[WRE UPDATE | BUSINESS]
CLAMP DOWN I
BY: TOM EICHER, DIRECTOR OF ENGINEERING, THE CALDWELL GROUP INC.
t is important that end users understand the design categories and service class of clamps and other lifting products, says Tom Eicher, director of engineering at Te Caldwell Group Inc. Clamps for lifting come in many designs and are used in a myriad of applications, including lifting plate steel, ingots, slabs, concrete barriers, pipe, coil steel, paper bales and paper rolls, to name just a few. Clamps can be used for attaching loads to a hoist, or for other load handling purposes such as anchoring or positioning. However, 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. How well do you know ASME BTH-1, Design of
Below-Te-Hook Lifting Devices? Did you know that ASME B30.20-2018 is a new version that references the BTH-1-2017 design specification? Many end users don’t realize that the manufacturer must meet BTH-1 design specifications to meet the ASME B30.20 standard. ASME BTH-1 provides designers and engineers of clamps and other ‘below-the-hook’ lifting devices with the design criteria, standards and structural requirements needed to manufacture reliable products for various lifting applications. ASME BTH-1 also provides fabrication requirements for welding processes and procedures. ASME recently released the new specification for B30.20, dated 2018, while BTH-1 was released a year earlier.
What defines a clamp? It’s important to establish the product to which this guidance applies. Clamps are designed to generate a clamping force perpendicular to the surface of the load during lifting. Tese clamping forces are generated from the clamp geometry by the pulling force on the lifting shackle of the clamp or tightening of a screw. Many clamps have features
that allow for specific lifting conditions. When the wrong clamp design is used for the application, it can lead to a lost load or clamp damage. A number of factors lead to such misuse, such as not following the instruction manual, unapproved modifications to the lifting device or a lack of maintenance or inspection.
76 SEPTEMBER–OCTOBER 2019 WIRE ROPE EXCHANGE
Importantly, the load being lifted must be able to support the amount of squeeze that the clamp applies to the load. One area where we see repeated misuse is picking the wrong clamp for the application. Some clamps are designed for vertical lift only, some are for upending plate, some are for 180 degrees plate flipping, or for flat surface versus curved surface. It is necessary to understand the application before selecting the clamp.
New service class C Updates to the BTH-1-2017 includes the new service class C. Te following are design requirements, including the original A and B service classes:
• Service class A is a 2:1 design to the material’s yield strength or 2.4:1 to the fracture strength of the material and connections.
• Service class B is a 3:1 design to the material’s yield strength or 3.6:1 to the fracture strength of the material and connections.
• Service class C is a 6:1 design to the materials yield strength or 7.2:1 to the fracture strength of the material and connections, using BTH-1-2017 design classifications.
Clamps can be designed for light loads to loads exceeding 100,000 lbs. or more. Some manufacturers have clamps that meet design category A, service class 0, while others meet design category B, service class 4. Te difference between these two scenarios is a design category A, service class 0 (A0) is a 2:1 minimum design to the material’s yield strength for use up to 20,000 cycles, while a B4 clamp is a 3:1 design to the material’s yield strength for use over 2,000,000 cycles.
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