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Grinding machines
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Published: 01 June 2019
Fig. 4 Accelerometer at left center is attached to a grinding machine. Tiny, complex vibrations caused variations in the quality of internally ground bores.
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Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.design.c9001551
EISBN: 978-1-62708-233-4
... indicating rotational vibration fatigue. Keeping bolts tight solved this problem. In another case, grinding machines were unable to produce surfaces of uniform quality and smoothness on steel bearing products. Measurements showed that self-excited vibrations were created when particular steels were ground...
Abstract
A multi-million dollar, four-color printing press used to produce a major weekly magazine was breaking pinions (shouldered shafts) on rolls. The cause of fracture was cyclic fatigue. Steel quality and heat treatment met expected standards. The pinion fracture showed multiple origins indicating rotational vibration fatigue. Keeping bolts tight solved this problem. In another case, grinding machines were unable to produce surfaces of uniform quality and smoothness on steel bearing products. Measurements showed that self-excited vibrations were created when particular steels were ground. It was found that the natural frequency of the wheel truing device was the culprit. A tuned damped absorber was designed and built to modify the resonance. This eliminated the problem.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.machtools.c0047964
EISBN: 978-1-62708-223-5
... of the grinding machine was reconditioned to eliminate the undulations and retained austenite was minimized by careful heat treatment. Bevel gears Cracks Gear boxes Magnetic particle testing Spalling Surface grinding 8620 UNS G86200 Rolling-contact wear The service life of a production gearbox...
Abstract
Drastic reduction in the service life of a production gearbox was observed. Within the gearbox, the axial load on a bevel gear (8620 steel, OD 9.2 cm) was taken by a thrust-type roller bearing (3.8 cm ID, 5.6 cm OD) in which a ground surface on the back of the bevel gear served as a raceway. Spalling damage on the ground bearing raceway at five equally spaced zones was disclosed by inspection of the bevel gear. The bearing raceway was checked for runout by mounting the gear on an arbor. It was found that the raceway undulated to the extent of 0.008 mm total indicator reading and a spalled area was observed at each high point. The presence of numerous cracks that resembled grinding cracks was revealed both by magnetic-particle inspection and microscopic examination. Spalling was produced by nonuniform loading in conjunction with grinding cracks. As corrective measures, the spindle of the grinding machine was reconditioned to eliminate the undulations and retained austenite was minimized by careful heat treatment.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c0047813
EISBN: 978-1-62708-229-7
... Abstract After being in service for ten years the ball-and-race coal pulverizer was investigated after noises were noted in it. Its lower grinding ring was attached to the 6150 normalized steel outer main shaft while the upper grinding ring was suspended by springs from a spider attached...
Abstract
After being in service for ten years the ball-and-race coal pulverizer was investigated after noises were noted in it. Its lower grinding ring was attached to the 6150 normalized steel outer main shaft while the upper grinding ring was suspended by springs from a spider attached to the shaft. A circumferential crack in the main shaft at an abrupt change in shaft diam just below the upper radial bearing was revealed by visual examination. The smaller end of the shaft was found to be slightly eccentric with the remainder when the shaft was set up in a lathe to machine out the crack for repair welding. The crack was opened by striking the small end of the shaft and the shaft was broken 1.3 cm away from the crack in the process. A previous fracture that resulted from torsional loading acting along a plane of maximum shear was revealed almost perpendicular to the axis of the shaft. Faint lines parallel to the visible crack thought to be fatigue cracks were revealed on examination of the machined surface. The shaft was repaired by welding a new section and machined to required diameters and tapers to avoid abrupt changes.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.machtools.c0091853
EISBN: 978-1-62708-223-5
.... The process continued until approximately 4.5 kg (10 lb) of the 75 μm product was deposited in the collection tray. The product was removed from the collection tray and the process repeated. Eventually, the machine failed due to grinding plate wear. Fig. 2 Macrographs of new (left) and worn (right...
