Plugging Hole in Pressure vessel via Staked in Ball 2

[BrianRoach]

Not sure where to post this so I am putting it here.

I am looking for design advice for plugging a hole in a hydraulic brake master cylinder by staking in a steel ball.
The hole I am plugging is shown in the image below:

The cylinder is filled with brake fluid at pressures up to 150bar. The hole that has to be plugged is approximately 6.1mm. The hole diameter can be varied as needed, but I want to us a 6.35mm ball for the plug. The cylinder is made out of extruded aluminum (6061). Currently we are using an Advil high pressure plug to fill the hole, but for manufacturing reasons and cost we want to change to a staked ball. The staked in ball would look like this image:

I need to determine the diameter of the hole, the shape of the staking tool, the required staking depth, the staking force, etc. Is there a way to determine these parameters through calculation or is the only way via experimination in the lab?

 

[vpl]

FYI: Your images didn't come through on my computer (consider using the file upload on engineering.com).



Patricia Lougheed

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[MintJulep]

Is an Advil plug like one of these?

http://www.farmingtoneng.com/

 

[BrianRoach]

Sorry. I followed the editing tips for posting an image to my post and it didnl' work. I will try again.

Also, I mistyped. We are using an Avseal II plug made by Avdel (Accument). Here is a link:

http://www.avdel-global.com/en/products/sealing-plugs/avseal-ii.html

 

[MadMango]

How thick is the sidewall of your extrusion?

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the be

 

[BrianRoach]

Here is another sketch with some dimensions. The master cylinder is basically a cylinder, so these dims apply around the perimeter of the part.

 

[MadMango]

Have you considered using a Koenig plug? No special tooling required for machining the seat or setting the ball.

http://www.sherex.ca/Products/Koenig_Sealing_Plugs/koenig_sealing_plugs.html

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the be

 

[hydtools]

I agree with MadMango. We used Koenig plugs in aluminum to seal to 3000 psi. Easy to install. Easy to inspect for correct installation.

Ted

 

[BrianRoach]

We have looked at these. Before we used the Avdel plugs, we used a different type of plug also by Sherex(same company that makes the Koeing plug). In all cases cost is the driving factor. Staking a ball always costs less than any standard plug that I can purchase.

 

[israelkk]

What about the legal aspects of using just the ball instead a qualified solution as Lee Plugs or Keonig Plugs. You should check the code you are designing the pressure system.

 

[hydtools]

Consider these costs. Development to determine correct, repeatable hole production. Development to determine correct, repeatable staking. Testing to prove your process to the satisfaction of withstanding product liability pressure, not just product application pressure.

Direct your cost control effort to more productive activities.

Ted

 

[unclesyd]

Here is the Lee plug that we used on all our hydraulic and polymer maifolds.

http://www.minstac.com/PLUGWEB2.NSF/Plugs!OpenView

 

[btrueblood]

What israelkk and hydtools said. You are apparently making an automotive brake manifold; the liability on those parts is enough to put your company out of business many times over should your product be linked to automobile accidents, injuries, or fatalities.

 

[BrianRoach]

Thanks for all of the advice, but I fully am aware of all legal/code/liability issues that may result from ball staking. These types of situations always occur within automotive products and it is up to the product engineers to ensure that all such risks are handles to ensure that no issues occur in the field.
I think you would find that the manufacturers of these standard pugs would assume very little liability responsibility in the event of any failure that might happen in the field.
As for the costs, I agree that all costs need to be considered, but we will be making approx. 1 million of these cylinders each year each with 5 of these holes that need to be plugged per cylinder. Therefore with, the cost savings of staking 5 million balls per year vs. buying 5 million standard plugs can be significant , and this costs savings will justify the engineering development necessary to determine the proper bal staking design. Also, manufacturing has difficulty feeding and installing any sort of standard plug that needs to be oriented (balls can be easily fed into the assembly line). So… back to my original question. Does anyone have any idea of how to design the hole & staking tool parameters without excessive trial-and-error in the lab? The lab work will still be necessary to confirm the design, but I want to get the design close before I start in the lab. Thanks for any help that can be provided.

 

[MikeHalloran]

I've seen something grossly similar done with lead ball plugs in zinc (or maybe aluminum) carburetor bodies... but they only had to withstand a few inches of head... and they didn't always do that.

I'm not saying it's impossible, but it's so obvious that someone must have tried it already... and designed it out, since we don't see it in practice.

To answer your question, most any mechanical engineering graduate should be able to analytically evaluate your starting design, without even using any fancy tools. I suggest you rent such an engineer for a while.

