Design a Hydraulic Actuator: Calculate Load & Choose Nuts/Screws

[jaymin]

i'm a mechanical student, and given 1 assignment to design a hydraulic actuator.
i need to calculate t load or force, so that i can choose the most suitable nuts and screw to assembly it.
do u all have those kind of drawing and the formulas for calculation?
please help! it's urgent..

 

[cristo]

jaymin, I don't think you'll get many people willing to simply give you drawings and formulae for your homework assignment. Plus, PF rules state that for such homework questions, we must first see some effort from you before we can help you. So, what thoughts do you have; what do you know about the subject?

 

[jaymin]

actually, i have surf onlline to find about the actuator..
t thing i don understand is that there are many actuator including valve actuator,rotary actuator and even steering actuator..
i don know what is the difference between them.
can u explain?

 

[brewnog]

An actuator is just something which causes movement.

A valve actuator is one which operates a valve, for instance you could use them in a simple hydraulic circuit to effect a valve to direct flow into a cylinder or motor.

A rotary actuator is one whose motion is in a rotary manner. A steering actuator could be used to effect a steering mechanism. It's all pretty self explanatory.

Back to your original questions, do you know of any formulae which relate force and pressure? Looking at the units of these factors might help you out. But cristo is correct, nobody is going to do your homework for you.

 

[FredGarvin]

I think the first thing you need to do is sit down and decide exactly what kind of actuator do you need to design. Is it a linear or rotary actuator? Also, it would help us if we knew what level of schooling you are at. Hydraulic design can get very complicated. If we don't need to get into the real details of design,, that would be nice to know.

 

[jaymin]

thanks for willing to answer my question..
actually do the screw and nuts really play a significant role in actuator?
i have some formulae but they don't related to the screw or nut..
are there any specific screw or nut for actuator?
because my lecturer told me that i have to mention the ISO number(or what we called it?) of the screw and nut..

 

[jaymin]

I think the first thing you need to do is sit down and decide exactly what kind of actuator do you need to design. Is it a linear or rotary actuator? Also, it would help us if we knew what level of schooling you are at. Hydraulic design can get very complicated. If we don't need to get into the real details of design,, that would be nice to know.

i'm now taking degree course in university..
my lecturer told that we have to draw each assembly part and mention the ISO number of the screw or nut that we want to use.

 

[brewnog]

Well do you know of a formula you can use to calculate the required strength of the bolts?

 

[jaymin]

sorry to tell that i don't know..

 

[jaymin]

from the explanation of fred, i think the most simple actuator to design is linear acyuator, right?

 

[brewnog]

Well yes, but it completely depends what you're wanting to do with it.

Perhaps you could post the full requirements of this assignment so we actually understand what you're trying to do? And along with that, the steps you've already taken or the work you've already done. Then we should be able to help you out some more.

 

[jaymin]

actually my lecturer just tell us what to do by words..
he don't even written down his requirement.
so all my coursemate now also confius..
he just ask us to draw a hydraulic actuator design together with the mounting..
details of screw and nut also needed..
t things i do is only searh online..
but it make me more confius about it..
i have look through some figure from internet but many of them seems different..
so i don't know what to do..

 

[brewnog]

Sounds like you need to go back and ask your lecturer to define what he wanted from you.

 

[FredGarvin]

You seem much more worried about the mounting hardware than the design of the actuator itself. What course is this project for? Perhaps that will shed some light on the matter.

 

[P.Ramesh]

I hope u need a fastner strength calculation.

Allowable axial pullout load = Pi x Mean Dia of bolt x Length of engagement x Yield stess / 3

 

[FredGarvin]

Be careful with that equation you are stating. You are making assumptions about the nature of the fastener failure that may or may not be correct.

 

[Dieseltwitch]

if your looking for what caps the ram then you need to look at the tensile strength of a bolt, this is calculated buy knowing a number of things about the bolts them self;

1. Bolt Shank Dia.
2. Tread Type (fine/ course)
4. Bolt Material
5. Heat Treatment Used

know how much pressure you going to need to contain is the first thing you need, from that you can then calculate the number of bolts and type needed.
the.

Now if your looking for the bolt that will mount the RAM to a flange or some other type of mount you need to look at the shear strength

I found this website to help you start with the math
http://www.roymech.co.uk/Useful_Tables/Screws/Preloading.html

I can tell you in my position, a teacher with that didn't give you any pressure numbers just pick some. i can tell you that most Hyd Systems don't reach pressures much over 3000 PSI they can but very rarely. so i would just state the pressures you have picked. then figure out how much weight your going to need to move and from that you can calculate the needed piston Dia.

i would also say that you need at least 4 bolts to hold the cap on.
again i would also say that you should leave 25% safety gap over the max pressure reached.

 

[Dieseltwitch]

I also found this. a Bolt Strengh Calculator but you need to know every thing to use this
http://www.norbar.com/torquetensioncalculator.php