Introduction
Wire straighteners are devices for guiding, killing, stress relieving, and casting of all types of wire, ferrous and non-ferrous. The wire straightening process is most often employed to remove or change curvature, such as cast and helix, produced in the wire during drawing. It is a cold-forming process in which rollers provide uniform bending of the wire and/or rod to change its shape and other characteristics in preparation for use in subsequent processing, such as spooling or forming.
Straighteners are used most often to treat round wire and cable but can be adapted to accommodate any shape of wire and tubing - square, oval, half-round, rectangular - in virtually any environment and for any application. |
The most common wire straightening applications are:
- Tire cord and bead wire used in the manufacture of steel-belted radials;
- Wire rope for draglines for use in the lumber industry, coal mines, and bridges;
- Fine wire for medical and wire mesh applications such as airbags;
- Spring wire for automobile manufacture;
- Low carbon steel wire used to make bolts, fasteners, paper clips, etc.;
- Non-ferrous wire: copper, aluminium and bronze;
- Speciality wire: exotics used in the medical and related industries
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For the most demanding applications, such as steel-belted radial tires, optimum wire straightening mandates that the straightener be engineered to meet the most rigorous requirements, among them:
- Tight tolerances;
- Precise alignment;
- Durability;
- Consistency;
- Flexible orientation to match application-specific requirements.
Other applications may not require the tightest tolerances or the highest precision. For these applications, simpler straightening equipment is adequate to get the job done, though there is still a need for high performance to reduce downtime and operator setting difficulties. Because of the wide range of functions required, this article will address the performance and feature requirements of various applications, and advise the reader in the choice of the right wire straightener for specific needs.
Matching the Straightener to the Application
When the highest performance, precision, and flexibility are absolutely required, the EC straightener from Sjogren Industries is an excellent choice. Sjogren engineers have designed a wire straightener with precision-grooved rolls that holds the tightest tolerances in the industry (±0.025mm). These tried-and-true modular units combine vertical and horizontal straightening processes, mounted in tandem.
Built of precision ground stock instead of cold-rolled bar stock, EC straighteners feature roller centrelines as close together as possible, making it easier to set the wire and reduce twisting. Other features of the Sjogren EC that contribute to its high quality are swallowtail or dovetail mounting with an adjustable gib to improve performance, reduce setting time, and extend the life of the straightener; and locking handles to minimise wear on the roll plate
Multiple wires in close proximity
This type of application is best served by the Sjogren Narrowline straightener. The Narrowline is a slim single-plan design which offers quick opening for use in straightening multiple wires in close proximity to one another
The moderate straightness and/or ease of re-stringing that it delivers recommend it for:
- Strand galvanising lines;
- Strand annealing lines;
- Wire mesh welding plants;
- Weaving machinery
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EC Straighteners
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Maintaining consistency with existing straighteners
Completely adjustable straighteners are the choice when consistency with existing straightening technology must be maintained. They are built to accommodate individual adjustments on all rolls in:
- Spring making machines;
- Four-slide forming machines;
- General job shop work
Short-length products
Sjogren Tilt Rail straighteners are the choice when simplicity of adjustment is critical, or for producing short-length products. They feature adjustable rolls on a single rail which is adjusted by tilting the rail with respect to the fixed rolls, as in:
- Nail machines;
- Fastener machines;
- Strand lines.
Rod or large-diameter wire
Heavy duty single plane straighteners are the choice when rod or large-diameter wire must be straightened, as in:
- Cold-heading machines;
- Screw, bolt, and nut making machines;
- Straightening and cutting machinery.
Narrow wire
Light-duty single-plane straighteners are compact units for wire ranges from 1.5mm to 7.0mm. These straighteners are a good choice when cost is an important factor and quick opening is not required. |
Tilt Rail Straighteners
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Sjogren Narrowline Straightener
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Three-Roll Straighteners
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Simple straightening tasks
Three-roll straighteners are designed for simple straightening tasks. Because the output shape is affected by variations in input shape, adding more rolls provides additional bending cycles and minimises change in the output shape
Three-roll straighteners are used for:
- Simple back tensioning;
- Casting;
- Guiding the wire
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Heavy Duty Single Plane Straighteners
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Light Duty Single Plane
Straighteners
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How to Choose a Wire Straightener
Choosing the right wire straightener is not a simple process. In addition to consulting specific application requirements and operator preferences, a number of parameters must be determined beforehand if the straightener is to be sized accurately and the right grooved roll selected for the application.
