EGR valve diaphragms finally getting off the ground

[raygreenwood]

So…this took so long its embarrassing. Just too many projects.

A Samba member sent me a working bus EGR valve about 3 years ago now to work with to try to make a diaphragm for it. Many projects and moving across a few states later. He needs it back. So I have to get this done.

I just happen....right now....to be also needing ball joint boots for my 412 or I cannot reassemble the front end….and I need some to finish some struts with….so I have to make some molds for a few things….NOW.

Typically, this type of work keeps getting put off because its delicate work that means sitting at my desk and workbench for hours at a time. That…and the materials can cost quite a lot. And….with only one single example part at hand to work with….one has to be careful to not destroy that part by accident.

Yes…Sorry SGKent…but you will be getting several parts finally…to replace the part that got destroyed years ago.

By the way…..the molding issue years ago….was contamination. When I started out, I was using platinum cured mold making resins. I have always used those because they are more accurate (less shrinkage) and a longer life for the mold.

The problem was that I had unknown sulfur contamination in the actual original part itself and not the mold release like I thought. So, the resin would not cure. Then I changed to tin-cure (no sulfur sensitivity) ….I then had issues with the mold release working properly with that type…. and finally I went to epoxy…..which defeated the mold release itself….glued itself into the micro cracks in the rubber….and destroyed the original part.

The big problem was getting the original part that had been baking in carbon and sulfur for decades…clean enough to cast. I’m well beyond that now!

Ok…..so I have kept quiet and not mentioning whose part this is but this is where I am in pictures. I hope I am not jinxing this by letting out status now….but at least nothing done so far will destroy the original part.

So here is the problem with the original part, SGKent’s part LOOKED nicer....it was more straight (but not by a huge amount)….but that was because it was far STIFFER. It was less pliable and had lots of micro-cracks….though it was straight and complete. The problem is getting this straight enough to mold with and you cannot see the cracks easily in this picture but you will later.

One thing that made this much easier is the fact that I finally had a whole EGR valve in hand. The metal shield in the left picture was instrumental is working this out.
It allowed me to make an accurate styrene shim…the white part in the next picture. The 3rd picture is the other side. The green layer is a .002” medical adhesive. The white shim is two layers of .010” styrene….so it’s making the flange area .024” thicker total

Not only does this stiffen the part it will make for a tougher part that will allow more clamping squeeze for sealing.

Here it is with the part with the shim applied. Its already pretty straight. You can see the cracks in the dome area…and you can see the other issue in the hole in the dome that we will get to in a minute.
A shim will get applied to both sides effectively making the flange 0.048” thicker.

NOTE: this was one of the issues I anguished over for ages. How precise does this part need to be? How much can I stiffen, thicken or modify it before it no longer works properly?

Once I got to see the whole valve at one time and see the function….I realized that its really a simple SEAL…and nothing more. It needs to be high temp. It needs to seal around the shaft and flange….and allow stroke length. That’s it.

This could probably be made out of flat sheet about 1/16” thick …if it were low enough durometer to stretch for the whole through of the valve …which is only about maybe 3/16”.

Here is the other issue. You can see the key shaped shaft end in the right-hand picture. You can see the ratty hole in the rubber dome in the 2nd picture. You can see the crappy fit in the third picture….AND…you can see the cracks in the rubber that make molding difficult.

So…..

In this 1st and 2nd picture you can see the 0.024” thick disk I applied on this side of the dome. That means that this area will be 0.024” thicker on the new part. In the third picture you can see the 0.024” thick keyhole disc I applied to the inside.
So, the whole dome will be 0.048” thicker at the tip. The keyhole shape that will be cast into the inside is just a cutting guide to cut the hole to shape.

The first picture shows a 0.100” styrene rod attached to the dome. This will be the feeder hole. The 2nd picture shows 0.080” half round rods attached to the edges. These are air vents. The third picture shows the assembly in the molding box. The rods will be trimmed to stay inside. This will be the bottom cast. It will have two locator pins installed.

The box will have the height raised by two more rows to have the inside buck cast. This is a silicone mold.

So here we are. I waited two days to post this to get into the molding

This is the first “pour” or layer on the left and in center. The tricky part is keeping the part level because I do not want to glue the center feedline sprue to the base. I “seemed” to be successful at keeping it level. Seemed….more on this later. After a full 24 hours (it can be shorter) and reapplying mold release…the second pour and then overnight to dry.

Here we are pulling off the blocks after curing.

Yes….its an ugly mold at first glance. The mold release was not 100% successful….and the part slumped about 0.030” on one side after molding while it was curing.
BUT….all of the important details are there. The micro bubbles…well…this particular rubber generally does not need a vacuum step but it will obviously have one from now on. They should not be an issue though.

