Today I learned that plastic is better than metal.

I put my new D630 into my backpack to take it to a store in order to test some laptop sleeves. I brought my AC adapter as well because I was going to go to the office and do a bit of work. The laptop was wrapped up in a cloth bag but the adapter still scratched the LCD lid. Bloody hell.

My Inspiron 8200 has been in that backpack without any wrapping for 3 years and there's not a scratch on it. It's been in machine shops. It's been out in the field. I've even had my 8 year old cousins borrow it.

The ABS plastic on the 8200 is much more resistant to scratching than the magnesium alloy case on the D630. Is there any advantage to having the magnesium alloy?

 

UMMM hardware component protection!?!?!?!?

What would you rather have....a pretty laptop with a broken hdd, or a scratched dented one with everything intact???

 

I would assume the magnesium alloy has better heat dissipation, but the main purpose of the magnesium alloy is likely to add to the "coolness" (style, not heat) factor of the notebook, just like those shiny, smudge-prone, piano-finish notebooks.

 

Plastic is the best heat dissipation material for notebooks, which is one reason why it's being used so much. Of course, the fact that it's very inexpensive counts too

Brushed aluminum is pretty bad at dissipating heat, it's an awesome conductor haha. I have it as the keyboard bezel and touchpad, and while it's sweet to look at, it never wears out, when my notebook gets hot, its noticeable

 

If you're hitting it that hard, it doesn't really matter what the case is made of. The hard drive will still be damaged from the sudden accelerations. And I think the plastic can bend and snap back after an impact that's hard enough to permanently dent the metal but not damage the hard drive.

They do a pretty good job making the alloy low key and not flashy, though.

 

As an angineer I will have to say two things:

- The plastic cannot bend and snap back from a force that would bend an identical metal piece. The yield strength (the amount of force that it takes to permanently deform the material) is far greater in metal than plastics! It is true that plastic will bend and snap back, as seen in various snap-fits on products, but this happens at much lower stresses than what would cause metal to bend.


- To quote "the National Institute of Advanced Industrial Science and Technology":

"Magnesium alloy is the lightest among metal materials for practical use, with specific gravity 2/3 that of aluminum alloy and 1/4 that of iron. Owing to its excellent heat dissipation, vibration absorption and EM wave shielding, magnesium alloy is widely used for housings of various portable electronic gadgets..."

http://www.aist.go.jp/aist_e/latest_research/2004/20040322/20040322.html

And Properties for ABS polymer vs. Magnesium Alloy (source: Matweb.com

Thermal Conductivity:

ABS: 0.128 - 0.19 W/m-K
Mg Alloy: 159 W/m-K

(Higher is better (more heat being conducted))

 

So should we be clamoring for plastic heatsinks?

 

ummmmm ThinkPad?????

 

You're right. I was playing with the two laptops just when I said that and thought, "The plastic snaps back when I press down on it, but the metal doesn't even deform unless I press hard enough to dent it". Of course, that's improper thinking. The mistake I made was that pressing down on plastic hard enough to bend it isn't actually a very large force but it looks and sounds like it is. In actuality, I probably pressed as hard or harder on the metal and because it doesn't move, it doesn't click in my head that I'm pressing that hard. Cognitive biases get me all the time. I should have looked at the numbers first.

This might be one reason why the bottom of my D630 feels about as hot as my Inspiron 8200 even though the Pentium 4 in the Inspiron is supposed to be notoriously hot.

So metal is stronger than plastic, conducts heat better but, depending on the paint job, easier to scratch.

I'll backpedal a bit and say that the plastic is better for what I put my laptop through. I've never hit it hard enough to damage the plastic (i.e. plastic is strong enough for me) and it doesn't scratch as easily.

Oh well, I got a sleeve for it now so it shouldn't scratch anymore. Just a bit unhappy that there's some scratching on the lid after having it for about a week.

 

Umm, plastic has terrible thermal conductivity. Otherwise heatsinks would be made of plastic not aluminum or magnesium alloy. Plastic is very cheap which is why it is used, not due to its thermal dissipation properties.