CAVITATION SHOTLESS PEENING

Presented by:DILIP.SS7 ME

INTRODUCTION Cavitation normally causes severe damage in hydraulic

machinery, Such as pumps, hydro turbines, and valves. However, impact as cavitation bubbles collapse can be utilized to peen the surface of metallic materials in order to improve the fatigue strength as is commonly done with shot peening. Peening by means of cavitation impact can peen the surface without the use of shot. Hence, it is a kind of shotless peening, and can be called ‘‘cavitation shotless peening.’’ The great advantage of cavitation shotless peening is that the peened surface is less rough compared with shot peening, since there are no solid body collisions involved. This means that the remarkable effects of peening can also be produced in soft metals.

PRINCIPLE Cavitation is a phase change phenomenon, which

means the water vaporizes due to a decrease in pressure by increasing the flow velocity. longitudinal cavitation, which consists of tiny longitudinal cavitation bubbles, as shown in Figure 1, causes severe cavitation impact (Soyama et al. 1994). This means that longitudinal cavitation can be useful for cavitation impact applications.

CAVITATING JET APPARATUS

WORKING Tap water was installed in a header tank and it was pressurized by a plunger

pump. The maximum capacity of the pump was 5 x 10 -4 m3/min and 35 MPa. The water was injected into a water filled test section through a nozzle and returned to the header tank through a filter. The nozzle was cylindrical, with a throat diameter ‘d’ of 2 mm and a throat length ‘l’ of 6 mm. The standoff distance ‘s’ is defined as the length from the upstream corner of the nozzle throat to the surface of the test specimen. The upstream and downstream pressures were measured by pressure transducers. The test specimen was exposed to the cavitating jet for cavitation shotless peening. The specimen was set perpendicularly to the jet axis and could be moved across the jet at various scanning speeds n. The specimen could also be rotated with a pitch of 2 mm, so that the specimen moves 2 mm with each complete rotation as shown in Fig. 2. The exposure time t to the cavitating jet is defined as the exposure time per unit length from the scanning speed v as follows:

t = n/v ……. (1) where n is the number of scans.

SCANNING OF SPECIMEN BY CAVITATING JET

TYPES OF CAVITATING JETS:

Normal water jetCavitating jet in airCavitating jet in water

NORMAL WATER JET

Normal water jet is a simple cylindrical nozzle

This type of jet is less powerful compared to other two

Exposure time is more resulting in erosion of surface

CAVITATING JET IN WATER

Cavitating jet in water is similar to normal water jet except the whole arrangement is placed in a water filled chamber as shown in the fig

Erosion of the surface is less compared to normal water jet

CAVITATING JET IN AIR A cavitating jet in air was

produced by injecting a high-speed water jet into a concentric low-speed water jet.

A typical ring erosion pattern of a cavitating jet was obtained by the cavitating jet in air, as shown in Fig.

The surface modification of cavitation peening, the surface was not eroded, as the exposure time as very short.

Most powerful jet

COMPARISON BETWEEN SHOT PEENING & CSP Although shot peening is an effective way of

improving the fatigue strength of metallic machine components, unfortunately, shot produces industrial waste and the danger of dust explosion. A peening method without shot using the cavitation impact induced by a cavitation bubble collapsing is called ‘cavitation peening’. In order to demonstrate the improvement in the fatigue strength of gears by cavitation peening, gears treated by cavitation peening and shot peening were investigated using a power circulating-type gear tester. Under the conditions used here, the improvement in the fatigue torque of a test gear treated by shot peening was 12% compared with that of a nNP gear, while that of a gear treated by cavitation peening was 24%. Thus, the fatigue strength of gears treated by cavitation peening was increased, with double the improvement gained by shot peening. It can be concluded that cavitation peening is a more effective surface modification method than shot peening.

COMPARISON BETWEEN SHOT PEENING & CSP

ADVANTAGES

Penned surface is less rough compared with shot peening.

It eliminate the chemical washing.Improves the fatigue strength of aluminum

alloy.Improves the corrosion resistance of steel.Introduces compressive residual stresses

APPLICATIONS Peen Forming of Duralumin Plate by Using a

Cavitating Jet in Air. Improvement of fatigue strength on stainless

steel by cavitating jet in air. The practical use of cavitating jet for gettering in

silicon wafer. Improvement of residual stress on material

surface by water jet peening. Improvement of corrosion resistance of carbon

steel surface by cavitating jet.

CONCLUSION A shot-free surface modification method was

proposed for the improvement of fatigue strength in metallic materials to enable lightweight transport equipment to be developed in a more sustainable way. Although shot peening is an effective way of improving the fatigue strength of metallic machine components, unfortunately, shot produces industrial waste and the danger of dust explosion. A peening method without shot using the cavitation impact induced by a cavitation bubble collapsing is more considerable