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Question about welding plastic, molding, and water bottle thickness for 1 gallon sized water bottle

Question about welding plastic, molding, and water bottle thickness for 1 gallon sized water bottle

Question about welding plastic, molding, and water bottle thickness for 1 gallon sized water bottle

(OP)
Hi all,

I have a question regarding water bottles. I'm trying to manufacture my own bottle from a factory in China, however, sometimes it's very difficult to tell if they're honestly offering me the best quality service- or even telling me the truth behind their designs.

So I have 2 questions, if someone with knowledge in this area can please answer them, that would be great:

(1) Based on my water bottle design, because most companies consider it complex, some parts of the bottle cannot be part of the direct mold with the whole body. So instead, they will utilize a welding process through heating and gluing to connect the part of the bottle that cannot be included in the total body mold. Here are two images they sent me. The first image, is the welding machine they are going to use. The second image, is an example of a welded bottle they have.

My biggest concern regarding the welded parts of the bottle is that.....won't it be cheaper quality? Won't the welded area of the bottle be more fragile than the part of the bottle that was actually included in the full mold? Won't the welded area of the bottle break down easily overtime? They ensured me that welding is just as good as molding, and that it will not be weakened or deteriorate the durability, and that it should not break or snap off due to applied pressure in the future. I'm not sure what to believe of this statement, as I have no experience with welding plastics. Can anyone chip in some insight on this?

(2) On average, most water bottles are 1mm-2mm thick. However, my water bottle will hold a gallon of water in it. It has a unique design, it's almost identical to the shape of a dumbbell really. Would having 3mm thickness for this water bottle be overkill? The reason is because I'm assuming the thicker the plastic is, the more impact resistance it will have if it falls- so it won't crack as easily. Should I choose a thinner thickness, such as 2.5mm? I'm not too experienced in this, and couldn't really get much insight from other people who I asked- thus, that is why I hope this community can help me conclude on what thickness I should choose for my bottle. I want to be sure that the thickness I choose for the bottle, that if it is dropped when its completely filled (so it'll be heavy, roughly 9 lbs), that it won't crack/dent/break.

My bottle will primarily be used by gym-goers, athletes, and maybe by runners/hikers. It may drop, and it holds a gallon of water, so it must not easily crack. I did cut up a bunch of water bottles in half and measured them and it seemed they fluctuated between 1.5mm - 2.5mm at the most. However, I wouldn't consider those bottles "heavy duty". It was just the typical brands such as CamelBak and Nalgene. I want to create a "heavy duty bottle" that won't break easily. The material I plan to use to create my bottle is with a high impact resistance plastic called Tritan, used by many other popular water bottle brands.

If someone can please offer their insight on these questions to me, that would be greatly appreciated! I look forward in hearing back :)

RE: Question about welding plastic, molding, and water bottle thickness for 1 gallon sized water bottle

I have seen some pretty complex bottles blow-molded without welding, so I'm really curious about what makes welding necessary for your particular bottle.
Can you share a drawing with us?

Mike Halloran
Pembroke Pines, FL, USA

RE: Question about welding plastic, molding, and water bottle thickness for 1 gallon sized water bottle

(OP)


Here's a picture. The orange octagon shaped lid on top will be welded to the top of the bottle as you can see in the picture. The brown octagon shaped lid on the bottom will be welded to the bottom of the bottle. I hope this helps as a good reference. I believe the manufacturer said the welding process will use glue and heat. For some reason, those lids cannot be included as a mold with the rest of the bottle. I don't know why the manufacturer cannot do this.

RE: Question about welding plastic, molding, and water bottle thickness for 1 gallon sized water bottle

The welding machine shown in your first photo is a generic ultrasonic welder, shown with tooling for welding some kind of small flanged cup. Not like the seam shown in your second photo, which was done differently, by some other machine, I'm not sure how.

My experience with ultrasonic welding has been all bad.
Maybe somebody knows how to do it well, but I haven't met them yet.

The design you have proposed requires four injection molds, including the cap.
The necked one will be fairly expensive.
... and I can't see a clean way of providing an energy director for the circumferential welds, for which you will need a much larger machine than the one in your first photo.


You can do it, I think, with three molds, with injection blow molding.
- One injection mold for the cap.
- One injection mold to make a preform/parison, sort of like a thick test tube with a finished neck.
- One blow mold that closes on the preheated parison, and inflates it in two places, making the finished bottle.

You will need to severely round off the larger features of your dumbbell, making it effectively two donut shapes with six flats on the periphery. Large radii all over, etc. No sharp corners.

The geometry of the enlarged sections makes it a difficult part. The entire area of each of the donut shapes has to be stretched from a short thick cylindrical section of the parison. The walls will be very thin. Study some multi-liter soda bottles.




Mike Halloran
Pembroke Pines, FL, USA

RE: Question about welding plastic, molding, and water bottle thickness for 1 gallon sized water bottle

For alternative ways to produce your product, when I read your first post, mentioning it is a bottle, I wondered why they haven't used blow molding. But obviously it is not a simple bottle and Mike has already made enough comments about the technique.

I understand your choice of Tritan material (I guess discussions on health issues are irrelevant), and I believe that is the best option since you are expecting the product to be glass-like and heavy-duty. However, I doubt that making the walls thicker can help it become stronger after some point, but it will make it a lot more difficult to process for the molder, maybe they would not give feasability for that, if they care to do.
Well, I have never worked with Tritan but I have some experience with ultrasonic welding and I am trying to imagine how they can make those parts' welding with that machine and horn. I am afraid it does not belong to your process, as Mike said, because of the circumferential inadequacy of the horn. Or maybe the Chinese have found a clever way to make it, which we can not imagine with the info/visuals we have.

RE: Question about welding plastic, molding, and water bottle thickness for 1 gallon sized water bottle

I should have mentioned that the 'horn', the part that connects the ultrasonic source to the joint in your part, typically has to be long, and tapered, and machined from a large solid block of titanium. A small horn typically costs as much as a completely finished medium size injection mold, and the need for one is typically revealed as a surprise, well after you are committed to ultrasonic welding. The few ultrasonic system sellers I have met were universally sleazy.

Mike Halloran
Pembroke Pines, FL, USA

RE: Question about welding plastic, molding, and water bottle thickness for 1 gallon sized water bottle

Is this your product?

RE: Question about welding plastic, molding, and water bottle thickness for 1 gallon sized water bottle

It appears that someone, perhaps us, has been hoaxed.
Thank you, dgsmith612, for finding that video.

Everyone please watch the video; it's rather fun.

Mike Halloran
Pembroke Pines, FL, USA

RE: Question about welding plastic, molding, and water bottle thickness for 1 gallon sized water bottle

It could also be made at lower tooling cost, but higher per-part cost, using rotomolding. This assumes (as Mike did) that the alternate end cap colors are not a desired "feature", or could be done with post-mold coloring or in-mold decals.

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