Hollow Wheel Manufacturing and shipping update #5

December 22, 2020

Hey Everyone,

Just wanted to give a quick update on the wheels. In the last update (https://momentum-boards.com/blogs/news/shipping-update-4), I said that I would provide an update on the 18th. Sorry, I am a couple days late as I am working on the next steps. First and foremost, thank you all for your support and patience.

I'll cut to the chase. The bond between the core and the thread needs to be stronger. There are signs of delamination between the core and the thread. The problem is that the core and the tread aren't melting together during the injection process; this is to say that the thread is purely relying on a mechanical lock and not a chemical lock (the core and the tread needs to melt together).

Here is a little picture. There is dirt getting trapped between the core and thread. That is not supposed to happen. Since the material is a little clear, I can see some dirt accumulation in the seam (hard to take a picture).

The wheel is undergoing a lot of stress and temperature fluctuation:

Torque fluctuations from acceleration and braking
Rapid compression oscillations
Major impact forces
High temperature generated from hard carving and high speed

As such a strong bond between the core and the thread is essential.

Here is what we are trying to achieve. The red and grey bars represent the two different materials. In our case, it is the core (the hard urethane) and the thread (the soft urethane). The first stage is the molten hot soft urethane is injected into the mold where the core is sitting inside). The molten hot soft urethane transfers heat into the hard urethane and fuses together. Upon cooling, the two urethanes are melted and locked together.

This might sound easier than it is. It can seem like an art more than a science. This is because if inject too hot, then we get a lot of deformation when the material cools down (Basically the wheel isn't too circular). This is called "Shrinkage".

...And it just gets harder to inject and generally control.

Moreover, if we go too cool, then we don't have any chemical adhesion. It just requires a lot of testing and adjustments.

But this is OK. I am not very worried. This is the first wheels off the mold and we just need to adjust mold temperature, injection temperature, injection pressure, and alter the material or introduce some bonding agents.

It's kind of like making pancakes. Sometimes the first pancake needs some work but then the other pancakes after come out a lot better after the first try.

Next steps:

We have made a bunch of new samples and have sent them to my material supplier. This meeting is occurring on Friday (they don't celebrate Xmas in China). They are going to look at the current samples and they are going to be guiding us on the necessary changes and things to test.
We are also working with the material supplier to determine shear tests so we can expedite testing - in this way, we don't have to ship to me on each sample. They can tear down the wheel and know what to look for and then shave a lot of down time.

Timeline:

Unfortunately, I don't know the timeline exactly, but hope to know more on Friday after the meeting of a testing game plan. I'll share those details with you all. I hope it isn't much more of a wait. I will be very honest and transparent with you all.

Cross Functional Collaboration targeting success

I have my China team diligently working and regularly working with the factory and conducting quality audits. Then, I have the material supplier company helping provide guidance on bonding and material specification formulation changes. Lastly, I have my plastic injection molding partners working to make this a success. We are all determined to make an amazing product.

Continued testing:

I will continue to do a lot of testing on the wheels to see if I can identify other areas of improvement in parallel. I have given them out to some of my friends to test as well. Also, I have been using the test rig to put more miles on them quickly. Moreover, I have been attending as many ESK8 road course sessions and trying to finish durability and performance testing before shipping.

Test Rig: