Galvanizing a chassis or part of (ie replacement outriggers)
Discussion
cjj799 said:
Very interesting alphaone.
I used to work in engineering myself and we regularly sent stuff for galvanising. I often wondered why sometimes it would come back with a nice shiny coating, and some times more of a dull grey.
I wonder if in the case of a chassis that is prone to flexing a bit the coating is less likely to remain intact?
The shiny coat depends on the amount of aluminium that is mixed with the zinc.I used to work in engineering myself and we regularly sent stuff for galvanising. I often wondered why sometimes it would come back with a nice shiny coating, and some times more of a dull grey.
I wonder if in the case of a chassis that is prone to flexing a bit the coating is less likely to remain intact?
(also to a lesser extent, weather causes the zinc to look greyer)
I'm sure I don't NEED to further champion galvanising, it seems that it's more widely accepted but to (almost) wrap up my own story, I got my galved chassis rebuilt and MOT'd last summer ... having a young family and expanding business to deal with I drove it about 4 times before the MOT expired this year. It's re-MOT'd now and I'm looking at MegaSquirt and electric power steering (when I'll have the time I don't know though!).
Sorry ... that's digressing!
I galvanised everything successfully, chassis (obviously), all suspension arms etc and it stayed perfectly flat. Having been set up for Geo at Neil Garners it feels fantastically well planted and balanced. Steering via the throttle is a joy and basically, well, it feels 'right'
So pull y'fingers out folks, galvanise and banish those outrigger worries for ever! Feels good :-)
Sam
Sorry ... that's digressing!
I galvanised everything successfully, chassis (obviously), all suspension arms etc and it stayed perfectly flat. Having been set up for Geo at Neil Garners it feels fantastically well planted and balanced. Steering via the throttle is a joy and basically, well, it feels 'right'
So pull y'fingers out folks, galvanise and banish those outrigger worries for ever! Feels good :-)
Sam
Yes, hot galvanized dip is probably the best answer for chassis protection but has anybody had experience of hot galvanized SPRAY. I believe the marine industry also use a hot aluminium spray on steel. They may be cheaper than the dip if it's just for the outriggers.
Glad I started this galvanic topic some months back on other forums but other Tives were already way ahead having gone and done their chassis. Vaurien is the guy who supplies stainless steel chassis.
All we now need is a stiffer chassis to enable Griffs and Chims to be faster than the MX5 on ALL THE BENDS of the EVO West Circuit.
Glad I started this galvanic topic some months back on other forums but other Tives were already way ahead having gone and done their chassis. Vaurien is the guy who supplies stainless steel chassis.
All we now need is a stiffer chassis to enable Griffs and Chims to be faster than the MX5 on ALL THE BENDS of the EVO West Circuit.
Edited by EGB on Wednesday 28th November 10:29
I'm convinced.
Tips on drilling holes. Holes top and bottom seems to be a given but do I need to drill holes close to the welds as has been suggested and if I do, do I drill holes at both ends of each tube ie. 4 holes per tube?
What have people used to plug the holes. It seems to me the following are the choices:
Tips on drilling holes. Holes top and bottom seems to be a given but do I need to drill holes close to the welds as has been suggested and if I do, do I drill holes at both ends of each tube ie. 4 holes per tube?
What have people used to plug the holes. It seems to me the following are the choices:
- Plastic plug (after powder coating as process may melt)
- Plastic threaded plug (after powder coating as process may melt)
- Plastic metal before powder coating
- Threaded stainless plug, either before or after powder coating
Pete Mac said:
I'm convinced.
Tips on drilling holes. Holes top and bottom seems to be a given but do I need to drill holes close to the welds as has been suggested and if I do, do I drill holes at both ends of each tube ie. 4 holes per tube?
What have people used to plug the holes. It seems to me the following are the choices:
Great :-)Tips on drilling holes. Holes top and bottom seems to be a given but do I need to drill holes close to the welds as has been suggested and if I do, do I drill holes at both ends of each tube ie. 4 holes per tube?
