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Some time ago, I finished designing a tea strainer and I had a prototype printed from a certain heat resistant type of plastic (https://xometry.pro/de/materialien/standard-heat-resistant-pc-artig/) using stereolithography. It's quite small - 45mm x 45mm x 34mm with tightly packed 0.5mm diameter holes. (In case you're wondering, it's designed to fit inside this product: https://www.taotealeaf.com/tao-tea-tumbler/)

Tea strainer prototype

The problem occurs when I submerge the strainer into water. When it is first submerged, everything is fine - the water passes through the holed walls of the strainer and within a few seconds, it sinks to the bottom. However, if I repeat this process, an air bubble emerges inside the strainer that prevents it from sinking again even when I try to force the strainer down.

Of course, this isn't a problem if the stainless steel version were to behave differently. The problem is, I don't know what causes this behavior. Anecdotally, other stainless steel strainers with similarly arranged 0.5mm holes have no problem with letting water through. Therefore, my question is twofold: Why does this plastic prototype float when it is wet? Will this problem persist with a version made of stainless steel?

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  • $\begingroup$ Where does this "one" air bubble form? $\endgroup$
    – Solar Mike
    Mar 18 at 13:26
  • $\begingroup$ Well, whichever side of it happens to be facing up when I drop it into water. $\endgroup$ Mar 18 at 13:42
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    $\begingroup$ fantastic. Then no worries about final product. What you describe sounds just like the effect of surface tension. This is related to hydrophobic/hydrophilic. I tried to give a qualitative description here: engineering.stackexchange.com/questions/58463/… $\endgroup$
    – Pete W
    Mar 18 at 13:51
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    $\begingroup$ If this is just a prototype, then maybe all you need to do is get the surface to be temporarily more hydrophilic. Or if it's just the weight of the part overcoming the same surface tension force, just add a temporary weight to represent what it would be if it were made from stainless $\endgroup$
    – Pete W
    Mar 18 at 13:52
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    $\begingroup$ I think this is how swimming mammals stay warm under water. Trapping an insulating layer of air with their hydrophobic fur. $\endgroup$
    – DKNguyen
    Mar 18 at 21:30

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The behavior you're observing with your plastic tea strainer prototype is likely due to the difference in material properties between the plastic and stainless steel, specifically their densities and surface tensions.

Density: Stainless steel is significantly denser than the plastic used in your prototype. When submerged in water, the stainless steel strainer will sink because its density is greater than that of water. However, the plastic prototype, being less dense, may have a tendency to float.

Surface Tension: Surface tension plays a role in how easily water can pass through the small holes in the strainer. While both materials have the same hole size, the surface tension of water may interact differently with the surface of the plastic compared to stainless steel. This could affect how easily water passes through the holes and how air bubbles form within the strainer.

The plastic material likely has a lower density compared to water, causing it to float. Additionally, the interaction between the plastic's surface and water may contribute to the formation of air bubbles inside the strainer, further enhancing its buoyancy.

It's unlikely that the stainless steel version will exhibit the same floating behavior. Stainless steel is denser than water, so it should sink when submerged. Additionally, the surface properties of stainless steel may result in different interactions with water, potentially reducing the formation of air bubbles inside the strainer.

Also, I would like to know what equipment you are making it from.

I'm very interested in this.

I have come across many similar screencases.

Made of stainless steel. Tea Filter, Soy Milk Maker Filtration, Juicer Filtration Mesh

enter image description here enter image description here enter image description here

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  • $\begingroup$ I may be wrong, but this text looks like it was generated with AI. It only answers the answer nominally - not in essence. $\endgroup$ Mar 19 at 15:35
  • $\begingroup$ I don’t care about the density because I pushed the plastic strainer downwards during testing. The air bubble was still present. $\endgroup$ Mar 19 at 15:36
  • $\begingroup$ What exactly is it about the surface properties of stainless steel that you think will make it more permeable? $\endgroup$ Mar 19 at 15:44
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    $\begingroup$ Materials with a high Cause value tend to have lower water droplet adhesion. Water droplets will form a smaller contact angle on their surface, making it easier to slide off the surface and less likely to stay. $\endgroup$
    – Nigen Xiao
    Mar 20 at 2:01
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    $\begingroup$ In the same way, the generation of bubbles can be related to the Cause value of the material, although this relationship may not be direct. Suppose the material used in the extrusion process has a higher Cause value. In that case, it indicates better corrosion resistance, which may reduce the possibility of corrosion leading to bubbles during the extrusion process. $\endgroup$
    – Nigen Xiao
    Mar 20 at 2:01

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