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Articles About Materials Testing


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1 High-Temperature Testing of Stanyl Plastic Gears: A Comparison with Tensile Fatigue Data (March/April 2010)

This paper shows an experimental study on the fatigue lifetime of high-heat polyamide (Stanyl) gears running in oil at 140°C. Based on previous works (Refs. 1–2), an analysis is made correcting for tooth bending and calculating actual root stresses. A comparison with tensile bar fatigue data for the same materials at 140°C shows that a good correlation exists between gear fatigue data and tensile bar fatigue data. This insight provides a solid basis for gear designers to design plastic gears using actual material data.

2 Large Pinions for Open Gears - The Increase of Single Mesh Load (January/February 2013)

This paper introduces mandatory improvements in design, manufacturing and inspection - from material elaboration to final machining - with special focus on today's large and powerful gearing.

3 Accelerating Validation Testing (January/February 2012)

Bringing new or improved products to market sooner has long been proven profitable for companies. One way to help shorten the time-to-market is to accelerate validation testing. That is, shorten the test time required to validate a new or improved product.

4 Selection of a Proper Ball Size to Check an Involute Spur or Helical Cear Tooth (September/October 1987)

A much-used method for checking the tooth thickness of an involute gear tooth is to measure the dimension over two balls placed in most nearly opposite spaces in the case of external gears, and the dimension between the balls in the case of internal gears. This measurement is then checked against a pre-calculated dimension to denote an acceptable part.

5 Viewpoint (May/June 1987)

Joe Arvin comments on his recent trip to Scandinavia and how U.S. defense dollars are being spent overseas. J.D. Smith responds to an article on gear noise from the previous issue.

6 Bevel Gear Development and Testing Procedure (July/August 1986)

The most conclusive test of bevel and hypoid gears is their operation under normal running conditions in their final mountings. Testing not only maintains quality and uniformity during manufacture, but also determines if the gears will be satisfactory for their intended applications.

7 Identification of Gear Noise with Single Flank Composite Measurement (May/June 1986)

Anyone involved in the design, manufacture and use of gears is concerned with three general characteristics relative to their application: noise, accuracy, and strength or surface durability. In the article, we will be dealing with probably the most aggravating of the group, gear noise.

8 Single-Flank Testing (October/November 1984)

It was very interesting to see Robert Smith's article on single-flank testing of gears...

9 Single Flank Testing of Gears (May/June 1984)

Presumably, everyone who would be interested in this subject is already somewhat familiar with testing of gears by traditional means. Three types of gear inspection are in common use: 1) measurement of gear elements and relationships, 2) tooth contact pattern checks and 3) rolling composite checks. Single Flank testing falls into this last category, as does the more familiar Double Flank test.

10 Material Selection and Heat Treatment (July/August 1985)

Before the optimum mechanical properties can be selected, the working stress must be determined, based on recommended allowable stresses.

11 What Is Runout, And Why Should I Worry About It (January/February 1991)

Runout is a troublemaker! Good shop practice for the manufacture or inspection of gears requires the control of runout. Runout is a characteristic of gear quality that results in an effective center distance variation. As long as the runout doesn't cause loss of backlash, it won't hurt the function of the gear, which is to transmit smooth motion under load from one shaft to another. However, runout does result in accumulated pitch variation, and this causes non-uniform motion, which does affect the function of the gears. Runout is a radial phenomenon, while accumulated pitch variation is a tangential characteristic that causes transmission error. Gears function tangentially. It is also possible to have a gear with accumulated pitch variation, but little or no runout.

12 Flank Breakage on Gears for Energy Systems (November/December 2011)

Gear flank breakage can be observed on edge zone-hardened gears. It occurs, for example, on bevel gears for water turbines, on spur gears for wind energy converters and on single- and double-helical gears for other industrial applications.

13 New Approaches in Roll Testing Technology of Spiral Bevel and Hypoid Gear Sets (May/June 2005)

This paper presents a new approach in roll testing technology of spiral bevel and hypoid gear sets on a CNC roll tester applying analytical tools, such as vibration noise and single-flank testing technology.

14 In-Situ Measurement of Stresses in Carburized Gears via Neutron Diffraction (May 2009)

This paper presents the results of research directed at measuring the total stress in a pair of statically loaded and carburized spur gears. Measurements were made to examine the change in total stress as a function of externally applied load and depth below the surface.

