CDS Vs BB

[dirtydiesel]

you disappoint me Dan with this "lightweight" business - what about 2" round bar? bit of a pain to bend but a lot stronger than red, blue or girly steel

The problem with 2" round bar is the mill scale on it eats the formers on the bender, and it takes a little while to scarf it

[Warthog]

Found this on http://www.offroadfabnet.com/? good fabrication site, US based and gives some referance to Pipe and Tube processes. Lot of reading but answers a few Q's

» Electric Resistance Welded (ERW)

» Cold Drawn Welded (CDW)

» Drawn Over Mandrel (DOM)

» Cold Drawn Seamless (CDS)

» Cold Rolled Electric Welded (CREW)

» Hot Rolled Electric Welded (HREW)

» What's the difference between Tube and Pipe?

» Types of Tube and Pipe

Electric Resistance Welded (ERW)

Cold formed, electric resistance welded tubing can be produced in round, square or rectangle shapes. ERW tube is produced by processing a flat rolled steel into strips which are cold-formed, welded and seam annealed or normalized (depending on the manufacturer). You can usually identify ERW tube by the blue strip down one side of the tube (which is the welded area). The ERW process can guarantee the weld to be as strong or stronger than the rest of the tube body. The origin from a flat strip results in a more concentric product than Cold Drawn Seamless (CDS). ERW can also be known as CREW (Cold Rolled Electric Welded).

Typical Applications:

Structural columns, beams, supports, heavy equipment frames with 58,000 PSI tensile.

Cold Drawn Welded (CDW)

Produced from a steel strip by cold forming, electric resistance welding (ERW) and cold drawing to finished dimensions, CDW is the most versatile and widely sold mechanical tubing grade. A variety of thermal treatments can be applied to alter the mechanical properties and machinability. CDW is used for a tremendous variety of machine parts where close tolerances and higher mechanical properties are needed.

Typical Applications:

Automotive components, shock absorbers, hydraulic cylinders, sleeves, bushings, axles and shafting.

Drawn Over Mandrel (DOM)

DOM is formed from strip and Electric Resistance Welded (ERW) then cold drawn through a die and over a mandrel resulting in improved inner surfaces and dimensional quality. This process, called cold drawing, may be repeated more than once to reach the planned OD, ID, or wall dimension. Multiple draws can also be used to increase the strength or improve the surface finish of the tubes. During the drawing operation, the tubes may be process annealed to increase the ductility of the material. Lower cost alternative to CDS with equal or superior physical properties.

Typical Applications:

Machined parts, rollers, shafts, sleeves, steering columns, axle tubes, drive shafts, bushings and is most readily adaptable in cylinder applications with a 80,000 PSI tensile.

Cold Drawn Seamless (CDS)

General purpose seamless tubing, which is a solid bar of carbon steel drawn over a mandrel to form the tube section. CDS allows selection of chemistry and rough tube size. Cold drawing produces higher physical properties without heat treating. Offers widest range of sizes and chemistries in mechanical tubing. Better tolerances and reduced machining allowances over Hot Finished Seamless (HFS).

Typical Applications:

Machined parts, bushings, spacers, bearings, rollers, shafts, sleeves and cylinders with a 75,000 PSI tensile.

Cold Rolled Electric Welded (CREW)

Cold rolled steels are steels that are shaped by high pressure rollers at normal temperature in the steel mill. Cold rolling work hardens the material substantially. The steel is then welded by the electric weld process. A cold rolled steel can be either a mild steel or a high carbon steel. Can also be termed as ERW (Electric Resistance Welded). See » ERW

Hot Rolled Electric Welded (HREW)

Hot rolled steel is steel that is rolled to size in the mill while red hot. Hot rolling steel does not work harden it as much as cold rolling. For this reason, hot rolled steel is more easily machined than cold rolled.

What's the difference between Tube and Pipe?

