Xencast PX90 Hard Flexible Polyurethane Resin

Glass Bubbles can be added to most resins to reduce the density of the cured material. However, bear in mind that they will reduce the clarity of the GlassCast resin, making it more of a translucent 'milky' appearance rather than transparent.

Assuming your skateboard wheels are perfect cylinders then the volume is quite easy to calculate using the formula Πr²h which in your case r = 25mm and h = 30mm giving a volume of 58.9 cm³. For Example, the density of PX90 is fractionally over 1g/cm³ which means you need 58.9g of resin per wheel or 235.62g for a set of 4. However check the density of the specific resin you are using in all cases so you multiply by the right figure to get an accurate weight.

However, most skateboard wheels have cut outs or hollows so the reality is you will use less resin. Calculating the volume in that case is a little more complicated as you need to calculate the volume of the cut outs then take it from the figures above to give the actual volume.

...the shore should be around 70 ish. Also, how well does it bond to metal, and can I treat the metal with a product to increase the adhesion?

Most commonly motor mounts (engine bushes) are made using something more like an 80 or 90 shore resin. In fact our PX90 has been used by a number of customers to create engine mounts.

If you're confident that you do need a 70 shore for your application then our closest shore hardness would be our PX60 but my opinion is that this would be too soft for most typical engine mount applications.

As for the bond to metal, we don't really have, and you shouldn't really need, an adhesion promoter for PU to aluminium - they should bond well. As usual, just make sure the surface is clean, completely grease-free (using acetone) and lightly keyed (using abrasive paper).

Yes we have a range of specific PU pigments which are compatible with the PX range of resins https://www.easycomposites.co.uk/polyurethane-solid-colour-pigment 

Our tinting pigments are also compatible with PU resins https://www.easycomposites.co.uk/translucent-tinting-pigment

You can certainly use this resin without degassing however we do recommend degassing to ensure maximum performance of the finished product by removing all traces of air. Bubbles can form weak points in the casting which promote tearing and ultimately early failure.

Due to the short pot life, if you do choose to degas the resin then we would recommend a degassing system that uses a high capacity pump so that there is enough time to degas within the resins pot-life. Our Professional Vacuum Degassing System - EC20-1 Vacuum Pump is the ideal one stop solution for degassing highly reactive resins with short pot-lives.

You can thicken most resin systems, including PU with Fumed silica. Just be aware that thickening a flexible or semi flexible resin is likely to reduce its flexibility making it more brittle in use.  

It probably wouldn't be practical to resin infuse PX90 into a Kevlar reinforcement to make a reinforced hose. The main issue would be the pot-life and cure time of the resin, the PX90 has a really short pot life - only around 5mins - and cures very quickly, far more quickly than you would be able to undertake a vacuum infusion unfortunately.

No, PX90 is not a UV stable resin and will yellow following prolonged UV exposure. Addition of pigments will help reduce the visibility of this but not stop it entirely and so the resin should be considered for mechanical applications, rather than cosmetic ones.

To use PX90 in a polyester or vinylester mould, you will need to use a mould release agent to ensure the resin does not stick to the surface. We would recommend using our Easy-Lease Chemical Release Agent due to its semi-permanent nature and the very good release properties.

The formulation of the PX90 PU resin is designed to produce a 90 Shore A hardness resin only.

If you are after 60 Shore A, then we would recommend our Xencast PX60 Medium Flexible Polyurethane Rubber.

For large castings, pouring in stages will help control the temperature of the resin ensuring it does not exotherm. The PU will bond to itself in subsequent layers no problem will need a degrease and thorough  key with abrasive paper before pouring subsequent layers.

Maybe. Metal powders will mix into the PX90 OK but the probably you're likely to have is sanding the resin to expose and score the metal powder which is likely to prove difficult on a flexible material, although it is possible that you could still find a way to do it. Without exposing the metal powder in this way, the metallic effect is much less pronounced.

If a good metallic finish is the priority then we would recommend a typical rigid curing polyurethane such as our Xencast P2 Fast Cast Polyurethane Casting Resin which can easily be sanded and polished to produce the metallic finish.