Technology and Invention is a series by Rogers Corporation about the innovation, pioneering spirit, and transformative technologies that are creating a cleaner, safer, more connected world. Part 1: Historical Milestones, Part 2: The Plastics Revolution.
The Birth of Electronics
The word “electron” was first proposed by Johnstone Stoney in 1891 when he realized that an electric charge had a natural unit which could not be subdivided any further. Shortly thereafter, a series of experiments by J.J. Thomson led to the discovery of a light particle that carried a charge; the name “electron” was applied to it. The many applications of electrons moving in a near-vacuum or inside semiconductors were later dubbed “electronics.”
The electron itself has turned out to be a bit different than what J.J. Thomson originally described. Albert Einstein and others showed that electrons aren’t either particles or waves, but in some conditions act like particles and in others like waves. In fact, J.J. Thomson’s grandson, G.P. Thomson, received a Nobel Prize for his work on the wave character of electrons. We now know that electrons are part of a whole family of related particles — all of them infinitesimal points carrying charge, mass, and spin.
Printed Circuit Boards
PCBs are a combination of mechanical and electrical connections etched from copper sheets and laminated onto a non-conductive substrate. The first printed circuit boards (PCBs) can be traced back to the need to eliminate complex wiring and provided consistent results. In 1903, a German inventor, Albert Hanson, described flat foil conductors laminated to an insulating board, in multiple layers. In 1904, Thomas Edison experimented with chemical methods of plating conductors onto linen paper. In 1925, Charles Ducas submitted a patent that involved creating an electrical path directly on an insulated surface.
The commercial development of PCBs began in the 1940’s, post-WWII. After years of discussions with lithograph companies, Dr. Paul Eisler began making the first real operational printed circuit boards in Austria. Eisler found no demand for his product until the Americans started work on the proximity fuse to bring down V1 rockets; printed circuits were a critical component. Following the end of the war, the USA released the secret of printed circuits, then all electronics in airborne instruments were printed.
In 1966, Rogers purchased technology from Westinghouse Electric Corporation that, although never used commercially, led to the development of flexible circuits for computers, telecommunications, and other electronics applications.
Also in 1966, Rogers established its first plant outside of Connecticut, in Chandler, Arizona, closer to where the electronics industry was growing rapidly. The new Circuit Systems Division began operations in a 40,000 square foot plant manufacturing flexible circuits, busbars, and the Mini/Bus, designed to distribute voltage to integrated circuits on printed circuit boards. The Microwave Materials Division spun off from the Circuit Systems Division and is now known as Advanced Connectivity Solutions.
Today, as circuit speeds continue to escalate and wireless communications proliferate, the need for high frequency circuit boards becomes paramount. Rogers’ high performance dielectrics, laminates and prepregs offer high frequency performance and low cost circuit fabrication for a wide range of electronic products, from adaptive cruise control to airborne antenna systems to network gear.
The Critical Role of Power Electronics
Power electronics technology converts and controls electrical power using high-efficiency switching mode electronic devices. The technology is embedded in AC and DC power supplies, electrochemical processes, heating and lighting control, electronic welding, photovoltaic and fuel cell power conversion, and motor drives. Power electronics play a central role in industrial automation, high-efficiency energy systems, energy conservation, renewable energy systems, and electric and hybrid vehicles.
Early power electronics technologies included mercury-arc rectifiers for converting AC to DC power, hot-cathode ray tube rectifiers first invented by GE, and virtually indestructible magnetic amplifiers. The modern era of solid-state electronics launched in 1948 with the invention of the transistor at Bell Labs. From the Computer History Museum:
Using improved semiconductor materials developed for radar detectors during the war, in early 1945 [William] Shockley experimented with a field-effect amplifier, similar in concept to those patented by Heil and Lilienfeld, but it failed to work as he intended. Physicist John Bardeen suggested that electrons on the semiconductor surface might be blocking penetration of electric fields into the material. Under Shockley’s direction, together with physicist Walter Brattain, Bardeen began researching the behavior of these “surface states.” On December 16, 1947, their research culminated in a successful semiconductor amplifier. Bardeen and Brattain applied two closely-spaced gold contacts held in place by a plastic wedge to the surface of a small slab of high-purity germanium. On December 23 they demonstrated their device to lab officials and in June 1948, Bell Labs publicly announced the revolutionary solid-state device they called a “transistor.”