Abstract
A 230 mm (9 in.) diameter disk attrition mill was scheduled to grind 6.35 mm (0.25 in.) diameter quartz particles to a 0.075 mm (0.003 in.) diameter powder. Due to severe wear on the grinding plates, however, the unit was unable to complete the task of grinding the rock. The mill consisted of a heavy gray cast iron frame, a gravity feeder port, a runner, and a heavy-duty motor. The frame and gravity feeder weighed over 200 kg (440 lb) and, in some areas, was over 25 mm (1 in.) thick. To obtain the operating speed of 200 rpm, a gear system was used to transmit the torque from the 2-hp motor. The runner consisted of a 50 mm (2 in.) diameter shaft and two gray cast iron grinding plates. Investigation (visual inspection, historical review, photographs, model testing of new plates, chemical analysis, hardness testing, optical macrographs, and optical micrographs) supported the conclusion that the primary feed material was harder than the grinding plates, causing wear and eventual failure. Recommendations included reducing the clearance between the flutes and possible material changes.
Series: ASM Handbook
Volume: 11A
Publisher: ASM International
Published: 30 August 2021
DOI: 10.31399/asm.hb.v11A.a0006826
EISBN: 978-1-62708-329-4
... raisers such as machining marks and grinding burns. Failures associated with the workpiece and machining process are often apparent in the production run or procedure development, while workpiece in-service failures due to undesired surface roughness, surface topography, and surface layer metallurgy...
Abstract
The first part of this article focuses on two major forms of machining-related failures, namely machining workpiece (in-process) failures and machined part (in-service) failures. Discussion centers on machining conditions and metallurgical factors contributing to (in-process) workpiece failures, and undesired surface layers and metallurgical factors contributing to (in-service) machined part failures. The second part of the article discusses the effects of microstructure on machining failures and their preventive measures.
Series: ASM Handbook Archive
Volume: 11
Publisher: ASM International
Published: 01 January 2002
DOI: 10.31399/asm.hb.v11.a0009222
EISBN: 978-1-62708-180-1
... Abstract This article describes the six fundamental factors that decide a tool's performance. These are mechanical design, grade of tool steel, machining procedure, heat treatment, grinding, and handling. A deficiency in any one of the factors can lead to a tool and die failure. The article...
Abstract
This article describes the six fundamental factors that decide a tool's performance. These are mechanical design, grade of tool steel, machining procedure, heat treatment, grinding, and handling. A deficiency in any one of the factors can lead to a tool and die failure. The article presents a seven-step procedure to be followed when looking for the reason for a failure. A review of the results of the seven-point investigation may lead directly to the source of failure or narrow the field of investigation to permit the use of special tests.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.process.c0047830
EISBN: 978-1-62708-235-8
..., the forgings were normalized, hardened and tempered to 28 to 32 HRC before being machined to increase fatigue strength and extremely rough surfaces were removed by careful grinding. Defects 4140 UNS G41400 Fatigue fracture Metalworking-related failures Textile-machine crankshafts like that shown...
Abstract
Textile-machine crankshafts forged from 4140 steel fractured transversely on one cheek during one to three years of service. The cause of failure for two forgings (one complete fractured forging and second a section that contained the shorter shaft fracture cheek) was determined. Indication of fatigue failure was revealed by visual examination of the fracture surfaces. Rough grooves from hot trimming of the flash were visible on the surface of the cheeks. The outer face of one cheek of the throw on the forging contained shallow surface folds. Slightly decarburized forged surface was identified around one of the folds and a fatigue crack initiated in the fold and propagated across the cheek. Properties representative of 4140 steel, quenched and tempered to a hardness of 20 to 22 HRC, were observed. Tempered bainite was revealed in the general microstructure. As a corrective measure, the forgings were normalized, hardened and tempered to 28 to 32 HRC before being machined to increase fatigue strength and extremely rough surfaces were removed by careful grinding.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.process.c0046028
EISBN: 978-1-62708-235-8
... a fractured latch tip that shows two of several small cracks (arrows at right) that extended through the hardened case to the core, and the burned layer on latch surface (dark band indicated by arrow at left) that resulted from grinding burns The stop arms were machined from 8620 steel. The latch tips...
