Phone: (720) 554-0900 Fax: (720) 554-0909 technical@galvanizeit.org WIRE TIES FOR OVERHEAD LIFTING 1. Scope 1.1 The wire tie guideline covers common practices and procedures in the galvanizing industry for use and maintenance of wire ties. 1.2 The enormous variety of work types that are hot dip galvanized requires fabricating specific equipment to secure the many different types of steel parts to cranes and hoists in a safe fashion. The use of wire ties allows all different types of parts to be handled in a safe and efficient manner as long as certain basic procedures are followed. 1.3 The Occupational Health and Safety Administration (OSHA) lists in the 29 CFR 1926.251 regulation details on rigging equipment for material handling. OSHA 1910.184 also lists requirements for material handling. 2. Referenced Documents ASTM Standard A 370 Test Methods and Definitions for Mechanical Testing of Steel Products A 510 Specification for General Requirements for Wire Rods and Coarse Round Wire, Carbon Steel A 853 Specification for Steel Wire, Carbon, for General Use McGannon, Harold E., United States Steel, The Making, Shaping and Treating of Steel, 1964. Kleingarn, J-P., VDF, Guidelines on the use of lifting and transporting equipment in hot dip galvanizing plants a contribution to accident prevention. Intergalva 88 Fifteenth International Galvanizing Conference, 1988. 2003 Process Survey 2003 Wire Tie Test Program 3. Terminology Disclaimer 3.1 Definitions of Terms Specific to This 1 The material contained herein has been developed to provide accurate and authoritative information about the practices and procedures to protect employees in the galvanizing industry from the hazards of using wires for overhead lifting. This material provides general information only and is not intended as a substitute for competent professional examination and verification as to suitability and applicability. The publication of the material herein is not intended as a representation or warranty on the part of the, Inc. Anyone making use of this information assumes all liability arising from such use.
Guideline 3.1.1 annealed-in-process wire steel wire that was thermally treated and subsequently redrawn 3.1.2 annealed wire wire that was drawn to size and annealed at finish size 3.1.3 carbon steel steel is considered to be carbon steel when no minimum content is specified or required for aluminum, chromium, cobalt, columbium, molybdenum, nickel, titanium, tungsten, vanadium, or zirconium or any other element added to obtain a desired alloying effect; when the specified minimum copper content does not exceed 0.40 %; or when the maximum content for any of the following elements does not exceed these percentages: manganese 1.65, silicon 0.60, or copper 0.60. 3.1.4 drawing the amount of reduction in the sectional area expressed in percent of the original area and is known as the draft; the operation itself is called drawing 3.1.5 hard drawn wire wire drawn without the use of thermal treatment 3.1.6 rated capacity or working load limit (WLL) the maximum combined static and dynamic load in pounds or kilograms that shall be applied in direct tension to an undamaged straight length of wire. 3.1.7 tensile strengths the ratio of maximum load to original cross-sectional area, also called ultimate strength 3.1.8 yield strengths stress or load at which the wire starts to permanently deform 4. General Information 4.1 Different types of equipment have been used for loading and securing parts to the crane. Chain, rope, and nylon webbing have been used besides wire ties. 4.1.1Wire ties are used because of the simplicity of the design and the ease of attaching different products onto a crane or rack. 4.2 The most common material used in the galvanizing industry is soft annealed No. 9 gage wire, according to the 1997 AGA Process Survey. This wire is referred to in the specification for wire, ASTM A 853, as annealed wire and not annealed-in-process wire or hand drawn wire. These later two wires are drawn to develop very high tensile strengths and become very hard to bend and twist into knots so they are not used in the hot-dip galvanizing process. 4.3 Annealing is employed as a heat treatment to low carbon steel wire to refine, soften, and make uniform the grain structure of the wire after the wire has been drawn to size. 4.3.1 Annealing is used to obtain a specific structure, and to give special properties to process wire. 4.3.2 Annealing is also used to soften wire after cold working, i.e. drawing or cold rolling. 4.3.3 The process to determine whether the annealed wire is correctly annealed uses four wires that are bent 90 degrees and straightened with minimal effort. 