You also might talk to some vibratory feeder suppliers; they have decades of experience orienting parts that are nearly but not quite symmetrical. I don't see expanding plugs as being particularly difficult to feed and orient.

The term of the financial balance equation that you seem intent on ignoring, and which the other members keep trying to highlight, is that you could easily lose five million dollars in a judgment resulting from a failure of any one of those five million cheap balls. Better hope you don't lose two.





Mike Halloran
Pembroke Pines, FL, USA

 

[Seano5150]

hi there all
I've been involved in quite alot of hydraulic manufacture and maintenance ,and ball staking is a common and accepted practice for sealing manufacturing holes in componentry with system pressures up to 10000psi... force is calculated on psi to surface area so the force against the ball is fairly minimal,all we used was a pin punch to pop the ball in and a 3/8 ball in the end of a punch to pein the hole over(these were only small production runs how you do this on a large scale would obviously differ.. oh on the legality side of things all hydraulics have peoples lifes in the balance every application the potential for failure is allways there be it a crane or a car!!

 

[BrianRoach]

Thanks Seano51450! You are the first poster who has attempted to address my original question. I must say I am disappointed by most of the replies. Everyone here appears to be implying I am an idiot for even considering this idea. However, as Seano5150 mentions, it is very common in the auto industry as a way to seal hydraulic cylinders. If you don’t believe this, just open the hood of your car and look at the ABS hydraulic unit as an example of where this is commonly done. As to some of the other comments posted:
1. I am a graduate mechanical engineer so I don’t need to “rent one”.
2. The calculations would appear to be straight forward, but it comes down to the fact that the force holding the ball in place is the normal force due to the interference between the ball and the hole and the friction level between the ball and the aluminum housing. So what is the simple calculation that tells me what the normal force is for a steel ball in an aluminum housing for 0.05mm interference? What about for 0.1mm interference? If I knew how to calculate this force, I wouldn’t have asked the question in the first place.
3. The manufacturing engineers I am working with have over 30 years experience with assembling similar products, including the types of plugs that have been mentioned, using various feeder devices (including vibratory ones), and they would prefer using staked in balls.

Just because we have a solution that works (plugs), doesn’t mean we are not constantly looking to find a better solution (balls) based upon cost, ease of assembly, etc. In fact in the auto industry, 90% of the design work is not inventing something new, it is optimizing/refining existing designs.
So I guess my point is, I realize there many ways to seal a hole in a hydraulic vessel, but I am looking for tips on how to do it using a ball from someone who has experience with this common approach. I am disappointed that of the many replies, only one addressed the question. Although I appreciate these other suggestions, I find it a little insulting that when I try to politely redirect the topic back to the original question, I am told I am an idiot for even wanting to do it this way in the first place! The whole reason for my post in the first place was that this is a very common practice and I was just looking for some advice from someone who has done this before on what I should be looking for in my design.
Thanks to everyone for all of the replies (good and bad). All comments/ideas/suggestiosn are always appreciated!

 

[hydtools]

Look at press fit equations. I am not near my references to quote equations. It looks like you have to resist about 100 lbs(440 N) of blowout force due to hydraulic pressure.

There are rotary staking tools available that could be set up to do the staking. Or simply a push tool to do the staking.

Drill a stepped hole to provide a step against which the inserted ball would stop.

Ted

 

[MikeHalloran]

It isn't very common among the experience _here_.

Seano just wandered through the door; he could be a high schooler for all you or we know.

The simple calculation is in Machinery's Handbook.

It gets less simple when you peen after pressing, and Mr. Poisson gets involved.



Mike Halloran
Pembroke Pines, FL, USA

 

[vpl]

Seano just wandered through the door; he could be a high schooler for all you or we know.

or a co-worker that's supporting your opinion (as has happened before.)

Nevertheless, you get what you pay for. Since this is free advice, you have to take the bad (in your mind) with the good.

I am a graduate mechanical engineer so I don't need to "rent one"...If I knew how to calculate this force, I wouldn't have asked the question in the first place.

But you're asking strangers on a free internet site to do the engineering with no idea of whether they're giving you good advice or not. ...which led to the recommendation that you hire someone. No one's questioning your competence, and you admit a few sentences later, that you don't have expertise in this area. And as several posts have pointed out, failure to properly design this part could have unpleasant repercussions.

Finally, making snide comments doesn't endear you to those who willingly provide free engineering expetise here. People are more likely to help those who are willing to help others rather than those that complain about the lack of free answers.



Patricia Lougheed

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.