September 1997

I Spring 1997

ISSN 1069-2010

International Newsletter for Shot Peening-Surface Finishing Industry Volume 11, Issue 3

Almen Strip Specifications by Jack Champaigne, Electronics Inc. A Brief History of the Almen Strip

Since the invention of the Almen strip and Almen gage by J. 0. Almen in 1942 the shot peening and blast cleaning industries have had a simple, inexpensive and reliable tool to gage shot blast stream intensity. Basically, the Almen strip is a small (3 inch by 3/4 inch) piece of spring tool steel that is blasted on one $ide and

. rriade to curve in response to the intensity of the impinging blast stream. The original sirip thick­ness was 0.050 inch and had no letter designa­tion until the "B" strip was developed. Although there doesn't seem to be any remaining records of the "B" strip, it can be surmised that it was quickly replaced by the "C" strip with thickness of 0.094 inch for higher intensity applications of the automotive sector. (It's not clear when the "A" strip thickness changed from Almen's 0.050 inch patent to the present value of 0.051 inch.)

Thus the "A" and the "C" strip were in common usage, primarily in the automotive industry. Eventually a thinner strip was needed for lower intensity peening of aircraft structural parts and accordingly Nobel from Pratt & Whitney developed a strip of 0.031 inch thick­ness and the "N" strip was introduced.

The most popular documents for control­ling the characteristics of the Almen strip are the U.S. Government specification Mil-S-13165 and

and the Society of Automotive Engineers (SAE) J-442. The government specification dates back to August 31, 1944 when a document number AXS-1272 was.published to describe a new technology for use by the U. S. Army. This document then evolved into Mil-S-13165 which was first issued on December 11, 1953. The Almen strip attributes in Mil-S-13165 Revision Care unchanged from AXS-1272.

The Society of Autom9tive Engineers, SAE, was also active in preparing Almen strip specifica­. tions. Their primary control document is SAE J-442 with supplemental specifications for aerospace applications corning from SAE AMS-2430 and SAE AMS 2432. Unfortunately, the evolution of J-442 allowed the strip attributes to change relative to Mil-S-13165. See Table l below.

Since shot peening often makes a dramatic improvement in a metallic part's performance, much of the early peening was done secretly. Eventually proprietary peening specifications . evolved to "enhance" the peening process beyond the customary specifications. Automotive, aero­space airframe and engine manufacturers were all active in promoting variations in the Almen strip specifications.

Continued on page 7

Table 1. U. S. Industry Shot Peening Specifications

Spec Date Length Width Thickness Hardness Flatness

13165C June 1989 3.000±.015 .745-.750 .051±.001 44-50 ±.0015

SAE J-442 June 1961 3.000±.015 .745-.750 .051±.001 44-50 ±.0010

SAEJ-442 Aug. 1979 2.992±.016 .744-.748 .051±.001 44-50 ±.0010

SAEJ-442 Jan. 1995 2.992±.016 .742-.750 .051±.001 44-50 ±.0010

AMS 2430L July 1993 2.992±.016 .742-.750 .051±.001 44-50 ±.0010

AMS 2432B Aug. 1996 2.992±.016 .742-.750 .051±.0005 45-48 ±.0005

Continuedfi-mn page 1

Table 2 shows the Almen strip characteristics of hardness, length, width, thickness and flatness requirements. Only the "A" thickness strips are included in the table. It can be surmised that hardness and flatness variations reflect a desire for more consis­tent and accurate intensity measurements. SAE aerospace speci­fication AMS-2432 was based upon SAE J-442 with enhanced hardness and flatness tolerance for the more critical peening applications using computer monitored equipment.

Electronics Inc. Almen Strip Grading and Inspection The following narrative will describe how Electronics

Incorporated became involved in supplying Almen strips and how they developed multiple grades intended to meet the various specifications. (See Table 3 on page 10.)

Electronics Inc. began selling Almen strips in 1989 to help underwrite the cost of The Shot Peene"r Newsletter. As a result of Almen strip specifications' diversity, Electronics Incorporated developed three grades of strips that allowed users

to choose the price/performance level best suited to them. Grade 3 strips were guaranteed to meet Mil-S-13 l 65C specifications and were bulk packaged in bags of 1000 pieces without special inspection or measurement. Grade 2 Almen strips were pack­aged in specially designed smaller protective boxes of 50 strips, had excess oil removed and were inspected for nicks, scratches, burrs, length and width. It was found to be very important not to remove the oil, especially by vapor degreasing or similar tech­nique since the strips are prone to rusting, even in a sealed zip­lock type bag. Grade 1 strips were 100% inspected for flatness to the more stringent SAE J-442 requirement (±.001 inch) and each lot of 1000 strips were sample inspected for hardness. When SAE aerospace created AMS-2432, a special grade of strip was required and grade 1 S was developed. Again, the strips were 100% inspected for flatness (±.0005) and each lot of 1000 was sample inspected for hardness ( 45-48 Hrc ).

