Monday, December 7, 2009

WET WIRE DRAWING MACHINES

Wet wire drawing machines are suitable to draw low, high carbon and stainless steel wire. For certain applications like CO2 welding wire and steel cord wire for automotive tires special machines types have been developed.

The machines are generally designed and built to draw intermediate size wire from about Max 3.5 mm to 2.0mm to a finish size of 1.2mm - 0.6mm. and are generally of the so called wet slip type.

There are 2 basic wet slip machine types.

A)

    The machine where the elongation is compensated for by increasing the draw race rpm via the transmission gear ratios. These machines are generally designed to accommodate anywhere from 6-19 dies.
B)
    The cone type machine where the the elongation is compensated for by increasing the draw race diameters sequentially, are generally designed to accommodate anywhere from 12 dies to in some cases as many as 32 dies. This is done by using different machines executions with 2 or 4 or 6 and exceptionally 8 couples of drawing cones each with 5-6 draw races per shaft.

Both machine types as an inherent result of the design have fixed elongation ratio between each die. As a result the die sizes has to be selected so that the area reduction through each die is slightly higher then the theoretical area reduction that would match the fixed elongation. This way the draw race for the second die will pull through more wire than is called for by the 3rd and subsequent drawraces and as a result the wire will constantly slip on the draw races. The slip factor is normally 1-3 %. While the finish diameter can be determined and adjusted by varying the inlet diameter and the reduction taken through the inlet die plus the number of draw races used the slip factor can to a degree also be used to fine tune a draft serie.

Below is a number photos of various machine types.

Steel making a brief introduction

For some steel wire products the wire rod represents more than 80% of the variable cost of the production. It therefore seems appropriate to dedicate a chapter to the process of steel making and the various techniques employed in producing the wire rod. This way the viewer gets a better understanding of the up-stream process steps that are neccessary to provide a wire rod that meets the specific requirements of the end product of various wire products.

Process flow chart

Electroplating

Electroplating is the process of producing a metallic coating on a surface by electrodeposition - i.e., by the action of an electric current. Such coatings may perform a mainly protective function, to prevent corrosion of the metal on which they are deposited: e.g., plating with zinc (electrogalvanizing) or with tin; or a decorative function: e.g., gold and silver plating; or both functions: e.g. chromium plating. The principle of electroplating is that the coating metal is deposited from an electrolyte - an aqueous acid or alkaline solution - on to the base: i.e., the metal to be coated. The latter forms the cathode (negative electrode). A low-voltage direct current is used; the anode is gradually consumed. Various substances (addition agents) are added to the electroplating bath to obtain a smooth and bright metal deposit. These are principally organic compounds, usually colloidal. Sometimes the objects to be plated are coated with two or more layers of different metals; for example, chromium plating cannot suitably be applied directly to a zinc-sprayed base; a coating of copper followed by a coating of nickel must be applied intermediately before the chromium is deposited.


Photo courtesey of Outokumpu WTT AB

To obtain a good and firmly adhering coating it is necessary to subject the objects or components to a thorough cleaning.. This may be achieved by by degreasing with organic solvents; or by chemical methods such as pickling with acid or degreasing by the action of alkalizes (saponification); or by electrocleaning, which is a method of cleaning by electrolytic action (more particularly the scrubbing action exercised by the evolution of gas at the surface of the metal). Wetting agents or emulsifiers may be added. The vats for electroplating baths differ greatly in size, shape and lining material (glass, lead, etc.), depending on the size and shape of the components to be plated and on the chemical character of the bath. Electroplating is normally done with direct current. However, particularly with cyanide copper baths, improved smoothness and uniformity of the coating can be obtained by means of the so-called periodic-reverse process, in which the polarity is periodically reversed, so that the metal is alternatively plated and deplated.

Wire is plated with zinc or with tin in continuous and largely automated high-speed processes. The electrolytic zink-plating process illustrated schematically above and in the picture below comprises the following operations: electrolytic cleaning in dilute sulfuric acid, pickling, electrodeposition of zink, so called progressive rinse and air wipe drying after which the wire is taken up on a carrier or spool.

Multi-wire and single-wire Electroplating plants like the one shown in the above picture are available for all types of electroplating and are designed in accordance with the customer's specification. The modern equipment offered includes a newly developed systems for plating at higher speeds (higher current densities) of zinc and copper, with acidic electrolytes. Wires of different diameters can be plated in the same plant. Typical applications include nickel and copper on stainless steel, tin and nickel on steel or copper alloys, silver on copper alloys, zinc on steel (staple wire) and brass on steel (tire cord).

Ione Exchange Plating

When steel wire is submerged in a solution of copper sulphate CuSO4 sulphuricacid H2SO4 and water the surface ions on the iron Fe steel wire surface will go into solution. As this happens the steel wire will get slightly negatively charged and attract a positively charged copper Cu ion. Hence the process name ione exchange plating. The process is commonly used in the production of copper coated MIG welding wire and office staples. It is imperative that the wire surface is clean prior to entering the plating solution. The Fig below shows the princip of an continous plating line.


