philipl Posted February 8, 2009 Author Share Posted February 8, 2009 Thanks guys i new there were probably a few engine gurus who had heard of or experienced this process i appreciate the responses from everyone!! Quote Link to comment Share on other sites More sharing options...
ZZZeee Posted February 8, 2009 Share Posted February 8, 2009 Phred... so do you recommend double media blasting (shot peening) to those with high quality hyper pistons who wish to spray a little nitrous? This is for a 400 SBC. Is this "primarily" for the piston domes? Quote Link to comment Share on other sites More sharing options...
Careless Posted February 8, 2009 Share Posted February 8, 2009 as far as i've been told by a competent turbo rebuilder and turbo powered engine builder... walnut shell is ideal. it's just as abrasive as using a scotch brite pad, and in reality the scotch brite pad is actually worse due to the uneven scores of lines they leave in the surfaces you are prepping. Walnut shell leaves a consistent slight texture that can be polished with ease. It's also ideal for adding ceramic coating to, and leaves the perfect amount of bite for the ceramic coating to hold onto, so that there are no high or low spots that didn't cure properly. Those spots will break off and fly around in your engine. The Ceramic is where the polishing can be done, as ceramic coatings can be brought to a near mirror finish. The same goes with piston skirts that take oil-retention coatings... they have to be sanded lightly or blasted with walnut shell to allow the coatings to adhere deeper than the level at which your tool used for checking tolerances and clearances will be reading from. Walnut shell is safe and basically turns into dust as you blast it. And it gets finer and finer as used... so if you're REALLY concerned, just ask to use some older walnut shell that is finer (they usually keep this stuff). Quote Link to comment Share on other sites More sharing options...
Phred Posted February 8, 2009 Share Posted February 8, 2009 First, ZZZeee shot peening is very rarely used on piston domes as it can be very aggresive and damage softer alloy's if not done very carfully. The strength of a piston dome comes from it's design and alloy. The only reason to blast piston domes is to clean during a rebuild, or prepare for a coating, or to blend the surface after reconturing, or diegrinding the dome after machining valve reliefs, or machining to lower dome volume. Many pistons as recieved from the manufacture, have sharp edges on the domes or valve notches. So it is not uncommon to take a brand new piston and deburr and blend the sharp edges away. Sharp edges on a piston dome can cause distubances in the mixture flow, and also cause hot spots which may lead to preingnition or detonation. After this work, the domes may be glass beaded to blend, and remove the surface scratches. Media blasting is the generic term for all the different substances that are used for surface modification/preparations. There are many different grades of glass and shot, garnet, plastic pellets, walnut shells, and the least known, soda. Soda is a wonderful basting media. The only downside to it, is it requires a special basting delivery system, which can be very expensive. The one I use at work cost well over $12K. It is a constant loss design, which carrys away the dirt and crud with the soda. The soda crystals explode on contact, and are sucked away as dust or fine powder. The most important feature of soda blasting is that it is biodegradable. You don't have to worry about getting all the soda out of the water or oil jackets. You just flood the part with water, and the soda is disolved. Presto, a perfectly clean part! Soda leaves a slightly duller, smoother finish than glass, as it does not change the surface texture or machine marks. A bright, freshly machined piece of aluminum will be turned a dull silver however. Which means soda can be used on the entire piston if desired, as it will not damage ring lands or pin bores. Different parts of the engine require different blasting media. Some parts require shot, some glass, and if you have it, soda. They all serve a different purpose, and you just need to know the limitations of each, and the desired results for a givin part. Phred Quote Link to comment Share on other sites More sharing options...
philipl Posted February 9, 2009 Author Share Posted February 9, 2009 This is way off subject but i do know i used to use crushed WALNUT shells to run through natural gas turbines to do what the company called carbo blasting this would run through the turbine and clean the high pressure and low pressure turbine wheels therefore making the turbine run more efficently this was done will the turbines were running.These were older turbines from the 50's known as ge frame three turbines... Quote Link to comment Share on other sites More sharing options...
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