Captivating concept

2 mins read

Delays on the assembly line where separate bolts, washers and nuts are involved can be deeply frustrating – and expensive. Here’s one solution that promises to overcome that.

Fiddling about with separate bolts, washers and nuts adds increased assembly time and cost, which no business wants.

One answer has been to produce what is known as a SEMS screw that involves captivating a washer onto a screw or bolt in a one-piece design, but this can be an expensive and time-consuming process that requires specialist manufacture.

“The new HEICO-LOCK Combi-Washer has a unique design that creates your very own SEMS screw at a fraction of the cost and effort,” claims the company. A traditional SEMS screw is created by placing the washer on the screw before it is thread rolled. Once thread rolled, the diameter of the screw is larger than the washer hole, thus ‘captivating’ the washer in place, ensuring that it does not separate from the screw.

The Combi-Washer combines an inner locking ring with inset tabs and the bolt securing qualities of the company’s HEICO-LOCK Wedge Lock Washers. The inset tabs of the inner locking ring grip on to the bolt thread, creating a captivated washer. “This means that, once applied, the washer will stay in place on the bolt, even when the joint is disassembled for maintenance or repair, and initial assembly during production is quicker and easier.”

The HEICO-LOCK Wedge Lock Washers use preload, rather than friction, to secure a bolted connection. The design has a combination of radial external teeth and internal wedge-shaped cams. As the angle of the internal cams is greater than the pitch of the bolt thread, any loosening causes movement in the region of the wedged cams. This creates an expansion in the thickness of the washers and, as this thickness is greater than the possible longitudinal movement of the stud along the thread, increases the clamping force.

“By integrating the inner locking ring with the bolt securing qualities of the HEICO-LOCK system, bolt security is assured, at a fraction of the cost and time of producing a bespoke SEMS screw,” states Heico Fasteners UK. “The Combi-Washer can be used in conjunction with all commercially available bolts, which means you can create your very own SEMS part with your existing bolts. Also, we can supply pre-assembled bolts, so it can be used as a SEMS part straight out of the box.”

Combining the Combi-Washer and bolt into one versatile fastener creates clear design and manufacturing benefits, not least bottom line savings for production. When using out in the field for onsite maintenance or repair, the created SEMS screw is easier to remove and re-install than separate fasteners, particularly where space is tight or conditions demanding, adds the company.

The Combi-Washer joins an already extensive range of its bolt fastening systems that includes the original HEICO-LOCK Wedge Lock Washers; the Ring Lock system with its outer polyamide ring; the Wedge Lock Nut, which combines a hex nut with a captivated wedge lock washer; and also the HEICO-TEC tension nut, for use with larger bolt sizes up to M120.

With easy assembly and permanent connection promised, the HEICO-LOCK Combi-Washer system would appear to offer a flexible, fast, bolted joint solution, particularly for highly loaded bolted connections.