15 Grinding Induced Changes in Residual Stresses of Carburized Gears (March/April 2009)

This paper presents the results of a study performed to measure the change in residual stress that results from the finish grinding of carburized gears. Residual stresses were measured in five gears using the x-ray diffraction equipment in the Large Specimen Residual Stress Facility at Oak Ridge National Laboratory.

16 Single Flank Data Analysis and Interpretation (September/October 1985)

Much of the information in this article has been extracted from an AGMA Technical Paper, "What Single Flank Testing Can Do For You", presented in 1984 by the author

17 Bending Fatigue Tests of Helicopter Case Carburized Gears: Influence on Material, Design and Manufacturing Parameters (November/December 2009)

A single tooth bending (STB) test procedure has been developed to optimally map gear design parameters. Also, a test program on case-carburized, aerospace standard gears has been conceived and performed in order to appreciate the influence of various technological parameters on fatigue resistance and to draw the curve shape up to the gigacycle region.

18 NASA's Return to Flight (May 2007)

Gear specialists at the NASA Glenn Research facility helped determine it was safe for the space shuttle to fly again.

19 The Uses and Limitations of Transmission Error (July/August 1988)

The concept of "transmission error" is relatively new and stems from research work in the late 1950s by Gregory, Harris and Munro,(1) together with the need to check the accuracy of gear cutting machines. The corresponding commercial "single flank" testing equipment became available in the 1960s, but it was not until about ten years ago that it became generally used, and only recently has it been possible to test reliably at full load and full speed.

20 Full-Load Testing of Large Gearboxes Using Closed-Loop Power Circulation (September/October 1991)

This method of testing large gearboxes or, indeed, any power transmission element, had numerous advantages and offers the possibility of large savings in time, energy, and plant, if the overall situation is conducive to its use. This usually requires that several such units need to be tested, and that they can be conveniently connected to each to each other in such a way as to form a closed-loop drive train. No power sink is required, and the drive input system has only to make up power losses. The level of circulating power is controlled by the torque, which is applied statically during rotation, and the drive speed. Principles, advantage, and limitations are described, together with recent experiences in the only known large-scale usage of this technique in Australia.

21 Pardon the Disruption (January/February 2018)

Emerging technologies such as robotics/automation, new materials, additive manufacturing and IIoT can and will change the course of gear manufacturing for the foreseeable future.

22 Practical Considerations for the Use of Double-Flank Testing for the Manufacturing Control of Gearing - Part I (January/February 2014)

Part I of this paper describes the theory behind double-flank composite inspection, detailing the apparatus used, the various measurements that can be achieved using it, the calculations involved and their interpretation. Part II, which will appear in the next issue, includes a discussion of the practical application of double-flank composite inspection, especially for large-volume operations. Part II covers statistical techniques that can be used in conjunction with double-flank composite inspection, as well as an in-depth analysis of gage R&R for this technique.

23 The Growth of Australian Regenerative Load Testing (January/February 2019)

Historically, gearbox original equipment manufacturers (OEMs) and repair organizations have tended to offer their customers no-load, full speed (spin) tests as a standard performance test. If a load test was specified, the supplier would probably offer a locked torque back-to-back simulated load test, which requires a large investment in tooling to connect shafts of the test and slave gearboxes.

24 In-Process, Complete Gear Inspection at Light Speeds (July 2018)

New GRSL technology adds value to high-volume transmission gear inspection by combining non-contact laser inspection with tried-and-true composite roll testing.

25 Globalization's Effect Upon Gear Steel Quality (January/February 2018)

Background on the development of a high-speed, automatic hardness tester for gear steels.

26 Measuring Residual Stress in Gears (March/April 2015)

I have heard that X-ray diffraction does not tell the whole story and that I should really run a fatigue test. I understand this may be the best way, but is there another method that gives a high degree of confidence in the residual stress measurement?

27 Setting Load Parameters for Viable Fatigue Testing of Gears in Powertrain Axles Part I: Single-Reduction Axles (August 2014)

This presentation introduces a new procedure that - derived from exact calculations - aids in determining the parameters of the validation testing of spiral bevel and hypoid gears in single-reduction axles.

