Si3N4 ball bearings

[Thrud]

My balls have flat spots - on my Flexbar Ball Bearing V-Blocks. This is normal - it happens over time. Replacing them is becoming annoying - they don't make balls like they used to!

I ordered some Cerbec (Saint-Gobain Advanced Ceramics) Silicon Nitride balls (Si3N4) to replace the Chrome Steel balls. They are Grade 5 balls and exhibit better properties than the steel balls. One thing I have noticed is they are extremely slippery compared to Chrome Steel. You can feel the friction differences by rolling the 15/16" test ball for the blocks on the regular BB's vs. the Cerbec BB's.

I am sold on these things.

I am working on a few projects with them - I want to try them on a set of ball centers. I just have to figure out how to join then to the centers. So far, my best guess is a blind hole drilled in the Cerbec with a diamond burr and then bonded to the steel center with a high temperature adhesive. I don't think they can be brazed on.

Any suggestions?

[billr]

hello again Dave.

might be out of my league here, but if you are talking about lathe centers, would a 60* countersink not work. center drill tailstock center and part. ball between them.

can't take credit for this as an original idea. saw something similar in a taper article i was reading.

how big are your balls? [loaded question there] i sure would like ot be able to afford some of those ball bearing v-blocks.

peace.
bill

[Rustybolt]

How much of the ball are you going to use for a center? Couldn't you just bore a socket and then roll the lip over the ball. Sort of like a ball point pen. Maybe drill a little hole in back for lubrication.

[darryl]

Just a thought, carbide teeth are brazed onto steel sawblades. Maybe those balls are too expensive to try brazing unless you know it works.

[wierdscience]

I can tell you this much,I wouldn't let anybody braze my balls

Maybe would it work to insert the ball into the center rather than vice versa,you could bore a blind hole with a radius bottom slightly deeper than half the diameter and maybe a half a thou smaller then shrink and roll the outside egde of the cup to hold it in.

[randyc]

wierd, see rustybolt's earlier post.

I don't think your suggestion is an optimal solution, there may not be enough of the ball protruding to give good bearing contact with the mating part.

But it's my opinion - circumstances are not general - it might work just fine, depending on the situation.

[wierdscience]

Well,I was thinking of a say 3/4" ball with a 7/16"deep hole,maybe even roll the lip in while its hot?Coarse if hes making something like a tooling ball then no it won't work.At that point I would say get some trimetal and flux and go at it.Heck use HF to make it neat.

[This message has been edited by wierdscience (edited 09-18-2003).]

[Bill Neufeld]

Dave:
How about using an EDM to burn the hole to the right size and depth. Fit the rod and braze in an inert atmosphere using a nickel bearing braze? Induction heated perhaps.
Bill.

[Thrud]

Bill N
I thought of that, the problem is I do not know if you can even braze Silicon Nitride at all. There is a company that has a foil that welds ceramics/metals together - but at $150 for a 1" square my thoughts at the moment are a high temperature adhesive.

I can turn the end off a hardened center with little effort. I had planning on using some Jacobs mt#2 -jt33 shanks I have laying about, boring a depression and attaching the Cerbec ball to it.

Rusty, Randy

I thought of that, but for turning tapers the crimp would get in the way (sooner or later). I need 5/8ths. of the sphere free. The pen nib concept will work for my "other" project - thanks for the idea

WS, Bill R
I thought about a shallow cup to hold the ball by pressure against the tail end of the shaft. My concern with that is cutting pressures could pop the ball out under under power on steep tapers.

[This message has been edited by Thrud (edited 09-19-2003).]

[winchman]

Could you use the end of a valve pushrod for this purpose? Seems like it would work, and they're easy to come by.

[randyc]

Thrud:

Hi-temp adhesive sounds like the right choice. I don't think that silicon nitride can be brazed without first metalizing the surface to be joined.

Since the ball will be subjected to temperature excursions, the choice of the adhesive is interesting. The compound must be able to withstand temperature deviations and maintain the bond without fatiguing.

But the joint also must remain "flexible" enough to accommodate the relative movement between the silicon nitride and the metal to which it is attached because of differences in thermal expansion.

This is a common problem in the electronic industry and is the reason that "kovar" was developed. Kovar is a pretty good match for glass and for many ceramics (linear Tc).

I've also used 440 stainless for high temperature fixturing of metalized ceramics to be brazed. This would be an admirable choice (if the Tc fits silicon nitride) since it can be hardened.

[Evan]

Brazing is out. Here are a few of the charateristics of Silicon Nitride. The last is the one that matters.

Good thermal shock resistance
Good high temperature strength
Creep resistance
Low density
High fracture toughness
High hardness and wear resistance
Electrical resistivity
Good chemical resistance
Good oxidation resistance and not wetted by molten metals

[darryl]

Another thought, is there some acid or whatnot that can etch silicon nitride, mask an area and rough it up before adhesive bonding. Or arc the area to be bonded to rough it up.

[Evan]

Thrud,

I did some poking around on Loctite's web site and found this: Hysolآ® E-214HP Epoxy Adhesive

The description:

PRODUCT DESCRIPTION
LOCTITEآ® Hysolآ® Product E-214HP is a light paste, industrial grade epoxy adhesive. This one-component, no-mix, heat activated formulation develops tough, strong, structural bonds which provide excellent peel resistance and impact strength. When fully cured, the product offers superior thermal shock resistance, excellent mechanical and electrical resistant
properties, and withstands exposure to a wide variety of solvents and chemicals.

TYPICAL APPLICATIONS
Bonds to a wide variety of materials, including metals, glass,
ceramics and plastics.

Try this link: http://www2.loctite.com/int_henkel/l...sp_language=en

[Bruce Griffing]

How about a variant on the ball point pen thing. Make a thread on cover that captivates the ball in a blind hole. That way you can remove it easily.