The art or process of wire drawing like the name implies is to draw a wire of a bigger diameter through a hole with smaller diameter hereby reducing the diameter through plastic deformation while the volume remains the same.

To do this a tool called a drawing die is used. See picture below.

If we assume that the inlet Diameter = Do and the length of the wire prior to drawing = Lo then the cross section Area prior to drawing Ao is Pi/4 x Do^2 and the volume V = Lo x Ao

If the diameter after it passed the die is D1 then the cross section Area after the wire has passed through the die is A1 and A1= Pi/4 x D1^2 and since the volume remains the same i.e. V = Lo x Ao = L1 x A1 where L1 is the length of the wire after it has passed through the die.

The ratio of length after drawing to the length prior to drawing L1/Lo is called elongation.

1 - A1/Ao is called the area reduction

and 100 x (1 - A1/Ao) is called percentage of area reduction.

Wire defined as a round string of metal dates back to early civilization 3000 B.C or earlier. The process of producing a wire by drawing a round piece of metal through a drawing die hereby reducing its diameter dates back to around 1300 A.D.

Here we will not dwell more on the history of steel wire drawing other than establish the fact that the industry continues to improve the manufacturing process.

We will instead present the various machine types in use and point out the features of the various designs.

The most common steel wire rod diameter is 5.5 mm or 7/32"

Steel wire work hardens during plastic deformation and the ductility (the degree of elasticity) is reduced while the tensile strength increases.

In general it is possible through subsequent or sequential passes through ever smaller dies to reduce the cross section area of a wire between 85-95%.

Further area reduction will require an intermediate anneal to restore ductility.

The degree of total area reduction possible without intermediate annealing depends on the composition of the steel.

A high carbon steel wire without alloys like rope wire can be drawn from size 5.5mm to size 1-0.8mm, while a carbon steel wire with 1.8% Manganese (Mn) work hardens with less amount of area reduction.

In order to establish production practices it is therefore necessary to know the work hardening characteristic of the steel quality (=grade) you want to process.

We will not elaborate further in this chapter but the importance becomes apparent by the following example.

A MIG welding wire of grade DIN 8559 SG2 (typical alloy composition C 0.1% Si 0.85% Mn 1.5%) can be drawn from size 5.5mm - 1.2mm without an intermediate anneal, while a MIG welding wire of grade DIN 8559 SG3 (typical alloy composition C 0.1% Si 1.0% Mn 1.7%) requires an intermediate anneal.

However a MIG welding wire of grade DIN 8559 SG2 (typical alloy composition C 0.1% Si 0.85% Mn 1.5) can be classified as of grade AWS A 5.18:ER 70S-6 as long as the Mn content is over 1.4 as the AWS classification (American Welding Association) for grade 70S-6 calls for 1.4-1.8% Mn

The maximum amount of area reduction theoretically in each die pass, if there was no friction and the inlet tensile before passing through the die and after it had passed through the die was the same is 50%. In reality there is friction and there is an increase in tensile as the wire passes through the die.

In a single pass it is often possible for low carbon steels like grade C 1006 wire for rebar to take as much as 40% area reduction.

However in products where subsequent draws are needed to reach the desired finish diameter much lower area reductions are used.

For a draw from 5.5mm inlet to 2 mm the standard is to choose an average area reduction per die of about 30%.

A lower area reduction per die gives you less of a reduction in ductility.

Pheripherals

Pointers

Typical driven roll pointer

Detail of roll assembly

Pointers as the name implies is used to put a taper (or point) on the start end of the wire so that it can be threaded through the die

Pull in dogs

Pull in dogs are used to grip the wire end as it comes through the die and once the dog is fastend to the block the wire can be pulled through the die and will then wrap round the block

Butt welders

Butt welders are used to join wire ends. This is done through resistance welding.

Single block machines

The wire enters the block via a die and on to the block where it collects.

From 1^st die wire enters a block with an 18" race the Wire wraps round the race 3-5 wraps and then exits out via the pulley on the left of the machine from which it enters the 2^nd die and on to the upper block race that has a diameter of 24". Note that while the area reduction through the first die can vary from around 25% up to about 35% the area reduction in the 2nd die must be bigger than 25% i.e. exceed the elongation of the block ratio 24" to 18" This means that the area reduction must be 1-18"/24" + a slip of ca. 2%

The wire then wraps around the 2^nd block race which is slightly tapered so that the wire can slip upwards on to 4-6 collector pins where the wire accumulates. The wire then exits the upper section (or collector pin section via a spinner arm and over the payoff pulley located over top. The spinner back tension can be adjusted via a disc brake.

