Pickling iron castings

S

SteveK

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I just received my set of Universal Pillar Tool castings from Martin Model. I've read several places that raw castings should be pickled to remove the hard layer prior to machining. I've successfully pickled hot rolled plate to remove the scale using 20% muriatic acid. Since I ran out of 20% I picked up 34% at HD. Can anyone tell me if 34% is too strong and should be diluted or used as is? Any guidelines on time? It was easy to tell with the hot rolled when the pickling was complete but with clean castings maybe not so much. If someone has experience with castings from Martin Model, maybe I don't need to do it at all. Thoughts? Thanks.

Regards all,

Steve
 
I'd think that the castings are already pickled for you. When I was the toolmaker in Williamsburg,sometimes we had to machine raw castings from the Geddy Foundry. They were not pickled,and I quickly found out they were next to impossible to cut!! I just went to the warehouse and got some muriatic acid. Put the castings(which were smallish) into a bottle and left them too soak outside for a few hours(ever let muriatic acid loose around steel tools?) After a while,there would be a surprising amount of sandy crud in the bottom of the jar. I heated up the rinsed off castings with our gas oven to completely drive off any remaining muriatic. Then,the castings machined fine,without ruining cutters.
 
George,

You may be right they were already pickled but a recent email exchange with Gary Martin on the subject I didn't get the impression they were. At least he didn't say directly that they were. I'm not sure how Martin Model & Pattern has their production set up. They may have an outside foundry run the castings for them. The foundry may have done it as a matter of course somewhere in the annealing process. I don't know for sure. One thing I just thought of is if the castings have been vibratory finished. That might be enough to remove the surface scale.

Do you recall the acid strength you used? I'm a bit nervous about the 34% stuff being to aggressive. I may just dilute it and give it a try.

Regards,

Steve
 
SteveK, Use caution working with acid ! Never pour water into a container of acid, Add the acid to water. Years ago when I worked at a battery plant one of the problems we had was heat created when cutting acid . We tried to cut our acid the evening before to give it time to cool. Also wear a face mask and gloves and also saftey glasses . Work Saftely Bubby Sharp in KY
 
I just used muriatic(brick cleaning) acid right out of the container. It is possible to remove scale from cast iron parts I GUESS by vibratory,tumbler,possibly sand blasting. I don't know how they might do it commercially.
 
George- Thanks for the info. The stuff I had been using was Parks muriatic at 20 % (probably similar to the stuff you were using) versus 34% from HD.

Bubby- Thanks for the safety heads up. Yes, I did know of this but it certainly bears repeating. One never knows the experience or knowledge of the audience. Keeping one's fingers, sight and other faculties is paramount in pursuit of one's hobby or profession.

----

Experimented over the last week. Dunked two castings into muriatic acid at 34%. Much fuming and vigorous activity. To the point where I pulled the castings after 10 minutes. One piece was still bright but the other was darkened quite a bit. I "tested" each casting to see if the surface was different. I used a coarse cut file to cut through the surface looking for a difference in how easy the cut. Didn't detect any real difference. Wire wheeled both castings the clean them up. One was still bright but he other was still darkened.

Diluted the 34% to 20% and dunked the dark casting for 15 minutes. No real physical change in appearance, other than the slight bubbling versus vigorous. Took the coarse file to it an didn't find any difference. If there is a hard oxide skin, it's pretty thin.

Starting to feel I'm chasing my tail...at least with these castings.

My conclusion is that this set of castings from Martin Model doesn't benefit from pickling in the conventional sense. (your experience may vary!) I'm going to machine them without further messing around!!

There may be times when picking is appropriate, it depends on the condition of the castings....

....what is this stinky stuff on bottom of my shoe?? Have I stepped in something...ohhh no!....

Regards All,

SteveK
 
I left my castings in the acid for about 2 hours. I doubt yours were cleaned in that short time.
 
George,

[FONT=&quot] [/FONT] From your experience when you pickled your castings did the entire surface of the casting bubble immediately on contact with the acid or gradually as the scale fell away? I think you may be correct that they have been pickled already. I've machined a bit of the base and it seems to cut easily.


Regards,

Steve
 
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