In line cleaning and plating line

Plating tank courtesey of
Welding Wire Machineries s.r.l.

Plating tank courtesey of
Outokumpu WTT AB

Cleaning - Single Wire

In line high-speed single-wire cleaning system in which compact equipment operates in front of and in-line with a wire drawing machine. The operation is based on either a hot water process or electrolytic pickling, and can handle sizes ranging from rolled wire rod to fine-gauge wire. The plant is available in a standard version, but with a multitude of variants. Typical applications include cleaning of cable wire, stainless steel wire, CO2 welding wire, wire of various copper alloys, and cleaning before drawing.


Candojet patented single-wire cleaning system
Courtesy of Outokumpu WTT AB

Cleaning - Multi-Wire

While batch cleaning lines are still widely used modern wire cleaning lines are continuous and can be supplied either as standard units or as customized systems. The plants have several parallel wire tracks and is based on either bipolar electrolytic cleaning or ultrasonic cleaning, or combinations of these two methods. The system is suitable for both degreasing (alkaline cleaning) and pickling (acidic cleaning). Typical applications include cleaning before annealing, hot-dip tin plating, and hot-dip galvanizing.

Chemical (caustic and acid) cleaning.

Prior to plating the wire surface needs to be cleaned and lubricant residue removed from the surface. A clean wire surface is imperative to obtain good adhesion to the wire surface of the plating metal. Batch cleaning lines are still widely in use but continuous single and multistrand process lines is the widely accepted state of the art for wire cleaning be it a chemical, electrolytic ultrasound or aggitated process. The Q.E.D. Multiple Stage High Turbulence™ Pickling System is a patented state of the art high speed wire cleaning process. With tanks constructed of composite materials and using advanced fluid flow technology, the design guarantees reliability and efficient pickling within a minimum length. This environmentally friendly system is a totally enclosed design that prevents acid fume escape.

Features

Highly Turbulent acid flow
Multiple stage cleaning
Straight through wire path
Double water curtain sealing
Three stage cascading rinse
Threading & Wiping Systems
Self draining acid trays
Low maintenance design
Rugged construction

pickling_system.jpg (14323 bytes)


HighTurbulence™ - Exceptional Cleaning at High Wire speeds!

highturbulanceline.jpg (13641 bytes)

The High Turbulence™ acid section represents the latest development in acid cleaning technology. The carefully designed flow patterns effectively break down the boundary layer pocket of spent acid adjacent to the wires, thus continuously supplying fresh acid to their surface. Pickling speed is further increased by the effective scrubbing action of the turbulent acid flow.

In keeping with today’s energy conservation concerns the acid section is designed in a series of modular stages, with each section having a separate optimally sized corrosion resistant pump, turbulence tray and re-circulating loop. The multiple stage design allows for lower acid consumption, by the efficient "stepping" of acid concentration levels. The modular system also ensures a lower spare parts inventory cost and eliminates the need of costly back-up pumps. The system can be operated at temperatures of up to 85 0C (185 0F) with a maximum of 20% HCl acid concentration.

The two entrance curtains and two rinse curtains are supplied with re-circulated water through special corrosion resistant pumps. The smooth laminar flow curtains effectively seal in the acid fumes and flood the rinse trays. The final rinse is accomplished by high pressure water spray.

Optional Features

Acid Heat-Exchanger
Quick lift-off hood
Temperature control system
Cooling Tower
Computer interface package

pickle_piping.jpg (20388 bytes)



All pictures on this page courtesy of Q.E.D.

Furnace Types

Fluidbed Furnaces

Used for:
Annealing, Tempering, Stress Relieving, Patenting,

Quenching Lead Furnaces

Used for:
Annealing, Tempering, Quenching, Patenting,

Muffle or Tube Furnaces

The Muffle or Tube Furnaces are built for the continuous in-line austenitizing or annealing of multiple wire strands. High velocity burners are mounted along both sides of the furnaces in a staggered pattern that produces excellent temperature uniformity. Pressure controled combustion available on some furnaces gives a high turn-down ratio and efficient multiple burner control.

Direct Fired Muffle and Tube Furnaces

Direct Fired Furnaces like the Muffle or Tube Furnaces are built for the continuous in-line austenitizing or annealing of multiple wire strands. High velocity burners are normally mounted along both sides of the furnaces in a staggered pattern in order to produce temperature uniformity. Generally used for: Austenitizing stainless steel wire

Annealing Oil Tempering Lines

Oil Tempering Lines consist of an Austenitizing Furnace, Quenching System, Tempering Furnace and Cooling and Coating Tanks. The Austenitizing Furnace can be Direct Fired, Fluidbed or Muffle Tube for atmosphere control. Following the heating section, the wires are rapidly quenched in a cooling medium of mineral based oil or water based polymer fluids.

Bell Furnaces

Bell furnace processing provides better control of the cooling process and also allows for a slower cooling period where the temperature can be held at a fixed intermediate temprature for an extended period. Bell Furnaces also allow for a more homogeneous and faster heat transfer.

