because sealant remains strong and solid in the porous areas of the cool side. The sealant may char next to the hot side, it never melts and is protected by the thermal conductivity of the metal. Examples of this are automotive cylinder heads and blocks.
How long will the impregnant last?
As long as the casting itself.
What else will impregnation do?
In addition to sealing for pressure tightness, impregnation is used to seal sintered components and other parts to avoid corrosion. It is also used prior to electro-plating to prevent bleedout from acid etches and electrolytes absorbed into porous areas which are sealed in by subsequent plating. Where bleedout and blistering due to porosity is a problem on other types of finishes, such as lacquers and baked enamels, impregnation before finishing eliminates out-gassing and blistering.
Next Steps
When a casting porosity problem occurs, the first challenge is to determine the type of porosity. The following porosity classification guide can help you determine the porosity type. This is important information to know, because the type of porosity will dictate the vacuum impregnation process to use.
In general, there are three basic classifications of casting porosity:
- Blind Porosity(highlighted in blue): From one surface only and therefore not forming a continuous passage for liquid.
- Through Porosity(highlighted in red): Stretching from one side of a casting to another thereby causing a leak path.
- Fully Enclosed Porosity (highlighted in green)>: Enclosed within the casting, and has no passage to the surface.
Blind and Through porosity cause immediate casting problems. Blind porosity can cause internal corrosion; while Through porosity will allow gas and liquids to seep through the casting. In addition, blind porosity can cause defects on the part surface when secondary treatments, like powder coating or anodizing, are done. This is because solutions used to clean the castings prior to the treatment will leech out of the voids after the surface finish process.
Fully enclosed porosity is not a problem unless secondary machining uncovers this porosity. Machining can break fully enclosed porosity, which will then turn it to either Blind or Through porosity. This is important to know, because porosity detection should not be done until machining of the casting is complete.
Related: Should Vacuum Impregnation Be Done Before or After Machining?
How to Seal Porosity?
The best way to seal Blind or Through porosity is with vacuum impregnation. Vacuum Impregnation eliminates the negative effects of porosity such as leaks, and corrosion, thus achieving completely sealed castings. Understanding the porosity and using vacuum impregnation will allow you to efficiently produce parts while minimizing costs.
Video: Understanding the Vacuum Impregnation Process
OSHA issued a new regulation changing current Hazard Communication Standard (HCS) to conform to the Global Harmonized System of Classifying and Labeling Chemicals (GHS).
Under the GHS, material safety data sheets (MSDS) will now be called safety data sheets (SDS). SDS’s will provide you with procedures for handling and working with our sealants in a safe manner.
The SDS for our 8 sealants are available for download. You can receive these documents by clicking on the link below.
We recently update our vacuum impregnation handbook. The handbook takes the complicated subject of vacuum impregnation and simplifies it. This handbook will allow you to better identify porosity and then learn what vacuum impregnation process and system is best to seal your porosity.
When porosity occurs in your part, you need to get it seal quickly.Use our handbook as a guide to help you find the best solution for your part. Flip through this easy to follow handbook to learn about:
- Porosity Types
- Vacuum Impregnation Steps
- Who Uses Vacuum Impregnation
- The Definition of Vacuum Impregnation
- Vacuum Impregnation Selection Variables
- Vacuum Impregnation Systems & Sealants
Our new Advanced Powertrain impregnation (APi) system simplifies and compacts the vacuum impregnation process so that you can bring vacuum impregnation equipment in house. The APi takes our patented front loading technology and increases the impregnation chamber for large parts-like engine blocks or powertrain transmission cases. (more…)
Years ago and even today, Batch System Vacuum Impregnation was the most common vacuum impregnation system. Despite a recent shift towards Single Piece Part Flow (i.e. HVLV, CFI, APi, and EcoSeal), there is still value in Batch System Vacuum Impregnation. Bottom line, the advantages of this process is that it is the best solution to provide capacity-multiple amounts of product can be serviced in one cycle.
Both batch and single piece part flow impregnation systems accomplish the same 4 basic tasks:
- Penetration of casting porosity/leak paths with sealant
- Recovery of excess sealant from tapped holes, cavities and outside casting surface
- Cleaning of the casting’s surface features to remove undesirable sealant
- Curing the sealant that has been impregnated within the casting walls.
So if all impregnation systems accomplish the same tasks, then how does a batch system work differently?
It’s simple; a Batch system is compiled of a large vessel, large tanks and large baskets.
Multiple castings are placed in baskets, which then are put through the impregnation process, first the vessel, then the wash and finally the cure.