Abstract
The 8620 steel latch tip, carburized and then induction hardened to a minimum surface hardness of 62 HRC, on the main-clutch stop arm on a business machine fractured during normal operation when the latch tip was subjected to intermittent impact loading. Fractographic examination 9x showed a brittle appearance at the fractures. Micrograph examination of an etched section disclosed several small cracks. Fracture of the parts may have occurred through similar cracks. Also observed was a burned layer approximately 0.075 mm (0.003 in.) deep on the latch surface, and hardness at a depth of 0.025 mm (0.001 in.) in this layer was 52 HRC (a minimum of 55 HRC was specified). Thus, the failure was caused by brittle fracture in the hardness-transition zone as the result of excessive impact loading. The burned layer indicated that the cracks had been caused by improper grinding after hardening. Redesign was recommended to include reinforcing the backing web of the tip, increasing the radius at the relief step to 1.5 x 0.5 mm (0.06 x 0.02 in.), the use of proper grinding techniques, and a requirement that the hardened zone extend a minimum of 1.5 mm (0.06 in.) beyond the step.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c9001730
EISBN: 978-1-62708-229-7
... stationary ring, between which are a set of grinding balls rolling in a horizontal plane. Force is applied through the stationary top ring (supported from the housing but free to move up and down within limits) to the lower revolving ring by springs which impose 18,000 lb of compression. The grinding ring...
Abstract
A shaft can crack twice before it fails. A Detroit electric plant had this experience with one in a coal pulverizer. Because the first crack rewelded partially (by friction) in service, the pulverizer remained serviceable until the second crack developed.
Series: ASM Failure Analysis Case Histories
Volume: 3
Publisher: ASM International
Published: 01 December 2019
DOI: 10.31399/asm.fach.v03.c9001761
EISBN: 978-1-62708-241-9
... Abstract An investigation of a damaged crankshaft from a horizontal, six-cylinder, in-line diesel engine of a public bus was conducted after several failure cases were reported by the bus company. All crankshafts were made from forged and nitrided steel. Each crankshaft was sent for grinding...
Abstract
An investigation of a damaged crankshaft from a horizontal, six-cylinder, in-line diesel engine of a public bus was conducted after several failure cases were reported by the bus company. All crankshafts were made from forged and nitrided steel. Each crankshaft was sent for grinding, after a life of approximately 300,000 km of service, as requested by the engine manufacturer. After grinding and assembling in the engine, some crankshafts lasted barely 15,000 km before serious fractures took place. Few other crankshafts demonstrated higher lives. Several vital components were damaged as a result of crankshaft failures. It was then decided to send the crankshafts for laboratory investigation to determine the cause of failure. The depth of the nitrided layer near fracture locations in the crankshaft, particularly at the fillet region where cracks were initiated, was determined by scanning electron microscope (SEM) equipped with electron-dispersive X-ray analysis (EDAX). Microhardness gradient through the nitrided layer close to fracture, surface hardness, and macrohardness at the journals were all measured. Fractographic analysis indicated that fatigue was the dominant mechanism of failure of the crankshaft. The partial absence of the nitrided layer in the fillet region, due to over-grinding, caused a decrease in the fatigue strength which, in turn, led to crack initiation and propagation, and eventually premature fracture. Signs of crankshaft misalignment during installation were also suspected as a possible cause of failure. In order to prevent fillet fatigue failure, final grinding should be done carefully and the grinding amount must be controlled to avoid substantial removal of the nitrided layer. Crankshaft alignment during assembly and proper bearing selection should be done carefully.
