# need information about Autofrettage system

• posted

Hello everybody,

I want to manufacture a cylinder for my ultra high presure pump (waterjet pump) but i do not know enough information about how to manufacture it.

The cylinder size is below

Inner diameter : 29 mm Outer diameter : 77 mm Length : 236 mm Materail : ?

4000 bar pressure in genereted inside the cylinder, so it is necessary to make auofrettage process to extend cylinder's service life.

I do not know the material of this cylinder. Can any body help me? Whic material is suitable for this cylinder? How can i make autofrettage process? How is the autofrettage process? what is the autofrettage pressure? How many seconds can i hold the cylinder under high pressure during autofrettage? How is this process?? Please advise me about this process and email me at mt snipped-for-privacy@yahoo.com

Any help would be highly appreciated Tastan

• posted

Without looking up any allowance for thick walls etc., I simply compute the wall tension for half the actual cylinder wall thickness so, across a longitudinal section through the cylinder on a diameter I compute the force as 14.7 psi X 4000 X 235 mm X 29 mm / (25.4 X 25.4) in lb (621120 lb)

I compute the stress on the wall as

621120 / (235 X 24 / 25.4 X 25.4 ) in psi (71050 psi)

Hmmmm....lets look for a yield strength > 80,000 psi in Matweb:

Steels: Any of the following, in appropriate condition/ heat treat......

1035 1045 1040 1050 1055 1060 1080 1095 1118 1132 1137 1141 1144 1340 1574 18Ni(200) 4023 4027 4118 4130

And that's as much as I can invest in helping you copy some existing design - or school assignment or whatever it is....

Good luck

Brian Whatcott Altus OK

• posted

Tastan- Fabricating equipment that will handle pressures of 4000 bars is not for amateurs. Brian Whatcott has given you a rough calculation of the stresses on the piston cylinder walls based on a water pressure of 4000 bars. However, you need to consider that 4000 bars is the average static pressure of the system downstream of the cylinder's check valves. The peak pressures inside the cylinder will be considerably higher.

Please consult with a professional engineer who has experience with high pressure hydraulic systems before proceeding further.

Good Luck, Paul D Oosterhout I work for SAIC (but I don't speak for SAIC)

• posted

So all you would like to know is what material to use, how to manufacture it, how to do it, and the tricks of the process? Would 11 x17 drawings be OK?

Do what most knowledgeable engineers do - pay for a consultant who has experience.

You knock-off cheapskates will never know if someone is giving you just enough bad among the good, to sabotage your efforts.

So pay the man who knows, pay him for his time spent learning.

Hint - Autofrettage of pumps is not something you ask about on the internet, other than for idle curiosity.

Advice? Find someone who knows, and if the local phone book and hydraulic network gets you no results, then try this on the NGs:

"Looking for consultant in autofrettage of hydraulic pumps. No local consultants available."

• posted

Hello,

This cylinder will work under cyclic 4000 bar, the pressure inside will change always between 0 and 4000 bar, and the stroke is 29 per minute. so the fatigue is the main problem on the service life of the cylinder.

Of course i know i need somebody who has knowledge on the process but there is no one i can consult.

Autofrettage pressure is higher than normal working pressure of the cylinder, it's about 10.000 bar, and this process must be performed in a closed room with no man for safety.

We just do not know the parameters of the process, i will put some gages outer surface of the cylinder and measure the displacements until i get plastic deformation inside of the wall thickness. After releasing the pressure, the inside of the cylinder will be plastic deformed and the outer wall will be elastic deformed and always preloading stresses will available through the center that will cause to extend service life of the cylinder.

ps : this is a discussion group and many people is sharing their knowledge here if they have.. As far as i know this is not a commercial group.

Tastan

hob yazdi:

• posted

My thoughts exactly...

I'm seeing more and more protectionist posts being made from people who just don't "get" Usenet... If you know how to do something, but don't want to tell because you are insecure about your future employability (gees just how long did it take to get the industrial revolution turning with that attitude???), then keep quiet, or send off an email to the OP offering your services for pay...