So when should a Batch system used? The system should be utilized when:
- Flexibility in range of part sizes and shapes
- Parts that have a more forgiving leak rate
- Large, heavy parts that do not have small blind threaded holes
- High quantity of raw (non-machined) castings where part-on-part contact is not an issue.
This condensed overview will provide you a better understanding on the benefits of a Batch system. Of course, this system is not a “one size fits all” for vacuum impregnation needs. At Godfrey & Wing, we manufacture and utilize both batch and single piece part flow. Both systems have benefits to different needs.
Next Steps
We are sometimes told by customers that they are unaware of what vacuum impregnation is. Ultimately, they have a casting with porosity that is leaking whatever is passing through the part (i.e. air, gas, water, etc.), and they need a solution to their problem. Here are some of the more common questions that we receive in regards to vacuum impregnation and porosity. Our intent is that you can use this information as a guide when you need to correct castings with porosity.
Would you like this information in a printable form? Of course! Click here to download it as a pdf.
What is porosity?
Porosity is an area of sponge-like texture in an otherwise sound metal casting. There are two types of porosity:
- Micro-porosity: Very small (almost invisible) interconnected air filled cells.
- Macro-porosity: Larger flaws in the casting visible to the naked eye.
Porosity is typically caused during the casting process by internal shrinkage, gas cavitation, oxide films and inclusions and the many combinations thereof.
What is vacuum impregnation?
Vacuum impregnation (also known as “impregnation” and “impreg”) seals the porosity in metal castings, thus making leaky castings pressure tight.
What is the process of vacuum impregnation?
In a nutshell, the impregnation sealant is introduced into the voids within the wall thickness of the casting through vacuum and/or pressure methods. Subsequent processing solidifies the sealant.
What are the types of porosity?
There are three types of porosity:
- Blind Porosity: From one surface only and therefore not forming a continuous passage for liquid
- Through Porosity: Stretching from one inner face to another thereby causing a leakage path
- Fully Enclosed Porosity: This can not be reached by impregnation.
How does impregnation improve product quality?
When casting porosity is reviewed during inspection, “good” castings are as porous as the “bad” castings because the porosity is blind and not completely inter-connected. Subsequent mechanical or thermal shock or stress often breaks the thin membrane in the “good castings” which keeps the blind porosity from being continuous, thus causing a “leaker”. Impregnation fills porosity from both sides preventing leaks even if the membrane does break. Therefore, impregnation salvages castings and improves quality, while inspection only sorts out leakers.
What materials can be impregnated?
All ferrous and non-ferrous metals, whether sand cast, gravity die, pressure die castings or forgings can be impregnated to eliminate porosity. Iron, bronze, aluminum, zinc, magnesium, steel, sintered metals and plastics, as well as alloys of these metals can be impregnated.
Can cracked castings be fixed through impregnation?
No. Impregnation will not increase the strength of a casting. The cracks will reopen when the casting is under pressure.
Can vacuum impregnation cure surface flaws?
No. This is because impregnation is within the part and not a surface treatment.
Should impregnation occur before or after machining?
Impregnation occurs after a casting is machined. This is because machining may potentially uncover additional porosity.
Will impregnation discolor or damage the casting?
No, because impregnation occurs within the walls of the casting. There is no film or coating on the part surface that will change any dimensional tolerances.
These are not the only questions we receive in regards to vacuum impregnation and porosity.
To discuss your specific questions, or situation, contact us at 330-562-1440 or send us an email.
Next Steps
The Albert Handtmann Metallgusswerk GmbH is the largest lightweight (aluminum) foundry in Germany. When the opportunity arose for the company to cast and machine one third of the entire world production of transmission cases and clutch housings for Mercedes Benz, not just any vacuum impregnation system would work.
They needed a vacuum impregnation system to meet:
-Stringent Quality Standards
-High Production Volumes
-Meet a Tight Cycle Time
-Fit in a Confined Space
To learn how Godfrey & Wing played an integral role in Handtmann’s manufacturing process,
click here to read the entire case study.
Our new Mexico vacuum impregnation plant is featured on the cover of the Fundidores April addition.
If you have not read the recent Fundidores from Metal Spain, then click here to download your free copy. FYI, the magazine is both in Spanish and English. The Englsih version begins on page 28.
Our Mexico service center opened towards the beginning of this year and is located in Santa Catarina, part of the Monterrey Metropolitan Area in the state of Nuevo Leon.
This new facility comprises 10,000 square feet and houses the HVLV, GW’s groundbreaking impregnation system that uses a patented single piece flow Dry Vacuum and Positive Pressure (DVP) process. Click here to learn more about our Mexico location.
For more information about Godfrey & Wing, please contact us by email or call +1.330.562.1440.
