Infusion Stations

So, after scrapping my first CF tub, I decided I needed to improve a lot of things (thanks Vic) before I should commit lots of materials for the next tub. First of all was to improve my vacuum management.

What I wanted to achieve was:

  • Make it much easier to route vacuum where i needed it
  • Be 100% sure that I have no leaks in certain parts of the vacuum chain
  • In my case, I want to be sure that everything from the new vacuum manifold inwards was leak proof
  • Prove everything from the manifold to and including the catch-pot was leak-proof
  • have a solid, reliable catch-pot

 

Firstly, I created a vacuum manifold, printed a bracket and mounted it on to the side of the compressor. The manifold is actually a gas manifold for a caravan gas supply, and I got it new from Ebay for about £30. The manifold itself actually has a non-return valve in each tap assembly, so I had to fettle that. Not a hard job and subject to a different post.

 

 

Next I mounted the catch-pot onto the vacuum tank (or an old compressor I repurposed). This was relatively painless – again I printed a bracket. This time it’s the orange thing under the catch-pot. All it is is something that is curved to the tank on one side, and level on the other. Thus I could mount the catch-pot on the level. I bonded it onto the tank with metal-epoxy, and used double-sided tape to stick the pot to the mount. The tape is monster tape – it’s fearsome stuff won’t let go easily. It will let go if I need it to.

Finally the whole thing was piped up (below) and tested.

Once I had this working, I decided I wanted another bench manifold, and made one out of push-to-fit pneumatic connectors. This means I can put my degassing chamber on the bench and not have to connect it directly to the vacuum pump. There’s little time between degassing and infusing, especially if you have 3kg of resin in a bucket – it’ll start exotherming quite quickly. With my manifold setup, i can hold the part under vacuum whist at the same time degassing the resin. Then I just need to connect the feed line to it and I can go.

 

What you can see here is one branch of the manifold. There’s a t-piece at the bottom, and a valve in the middle. The top is the output. Again, I printed some brackets to give me just the mounting I wanted, and the white bracket in the middle is actually a 15mm hinge-clip for attaching standard poly-pipe when plumbing. They’re £6 for 100, so I bought 100. I have many spares. The top blue bit is the outlet at this part of the manifold. It lets me plug an 8mm pipe straight in to the quick-release connector.

 
This is the final manifold – the picture isn’t great, but you can see three outlets. It’s set on an old tool-board I used which I didn’t need anymore – far better reuse that (considering it was already bonded to the wall).

Scrapping Tub 1.0

So, here is the tub out of the mould. I had a lot of issues infusing this, and I’ve learned quite a lot whilst doing it. It’s gutting to scrap it, but it’s the right thing to do. Next time it’ll be right.
There are some high level mistakes that were mine, and they led to some lower level quality issues. It’s the first time I’ve done an infusion of this size and at the same time with a positive mould, rather than the usual negative mould. Doing it on a positive mould means I have to be very careful about the layer thickness otherwise I have a too large or too small gap between the part and the chassis rails I want to bond it to.

Some of the mistakes were down to layup technique, and some were down to getting the infusion wrong.
 I infused over a hexagonal core, and the hexagons were too large to not have a hole put through the middle.
Here’s another picture of the quality issues up close – now for the lessons learned:

Lessons Learned

  • I over engineered the part – too much carbon meant it was too heavy. When I cut it open I had great consolidation – all the issues are cosmetic.
  • In the spirit of making it ultra strong, I had core everywhere. Next time it’s going to be core in the floor, up the back and the top of the tunnel only. The core interfered with the close fit needed to bond it to the chassis. Again, this is due to a male mould. Normally I’d overlay layers in certain areas to achieve this. In this instance, I have to stick to the required layers to achieve a 2.5mm thickness up the sides and at the bonding areas.
  • More holes in the core, and a thinner core
  • The catch-pot imploded. I made one out of plastic. Air got in. A lot of air. I made one out of plastic and tested it for a week – it was strong. With the heat of the part (I had the tub heated to 35C) the pot weakened and imploded. Back to my all steel pot.
  • The tubing sucks up a load of resin. I had 6kg mixed and it flew into the part. This caught me off guard and I didn’t have enough mixed. A small amount of air got in. If I’d had really strong vacuum (i.e. No pot death) I might have recovered.
  • Have one KG of resin and hardener ready to mix. Even two.
  • I took 4 attempts to get the bag on – next time I’m going to make a huge envelope bag instead – it should increase my chances of a perfect vacuum.
  • No gel-coat. It’s a long layup and I was up against the clock. This drove some of the other mistakes. I’ll not be up against a schedule this time.

If I get another output that isn’t cosmetically great, I’ll spray it and be done. If it’s of a cosmetic quality, I’ll have it sprayed in two-part lacquer. This will give a great finish.

