E-Archive


Vol. 19
March Issue
Year 2018
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Cover Page


in Vol. 19 - March Issue - Year 2018
A Revolutionary New Product For Advanced Peening Capabilities



Micro Shot


Micro Shot vs Ceramic


Micro Shot vs Ceramic


Micro Shot vs High-Performance MS 1 and High-Performance MS 2


Micro Shot vs High-Performance MS 1 and High-Performance MS 2


Micro Shot vs Ceramic


Micro Shot vs High-Performance MS 1 and High-Performance MS 2


Micro Shot vs Ceramic


Micro Shot vs High Performance MS 1 and High Performance MS 2
















Micro Shot

For years, the only viable good option for shot peening media to peen in very small radii and filet root radii, small coil springs, etc., was ceramic media. Ceramic media does work, but it is definitely not a panacea.

Ceramic is expensive and has a high breakdown rate, which creates two main issues; one is cost, and the other is jagged edges from breakage of the media, which can cause micro tears in the substrate being peened. It has the hardness, but lacks the mass of metallic shot, so higher pressures must be used, and as such, has higher breakdown.

This author and a business colleague friend, Steve Carpenter, discussed this for quite some time and determined there is a real need for a superior product in the shot peening industry. They then addressed a reputable manufacturer of quality steel abrasives in Michigan. The desired parameters were reviewed with the manufacturer including: small particle size, high mass, good sphericity, high hardness, and low breakdown rates.

Micro Shot

A product was finally arrived at, Micro Shot, which met these parameters. The micro shot is a high alloy (Iron, Boron, and Silicone) shot, which is made through centrifugal atomization in a controlled atmosphere for rapid solidification, which assures a high level of sphericity, which as all shot peeners know, is critical to quality peening. The hardness is +65HRC and the size distribution is 45µ (0.002”) to 150µ (0.006”). The hardness helps off-set the lower mass due to size, and changes the elasticity of the collision of the shot more in favor of the micro shot to the substrate being shot peened. This is now a product that has hardness, mass, sphericity, and longevity. Also, due to the alloy, it is non-corrosive, and any rust discoloration of parts has not been seen.

Test Results

Testing was done to check the durability and comparison to other media, XRD to measure the residual stress measurement curve for depth of compression, as well as comparison between media, and saturation curves to compare Micro Shot to ceramic media at equal pressures.

Durability

Testing was done by propelling the media against a steel target plate. There was no replenishment made, but fines were removed after 1 hour. The testing was done to compare Micro Shot to Ceramic Media (High Performance Micro Shot), an offshore ferrous micro shot (High Performance MS 1) and a quality carbon steel shot, S-70 (High Performance MS 2). The charts below show the relative results.

As can be seen, after 1 hour, there was virtually no loss with the Micro Shot, and there was 20% loss with the ceramic. After 6 hours, there was a 1% loss with the Micro Shot and a 98% loss with the ceramic. Net result is the Micro Shot lasts 70 times longer than the ceramic. This amounts to a significant cost savings in material, as well as avoiding the pitfalls of jagged edges from media fracturing.

As can be seen here, the Micro Shot is significantly more durable than the other two ferrous abrasives. What is interesting here is how the breakdown of the offshore micro shot accelerated, indicating buildup of internal stresses that exceed the cohesive forces of the material before breaking apart.

XRD-Residual Stress Measurement Curves

During the evaluation testing, several XRD-Stress Measurement Curves were run. The two sets of data shown here contain all of the germane and important data. One of the curves shows the Micro Shot vs Ceramic and the other shows the Micro Shot vs The High-Performance MS 1 and High-Performance MS 2.

You will notice in the first plot, Micro Shot vs Ceramic that the air pressure was only 40 psi. This was to guard against any premature break down of the ceramic media. You will notice that at the depth of 0.001”, the level of compressive stresses with the ceramic started to taper off at a faster pace than with the Micro Shot up to the point where they passed out of compression. Also, notice that the Micro Shot stayed in compression for an additional 0.001” as compared to the ceramic. As stated earlier, this was shot using only 40 psi air pressure to avoid any premature breakdown of the ceramic. When viewing the next data where all of the media was non-ceramic, 80 psi was used, and there is a significant difference in the depth and magnitude of compression.

The next plot shows the XRD data for Micro Shot and the High-Performance MS 1 and High-Performance MS 2. These tests were run at 80 psi as there were no concerns for premature breakdown. You will notice that all three were essentially the same at the surface, but the Micro Shot continued to go deeper in compression, while the other two remained relatively flat to the 0.002” depth, At this point, all three began to drop off in compression, but the Micro Shot at a more shallow slope, and remaining in compression for 0.0005” deeper. Additional data run at 100psi showed an even more dramatic difference, but there was breakdown of the MS 1, which indicated that 100 psi was too strong for the product.

