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Violin Cases and Thermal Insulation: What’s better? Wood laminate, carbon fiber, composite plastics, or...?

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Published: March 13, 2015 at 1:00 PM [UTC]

You want your violin to be well protected from heat and cold, and one way to ensure this is that the shell of your case be a poor heat conductor. That means that if the case is placed next to a heat source (radiator or light bulbs), left in the sun or in a hot automobile, or placed on a cold sidewalk in the winter, the heat (or cold) will spread more slowly through the shell and within the case, keeping your instrument happier.

case

Case manufacturers choose the materials they use for their own reasons, but many claim that their cases give good heat/cold insulation even when they don’t. Well, hype and advertising aside, we can discover the truth if we look at the materials themselves, and their heat conductivity properties expressed in Watts per meter per degree Kelvin (W x m-1 x K-1)

Average heat conductivity of case shell materials

Wood laminate 0.13
Composite plastic (FRP) 0.23 – 1.06
Fiberglass 0.60
Carbon fiber (molded) 5
Steel 16 - 24
Aluminum 210

Wood laminate is clearly more protective in this sense compared to composite plastics by a factor ranging between 1.8 to 8.1; to fiberglass by a factor of 4.6; to molded carbon fiber by a factor of 38.5; all the way up to aluminum (factor of 1,615!).

This is unbiased proof that wood laminate remains a superior material for violin case shells, despite newer materials being available.


From 86.141.221.37
Posted on March 13, 2015 at 6:56 PM
I saw a test this week comparing the heat inside cars painted in dark and light colours and left in the sun. Testing the inner temperature by reading the external heat radiated from the glass it seems there is not much difference between white and black cars internally .
From Laurie Niles
Posted on March 13, 2015 at 9:15 PM
Dimitri, someone on the Violinist.com Facebook page was asking about styrofoam. What is its heat conductivity of styrofoam? Would it be under one of these listed materials, or is it another number?
From 128.149.76.33
Posted on March 13, 2015 at 9:27 PM
Google says heat conductivity of styrofoam 0.033 W(m K). In other words, better than wood.
From John Rokos
Posted on March 13, 2015 at 10:06 PM
(Re-edited) An internet source gave the density of pressed wood as 190kg/m^3 and styrofoam as 300kg/m^3. Therefore, I assumed the styrofoam used for styrofoam violin cases to be a material both denser and stronger than the ordinary expanded polystyrene with which I lined the laboratory cold chamber I designed and used in 1967-8 in lieu of a cold room). Expecting conductivity of organic materials to vary with density (the more air trapped in the material, the less it conducts), I predicted the conductivity of styrofoam to be right at the lower end of the range for composite plastics. As Tomlin and a couple of convicts (see below) have pointed out, I was wrong.
As regards cars left in the sun, I would think their reflectivity was more important than their colour. I think it would probably be a good idea to place a layer of aluminium foil inside the material of a case, for its reflectivity. And how about a thinsulate or thermolactyl lining for the case cover?
From 69.62.165.45
Posted on March 13, 2015 at 10:58 PM
Well, I cannot remotely afford a Musafia case, but I'm glad I went for well built, reasonably good-looking case with a wood frame. :)
From Tomlin Su
Posted on March 13, 2015 at 11:06 PM
Actually John, styrofoam is highly insulating with a thermal conductivity of 0.033. Not sure if case makers use styrofoam as padding, but it has pros of being light and cons of being easily damaged. Also, adding a layer of foam around the case may make the case a lot bigger than normal.

(source for thermal conductivity: http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html)

From 202.89.191.86
Posted on March 13, 2015 at 11:06 PM
EPS sheet has a thermal conductivity of 0.038 W/(m·K) at 15 kg/m3, and it can be reduced to 0.03 with an increase in density, and/or other additives.

Wikipedia is a good starting source for these kinds of data


Note that this is about a third of that of laminated wood (0.13).


From 69.62.165.45
Posted on March 13, 2015 at 11:13 PM
The figure given in a post regarding the density of Styropor /Styrofoam is dead wrong. Imagine one cubic meter of Styrofoam weighing over 300 kilograms! That's more than 600 pounds! Roughly one third as heavy as water.

One would never be able to move medium-size and large devices packed in it.

Someone misinterpreted the density of polystyrene, a very hard, clear and brittle aromatic polymer, BEFORE it is foamed and turned into STYROFOAM.

Note that Styrofoam has a relatively low melting point. It does not look very promising as a substance for the frame of a violin case.

Wood 1, Styrofoam 0.

From 32.215.168.6
Posted on March 13, 2015 at 11:39 PM
John Rokos your numbers are completely messed up.

First off, styrofoam is much much much less dense (for typical) than your sg=0.3

Secondly, "compressed wood" is much much denser than that (sg = 1.1 to 1.4) but nobody wastes money using compressed wood!

Wood other than balsa ranges from sg= .35 to sg = .85 depending on species.

Styrofoam weighs next to nothing. sg = 0.02 to 0.06.


From Paul Deck
Posted on March 14, 2015 at 2:31 AM
Of course aluminum is at the high end of thermal conductivity compared to wood or plastic.

But are any cases made completely of aluminum? Or is a typical aluminum case lined with something that is sufficiently thermally insulating? I could easily envision a thin aluminum or fiberglass shell surrounding a styrofoam core. I have no idea how those types of hybrid constructions could compare to plywood ("wood laminate") for impact resistance.