Today, power MOSFETs, which first appeared on the market in the 1970s, have become popular for low-voltage, high frequency applications. The insulated-gate bipolar transistor (IGBT or IGT), invented in 1983, is the most popular semiconductor device for medium-to-high power applications.
Improving Transmission Efficiency with Busbars
Rogers developed the busbar product line – strips or bars of copper, brass, or aluminum that collect and distribute electricity within electrical devices –in 1959 as an engineering solution to the problem of power distribution in the first transistorized computer, the IBM 1401. These busbars quickly captured a main share of the growing computer market.
By the mid-1960s, virtually all manufacturers of mainframe computers were Rogers’ customers. This was the company’s first significant step toward vertical integration from materials into components, using Rogers’ materials as the base. This was to become one of the key aspects of growth in the next twenty years.
ROLINX PowerCircuit busbars help attain higher power efficiencies by limiting switching losses. They serve as power distribution “highways” that connect power sources with capacitors, IGBTs, or complete modules. These busbars combine the traits of traditional laminated busbars with the processing capabilities of PCB assemblies. The result is a high-performance busbar that supports 3D design, helps achieve optimum thermal management, and is well suited for medium-to-high-volume assembly processes.
Power Substrates for High Heat Conductivity
In 2011, Rogers acquired curamik Electronics GmbH, a manufacturer of power electronic substrate products headquartered in Eschenbach, Germany. Founded in 1983, curamik develops and produces direct copper bonded (DCB) ceramic substrate products used in the design of intelligent power management devices, such as IGBT modules.
These ceramic substrates are found in a growing array of clean technologies that are powering the world. The basis of the substrate is a ceramic isolator to which pure copper is applied. The result is ceramic substrates with high heat conductivity and great heat capacity, and heat spreading provided by the thick copper layer.
curamik’s DBC (Direct Bond Copper) substrates are manufactured by bonding copper foils directly to electrically insulating industrial ceramics. curamik also uses AMB technology (Active Metal Brazing), another form of joining metal to ceramic. The result is customized ceramic substrates for highly efficient thermal management, providing high-performance electrical power management.
Rogers Corporation provides innovative solutions for power electronics, advanced foams for cushioning and protective sealing, and high-frequency printed circuit materials. For over 180 years, we have empowered breakthroughs in reliability, efficiency, and performance, to help our customers build a cleaner, safer, and more connected world.
By John Coonrod, Technical Marketing Manager, Rogers Corp., Advanced Connectivity Solutions. As seen in The PCB Design Magazine (Dec 2015)
A variety of different test methods may be used for any one electrical concern. This article will discuss the issues related to determining the dielectric constant (Dk) and dissipation factor (Df or Tan-Delta). On a data sheet, a designer may see a Dk value for a material to be 3.5, as an example. Once the designer buys the material and performs necessary evaluations, it may be found that the Dk of the material is 3.8. In some applications this difference in Dk is probably not meaningful; however, for many RF and high-speed digital applications, this difference could be very significant. What is really interesting about this example is that the two Dk values may both be correct, depending on the test methods used.
Most laminates used in the PCB industry are anisotropic and this means that the electrical properties are not the same on all three axes of the material. Typically the thickness (z-axis) of the material will have a different Dk value than the x or y axes of the material. The reasons for this depend on what type of material is being considered.
The laminates used in the PCB industry are typically woven-glass reinforced, however there are notable exceptions. The glass reinforcement layer typically has a different Dk and Df than does the raw substrate of the laminate. The standard E-glass most often used in PCB laminates has a typical Dk value of about 6 and a dissipation factor of around 0.004. The common FR-4 laminates use relatively simple resin systems and the resin itself has a Dk that is around 3 and a Df of about 0.03. Different ratios of resin to glass will cause the laminate to have a Dk that is somewhere between the value of the resin and that of the glass. However, the glass-resin ratio impact on Dk is usually considered when evaluating the material through the thickness axis and if the x- or y-axis is evaluated, the Dk value may be very different than the z-axis result.
