Engineers tend to think differently than the rest of the population. An engineering education, while chock full of advanced math, statistics and physics, primarily teaches students how to think critically and solve problems. Working engineers exhibit habits of mind like creative problem-solving, visualization, systems thinking and striving for constant improvement. In short, engineers seek to make things that work or make existing things work better.
Recently on Engineering360’s sister site, the CR4 forum, a non-engineer posed an intriguing question and got some equally intriguing answers. CR4 user 'Peco' is managing a coconut production operation in the Pacific Islands and oversaw the construction of a brick oven for drying grated coconut. The group laid down two 4-foot by 8-foot, 2-millimeter-thick stainless steel sheets as a surface, which is heated by a fire within the oven.
The coconut must be dried quickly and must not be toasted, so the stainless steel must get very hot very quickly. Peco reported that when the stainless steel sheets — which are welded together — are heated, they tend to warp and make the coconut drying process difficult.
A Problem and Potential Solutions
There are many smaller issues behind the main problem of a warping metal sheet. The oven’s surface must be stainless steel due to food-grade requirements, but its high thermal expansion and low thermal conductivity make it especially prone to warping, both during welding and rapid heating in general. Unfortunately, stainless steel becomes a necessary evil: it’s called for by regulations but causes a number of problems during the actual process.
Other CR4 users jumped in with suggestions and solutions, many of which focused on the welding process used to join the two sheets. User 'spades' recommended preheating the assembly and supporting the sheet against the frame to relieve stress. Other users focused on heating the sheet to non-uniform temperature during coconut processing and recommended using a thicker sheet or trying to spread out the oven’s heat more evenly. Others recommended not welding the sheets at all and using mechanical fasteners instead.
After all was said and done, Peco received the following advice for solving the application issue:
- Avoid welding the stainless steel whenever possible
- Limit restraints on the steel sheets to allow for expansion
- Preheat the sheets and avoid extreme temperature changes when welding
- Form the sheets into a trough during fabrication to neutralize expansion during processing
- Look into sourcing a one-piece stainless steel roll to eliminate welding
Do you have an engineering question or interest in initiating an engineering discussion? CR4 is a great place to start.