Best Method, glue? weld? What material, pp? pe? abs? Opinions needed.

[n8scstm]

I am forming a 1 inch hollow pipe with a 90 degree bend in the middle. The total length is about 20 inches. The diameter is about 1 inch. Wall thickness is about 1/8" but could be as small as 1/16". In addition to the bend there are also 3 tees in the pipe. My first thought was to make rotational moldings, but that is too costly. Then I decided to have abs, pp, or pe extruded to the diameters that I need and then cut the pieces to spec and hot plate weld them together. This is still a viable means as far as cost and time go, but the extrusions are custom and are still a little on the expensive side. Instead of welding I have contemplated gluing but I cant find any suitable glues. Another option that I came up with is to build my own vacuum form, trim the edges and weld or glue the two pieces together. What materails and glue would I use for this? One last hitch! The material and glue need to be suitable for consumable liquid to flow through. Production numbers will start out at about 100 units. However, this could change to thousands. What are some opinions on this topic? Anything will be helpful.

 

[patprimmer]

I am sure you can buy pipes and fittings in a range of sizes, including 1 inch or close to it.

Have you tried PE irrigation pipe.

PE pipe systems for beer and beverage.

Nylon 11 or 12 gas or air lines

The PE pipes will need compression or grabber fittings, but I am sure thatsystems exist.

The nylon can be glued with a proprietory glue, but I am not sure about food contact with the glue, or it can be glued with methacrylate glues, but joint strength will be marginal, or you can use formic acid as a glue, but it can be messy and dangerous to handle

Regards
pat

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[n8scstm]

Thanks, Ill check out those glues. I dont want to use fittings though. This part needs to be asthetically appealing. Thats the reason that I would cut my own sections and glue or weld them. Joint strength shouldn't be an issue because it is only subjected to atmospheric pressure.

 

[patprimmer]

The glues mentioned only apply to nylon.

PP and PE are very difficult to glue.

ABS is very easy to glue with solvents, but the food contact might be an issue with the solvents

Regards
pat

eng-tips, by professional engineers for professional engineers

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[n8scstm]

So I could pressure form 2 halves of the part, and use one of the mentioned glues to bond them together?? I guess my real question now is, should I pressure form to halves to form a hollow pipe, or use extruded pipe, cut and glue/weld them together. I feel inclined to try the pressure forming because I think I can get ahold of an aluminium mold easier than I can get some pipe extruded to my specs. So if I try this, should I try to glue the halves together or weld them? What I'm after is the least expensive, per part, cost with a resonable start up cost. I think I can get the molds for free at my work so that wont be an issue. Hot Plate welders are relatively inexpensive too.

 

[patprimmer]

Glueing is a messy process, and welding always displaces some material, so both can be unsightly unless the joint is designed to hide or cantain the material displaced on the joint line.

Also with a large complex part, it will be hard to accurately align the entire joining surface, so leaks and mismatch will be a real challenge.

Thermoforming plastic sheet is not a very precise process.

Buying pipe is by far, my prefered method, possibly with nice neat compact glue together fittings. The socket and spiggot connection with glue together fittings makes for a strong joint. The nylon gas pipe system is that design.

You can also weld PP and PE with a hot air gun and plastic welding rod. This way you get a strong joint and some reinforcement by the build up of weding rod at the joint.

Regards
pat

eng-tips, by professional engineers for professional engineers

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[mrglynn]

A lot of good responses and suggestions here. I will weigh in with some comments. First, from a materials perspective, the choice of an amorphous (ABS) vs crystalline (Nylon) material is going to have an impact on joining. Heat driven processes (sonic, hot plate, hot air) and solvent bonding are good for amorphous materials. For crystalline materials, you should look at specialty adhesives or pressure bonding (spin welding).
Not knowing what the flow rate needed for this apparent "manifold", but seeing that there might be some volume for the future, you might want to explore 'gas assist' injection molding. This can make a hollow part in virtually any configuration and material. Think of the handles on a chainsaw or weed wacker for example. Start with a low cost aluminum tool. Still expensive, but accurate and no muss or fuss. Hope this helps.
Mike Glynn
763-428-6180

 

[stanier]

One problem with welding ABS is that the material may have up to 3% inherent moisture. Hence when you weld the water becomes a vapour and wrecks the weld. The only successful process is hot extrusion gun wleding. Not suited to your small sizes.

Welding of PP or PE sounds the most promising.

 

[n8scstm]

I came up with yet another idea. I found extruded acrylic pipe already made in my dimensions. Cheap too! I could cut the components that I need and use solvent to bond the services together. What does everyone think about that. I bought some small samples and I'm gonna attempt a prototype. Hopefully it comes out nicely. This is the cheapest method yet, startup and per piece, so I am excited about this one. Plus there are a variety of colors for virtualy no additional cost.

 

[patprimmer]

Acrylic is very easy to form , weld and glue. If it has the mechanical properties you require, it will be fine.

Take care when machining it as it will easily pick up in the machine and break. Use sharp, woodworking tools with plenty of back clearance and set so as not to generate to much heat, and use low rake angles so it does not want to self feed and grab.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[n8scstm]

Flow rate is about 4 gpm. I'm gonna use .75 id. With atmospheric pressure acting on 3 colomns of water each at a height of 10 inches, this should be about right.(I hope)

 

[cpretty]

Beware of stress cracking.

Using solvents on acrylics is difficult when stress is involved. The solvent induces stress cracking (minutes to weeks after joining). Be carefull not to create tight interference fits, as these are especially prone to it.

Anneal the finished product in an attempt to relieve stress, as this should protect the part from solvent attack, and future cracking.

Trick for solvented joints: Add a small quantity of acetic acid (vinegar) to methylene chloride (usual solvent to use), as this stops the joint having the unsightly bubbles that usually occur in large joints.

hope this helps

Craig

 

[n8scstm]

I will keep this in mind. Tnanks for the advice. All my joints are relatively samll. Ive got 2 - 1" OD, 1.875 ID pipes that joint together to form a 90 degree angle. And 3 more fittings of the same size that form tee's off of the main pipe. These are the joints that I'm concerned with. I can do them one of two ways. The first would be a v-shaped joint. This would be done by drilling a hole into the main pipe that has a diameter equal to the OD of the pipe. Then drilling a hole into the tee with the OD diameter thus cutting the pipe in two. Then the two pieces would fit togther. The other way is to make a y-shaped joint. This would be done by cutting the tee at 2 - 45 degree angles forming a point in the middle. Then cut one end of the main pipe the same way and the third piece at a 1 - 45 degree angle. I hope you can visualize this configuration and see how it will form a y. IN my opinion the later would be weaker because the main pipe is cut in two. The only advantage is when gluing, the joints remain in one plane. This is the way that they hot plate weld abs pipes together. If this is confusing let me know and ill put some cad files on my site. Thanks for the input.