Advice welcome on linkage hinge

[setdesigner]

I have been working on a hinge for a trap door. This is what I can up with, using 1/4" flat aluminum bar that I can easily machine on a cheap cnc router. Pivot are in bronze, but also considering stainless steal, not sure what is best in contact with aluminum for and exterior application. I also don't have any idea on how to calculate the spring cylinder force to help lift the door.
Comments and advices are welcome !
Thanks

 

[BigKahunaFL]

Your linkage is a bit more complicated than I'm used to seeing, but I've had great success with the help of this company's ( Gasspring.ca ) calculator.

 

[setdesigner]

I will send them a request, thanks !

 

[BigKahunaFL]

You could just click the link, if you want. It will take you directly to the calculator to play around with. It's wonderfully done. Good luck !

 

[setdesigner]

Yes, I did made a simulation, it is great platform !

 

[Stu3d]

Be careful of corrosion due to dissimilar metals. I have a car with chassis, suspension etc which is mostly aluminium and any steel parts are separated from aluminium with anti-corrosion compound, even steel bolts into aluminium. I believe stainless steel is even worse, when replacing undertray steel bolts for s/steel ones I use nylon washers to prevent corrosion. I have seen aluminum turn to powder leaving a big hole.

 

[simonb65]

Be careful of corrosion due to dissimilar metals. I have a car with chassis, suspension etc which is mostly aluminium and any steel parts are separated from aluminium with anti-corrosion compound, even steel bolts into aluminium. I believe stainless steel is even worse, when replacing undertray steel bolts for s/steel ones I use nylon washers to prevent corrosion. I have seen aluminum turn to powder leaving a big hole.

Steel bolts are usually cadmium plated when used with Aluminium. Stainless and Aluminium is not too bad, but it depends on the grade of Aluminium as to how much galvanic corrosion occurs and the rate at which it occurs. You can use chromium based compounds between dissimilar metals to reduce the galvanic problem ... a standard practice in aircraft construction.

 

[DavidJ]

Steel bolts are usually cadmium plated when used with Aluminium

Very difficult to get Cadmium plated fasteners these days (at last in UK/Europe), even aircraft industry has alternatives now I'm told.

I do quite a lot of work with designs from 1950's, '60's, '70's and this issue recently came up when one of those called for Cd plating on some fasteners.

 

[HaroldL]

At my work we had to comply with the EU RoHS directive and went through a long process eliminate all the yellow zinc chromate plating on the fasteners we used. All zinc plated parts that had Hexavalent chromium plating (Yellow) were changed to a Trivalent chromium plating (Clear). AND they all needed a signed compliance certificate from the supplier. Even internal components that we made for the enclosures (latches, latch rods, etc.) were affected by the RoHS directive.

 

[silver2row]

I want to say something and it will not be as intelligent as some of may think it could be currently...

Zinc plating seems to be oil field related, i.e. especially for attachments (of course). I am not too familiar with types, formats, and/or plating because I mow. Grass...that is.

Anyway, from what I can tell so far, the shops in town purchase bolts and studs in the form of Teflon coated to zinc plated for various fixtures and assemblies.

Seth

P.S. For marine or offshore oil field related ideas, specific types of corrosion prevented measures take place in specific materials like 816 or 304. Now, although I find nothing in the form of 816, I found 13-8 which may be what was discussed to me. I am at a loss now...

Maybe whomever chatted with me sold me fortunes while telling me fibs. Who knows now? Sheesh. Anyway, I think 816 now does not exist. Hmm. Odd.

 

[Stu3d]

P.S. For marine or offshore oil field related ideas, specific types of corrosion prevented measures take place in specific materials like 816 or 304. Now, although I find nothing in the form of 816, I found 13-8 which may be what was discussed to me. I am at a loss now...

Maybe whomever chatted with me sold me fortunes while telling me fibs. Who knows now? Sheesh. Anyway, I think 816 now does not exist. Hmm. Odd.

316 is the superior stainless steel you are thinking of.

 

[HaroldL]

Zinc plating seems to be oil field related

Zinc plating is used where ever there is a concern about corrosion. Especially with electrical and electronic components and fasteners. It may be rare to buy fasteners without any plating or corrosion protection.

 

[sacherjj]

Bolts used in aircraft (AN hardware) are Cadmium plating as others have said, to go through aluminum. Also, depending on loading, you can also look at isolating metals with using UHMW bushings or similar. Stainless is best if you are going to pivot directly on the bolt. Otherwise I would have a thin wall tube that is the pivot and spacing washers go over that. This makes the lubrication for the pivot to be the plastic itself. For low speed and cycle count, this is likely a no maintenance design at that point. I would think that stainless to aluminum would require grease periodically. You don't use cadmium plated as pivots as the protection would get warn off.

 

[sacherjj]

Also not sure about loading, it looks like a single door would allow solid beams span the full space. It seems like tons of force will be on the hinges when done as two cantilever doors.

 

[tyc]

For force calculation, draw the kinematics in a sketch. Apply the weight at correct spot as a vertical line which its length is equal to the value of weight. 90lbs = approx 400N
Calculate reaction forces using torque formula. and apply them appropriately as vectors in the sketch.

I'm baffled in explaining it with words. Sorry if it doesn't make any sense. I'll try to make an example and upload here some time.

Your design reminded me this hinge I used for one of my designs not long ago. https://www.pinet-industrie.com/en/products/1567-concealed-hinge-b-900-opening

 

[NateLiquidGravity]

Don't worry about the corrosion of the bolts too much. They can always be swapped out later if necessary. Design, prototype, test, revise...

 

[setdesigner]

Many thansk for all the comments and suggestions !
I modified the design to use nylon between the stainless steel pins and the aluminum bars, avoiding direct contact to prevent corrosion.
And using abs washers to separate the aluminum bars to avoid friction.
I also removed the gasspring from the hinge and I plan to use them directly on the trap door

 

[silver2row]

Sorry to be way off base. I now see what you were describing with the final product. I thought this was going to be at ground level and slip open to catch a thief (for some reason). Blah.

Seth

P.S. Good showcase nonetheless and very detailed. I am a learner in this field, i.e. so any ideas help me better than no ideas!