The general term for pipe was that it was primarily used for carrying gas or liquid. It was not intended for structural use because the dimensions used in describing pipe was not dimensionally accurate. Measurement was referred to its inside diameter and wall thickness. The inside diameter was a true dimension, but over the years had become "nominal" (in name only) so that when pipe size was referred to, it was an approximate inside diameter measurement with the thickness described by the term "schedule".

• Pipe is generally more rigid than tube, and is usually produced in heavier wall thicknesses.

• Pipe is specified by a nominal dimension which bears little or no resemblance to the actual dimensions of the pipe. 1" Schedule 40 pipe, for instance, has an actual OD of 1.32", a wall of 0.133", and an inner diameter of 1.049". Tube dimensions are actual dimensions.

• Pipe fittings are sized to meet pipe sizes, but not tube sizes. A 1" schedule 40 nipple will fit correctly on a 1" schedule 40 pipe, but not on a 1" OD tube.

Tube refers to round, square, rectangular or any shape of hollow material of uniform thickness which is defined by the outside diameter and wall thickness dimensions. It is the grade of the metals and how tube is produced and processed that is important.

• Structural Tube is generally produced using the ERW (Electric Resistance Welded) process. Identified under the Circular Hollow Section (CHS) or Hollow Structural Sections (HSS) class. Some steel mills specifically develop structural tube for roll over protective structures.

• Mechanical Tubing is usually produced as seamless, as-welded or DOM (Drawn Over Mandrel) tube.

Types of Tube and Pipe

Structural Tube - high strength welded steel tubing

Mechanical Tube - seamless, as-welded and drawn over mandrel

Stainless Tubing and Pipe - several seamless and welding processes requiring resistance to corrosive materials

Standard Pipe - several seamless or electric weld process, carries liquid or gas

[biasbilt]

Having spoken to Vic Palmer (one of the two top scrutineers in the AWDC and a very highly qualified scrutineer in roundy roundy too) when I started planning my comp safari car, he said that he'd prefer me to use BB as it deforms better in a big crash, so absorbing impacts more gently (important when we generally don't have bodywork deforming to absorb energy) rather than CDS, which has been known to snap/shear in offroad situations. As a bloke whose seen more offroad accidents than I've had hot breakfasts (and for those of you who know him, he's had lots of those too ), I respect his judgement and went for BB.

As has been said before, the most important factors are design, quality of fabrication/welding and formation of the bends, which means using high quality (expensive) kit and not the old carp from MM or HF. If you're not 100% confident in your ability to build a structure that could very well save your life, get someone else to do it for you. It does not ned to be expensive, but what price can you put on your life or your friends'/family's?

[white90]

Mr Bias

where in Devonia are you then?

[Daan]

he'd prefer me to use BB as it deforms better in a big crash

I find that statement a bit worrying especially because the FIA specifically states you cannot use it, because it isn't strong enough. I am surprised that a scrutineer thinks that scaffold tube (which is bb I believe) is the prefered material.

Daan

[biasbilt]

Mr Bias

where in Devonia are you then?

Work just outside Honiton, live in Exeter, and have the toyshop on Heathfield Industrial estate. What part of Exmoor do you hail from, and don't tell where the sheep are, cos there are more on Dartmoor?! Seems there's lots of us in the area (people who enjoy playing in the mud, not with sheep, before you all jump to the wrong conclusion!

[white90]

live not far from Wheddon Cross

work in Exeter.

sheep are a bluddy nuisance when they break into your fields and are buggers to get out again

[biasbilt]

live not far from Wheddon Cross

work in Exeter.

sheep are a bluddy nuisance when they break into your fields and are buggers to get out again

Why do they always chose a leader who's the thickest in the flock?

Beast of a journey everyday, that road's carp! Do you know Olly Maxwell who owns Exford Service Station? Give me a shout some time when you're down in my neck of the woods and come and have a look at my junk. 07970 600653.

Toby

[Diff]

I find that statement a bit worrying especially because the FIA specifically states you cannot use it, because it isn't strong enough. I am surprised that a scrutineer thinks that scaffold tube (which is bb I believe) is the prefered material.

