Happy Plate — The Kitchen Series
Designing reasonably cheap utensils for the kitchen
This is the second design concept in my Kitchen Series, my attempt to design three products for the home. If you haven’t read the first one, it’s here.
While it may not be the best thing ever, I enjoy hot food. Not too hot, just hot enough. Not 100 degrees, definitely not room temperature either.
I probably inherited this from my mother and, true to form, when food was freshly cooked or freshly warmed that it was too hot to eat it she would place the plate inside a shallow bowl with water in it to cool it off. My mother was a nurse in those days, but this was my first convective heat transfer class.
Of course, you could probably blow on your food until it was cool enough to eat but I found that I preferred the plate in a shallow bowl as it cooled the food more evenly. Also, it cooled the food slowly which as I explained in the previous design concept is how many people like to enjoy hot food items.
I figured that this would make a good combination for a kitchen utensil, designed for kids. A plate that slowly cooled hot food. Taking some extra time to crawl the internet, I did not find anything that currently did that. Which could mean two things: it’s an incredibly silly idea or no one would like it.
Challenge Accepted.
As usual, this post is about the concept, how it can be made and how the new design is compared to the original or what’s currently available.
Concept
Based on the idea, the solution should have two parts: a plate where food is placed to be eaten, and a tray that can be filled with water to cool the food.
It is important that the water be poured in before the plate is placed over it, but it is also important that the whole product — when carried with water and food — is not too heavy for a child between 4 and 8. It is also important that the water should not spill as it could be hot or cause a trip hazard.
As the food is hot, it’s important that the child (or parent) should be able to carry the plate without coming in contact with a hot surface.
It’s also important for the product to look fun, with colour and size that makes sense for a child to use. I had this idea to make the whole product look like a smiling face (or emoji) from the top.
Research
I wanted to know what the typical diameter of plates are and what weights are advisable for a child to carry. Plates tend to average about 25cm (about 10 inches) in diameter.
However, there wasn’t much information on weights except for backpacks— which should not be more than 5–10% of the child’s weight. So, I had to go with other products in the market as a guideline. From the examples I saw, 13 ounces (about 0.37Kg) was a good average point for plastic plates.
Design
Again, I used Onshape for CAD. It has now become my staple tool.
I decided to use the tray handle as the lock for the plate, so that way it could be a little latent. I used the Beaming Face with Smiling Eyes emoji as inspiration for the final plate design.
For the tray, I went with a semi-circular groove around the body of the part. The section through the centre of the design shows how the two parts relate.
The red line above is where water should be filled into the tray before the plate is placed on top of it, the plate will then displace some water to cover the entire bottom surface of the plate as a site for convective heat transfer.
Materials & Production
The tray (plastic) can be injection molded, but the most important production piece is that it should be annealed after. This process helps the tray resist heat better and will be better for the longevity of the product.
The plate can be made using a deep drawing die working with a hydraulic press after the stainless steel has been cut into the development shape.
Analysis
Most of the plates for kids on the market, look like the two below.
The two represent the range from colourful to functional, the plastic one on the right will insulate the heat from the hot food better but may not be the choice for kids once they grow past a certain age.
Also, colourful plates like that are made out of melamine — an organic plastic that is machine washable — which is quite brittle. Although it is resistant to shock and drops, it starts to chip away at the sides pretty early.
More functional plates, like that on the left, is made out of aluminium or stainless steel which can get quite hot to touch with hot food placed on it. But food placed on it tends to get cooler quicker as those metals are good conductors.
Again, I tried out SimScale for the thermal analysis, using 90 degrees as the temperature of the food (the left dial below is graduated in Kelvin though).
The good news is that the bottom of the product is kept at room temperature as well as the handles to carry the plate.
Note: There is a little error in the simulation as SimScale shows the whole base of the plate as the boundary (to keep the convective boundary condition) because some parts of the base are extruded out from it — that’s a flaw with SimScale.
Final Rendering
I used Keyshot, the first time of trying, to render the final design.
To use, water is filled into the bottom tray and when food is placed on the plate, the plate is lowered onto the tray and rotated counter-cockwise to lock the plate in position. Then the product assembly can be carried.
As it is a product for kids, it makes sense to have variations in bright colours.
Thanks for reading! I’ll be designing or redesigning the next item in my Kitchen Series next month, please leave me feedback or lessons for improvement. I’m also looking for a design engineering opportunity, so hire me :)
