How to Best Ship Stereolithography Parts

One common concern in shipping stereolithography (SL) parts during the summer is that temperatures can frequently exceed the published heat deflection limits of many resins. Highs of 140°F have been recorded in closed, parked carrier vehicles during the summer in southern climates, and the U.S. military assumes a worst-case high of 160°F (71°C).

In order to prevent environmental damage, a solution that some have considered is using dry ice, available in both block and pellet form, when shipping SL parts. The dry ice helps ensure that parts remain dry and do not warp or distort due to high temperatures-a primary consideration when using resins, which are not water-resistant and may be subjected to extremes in humidity during the shipping process.

Dry ice is an ideal packaging method due to the fact that it is frozen carbon dioxide and does not melt, but sublimates-going from a solid to a gas without a liquid phase. The rate of sublimation is dependent upon the outside temperature, air pressure (the lower the air pressure, the faster it sublimates) and the insulation of the shipping container.

There are a number of considerations when using dry ice in shipping, including the following:

1. Dry ice is considered a dangerous goods shipment and requires additional documentation. The paperwork becomes more complicated when shipping more than five pounds of dry ice. Your preferred shipper can provide the documentation labels to you through their hazardous materials personnel. Once the container is ready for shipment it is necessary to take the package to a staffed shipping location. Shippers will not accept packages containing dry ice if they have been left at a drop-off shipping location.

2. If the amount of dry ice exceeds five pounds, some shippers will not guarantee a delivery schedule due to the special shipping requirements they need to follow. The maximum amount of dry ice that can be shipped in a package is 200 kg.

3. Additional packaging materials, such as styrofoam peanuts, are recommended to fill any unfilled volume within the package as empty space causes dry ice to sublimate faster.

4. Do not place the dry ice at the bottom of the package because cold air will not circulate.

5. Two containers are needed to ship dry ice: an insulated container that holds the dry ice and a second outer box that holds the insulated container. Do not seal the inner insulated containers as venting is required to allow some carbon dioxide gas to escape the package. The outer container should be sealed with pressure sensitive plastic tape.

6. The amount of dry ice needed for shipment varies depending on the product mass, the volume of the container and the effectiveness of the containerÕs insulation. For an overnight shipment, 5 to 10 pounds of dry ice should be sufficient. In order to verify that this is sufficient, there is an ASTM Test Method D3101, "Standard Test Method for Thermal Quality of Packages" that can be referred to in order to evaluate the effectiveness of shipping a package with dry ice.

Resources

Most shipping companies have a Packaging Design and Development Department that can also provide a list of recommended suppliers.