3D printed parts for resin infusion

 This is a vacuum exhaust fitting. I’ve designed it to be deliberately flat so the release film will stretch around it. I’ve previously used these silicone connectors from easy composites. They’re quite good and just over 3 pounds each. The connector I’ve printed has a hole for a 6mm hose and a stop at the bottom so the hose just doesn’t sit on the mesh. They also have a larger surface area sat on the mesh to help pull vacuum out. Mine aren’t reusable, and only cost 19p each to print, and take about 15 minutes. 
I did a large infusion for the tub recently, and had no end of problems, to the point of scrapping the tub. I’ll write that up later, but one of the issues was that one of my pipes jumped off the clamp and sucked air in. Rather than use a simple OTS clamp, I’ve printed something specific for a 10mm hose and a 10L bucket. The hose is a snug fit and the height from the bottom of the bucket can be nicely set and held just with friction. No more springing hoses ever again. 

Thinking out loud for the resin load

Area Cloth Layers Weight
4.5 600 4 10800
4.5 300 2 2700
Sum 13.5
Resin 5.4

 

So, I can expect to need 5.4kg of resin to infuse this part, assuming a load of 40% by the time you include pipework, mesh, etc. The actual part itself should only take a load of 30%, but I can measure the weight of the part afterwards to see what the actual load is.

Release Agent – pics of the shiny mould

So, the Marbocoat mould-sealer claims to leave the mould more shiny than if it was just ordinarily treated. Well, if you look at the pictures above, you can see that it actually does. Five coats of sealer and five coats of release agent and you can see the result. 

I masked off the mould for about one inch (I know, thinking in old money – don’t care) around the perimeter so there wouldn’t be any issues with the tack-tape struggling for adhesion. As a comparison, masking tape applied to the treated surface just curls off. 
The mould is treated, the templates are made. The modifications to an old compressor to make a vacuum chamber are nearly done (subject of another post soon), and the spray-booth is complete. The next post illustrates just how Dexter I’ve gone.

3D Printed Intake Trumpets

Or ram pipes, or velocity stacks – whatever.

I’ve made these trial pieces. The plan is to have a veritably huge amount of length variations, so when I set my engine up on the rolling road, I can mix and match to get just the variances in length I need. When I say I, I mean Damien from Daytuner, but you know what I mean.

A study in cores for my tub

Problem

So, I need to decide which core to use in the sides of the tub, where I don’t really need huge stiffness like I do with the base, but I still need to do a trade-off between thickness, ease of working, stiffness and weight.

Weight wasn’t going to be my only trade-off here. I have some others to think about

  • Ease of preparation started to become important when I started calculating the time required to prepare a standard foam such as the Airex. It needs to be scored every 20mm as a grid, and then at each intersection, needs to have a hole pit in (only 2mm or so) to allow the resin to flow through to the other side of the core. I did a square metre of it, and it took over two hours. Very tedious to do accurately.
  • Ease of layup is also a significant factor. Some cores are very bendy, some are very rigid, and some will thermoform. I don’t want to choose a core of marginal better physical properties if it takes me days of frustration to get it into the stack. This isn’t just a simple flat sheet, but a large female mould with complex curves in multiple planes.
  • Physical strength

Method

img_0110-1

 

 

img_0111

  • do a flex-test to see how rigid it is (clamp one end to a flat surface – hang a standard weight off the other end). You can see how the steel rule is horizontal, and the part has deflected.. 24g is the weight.

Results

  • Weight – Soric (24g), 3D Core (23g), airex (29.5g). So, the airex is 2/5 thicker than the other two, and is 26% heavier.
  • Deflection (therefore infer stiffness) – Soric 30.9mm, 3D Core 31.6mm and airex – 20.5mm

Ease of layup

  1. Soric first – it’s more or less like a thick cloth, and will bend into most angles without being damaged
  2. 3D Core second. It’s a bit like hexagons of foam which are stitched together. It will easily follow simple curves, and can be thermoformed into the tighter ones. It’s not great in tight curves and will separate at the meeting points between the hexagons
  3. Airex last. It has some flex but does thermoform very well. However, getting the hot-air gun in there and pushing and shoving to thermoform it is going to be an arse.

Conclusions

  • I was surprised a bit between the 3D Core and the Soric. Deflections were very similar for very similar weight, which is what one would hope to see. This means the cores were performing as a function of the distance they separate the cloth. I thought the Soric would hold a lot more resin than the 3D core mind, and the results were so close.
  • The airex outperformed for stiffness, which is a symptom of the thickness it separated the cores. Interestingly, i could hear the fibers snap when i weighted this core, and it deformed at the end. Not sure why – further thought is needed.
  • I will use Soric for the side pieces. The ease of putting it into the stack and having it follow tight curves makes it far better for me than the foam. The time and effort to score, hole, form and shape these pieces isn’t worth the extra 600g of weight the chassis will carry as a result.

Hard Point design for the tub

Here’s the design for my hard-point for harness mounting bolts. It’s 3mm thick steel, and the channels are 2x1mm cuts. What you’re looking at is the underside. The channels and holes are to allow resin to flow through and past the hard-point. The big hole in the middle is where the 7/16 insert will go and get welded. Each channel has been tapered down at the entry point so the resin can easily flow into the part.

I’m hunting around now for prices to get them CNC’d. I need 6 per side (six point harnesses) and I’m getting a couple of spare for welding practice.

When they actually go into the part, they will need a layer of glass-cloth either side to insulate them from the carbon to avoid any galvanic issues.