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Ellwood Deep Rolling Fatigue Enhancement Process

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					Ellwood Crankshaft Group

         Ellwood Deep Rolling Fatigue Enhancement Process

The Ellwood Deep Rolling Fatigue Enhancement Process is a proprietary in-house
developed method utilized to enhance crankshaft fatigue performance. Crankshaft
journal radii are mechanically deep rolled to induce surface residual compressive stress
into the crankshaft and improve fatigue life.

The radius surface is prepared for roll hardening through machining operations of lathe
turning or milling. The compressive stress is generated in the workpiece at the contact
point during the rolling process. Upon completion of the rolling the stress remains in the
penetrated zone.

Figure 1 below is a model replicating the Ellwood Deep Rolling Fatigue Enhancement
Process. The model shows treating a main bearing journal radius of a medium size diesel
marine crankshaft.




              Figure 1: Deep rolling tool profiling a diesel marine crankshaft main bearing radius.


The process utilized by Ellwood is beneficial in that the enhanced surface remains
uniform throughout the entire radius. The process also does not create micro notches or
local stress risers.




              2727 Freedland Road Hermitage, PA 16148 (724)347-0250 (800)247-1326 Fax:(724)347-0254
Ellwood Crankshaft Group




Figure 2: The left journal radius has been treated using Ellwood Deep Rolling Fatigue Enhancement technology. The right
                         journal is untreated and shows the lathe turned condition prior to rolling.



Figure 2 above compares an untreated lathe turned radius to a lathe turned radius that has
been treated with the Ellwood Fatigue Enhancement Process. Figure 3 below depicts the
radius geometry and configuration of the crankshaft tested to produce the data in Figure
4.




  Figure 3: Radius profile of Ellwood test specimen as described in the paragraphs below. Main bearing diameter was
                                     8.2677” (210mm). Figure is in English units.



                 2727 Freedland Road Hermitage, PA 16148 (724)347-0250 (800)247-1326 Fax:(724)347-0254
Ellwood Crankshaft Group


When compared to the traditional shot peening methods, it is well documented that shot
peening only achieves approximately 1/3 the penetration depth as the Ellwood Deep
Rolling Process. To further support this documentation the below graph shows results
testing radii treated with the Ellwood process and compares them to published data of
shot peening and carburizing. The induced negative compressive stress using the
Ellwood process reaches a maximum penetration depth of .020” (0.508mm) and .025”
(0.635mm), this is 2-3 times the achieved depth using traditional shot peen and
carburizing techniques.



                                                          Residual Stress Profiles                                           Ellwood
                                                                                                                             Lathe
                          200                                                                                                Turned
                                                                                                        1275                 Radius
                          150
                                                                                                                             Ellwood
                                                                                                        775                  Turned &
                          100
                                                                                                                             Deep Rolled
                           50
  Residual Stress (ksi)




                                                                                                        275
                                                                                                                             Typical
                            0
                                                                                                               MPa
                                                                                                                             Carburized
                                                                                                        -225                 Gear
                           -50

                          -100                                                                          -725                 Rc 61 Shot
                                                                                                                             Peened
                          -150
                                                                                                        -1225
                          -200
                                                                                                                             Ellwood
                          -250                                                                          -1725                Turned,
                             0.000               0.010               0.020               0.030                               Polished &
                             0.000               0.254               0.508               0.762                               Deep Rolled
                                                   Depth Below Surface (in. , mm)

 Figure 4: Graph shows results of negative induced residual stress versus depth comparing documented results of standard
 carburizing and shot peening to tested results of lathe turning and using the Ellwood Deep Rolling Fatigue Enhancement
                                                           Process.




                                     2727 Freedland Road Hermitage, PA 16148 (724)347-0250 (800)247-1326 Fax:(724)347-0254
Ellwood Crankshaft Group

The depth versus residual stress testing was performed using X-Ray Diffraction analysis.
This allows for the radii to be sectioned to test and determine the induced stress and
achieved penetration depth values. The set-up and testing of a treated sectioned radius is
shown in the Figure 5 photo below.




              Figure 5: A sectioned crankshaft journal radius being tested using the X-Ray method.



There have been numerous documented studies and results proving that roll hardening
can increase fatigue strength from 30% up to 150% when applied to carbon, CrMo, and
NiCrMo alloy steels. It is also documented that deep rolling procedures are able to
increase fatigue life by greater amounts than other crankshaft enhancement treatments
such as nitride or induction hardening. The data in Figure 6 below shows the increase in
fatigue limits when deep rolling is utilized on diesel marine alloy crankshafts. Fatigue
life nearly doubles when applying a rolling procedure or a rolling then grinding
procedure to the crankshaft radii. Figure 7 below compares fatigue increases in 40CrMo
modified steel documenting untreated, nitrided, induction hardened, and deep rolled
results.




             2727 Freedland Road Hermitage, PA 16148 (724)347-0250 (800)247-1326 Fax:(724)347-0254
Ellwood Crankshaft Group


                                                                 Fatigue Enhancement

                                   900
                                                                            93% Increase                93% Increase
                                   800

                                   700
             Fatigue Limit (MPa)




                                   600

                                   500

                                   400

                                   300

                                   200

                                   100

                                     0
                                                 Non -rolled                   Rolled                 Rolled and Ground

Figure 6: Graph is regenerated using deep rolling data from test specimen CrMo, medium size, diesel marine crankshaft:
                                                  Takami et al 1995.



                                                   Increase in Fatigue Strength - 40CrMo mod

                                   160

                                   140

                                   120

                                   100
             Percentage




                                    80

                                    60

                                    40

                                    20

                                     0
                                              Untreated        Induction Hardened          Nitrided         Deep Rolled

   Figure 7: Increase in fatigue strength comparing various enhancement procedures generated from customer data.




                                   2727 Freedland Road Hermitage, PA 16148 (724)347-0250 (800)247-1326 Fax:(724)347-0254

				
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posted:11/7/2011
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