4.4 Wire ties for use in hot-dip galvanizing come into contact with molten zinc at a temperature of 850 F and this lowers the effective tensile strength of the wire by 30 % according to the American Galvanizers Association 2003 Wire Test Program. 5. Advantages and Disadvantages of Using Wire Ties 5.1 An advantage of using wire ties is that the wire ties represent a universal attachment medium that is adaptable to the main components of the general product range in a hot-dip galvanizing plant. 5.1.1 Wire ties are generally used once and therefore do not require inspection, maintenance or repair. 5.1.2 Wire ties can be recycled. 5.1.3 Wire ties have the lowest possible surface area compared to other lifting aids such as chains or hooks, so as to minimize the amount 2
of zinc carried out of the galvanizing bath on the wire ties. 5.2 A disadvantage is the behavior of wire under practical conditions is harder to calculate because the wire must be tied by human hands. 5.2.1 For the wire ties to be used safely, the wire ties must be used only once and then discarded. 5.2.2 There is a risk of accidents occurring in the course of handling puncture wounds during tying and untying, trip hazards if wire ties are left on the plant floor, etc. 5.3 Another disadvantage is that most wire ties are often made out of scrap material if it is not purchased to ASTM Standard A 853. 5.3.1 The scrap material is often drawn down before annealing to the required dimensions specified by a customer. This results in a coarse grain structure that can give variable material properties upon annealing because of the critical deformation levels. The pull strength of scarp wire can be variable and must be tested for each spool of scrap wire that is not manufactured to ASTM A 853. 5.3.2 Microstructures of this variable kind increase the likelihood of fracture in subsequent use so this wire must have adequate safety factors for the working load limit. 6. Mechanical Properties 6.1 The mechanical properties of any wire will depend upon the chemical composition and quality of the steel, as well as the exact nature of the drawing practice and of the heat treatment the wire has undergone. 6.2 The particular application or method of fabrication helps to determine the grade of wire necessary. 6.3 Carbon steel wire should meet the tensile strength requirements from ASTM A 853 for the condition specified when testing in accordance with A 370 Test Methods and Definitions. 6.4 Tensile tests made during the American Galvanizers Wire Test Program and reported by J.P. Kleingarn at the 1988 Intergalva have shown the following results on the use of wire ties: 6.4.1 Wire ties are made by manual twisting of the wire, and under certain circumstances can pull apart and separate. 6.4.2 The fracture load of wire ties has great variability. 6.4.3 Wire fracture often occurs at the start of the first 180 degree bend. 6.4.4 The wire ties are severely attacked in the pickling bath. 6.4.5 When subjected to the temperature of the molten zinc bath, the wire tie strength is decreased from the value at ambient temperature. 7. Selection and Inspection of Wire 7.1 Material certification of the wire ties should be obtained from the wire manufacturer and wire should be purchased to ASTM A 853 to insure that the wire properties are uniform and repeatable. 7.1.1 The wire certification shall include the specification number, year date of issue, and revision letter, if any. 7.2 When wire is received at the galvanizing plant, the wire should be inspected. The wire should be smooth and substantially free from rust and kinks. 7.2.1 No detrimental die marks or scratches may be present. Each coil should be one continuous length of wire. Welds made during cold drawing are permitted. 7.2.2 The straightened and cut wire should be substantially straight and not show excessive spiral marking. 8 Record keeping 8.1 When a shipment of wire is sent to the galvanizing plant, the information on the type of wire, tensile strength of the wire, date, and the 3
