Bending PVC

I once bent 3/4" pvc using a similar technique to bending glass tube

Slowly applied heat and pressure.

Will try 4" and 5" tonight and see if it can be done.

A bend radius of 12" seems pretty tight for 4" PVC pipe, especially for Schedule 40 or thinner wall. The sand packing may help, bit I would worry about thinning along the outer circumference of the bend. If the pressure will be substantially less than the normal rating, this might not be a problem. I'm curious to know how this works out.

PVC is commonly sold in Sch 80 and 40. The thinner wall versions are usually rated in psi rather than by schedule; that may be why Sch 20 is rare.

After 5 attempts, my method of heat and bend and roll and heat and bend and heat and roll, FAILED miserably. I dont recommend my way.

Dry Sand packed firmly? Need to spend more time for it. It is not that critical. Just don't burn the pipe. I do it on a plywood to not lose too much heat to the floor. The warming up process takes long - about 15 minutes. When the radius is very important, do it against a pipe or something circular. If you fail, you can even do it again with the same pipe on the same spot. Once I did it with a spring and a rope inside. Too short bends don't work that way. Couldn't get the spring out. You can also pull a series metal balls through till it stiffens. The 4" pipe needs 2 persons - you need more hands - and water to cool it down once it is formed. Don't give up.

Thank you.

I tried everything you said but the metal balls pulled through it.

I was trying to bend it around a rim for a spare tire off of a small car

I tried a propane torch and scalded the pipe

heat gun was shorting out internally, so I gave up on it

gonna try the balls, Just to see if I can do it

The pipe is for a dust collection system. I think I'll try a long sweep ell used for sanitation systems. I know about the ones made for dust collection systems. They are just not available to me locally. After buying one by mail and paying for shipping, it can get pretty pricey.

You might take a look at ABS rather than PVC. Sweep ells are readily available, and I think less expensive than PVC pipe and fittings.

You could try Sceptre, electrical plastic conduit, maybe you have a local electrical supply house. Sceptre elbows are available in several radii.

If its for a dust collection system then You want it as smooth as possible. any elbow let alone one with pits or other abnormalities will really cut into the efficiency of the system.

oilcan13

I forgot to add that these elbows for dust control systems are available thru several manufacturers. Pick up a woodworking magazine, in the back they list a few manufactures.

oilcan13

You can insert a tension spring inside the PVC pipe and bend it directly without heat. Then draw the spring out.

bend 4 1/2" PVC pipe directly without heat, no way...

If the bend radius is say 10 feet or so, this can be done rather easily.

IT IS CORRECT, MUST USE SAND AS FILLER.

BUT, IT IS EASIER WITH AN INFRARED LAMP (WHILE TURNING THE PIPE IN FRONT OF IT) TO HEAT IT UP TO THE SOFTENING POINT (ALL ARROUND), THEN, UPON A MOLDING CURVE (WOODEN OR STEEL RIBON) COOL IT DOWN WITH WATER SPRAY.

YOU CAN EVEN MAKE THE FITTING SOCKET AL ONE END.

Rather than trying to bend a 90, look at your package space and see if you can use a standard 45 and a street 45. You will find the radius will be greater than that of a 90. Space permitting there are 22.5 in that diameter so you can get to 90 using one 90, two 45s, four 22.5s, or one 45 and two 22.5s.

All of these will increase the radius over the 90

Once had to attempt to do this for a former employer. Originally told him that it would be extremely difficult if not impossible to do so in shop or field but he insisted that we do it. After much expensive labor, material and time it was impossible to refab pipe into elbow with same radius as moulding/extrusion of original manufacturing process.

Use a electrical "Sched 40 PVC 4" conduit sweep elbow" instead.

http://www.mcmaster.com/#conduit-elbows/=7nyih9 but buy it from a local electrical supply house. This is available in several different radius. A "Sched 40 PVC 4" conduit elbow" will have a smaller radius if that is what is of interest to you.

