Ceramic object - fiberfill? [Archive]

benjamin_wooten

03-23-2016, 09:42 AM

Hi all! I have not been on the forums in some time. I was a gallery preparator for four years, between 2007-2011. I did some simple packing/shipping there almost exclusively of framed works on paper. After a break from that work, I am now making crates for a handling company in Canada, who is getting into art moving and museum services. As this looks to be a long-term proposition for me, I need to educate myself as best I can, so that I do appropriate work to the proper standards. I do not have the luxury of a mentor up here, so I am hoping to start in these forums.

We are crating a ceramic sculpture for transport from Canada to India. It's been sold to a client, so this is a one-way journey... not a crate for long-term storage or anything like that.

The object is essentially an orb, roughly 18x18x18. The object weighs 10lbs., and there is a 10lb. steel base to make the journey in the same crate. The ceramic piece has a lot of spiky protrusions (see attached image). The artist has a preference for how she has shipped it in the past, however I have some questions/concerns, and seek your guidance.

http://www.paccin.org/attachment.php?attachmentid=1743&stc=1

My plan is to build a 1/2" ply crate with battens, and an interior gator-board box to hold the ceramic piece. Gator-box will be cradled by ethafoam, and the steel base will be bubblewrapped and set in an ethafoam frame on the bottom of the crate.

Inside the gatorbox I am planning on tissue paper around the ceramic, two layers of face-to-face bubble around that, then fiberfill to fill the voids. Is that a good option? You can see from the image that the artist has jammed small bits and pieces of various foams between the protrusions in a past shipment. This worries me... wondering if vibration or shock could transfer in there and spring-fire a chunk of foam against a protrusion and snap it off. Should those spaces be packed with fiberfill instead, before the object gets wrapped in tissue?

As for the ethafoam... the artist says she prefers solid 3" thick all around, which seems really excessive to me. I was planning on 2" thick (at most) strips between crate and gatorbox. Now I am doubting myself, and decided to get more accurate. I started using this chart (http://www.conservation-design.com/newsletter_artpacking.html) as a guide. I am interested in learning how to apply this information to this object, and others in the future.

However, I seem to have more questions now than when I started. Have any of you used these charts before to calculate how much foam should be in contact with an object? Do the same rules apply with the box-in-box technique I plan to employ, or are there other considerations? Are there simpler ways/rules to sort these concerns out?

Thanks everybody, any advice or conversation is appreciated.

Chris Barber

03-24-2016, 10:01 AM

Hi Benjamin,
Great questions!

Based on how you describe the elements, I like the plan of packing the ceramic in an inner box inside the crate, and packing the base separately in the same crate. Given the object's relatively light weight, I would suggest you consider cavity-packing as a model for your packing approach. This would not create an appropriate amount of cushioning inside the inner box, but that is OK. Instead, it would provide more evenly distributed support for the delicate protrusions around the ceramic. Most alternative approaches would be to secure the object by only a few of its elements, creating undue stress in those areas. Since the ceramic will be secured in an inner box, you have the option of applying the optimal amount of cushioning to the box exterior via pads on the crate walls.

This object is way large for a typical cavity pack, but what I mean to suggest does not necessarily have to begin with solid fill of foam, and then the somewhat wasteful removal of 1.5 cubic feet of it to make the form-fitting cavity. An alternative you can consider is lining the box with 2" of foam, then adding wedges and other shapes from scraps to fill in the gaps. I would recommend either 2 lb ester foam for this, or a 0.9 lb polyethalene laminate, essentially anything not too soft or too firm. Wadded tissue or bubble wrap could also serve to fill spaces around the object, but be wary of applying such materials in a way that they can snag on the object's fragile elements. Ideally you want it to be possible to lift the object up & out of the resulting cavity cleanly, without bringing any dunnage with it. If it is safe to wrap or drape the object before dropping it in, that can help mitigate snags when it is removed.

If an oversized quasi-cavity pack sounds impractical, then I would recommend guillotine packing with 2" ethafoam guillotines, and more than usual. The point of either option is to secure the object inside the inner box with the maximum amount of surface contact feasible. The more form-fitting surface contact there is, the less this object's individual protrusions will be stressed by that contact. Without knowing more about the piece, I would advise against using the small wedges of material as seen in the photo if any other contouring approach can be agreed upon. It is clear what the intention is with the wedges, but they would require a lot of careful handling to remove without damaging the piece, and the protruding bits of foam can create uncontrolled stresses in various directions when securing the object in the inner box.

I usually like to 'float' small delicate elements in empty space when possible, but this object appears to allow little access to stronger areas.