A large number of test methods are available to evaluate materials for Dk and Df. The methods that are most often used in the PCB laminate industry for making these measurements are typically tailored to evaluating materials in very large volume. Because of this issue, these test methods need to determine Dk and Df relatively fast, have good repeatability, and be used for quality control. A common test method used is the clamped stripline resonator, where a clamping fixture is used to form a stripline structure; the layer structure of a stripline is ground-signal-ground. This test method determines the Dk and Df of the material in the clamped fixture and more specifically, it is reporting these values related to the thickness axis of the material.
Other tests used in high-volume testing include SPDR (split-post dielectric resonator), rectangular cavity and open cavity resonance methods. All three of these methods have electric fields oriented perpendicular to the material, which means these test methods will evaluate the x-y plane of the material and not the z-axis. In the case of the common FR-4 material which is a resin-glass composite, the Dk number can be very different in the x-y plane than in the z-axis due to the impact of the glass.
Returning to the original example, where a material is tested and found to have a Dk of 3.5 and then another test is done on the same material and the Dk is found to be 3.8, both of these numbers can be correct when using two different test methods. These numbers are actually based on real life experience when testing high frequency laminates that are PTFE based with ceramic filler and have woven-glass reinforcement. With this type of material it is possible to have the same piece of material tested in the clamped stripline test and get a value of 3.5 and then tested in SPDR and obtain a result of 3.8. Since the clamped stripline test is evaluating the z-axis of the material and the SPDR is evaluating the x-y plane of the material, both results are obviously different but still correct. Essentially, these measurements show to some degree how anisotropic the material is, where the z-axis Dk of the material is 3.5 and the x-y plane Dk of the material is 3.8.
Knowing the anisotropic Dk values of a laminate is typically critical for RF applications with edge-coupled features. In the case of high-speed digital circuits, these values can be important for differential pair structures. Having these values can be important, but also having a modeling software which can incorporate these values into predicted circuit performance is an important supplement to the design process.
It is always recommended to contact your material supplier if you have questions about the Dk or Df of a laminate. You should ask which test method is used and which axis or axes of the material is being evaluated. Another good question to ask your material supplier is the frequency at which these values are generated, because the Dk and Df of a material is frequency dependent. Having the most accurate laminate information for the design phase of a project is critical to its success.
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Microwave circuit dimensions are related to their wavelengths / frequencies and to the dielectric constant (Dk) of their substrates. Quite simply, higher-frequency signals have smaller wavelengths and their electromagnetic (EM) energy of those smaller wavelengths will propagate through circuits with smaller dimensions. Phase velocity is related to wavelength, with slower EM waves having shorter wavelengths which propagate through circuit structures with smaller dimensions than faster waves with their longer wavelengths.
For a given frequency / wavelength, the circuit dimensions can also be reduced in size by fabricating the circuits on laminates with high dielectric constants, such as RO3010™ and RT/duroid® 6010.2LM circuit materials from Rogers Corp. The high Dk values of these circuit materials results in shorter wavelengths and smaller circuit dimensions, but also slows the propagation of the EM waves along the conductors of a printed circuit board (PCB).
Transmission-line conductors on PCBs for RF/microwave circuitry take on various forms, such as microstrip, stripline, coplanar waveguide (CPW), and even substrate-integrated-waveguide (SIW) transmission lines for circuits at millimeter-wave frequencies. For a conventional microstrip transmission line with solid conductors, for example, the phase velocity has relatively high speed. It is related to the current density, with most of the current running along the edges of the solid microstrip conductors in a circuit. If the solid conductors are modified into a conductor pattern that is not solid, such as a ladder pattern, the phase velocity will be slowed and the wavelength will be reduced.
The phase velocity is a function of the separation distance between the storage locations in a conductor for the EM energy’s electric and magnetic field components, resulting from capacitive loading (and storage capabilities) within a transmission line’s conductors. When the magnetic and electric energy storage locations are in close proximity, the phase velocity is higher or faster than when the magnetic and electric energy storage locations within the conductor are further apart. For the slower phase velocity, the wavelength of the transmission-line’s conductors is shorter than for the conductors with the faster phase velocity. Slowing the phase velocity of a microstrip transmission-line’s conductors is a way to miniaturize circuits fabricated on PCB materials with a given Dk value.