I surmise that the 4-1/2" you state is the actual o.d. of the pipe. This is the same as the actual o.d. of the 4" nominal size that is the industries wide term for this size.

All you will need to incorporate this into your piping scheme is a coupling at each end to connect it into the piping. No hassles with heating, packing.

Note- electrical conduit elbows have a much greater radius than pipe fittings in order to accomodate the insertions of pulling snakes and also to pull the wire through the conduit easily and not destroy the insulation.

Good Luck

"Note- electrical conduit elbows have a much greater radius than pipe fittings", this might be a good thing in a dust/debris extraction system.

Cheers

Baxterm-

Yes you are correct, it is. It also makes them good for such things as elbows for drainage systems that don't have much velocity and have solids within the liquid such as drainage water with silt in it. They don't have a fast change in direction so solids tend to stay in suspension as the fluid flow vs. the abrupt change in direction of a close raduis of a pipe fitting. This is also why Sched 40 "pressure pipe" fittings have a much smaller radius than that of the same size "DWV- Drain Waste & Vent" fittings used for drains. Many DWV fittings also are available in "sweep" styles such as sweep "Y", sweep "t", sweep elbow, etc. which have wider radius'.

I notice that "Scepter", a Canadian brand of electrical conduit, specifically markets a dust collector version of its conduit,, I wonder if it has sufficient electrical conductivity to deal with the static problem?

Half of your notion is correct. yes, you fill it up with sand, but I have strong doubt that steam or hot water will prove practical. I suggest to make a wooden template of this radius and after filling with sand slowly heat it with a blow torch with a soft and constantly moving flame. After a short time it will become very soft and you can bend it on the template. This is the most practical method of bending PVC pipe. I have seen experianced persons bending pipes without filling, but that ofcourse is good for smaller diameters. For bigger diameters it is adviseable to bend it filled to avoid the risk of collapsing.

Before you use a torch to heat your conduit you may want to read this article from the NEC:

352.24 Bends — How Made.
Bends [in PVC conduit] shall be so made that the conduit will not be damaged and the internal diameter of the conduit will not be effectively reduced. Field bends shall be made only with bending equipment identified for the purpose. A blanket heater like this one is rated for this purpose, but it's a little pricey if you do not do this work professionally. (Propane torches and portable kerosene room heaters are not rated for this purpose - though the do work pretty well .)

Also from 352.24:

The radius of the curve to the centerline of such bends shall not be less than shown in Table 2, Chapter 9.

From Table 2, Chapter 9, Radius of Conduit and Tubing Bends:

The minimun radius for a 4" conduit 90 is 16 inches if you have a bending shoe that fully supports the radius of the bend, and 24 inches for any other type of bend.

If you do not get the results you want bending yourself, try looking at www.usplastics.com They deal almost exclusively with plastics, have a very thorough line, and have live people that answer their phones. Good luck.

It appears to be very easy to bend correctly, here is a video (not the only one!) that I found on YouTube:-

http://www.youtube.com/watch?v=aZ4U7XdTIFQ

Search on YouTube, there are several more like:-

http://www.youtube.com/watch?v=47j95zGD-a0&feature=related

http://www.youtube.com/watch?v=2Qs-PILTCbw&feature=related

Just search with "Bending PVC"....on YouTube of course....

This job is perfect for a "lost wax" molding method.

I suggest you buy a large panel of Dow Corning's pink insulation form. Band saw it into as many pieces as are needed to give build up a block large enough to carve your design. I use an aerosol spray adhesive (3M) and tooth picks to fix the blocks in place.

Now sand and carve the material to the shape and bend radius you want. Wrap the entire piece with tightly stretched Saran wrap.

Then simply build up the exterior with as many plies of Bi-Directional fiberglass and two part vinyl-ester epoxy as you feel are needed to give it strength.

When cured, drill a hole an inch or so in diameter in the fiberglass in an appropriate spot and pour in some gasoline.

