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TESTING CRATES - Determining Crate Loads

A common questions is asked - " How do I determine the load my crate can tolerate?"7

 "Testing Crates." Wood Crate Design Manual. Vol. 252. Dept Of Agriculture. 73-74. Print.

The following is an excerpt from the manual. Please refer to the full article for each testing method information on each factor that determines load tolerances. 

There can be no absolute standards or rules for designing crates. For example, while a crate top may be designed for loads up to 200 pounds per square foot, it might be subjected to a load of twice this limit under difficult storage conditions. However, because of the safety factors included in the design, short-time application of such static loads does not ordinarily cause failure. Nevertheless, it is reasonable to assume that some crates will be subjected to loads that will cause failure. 

But designing all crates to resist. every stress is not economical. Thus, both design standards and tests to check them should be based on conditions to which the majority of crates are subjected. The design of a crate may vary greatly for any item, depending on the means of transportation and the destination.

FACTORS THAT AFFECT CRATE DESIGN The selection of a crate depends on, in general order of importance, contents, destination, method of transit, handling hazards, storage conditions, and costs. These factors overlap, but each will be outlined separately to aid the designer or shipper in selecting the proper crate.

Domestic shipment of most items will not ordinarily involve as great or as many hazards as shipment overseas. Consequently, in domestic crates frame members may be smaller and fastenings less rigid. But some means should be used to evaluate a newly designed pilot crate, whether for domestic or export shipment. Tests should simulate actual shipping, handling, and storage conditions as closely as possible in order to determine the suitability of construction. 

The development of crate design criteria at the Forest Products Laboratory led to a series of tests designed to include those hazards ordinarily imposed on crates during storage, handling, and shipping. These tests were used on scores of containers of all sizes and types, from small open to large sheathed crates. The following sections outline the various test methods that might be used by the designer to improve crates or to verify construction details. However, with a crate design based on engineering principles, a limited crate testing program may be satisfactory. A good indication of the crate ís adequacy could be gained from superimposed load, edgewise-drop and cornerwise-drop tests.


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