Some new gasket material technology

[raygreenwood]

So.....I was asked in a PM yesterday about transmission gaskets. How very timely!

Bear with me now...there is always a back story

I have been working on the gaskets for my ball joints. WTF ball joint gaskets you ask?

To make 411/412 ball joints grease-able and survivable....you need to add a small grease hole in the very center of the ball joint inside the back cup. This drilled hole goes into the cavity in the middle of the spring. It will not hurt the joint at all.

It allows you to use that cast in "weep hole" on the inside near the strut tube to install a grease fitting. This allows you to pump grease into the back cavity and force it through the joint and into the boot area.

However....that very term "weep hole"....is a problem. It exists because this area is NOT watertight fro the factory. When water gets in..its why many times the steering knuckle and strut tube are rusted together...which degrades the nice machine fit.

So...when you put this all back together...you need to ut gaskets between the strut tube and the steering knuckle on top...and the steering knuckle and ball joint on the bottom.

The problem is that...just using RTV does not work well at all. Also...using most of the cheesy vegetable parchment gasket materials...leaves you a gasket that it is overly compressible. This can cause loosening in the bolts...bad by itself...and leakage...which is worse because now you have a grease hole into the ball joint inner cavity.

So....in the quest for decent gasket material...and not just for the ball joints....but for items like the steering box, the phenolic blocks and the manual transmission.....I have been working.

The definitions/characteristics I wanted for the gasket paper/material:

1. It must have malleability....meaning some compressibility ...so it can seal fine imperfections between machined surfaces

2. It must reach a load point where it no longer compresses...so torque/compression on the gasket does not change

3. It should have an elastomer outer face so that it can be applied DRY or wet with a sealer

4. It should have very high temperature range....550F minimum

5. It should be precise in thickness. I need to be able to install one....and make sure that when it reaches its crush limit...it is the proper thickness. This is critical for transmission housing gaskets.

6. It should be rot proof and waterproof

So....a while back...I thought that precision aluminum sheet/shim stock cut into gasket shapes would be ideal....especially for transmission gaskets. The problem I ran into is A. getting it in alloys that were soft/malleable enough and B. getting it in a range of useful thicknesses and C. being able to make it flat and cut it...with or without a die.

Starting checking out copper...etc. Whatever metal I used...I know that I can either precision roller apply or print...high temp silicone on the outside for the outer elastomer seal.

So......I was making baked potatoes and corn on the grill this last weekend...using lots of aluminum foil.... WTF

So.....The first gasket sets I made are done and are for the ball joints.

I applied precise layers of 600F RTV with a roller to smoothed foil....and applied each layer with a nip roller.
I can generally control RTV and other elastomer applications to within about +/- 2 microns....but I had some trouble with this one (found the fix after I was done)....and didn't really know how many layers of foil to start with.

So..these came out a little thick for where a thinner gasket is needed. But..they are very precise and uniform in thickness...and nice and flat....and rigid.

These gaskets came out to .022" thick. They variance in thickness is +/- .0002". Not bad.

These have 8 layers of foil and 9 layers of RTV. The foil is .00096" thick on each layer....putting the RTV layers at about 22 microns each including the 0uter layers...which is just under .001" per RTV layer.

In future applications the inner layers will be held to about 12 microns or about .0005" or less
The outer elastomer layers were printed and then calendared to make thickness and texture uniform.

Some pictures:

the gasket on top of the ball joint

Tipped so you can see the texture

Close up of texture

Microscope shot (60x) of the layers


The crush on these takes them down to about .016" and they lock up rock solid.

Sorry the bolt holes are a little rough. My 10mm punch was to dull to to do them justice so i cut them by exacto knife.

Ray

[Lars S]

Nice developement Ray! Cheap stuff too.
The microscope shot, is it before or after the compressing?

Lars S
_________________
Porsche 914 -72, Bahia Red daily driver
VW411 2-d -70, White, sold
VW412 4-d, -73, Gold Metallic, daily driver
Suzuki T500, -69, Candy Gold, sold
Suzuki K50, -77, Black, daily driver
BMW R69S -69, White, sold
Husqvarna 118cc, -47, Black, Sold

[raygreenwood]

[raygreenwood]

So I did some crush testing last night and did some looking through my standard 600X microscope. I wish I could photograph through it easily (I have a 500X electronic/USB microscope but its out for repair to the polarizer).....