The gasoline will dissolve the foam, Pull out the remnants of Saran wrap. Sand and detail as needed.

For over 30 years I've used this method of composite construction for everything from aircraft parts to intake manifolds. I find it especially effective for making custom fuel tanks.

Don't skip the Saran Wrap. It's needed to cover the spheres that were sliced open during the shaping process and insures a smooth surface.

Don't use Polyester based resins. Aside from being toxic, the MEKP hardener will attack everything but the family dog.

Have fun!

L.J.

Great post. Thanks.

Thank you Bob!

L.J.

ronseto,

This is not easy. If you are going to pull wires through the bent tube, you will need the circular cross section area to stay smooth and fairly constant. Have you considered using a pulling-ell? If you want to try it anyway you will need to control the heating carefully and you will need to use some kind of die to control the radius and a spring inside to hold the cross section. Use SCH 40 and you may end up with a wall on the outside closer to Sch 20. Heat guns (hot air) are the best heaters to use. Move the guns and avoid hot spots and sags from overheated areas. Apply a steady force to bend the tube into the radius form. Good luck. You might find a clothes dryer duct will give up enough spring wire to support the bend inside. If the wires stick inside, leave them.

Luther M

My electrical contractors do this all the time. There's not much difference between PVC pipe and PVC conduit. They have a tool that looks like a tool box that contains rollers and heaters. If you know someone that works as an industrial electrician they can probably help you out........gratis.

thank you all for your advise and ideas. Naturally I'm looking for the cheapest way and I'm happy to add new knowledge to my database.

How about this: get a large long balloon; inflate it to the internal diameter of the pipe (OK: needs careful selection of balloon); wrap the balloon in duct tape, making sure that there are no weak spots; deflate it; 90% fill it with water; insert in pipe; fill with water; tie off; seal in the end with more duct tape; use a hot air gun to evenly heat the pipe, and, bend round a former. It might be better to start with a bent balloon to avoid the wrinkles in the duct tape when the pipe starts to bend.

That reminds me of an old German joke:-

Young man goes to the supermarket to complain in a loud voice that the Condoms he recently bought from them (Rubbers in USA), break sometimes when in the middle of the sex act!!

An old man going by hears the kefuffle and chimes in with "and they also sometimes bend in the middle!"

Try using a spring placed at the bend easy to remove and the spiral of the spring keeps the pvc from bending.

How about getting a length of cloths dryer ducting. Bend it into the exact shape you need. Use that, OR, cover the duct with mould making rubber, and let set. Slice the mould open and remove the ductwork. Now use the pattern to cast a pipe out of low temperature acrylic plastic. Allow to set thoroughly, and remove. Now carefully carve out the middle.

Hey, it is no worse than some of the other suggestions so far. Have fun.

Since this is for a dust collection system, make sure to plan for dissipating static buildup in the pipe sections.

Want to know something?

A sand filled 4 inch pipe, say 10 feet long.

Move the bending area over a gas burner (stove type e.g. on a barbeque)

Turn and slide.

With 2 persons. Lift it about 6 inches above the flame.

When hot enough - it will be difficult to keep it straight - It will bend by itself- Just warm a little bit longer and put the pipe on a floor in the radius you dream of.

I have done this many times. 0- 90 degrees, U bends, S bends. Here are no common bends available too.

In Belgium we made several post delivery system pipes with PVC pipes of 4 inches and made all the bends this way right at the site. And containers were shot through it. That is no computer science, but in the field experience. If for air ducts, make it anti static.

better late than never. does it have to be pvs / ads. if not, instead of using up the worlds supply of pvc and a 1000 hours of over time, why not take a ride to the local exhauhst fabrication shop and have them make you one out of steel,aluminum or stainless to the exact length and degris. pay them their 75 bucks and get back to work. they can even expand or contract the ends to fit back in to your system.or use dresser couplings. school bus exhaust pipe is a standard 4" shelf item.