manufacturer of the wire should be recorded and the information stored for later access. 8.2 Wire should be kept in an area easily accessible to the loading of parts. After the wire is used, a container to hold the used wire ties should be placed at the unracking area to promote good cleaning practices around the galvanizing plant. 9. Measurement Standards 9.1 A number of formal mechanical test procedures have been developed. Producers use these tests as control tests during the intermediate stages of wire processing, as well as for final testing of the finished product. This applies particularly to specification wire and wires for specified end uses. 9.2 The following pull test information was performed on annealed No. 9 gage wire ties. The tests were conducted using a 1-½ ton Levert hoist and a 15000 lbs. Dillon Dynamometer. 9.2.1 The wire ties tested are tied differently than what is commonly done at a galvanizing plant. The wire ties are tied so that the knot tightens on itself and not on the wire (Wire Tying Method # 1 from Appendix 1). 9.2.2 Table 1 shows the results of the pull tests done on No. 9 gage wire ties ( Wire Tying Method # 1 ) at ambient temperature. The wire broke before the knots did. The twisted ends of the wire ties held. Table 1. Number of Sample Amount of Weight before Wire Broke #1 1500 lbs. #2 1650 lbs. #3 1700 lbs. Wire Tying Method # 2 in Appendix 1 ) at ambient temperature. The type of knot tested was a wire tied with three twists. Table 2. Type #1A twist eye pulled out on one end #2A twist eye pulled out on one end Amount of Weight before Knot came Undone 500 lbs. 650 lbs. 9.3 The performed a test program in 2003 to determine the breaking strength of 9-gauge wire at its weakest point in the galvanizing operation, when it is withdrawn from the molten zinc bath. The wire is at its weakest point when it reaches the galvanizing temperature: 850 F. When the parts being lifted are withdrawn from the galvanizing kettle, the wire must support the original steel load plus the added weight of the hot dip galvanized coating while it is at the galvanizing temperature. 9.3.1 Wire tying methods that were used in the testing are described in pictorial form in Appendix 1. These wire tying methods were tested at temperatures approaching 850 F. Two wire suppliers and two hot-dip galvanizers participated in the study. 9.3.2 The following charts show the performance of each wire tying method at galvanizing temperature. Wire Tying Method #1 Table 3a. Pull test average STD DEV. Galvanizer A 302 lbs. 118 9.2.3 Table 2 shows the results of types of wire tie and the breaking strength for the knot ( Galvanizer B 523 lbs. 129 4
Wire Tying Method #2 Table 3b. Pull test average STD DEV. Galvanizer A 311 lbs. 88 Galvanizer B 440 lbs. 132 Wire Tying Method #3 Table 3c. Pull test average STD DEV. Galvanizer A 551 lbs. 64 Galvanizer B 669 lbs. 30 9.3.3 The information from the wire testing indicates that the first two wire tying methods are very dependant on the human factor. The results are scattered and the standard deviation is high. The third wire tying method gives more consistent test results with a low standard deviation indicating that the human factor has been significantly reduced. 9.3.4 A second round of test confirmed the results for wire tying methods 1 and 2. The obvious difference between high pull strength wires and low pull strength wires was the amount of wire deformation for each wire. The looser the twists and knots, the lower the pull strength. 10 Working Load Limits 10.1 The working load limit can be calculated by taking a percentage of the breaking strength, depending on the type of wire tie and the wire tying method used in the galvanizing operation. 10.1.1 The de-rating factor is found by taking into account the decrease in the effectiveness of the strength of the wire ties at elevated temperatures. 10.1.2 Since the pull strength of wire at the galvanizing temperature for wire tying methods 1 and 2 are variable, the de-rating should be 10% of the initial breaking strength of 1000 lbs. at ambient temperatures. This takes into account both the high temperature usage and the variability of the wire tying method. 10.1.3 Since the pull strength of wire at the galvanizing temperature for wire tying method 3 was consistent, the de-rating factor should be 30% of the initial breaking strength of 1000 lbs. at ambient temperatures. 10.2 For the initial breaking strength of the wire at ambient temperatures, the strength can be calculated by dividing the maximum load the specimen sustains during a tension test by the original cross-sectional area of the specimen. 10.2.1 The breaking strength can also be calculated from the tensile strength. An example calculation for breaking strength is shown below: For a No. 9 gauge wire tie with a tensile strength of 60000 psi, the breaking strength is as follows: AREA = PI*R 2 PI = 3.14 R = radius of wire in inches (for No. 9 gage, the diameter is equal to.148) Area = (3.14)*(.148/2) 2 =.017 in 2 Breaking strength=(60000 psi)*(.017 in 2 ) = 1032 lbs. 10.2.2 The working load limit can be found in similar fashion for wires of other gauges such as 10, 11, or 12 if used in the galvanizing operation. These gauges are smaller than 9 gauge so their working load limits will be smaller than the value calculated in 10.2.1. The 5
