Silicon Bronze Bolts

[TestBeforeTouch]

Does anybody have any experiance in selecting between the different types of silicon bronze hardware for joining busbars?

I know that Silicon bronze is a general term that describes various types of copper-silicon alloys manufactured under trade names such as Everdur, Herculoy, Duronze."

The names seem to represent different types of metalurgy. For example,

Everdur = 95% Cu, 4%Si, 1%Mn
Herculoy = 92% Cu, 4%Si, 4 % Zn
Duronze is available in several different compositions.

But I have not been able to find any information on the benefits of one alloy over another.
Any help would be appreciated.

 

[CarlPugh]

Have you searched the WWW? There should be standards for bus bar sizes, number of bolts required for different current and other requirements.
If you can obtain a copy of "Alcoa Aluminum Bus Conductor Handbook" it has more information than you want to know on aluminum bus bars.

Many years ago we joined aluminum bus bars using plain old steel bolts. (If joining aluminum, use joint compound for sure)
Only problem we had was when someone used an aluminum bus bar that had transformer varnish on it. They very carefully cleaned the varnish where it could be seen. When the equipment was turned on, the bolt melted in half and shot out. It was though that the joint had not been tightened and they were told to replace the bolt and tighten the nut securely. When the same thing happened again, the joint was disassembled and the transformer varnish was obvious.

 

[cuky2000]

Check if the enclose info could help you.

http://www.hubbellpowersystems.com/powertest/catalog_sections/PDF_connect/ST.pdf

 

[TestBeforeTouch]

Thank you for your replies. I do not know if I will find an answer to the original question which asks which silicon bronze is better.

I guess I am now wondering why does the electrical industry prefer that we use silicon bronze over stainless steel?

Stainless is cheaper, easier to obtain, and by almost all accounts appears to be an acceptable alternative. The resistivity of stainless is about 1/2 silicon bronze, but resistance of the fastener is not what is important. Silicon bronze is nonmagnetic, which may be an advantage in high current applications, but some stainless steels are nonmagnetic also. Silicon bronze may have better corrosion resistance outdoors than stainless but most busbars are enclosed.

Any other thoughts on why we would choose silicon bronze over stainless would be appreciated.

 

[MikeDB]

Our firm used to specify aluminum bolts on all aluminum connections, bronze for copper connections and stainless steel for mixed connections. Trouble removing aluminum bolts and problems getting crews to put the right bolt in the proper connection have lead us to specify all stainless steel bolts for bus connections in substations. Using proper joint compound and preparation is still required.

 

[jghrist]

The reason to use bronze bolts instead of steel is to keep the thermal coefficient of expansion the same as the bus material. This way, the connection does not get tighter (possibly deforming the bus bar) or looser (making bad connections) with temperature change.

 

[TestBeforeTouch]

I am no longer convinced that the thermal expansion issue is important for copper bus joints. It obviously is for aluminum. The reason I say this is that Allen-Bradley joins their copper bus MCC's with carbon steel hardware. According to AB these connections do not have to be torqued for the life of the equipment. Also, all the information I have indicates that both stainless, and galvanized steel are acceptable alternatives to silicon bronze.

The one place silicon bronze seems to excel is in outdoor applications due to corrosion resistance, but why not use stainless if it is cheaper?

 

[cuky2000]

The type of hardware used for joining busbars has significant effect on the pressure and ultimate electrical contact resistance of the join. The enclose graph will provide some idea of the effect of pressure on the contact resistance of a joint between two copper conductors.

” ……. galvanised steel bolts are normally used but brass or bronze bolts have been used because their coefficients of expansion closely match the copper conductor and hence the contact pressure does not vary widely with operating temperature. Copper alloy bolts also have the advantage that the possibility of dissimilar metal corrosion is avoided. Because these alloys do not have an easily discernible yield stress, however, care has to be taken not to exceed the correct tightening torque”

For additional info in this subject, check table 9 and other related section in the enclose site

http://www.cda.org.uk/megab2/elecapps/pub22/sec7.htm#7. Jointing of Copper Busbars

 

[TestBeforeTouch]

According to the Burndy catalog the recommended tightening torques for Silicon Bronze and Steel Hardware are the same so contact pressure is not the issue.

The Coefficients of Expansion (COE) for the different metals are in units of 10E-6 inch/inch/deg F:

Copper 9.8
Durium Silicon Bronze 10
316 stainless 10.2
Steel 8.6
Aluminum 13.7

Calculating the % change in the COE vs Cu

Silicon Bronze 2%
Stainless 4%
Steel 12%
Al 40%

The COE change from Silicon bronze to Stainless is only 2%. A different way to look at it is that the % change in COE for Stainless is double that of Silicon Bronze. Is that significant enough to exclude using stainless in some applications?

Just based on thermal expansion the choice for fastener would be:
1.Silicon Bronze
2. Stainless
3. Steel.
Based on cost the order would be reversed.

 

[QCE]

Is the cost of a bolt the main concern when one failed connection can be a very costly issue?

 

[TestBeforeTouch]

If I was convinced that by using stainless steel hardware I might have a failure that I could avoid by using silicon bronze than I would choose silicon bronze.

Should I pay 2x for silicon bronze over stainless to make myself 2% better? It seems hard to justify if there is no evidence that it makes any difference. When the largest MCC manufacturer (Allen-Bradley) tells me they use Carbon Steel to join their copper busbars together and that the never need to be retorqued I have serious doubts about the need for silicon bronze.