Colllinued on page JO

Table 2. Almen "A" Strip Specifications Comparison

# Owner Specification Date Length Width Thickness Hard Flat

l SAE AMS2432 B Aug 1996 2.992±.016 .742-.750 .051±.0005 45-48 ±.0005

2 Boeing BAC 5730 M Mar 25, 1992 3.000± .. 015. .745-.750 .051±.001 45-48 ±.0015

3 Pratt & Whitney PT-444143 A 2.992±.016 .742-.750 .051±.0005 45-49 ±.0005

4 General Electric Pl 1TF8 SS Nov 29, 1994 3.000±.015 .745-.750 .051±.001 44-50 ±.0005

5 U.S. Army Mil-S-13165 c Jun 7, 1989 3.000±.015 .745-.750 .051±.001 44-50 ±.0015

5 BAe BAEP2009 Jan 1990 3.000±.015 .745-.750 .051±.001 44-50 ±.0015

5 deHavilland PPS 17.03 4 Jan 22, 1987 3.000± .. 015 .745-.750 .051±.001 44-50 ±.0015

5 General Dynamics FPS-1032 Sep 30 1963 3.000±.015 .745-.750 .051±.001 44-50 ±.0015

5 General Electric Pl 1TF3 12 Nov 29, 1994 3.000±.015 .745-.750 .05±.001 44-50 ±.0005

5 General Motors GM 4283-P Feb 1966 3.000±.015 .745-.750 .051±.001 44-50 ±.0015

5 Hamilton Standard HS102 H Jan 15, 1991 3.000±.015 .745-.750 .051±.001 44-50 ±.0015

5 Sikorsky SS8767 3 May 15, 1969 3.000±.015 .745-.750 .051±.001 44-50 ±.0015

6 SAE J-442 (61) Jun 1961 3.000±.015 .745-.750 .051±.001 44-50 ±.001

6 U.S. Army Mil-P-81985 Oct 18, 1974 3.000±.015 .745-.750 .051±.001 44-50 ±.001

6 Bell Helicopter BPS FW 4409 B Nov 21, 1979 3.000".015 .745-.750 .051±.001 44-50 ±.001

6 Hawker Siddeley S.29.46 2 Apr 1977 3.000±.015 .745-.750 .051±.001 44-50 ±.001

7 SAE AMS2430 L Jul 1993 2.992±.016 .742-.750 .051±.001 44-50 ±.001

7 SAE J-442 (95) Jan 1995 2.992±.016 .742-.750 .051±.001 44-50 ±.001

7 Pratt & Whitney 70-41-02 Oct 1, 1991 2.992±.016 .742/.750 .051±.001 44-50 ±.001

7 Pratt & Whitney TAM-34744 J 2.992±.016 .742-.750 .051±.001 44-50 ±.001

8 SAE J-442 (79) Aug 1979 2.992±.016 .744-.748 .051±.001 44-50 ±.001

8 Intl. Harvester A-39 May 1978 2.992±.016 .744-.748 .051±.001 44-50 ±.001

9 Lockheed-Georgia MPS 73401 Nov. 1, 1978 3.000±.015 .745-.750 051±.001 44-50 ±.0003

9 Lockheed Georgia STP51-501 J Oct 15, 1975 3.000±.015 .745-.750 .051±.001 44-50 ±.0003

JO ASTM B 851-94 May 1994 2.992±.016 .744-.748 .051±.001 44-50 ±.0015

11 AiResearch EMS92406 Apr 18, 1990 3.000±.015 .745-.750 .051±.0005 45-48 ±.0005

12 Snecma AMN 332/86 Jun 30, 1986 3.000±.016 745-.751 .051±.001 44-50 ±.001

The Shot Peener II Volume I I, Issue 3

Figure I Master Flow Chart

.0515

.0505

.750

.745

3.015 2.985

±.0005

w

L

F

EMS92406

.750

.742

3.008 2.976

±.0005

45 48

L

F

AMS2432B

T

.052 .0505

.750

.745

3.015 2.985

±.015

w

L

F

BAC5730M

The Shot Peener II Volume I I, Issue 3

Start

49 45

.0515

.0505

.750

.742

3.008 2.976

±.0005

H

T

w

L

F

PT-444143A

±.0003

MPS 73401 STP51-501J

.750

.745

L

3.015 2.985

F

±.0010 ±.0005

J-442(61) MIL-P-81985

BPS FW 4409B S.29.462

Pl ITF8S5

50 44

.052

.050

±.0015

MIL-S-l 3 I 65C BAEP2009 PPS 17.034 FPS-1032 Pl 1TF312

GM 4283-P HSI02H SS87673

T

w

H Hardness

T Thickness

w Width

L Length

F Flatness

0 See appropriate number in Table 2, page 7

.750 .748

.742 .744

L L

3.008 3.008 2.976 2.976

F F

±.0010 ±.0010 ±.0015

AMS2430L J-442 (79) B 851-94 J-442 (95) A-39 70-41-02

TAM-347441

The Shot Peener II Volume II, Issue 3

.751

.745

L

3.016 2.984

F

±.0010

AMN 332/86

Table 3. Electronics Inc. Grade Table

Grade 3 Bulk packaged (meets Mil-S-13165)

Grade 2 50 pcs. packaged, minor inspection

Grade I as above, flatness 100% inspected to .00 I inch