Yes, solid 3" ethafoam in the outer crate does sound too stiff for this object packed in a gator board box. Tables like those in your link are one way to look at foam cushioning options. The difficulty there is that static load calculations are not easily solved for X, which is the static load. In other words it is easy to start with a known static load for a foam in a specific scenario, then look up the lowest G's it will safely support in that scenario, and leave it at that. Consequently, I think people can easily misinterpret such tables, understandably thinking that foams have fixed optimal static loading. However, any given foam's optimal static load is contextual, based on an assumed drop height, thickness, and whether you assume a single drop or more than one. In our profession, we are typically looking at the issue from the other direction (At least I am): What is the optimum static load of ___ foam at ___ thickness for an object of ___ fragility, at ___ drop height, and what is the effective range of same? Visual graphs called 'dynamic cushion curves' are more user-friendly than tables in this way, and represent much more information about your scenario's effect on static loading. Ask your foam supplier for the foam manufacturers' cushion curves. You can keep a whole library of them in a small file, or on your computer in PDFs. Here is a set of curves for for ethafoam 220 at multiple 24" drops:

http://www.paccin.org/attachment.php?attachmentid=1744&stc=1

Once you have a foam selected & its optimal static load determined for your risk scenario, divide the weight of the package by that psi to see the optimal area of foam in square inches to use on each face of your inner box. It is advisable to stay as close to the optimal static load as possible, but often helpful to see the full range of effective SL. When it would be awkward to accommodate the optimal SL for your current foam selection, (fairly common for objects that are lightweight for their size), you can change the thickness, consider a different density, a different type of foam, or you can confirm that the closest possible SL falls well enough inside the curve (within the range of safety).

As you say, there is a potential issue of providing too much cushioning when employing inner boxes, but this can be avoided by employing stiffer packaging inside the inner boxes. Cavity packing is one example of a more firm packing method, so the load bearing area of foam on the crate walls can be calculated separately.

You can find out more about using cushion curve charts online, in publications like Art in Transit, or by asking this community. I have an article on PACCIN (http://www.paccin.org/content.php?293-Dynamic-Cushion-Curve-Prediction) about cushion curves, or more precisely about building a versatile formula that sources those curves to predict off-chart behavior in unusual scenarios. It is long, but there is a very brief primer on reading cushion curves within the article.

Looking at your scenario: If I took an object that was 18 x 18 x 18" and 10 lbs, packed it in a gator box with ester foam cavity fill, I would estimate a resulting weight of around 26 lbs for that package. Since the crate would be fairly small, I would assume multiple drops at 24" minimum. With these variables I calculate an optimal SL @ 0.81 psi for 2" ethafoam 220 (see the bottom-most point of the red curve in the chart above). Dividing the estimated weight of the package by this psi results in a measly 34 square inches in optimal load bearing area (LBA). That is a very small amount of foam, roughly 6% of the area of gator on each side of the inner box, or four 3 x 3" pads in the corners of each side, and you would probably want a small pad in the middle of the bottom wall for support. If you are not comfortable using such small pads, I think switching to 2" 2# ester foam would make it easier to meet the recommended optimum LBA. My calculations recommend roughly 26% coverage for ester in the same scenario. The small ethafoam pads would be more cost-effective and environmentally friendly, but the larger amount of ester foam recommended may serve to appease a client who thinks they want solid foam. I am assuming the object has about 50 Gs fragility, but this does not affect the optimal static load - it only increases or decreases the range of effective static loads, with a minimum range of 0 (completely inadequate).

If you want to see what 3" thick ethafoam does to the static load, find the light blue curve on the same chart displayed above (optimal SL for 3" in this scenario is approx 1.185 psi according to my method).

Of course this would need to be modified by the specs of the metal base, whatever packing method you use for that, and how it interacts with the cushioning for the ceramic's inner box. For example, if you pack the 10 lb base into a second inner box and stack the ceramic box on top, then their weights can be combined to allow for a slightly larger optimal LBA on the bottom wall of the crate.

Some folks might increase the assumed drop height for a crate this small. In that case you may want to consider thicker ethafoam pads, or other foam options. For multiple 30" drops, 2" ethafoam 220 appears to cover objects @ 60 Gs fragility, but not 50 Gs. For multiple 36" drops, it appears to cover objects @ 70 Gs, but not at 60. Given where we typically place crate handles at Artex, I think multiple 24" drops is a reasonable parameter for multiple people lifting this crate manually.

None of this addresses another potential reason for the client's request of solid foam - thermal protection. If they want a foam thermal insulate for this shipment, it should be added in another layer of foam on the crate walls, outside the cushion pads.

Chris