So....a couple of observations that lead me to this experiment and the choice of materials.

1. Over time the need for a gasket that has a surface malleable enough to fill in grooves, file marks etc.....lead me to the aluminum foil thought process. In several industrial processes we use simple aluminum foil to make detailed but quick and dirty....surface texture impressions of machined, cast or worked surfaces on both plastic and metal.

Take a sheet and burnish it down....or clamp it between two surfaces. Peel it back up and you can see where it extruded itself into or over surface imperfections.

2. The problem with ever seriously thinking about using aluminum foil...commercially available aluminum foil...for a gasket facing is that the very characteristics that make the aluminum foil malleable enough to "flow" into surface imperfections...make it terrible on its own as a gasket face.
A. It has very low strength when pulled or twisted laterally in a plane
B. It has no "memory". Once you force it into shape between two mating surfaces with pressure....if there is any lessening of pressure...due to heat expansion/contraction, bolt stretch or vibration....the aluminum foil does not spring back.

3. Because of "B"....using the foil as a facing for a gasket would require something in the inter-layers with elastic memory, serious adhesion properties and the ability to reach a crush/compression point where it becomes a solid and "locks" up....to prevent thickness reduction that may stretch the foil layers enough that they reach the tearing point of the aluminum.

So....in starting this I chose the RTV product on my shelf that had high tack, high adhesion and the highest durometer of the bunch (this is about 42-45 durometer when dry)...very close to, but a little less than normal Buna N rubber.

Findings so far:

1. In the original pictures, the surface texture while it looks heavy...is actually pretty good for a gasket facing....but still large. I can make it about 50% smaller texture.

2. There is interlayer texture to the RTV as well. It is much less than the external facing texture.....but enough that what is happening is that malleable aluminum is wrapping itself around the texture. This is why you get the "wavy" look....kind of like taking a cross section of a Lasagna

On one hand this is excellent!...it means that the aluminum foil layers are malleable enough to extrude themselves into the valleys between the peaks in the RTV texture...effectively sealing any gas or oil travel.

The largest valleys in the the thinnest RTV layers are between 8 and 12 microns. I have found no voids so far.

3. On the other hand ...the the durometer of the RTV is high enough that it acts like a spring...it will crush down....but springs back.

The permanent reduction of about .003"....is from the foil layers flattening out and flowing into the valleys.

4. During crush, the gasket reduces thickness by about .006"........but about .003" of that returns from the spring expansion of the RTV when you take pressure off.

Thats what I was looking for. A gasket that can expand and contract with temp change and bolt stretch.

Its also clear that the RTV is keeping the aluminum foil from tearing from lateral pull/expansion. What I need to find out is if....this can still hold true without an outer layer of cured RTV.

If so...the aluminum itself would be excellent as the outer gasket face as its ability to extrude itself into surface imperfections....and not have any texture with possible pores in the valleys of the texture for oil to leak past.

I can reduce the texture of the RTV...but some of that is within the nature of each RTV itself and how well it can shear thin (if at all) on application. Some RTVs I have worked with...I can already achieve surface profile Rz of down around 6-8 microns.
The current Rz of the gasket I just made...is about 15-18 microns......before you crush the peaks when you clamp it.

In the picture I took last night of a part I clamped....with almost 70 ft lbs of torque show the thinning/ extrusion into the valleys of the aluminum...and the fact that the RTV rebounded to its previous thickness perfectly.

Pictures:

These are done at 230X magnification

This picture is of the edge of the cut gasket before crimping. Its angle shows a lot of highlights at the edge of the cut aluminum from the aluminum being burnished over...even though I used a zirconium plated blade. But it shows the fairly even distribution of the aluminum...as will as that one thick middle layer I lost control of.

This picture is again...before crimping/compressing of the same general area of the gasket above...but the angle shows the uniformity of the aluminum llayers...meaning fairly flat and even. It also shows how much thicker the RTV is. I dont know if the RTV being that thick is a plus or minus yet.

Same area after crimping/compression...note that the aluminum appears to "flow" into all of the peaks and valleys...and has gotten slightly thinner

Same area with different lighting angle.

These last two pictures are done with side lighting instead of the ring-light on the microscope because once they are compressed there are so many angles to the aluminum edge that the polarizer cannot cope with them.

More to come...Ray