Large Press Column Bolting Alternative

Proper tie-rod tensioning is one of the key elements to keeping a press running smoothly. However, obtaining accurate and proper pre-stress can be difficult, time consuming, costly or even dangerous. Additionally, since nut removal is often difficult and problematic, the chances of a speedy turnaround for machine maintenance or repairs are greatly hindered.

Common methods for tensioning include thermal heating and hydraulic tensioning, because it is usually difficult to use torquing methods. Both of these methods require high-powered equipment and can be pricey. Thermal tensioning can also be time-consuming considering all the rods must be heated evenly, and tension cannot be measured until all the tie-rods have completely cooled.

One unique solution for difficult tie-rod bolting applications is the Superbolt® multi-jackbolt tensioner (MJT). Even for large diameters, they only require hand-held tools such as calibrated torque wrenches and small electric/air impacts to achieve accurate pre-stress.

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MJTs achieve this by dividing the load among a number of jackbolts, which are threaded through a round nut body. To install, the nut body is threaded onto the stud or bolt, hand tight, against a hardened washer. The jackbolts are then tightened, and they thrust against the hardened washer, pushing the tensioner body away from the surface to create tension (Figure 1). Because only small tools are used, they are relatively fast and easy to install. They are also accurate and no pre-load is lost from relaxation, which is typically associated with thermal and hydraulic tensioning.

MJTs have been effective in making installation an easier and safer task, but they also eliminate galling and seizing problems often encountered during removal with standard methods. Removal is accomplished by gradually loosening the jackbolts until the nut body is loose.

While the MJT can be an ideal solution for large diameter bolting, Superbolt recently patented a new style of tensioner that makes tensioning even easier for large press columns. Split-Nut Thrust Collars (STCs) have a threadless ring with jackbolts threaded through it (Figure 2). A split-nut threads loosely over the ring, and the two halves are clamped together by small MJTs, once in place. When the jackbolts are tightened, the ring transfers jacking force to the split-nut to tension the tie-rod.

STC tensioners are much easier to install and remove than other large threaded fasteners. Typically, large thread sizes can be difficult to tighten and loosen - any kind of nick in the thread can keep the nut from spinning on. Additionally, surface pressure on the threads can cause galling and seizing, and large threads are more susceptible to cross-threading. With STCs, because the tension is created by the jackbolts, there is little pressure on the threads while threading on the split-nut. Further, this set up is more tolerant of slight thread variations between nut and tie-rod, which is a huge concern, especially when mating new nuts to existing tie-rods.

Having a properly bolted press column is critical to smooth operation. The goal is to find a bolting method that is accurate, fast and effective, as well as safe for workers. Superbolt STCs could be an ideal solution to industry bolting problems.

For more information contact:
Superbolt, Inc.
Tel: 1-800-345-BOLT (in U.S.) 1-412-279-1149 (outside U.S.) | Fax: 1-412-279-1185
Email: bolting@superbolt.com | Website: www.superbolt.com