Removing cement-like substance from a white-cast iron

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Discussion Overview

The discussion revolves around the challenge of removing a cement-like substance from mixing paddles made of white-cast iron used in a pugmill for a thesis on wear rates in sliding abrasion. Participants explore various methods and chemical solutions for effectively cleaning the paddles without damaging the underlying materials.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant describes the context of their thesis, detailing the materials involved and the issue of cement build-up on paddles.
  • Another participant suggests using commercial cement removers that contain phosphoric and formic acids.
  • A question is raised regarding the potential detrimental effects of these acids on the iron paddles.
  • Further inquiry is made about the concentrations of acids typically found in cement removers.
  • Concerns are expressed about the corrosive nature of stronger acids like sulfuric or hydrochloric, which could damage the metalwork, while noting that phosphoric acid is less aggressive and can be used for passivation.
  • A reference is made to literature suggesting that concrete can be attacked at pH levels below 6.5, with increasing severity at lower pH levels.
  • Another participant recalls that mechanical removal methods, such as hammering, were often attempted before resorting to chemical solutions.

Areas of Agreement / Disagreement

Participants express varying opinions on the best method for cement removal, with some advocating for chemical solutions while others caution about potential damage to the paddles. The discussion remains unresolved regarding the optimal approach.

Contextual Notes

There is uncertainty regarding the specific type of cement used and the exact concentrations of acids in commercial removers. The discussion also highlights the limitations of available information on this topic.

happycamper
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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