Principles of Bonding Cast Polyurethane to Metals | Gallagher Corporation
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When we say that a part is bonded, we mean that the urethane elastomer is chemically bonded to the substrate. There are other methods of attaching polyurethane during molding, such as a mechanical lock, but those won’t be covered in this video.
We can start out by looking at the end result when polyurethane is successfully bonded to metal. This is one of the bond tests conducted at Gallagher Corporation on a regular basis. Our polyurethane elastomers in raw form are a liquid. This allows them to be cast, similar to how metals can be cast in a foundry. Part designs that call for metal reinforcement can be accommodated by forming a chemical bond during the casting process. Metals are coated with primer we call a bonding agent. The bonding agent reacts with the metal surface and will react with the liquid urethane as it cures. The result is an extremely tough chemical bond that is stronger than the urethane itself.
The key to a good bond is proper metal preparation. Because most bond tests are destructive and because you can’t physically see the bond before placing a part into service, it’s vital that a tightly controlled bonding process be followed. The bonding process that has been refined over the years here at Gallagher Corp includes: degreasing the metal, abrasive grit blasting of the metal, applying the chemical primer, and finally casting the part. Now let’s take a closer look at each step of the process.
In the first step of the bonding process, the parts are thoroughly washed with a solution of hot alkaline detergent and water. The washing cycle is timed such that each part is bombarded with direct spray from the high pressure nozzles in the washing cabinet. After a short dwell, the parts are then rinsed with fresh water to remove any residual detergent. Daily titrations are done on the washing solution to ensure that the concentration level of the detergent is correct. It’s vitally important that all oils are removed from the raw metals at this step in the process, because any residual oil would prevent the chemical primer from properly adhering to the base metal.
Following the washing step, sample parts are tested for cleanliness using a tool called the Surface Analyst. Essentially, this tool performs the water break test on a sample part and provides a numerical data point indicating the cleanliness of the sample.
A high angle reading indicates that the part still has residual oil on the surface, think of when a water droplet beads up on a freshly waxed car. This part is reading _ _ degrees. That is indicative of a very clean surface. It should also be mentioned here that after the part is washed, it’s important not to touch the part again with bare hands. Oils from the skin would contaminate the part and threaten bond strength.
After a part is washed, it is abraded by grit blasting. The grit blasting operation removes any scale or oxidation on the surface of the metal. Grit blasting also produces an anchor pattern on the metal which increases surface area and helps the primer to fully attach to the base metal.
By increasing the surface area and achieving an anchor pattern of peaks and valleys, the mechanism for peeling the elastomer from the base metal becomes a combination of shear and tensile stress, in comparison to pure tensile stress on a perfectly smooth surface.
It’s important that the blasted surface isn’t too rough or too smooth. A surface that’s too smooth doesn’t take full advantage of the operation. A surface that is too rough will complicate the process of properly applying the primer.
The target roughness average for the grit blasting step is approximately 250 Ra. Surface roughness is checked regularly using a roughness gauge to ensure the process is within spec.
After the parts are grit blasted, any residual dust from the blasting process is removed. A simple test for cleanliness after the blasting operation can be done with clear packaging tape. The tape test will pick up any dust or residual blasting media from the surface of the blast part....
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The bonding process at Gallagher Corporation is documented and tightly controlled to ensure quality. Sample parts are pulled from production every day for quality assurance bond testing. Bond failure is not an option for any Gallagher Corporation customers. That’s why we put so much effort into getting it right every single time.
Пікірлер: 34
Very informative and compelling. Thank you!
I didn't know there was so much theory to my everyday work EZ. Great tutorial 👍
Great video
Very informative, well produced and comprehensive. 👏👍💥
@GallagherCorporation
3 жыл бұрын
Thanks! Glad you enjoyed it.
I used polyester powder coating on metal (stainless steel and steel) as a primer before casting 90A shore polyurethane 2 part resin. It works great. Again, I used just regular white polyester powder coating baked with high temperature. The bond is so strong that It is very hard to remove polyurethane from metal surface.
@GallagherCorporation
2 жыл бұрын
Hi Tigran, which polyester powder coating formulation did you try with success? Was it a TGIC polyester or the non -TGIC (or HAA type, also called Primid type)?
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Hi, first of all, thank you for the informative video. I know that polyurethane is a mixture of isocyanate and polyol components and these parts react with each other by the time they become together. How in the spray coating of polyurethane the parts are mixed and how they become stable when they mixed? I would be grateful if you answer.
@GallagherCorporation
4 жыл бұрын
Thanks for watching, Gizem! We are not familiar enough with spray polyurethane to comment on that. We cast mold, injection mold, and 3D print polyurethane.
If a Polyurethane to steel bond is purely shear loaded (so no peel), should the surface roughness still be Ra250? And how well does the bond perform on a pure shear application? Application is a PU disc with diameter 500 mm and thickness 150 mm bonded to a steel bottom and top plate under shear load.
@GallagherCorporation
Жыл бұрын
Bonding to two surfaces at the same time can be tricky. Reach out to us if you are experiencing failures and we can talk more.
Which is the bonding primer used? And also for different base metals like iron,steel or aluminium primer is same or different?
@GallagherCorporation
5 жыл бұрын
Hi Nagaraja, we use several kinds of bonding agent depending on the application. It is possible to use the same bonding agent on a variety of metals.
@musmantaiq6711
Жыл бұрын
@@GallagherCorporation Which bond are you use tpu to aluminium bonding
Thanks for the vedio
@GallagherCorporation
4 жыл бұрын
Welcome!
Hi, can you tell me what machine you used to test the bonding on that video?
@GallagherCorporation
5 жыл бұрын
Instron Machine
Good
These guys flew delta way too much. I feel like I'm watching the pre flight boarding video lol. Good video though, I appreciate the info!
What is your bond strength value as N/mm for your polyurethane wheels, i didn't see any information about that in your official site
@GallagherCorporation
2 жыл бұрын
Ultimately, the bond strength of our products exceeds the materials strength. The values obtained from bond testing are influenced heavily by the urethane compound. Due to this, two parts cast with different materials can both have exceptional bond, but very different values from our bond test.
@kargunbatur1369
2 жыл бұрын
@@GallagherCorporation I see, can i ask a question too, according to which standard are you testing the bond strength ?
Hello friends, I am working in a grinding wheels production company and we produce various types of grinding wheels. We also produce Resin bonded wheels in which we experience a problem of abrasive resin layer getting slipped of from the metal base(aluminium). Normally for good adhesion of the abrasive layer, we used to create seration on the aluminium body, grit blast it, also we used to apply a layer of primer on the grit blasted area. But still after all the processes are done our abrasive wheel gets slipped of from the metal base. Can you guys suggest me any good idea how to overcome this issue.
@GallagherCorporation
4 жыл бұрын
Thanveer, it's hard to say. There are so many contributing factors.
Which bond are you use for bonding of tpu to aluminium
@GallagherCorporation
Жыл бұрын
We could get into the specifics if we partner on something.
in that kind of wheel how much is A ? ( hardness of polyurethane )
@GallagherCorporation
4 жыл бұрын
Find out more about the hardness of polyurethane here - gallaghercorp.com/polyurethane-durometer-hardness/
is hand casting / Manual casting good for polyurethane process? or machine casting is better
@GallagherCorporation
Жыл бұрын
We would confidently say that using meter-mix machines is the way to go.
Can we use polyurethane for sealing holes in water galvanized steel tanks?
@GallagherCorporation
2 жыл бұрын
Hello Adeeb, we mold solid polyurethane elastomers. You should reach out to someone that works in sealants. Thank you.