Shipbuilders and other marine stakeholders have recognized The Caldwell Group’s status as a manufacturer that meets ASME BTH (below‑the‑hook) Design Category C. Further, J.C. Renfroe, a subsidiary of Rockford, Illinois‑based Caldwell, likely remains the only clamp manufacturer in the world that can meet this stringent criterion.
Shipbuilding is one of the most demanding end‑use sectors in which lifting gear is applied, along with other heavy duty industries, such as forging/ forming houses, heavy construction, etc. The C design category was introduced relatively recently but Renfroe clamps were always designed with the appropriate ruggedness, so it was natural for the company to get them reclassified accordingly.
Dale Kelly, Engineering Manager at Caldwell, said that the C class has a higher design factor than the B category, which provides a larger margin of safety to the end user against failure and industrial accidents due to clamp failure. The B class has a design factor (what the clamp can withstand/ rated load) of 3:1, whereas the C class has a 6:1 design factor minimum. That should mean something to anyone around a dockyard in real terms.
“In fact,” Kelly said, “Many of these clamps are manufactured to a much higher design factor than that.”
The new standards provide a measure of clamp quality. It reflects a clamp’s ability to do its job over the long haul. Inescapably, higher ratings equal a better clamp. For example, an A0 clamp is a low rated clamp and could be of inferior quality. A C4 rated clamp is the best clamp there is.
Kelly added: “Keep in mind that this is self‑regulated so the manufacturer rates his or her own clamps. In our case we back it up with laboratory testing. Many Renfroe clamps were designed to withstand severe duty before the standard was written and in that sense the standard is catching up with Renfroe. There have been many changes over the years related to manufacturing processes and materials; we are retesting each clamp that is reclassified to ensure the integrity of the clamp is still valid.”
This provides distributors and end users in the dockyard sector with an immediate indication as to how good a clamp is. The customers can now look at this rating and immediately determine—if they know standard—the relative robustness of any clamp. This provides them with a quick assessment tool without a lot of research.
“It’s hard to say how other manufacturers will respond,” Kelly continued. “Truth is that many clamps do not hold up well to the environments we cater to. We have dominated this sector of the market and many users try other clamps and return to Renfroe. We have performed independent lab testing on our and competitors’ clamps to validate the relationship of this standard to the strength and robustness of their clamps. Unfortunately, these tests are expensive and time consuming and many will not do these to confirm the designs.”
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. Caldwell is changing that.
“End users should be more aware of the manufacturing origins of the products they use to generate a clamping force perpendicular to the surface of the load during lifting.” Kelly concluded.