twin-path® slings in action - Hanes Supply, Inc

YOUR SLING AND RIGGING SPECIALISTbasic lift engineeringeffect of anGlesVarious sling manufacturers refer in theirspecification tables to leg angles of slingsduring lifts – since these angles have a directrelationship to lifting capability of asling. Regardless of how the sling anglemay be stated, or the method used to computestress in a sling leg, the sling is thesame. Capacity does not change – butstresses on sling legs change with riggingangles.Much misunderstanding results becausethe carrying capacity of a sling leg is reducedby the rigging angle. What happensis that the operator is lifting the loadstraight up (vertical) while the legs arepulling at an angle, thereby causing a disadvantage.For quick figuring in the shop, a 60-degreeleg angle causes a loss in lifting capacityof 15%... a 45-degree angle reduces capacityby 30%... and a 30-degree angle,50%. This rule of thumb is not 100% accurate,but is easy to remember and slightlyon the safe side.It is always good practice, within limits, tokeep the sling leg angle as large as possible.The length and width of the load slinglength, and available headroom are determiningfactors in this sling angle.It is neither economical nor good practice toexceed a 45-degree sling leg angle.Angles less than 45 degrees not only buildup tension in the sling legs out of all proportionto the weight of the load, they also createa much greater "in-pull" on the ends ofthe load. This produces eccentrically loadedcolumn effect, as an engineer would describeit – meaning simply that long, slenderobjects have a tendency to buckle. Anglesless than 45 degrees indicate some thoughtshould be given to the use of a lifting beamor other device in connection with the lift.Studying typical sling charts readily revealsthat lifting capacities on slings are misleadingunless the sling angle is stated. Thesame sling that will handle 10 tons at an 85-degree leg angle will only handle 5 tons ifthis angle is decreased to 30 degrees.GooD slInG PRactIceRegardless of what type of sling may be employed,there are accepted good workingrules which will help increase useful sling life– as well as improve safety. These include:1. Use the proper sling for the lift. WhetherTwin-Path, Web, Chain, or Wire Rope, theproper sling is the one with the best combinationof work and handling feature – ofthe proper length and rated capacity forthe situation.2. Start and stop slowly. Crane hooksshould be raised slowly until the sling becomestaut and the load is suspended.Lifting or lowering speed should be increasedor decreased gradually. Suddenstarts or stops place heavier loads on asling – comparable to jamming thebrakes on a speeding automobile. A ruleof thumb: Shock loads can double thestress on a sling.3. If possible, set the load on blocks.Pulling a sling from under a load causesabrasion and "curling" – making the slingharder to handle on the next lift, while reducingstrength through loss of metal.4. Sharp corners cut slings. Use protectorarcs, Cornermax and Synthetic ArmorWear Pads between sharp corners andthe sling body.5. Store in a dry room. Moisture is a naturalenemy of wire rope – as are acidfumes and other caustic gases.6. Avoid handling hot material or objects indirect contact with the sling. Strengthgoes down as temperature goes up!7. Dropping casting, tools or heavy objectson slings, or running over them withtrucks, can cause damage. Always hangslings when not in use.8. Use hooks properly. "Point loading" reduceshook capacity. Pull should bestraight in the line of lift.selectInG a slInGThe following is presented as a guide onlyto help in selection of a sling for a lift.1. Determine the Load: The weight of theload must be known. This is always thestarting point.2. Decide the Hitch: Shape and bulk of theload must be accommodated as well asweight. Determine whether a straight attachmentat some point on the load, achoker around the load, or some form ofbasket hitch will best control the loadduring the lift.3. Adequacy of Lifting Device: The liftingdevice must have adequate capacity formaking the lift, and provide any maneuverabilityrequired once the load ishoisted.4. Room to Lift: Make certain the lifting devicehas sufficient headroom to raise theload to the height required. Headroomwill affect the length of sling.5. Length of Sling: By applying your decisionon the type of hitch to knowledge ofthe headroom offered by the lifting device,the length of sling can be calculated.6. Use Rated Capacity Chart: Always double-checkthat the sling type and capacityyou choose, when rigged at the angle determinedby the length of the sling, or thespecific type of hitch, will handle the load.Attaching the sling and completing the liftshould be an orderly procedure without "surprises"when these steps have been followed.Two further precautions should benoted, however.First, plan to protect both load and sling fromdamage at sharp corners, etc. Cornermaxand Synthetic Armor Wear Pads should beprovided at the lift site. A protective padshould be used anytime a sling passesaround a sharp corner.Last – by no means unimportant by beinglast – every sling should be visually examinedfrom end to end BEFORE EVERY LIFT.It must always be kept in mind that the manufacturer'sRated Capacity applies only to anew sling in "unused" condition. A slingshould be carefully examined to determinethat it is in as nearly new condition as practicablebefore each lift.There are specific standards on the use andcare of slings in industries such as shippingand construction, and these provide someguidance for sling inspectors. Consensusstandards published as ANSI B30.9 are particularlyhelpful.ANSI Standard B30.9 specifies that a wirerope sling should be removed form serviceany time any of the following conditions aredetected:1. Ten randomly distributed broken wires inone rope lay, or five broken wires in onestrand in one rope lay.2. Kinking, crushing, bird caging or anyother damage resulting in distortion ofthe wire rope structure.3. Evidence of heat damage.4. End attachments that are cracked, deformed,or worn.5. Hooks that have been opened more than15% of the normal throat opening measuredat the narrowest point, or twistedmore than 10 degrees from the plane ofthe unbent hook.6. Corrosion of the rope or end attachments.It is apparent from the foregoing that inspectionof a wire rope sling to meet theseremoval criteria requires more than a casualunderstanding of wire rope design andmanufacture, and the responsibility fordaily inspections must be in the hands oftrained personnel.Most of the foregoing applies equally to anytype of sling and careful inspection by atrained inspector is necessary for safe slinguse. If you require training for any type ofsling inspection, contact Hanes Supply formore information.HEADQUARTERS: 55 James E. Casey Drive • Buffalo, NY 14206 PHONE: 716.826.2636 FAX: 716.826.4412 www.hanessupply.com150