Daan

Hi Daan,

I think this is where the confusion sets in and why so many people regard BB (Blue Band) built cages to be inferior to CDS cages.

Blue Band tubing is NOT the same as scaffold tube, it is very different and made to a specific British Standard. I believe it is suitable for high pressure steam and as such is designed to be able to be bent for use in industry.

It is because it is built to a british standard, that its performance characteristics are known, consistent, respected, and accepted by the MSA for our offroad sport.

Scaffold tube is very different, NOT designed to be bent, and very definately unsuitable.

Regards,

Diff

[biasbilt]

Hi Daan,

I think this is where the confusion sets in and why so many people regard BB (Blue Band) built cages to be inferior to CDS cages.

Blue Band tubing is NOT the same as scaffold tube, it is very different and made to a specific British Standard. I believe it is suitable for high pressure steam and as such is designed to be able to be bent for use in industry.

It is because it is built to a british standard, that its performance characteristics are known, consistent, respected, and accepted by the MSA for our offroad sport.

Scaffold tube is very different, NOT designed to be bent, and very definately unsuitable.

Regards,

Diff

I missed Daan's reply, so thanks for putting that in Diff. You're absolutely right, because although scaffold tube is a high spec (as it is used for structural work) it is not up to the same standard as BS1387 Gas Barrel Medium weight, which is what Blue band is. Red band is the same but heavy weight, the difference being the wall thickness, nominally 3.2mm for BB and (I think) about 4.5mm for RB (would have to check to be absolutely certain). The MSA specify it as an acceptable material for off-road motersport where maximum average speeds are lower than that used for either rallying or circuit use. That said, with top speeds approaching (or even exceeding, depending who's telling you) 100mph, there is a choice to be made.

As stated previously, design and fabrication have a more important part to play than material in my opinion, and I would personally not trust half the cages I see to save my life, as to be honest, the workmanship is poor.

Toby

[Superpants]

I have attached an extract from the BS. It comes from a book dated 1972 so isn't the current version, but may be of interest.

1387_20Extract.pdf

[landmannnn]

Having talked the theory, has anyone got any real life experiences of failed roll cages?

I have only seen a couple of bad failures, one was scaffold tube which broke at bend and the other was bb which had a weld failure. Both looked well made (before they broke).

[Mark90]

My mate end over ended his racer last year at Minehead in the bottom field, Toby may remember as he was there racing that day as was Steve Hiatt (although he was broke down in the woods). The cage was made from BB, both front and rear hoops did deform slightly and I mean only slightly, both driver and co-driver walked away with noyhing but a stiff neck and a scrapped shin between then, although the chassis was f***ed.

[biasbilt]

Having talked the theory, has anyone got any real life experiences of failed roll cages?

I have only seen a couple of bad failures, one was scaffold tube which broke at bend and the other was bb which had a weld failure. Both looked well made (before they broke).

Wrong material and poor fabrication!

My mate end over ended his racer last year at Minehead in the bottom field, Toby may remember as he was there racing that day as was Steve Hiatt (although he was broke down in the woods). The cage was made from BB, both front and rear hoops did deform slightly and I mean only slightly, both driver and co-driver walked away with noyhing but a stiff neck and a scrapped shin between then, although the chassis was f***ed.

[/quotet

I don't remember as I'd driven into a tree and was busy straightening a wing and rebuilding a hub, but I've seen a number of end over ends at hign speed, and have seen CDS tubes shear and BB just deform. The worst of these was on a TMC 100" LR, with a multiple end over end then roll at about 60mph, where the front hoop moved about 12" to the side, exposing the drivers helmet to the ground. The helmet was knackered, the car was written off, but most importantly, the driver was okay apart from a little bruising and being well shaken. With a diagonal in the roof (it only had 2 bars joining the 2 hoops), there would have been far less deformation. I looked at it carefully and athough the cage had bent, the tubes had not fractured, or started to, the welds had held and it did its job, which is the important thing.

[lard]

what did the tomcat have cds or bb ????