Restrictor - ABS Plastic

[Horace]

Hi,

I'm thinking of using a rapid prototyping machine to make our restrictor for the air intake instead of lathing it with aluminum. However, after some manhandling with the plastics and looking at their specs, its E=290000psi which is 34+ times weaker than aluminum worries me. After doing Cosmos it shows that it holds up well, but I also know that Cosmos isn't too accurate with our other parts since it has limited modeling control.

Can I get some advice on past experience of other teams using ABS Plastic for intake construction?

Thanks you

Horace

[Horace]

Hi,

I'm thinking of using a rapid prototyping machine to make our restrictor for the air intake instead of lathing it with aluminum. However, after some manhandling with the plastics and looking at their specs, its E=290000psi which is 34+ times weaker than aluminum worries me. After doing Cosmos it shows that it holds up well, but I also know that Cosmos isn't too accurate with our other parts since it has limited modeling control.

Can I get some advice on past experience of other teams using ABS Plastic for intake construction?

Thanks you

Horace

[Brett Neale]

We've been using it for about 5 years now I think. We use SLS Nylon, specced at 19mm and reamed with an adjustable reamer out to 20mm. It's a challenge designing stuff with the material, but it's worth it when you have your intake a week after sending it away to be made!

The only problem with the SLS is the amount of finishing required. If you want a silky smooth internal surface on your restrictor then don't bother with SLS unless you want to sand your life away. I'd imagine a turned aluminium one would be much easier to get a nice surface finish on.

[BenB]

Use an SLA machine. SLA has the highest surface quality of any rapid prototype process. F1 uses these machines to make wind-tunnel models of their cars for this reason.

[Horace]

Is it strong enough if the ABS Plastic restrictor is made with a webbed wall instead of a solid wall?

I'm new to rapid prototyping and plastics, as I'm sure most of you can tell

[Brett Neale]

Ours isn't webbed. Make sure you over-engineer these things if you're not confident, cos a) they're expensive and b) they're quite critical... We took a few years to get to grips with using it.

[Horace]

Hm, good point.

What are the forces on the restrictor in critical condition?

100Pa outside and 0Pa inside?

[mtg]

Just be careful about the coefficient of thermal expansion. When I was in school, we almost accidentally got into trouble because of measuring our nylon restrictor after endurance when the whole engine bay was hot- and the restrictor grew in size.

[Brett Neale]

Another good point! We stuck ours in the wind for that reason.

Other loads you might have could be the weight of the throttle. If it's cantilevered on the end (might be a sizeable weight too...) then it could vibrate.

[jpusb]

I think we will be trying it with ABS this year for the whole intake AND throttle.
My worries aren't really about the intake restrictor. If you use a decent wall thickness, the restrictor is so small that it will be really hard to deform, and the loads there are far, far away from the 22 MPA it holds before yielding. What I fear most is deflection in the plenum walls, the one looking to the runner entrances, since one of these walls is almost a flat wall (because of the shape we needed it to be).
About the throttle I will have it build for about 1 mm less than the final ID I need for throttle sealing. What I'm worrying about are the bearings seats there.
I think that for us (newbies this year at the rapid prototyping stuff) testing will be the best way to learn...

[Faterooski]

We too are building our restrictor out of rapid prototyped ABS. We went with a 3mm wall thickness and made sure to round, chamfer, and fillet every edge and corner. The guys who are building it for us said as long as you do that and use a reasonable wall thickness you should be fine.

[Horace]

Do all of you make yours solid or have you experimented with webbed?

[Dan Lentsch]

We used an ABS plastic restrictor last year.. it worked great! to address the durface finish, we speced ours to 21 mm and smeared epoxy on the inside untill smooth.. sounds odd, but it worked really well and was super smooth

oh, and we went with solid last year.. we experimented with webbed and it was pretty flimsy