28 Practical Considerations for the Use of Double-Flank Testing for the Manufacturing Control of Gearing - Part II (March/April 2014)

Part I of this paper, which appeared in the January/February issue of Gear Technology, described the theory behind double-flank composite inspection. It detailed the apparatus used, the various measurements that can be achieved using it, the calculations involved and their interpretation. The concluding Part II presents a discussion of the practical application of double-flank composite inspection -- especially for large-volume operations. It also addresses statistical techniques that can be used in conjunction with double-flank composite inspection, as well as an in-depth analysis of gage R&R for this technique.

29 Hardness Testing (May 2013)

This back-to-basics article describes the main methods used for hardness testing of gears: Rockwell, Brinell, Vickers and Knoop.

30 SPC Acceptance of Hobbing & Shaping Machines (September/October 1991)

Today, as part of filling a typical gear hobbing or shaping machine order, engineers are required to perform an SPC acceptance test. This SPC test, while it is contractually necessary for machine acceptance, is not a machine acceptance test. It is a process capability test. It is an acceptance of the machine, cutting tool, workholding fixture, and workpiece as integrated on the cutting machine, using a gear measuring machine, with its work arbor and evaluation software, to measure the acceptance elements of the workpiece.

31 Do No Destructive Testing (January/February 2013)

An overview of nondestructive testing and its importance in the manufacture of big gears.

32 Gear Damage Detection Using Oil Debris Analysis (January/February 2003)

The purpose of this paper was to verify, when using an oil debris sensor, that accumulated mass predicts gear pitting damage and to identify a method to set threshold limits for damaged gears.

33 Gear Surface Durability Development to Enhance Transmission Power Density (July/August 2002)

Gear pitting is one of the primary failure modes of automotive transmission gear sets. Over the past years, many alternatives have been intended to improve their gear surface durability. However, due to the nature of new process development, it takes a length of time and joint efforts between the development team and suppliers to investigate and verify each new approach.

34 Gear Oil Micropitting Evaluation (September/October 2000)

During the last decade, industrial gear manufacturers, particularly in Europe, began to require documentation of micropitting performance before approving a gear oil for use in their equipment. The development of micropitting resistant lubricants has been limited both by a lack of understanding of the mechanism by which certain lubricant chemistry promotes micropitting and by a lack of readily available testing for evaluation of the micropitting resistance of lubricants. This paper reports results of two types of testing: (1) the use of a roller disk machine to conduct small scale laboratory studies of the effects of individual additives and combinations of additives on micropitting and (2) a helical gear test used to study micropitting performance of formulated gear oils.

35 Eddy Current Examination of Gear Systems (May/June 1997)

Nondestructive examination (NDE) of ferrous and nonferrous materials has long proved an effective maintenance and anomaly characterization tool for many industries. Recent research has expanded its applicability to include the inspection of large, open gear drives. Difficulties inherent in other NDE methods make them time-consuming and labor-intensive. They also present the user with the environmental problem of the disposal of used oil. The eddy current method addresses these problems.

36 Minimizing Backlash in Spur Gears (May/June 1994)

simplified equations for backlash and roll test center distance are derived. Unknown errors in measured tooth thickness are investigate. Master gear design is outlined, and an alternative to the master gear method is described. Defects in the test radius method are enumerated. Procedures for calculating backlash and for preventing significant errors in measurement are presented.

37 Single Flank Measuring; Estimating Horsepower Capacity (September/October 1991)

Question: What is functional measurement and what is the best method for getting truthful answers?

38 State of the Gear Industry Special Edition (January/February 2019)

Gear industry experts give their opinions about the most important trends facing gear manufacturers today.

39 Material Assets (November/December 2017)

You get one shot to make a first impression. One opportunity to show your customers, vendors and suppliers that you provide a steady, reliable product that will generate repeat business. How do you make this happen? What tools and strategies are available to get gear materials (forgings, gear blanks, etc.) shipped faster and more efficiently in today's tech-heavy, fast-paced, manufacturing environment?

40 Influence of the Defect Size on the Tooth Root Load Carrying Capacity (November/December 2017)

The objective of this work is to introduce a method for the calculation of the tooth root load carrying capacity for gears, under consideration of the influence of the defect size on the endurance fatigue strength of the tooth root. The theoretical basis of this method is presented in this paper as well as the validation in running tests of helical and beveloid gears with different material batches, regarding the size distribution of inclusions. The torque level for a 50 percent failure probability of the gears is evaluated on the test rig and then compared to the results of the simulation. The simulative method allows for a performance of the staircase method that is usually performed physically in the back-to-back tests for endurance strength, as the statistical influence of the material properties is considered in the calculation model. The comparison between simulation and tests shows a high level of accordance.

