Slotted bolt holes allow for expansion in Schmitz design

Schmitz Cargobull, Germany's largest trailer manufacturer, solved the problem of differences in heat expansion of the two metals using slotted bolt holes when fastening aluminum sides to a steel floor.

The problem is especially acute when hauling asphalt at 200° Celsius (392° F). The Schmitz dump body is 7.3 meters (24 feet) long. At 400° F, the aluminum portion of the body would expand 32 mm (1.26") in length. However, the steel portion would grow only 20 mm (.79'). That's a difference of 12 mm, almost half an inch.

The neck of the bolt is ribbed so that it cannot move when pressed into the aluminum sidewall flange. The bolt holes on the steel floor assembly are elongated so that the bolt can move in this slot. A sliding plate of galvanized steel is placed between the aluminum and the steel members during assembly.

In the Schmitz design, the Hardox 450 steel floor is 4mm (.157") thick. The aluminum sidewalls are 5mm (.197") thick. The completed body weighs 700 kg (1,540 lb) less than an all-steel body. That is, 24.5 m3 (32 cubic yard) body with 1460 mm (57") high sidewalls would weigh about six metric tonnes (13,200 lb) including the steel 3-axle chassis, and a tarpaulin. The same all-steel body and chassis would weigh 6700 kg (14,775 lb). An aluminum bodied trailer would weigh 5700 kg (12,550 lb).

This bolted body has more advantages for the Schmitz company, which sells throughout Europe and has satellite assembly plants in other countries. The body consists of five pieces: two sidewalls, a front end, rear gate, and steel floor.

Twelve of these knock-down bodies can be stacked on a truck and shipped to, for example, the newest Schmitz assembly plant in Zaragosa, Spain. Eight dump trailer chassis make a load. At the satellite assembly plant, no welding skills are required. The bodies are bolt assembled using modules that are largely self-fixturing.

The modular design of the body provides a range of weight and cost variations. Five material combinations are possible:

  • Steel floor and steel walls bonded together.
  • Steel floor and steel walls welded together.
  • Aluminum floor and aluminum walls bolted together.
  • Aluminum floor and aluminum walls welded together.
  • Steel floor bolted to aluminum walls.

Bolting of the modular components allows easier repair of damaged components. Schmitz Cargobull AG, Bahnhofstrasse 22, D-48612 Horsstmar, Germany.

TAGS: Trailers
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