Image
Published: 01 January 2002
Fig. 17 Forged 4140 steel textile-machine crankshaft that fractured in fatigue originating at machining marks and forging defects. (a) Configuration and dimensions (given in inches). (b) Fracture surface. (c) Hot trim marks. (d) Snag grinding marks. (e) Hot folds. (f) Section through a hot
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Image
in Fatigue Fracture of a 4140 Steel Forged Crankshaft Resulting From Stress Raisers Created During Hot Trimming
> ASM Failure Analysis Case Histories: Processing Errors and Defects
Published: 01 June 2019
Fig. 1 Forged 4140 steel textile-machine crankshaft that fractured in fatigue originating at machining marks and forging defects. (a) Configuration and dimensions (given in inches). (b) Fracture surface. (c) Hot trim marks. (d) Snag grinding marks. (e) Hot folds. (f) Section through a hot fold
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Image
Published: 30 August 2021
Fig. 28 Forged grade 4140 steel textile-machine crankshaft that fractured in fatigue originating at machining marks and forging defects. (a) Configuration and dimensions (given in inches). (b) Fracture surface. (c) Hot trim marks. (d) Snag grinding marks. (e) Hot folds. (f) Section through
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Series: ASM Handbook Archive
Volume: 11
Publisher: ASM International
Published: 01 January 2002
DOI: 10.31399/asm.hb.v11.a0001814
EISBN: 978-1-62708-180-1
...-working and hot-working applications. It reviews problems introduced during mechanical design, materials selection, machining, heat treating, finish grinding, and tool and die operation. The brittle fracture of rehardened high-speed steels is also considered. Finally, failures due to seams or laps...
Abstract
This article describes the characteristics of tools and dies and the causes of their failures. It discusses the failure mechanisms in tool and die materials that are important to nearly all manufacturing processes, but is primarily devoted to failures of tool steels used in cold-working and hot-working applications. It reviews problems introduced during mechanical design, materials selection, machining, heat treating, finish grinding, and tool and die operation. The brittle fracture of rehardened high-speed steels is also considered. Finally, failures due to seams or laps, unconsolidated interiors, and carbide segregation and poor carbide morphology are reviewed with illustrations.
Series: ASM Handbook
Volume: 11A
Publisher: ASM International
Published: 30 August 2021
DOI: 10.31399/asm.hb.v11A.a0006818
EISBN: 978-1-62708-329-4
... treatment. Thus, some final grinding is usually needed after heat treatment. The presence of decarburization is generally quite detrimental. Also, because stresses are high in heat treatment and in service, rough machining marks must be avoided. Identification stamp marks are another common source...
Abstract
This article discusses failure mechanisms in tool and die materials that are very important to nearly all manufacturing processes. It is primarily devoted to failures of tool steels used in cold working and hot working applications. The processes involved in the analysis of tool and die failures are also covered. In addition, the article focuses on a number of factors that are responsible for tool and die failures, including mechanical design, grade selection, steel quality, machining processes, heat treatment operation, and tool and die setup.
Series: ASM Handbook
Volume: 11
Publisher: ASM International
Published: 15 January 2021
DOI: 10.31399/asm.hb.v11.a0006765
EISBN: 978-1-62708-295-2
... effective. Besides these papers, there are several other options available. One option is to planar grind the specimens with a conventional alumina grinding stone. This requires a special-purpose machine, because the stone must rotate at a high speed, ≥1500 rpm, to cut effectively. The stone must be dressed...
Abstract
Metallographic examination is one of the most important procedures used by metallurgists in failure analysis. Typically, the light microscope (LM) is used to assess the nature of the material microstructure and its influence on the failure mechanism. Microstructural examination can be performed with the scanning electron microscope (SEM) over the same magnification range as the LM, but examination with the latter is more efficient. This article describes the major operations in the preparation of metallographic specimens, namely sectioning, mounting, grinding, polishing, and etching. The influence of microstructures on the failure of a material is discussed and examples of such work are given to illustrate the value of light microscopy. In addition, information on heat-treatment-related failures, fabrication-/machining-related failures, and service failures is provided, with examples created using light microscopy.