41 Gear Material Risks and Rewards (August 2011)

Technology investments lead to product innovation at gear materials suppliers.

42 Gear Material Quality: How To Judge It...Pitting: How To Prevent It (March/April 1993)

How do we know when the gear material we buy is metallurgically correct? How can we judge material quality when all gear material looks alike?

43 Production Testing of a Chromium-Free Carburizing Grade Gear Steel (May/June 1989)

For many years chromium has been a popular alloy for heat treatable steels because of its contribution to hardenability more than offsets its costs. As a consequence, it is specified in such high-tonnage steel grades as the 5100, 4100, and 8600 series; and, as a result, about 15% of the annual U.S. consumption of chromium is used in constructional alloy steels.

44 Factors Influencing Fracture Toughness of High-Carbon Martensitic Steels (January/February 1989)

Plane strain fracture toughness of twelve high-carbon steels has been evaluated to study the influence of alloying elements, carbon content and retained austenite. The steels were especially designed to simulate the carburized case microstructure of commonly used automotive type gear steels. Results show that a small variation in carbon can influence the K IC significantly. The beneficial effect of retained austenite depends both on its amount and distribution. The alloy effect, particularly nickel, becomes significant only after the alloy content exceeds a minimum amount. Small amounts of boron also appear beneficial.

45 Selection of Material and Compatible Heat Treatments for Gearing (May/June 1986)

The manufacturing process to produce a gear essentially consist of: material selection, blank preshaping, tooth shaping, heat treatment, and final shaping. Only by carefully integrating of the various operations into a complete manufacturing system can an optimum gear be obtained. The final application of the gear will determine what strength characteristics will be required which subsequently determine the material and heat treatments.

46 Austempered Ductile Iron: Technology Base Required for an Emerging Technology (October/November 1984)

This paper addresses Austempered Ductile Iron (ADI) as an emerging Itechnology and defines its challenge by describing the state-of-the-art of incumbent materials. The writing is more philosophical in nature than technical and is presented to establish a perspective.

47 LMT Fette Introduces SpeedCore (October 2011)

New material technology allows for more efficient and flexible hobbing.

48 Design, Development and Application of New, High-Performance Gear Steels (January/February 2010)

QuesTek Innovations LLC is applying its Materials by Design computational design technology to develop a new class of high-strength, secondary hardening gear steels that are optimized for high-temperature, low-pressure (i.e., vacuum) carburization. The new alloys offer three different levels of case hardness (with the ability to “dial-in” hardness profiles, including exceptionally high case hardness), and their high core strength, toughness and other properties offer the potential to reduce drivetrain weight or increase power density relative to incumbent alloys such as AISI 9310 or Pyrowear Alloy 53.

49 Mechanical Behavior and Microstructure of Ausrolled Surfaces in Gear Steels (March/April 1995)

Ausforming, the plastic deformation of heat treatment steels in their metastable, austentic condition, was shown several decades ago to lead to quenched and tempered steels that were harder, tougher and more durable under fatigue-type loading than conventionally heat-treated steels. To circumvent the large forces required to ausform entire components such as gears, cams and bearings, the ausforming process imparts added mechanical strength and durability only to those contact surfaces that are critically loaded. The ausrolling process, as utilized for finishing the loaded surfaces of machine elements, imparts high quality surface texture and geometry control. The near-net-shape geometry and surface topography of the machine elements must be controlled to be compatible with the network dimensional finish and the rolling die design requirements (Ref. 1).

50 Material Integrity in Molded Plastic Gears and its Dependence on Molding Practices (June 2008)

The quality of molded plastic gears is typically judged by dimensional feature measurements only. This practice overlooks potential deficiencies in the molding process.

51 Corus New Gear Steels Reduce Alloys Without Sacrificing Achievable Hardness (September/October 2005)

Corus Engineering Steels' formula for its new gear steels: Maintain achievable hardness while using fewer alloys, thereby cutting steel costs for gear manufacturers.

52 Gear Design: Multipoint Properties are Key to Selecting Thermoplastic Materials (November/December 2006)

The palette of thermoplastic materials for gears has grown rapidly, as have the applications themselves. Designers need to be aware of key properties and attributes in selecting the right material.