Bull Block with riding stripper equipped to operate with either 1, 2 or 3 dies.

This type of machine is popular among producers of rebar and weld-mesh.

Note the inlet roller gate on the first die box that can direct the wire either to the 1^st (16") 2^nd (22") or 3^rd (30") draw-race allowing any wire size from 25mm down to 3.25 mm to be produced in one single operation from wire rod that range in size from 32mm - 5.5mm.

View of large riding stripper of collapsible type.

Before the operation starts the stripper is placed on top of the stripper block and secured (see picture above). During processing wire will collect on the block and the stripper. When full the stripper will be lifted by a crane and the wire stripped off the block. The stripper with the wire is then moved over a tubular carrier and collapsed where by the wire drops down over the carried.

View of Inverted Bullblock or Gravity Block

Inverted drawing machines (or Gravity Blocks) have a special range of applications.These machines are mainly used for coarse wire sizes, which have to be delivered on carriers with higher weights as achievable with a stripper block. Used in place of the conventional vertical type block for drawing or coiling wire that requires a mar free surface such as a plating quality wire.

View of Bullblock mounted on horizontal shaft

The drawing block can also be placed on a horizontal shaft with the wire moving axially along the block from which it falls off the block on to a carrier. These kind of machines are commonly used for cold heading wires with wire inlet diameter sizes of up to 50 mm

In order to draw wire through a number of sequentially placed drawing blocks an array of different machine types have been developed. As drive motors and controls became more affordable machinery builders were able to develop machinery that were both faster and more productive requiring less and less labor per ton produced. However a lot of machinery are still in operation why it is warranted to describe the more common types.

Note that the first block on the machine has 2 drawing races allowing the inlet block to pass 2 consequtive drawing dies before entering block 2. The wire exits the first block via a stationary pulley makes a loop round a pulley mounted on a springloaded arm and then enters the next die via a pulley placed on the soap box goes through the die and on to the 2nd block. The positioning of the loop arm on block 1 regulates the speed on the second block and the positioning of the loop arm on block secondblock regulates the speed on the following (3rd) block etc. The main feature with the loop arm machine was that it allowed the wire to pass from block to block in a straight line without the twist in the earlier overtop machines. A feature shared with the B-B machine shown but with the added advantage of less maintenance. When the Vaughn machine company originally introduced the machine it was powered by a DC motor generator set that fed a common armature voltage to all the individual drive motors and the positioning of the loop arm regulated the motor field voltages. Thousand of these machines were built until 1976 when the company went out of business. We show this machine simply because 25 years later there are still many machines in operation.

8-block wire drawing machine of tuner line type

Several suppliers to day offer sensor roll control machines. Below is a photo of Eurodraws MTS 1200 machine

GENERAL FEAUTURES

The MTO machine by Euraw draw is a multiple-block machine with horizontal-axis drawing capstans, sensor arm speed synchronization and an additional dancer arm on the finishing block. The high degree of automation and remarkable efficiency of MTO drawing machines, coupled with their sturdy, low-maintenance mechanics, contribute to achieve high quality production at the lowest possible operating cost.

DRAWING BLOCKS

MAIN BLOCK FRAME

TRANSMISSION

MAIN MOTORS

SENSOR ARMS

DIEBOXES

SAFETY GUARDS

WATER COOLING AND VENTILATION

ELECTRIC EQUIPMENT

Speed is adjusted as follows:

with constant torque: from 0 to max. speed with constant power: max. speed + 50% The stability and synchronism of each motor is controlled by an electronic data processing system which compares the reference signals with the data coming from the A.C. motor taco generators and angle transducers on the sensor arms, and acts on the motors accordingly. The angle transducers are specifically installed to achieve the area reduction range specified in the drafting table. The sensor arms are automatically centered while the machine is running. The dimensions of the electric cabinet comply with container shipping requirements (max. height 2000 mm). Standard machine is colored in blue, yellow and white, with oven-dried epoxy powder The electrics are contained in a modular, dust-proof cabinet equipped with an air/water heat exchanger, access doors at both front and back, and removable side panels.