[WRE UPDATE | BUSINESS]
“
...DESPITE BEING COMMON TOOLS IN EVERYDAY USE, CLAMPS ARE OFTEN MISUSED AND REMAIN WIDELY MISUNDERSTOOD. FURTHER, KNOWLEDGE ON INSPECTION, REPAIR, TESTING AND MAINTENANCE IS OFTEN LACKING.”
It should be noted that a design category A should only be specified when the loading and environmental conditions are not severe and the loading is known and predictable. Design category A is limited to a service class 0 (maximum of 20,000 cycles):
Te service class of a lifter establishes the design parameters of the lifting device and are defined as follows:
Service Class 0: 0 to 20,000 cycles Service Class 1: 20,001 to 100,000 cycles Service Class 2: 100,001 to 500,000 cycles Service Class 3: 500,001 to 2,000,000 cycles Service Class 4: over 2,000,000 cycles
As discussed, ASME B30.20-2018 was recently revised to include a new chapter (20-6) for clamps, as follows:
Chapter 20-1: Structural and Mechanical Lifting Devices Chapter 20-2: Vacuum Lifting Devices Chapter 20-3: Close Proximity Operated Lifting Magnets Chapter 20-4: Remotely Operated Lifting Magnets Chapter 20-5: Scrap and Material-Handling Grapples Chapter 20-6: Clamps
Within Chapter 20-6, clamps are categorized as follows: • Load supporting clamps. • Friction-type pressure-gripping clamps. • Indentation-type pressure-gripping clamps.
• Anchoring and positioning clamps. Anchoring clamps can be used for suspending or attaching detachable rigging hardware. Positioning clamps are used to hold or locate parts during assembly operations.
• Hybrid clamps use a combination of categories above.
It’s worth noting that other items that influence the design of a lifter is extreme cold or hot environments. Te current standard is applicable at temperatures from 25 degrees F to 150 degrees F (-6 degrees C to 66 degrees C). Temperatures beyond these limits require additional design considerations and may require special materials that are better suited for extreme cold or extreme heat.
Modifying a clamp We urge users and industry generally to proceed with great caution when it comes to considering modifications to clamps. At the outset of this article we looked at the many different scenarios that use clamps—plate steel, ingots, slabs, concrete barriers, pipe, etc.—and each of these
applications present their own specific requirements for the clamp. However, it is never ok to modify a clamp without consulting the manufacturer—period. Even at the very first consideration that a modification might enhance productivity or efficiency as it relates to that particular application, the manufacturer of the clamp should be contacted. We’ve seen scenarios where a user
has welded a chain or a handle onto a clamp, thinking that it is safe to do so. Practically, it might have aided operation, but it did so at great compromise to the integrity of the clamp itself. When we do work with a user to modify a clamp, we produce a drawing and are particular about the materials used and type of weld wire, for example, and offer other guidance such as not to disturb the base metal. Additionally, we require written or photographic evidence that the modification was completed in line with that instruction. As a general rule of thumb, always consult the
JC Renfroe model LPA (top) is design class B, while the model TLA (bottom) meets the new design class C.
manufacturer about better tailoring or adapting a product for a specific application. In some cases, an alternative solution already exists. As stated, so much of safe operation starts with selecting the right tool for the job in hand. Modifying the right tool can turn it into the wrong one. y
Tom Eicher is Director of Engineering at Te Caldwell Group Inc. He started his career at Beloit Corporation, designing equipment for the paper industry, and joined Caldwell in 2004. He contributes to a number of industry groups, including the ASME B30.20 subcommittee. Tom is also chair of the BTH-1 committee for Associated Wire Rope Fabricators (AWRF) and the below-the-hook committee for the Crane Manufacturers Association of America (CMAA). Prior to his professional career, he graduated with a Bachelor of Science degree in Mechanical Engineering from Michigan Technological University in 1987. Tom is married to wife Dorothy and has four children and eight grandchildren.
WIRE ROPE EXCHANGE SEPTEMBER–OCTOBER 2019 77
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85