53 Tolerance for Overload Stress (March/April 1985)

The performance of carburized components can be improved simply by changing the alloy content of the steel.

54 Austempered Nodular Cast Irons (March/April 1985)

Austempering heat treatments (austenitizing followed by rapid cooling to the tempering temperature) have been applied to nodular irons on an experimental basis for a number of years, but commercial interest in the process has only recently come to the surface.

55 Gear Heat Treatment: The Influence of Materials and Geometry (March/April 2004)

Gear designs are evolving at an ever accelerating rate, and gear manufacturers need to better understand how the choice of materials and heat treating methods can optimize mechanical properties, balance overall cost and extend service life.

56 ADI - A Designer Gear Material (March/April 1995)

If someone were to tell you that he had a gear material that was stronger per pound than aluminum, as wear-resistant as steel, easier to machine than free-machining steel and capable of producing gears domestically for 20% less than those now cut from foreign made forgings, would you consider that material to be "high tech"? Probably. Well, throw out all the pre-conceived notions that you may have had about "high tech" materials. The high-performance material they didn't teach you about in school is austempered ductile iron (ADI).

57 Comparison of Surface Durability & Dynamic Performance of Powder Metal & Steel Gears (September/October 1995)

Surface-hardened, sintered powder metal gears are increasingly used in power transmissions to reduce the cost of gear production. One important problem is how to design with surface durability, given the porous nature of sintered gears. Many articles have been written about mechanical characteristics, such as tensile and bending strength, of sintered materials, and it is well-known that the pores existing on and below their surfaces affect their characteristics (Refs. 1-3). Power transmission gears are frequently employed under conditions of high speed and high load, and tooth surfaces are in contact with each other under a sliding-rolling contact condition. Therefore it is necessary to consider not only their mechanical, but also their tribological characteristics when designing sintered gears for surface durability.

58 High Speed Steel: Different Grades for Different Requirements (September/October 2004)

Hobs, broaches, shaper cutters, shaver cutters, milling cutters, and bevel cutters used in the manufacture of gears are commonly made of high speed steel. These specialized gear cutting tools often require properties, such as toughness or manufacturability, that are difficult to achieve with carbide, despite the developments in carbide cutting tools for end mills, milling cutters, and tool inserts.

59 Deciding When to Go Plastic (July 2014)

Can my metal gear(s) be replaced with plastic gears?

60 Performance and Machining of Advanced Engineering Steels in Power Transmission Applications - Continued Developments (May 2017)

It is becoming increasingly apparent that material properties can and will play a greater role than before in addressing the challenges most transmission manufacturers are facing today. Making use of materials' intrinsic fatigue properties provides a new design tool to support the market changes taking place.

61 Inclusion-Based Bending Strength Calculation of Gears (May 2017)

Reduced component weight and ever-increasing power density require a gear design on the border area of material capacity. In order to exploit the potential offered by modern construction materials, calculation methods for component strength must rely on a deeper understanding of fracture and material mechanics in contrast to empirical-analytical approaches.

62 Upgrading Your Toolbox (May 2017)

Manufacturers focus on tool design, materials, coating, machine tool options and cutting parameters.

63 Innovative Steel Design and Gear Machining of Advanced Engineering Steel (August 2016)

The increasing demands in the automotive industry for weight reduction, fuel efficiency and a reduced carbon footprint need to be addressed urgently. Up until now, widely used conventional steels have lived up to expectations. However, with more stringent emissions standards, demands on materials are increasing. Materials are expected to perform better, resulting in a need for increased fatigue strength. A possibility to increase torque on current generations without design changes can be achieved by selecting suitable materials.

64 Improved Broaching Steel Technology (July 2016)

Broaching is a machining technique commonly used to cut gear teeth or cam profiles for the high volume manufacture of power transmission parts used in vehicles (Refs. 1–2). This article shows how the right gear blank material can make all the difference if you want to get more parts out of each tool.

65 Loaded Behavior of Gears Made of Fiber-Reinforced PA6 (July 2014)

This paper presents an original method for computing the loaded mechanical behavior of fiber reinforced polymer gears. Although thermoplastic gears are unsuitable for application transmitting high torque, adding fibers can significantly increase their performance. The particular case of polyamide 6 + 30% glass fibers is studied in this paper.