Saturation Curves

Next, Saturation Curves were run with all of the materials. Again, one of the curves shows the Micro Shot vs Ceramic and the other shows the Micro Shot vs High-Performance MS 1 and High-Performance MS 2. Again, the test with ceramic was run at only 40 psi, while the other materials were run at 80 psi. The plots below show the comparative data.

While running at only 40 psi due to the ceramic breakdown issues, it is interesting to note that with the E-Micro Shot, saturation of ~0.0035”A was reached in ~7 seconds, while the ceramic took ~13 seconds to reach a saturation point of ~0.003”A.  Again, this demonstrates the benefit of higher density vs. the ceramic shot.

When running the saturation curves for the metallic media, higher air pressure, 80 psi, was used. Again, due to no problems of the media fracturing like ceramic does. One thing that is interesting in this data is that the results again follow the hardness relationship. The Micro Shot is +65HRC, MS 1 is +55HRC, and the MS 2 is 48-50HRC. The Micro Shot achieved saturation of ~0.006”A in ~6 seconds; the MS 1 reached saturation of ~0.005”A in ~9 seconds, and MS 2 reached saturation of ~0.0035”A in ~ 5 seconds. This data definitely bears out the relationship of the media hardness, because as mentioned earlier with roughly equal mass, the hardness of the media has a definite impact on the elasticity of the impact of the media to the substrate.

Also, this data all points to the superiority of the Micro Shot over ceramic beads, and over the other micro shot in terms of durability and energy transference allowing greater depths as well as higher magnitudes of compression in the shot peening process. The caveat here is that the Micro Shot can deliver these benefits in very confined areas that are inaccessible with conventional peening media.

Results

Micro Shot has been used on several components with fatigue stress points that are in critical areas that conventional shot peening cannot access due to size. Most of these components are proprietary in nature, limiting the information that can be shared, but the benefits in terms of increased life cycles can be shared with due protection to the proprietary and confidential information about the components.

1. A Titanium component undergoes several flexing cycles in operation down hole. The component needed to last at least 1 million cycles, but always failed in the range of 600K cycles with conventional steel or ceramic shot.

The failures always occurred in the small radii, at both ends, as indicated in the sketch. After peening these radii with the micro shot, the tests were consistently considered a run-out after 1.1 million cycles.

2. A down-hole holder that underwent extreme torsional loading while being driven down axially experienced premature fatigue failures initiating at the indicated radii.

Life was increased by a factor of 4X with the micro shot vs conventional shot peening with steel shot or ceramic.

3. Premature failure was experienced in a sealing ring due to high flexing in the seal groove area and thin wall.

Life was increased by 2X vs conventional shot and ceramic.

4. Another coupling experienced premature fatigue failure in an I.D. radius. The diameter of this part was 1.9”

After peening with micro shot, the life increased by 4x vs conventional shot and ceramic.

5. Small springs always represent a challenge. Micro shot was able to increase the life of these springs by +30% and higher, up to 200% over conventional shot or ceramic. These springs are all in the range of 3/8” diameter or less.

Summary

The need for a viable media substitute to ceramic bead for peening small, difficult-to-access areas has been long-felt. With the advent of the Micro Shot, it is now evident that there is a very viable substitute/replacement for ceramic media for peening small, critical areas. Additionally, in other testing, micro shot has been found to be a viable substitute for conventional S-70 and S-110 in certain applications. The micro shot gives up to a maximum intensity of 0.010”A, but with an extremely smooth finish, as well as reaching 200% coverage prior to saturation in some instances. Additionally, the breakdown rate of micro shot is significantly less than with certain conventional cast steel shot sizes, as well as vs ceramic. The other metals that we have peened with the Micro Shot are 4340 steel, P550 non mag stainless steel (yield of 150-180 KSI), several other stainless alloys, and some aluminum alloys. The results were all acceptable.

The Micro Shot will not take over the total shot market, but for the applications discussed within this paper, it is absolutely the best alternative currently available for shot peening.



For Information:
Superior Shot Peening, INC.
13930 Luthe Road
Houston, Texas 77039, USA
Tel. +1.281.449-6559
E-mail: dspinner@superiorshotpeening.com
www.superiorshotpeening.com

Note from the Publisher:
It is with great sadness to report that Dan Spinner
has passed away end of January, 2018.


 
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