Series: ASM Failure Analysis Case Histories
Volume: 2
Publisher: ASM International
Published: 01 December 1993
DOI: 10.31399/asm.fach.v02.c9001350
EISBN: 978-1-62708-215-0
... Selection Small interconnecting holes were drilled around the two nozzles to remove the cracked regions. The nozzles were then separated from the cut-out disks by machining the fillet weldments, taking care that sufficient weldment material remained with the disks ( Fig. 3 ). The two disks contained...
Abstract
Upon arrival at the erection site, an AISI type 316L stainless steel tank intended for storage of fast breeder test reactor coolant (liquid sodium) exhibited cracks on its shell at two of four shell/nozzle fillet-welded joint regions. The tank had been transported from the manufacturer to the erection site by road, a distance of about 800 km (500 mi). During transport, the nozzles were kept at an angle of 45 deg to the vertical because of low clearance heights in road tunnels. The two damaged joints were unsupported at their ends inside the vessel, unlike the two uncracked nozzles. Surface examination showed ratchet marks at the edges of the fracture surface, indicating that loading was of the rotating bending type. Electron fractography using the two-stage replica method revealed striation marks characteristic of fatigue fracture. The striations indicated that the cracks had advanced on many “mini-fronts,” also indicative of nonuniform loading such as rotating bending. It was recommended that a support be added at the inside end of the nozzles to rigidly connect with the shell. In addition to avoiding transport problems, this design modification would reduce fatigue loading that occurs in service due to vibration of the nozzles during filling and draining of the tank.
Series: ASM Handbook Archive
Volume: 11
Publisher: ASM International
Published: 01 January 2002
DOI: 10.31399/asm.hb.v11.a0003560
EISBN: 978-1-62708-180-1
... crusher wear, electronic circuit board drill wear, grinding plate wear failure analysis, impact wear of disk cutters, and identification of abrasive wear modes in martensitic steels. abrasive wear failures abrasive wear mechanisms adhesive wear erosive-type wear wear failure analysis...
Abstract
Wear, a form of surface deterioration, is a factor in a majority of component failures. This article is primarily concerned with abrasive wear mechanisms such as plastic deformation, cutting, and fragmentation which, at their core, stem from a difference in hardness between contacting surfaces. Adhesive wear, the type of wear that occurs between two mutually soluble materials, is also discussed, as is erosive wear, liquid impingement, and cavitation wear. The article also presents a procedure for failure analysis and provides a number of detailed examples, including jaw-type rock crusher wear, electronic circuit board drill wear, grinding plate wear failure analysis, impact wear of disk cutters, and identification of abrasive wear modes in martensitic steels.
Book Chapter
Series: ASM Handbook
Volume: 11
Publisher: ASM International
Published: 15 January 2021
DOI: 10.31399/asm.hb.v11.a0006790
EISBN: 978-1-62708-295-2
... ): Design Improper selection of material Heat treatment Fabrication Improper machining and assembly These factors may be related to the occurrence of a failure in various ways, for example, the initiation of a crack or the increased susceptibility to wear or corrosion. General...
Abstract
Engineered components fail predominantly in four major ways: fracture, corrosion, wear, and undesirable deformation (i.e., distortion). Typical fracture mechanisms feature rapid crack growth by ductile or brittle cracking; more progressive (subcritical) forms involve crack growth by fatigue, creep, or environmentally-assisted cracking. Corrosion and wear are another form of progressive material alteration or removal that can lead to failure or obsolescence. This article primarily covers the topic of abrasive wear failures, covering the general classification of wear. It also discusses methods that may apply to any form of wear mechanism, because it is important to identify all mechanisms or combinations of wear mechanisms during failure analysis. The article concludes by presenting several examples of abrasive wear.
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