66 The XL Gears Project (January/February 2014)

Much of the existing guidelines for making large, high-performance gears for wind turbine gearboxes exhibit a need for improvement. Consider: the large grinding stock used to compensate for heat treatment distortion can significantly reduce manufacturing productivity; and, materials and manufacturing processes are two other promising avenues to improvement. The work presented here investigates quenchable alloy steels that, combined with specifically developed Case-hardening and heat treatment processes, exhibits reduced distortion and, in turn, requires a smaller grinding stock.

67 Plastic Gear Design Basics (July/August 1996)

Plastic gears are serious alternatives to traditional metal gears in a wide variety of applications. The use of plastic gears has expanded from low-power, precision motion transmission into more demanding power transmission applications. As designers push the limits of acceptable plastic gear applications, more is learned about the behavior of plastics in gearing and how to take advantage of their unique characteristics.

68 High Temperature Gear Materials (November/December 2013)

What gear material is suitable for high-temperature (350 – 550 degree C), high-vacuum, clean-environment use?

69 Minimization of In-Process Corrosion of Aerospace Gears (July/August 2002)

Carbon steels have primarily been used to manufacture aerospace gears due to the steels' mechanical characteristics. An alloyed low carbon steel is easily case-hardened to obtain a hard wear surface while maintaining the ductile core characteristics. The microstructure achieved will accept the heavy loading, shocks, and elevated temperatures that gears typically experience in applications. The carbon steel machinability allows for general machining practices to be employed when producing aerospace gears versus the more advanced metal removal processes required by stainless and nickel-based alloys.

70 Increased Load Capacity of Worm Gears by Optimizing the Worm Wheel Bronze (May/June 2002)

The lifetime of worm gears is usually delimited by the bronze-cast worm wheels. The following presents some optimized cast bronzes, which lead to a doubling of wear resistance.

71 The Effect of Material Defects on Gear Perfomance - A Case Study (March/April 2000)

The quality of the material used for highly loaded critical gears is of primary importance in the achievement of their full potential. Unfortunately, the role which material defects play is not clearly understood by many gear designers. The mechanism by which failures occur due to material defects is often circuitous and not readily apparent. In general, however, failures associated with material defects show characteristics that point to the source of the underlying problem, the mechanism by which the failure initiated, and the manner in which it progressed to failure of the component.

72 Cast Iron: A Solid choice for Reducing Gear Noise (September/October 1999)

Material selection can play an important role in the constant battle to reduce gear noise. Specifying tighter dimensional tolerances or redesigning the gear are the most common approaches design engineers take to minimize noise, but either approach can add cost to the finished part and strain the relationship between the machine shop and the end user. A third, but often overlooked, alternative is to use a material that has high noise damping capabilities. One such material is cast iron.

73 Powder Metallurgy Innovations (September/October 1999)

Powder metal. To gear makers today, the phrase conjures images of low power applications in non-critical systems. As powder metal technology advances, as the materials increase in density and strength, such opinions are changing. It is an ongoing, evolutionary process and one that will continue for some time. According to Donald G. White, the executive director of the Metal Powder Industries Federation, in his State-of-the-P/M Industry - 1999 report. "The P/M world is changing rapidly and P/M needs to be recognized as a world-class process - national, continental and even human barriers and prejudices must be eliminated - we must join forces as a world process - unified in approach and goals."

74 Metallurgical Aspects to be Considered in Gear and Shaft Design (March/April 1999)

In his Handbook of Gear Design (Ref.1), Dudley states (or understates): "The best gear people around the world are now coming to realize that metallurgical quality is just as important as geometric quality." Geometric accuracy without metallurgical integrity in any highly stressed gear or shaft would only result in wasted effort for all concerned - the gear designer, the manufacturer, and the customer - as the component's life cycle would be prematurely cut short. A carburized automotive gear or shaft with the wrong surface hardness, case depth or core hardness may not even complete its basic warranty period before failing totally at considerable expense and loss of prestige for the producer and the customer. The unexpected early failure of a large industrial gear or shaft in a coal mine or mill could result in lost production and income while the machine is down since replacement components may not be readily available. Fortunately, this scenario is not common. Most reputable gear and shaft manufacturers around the world would never neglect the metallurgical quality of their products.

75 Vickers vs. Knoop Hardness Testers for Measuring Case Depth in Carburized Parts (January/February 2020)

What are the pros and cons of using Vickers versus Knoop hardness testers for measuring case depth in carburized gears?