Hot zinc spraying causing steel box to warp?

[Trevorleach]

Built a pullout for a trailer, boss wanted it hot zinc sprayed, got it back and the box was warped approx 6 to 10mm over its entire 2.5 meter length, and now the bugger will not fit in its socket without binding up!
Is this something others have seen happen before?
Box is 200/100/8mm and bloody heavy, it never even occurred to me it could warp.
The zinc spray finish is very rough, much worse than galved steel.

 

[awemawson]

The zinc spray gun will be oxy acetylene or oxy propane fuelled to melt the zinc wire as the air turbine draws it through concentric with the flame. So the item being coated will inevitably heat up and thus be prone to warping.
The clue is in the name Hot Zinc Spraying!

 

[Smallfry]

Doesn't the item to be sprayed have to be heated too ??

I have seen some items that had been sprayed, and yes quite a rough finish, but even hot dip is not as good as it once was either.

 

[brightspark]

Doesn't the item to be sprayed have to be heated too ??

I have seen some items that had been sprayed, and yes quite a rough finish, but even hot dip is not as good as it once was either.

is anything these days bought 3 heavy farm gates 40 years ago and theres not a patch of rust on them

 

[nickk]

is anything these days bought 3 heavy farm gates 40 years ago and theres not a patch of rust on them

Often,the tubes are 1.5mm !

 

[brightspark]

Often,the tubes are 1.5mm !

was doing an electrical job at a farm machinery supplies and saw the gates asked for a price. he done me a good deal think they were 40 quid each heavy duty to stop beast bending them

 

[minimutly]

Lol, heavy duty yes, but if a ton and a half beast decides to vault it, the thing will be bananard

 

[RWD3M]

Built a pullout for a trailer, boss wanted it hot zinc sprayed, got it back and the box was warped approx 6 to 10mm over its entire 2.5 meter length, and now the bugger will not fit in its socket without binding up!
Is this something others have seen happen before?
Box is 200/100/8mm and bloody heavy, it never even occurred to me it could warp.
The zinc spray finish is very rough, much worse than galved steel.

Something else has gone amiss there. Hot zinc spraying is a molten zinc process but as the metal being coated doesn't need heating, the heat from the molten zinc would dissipate very quickly, especially on something that heavy duty. The Hot Zinc spray process is used on the undersides of motor vehicles with no ill effects. But yes, it does have a rough finish.

 

[Trevorleach]

Something else has gone amiss there. Hot zinc spraying is a molten zinc process but as the metal being coated doesn't need heating, the heat from the molten zinc would dissipate very quickly, especially on something that heavy duty. The Hot Zinc spray process is used on the undersides of motor vehicles with no ill effects. But yes, it does have a rough finish.

Right so it could be where I have welded it, if zinc spray does not wreck car bodies I cannot see it bending a large steel box section.
I will try and get a pic to load as it keeps saying the file is to large.

 

[Trevorleach]

This is the box, U channel is for the loading ramps to sit in.
Handles on the bottom (old u-bolts) are for the drivers to pull the pullout out/in.
Hole in the back side is to get a large weld onto the top of the sliding box section that fits into the bottom of the main box section, this sliding bit actually protrudes a few mm below the bottom edge pf the larger box section, and has quite a bit of weld on it as has to be manly otherwise they bend, so thinking this larger weld and heat might be the issue?

 

[Trevorleach]

This is overall pic, the arms have a piece of angle to hold them parallel whilst being worked on, also for the guys to use as a lift point, this of course is cut off before use!

 

[Smallfry]

I can't see hot zinc spray would distort that. Hot dip might, if the arms were unsupported.

All the mill scale would need removing though, otherwise galv does not take or work properly.

I would have thought that an item like this would need some degree of pre heat for the zinc to bond, AND smooth out a bit. With hot dip, the whole lot was brought up to the same temperature as the molten zinc, or it ends up lumpy.

 

[Trevorleach]

I can't see hot zinc spray would distort that. Hot dip might, if the arms were unsupported.

