Pressing is the part of the process where the snowboard is moulded into its final shape while the epoxy resin cures - so the board will then retain the moulded form. Pressing drives out excess resin, and air voids to produce a lighter, stronger laminate with an optimal resin to fibre ratio. Epoxy resin also bonds all the components together into one structure. There are a few ways to do this, the most common industrially being platen-pressing, and for the homebuilder, vacuum moulding.
The mould is the crucial component in the press / vacuum setup and is essentially designed to create the shape of the snowboard when viewed in profile from the side - curved up tip and tail and a cambered running length. Vacuum moulds can be built slightly lighter than press moulds but in all cases, the mould should be as solid, flat and rigid as possible.
Build the mould using a stiff heavy MDF base ideally backed with a rigid steel or wooden frame. For the profile itself, cut shaped pieces from MDF and align them side by side. We built our mould by cutting curved camber sections in MDF, and curved tip sections. Underneath the running length of the board, the mould is solid - there are no gaps between the MDF camber sections. At the tips, we interleaved the tip curved sections with the camber sections. This enabled us to sink the tip ribs beneath the camber ribs - to get a smooth curve up into the tips - and to do so without having to cut the MDF down to zero thickness at the ends of the curves. A router and template setup guarantees you precise cutting and a good result. This mould can be used for both vacuum and press forming.
^ MDF camber ribs, routed to shape from a template
^ Routing the tip section ribs from MDF strips
^ Cutting the tip section rib from the MDF strip
^ The completed tip rib
^ The tips interleaving with the camber section give a smooth transition
^ The board is under vacuum, with a gauge to check the pressure. A good seal is obviously critical...
Link : A detailed explanation of the vacuum bagging process
^ Animated view of our press in action
A press consists of two matched shapes, one under the board and one on top which can be brought together under pressure by hydraulics, pneumatics, weights, levers or screwthreads.
The press must be constructed using a rigid frame to exert the pressure onto the mould and snowboard below. For a heavy duty press powered by pressurised air, the frame consists of steel beams above and below with a ‘cavity’ in the middle into which the mould is inserted. Suspended above the mould is a ‘cat track’ which is a series of square section aluminium tubes strung together on cables. This provides a surface which is flexible along its length and stiff across its width. It is important that the cat-track flexes along its length because it can adapt to the shape of the mould – and more importantly to changes in thickness along the length of the snowboard. You could of course make two matched moulds – an upper and lower half – but then you’d be stuck with the same flex pattern.
Between the cat-track and the upper frame is a length of wide diameter firehose, which is sealed at either end with heavy steel bar bolted through, and with a valve connector at one end. By inflating the firehose using compressed air, the cat track is forced down onto the mould where it exerts pressure on the snowboard and forces it into shape – and squeezes out any excess air and resin from the whole thing. The higher the pressure, the more epoxy comes out of the board and the tighter / lighter the layup. Too much pressure can lead to ‘print through’ where the glassfibres make an imprint in the topsheet. We press at 6 Bar in the firehose which gives us a nice tight layup – there’s only as much resin as we need. When applying the pressure we apply it slowly – creep up to 2 Bar and dwell for a while allowing resin and air to flow out. Then creep up to 4 Bar and do the same until we finally settle at 6 Bar. If we cranked it right up to 6 Bar in one go, there might be some sealing in places which would prevent the resin flowing out effectively and could cause us some problems.
^ Smooth curves and even heating...
^ Double cat-track action - the board goes between the two cat-tracks
^ Hot and getting hotter...
^ Our first snowboard press - screwthread clamps add pressure
You can also build a much simpler style of press - our heavy I-Beam press is only really necessary if you are serious about building skis or snowboards - it`s a fairly big investment and requires space, time and effort to create.
We built our very first boards using the simple screwthread press above - angle irons clamp across an upper sheet of MDF using threaded bar. The board is built on the bottom half of the press, the top is put over, and the angle-irons clamped down evenly, working from the center to the outside.
We modified the press after this picutre was taken to add gutters to catch excess epoxy. It`s a pain if the resin gets on the screwthreads !
An autoclave is used in conjunction with a vacuum bag to increase the amount of pressure you can exert on the board. At atmospheric pressure the minimum possible pressure inside the bag is -1 bar. So to pull even harder you have to raise atmospheric pressure. An autoclave is a sealed pressure vessel which can be pumped up with air, the vac-bag goes inside it with the air sucked out, then the autoclave is sealed. The bag needs to have a hose venting to the outside of the autoclave (1 bar). Inside the pressure can be increased and at a certain point you can release the vacuum on the bag by opening the vent which goes outside the autoclave. For example if the autoclave is pressurised to 5 bar, and the outside air pressure is 1 bar you get an effective `vacuum` of -4 bar, whereas at normal pressure you only got -1 bar. These machines are big expensive things used by major composite industry to build aircraft parts and Formula-1 car components.