25
votes
Accepted
How can I tell if I got counterfeit aluminum?
I figured out a simple test.
Since the density of 6061 is 2.5 g/cm3 and the density of zinc is over 7 g/cm3, all I had to do was measure the density of the material.
This showed that indeed it was ...
- 1,625
21
votes
Accepted
What material is used to hold molten iron in a furnace?
Summary
Crucibles are lined with refractory materials. Steel processing makes use of graphite or a combination of chromite and magnesite for direct contact with the melt. Cast iron processing often ...
- 4,041
21
votes
Can titanium be used as I-beams?
Not to repeat, but in addition to being very expensive it is very expensive to work with. So, pretty much only governments can afford it. It absorbs oxygen and nitrogen from air at the hot ...
- 6,112
19
votes
Can titanium be used as I-beams?
Yes, but titanium is very difficult to roll into structural shapes like I-beams in a rolling mill and extremely sensitive to chemical attack by washing solutions that contain chlorine, for example. So ...
- 14.3k
17
votes
Copper is more conductive, so why use lead battery terminals?
Yes, copper is more conductive than lead, but that is not necessarily the primary criterion for selecting the connector material.
For car batteries, making sure there's a good connection between the ...
- 6,874
16
votes
Why does faster cooling produce smaller grains?
Grain boundaries cost energy—the bonding quality is worse there—so there's always a driving force to form one giant grain. However, slow kinetics limit this process, so we generally encounter only ...
- 1,565
15
votes
Accepted
Unknown metal-piece connected to the case of an iPod Nano 2
It's a naked piezoelectric buzzer.
Some piezoelectric crystal grown on a metal circle are the active part and the bottom contact glued on the back cover.
The top is then metallised to get the second ...
- 295
12
votes
What is the purpose of grid-like details on engine blocks?
This pattern is to provide sufficient strength while minimising the mass of the block.
These "webs" are designed to prevent any vibration, if the block wall was made thin and the full length and ...
- 15.5k
12
votes
Can titanium be used as I-beams?
Yes. Besides aerospace, titanium structural elements are fairly common in offshore oil and gas and chemical industries.
You can order titanium I-beams online, with prices available at some websites. I'...
11
votes
What material is used to hold molten iron in a furnace?
Molten ferrous metals are often handled in steel ladles with a refractory lining.
It's only since about the 1860s that any ferrous metals other than cast iron (which has a significantly lower ...
- 15.2k
11
votes
Why does corrosion take place at certain stressed regions?
One of the mechanism that affect corrosion is known in the literature as Stress Corrosion Cracking (SCC). The idea is that tensile stressed regions are prone to crack development. Crack development ...
- 24.3k
10
votes
Why use a 'dogbone' shape for tensile testing specimens?
You half-answered your own question. Preventing failure in the grips is important. Additionally, grips of tensile testing machines have teeth to achieve a sufficiently strong grip that can withstand ...
- 4,041
10
votes
Accepted
Galvanized Steel (Zinc Plated Steel) vs Stainless Steel
Stainless steel can be used up to temperatures of about 1000C. The corrosion resistance of zinc plating decreases rapidly above 100C, and embrittlement can occur above 500C.
Zinc plating has lower ...
- 12.5k
10
votes
How can I tell if I got counterfeit aluminum?
You can confirm the alloy and heat treating condition by measuring conductivity. It's like a fingerprint for any given combination of alloy composition and heat treatment.
Reference values can be ...
- 201
9
votes
Copper is more conductive, so why use lead battery terminals?
A lead-acid battery has only lead and acid. If copper was used for the terminal posts galvanic corrosion would eat them. It is better to keep the same metal for the cell plates and the terminals. Also ...
- 91
9
votes
Can titanium be used as I-beams?
Yes, Titanium can be used as a structural material (not necessarily I beam), though rare. Here are two structures made of titanium, Monument to Yuri Gagarin and Monument to the Conquerors of Space, ...
- 8,109
7
votes
Is there a maximum life for things made out of stainless steel or cast iron?
Strictly speaking, very few metals are "stable" in terms of the laws of thermodynamics. True chemical stability is when the atoms are in their lowest energy state. For most metallic elements,...
- 191
7
votes
How can I tell if I got counterfeit aluminum?
Unlikely you have anything except aluminum alloy. What is the heat treatment supposed to be ; what grades are offered in the spec? On the net, I see reference to T-5, that is- as extruded, then aged; ...
- 6,112
6
votes
Accepted
Schaeffler, De Long, and WRC welding diagrams - which steels can be used?
You are not exactly right. The purpose of Cr and Ni in stainless steel, besides the stainless part, is to tailor the microstructure. Cr promotes ferrite, Ni promotes austenite. Other elements have ...
- 4,041
6
votes
Accepted
Determining the microstructure of steel after welding in modern computer software
Summary:
1) The answer to this question is difficult. You would need to know how austenite and ferrite behave in relation to what you are doing to them. You would also need to know their compositions,...
- 4,041
6
votes
Why use a 'dogbone' shape for tensile testing specimens?
Starrise gave a good explanation of the reasons why a dog-bone shape is important to the tension portion of a tension test, but there is another property that is typically measured at the same time: ...
- 10.7k
6
votes
Accepted
Word for the tendency of one metal to rub off on another?
"Galling" is probably the word you want here. It's the tendency of a (usually) soft metal to break down under pressure and adhere to the harder material.
It's common with soft metals like aluminium, ...
- 275
6
votes
Accepted
Why are vacancies in solids called as equilibrium defects?
Imagine you have two boxes separated by a removable partition. Each box is filled with a different pure monatomic gas. When you remove the partition, the gases mix. Their equilibrium state tends ...
- 4,041
5
votes
Accepted
Why is strain also normalized to the parameters of engineering strain?
From what I understand of the question, there are three interlinked concepts that are causing confusion, each of which could be a separate question.
1. Is axial stress dependent on length of a ...
- 4,041
5
votes
Accepted
Does unloading beyond yield point also affect tensile strength?
Summary: If you are loading and unloading the same sample, the stress-strain curve will not change and the tensile strength will be the same, because stress and strain are calculated from the initial ...
- 4,041
5
votes
Theoretical strength of pure and perfect crystals are way higher than the strength of crystals with dislocation?
Assume for the rest of my answer that, unless otherwise stated, the material in question is a macroscopic single crystal of some metallic element, free of volumetric defects (e.g. carbides, graphite, ...
- 4,041
5
votes
How can dross/slag formation be reduced during aluminum recycling?
The dross is mostly composed of aluminium oxide which is already present on the surface of the metal before it even goes into the furnace, as the aluminium melts the oxides separate and float to the ...
- 15.2k
5
votes
What material is used to hold molten iron in a furnace?
As Brian Drummond noted, the "basin" is called a crucible:
A crucible is a container that can withstand very high temperatures and is used for metal, glass, and pigment production as well as a ...
5
votes
Copper is more conductive, so why use lead battery terminals?
Lead is more corrosion resistant to sulfuric acid . And copper is more expensive. That is; copper in the battery would dissolve in less than one year.
- 6,112
4
votes
Accepted
How small can you get a stream of molten steel to be at low pressure?
Making a nozzle with that long and thin of a hole is not feasible, but you could make a larger hole behind it and just have the last 3mm be 0.6mm in diameter. This would be feasible in a ceramic, but ...
- 1,335
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