Most large plastic storage containers like those produced by sterilite have sloped sides so that the top is wider than the base. This of course means that when placed side by side there is a large gap between them of wasted space. Is there a reason for this? Easier to manufacture? Structural integrity?
Edit: Thank you very much to all of you for your responses!
In: 94
I work in injection molding, it’s been answered here already, but I’ll give a bit more detail.
Shipping — As others have noted, the lids and containers can be nested separately during shipping to save on space. Many manufacturers will ship parts in plastic bins, and have those bins returned to them to reuse instead of shipping corrugated fiberboard that is easily destroyed or metal containers that add too much weight.
Manufacturing — Again as others have noted, it helps the part release from the mold. This is because when the part is molded, it shrinks as it cools and creates a vacuum. Instead of fighting the vacuum, it is preferable to add draft angle to the mold. I like to use the situation of getting two plastic buckets stuck together, they’re *difficult* to unstick. Most molders rely on high cavitation rates (low cycle times), so the parts aren’t completely cooled when they’re ejected from the mold and as a result they’re still soft. Ejecting the parts while they’re still soft can lead to all sorts of problems (warping, pin push, etc.) and pushing the part out straight without allowing air into the vacuum behind the part risks drag marks. One commenter stated that these sloped wall containers create more complexity, but the opposite is true. A straight walled container would require slides or actuating cores to prevent drag marks on the finished product.
Structural — This likely isn’t taken into consideration as a priority, since the speed at which these molds are filled with plastic the molecules are highly oriented and stronger in that direction and the plastics these things are made from are pretty strong and flexible. The shape likely doesn’t hurt either, but I’m not sure on that one and can’t answer it with any real knowledge.
As others have said, stacking and production. But also it prevents from your stuff from getting stuck in the box. This way, pulling upward always work. If they were vertical, then you could deform them sides a bit by pushing something in and it would hard to take it out.
To add to all of this, a lot of cheaper plastics are made from flat sheets drawn by vacuum or pressure into a hot mould, this is called Thermoform. It’s a cheaper method than injection moulding especially when it comes to setup costs and requires a minimum slope angle to ensure holes don’t form when the hot sheet is drawn.
Source: packaging development for food
Sorry it’s nothing to do with nesting. When you plastic inject a part on a mould tool you can’t have parallel sides that run Perpendicular to the tool surface otherwise you would never get it out of the tool. Each side has to have a draft angle so when you pull it it releases. Draft angle tend to be larger on larger tools with cheaper plastic to account for any distortion on the part.
TLDR, you need the angle to be able to remove it from the mould tool.
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