We design and mass produce custom polyurethane products.
Cast Molding | Injection Molding | 3D Printing
Thousands of OEMs have trusted us.

https://GallagherCorp.com
847-249-3440

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....

...

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.