The mold release is always an issue. This one is a micro-powdered, non-sulfur, non-silicone... wax. It works very well…but is very hard to get evenly applied and can get “washed” or pushed away and around by the flow of the casting compound as you will see later.

I have a client that has a proprietary version of this (wax based) that has a UV tracer so I can SEE the application level. I am working on getting some.
Otherwise, now that “A” mold is finished I may go back to PVA as a mold release because I can see it.

The molded part. Not bad….needs to be de-flashed and trimmed….has some small surface nodules from the mold bubbles…but actually should be functional.

The mold itself, you can see how it had some bleed across the separating line (not an issue) and you can see how the 60 durometer high temp silicone has actually filled the micro bubbles so the next molded part will actually be smoother.

BUT….the mold rubber durometer is supposed to be 29A to 35A. Its a bit low. This is why even with moderate to high pressure holding the mold halves together…we get some bleed through between the halves when pumping the rubber in. The mold is a bit too soft.

So…I will do a post bake of the mold. It should bring up the hardness slightly and make molding the next ones better.

The molded part itself is supposed to be 60 durometer rubber. Its at about 50. This rubber needs a post bake as well. It should harden up. That is also a worry.
Its nicely pliable and stretchy now….but could get a little too hard. But it may not. The gauge may be lying slightly. This type of rubber has what is called “creep”. It takes either a special durometer gauge with a recording needle or a timed usage of the one I have. With a one-minute hold it is showing creep so the 50 may be accurate. The second gauge reding shows what it crept up to after 1 minute.

Materials:

This is a fairly common 50-60 durometer tin cured red silicone. It is good to 550°F for moderate periods and about 450°-475°F constant. So, it easily works with heat as well as Viton. My worry is stiffness.

It works ….”well”….with oils and hydrocarbons. I say that because there are better silicone materials I can…and will,,, use. But….at $300 a quart I will have to wait a bit to make sure all else is well. This current silicone rubber type I already know this should work well enough for an EGR diaphragm.. My testing of this rubber a couple of years back shows that it will work well with grease…most greases. So it will work well for a ball joint boot. But for a PCV diaphragm….no. The oils with fuels in it …not 100%.

The next parts that are going together right now for molding…..411/412 ball joint boots…..and Bay bus ball joint boots! Possibly tie rod end boots…and for sure gaskets for the TB to plenum joint.

So…lastly….the design of this part. Back a few years ago when I did not have a complete valve….I though this part NEEDED to be delicately and precisely designed and fitted. It does not.

Its just a flat seal with a boot that is not really any different than a tie rod boot…just smaller. It is just a stretchable flat seal to allow maybe 0.300” of movement without tearing r overly resisting.

Now that I know the full function….I can make a new buck of this even simpler and easier to mold. It does not need the “accordion” furrow. That can simply be a thicker spot to resist wear where it flexes. It does not need the “half o-ring” on the outside face. That can simply be a 0.060” raised, square edge ring that compresses to seal. The dome of the boot is nothing special at all. It can be rounded, conical or even a square shaped cylinder. Whatever is easiest to mold. It will function.

More to come!

Ray

[SGKent]

[ivwshane]

Omg!!

I only made it 1/4 of the way down, I’m too excited!

So how much and when can I send you money:D
_________________
77 westy 2.0 FI
69 ghia coup 1600dp
70 single cab

[raygreenwood]

[ivwshane]

Wow Ray!! That's freaken awesome of you!

Put me on both your lists and I'll be the first to buy both!
_________________
77 westy 2.0 FI
69 ghia coup 1600dp
70 single cab

[andrewtf]

Put me down for both as well. (No EGR currently installed, but I like to have the option to go back to stock when I want to.)

I need to do my ball joints soon. Depending on the time frame - it may be some Saran Wrap for a year and I'll do them with Robbie (parts critic for evaluation) about next May-ish. His evaluation might also provide some value.

Andrew
_________________
'75 Riviera - 'BIG EMMA' (Pan American highway trip paused for a make over)
'77 Riviera - Murphy' (being reborn.... slowly)
'63 Austin Healey

[andrewtf]

Sorry - odd follow up......

As stated above, I currently have my EGR 'uninstalled'.
I have a cover/block off plate that I made out of.....something.
To install it, I made my own gasket to go below. This would be a much preferred alternative.

So....... Can I:
1) just use it as a gasket and 'squish it' flat below a flat plate?
2) make a run for those of us who have eliminated the EGR that is just flat to use for this purpose. I know I looked for quite a while to try and find this gasket and don't think I ever did. I'd definitely pay for one of those.

Andrew
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'75 Riviera - 'BIG EMMA' (Pan American highway trip paused for a make over)
'77 Riviera - Murphy' (being reborn.... slowly)
'63 Austin Healey

[Abscate]

Ray

Price at $45 for the first batch, pay your self something for your time , and you can send the rest to the Samba for the rare, coveted , double yellow star
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.ssS!