There is a "share" side to the internet, and Usenet is really geared towards that goal... if you don't want to share secrets (sharing usually hints at bi-directional flow), then why do you hang here? Just hoping to "steal" some information for your personal gain?... Or just hoping to drum up work?

Of course the OP realises I'm not talking at him here... I'm talking at the people who's input seems to be limited to "hire a professional"....

Al...

• posted

Al, I agree with the general thrust of your argument. Knowledgeable news group participants should either respond with useful information or keep quiet.

I am an engineer with a fair amount of experience with high pressure systems. When when a person says they are going to fabricate a cylinder for a piston pump that is going to operate at 4000 bar - alarm bells start going off in my head! Proper design, material selection, fabrication techniques, and testing procedures are critical if the pump is going to operate safely and reliably.

There are many knowledgeable engineers who post to this news group seeking advice on various problems. Most of these engineers are well aware of the technical and safety issues related to their projects.

But, there are also many other people with little or no technical knowlege who post questions on this news group. These people are often students or amateur builders. They may not be aware of the potential dangers of the projects they are working on.

Sometimes its hard to tell which group a poster falls into. So when a person says that they want to build something - something that could cause fatal injuries if it not designed properly - then I feel that we should sound a note of caution and advise that the person seek help from a qualified engineer.

Tastan, I don't what exactly what your technical qualifications are, but your later post indicates that you are somewhat knowledgeable about high pressure pumps and that you aware of the dangers inherent in the equipment you are working on. I apologize for suggesting that you "hire a professional".

But I'm also reluctant to suggest a material for your cylinder. Material selection for this application is not a trivial problem. I just don't have the time to do the calculations and study the properties of the various candidate steel alloys. Sorry.

Paul D Oosterhout I work for SAIC (but I don't speak for SAIC).

• posted

If you know the history of at least some of the folks taking that side, you might tend to think the terms human safety and liability are in their minds when making such recommendations. High pressure systems are nothing to trifle with, that's why there's the ASME codes.

• posted

Autofrettaging is a way of strengthening gun barrels and thick cylinders by applying a sufficiently high pressure, called plasticizing pressure so that the inner half or two-thirds goes into plastic condition, but returns to elastic condition and then is compressed by grip of outer layers while autofrettaging pressure is slowly released. It is also called pre-stressing. An easy way is by driving in calculated dimension oversized inner cylinder to have an effect of heated shrink fit in a steel cylinder situation.

It is dealt with as an Advanced Strength of Materials subject in post graduate classes of Engg mechanics.Thin shell formulas indicated in earlier post here won't suffice. At the thick shell inner radius, fiber stresses peak up 2 to 3 times compared to the thin shell circumferential values.

There are 3 options for serial consideration:

1) Single thick cylinder only: Calculate plasticizing pressure,and the benefit over the thick cylinder values. Also check whether such high pressure facility is available. 2)Two sleeves shrink/interference fit.Calculate for the interference amount in mm needed from the elastic properties and dimensions of the two parts. 3)Choice of composite fiber/filament overwrap on a thinner liner.

Text book 'Advanced Strength of Materials' by Den Hartog outlines the process and design methods is good for a start for first two cases. But it is best to depend on expertise and may be some training in a participatory mode.The first design document is valuable.

Stainless steel liner and carbon fiber overwrap combination is easily implementable for the small size you have in mind, but is another new line of technology. By a careful calculation procedure that accounts for all properties of liner and composite overwrap one has to keep fiber and liner stresses in limits and avoid liner buckling when autofrettaging pressure is released.

In Aerospace applications one uses Kevlar and Carbon fibers impregnated with epoxy resin and cured after Filament Winding process/winding on cylinder at certain helix angles. Aluminum and other non-ferrous alloys can be used to pressure contribute as liners, a special design process prevents buckling. It reduces pressure vessel weight in space application, but here Carbon/Kevlar can be main tension carriers.

G.L.Narasimham

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I agree with the safety first attitude shown here, and I also am aware of the "fail dangerous" nature of the current topic...

I was just venting on the tone of some of the replies, and an accumulation of simular replies on different (some non-critical) subjects over the past year or so...

Al...

• posted

Venting on the behavior of news group participants is best left to the professionals... :-)

Paul O.

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