Grade IS as above, flatness I 00% inspected to .0005 inch

It wasn't long after these four grades were established that special requests for other variations arose. Boeing requested a variation that didn't fall into the standard categories. General

4 Pl ITF8S5

0 MIL-S-13165C

BAEP 2009 PPS 17.034 FPS-1032 Pl ITF312

GM 4283-P HSI02H SS87673

0 J-442(61)

MIL-P-81985 BPS FW 44098

S.29.462

0 AMS2430L J-442 (95) 70-41-02

TAM-347441

J-442 (79) A-39

MPS 73401 STP51-501

@ B 851-94

@ AMS 332/86

Hardness

49 45

3 PT-444143A

48 45

I AMS2432B

0 BAC5730

@ EMS92406

Figure 2. Hardness flow chart

Electric asked for another variation, and differences in the Pratt and Whitney specifications were noticed. Someone noticed that SAE J-442 length, width and thickness didn't match the Mil-S-13165 dimensions when the metric measurements were converted to inch measures. The multitude of variations prompted the development of Table 2 which shows 12 distinct Almen strip requirements.

The master flow cha.it shown in Figure I (pages 8 and 9) helps to visualize the differences required by the various specifi­cations. At least 12 distinct specifications were identified for this article. To further illustrate the differences in individual attributes Figures 2 through 6 help to quantify the individual attributes of hardness, thickness, width, length and flatness.

.051±.001

2 BAC5730

0 PIITF8S5

0 MIL-S-13165C

BAEP2009 PPS 17.034 FPS-!032 Pl ITF312

GM 4283-P HSI02H SS87673

J-442(61) MIL-P-81985

BPS FW4409B S.29.462

0 AMS2430L J-442 (95) 70-41-02

TAM-347441

0 J-442 (79)

A-39

MPS 73401 STP51-501

@ B 851-94

@ AMS 332186

Thickness

.051±.0005

0 AMS2432B

0 PT-444143A

@ EMS92406

Figure 3. Thickness flow chart

The Shot Peener m Volume II, Issue 3

.750

.745

2 BAC5730

PIITF8S5

0 MIL-S-13165C

BAEP 2009 PPS 17.034 FPS-!032 Pl ITF312

GM 4283-P HSI02H SS87673

J-442(61) MIL-P-81985

BPS FW 44098 S.29.462

MPS 73401 STPSl-501

@ EMS924(l6

3.000±.015

2 BAC5730

0 PIITF8S5

0 MIL-S-13165C

BAEP2009 PPS 17.034 FPS-1032 Pl ITF312

GM 4283-P HSI02H SS87673

J-442(61) MIL-P-81985

BPS FW 44098 S.29.462

MPS 73401 STPSl-501

@ EMS92406

Width

.751

.745 .748 .744

.750

.742

12 8 MIL-P-81985 J-442 (79)

A-39

® B 851-94

Figure 4. Width flow chart

Length

3.000±.016 2.992±.016

I 12 Ai'vlS2432B

0 PT-4-l4143A

0 AMS2430L J-442 (95) 70-41-02

TAM-34744)

J-442 (79) A-39

® B 851-94

M!L-P-81985

Figure 5. Length flow chart

I AMS2432B

0 PT-4-l4143A

0 AMS2430L J-442 (95) 70-41-02

TAM-347441

Flatness

.0003 .0005 .0010 .0015

9 I 6 2 MPS 73401 AMS2432B J-442(61) BAC5730 STP51-50!

0 MIL-P-8!985

BPS FW 44(l9B 0 S.29.462

0 PT-44l!43A MIL-S-!3165C

0 BAEP2009 PPS 17.034

AMS2430L FPS-!032 J-442 (95) Pl!TF312 70-41-02 GM4283-P PIITF8S5 TAM-347441 HSI02H

0 0 SS87673

® MIL-S-! 3165C J-442 (79) BAEP 2009 A-39 PPS 17.034 8851-94 FPS-1032

@ PIITF312 GM 4283-P

HSI02H SS87673 AMS 332/86

@ EMS92406

Figure 6. Flatness flow chart

To help satisfy the various (and occasionally conflicting) requirements, Electronics Incorporated began charting his­tograms of the length, width, thickness, hardness and flatness attributes (30 piece sample per lot of 1000 strips based upon MIL STD 105 inspection requirements). The histograms, shown in Figures 7 through I 1, provide the information needed to certi­fy that strips will meet any of the specifications that might be required.

