Prepping the metal?

[TedDanson]

Chaps,
As a novice this might sound a bit of a daft question so apologies beforehand but does "new" sheet metal require any prepping ie sanding/grinding down before welding?
I've been reading through lots of previous posts on the forum and on some the advice has been to get old metal "angle grinder shiney" before any welding is done.
Would this also apply to new sheet metal as well?
The new sheet 0.8mm i have bought in readyness for my repairs is new but quite dull in appearance - is this ok?

 

[cobminor]

New sheet usually has a protective coat of some sort of waxy substance on to protect in storage. This needs cleaning off. Generally the material should be clean to bare metal, no rust, grease, dirt, oil, etc. etc. There is no need to abrade the clean surface of new sheet.

 

[Drains]

I would expect to be able to weld new sheet without any cleaning. It's worth checking though to see if, as Cob suggests, there is a protective coating. If there is, a spot of acetone, brake cleaner, meths or turps should do the job, or at most a touch over with a flap disc, gently! Don't take a grinding disc to thin steel as it's thin enough already! (Or use emery, by hand, but watch the edges of the steel, use gloves)

You may find that any coating on there is 'weld through', and won't affect the quality of the welds.

Si

 

[Baz-Cem]

Whenever I have box section it is always covered in a thick greasey substance but the rest is always bare.

 

[Welderpaul]

Whenever I have box section it is always covered in a thick greasey substance but the rest is always bare.

Solid section types i.e flat or round bar have mill scale on them as a result of the manufacture process. This prevents the steel from rusting whilst it is sitting in the stockholders or in your shop waiting to be used. Hollow sections are formed differently, and do not have this millscale, so are coated in the horrible grease to prevent corrosion. Always important to degrease any steel section to prevent the paint falling off. I always degrease it before it goes into sawing as its easier to do, plus it keeps the old doddery sawman happy (ier). The old git
If you have ever seen shot blasted steel i.e totally bare steel, it will flash rust within a few hours, so needs to be painted asap after cleaning.