January 9, 2006Mr. John TignorSafety & Ergonomics DirectorCargill, Inc.East Highway 154Dodge City, KS 67801Dear Mr. Tignor:Thank you for your February 9, 2005, letter to the Occupational Safety and Health Administration's (OSHA's) Directorate of Enforcement Programs (DEP). This letter constitutes OSHA's interpretation only of the requirements discussed and may not be applicable to any questions not delineated within your original correspondence. You are requesting an interpretation of the OSHA standard 29 CFR 1910.219, and whether or not rotating round shafts must be guarded. Your paraphrased scenario, question, and our response are provided below.Scenario: The exposed round shafts are completely smooth and have no bolts, holes, or keyways. The shaft's diameters that can be used are 3-inch, 4-inch and 4 5/16-inches. The length of the exposed shaft is approximately 7 inches. The shafts revolutions range from 17 to 54 per minute (rpm). The measurement from the outside of the motor mounts to the outside of the shaft varies from 8 inches to 13 inches depending on the equipment.Question: Would OSHA provide an interpretation of 29 CFR 1910.219 as to whether these shafts must be guarded, because the manufacturer believes that the American National Standards Institute's (ANSI's) guarding requirements refer to rectangular shafts only?Response: From your incoming letter, we were not able to determine the installation heights of the shafts. As you may know, 1910.219, Mechanical Power-Transmission Apparatus, does not reference square or rectangular shafts, nor does it exempt round shafts from its guarding requirements. Also, OSHA's standard provides no exemption for shaft size or speed (rpm).OSHA standard, 1910.219(c)(2)(i) states, "All exposed parts of horizontal shafting seven (7) feet or less from floor or working platform, excepting runways used exclusively for oiling, or running adjustments, shall be protected by a stationary casing enclosing shafting completely or by a trough enclosing sides and top or sides and bottom of shafting as location requires."However, 29 CFR 1910.219(c)(5), provides guarding exemptions for all mechanical power transmission apparatus located in basements, towers, and rooms used exclusively for power transmission equipment.In addition, if the housing/mount is designed or constructed in such a manner as to prevent employees from having any part of their body, clothing, jewelry, or the like (such as neckties, scarves, and necklaces) contact the shaft, then it would be considered as guarded by location and would be compliant with the provisions of 1910.219(c)(2)(i). Otherwise, all rotating shafts seven feet or less from a floor or work platform must be completely enclosed as required by the standard.Please note that ANSI's standards are promulgated for voluntary use, whereas OSHA's standards have enforceable mandatory provisions. Further, OSHA does not interpret consensus standards. For an official interpretation of American Society of Mechanical Engineers' standard, you may contact ANSI/ASME at:
A rotating body consisting of a rotating shaft and bearings inevitably generates voltage and current. The potential difference between the bearing and the shaft is the main cause of electrical corrosion, which causes motor failure, shortened bearing life, and many safety issues. To prevent corrosion, passive shaft-grounding devices use conductive materials and brushes; however, these devices cannot be completely grounded, so there is a difference in local potential, and brush friction generates a shaft current. The cumulative effect causes electrical corrosion; therefore, in this study, an electrical corrosion protection device for the rotating power supply shaft was developed. It detected current and potential difference and established a feedback system on the rotating shaft. It also energized the rotating shaft using an external power supply to eliminate the potential difference on the shaft and reduce electrical corrosion. The result was prolonged motor life and improved stability, operating efficiency, and operability of related equipment. In this study, a rotating-shaft test rig was set up, and a constant current was applied to simulate the potential difference and verify the performance of the anti-corrosion device. Gradually, the design scheme was optimized; the potential difference on the rotating shaft was accurately quantified; and the goal of controlling the potential difference within 2 mV was achieved. Finally, the electrical corrosion protection device was applied to the rotating shaft of a merchant ship, and the current and potential difference on the rotating shaft were monitored for 30 days. The results showed that the device had excellent performance in reducing the potential difference on the rotating shaft and preventing electrical corrosion.