[raygreenwood]

So both of these points are a worthy segment of this whole discussion:

[Abscate]

Exactly, Ray

$11 sale price
$34 shipping and handling

That dove tails nicely into the shipping costs thread



Thank you for your efforts and service , to boot.
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.ssS!

[SGKent]

Ray - if the folks we are waiting on for a EGR body make them (they made the prototypes from plastic before Covid hit), then what makes sense is to make a bunch of them all at one time, make some gaskets and sell them as a repair kit for the factory egr.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[raygreenwood]

[SGKent]

you know more about the molding process than I ever will.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[raygreenwood]

An update:

Running a little behind!. Between work…and the daily driver Golf has a crapped out ignition switch at 214,000 miles (gotta love it!)…..
I did not make the “quad” mold yet….and for good reason.

Typically, if there is going to be a chemical or material issue…why f*ck up 4X the material and parts? Plus….I had to slightly re-design the part. So if this one works better...I will make three more molds of this new "form" or buck.

Not to get into a rant…but I am going to…..with regard to “re-pops” or repro’s….a lot of people have no idea of the difficulties involved….with “remolding” or re-casting a rubber or plastic part.

To put this bluntly…even if you have the existing legacy molds/dies (like so many have asked and anguished over in a million threads)….like we see threads full of statements of….”why cant (insert OEM mfg here)…just take the original molds they had decades ago and make us some parts”…..well….because…..

Even if you have the old mods...and they are not rusted, busted or worn out....Unless you have the exact original formula rubber/plastic used in the original part…even if you have the original molds/dies…..the part will usually have to be partially or totally redesigned…to actually FUNCTION…when molded in a different material.

When tensile strength, coefficient of elasticity and elongation change…when durometer changes…when rebound and tear strength change…..the cross sections of the part must usually change to some degree.

THIS IS….exactly why….when some enterprising small company or person (like me)….takes an original part and ….”re-pops” it…makes a mold from the original part….but uses a TOTALLY different material…..the original shape may not actually be correctly functional anymore.

It may not have any lifespan. It may not work well. Those damn steering column couplers are a case in point.

What worked in a thin cross sectional area with one material….may not work with another. This is not saying the new material is not “workable”….it just may not be workable with cross sections of a given thickness or thinness in the same areas.

This IS what I have found to be the case in this process.

One must understand that in a rubber that was originally injection molded ….like the stock Viton….in an injection mold…you CAN get a higher overall DENSITY of the material or rubber because of the high pressure capability of the injection molding process.

Gravity casting…like I am doing….is at atmospheric pressure. So…certain areas that worked in the thin cross section with high density injection molded rubber…must be re-designed to work in lower density rubber.

This is exactly why ….so many promising “re-pops”…turn out to suck….function wise. It may not actually or always be a rubber formulation thing. It may be a density/pressure thing.

In dissecting the first couple of parts…I have found that to be true. I expected it…but hoped it would not be a big deal. It is.

But no matter…..I expected that.

Here is a dissection of the first one. It did not take much. It tore at the thin flex joint between the dome and the flat gasket area where the yellow arrow is.

The other issue is this. The original part…functional though it was…was kind of “designed” stupidly. Or really it was designed around its material.

My point: See that stainless steel shell that covers the rubber dome? That is in effect…the stroke limit for the valve rod and diaphragm.

So…since the diaphragm is not being used as a vacuum or pressure diaphragm…meaning its not the mechanism that makes the valve move or operate…(that’s what the lever is for)…..further meaning its NOT like a brake cylinder cup seal…or a hydraulic/pneumatic cylinder seal…..why did they make it like one?

See…the valve section has a stroke from seal face to seal face of ~0.240”. So, the amount of stroke from open to closed is roughly 0.125” in either direction.
The amount of space under the steel dome for the rubber dome to operate in is right at 0.335”…right at 0.100” extra.

The original dome diaphragm is kind of in the middle in total height inside that steel dome. This means that it must STRETCH as the valve moves to meet the end of the stroke.

There is no need to have the rubber diaphragm constantly loaded with STRETCH in the closed direction. Why stress the dome in its materials weakest direction? Just make it nearly full length under the steel dome so that its “neutral” in load. On the open stroke it can simply compress like an accordion…also a low stress load.

Here is the updated design:

Looking from the o-ring side. The flange area of the diaphragm will be 0.050” thick. This is made in this “buck” by using two 0.020” sheets of styrene stacked on a 0.010” sheet which is the main surrounding sheet.

The hole around the o-ring is wider than the hole for the dome part…so the 0-ring is recessed into the surface of the surrounding sheet 0.040”....and its a 0.080" cross section o-ring...so it will be like the stock o-ring....a half surface o-ring.

