VOL. 6 March ISSUE YEAR 2005

MFN Trainer Column

in Vol. 6 - March Issue - Year 2005
From Basic Shot Peening Knowledge to Basic Blasting Applications
Author Fran

Author Fran

The MFN Trainer Column

This column is a regular feature and will be written by one of our MFN trainers. Readers are invited to send comments or questions to info@mfn.li. For more information about the trainers, see www.mfn.li link workshops.

by François-Xavier Abadie, Official MFN Trainer and Product Manager for Surface Treatment, Saint-Gobain ZirPro

At first, I would like to take this opportunity in the MFN Trainer Column to thank the MFN team for the fine welcome that I received. What I feel is an open mind and high faculty to share experiences and knowledge, which is very promising for advancement of the technologies that MFN is promoting.
Thus, joining the MFN trainer team, I would like to help in transferring the shot peening knowledge to some basic applications, which is more or less my every day commitment. As a matter of fact, peening knowledge can be very useful to basic non fatigue fighting applications such as cleaning, descaling, surface preparation, finishing, fighting against pitting, corrosion, fretting, galling...
Simply, shot peening can be considered as the work of the strong and courageous blacksmith in the old days. Thus, shot peening technology is actually mastered on one side with Almen intensity related to kinetic energy, therefore, the mass, shape and hardness of the hammer, the stroke of the blacksmith‘s arm, altitude of start and hitting speed, and on the other side with the coverage rate or quantity of treatment which is the total number of hits. This is actually controlling any blasting process, with the condition that you can link the parameters with the process results such as roughness, cleanliness, residual stress distribution, microstructure and whatever is expected as allowing final product characteristics to be matched.
In this way, new fields of applications can be mastered such as the replacement of chemical pickling, or heavy hand work, saving costs and the environment and bringing added value to all the players in the blasting and peening business.
Almen testing is a very accurate way to measure the amount of energy stored in the target after the impact treatment. It can detect very low variations of kinetic energy. For example, this allows one to quantify the change in efficiency versus impingement angle, or distance to the target, or shot size, shape and hardness. It then becomes possible to precisely master the blasting stream of a wheel turbine or an air nozzle and define the optimal mass flow for a given rpm or air pressure. Not only Almen intensity, but even saturation speed and maximum arc height can be interpreted.
Whatever the application, it is helpful for equipment design when several wheels or nozzles are working together on the same part.
For example, in heavy descaling of special steels, Almen intensity was used for the design and control of the wheel turbine equipment and process, saving a lot of energy media and spare parts, also improving efficiency, quality results and process reliability.
Coverage rate can be difficult to control, in particular when working with low impact speed on very hard or brittle materials. Thus, the door is open for the design of new measurement methods adapted to each situation.
Nevertheless, a lot of process results change with coverage for a given Almen intensity!
Roughness and residual compressive stress at the surface are well described in shot peening literature. This is particularly true for the finishing of stainless steel when very high coverage with low Almen intensity can bring final roughness lower than the initial value and induce very high corrosion and scratch resistance.

For continuation, may I invite MFN writers to continue this as a recurrent open topic?

Best Regards
François-Xavier Abadie

Author: François-Xavier Abadie