How do you ensure good adhesion to your part?

One of the most frequent questions Robafoam gets asked when speaking to potential customers is ‘Will the foam stick to our part?’. The short answer is yes, but it may take some other processes before achieving a suitable adhesion.

Some substrates have a natural adhesion and therefore don’t require additional interference. If there isn’t a natural adhesion then there’s usually something we can do to achieve it. Here, the experts from Robafoam discuss adhesion further and look at a previous example of when the company has overcome difficulty with adhesion.

The adhesion of the Robafoam seals to a component’s surface is dependent on the surface energy of the material or the surface treatment in question, as well as any possible contamination of the surface. Different material surfaces exhibit different levels of natural adhesion depending on their surface energy. Surface energy is measured in Dyne/cm² and the optimal value for adhesion with our foam products is 50 Dyne/cm².

One way to change the surface energy, to ensure the adhesion of the foam, is through the application of ‘atmospheric plasma’. All of the company’s 6-axis robots are equipped with a plasma system to use with its contract gasketing customers. The application of plasma is part of the same process, carried out just before the foam bead is applied.

Another way of increasing adhesion is by using liquid surface primers. By increasing the ‘wetting’ of the foam to the surface part, adhesion can be improved, however, this may compromise the height of the bead as the foam has an affinity with the surface and wants to spread.

Airline smart trolley latch

In 2016, a company that had developed a product to overcome security difficulties with airline trolleys approached Robafoam to apply a seal to its part. The part was a complex double-faced, 3D part, made of polycarbonate material and was the outside case which enclosed a number of electrical components as well as a GPS system.

The airline trolleys (holding food and gifts) are usually delivered with a security tab attached to the opening latch, which is removed by airline staff when setting up the plane. After some testing, these tabs were found to be very easy to open by non-airline staff, who could change the contents and apply a new security tab. The ability to plant an item on these trolleys that don’t require to go through security measures obviously then compromises the safety of the aeroplane. A new product was developed which held a smart security seal, allowing the trolley to be connected to electronic keys held by airline staff and therefore ensuring others are unable to open the trolley.

The part was brought to us during the prototype stage and required a IP69K rating, which means that the seal needed to withstand being sprayed by high-pressure water at point-blank conditions. When applying the foam to the prototypes, there was a natural adhesion to the samples and the testing all went smoothly and achieved the required IP rating. The product then moved onto production, and Robafoam received the first production parts to seal; however, it found all the foam gaskets applied began to peel off.

After much discussion with the customer, it was realised that a fire-retardant additive, which had been added by the injection moulding company to the final production parts but not the initial prototypes, was causing a change in the Dyne/cm² value of the part and therefore affecting the adhesion. Once plasma was incorporated into the process of the seal, all was solved and the parts were retested and able to be used.