All the mill scale would need removing though, otherwise galv does not take or work properly.

I would have thought that an item like this would need some degree of pre heat for the zinc to bond, AND smooth out a bit. With hot dip, the whole lot was brought up to the same temperature as the molten zinc, or it ends up lumpy.

The boss seems to think they preheat it, but as usual no one is sure, unsure if it was blasted either.
More questions for later on this week I think.

 

[Smallfry]

The boss seems to think they preheat it, but as usual no one is sure, unsure if it was blasted either.
More questions for later on this week I think.

My friend, best man at my first wedding, worked for Medway Galvanising at Sittingbourne Kent. I could get small things done for nothing then. Was great when I was rebuilding Land Rovers.

I have no idea about the process of hot zinc spraying TBH, but I know that they would absolutely not galvanise anything unless it had been cleaned of millscale. They could do this onsite if necessary. Chargeable of course. Was then acid dipped before galvanising. Watched my stuff being done a couple of times. Not a job I would want though !

 

[Trevorleach]

My friend, best man at my first wedding, worked for Medway Galvanising at Sittingbourne Kent. I could get small things done for nothing then. Was great when I was rebuilding Land Rovers.

I have no idea about the process of hot zinc spraying TBH, but I know that they would absolutely not galvanise anything unless it had been cleaned of millscale. They could do this onsite if necessary. Chargeable of course. Was then acid dipped before galvanising. Watched my stuff being done a couple of times. Not a job I would want though !

Used to go up there every month or so to the Merc truck dealer just around the corner from the galvanisers, and a few years back the Scania dealer who were further along the estate.

 

[HughF]

@sasquar

 

[Smallfry]

Used to go up there every month or so to the Merc truck dealer just around the corner from the galvanisers, and a few years back the Scania dealer who were further along the estate.

Sparshatts ? I cant remember who did what !

 

[Trevorleach]

Sparshatts ? I cant remember who did what !

Yes Sparshatts is merc dealer, always looking for fitters, money not very good!

 

[sasquar]

A little late to the party here, but we do this sort of job for a living, so my 2p......

It will have been blasted before spraying, the zinc will come off ever so easily if the surface is unblasted.

Spraying wont have warped it, as someone else mentioned, we can do the underside of cars etc, with no ill effects. Although the zinc is very much molten when sprayed, it freezes on impact, the base material is generally kept below 100 degrees c. Again, as someone else mentioned, hot dip is far more likely to warp stuff, normally tsz (thermally sprayed zinc) is specified over hot dip, where warping is undesirable. In this instance, given the sheer size of the part, id put money on it not getting to more than about 50c.....

Very unlikely the part was preheated, you can, (and we do in certain circumstances, usually offshore based stuff where the people writing the spec are idiots - im abbreviating, usually I have to be a lot more polite when making that statement) but its generally un completely unnecessary step, which adds expense, and time.

 

[Smallfry]

A little late to the party here, but we do this sort of job for a living, so my 2p......

It will have been blasted before spraying, the zinc will come off ever so easily if the surface is unblasted.

Spraying wont have warped it, as someone else mentioned, we can do the underside of cars etc, with no ill effects. Although the zinc is very much molten when sprayed, it freezes on impact, the base material is generally kept below 100 degrees c. Again, as someone else mentioned, hot dip is far more likely to warp stuff, normally tsz (thermally sprayed zinc) is specified over hot dip, where warping is undesirable. In this instance, given the sheer size of the part, id put money on it not getting to more than about 50c.....

Very unlikely the part was preheated, you can, (and we do in certain circumstances, usually offshore based stuff where the people writing the spec are idiots - im abbreviating, usually I have to be a lot more polite when making that statement) but its generally un completely unnecessary step, which adds expense, and time.

Thats interesting info. Thanks !

I would have thought that some preheat would help the zinc bond better !

Just to be clear though, when you say "freezes" on impact, you mean solidfies, not actually freeze (cold) ?