Peening

Mechanical Plating. Impact or peen plating is a mechanical process whereby the metal powder is compacted and welded to parts by mechanical energy. This process is limited to relatively small parts of no more than about one kilogram. The parts are placed ia a specially desigaed barrel... 

The surface may gain a very high (eg, 1000 Vickers) hardness from this process. Surface deformation also produces a desired high compressive residual stress. Figure 9 illustrates the improvement in fatigue properties of a carburized surface that has been peened (18). 

Fig. 9. Effect on fatigue strength of the plastic deformation of a carburized steel surface by shot peening (B) as compared to nitriding (A) and heat treating...

Newer high velocity thermal spray coating processes produce coatings in compression rather than tension because of the shot peening effect of the supersonic particles on impact. This has permitted coating as thick as 12,500 p.m without delamination as compared to older processes limited to 1,250 p.m. The reduced residence time of particles at temperature minimises decomposition of carbides present in conventional d-c plasma. This improves wear and hardness (qv) properties. 

Contain tensile residual stresses which are usually as large as the yield stress. Weld liable to fatigue even when applied stress cycle is wholly compressive. Reduce residual stresses by stress relieving, hammering or shot peening. 

Fig. 5-4 Cell currents between a coated specimen (5 = 300 cm ) and uncoated steel electrode (5 =1.2 cm ) in NaCl solutions at 25°C. Left shot-peened steel sheet, 150 pva EP-tar. Right hot-dipped galvanized steel sheet, 150 jim EP-tar.

Fig. S-6 Relation between the density of cathodic blisters and potential shot-peened steel sheet without primer ( ) and with about 40 /tm primer coat (Zn ethyl silicate + polyvinyl butyral) ( ) top coat 500 /tm EP-tar ...

Fig. 5-7 Effect of potential on the composition of the blister liquid, shot-peened pipe with 300 to 500 jim EP-tar, artificial seawater, 1300 days at 25°C.

Post-processing, e.g. machining (for dimensional restoration) or shot peening (remove residual stresses), can be an added source of variability. 

Training must be the eentral theme. The days of the meehanie armed with a ball-peen hammer, serewdriver, and a ereseent wreneh are gone. More and more eomplieated maintenanee tools must be plaeed in the hands of the meehanie, and he must be trained to utilize them. 

Blast Peening—a treatment for relieving tensile stress via inducing beneficial compressive stress in the surface by kinetic energy of rounded abrasive particles. 

Peen Plating-the deposition of the coating metal (in powder form) on the substrate via a tumbling action in the presence of peening shot. 

Pinksalz, n, pink salt (ammonium chlorostan-nate, (NHilaSnCU less commonly, potassium sodium tartrate), -bad, n, pink-salt bath. Pinne,/, (Tech.) pin, peg, tack (of a hammer) peen quill feather. 

Further evidence of the relative resistance of maraging steel is reproduced in Fig. 3.33 from Reference 24. Maraging steel is shown to be superior to a die steel and low alloy steel (both unidentified) in bent beam tests stressed at 75% of the yield strength in distilled water. Also shown is the beneficial effect in smooth surface tests of cold rolling. Shot peening has a similar beneficial effect . 

Shot peening is a beneficial surface treatment since it puts the surface into a state of compression and generally obscures the grain structure. Subsequent painting of the peened surface is often useful. If pitting occurs then cracking can be expected in susceptible material when the attack penetrates the depth of the compressed surface layer. 

A typical anode for practical use would be in the order of 25 to 48 mm in diameter, with hard platinum alloy pins of 0-50 mm diameter by 10 mm length, spaced every 150 to 300 mm and progressively positioned around the circumferenceThe pins are a press fit into holes in the lead or lead alloy (approximately 01 mm diametric interference) and lie flush with the surface. The lead is peened around the pins to improve the mechanical and electrical contact. 

Peen plating Adhesion brought about by the intimate contact of two chemically clean solid surfaces powder "h M2(or M] ) impacted solid coaling M, Zn Mj. Fe... 

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