What have people used to plug the holes. It seems to me the following are the choices:
- Plastic plug (after powder coating as process may melt)
- Plastic threaded plug (after powder coating as process may melt)
- Plastic metal before powder coating
- Threaded stainless plug, either before or after powder coating
I used plastic metal, I was dubious but it really bonds like hell and as such I think it provides the best chance of a spray-proof seal. Threads/plugs etc feel to me like they will always gradually allow stuff in and/or work loose.
Initially I tried 'Chemical metal', it was a bit of a pain in the ass to apply and felt a bit too much like bodging with bodyfiller. That is probably more psychological than factual ... the 2x holes I did this way are of course incredibly strongly filled and that's that.
I switched very quickly though to using 'Quick Steel', this is the putty that comes like a sausage roll. You break some off and knead it to mix the two materials then apply before it goes off. It's really easy to work with as you can just work it like putty in your hand (though you would want latex gloves, it stains the old skin and probably kills you within 100 years!) and push it where you want it.
Some people have filed these repairs flat but I a) don't have the patience, b) felt that more a small overspill onto the surface would aid long term strength / seal better and c) I don't have the patience, still.
it does look a bit like someone has left lumps of chewing gum everywhere then painted over them but as I say, I felt that despite aesthetics this had to offer better results in the very long term.
Well, hope this helps ... one of many ways to skin a cat
Cheers
Sam
This is all very interesting but a word of caution reference all the holes required in the galvanising process,if one was to test the strenght of a section of chassis of good condition versus a chassis with vent holes driled to all the bracing tubes you will find that under compression which is the loading designed in a geodetic construction is reduced by about 60 percent the thing with a tube is it is only strong when complete drill a hole in it and it collapses very easily compared to its complete brother obviously people have galvanised chassis running but under extreme conditions accident etc. personally not for me on a ladder section i.e. landrove not a problem the problem is the type of construction of the tvr chassis each component effectivly leans on its counterpart to stay sructurally strong if one fails the whole pack fails just my thoughts.
John
John
John, I'm sorry I would have to see your calculations that demonstrate that 'under compression the strength of the geodetic construction is reduced by about 60 percent' for a drilled chassis. In fact before I do this myself I will do some investigation on the effect of drilling the chassis tubes and come back to this forum with some independent calculations to close this issue out.
I have done some research and got a bit of advice from the Galvanizers Association as follows. This may be on other blogs but....
Requirements for galvanizing would be as below:
The chassis would need to be fully blast cleaned to remove any signs of an existing organic (paint or powder coat) coating. Note rust will not be a problem as the chassis will be pickled in HCl.
Each sealed hollow section will require as a MINIMUM of 2 vent holes, 1 located at either end and diagonally opposite one another (e.g. one on top face other on bottom face). If you are able to provide 4 vent holes (2 each end) this makes the work easier to jig.
Vent hole size varies with hollow section size with larger sections requiring larger vent holes as indicated below.
<25 mm = 10 mm vent
25-50 mm = 12 mm vent
50-100 mm = 16 mm vent
100-150 mm = 20 mm vent
>150 mm = consult galvanizer
So first question to those who have had their chassis galvanized is what size holes did the galvanizers insist you used? Was it less than 10mm?
Weakening of Chassis from Drilling:
On the matter of weakening the chassis from drilling, I am trying to get some further 'back of a fag packet' advice. However reading into the subject (and I must stress I am not an expert):
In a given size and diameter tube or diagonal, compression will always cause the tube to buckle long before the same force would cause the tube to pull apart in tension. As an experiment, try pulling on the ends of a drinks can, one end in each hand. Then, try crushing the can by pushing on both ends. The crushing is much easier, or at least humanly possible, compared to pulling the can apart.
TVRs use a spaceframe chassis, which is made up of longitudinal tubes, which are supported by a series of perpendicular and parallel tubes. In order to give these tubes the required strength they are braced diagonally to effectively form a triangulated box.
The triangulated box imparts strength by stressing the diagonal in Tension (not compression). For any tube that is under compression, there will be strength and bracing support given by the other tubes in Tension.