~ Std Dev: SlreWll6ss:

30 2.99177 .0018641 1.1914

Lot:1737 Ctl:830154-A Type:A Grade:SAE J442 JAN95 LENGTH

LSL

Cp/c Cp· Cpm:

-:,,P

Target

2.819 2.861 2.838

.,,,,

JspUm: Target

~~

USL

(2.9862, 2.9974) 2.992

( 2.976, 3.008) ( .0000, .0000)

Figure 7. Length Histogram

The Shot Peener m Volume I I, Issue 3

20

Samplos: Mean Std Dev: Skewness:

Lot:1737 Ctl:830154-A Type:A Grade:SAE J442 JAN95 WIDTH

LSL

30 .745967 3.0559E-o4

·.24994

~· Cpm.

Target

-Jsp 1-Jsp

4327 4.363 4.337

3spLim: Target:

~~'-!:f:

USL

( .74505 •. 74688) .746 (.742, .75) ( .0000 .. 0000)

Figure 8. Width Histogram

25-·

20-·

15 ..

, ..

42

Sample, Mean: SldDev: Skewl'less:

30 458567 .25975

-.077074

Lot:1737 Ctl:830154-A Type:A Grade:SAE J442 JAN95 HARDNESS

LSL

Cpk Cp· Cpm:

2.383 3.85 .8393

3spLJm: Tarpet:

~~

USL

(45077, 46636) 47 (44, 50) ( .0000, .0000)

Samples: Mean­StdDev: Skewness

LSL

30 0508433 7.9454E-05 2027

Lot:1737 Ctl:830154-A Type:A Grade:SAE J442 JAN95 THICKNESS

Cpk· ep· Cpm

3538 4.195 1.872

r,,ge1

3spl.Jm· Ta,ge/ Spec Lim Es/%out.

USL

(.050605. ,0510B2) .051 (.05, .052) ( .0000, .0000)

Figure 9. Thickness Histogram

Figure JO. Hardness Histogram The Shot Peener m Volume I I, Issue 3

Lot:1737 Ctl:830154-A Type:A Grade:SAE J442 JAN95 FLATNESS

Figure 11. Flatness Histogram

Conclusion

Samples: Mean· Sl'dDev. SkewneS3:

60 ·.000085 2.3928E-04

·34786

LSL

·3sp

1.275 1.393 1.311

If you were wondering what is done to inspect and ship Almen strips to meet the increasing demands of a growing industry, now you know the rest of the story. It has become necessary to continually review Almen strip specifications to assure proper compliance with the requested attributes. Assumptions about Almen strip quality and outdated practices of "rejecting for non-compliance" have been replaced with modern techniques of statistical process control as verified by sample histograms. Requests for tighter hardness range (i.e. 45-48 Hrc) or tighter flatness tolerance (i.e. ±.0003 inch) are now easily met. The certification that is provided with the Almen strip ship­ment provides the customer assurance that he will be using

The March of Progress "Today the watch you are wearing on

your wrist contains more computing power than existed in the entire world before 1961. The cost of computing is 8,000 times less than it was 30 years ago. That's the equivalent of get­ting a Boeing 747 for the price of a pizza:'

-Morley Winograd, Vice President of AT&T

3spLim Target

~~-

•3,p

USL

(-8.028JE.Q4, 6.3283E-04J 0 (-.001, .001) ( .0065668, .0002861)

Almen strips that do, indeed, meet all applicable requirements and specifications.

Caution: Every attempt has been made to insure the accuracy of this article but the author makes no claims as to its accuracy. Any and all specifications are subject to revision without the author's knowledge. Any corrections received by the author will be reprinted in the next issue of The Shot Peener. The informa­tion presented in this article is meant to be illustrative and should not be relied upon for the performance of any peening or cleaning contracts.

Five Ways to Blow a Sale 1. Don't follow through

2. Bad-mouth the customer

3. Sell when you shouldn't

4. Don't listen

5. Assume you know what customers want

-from Inc. magazine

The Shot Peener m Volume I I, Issue 3