Removing cement-like substance from a white-cast iron

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The discussion centers on the challenges of removing hardened cement buildup from mixing paddles in a pugmill used for a thesis on wear rates in low-stress sliding abrasion. The paddles are made from various materials, including white cast iron and tungsten carbide hardfacing, which complicates the removal process. While chiseling works on smoother surfaces, the rougher tungsten carbide surfaces present difficulties. The inquiry explores the potential use of acid baths for cement removal, specifically mentioning phosphoric and formic acids, which are commonly found in commercial cement removers. Concerns are raised about the impact of these acids on the metal paddles, particularly regarding their corrosive effects. Mechanical removal methods, such as hammering, are suggested as initial approaches. Additionally, references to pH levels affecting concrete and recommendations from concrete properties literature are provided for further guidance.
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Hi all

I have kind of an odd question, it has been quite hard to find an answer for.

I'm doing a thesis comparing wear rates and patterns in low stress sliding abrasion between field conditions and labratory-based tests.

The field trial uses a quarry 'pugmill', which is essentially a giant mixer that combines roadbase and a cement (unsure exactly what type). The wearing parts are the mixing paddles, usually made from white-cast irons - for the thesis I'm testing four different types (OEM, hard-faced etc). For dust suppression, a water mist is used - however this causes a build up of hardened cement in patches on the paddles over time.

I was wondering what would the best way to remove this cement build up on the paddles would be - accurate before and after weights are required for wear-rates. Some of the paddles have smooth surfaces, and the cement can be removed easily enough with a chisel. However some surfaces (such as the tungsten carbide hardfacing) are quite rough and the cement is hard to completely remove.

Paddle materials:
1) 27 Cr White Cast Iron (OEM paddle)
2) CC1500 CrC wear plate overlay - 8mm hardface on 8mm backing plate on 20mm Hardox 400 base
3) 'Duaplate' CrC wear plate overlay - 8mm hardface on 8mm backing plate on 20mm Hardox 400 base
4) Tungsten Carbide Hardfacing - 4-5mm hardface on 32mm Hardox 400 base


I was thinking along the lines of an acid bath of some description, however I'm unsure what acid to use. Any other ideas, or nudges in the right direction would be appreciated as well

Thanks



p.s.

Picture of a pugmill (from google), take note of the mixing paddles.
[PLAIN]http://www.claymineadobe.com/auction/Pug-Mill-Paddles-x-40-ea..jpg
 
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Commercial cement removers use some mixture of phosphoric and formic acids for this purpose.
 
Would this have a detrimental effect on the iron paddles?
 
And in addition, what sort of concentrations are the acids in cement removers?
 
The difficulty with strong acids such as sulphuric or hydrochloric is that they all too readily also attack the metalwork. The acids I mention are more benign, removing only a microscopic surface layer (you have to give something) but for instance phosphoric acid baths are used to passivate and prepare ferrous metal for painting.

You are correct that direct information on this subject is hard to find. It was a long time ago that I was involved with this - I suggest chatting to your local ready-mix concrete plant. In general I remember mechanical removal (hammering) was tried first.

Neville (Properties of Concrete) suggests that "concrete can be attacked below pH of 6.5, severe below 5.5, very severe below 4.5"

He also lists a number of possible acids. As do ACI 515.1R and ACI 201.2R-92
 

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