By modifying conventional microstrip conductors into unconventional patterns, such as a ladder configuration, distances between stored magnetic and electrical energy field components are increased beyond the separation distances for standard solid microstrip conductors. A microstrip ladder pattern effectively conducts EM energy, but with slower phase velocity than a solid microstrip transmission-line conductor because of its greater distance between magnetic and electric energy storage locations. Just how much slower the phase velocity is than a standard solid microstrip conductor will depend upon the geometry of the microstrip ladder pattern.
Such slow wave structures reduce the group velocity of a transmission line, effectively increasing its group delay compared to a conventional solid microstrip transmission line, and reducing its wavelength compared to the wavelength of a conventional microstrip transmission line. As an example, consider a half-wavelength gap-coupled resonator constructed from microstrip transmission lines. When fabricated with a standard solid conductor pattern on 20-mil-thick RO4835™ laminate from Rogers Corp., with typical Dk of 3.48 at 10 GHz in the z-direction of the material, the circuit structure will resonate at 4 GHz. When using the appropriate microstrip ladder conductor pattern on the same material, the resonant frequency of the gap-coupled resonator circuit can be reduced by 25%, to 3 GHz.
Coupled resonators are often used to realize various high-frequency filter functions, so this gap-coupled-resonator example with its microstrip ladder pattern of conductors can be applied to these types of filters to achieve a reduction in the size of the filter circuitry for a given design frequency. An even greater reduction in filter size can be gained by combining the ladder conductor pattern approach with high-Dk PCB material, such as RO3010 ceramic-filled polytetrafluoroethylene (PTFE) laminate with a Dk of 10.2 measured in the z-direction of the material at 10 GHz and RT/duroid 6010LM ceramic-PTFE composite material with Dk of 10.2 in the z-direction at 10 GHz.
What is the impact on circuit size when using one of these high-Dk PCB materials? If a circuit material such as RO3003™ laminate with a Dk of 3.0 in the z-direction at 10 GHz is used as a starting point for a filter circuit with microstrip edge-coupled structure, including edge-coupled resonators, and the same filter is designed on a PCB material with much higher Dk, such as RT/duroid 6010LM laminate with its Dk of 10.2, a healthy reduction in size is possible. The size of the same microstrip edge-coupled filter function will be about 30% smaller on the higher-Dk material.
By combining slow-wave circuit patterns such as the microstrip ladder pattern with high-Dk circuit laminates such as the 10.2 Dk RO3010 or RT/duroid 6010LM PCB materials, the circuit-shrinking effects of both approaches can be applied to an RF/microwave circuit design for a significant reduction in circuit size. Both of these low-loss circuit materials feature tightly controlled Dk values for excellent high-frequency performance and reduced circuit sizes.
Ladders are just one type of microstrip conductor pattern that can be used to create slow-wave structures, with many different patterns capable of achieving slow-wave propagation and contributing to a reduction of circuit size for a given design frequency and circuit laminate Dk value. The key to success for forming any slow-wave pattern (and shrinking the dimensions of a high-frequency circuit) lies in separating the electric and magnetic energy storage within the structure, thereby slowing the phase velocity and reducing the wavelength of the transmission line for a given circuit material and Dk value.
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Download the ROG Mobile appto access Rogers’ calculators, including the popular Microwave Impedance simulation tool, literature, technical papers, and the ability to order samples of the company’s high performance printed circuit board materials.
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Product Life Cycle Cost Analysis, Cost of Ownership, LCA (Life Cost Analysis), Whole Life Cost, and “Cradle to Grave” Costing – what do these names and acronyms have in common? The answer is they all are used to define the calculation method that evaluates the cost of a product throughout its time in service.
This is certainly nothing new to the mass transportation industry. In fact, many governments and municipalities require an LCA as part of a tender offering; and some transit authorities have expanded the criteria to include end-of-life costing and the triple bottom line (financial, ecological, social performance) of the cost impact upon environmental sustainability. Surprisingly, LCA is oftentimes misunderstood or only partially considered in tender awards.
In defense of the transit authorities (and from their perspective), many vendors enhance or misrepresent their respective products’ life performance claims and either omit substantiated time-simulated data or exaggerate future savings. Typical cost models have the tendency to be over-simplified and lack the flexibility needed to accommodate specific and customized variables not shared among transit authorities. Lastly, there are hidden, intangible and questionable costs that may be difficult or impossible to estimate.