I spoke to someone in the British Constructional Steel Association, he gave me the following ‘back of a fag packet’ method of calculating the % weakening of the tube from drilling, when in Tension:
For a tube in tension and assuming a diameter of 30mm and wall thickness 3mm then the total volume of the tube will be:
Pi x 30 x 3 = 282
If you drill a 10mm hole then the volume will be:
282- (10x3) = 252
Therefore the loss in strength under Tension will be:
(282-252)/282 = just over 10%
He said the loss in strength under Compression would indeed be higher, however it is not so easy to estimate, however given that we have already said that a member under Compression is braced by members under Tension then I guess the effect is much smaller.
He did stress that holes should be drilled as close to the welds as possible as this would minimise further any weakening from the drilling.
Unless someone can tell me the length, diameter and wall thickness of each of the chassis members it is difficult to go much further.
I still believe that the TVR chassis was almost certainly over designed/engineered and coupled with the long term integrity offered by galvanizing together with the consideration of the number of TVRs that are probably being driven on chassis significantly weakened by rust then I would still go the galvanizing route.
Sorry if this has been a bit anorakish but if I get any more info I will add it to this blog
Requirements for galvanizing would be as below:
The chassis would need to be fully blast cleaned to remove any signs of an existing organic (paint or powder coat) coating. Note rust will not be a problem as the chassis will be pickled in HCl.
Each sealed hollow section will require as a MINIMUM of 2 vent holes, 1 located at either end and diagonally opposite one another (e.g. one on top face other on bottom face). If you are able to provide 4 vent holes (2 each end) this makes the work easier to jig.
Vent hole size varies with hollow section size with larger sections requiring larger vent holes as indicated below.
<25 mm = 10 mm vent
25-50 mm = 12 mm vent
50-100 mm = 16 mm vent
100-150 mm = 20 mm vent
>150 mm = consult galvanizer
So first question to those who have had their chassis galvanized is what size holes did the galvanizers insist you used? Was it less than 10mm?
Weakening of Chassis from Drilling:
On the matter of weakening the chassis from drilling, I am trying to get some further 'back of a fag packet' advice. However reading into the subject (and I must stress I am not an expert):
In a given size and diameter tube or diagonal, compression will always cause the tube to buckle long before the same force would cause the tube to pull apart in tension. As an experiment, try pulling on the ends of a drinks can, one end in each hand. Then, try crushing the can by pushing on both ends. The crushing is much easier, or at least humanly possible, compared to pulling the can apart.
TVRs use a spaceframe chassis, which is made up of longitudinal tubes, which are supported by a series of perpendicular and parallel tubes. In order to give these tubes the required strength they are braced diagonally to effectively form a triangulated box.
The triangulated box imparts strength by stressing the diagonal in Tension (not compression). For any tube that is under compression, there will be strength and bracing support given by the other tubes in Tension.
I spoke to someone in the British Constructional Steel Association, he gave me the following ‘back of a fag packet’ method of calculating the % weakening of the tube from drilling, when in Tension:
For a tube in tension and assuming a diameter of 30mm and wall thickness 3mm then the total volume of the tube will be:
Pi x 30 x 3 = 282
If you drill a 10mm hole then the volume will be:
282- (10x3) = 252
Therefore the loss in strength under Tension will be:
(282-252)/282 = just over 10%
He said the loss in strength under Compression would indeed be higher, however it is not so easy to estimate, however given that we have already said that a member under Compression is braced by members under Tension then I guess the effect is much smaller.
He did stress that holes should be drilled as close to the welds as possible as this would minimise further any weakening from the drilling.
Unless someone can tell me the length, diameter and wall thickness of each of the chassis members it is difficult to go much further.
I still believe that the TVR chassis was almost certainly over designed/engineered and coupled with the long term integrity offered by galvanizing together with the consideration of the number of TVRs that are probably being driven on chassis significantly weakened by rust then I would still go the galvanizing route.
Sorry if this has been a bit anorakish but if I get any more info I will add it to this blog
or a good welder with the correct welding proses and the right grade steal could weld a strong stainless chassis were you don't need the drill holes for galvanizing and or even paint to protect.
On one side more expensive (stainless steal chassis) but on the other side less time consuming then all other processes used to make/get a good galvanized chassis and or paint/powdercoating.
On one side more expensive (stainless steal chassis) but on the other side less time consuming then all other processes used to make/get a good galvanized chassis and or paint/powdercoating.
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