The screw holes drawn onto the part in this picture are just place keepers. More on that later

Here it is from an angle so you can see the thickness.

NOTE: I mentioned this last week. The reason why its on a large surround sheet …and will stay that way for molding…is that:
A. that 0.010” thick sheet gave me the exact stack up I wanted…..and

B. that sheet will be a “flashing” area where any air bubbles will have plenty of room to slide outward and collect. Its all going to be trimmed off.

This 0.010” sheet was placed on the bottom…the dome side….the first section cast during mold making….so give me as clean of a surface as possible so we do not trap air.

Like this…..this is the dome mockup from the other side. You can barely see the outline of the flange styrene on the other side.

Here is the fairly complete “buck” waiting for some sanding and trimming…

Notice if you can see this….that the screw holes…are no longer “drawn” on.

Those are exact diameter discs of 0.010” styrene made with the punch that will be punching them out…glued on. This will give me raised witness marks for setting the punch once these gets molded. And…its on the top side now for the second half of the mold making…where I can use a pick to remove any bubbles that collect while pouring.

This is the dome side. With its flat 0.035” thick cap disc. This needs filling around the dome to sheet joint and a little sanding,

OK…the flat dome face….

This diaphragm locating step is ~0.065” to 0.067” high. I am using 0.050” of that for the diaphragm thickness leaving right at 0.015” for the flange washer below to locate. That’s all it needs.

Here is the new form or “buck” in the old mold box. I will be making a larger box.

It is sitting on four pegs…one under each corner. This keeps it level and allows me to clamp it so it will nit float while pouring.

You can see how high the dome comes up inside of the shield …compared to the old one below.

Here is the first half curing after the pour. The two arms hold it flat and tight against pegs in each corer. . The 2nd half will be in the am.

A couple of quick note about producing this kind of stuff. I noted last week that actually the prepping and molding do not take that much time.

What time is not captured.....is the thought process and design time and searching for materials time. I have spent YEARS with this and numerous other projects on notebook sheet. I drive hours and days at a time for work. If I am not on the phone in the car....I m thinking about various projects and how to get to the next step.

Every time I am somewhere...whether its in a store, on a website, in a factory etc.... where I see a part, material or chemical or idea that may help for projects I have running...I either take pictures, make notes or take a sample or buy a piece.....add it to the collective bucket of work for various projects.

The ball joint boots, tie rod end boots and several other rubber molding parts are all tied into this. Yes...its a long time between doing anything with this planning and knowledge....but it keeps me from making dozens of expensive mistakes in a row for trial and error.

Other vast pages of projects are things like rear disc brakes for the 412, rear trailing arm bushings, new bearings for the countershaft, windshield gaskets, interior parts....Jesus the list goes on!

More to come!
Ray

[ivwshane]

Correct me if I’m wrong but isn’t the rubber diaphragm just a seal? Are there no other designs that can seal such a piece while still allowing the plunger(?) to work? If so, does that change/affect the material choice?
_________________
77 westy 2.0 FI
69 ghia coup 1600dp
70 single cab

[raygreenwood]

[raygreenwood]

Vents and feeders went in last night:

Second pour is done. I will get to see if the mold is clean and sharp later today.

This mold should be cleaner and sharper than the first one. This particular silicone is a low viscosity version. But...normally the manufacturer states that it "should" not need vacuum degassing ...and usually I find that to be true with this product.

But...the first mold had too many fine bubbles. So I pump this batch down on each pour. I saw about a 45% expansion of the silicone in the vacuum cup....and then it dropped down to normal after about five minutes of vacuum to about 25".

The main casting silicone for making the part is about twice the viscosity. It DOES recommend vacuum. Its more difficult to do and takes longer.

Ray

[ImAddicted]

I have nothing substantial to contribute to this thread other than...

... damn, this forum is kick ass because of the people. Seriously. Ray, I love all the sciency stuff, too. While I know I'll never go down the road you are, I feel smarter and more empowered just be reading this thread. Thank you.
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1979 Transporter (sold)
KC1MUR

[raygreenwood]

Muuuuuuch nicer mold this time around!

The little white part on the edge of the dome is just lint/crap stuck there from demolding. It came out pretty smooth. The hole right in the dome center is where the silicone will be injected. All of teh others are bubble vents.

After separating the top from bottom. It came out very clean so the mold release was working much better this time. It was iffy last time....but the fix was all in application technique.

The inner mold face is very smooth. Excellent for keeping bubbles out when we mold.

So vacuum de-gassing really helped this time.

But...these molds are very soft and slimy . This typically means they have a lot of silicone oil in them . Some of this will cross link further over night but I will post bake them to drive out more.

The 60 duro high temp silicone will be interesting to outgas. It will take longer.
Also....outgassing and getting rid of bubbles helps the tear strength.

More to come!

Ray

[Clatter]

Damn…

You GO Brother…!
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