Seating Life Cycle Analysis
While life cost analysis can be assessed for any rail car or vehicle component, seat cushion tenders offer the best opportunity to scrutinize the validity of an LCA model. Within the interior, seating is one of the five most costly elements of the rail car and is at the top of the list for future refurbishments. Assessing new build costs with forecast refurbishment estimates is seemingly straightforward. As a start, a Whole Cost Analysis would include the following factors:
- The cost of seating for the initial new-build delivery,
- Assumptions of how far into the future the transit authority will keep the seats in service before a full or partial refurbishment,
- Estimated costs of the refurbishment, and
- Historical costs for replacements between refurbishments.
Other considerations may include the cost of labor and lost revenue while the seat or rail car is in refurbishment or out of service. Ridership dissatisfaction due to seating discomfort or style could also be identified as an intangible cost. But, regardless of the depth of such an analysis, this list is relatively common and generally used in the decision matrix. There are, however, hidden costs that rarely come to the surface.
In the development of a seating life cycle cost analysis, Time-to-Refurbishment is most commonly coupled to Loss-of-Comfort. An argument can be made, however, suggesting Compromised Safety as another criterion, which could become a significant source of hidden cost. The notion of Compromised Safety is predicated upon the global rail standards that address flame, smoke, and toxicity (FST), such as ASTM D 3675, BS 6853, NFF 16-101, and DIN 5510. Full seat assemblies or the individual materials in the construction of a seat and seat cushion are mandated to conform to specific FST measurements dependent upon the category of the train. In practice, certified third-party FST test reports must accompany a seating tender as verification of conformance. Thus, the qualification testing of a material or full seat is of the utmost importance. Conversely, there are significant consequences if the test report comes back as a NO PASS or at a rating lower than intended.
The language in the standards, as well as the testing methods, is the result of professional expertise and years of collaboration. They are well-defined, sophisticated and strictly reviewed. Thus, the preparation of a vendor sample designated for testing submission will be of the highest level of engineering and craftsmanship. For example, a seat, which is to be submitted for a British Spec (BS) 6853 Category 1a burn test, will be meticulously assembled, with special attention to the wrapping of the fire barriers and upholstery fabric over the foam seat cushion. The tighter the fit of the upholstery folds and tucks, the lower the risk of air paths between the fabric and foam cushion. An air path has the potential of becoming an oxygen source for accelerated flame spread. Objectively, the entire process is logical, legitimate, and of the utmost regard for the safety of the ridership.
Why, then, is this a discussion on hidden life cycle costs? The answer to this question is built upon cycle-testing data, field observations, and a hypothesis. It has been established that achieving good FST results is partially dependent upon the best-of-the-best material samples and assembly practices. What would be the FST results if a mass-production seat were pulled out of service after thousands of cycles and months or years of usage? Depending on the type of foam specified for the cushioning, the cycling of a seat can result in a loss in foam thickness, reduced spring-back force (the resultant force the foam will have upon the load of the passenger, which is directly related to comfort), and compromised weight distribution, which directly affects comfort performance. This deterioration will cause the fit between the upholstered fabric, fire barriers, and foam to become loose and crumpled.
In a lab study performed in the UK, a 100,000 cycle test was conducted on two upholstered foam cushions: fire-retardant open cell polyurethane foam and open cell silicone foam. The empirical data is astounding. The fire retardant polyurethane material diminished in thickness by >10% with a spring force loss of >50%, while the silicone foam deterioration was negligible in both thickness and spring force. In addition, the polyurethane cushion took on a compression set with a concave shape replicating the shape of the Jounce and Squirm impact apparatus. The discoloration, as seen in the photo, is the remnants of the fire retardant filler after having eroded away the cell walls of the polyurethane foam. (See Figure 1).
In complete contrast, the silicone foam shows no shaped compression set and has no visual defects. While this is test data, it has been observed in the field as well. The photo of the cycle tested upholstered polyurethane cushion is comparable to worn and loose seats found in service. (See Figure 2).
Back to LCA!
Would this 100,000 cycle tested seat still pass the FST requirements as did its hand-crafted predecessor without any cycling or wear? Is this a compromise of safety? Also, is this a hidden cost that should be included into an LCA? None of these questions is to be answered in this discussion, but only offered up as a question for serious thought. Comprehensively, a thorough life cycle cost analysis should include a systems approach – analyzing potential costs, with probabilities, of a system or module failure due to performance degradation of the component under evaluation.