In any event, since a case is a complete system, better to test whole cases than just one component thereof. The easy way to test a violin case for its insulating capability is to feed a copper-constantan thermocouple into the case, put the case into your chest freezer, and see how fast the internal temperature goes down.

From Dimitri Musafia
Posted on March 14, 2015 at 6:14 AM
OK, time to address some queries.

Styrofoam is definitely the best material to make case shells from the standpoint of thermal insulation, having a conductivity of about 0.015 in the standard 25kg/m3 density.

The problem is that it is an inferior material to make case shells out of in terms of durability, stress fatigue, resistance to traction, and a whole lot of other issues. Having built over 2,000 cases with this material, I know, believe me! Which is why I didn't include styrofoam in this list.

I included aluminum because, yes, years ago there was such a case on the market made by an important manufacturer and I assume these products are still in circulation. Flight cases usually make extensive use of aluminum too.

Lastly, Paul, you are absolutely correct that a case is a system. I singled out case shell materials in this post because there are case manufacturers in the real world that do the same in their advertising.

From 32.215.168.6
Posted on March 14, 2015 at 11:44 PM
The interesting thing about wood is that it has a set of properties that is quite close to optimum all by itself, for a case.

Wood is cellular and therefore has that thermal advantage of foam, yet unlike foam, it has considerable strength. Also unlike foam, it is anisotropic in strength which is actually advantageous in terms of toughness--and especially energy absorption under limit loading. Wood will produce robust cases at near optimized weight.

To outdo wood, you need to go to a epoxy matrix kevlar-carbon skin with high density structural foam core. That can be built at about 30% less weight but the same thermal properties (approx) and roughly the same limit load. But the cost is ridiculous. The downside is that to keep that weight less than wood, you have very thin skins subject to puncture. Again, here is where wood is nearly impossible to better.

It is interesting to note that the density of cellulose is about 1.55. Carbon fibers are about 1.75, and kevlar about 1.44. But wood is "foamed" by an evolved sophisticated cellular structure whereas all composites are crude laminated epoxy saturated systems. The lignin in wood serves the job of epoxy but it doesn't fill the pores. As such, wood has both local resistance to buckling as well as global buckling stiffness. High performance compoxites are much poorer in buckling. The foam core is required to stabilise but must be lighter density--and inherently weak--compared to wood. It is too complicated to explain why the isotropic nature of foam is deleterious to toughness but just take my word on this (wood has a "weak" direction which actually makes it tougher in ultimate behavior).

Steel would be the toughest, except for one problem--it is much too heavy. It makes optimum tough structures for cars, but not for small things.

In terms of limit loading, I'm thinking of car driving over case.

From 70.215.75.221
Posted on March 15, 2015 at 2:28 AM
There are pro's and con's to all materials. An extremely structurally sound carbon fiber case that lacks in thermal protection can be placed in an insulated, waterproof cover with nice pockets and backpack straps. Just saying '...
From 47.72.46.66
Posted on March 16, 2015 at 10:27 PM
I have got a BAM case which is very nice but quite heavy with inner lining out of Latex material. The Latex suppose to be good for creating a good climate for the Violin. The shop keeper in Cremonas Instrument Shop recommended this Case to me for that reason. Unfortunately these cases are not build any more because of too much expense and not being able to compete with the chinese market.
Does anyone know about this Latex material and how it is for providing a good climate for storing the Violin? I know that some mattresses are made out of Latex and some people really like them.
From Dimitri Musafia
Posted on March 17, 2015 at 8:33 AM
Are you sure the case is lined in Latex? That would be one of the worst possible materials with which to surround the violin.

To keep a stable microclimate within the case you need hygroscopic materials, which absorb and release moisture as necessary to slow changes of relative humidity, protecting the instrument.

Latex is a form of rubber, which does the opposite: it is waterproof to the point that medical gloves and condoms are made with this material.

From 98.118.42.5
Posted on March 17, 2015 at 8:26 PM
Dimitri, do you find that the specifics of the cellulosics (hydroscopic materials) used inside are an important consideration?

For instance, does a velvet or velveteen move moisture in/out of the air faster than an 8 harness satin? Is rayon different from cotton for the same denier and weave? Is there a way to measure or design the amount of cellulosic material in the system relative to rates of humidity change?


From Dimitri Musafia
Posted on March 19, 2015 at 8:51 AM
The hygroscopic qualities of the interior lining are important, but only up to a point. That is because the case is usually opened and closed often (recycling the air mass within) or it's left in storage in conditions of constant or slow-changing humidity and temperature.

The more the interior lining is hygroscopic, the more it flattens out the dips and peaks of relative humidity changes by absorbing and releasing humidity depending on the current and previous conditions.

For example, if the case is moved from a humid environment to a dry one, the lining will release the humidity it had absorbed previously, helping protect the instrument from the effects of dryness.

From 47.72.63.68
Posted on March 19, 2015 at 9:26 AM
Dimitri, I checked my BAM case if the foam was latex. You are right, it is not! In an unimportant place i managed to get some foam out and burnt it. It did not have the typical latex-burning-smell. So its just some kind of synthetic foam.
Thank you for pointing out the need for hygroscopic materials in cases.
Maybe there was a misunderstanding between me and the Cremona Music shop keeper. I really liked the Music Shop and the service.

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