Size of the straightener
To decide upon the size of the straightener, the following must first be established:
Input parameters of the wire:
- size: diameter or dimensions,
- material: steel, aluminium, copper, etc.,
- shape: solid, tube, cable,
- tensile strength of the material in units of kg/mm,
- surface conditions: coating, lubricant, etc.,
Process parameters:
- pay-off type: rotating spool, stationary spool with flyer,
- attitude of wire: curvature just prior to straightener,
- line speed: meters per minute,
- line temperature,
- line tension,
Output parameters of the wire:
- desired straightness: best is 0.12-0.15mm/m,
- desired out-of-straightness: cast or helix,
- increased process line tension: add back tension,
- effect on surface: marking, flattening, etc.,
- material properties: change in strength.,
Once the input, process, and output parameters are known, the type and size of straightener can be determined with confidence.
Sizing a straightener for non-rounded wire
With a straightener for wire other than round, a simple calculation equates the cross-section moment of inertia of the shaped wire to that of an equivalent size of round wire. That equivalent diameter is an aid to selecting the proper straightener size. For example, the formula for rectangular or square wire is:
Equivalent Diameter
= (1.7 x thickness3 x width)1/4
= (1.7 x width3 x thickness)1/4
For rectangular wire, the width dimension should not be larger than double the thickness. The formula for non-rectangular shapes is available from Sjogren sales professionals.
Number of planes
Next, the operator should choose the number of planes: one plane for cast removal or back tensioning, two planes for cast and helix removal
Number of rolls per plane
Finally, the operator must choose the number of rolls per plane. Five rolls are the minimum recommended for general straightening; seven or nine rolls the minimum recommended for better quality in straightening of product from soft materials such as mild steel up to 721 MPA tensile. As the tensile strength of the material increases, more rolls per section (up to 13) are recommended. The rule of thumb is, when in doubt, add more rolls. Additional rolls simplify adjustment.
Precision-grooved rolls
Precision-machined grooved rolls are key to quality straightening. Tolerancing of grooves for size, concentricity, centrality, and side run-out should be held as close to 0.025mm as possible. There are three roll-groove designs:
- Radius-groove style for dedicated size of round wire and tubing, or for closing of a stranded cable;
- Vee-groove style for a range of wire diameters;
- Special-shape groove to suit other wire shapes.
Radius-groove style
- Select this when only single-size wire needs to be run. A radius-groove roll does the best job of straightening and lasts longest, but it is the most limited in terms of the size of wire it will accept;
- A radius-groove style must be used for cable, or when marking may be a problem with material that has been plated;
- If marking is a significant problem, and a radius-grooved roll cannot solve it (as with gold or silver), a plastic or synthetic roll can be used, although it will not be as durable;
- For shaped material it is necessary to know the corner radius, particularly for square and flat wire;
- The corner radius must be obtained from the customer. Minimum corner radius is 0.13mm. If it is smaller, the engineering department must be consulted for custom fitting.
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Adjustable Straighteners
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Vee-groove style
- Standard vee groove is the most common and cost-effective choice;
- It offers the greatest range in terms of size of wire, allowing for change of wire size without roll changeover;
- The limitation of the vee groove becomes apparent when a given size of wire is used over an extensive period of time. The wire will begin to wear the vee groove.
Special-shape groove style
- For custom production a sketch or print from the customer will dictate the tolerancing;
- For special-shape grooves the actual diameter and tolerance are important;
- The customer will indicate the gauge.
Conclusion
Because of the complexity of straightener requirements and the many applications for wire tooling, it is wise to contact a wire straightener manufacturer to discuss exact requirements before making a final decision on type and size required for the particular application.
About the author:
Carl Sjogren is president of Sjogren Industries, a leading provider of high-quality machinery, tooling, and accessories for the wire and cable industry. The company manufactures a full range of wire straighteners, grooved rolls, pullers, roller guides, and permanent magnet brakes and clutches. Founded in 1927 by Carl Sjogren's grandfather, Sjogren Industries enjoys a 55% share of the wire tooling market in the United States. It recently announced a deepened commitment to Europe with sales distributors in ten European countries and production facilities in The Netherlands. Customer service world-wide includes distributorships in Korea and Taiwan.
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