In the case of the seats, there may be a point in time when loss of thickness, spring back force, or a shaping from compression set could cause a system failure. The system failure could range from acceptable comfort to something as severe as non-compliance to an FST standard.
Rogers Corporation, the manufacturer of BISCO MF1 open cell silicone foam specially formulated for rail car seating cushions, has launched a Seat Cushion Cost of Ownership Tool (See Figure 3) that allows the user to simulate a specific scenario: size of seat cushion, number of seats per car, number of cars in the fleet, average number of years between refurbishments, cost of competitive materials, labor rates, estimated number of replacements, need for fire barriers, and revenue loss.
The calculator presents a picture of the total cost of ownership for each material along with metric tons of material that will be designated for landfill over the time period.
It will be up to the user to add in the hidden costs – if there are any – as suggested in this discussion. Hidden costs can be difficult to measure, but that doesn’t make them any less significant, especially when it comes to any potential compromise of safety.
It is an understatement to say that the design, development, and eventual tender and sale of passenger rail cars ranks among the most cost competitive products in the world. Designers, engineers, and supply chain managers are under extreme pressure to deliver high quality, high-performing, and very long-lasting products to the market. Meeting cost budgets is made possible by ingenuity, technology, and strategic manufacturing and marketing.
As with any purchasing decision, the price of any one rail car component or module has a cost-value relationship. And more often than not, there is a significant amount of emphasis and evaluation placed upon the selection of the materials used within the more prominent features of the interiors. This includes composite materials for side wall and ceiling liners, seat cushion foams and upholstery, and flooring structures, to name a few.
In addition, specialty materials are also specified in combination with highly sophisticated HVAC and control system hardware. Buyers and sellers will negotiate the integrity and different levels of performance among the choices (and prices) available – balancing budget with cost and value.
However, what is frequently ignored is the hidden value and importance of the multitude of gaskets and seals that protect, preserve and actually integrate the various interior systems and modules together. While one of the main functions of a rail gasket or seal is to keep moisture or water from leaking into an undesired place, there are also many other considerations that should go into gasket selection. A great deal of engineering effort is spent determining vibration isolation and damping, acoustic blocking and absorption, as well as contribution to EMI/RFI protection and conformance to flame, smoke and toxicity requirements.
The cost of a rail gasket is driven mainly by the selection of the material that will be used for fabrication. And being that the full range of a gasket’s importance is often unknown, the materials for gaskets have occasionally been identified as a potential cost-cutting initiative. This is where one must fully appreciate that the cost of a gasket is much more than its price. Depending on its application, a specific sealing strip could be the main vibration isolator between two expensive wall panels. Should the sealing strip be fabricated from a less expensive material, it will most likely have a shorter life.
The life of a strip or gasket is determined by many characteristics. One is its ability to not take a “compression set,” to experience a permanent decrease in thickness over time. Another is its “degradation of force deflection” over time, which relates to a material’s resultant force when in compression. In this example, a decline in the vibration isolation performance capabilities could allow for the wall panels to fatigue at a much quicker rate than design intent. This could result in many scenarios such as a noisier and more uncomfortable ride, displeasing passengers – or potentially opening up the need to replace failing wall panels earlier than according to the MRO budget.
There are other and more critical examples, such as the protection of controls equipment in each car of an EMU train or the requirement to meet a BS 6853 Category 1a or NFF 16-101 M1F1 FST standard. In any of these hypothetical situations, the cost of the seal or gasket can be extrapolated into multiples of the price.
Today, there are countless train builds that have embraced the need for high-performing, long life materials for seal and gasket design. Solutions designed from silicone materials are either in final design or in service with many high-profile projects, including the many CHR (China 380 km high speed rail) projects, the Sydney, Australia PPP project, as well as leading designs throughout Europe.
BISCO Silicones from Rogers Corporation, which offer a portfolio of materials specific to the rail industry, offer application-specific solutions to meet all objectives, and can assist in determining the full cost impact that a poorly designed gasket or specified material could have.
For more information on flame standards, read “Don’t Get Burned by Flame Standards” in Machine Design.