If the weight and the resulting weight forces of the packaged goods are extremely high, the cross sections of the longitudinal skids may be very considerable if they are dimensioned (calculated) properly. This may make construction difficult or uneconomical. In this event, it is possible to construct the floor from steel profiles in place of lumber. Here again, calculations are used to dimension the steel components correctly. The box/crate is then constructed with lumber.
Slinging points: Protection of skids and edges on load-bearing packages
To prevent the ropes/chains from cutting into the longitudinal skids and the edges of the lid during craning, the slinging points of boxes with a gross weight of 3,000 kg or more must be fitted with sheet steel edge protectors.
Note: 3,000 kg gross weight is a value derived from the experience of packers
Figure 92: Edge protection on the floor of the box
Figure 93: Positioning of the edge protection
Figure 94: Design of the lower edge protection
Figure 95: Design of the upper edge protection
On load-bearing packages up to a gross weight of 5,000 kg, the edge-protection corners can be attached by nailing; above 5,000 kg, they must be attached with screws. The screw holes must be pre-drilled.
The thickness of the steel plate used for the edge-protection corners depends on the gross weight of the packages. It should be chosen in such a way as to ensure that the steel corner cannot be deformed by the forces generated by the ropes or chains. The following guideline values can be taken:
Table 14: Guideline values for sheet metal thicknesses
The contact area of the edge-protection corners, in particular the bottom corners attached to the longitudinal skid must be dimensioned in such a way as to ensure that the crushing resistance of the lumber is not exceeded.
The edge protection on the lid must be sufficiently long as to ensure that it covers a full range of slinging angles.
In the case of packages with a gross weight > 50 t, the upper edge-protection corners must always cover two lid-support members. Squared-lumber fillers must then be placed between these lid-support members and must be braced by additional squared-lumber supports in the direction of the lid-support member.
Edge-protection corners are also used on the floors of sleds and squared-lumber constructions.
Figure 96: Upper edge protection for gross weights > 50 t