same reduction factors will be used for wire tying methods 1, 2, or 3. If other wire tying methods are used the breaking strength of these other methods must be tested at galvanizing temperatures before a derating factor can be applied to find a working load limit. 10.3 When preparing to load parts, be sure to use only approved wire and the proper gauge for racking parts. 10.4 Be sure that the safe working load limit is known for the wire tie and wire tying method before loading a part. Some guidelines to use for 9 gauge wire ties are in Table 4. Table 4. Type of Wire Tying Technique Rating of the Wire Tie Method #3 300 lbs./strand # 3 Multiple Strands <4 300 lbs./strand # 3 Multiple Strands >4 225 lbs./strand Method #2 100 lbs./strand Method #1 100 lbs./strand #1& 2 Multiple Strands <4 100 lbs./strand #1& 2 Multiple Strands >4 75 lbs./strand 10.5 Ascertain the weight of the load being lifted. If in doubt, err on the side of safety. The load should not exceed the safe working load limit of the wire ties to attach the load to the overhead lifting system. 11 Wire Tying Techniques 11.1 Using wire to tie a part can be done several ways. The most common way is to use multiple loops twisted together in a single knot. 11.2 For maximum wire strength when hanging parts by wire, a good practice is to bend the wires approximately 180 degrees. Then wind the wires over themselves to a length of 9 to 15 inches long. Make at least three complete turns and then bend the wire down to avoid any protruding ends. 11.2.1 A diagram of different wire tying methods is shown in Appendix 1. 11.3 The required lifting capacity is achieved either by using multiple loops of single diameter wire or by using larger diameter wires to achieve the lifting capacity that exceeds the weight of the steel part. 11.3.1 Where multiple loops are used, the ends should be twisted together into a single knot in a way that ensures that the load is evenly distributed across all of the loops, not concentrated on only one. 11.3.2 Knots should be twisted and the knot then bent back to avoid protruding ends. 11.4 After hanging the part, check to make sure the part is secure by pulling on the joint. Make sure there is enough space between parts to prevent heavy banging and shearing of wires. 11.5 Holes with sharp or cut edges can damage wire that bears on them. Care should be taken as far as practically possible to ensure that wire does not bear on such edges or holes, but where this is unavoidable, it is advisable to increase the safety factor by using a heavier gauge wire and/or extra strands. 11.6 Safe working loads should be calculated from the results of tensile strength tests with a safety factor applied that de-rates the load. 12 OSHA Regulation 1910.184 and 1910.251 12.1 These regulations specify material handling techniques in using rigging equipment. 12.2 OSHA recommends that for sizes, classifications, and grades not included in the regulation, the safe working load recommended by the manufacturer for specific, identifiable products shall be followed, provided that a safety factor of not less than 5 is maintained. OSHA also recommends that wire ties shall have not less than three full tucks or twists. 12.3 Wire shall also not be used if, in any 6
length of eight diameters, the total number of visible broken wires exceeds 10 percent of the total number of wires, or if the wire shows other signs of excessive wear, corrosion, or defect. 13 Recommendations for Wire Ties 13.1 Wire ties used for loading parts in a hotdip galvanizing plant should be in accordance with ASTM A 853. 13.2 The wire ties should be cold drawn and soft annealed. 13.3 The steel type should be in accordance with ASTM A 510 Specification for General Requirements for Wire Rods and Coarse Round Wire, Carbon Steel. 13.4 The tensile strength should range from 60,000 to 70,000 psi. 13.5 Wrapping tests should be conducted on wire ties at 1 x wire diameter, with a minimum of 8 turns without fracture. 7
APPENDIX 1. SKETCHES OF WIRE TYING TECHNIQUES 8
Wire Tying Method #1 1. Twist once 2. Then knot 3. Then twist at least 3 times Wire Tying Method #2 Wire Tying Method #3 A. B. C. D. E. A. Red/Black wire B. Black over red C. Black down & under red, then up & over red. This is a halfhitch like the start of tying a shoe. D. Red down & over black, then up & under black E. Cross red over black, twist 3 times & turn ends down 9