This shaft allows an RDE tip (E3 Series or E4 Series only) to be used as a non-rotating, stationary working electrode. The upper end of this shaft has a banana jack which can accept a standard banana cable, or alternatively, a banana plug (included) can be installed in the banana jack, and this plug can accept an alligator clip.
The use of finite elements for simulation of rotor systems has received considerable attention within the last few years. The published works have included the study of the effects of rotatory inertia, gyroscopic moments, axial load, and internal damping; but have not included shear deformation or axial torque effects. This paper generalizes the previous works by utilizing Timoshenko beam theory for establishing the shape functions and, thereby including transverse shear effects. Internal damping is not included but the extension is straight forward. Comparison is made of the finite element analysis with classical dosed form Timoshenko beam theory analysis for nonrotating and rotating shafts.
Mechanical seals, invented in the early 1920s, became the go-to rotating shaft sealing method in the 1950s within the oil and gas industry and continued to gain market share through the 1990s, becoming common in most process industries and applications. Their ability to seal rotating equipment better than the traditional braided packing methods was evident. Over the last 30 years, their usage has become a standard procedure for many application maintenance programs.
Modern mechanical seals use ultra-precise, ultra-flat opposing faces, one stationary and one rotating with the shaft. The opposite faces are so precisely paired that they leave a gap measured in microns. The microscopic gap causes the pumped medium to vaporize as it is moved centripetally to the seal edge. The result is a seal that does not measurably leak. It also creates a low friction environment for rotating shafts; low friction at the stuffing box results in lower energy costs for rotating equipment.
While mechanical seals, when installed and maintained correctly, create effective seals, they can be problematic because of their inherent complexity and the need to keep the opposing faces perfectly mated and cooled. Installing these seals on equipment with shaft runout, a scored sleeve, or worn parts can lead to premature failure and costly downtime.
In some applications that require a mechanical seal on worn equipment, you can install an o-ring mounted bearing to mitigate shaft movement, which can protect the critical seal faces. (see the SealRyt ORM)
Bearings work similar to mechanical seals but without the ultra-precise, micron-level clearances. Bearings stabilize the shaft, reducing runout or wobble, bringing the shaft into concentricity. Bearing systems work in concert with packing or mechanical seals to create a close clearance seal at the bottom of the stuffing box that stabilizes the shaft, then the braided packing is layered into the remaining space and compressed using the gland follower. The combination of shaft stabilization and close clearance fit provided by the bearing allows the packing to seal effectively and longer than packing alone.
The difference between bearings and bushings is simple: Bearings are designed to bear the load and contact the rotating shaft. Bushings are designed to be a non-contact spacer and, depending on design, to alter flush flow characteristics. So there are two main differences: clearances and materials. Bushing clearances are much larger to ensure that the part DOES NOT come into contact with rotating shaft. Contact with the shaft leads to damage of the bushing material. Bushing material tends to be low durometer materials such as rubber, polyurethane, and other semi-hard plastics such as carbon-filled Teflon.
Packing has been used for centuries, since the first use of rotating equipment as pumps. Rope packing gets its name from jamming rope around a rotating shaft to be sealed. The term stuffing box is a relic of this early sealing method. It's the most common rotating shaft sealing method because it's relatively inexpensive and reasonably effective.
Packing has come a long way from using organic twisted fiber. Today modern braided packing is made from high-tech synthetic fibers woven into complex patterns that create a square-shaped packing compressed into a stuffing box in layers. The packing gland is then tightened enough to create a seal but allows the shaft to rotate. Essentially, packing seals through both friction as well as hydraulic pressure break-down.
Using braided packing to seal requires the correct combination of material characteristics depending on the temperature, rotational speed, and medium being sealed. The packing should be low friction as it contacts the shaft and be durable to withstand the rotational wear. Packing that has heat conductivity is a huge plus as well.
SealRyt Corp. is the industry leader in rotating shaft sealing technology. Our engineers have years of experience in the science of sealing. That's why we hold multiple patents on sealing technology. That's also why our products last longer, get better results, and simply seal better than any other products available. 041b061a72