Salt bath furnaces

Salt bath furnaces are used for a number of heat treatment applications such as: Preheating • Austenitizing • Martempering • Neutral Hardening • High-Speed Tool Hardening • Tempering Nitriding • Carburizing • Solution Heat Treating • Dip Brazing Modern systems offer quick ramp-up and high heating uniformity

Salt bath furnaces

Modern Salt bath furnaces are used for a number of heat treatment applications such as: Preheating • Austenitizing • Martempering • Neutral Hardening • High-Speed Tool Hardening • Tempering Nitriding • Carburizing • Solution Heat Treating • Dip Brazing

Modern systems offer quick ramp-up and high heating uniformity with temperatures maintained to within 5 degrees throughout the bath providing high and uniform processing results

Today's furnaces are heated by electricity, oil or gas. In procuring Salt Bath Furnaces special attention should be given so operator safety standards and local environmental requirements are met and that waste treatment technologies involved meet government regulations and provide for a comprehensive and cost-effective waste management such as effective sludge removal systems.

Modern systems included modular stages in order to accomodate pre- and post-treatments that are combined with fully programmable controls that offer precise in-line processing capabilities.

Typical wire and wire rod applications include: Annealing •Nitriding •Melting •Tempering •Hardening •Brazing •Galvanizing •Aluminizing as well as Surface treatment of various metals & alloys

Typical processing tempratures for wire applications are 500°C to 1100°C (900°F to 2000+°F)

The electrically heated furnaces are equipped with either resistance or silicon carbide heating elements, mounted externally to either a square or round metal pot holding molten media.


At elevated temperatures silicon carbide heating elements are prefered. The elements are made in one piece from high-density, high-purity, self-bonded silicon carbide.

For a round pot furnace helically-wound wire heaters are a common configuration.

Schematic view of Furnace with over - the - top mounted electrodes
Features include: 6" thick tile walls make the pot last for years. The removable electrodes can be changed without emptying furnace.
The use of large cross section electrodes assure long heater life and provides electrodynamic circulation for uniform temperature.


Furnace with submerged electrodes Operating temprature 850&degC to 1260&degC (1550°F to 2300°F) for Austenitizing

Submerged electrodes provides long life & trouble free service with periodic maintenance. Electrodes, embedded in the wall, below the salt line,are sealed against corrosive attack at the air-salt interface. The submerged electrode design also lends itself to economical 3 phase operation in deeper furnaces when 2 or more tiers of electrodes are utilized.

Isothermal Quench Furnaces
For Austempering & Martempering

Molten salt quenching for austempering or martempering requires a furnace capable of several functions, and the resulting designs are much different from salt bath furnaces employed in heating or austenitizing work.

Four primary factors should be considered for all Quench Furnaces:

1.Bath Temperature Uniformity is essential for consistent metallurgical properties. Internal heating of the bath can be accomplished electrically by using either immersion heaters or electrodes. Gas-fired immersion tubes can also be employed. It is important to automatically dissipate heat from work being quenched by either internal or external cooling means. For light duty, forced air or air/water can be directed to the exterior of the pot. For heavy duty, controlled cooling is provided by internal coils, using water or air/water injection.

2.Proper Agitation of the bath is necessary to remove heat quickly and efficently from the work.mConstant or variable speed propeller agitation provides a uniform flow through the workload being quenched.

3. To achieve optimum hardness and other physical properties, foreign bath contaminants must be removed. In most furnaces this is accomplished by a continuous filtering and automatic dumping. A common system like that supplied by AJAX Electric Company comprises a scoop-shaped filter basket connected to a driving cylinder mounted adjacent to the furnace wall, the basket is automatically raised up and out of the bath - automating chloride removal. Readily installed on new furnaces, the mechanism can also be retrofitted on existing salt baths.

4. For isothermal quenching of heavier sections, water increases quenching power. Small amounts of water added to a nitrate-nitrite salt drives vapor from the bath as hot work enters and gives a faster cooling rate. Both manual and automatic systems are available for adjusting the frequency and duration of water additions.

Bell Furnaces

The advantage with Bell furnace processing versus continuous furnace processing is mainly that the cooling process can be more closely controlled. For example a long cooling period with the temperature held at the AR1 (Arret refrois) point in the steel carbon diagram will result in the formation of large perlite crystal structure in the steel producing a soft malleable and ductile wire suitable for cold heading.

Another advantage with Bell Furnaces is that the convection system can not only transfer the heat homogeneous and faster, but the convection-speed can also be adjusted to the temperature of the annealed wire i.e. Convection speed can be automatically changed with the annealing heat.

There are two basic types of bell furnaces. The vacuum furnace and the protective (inert) gas furnace.

The vacuum furnace as well as the protective (inert) gas furnace will both produce a wire surface free from oxide suitable for plating or coating.

The vacuum furnace is more energy efficient and is gaining market share.

Oil Tempering Lines

Q.E.D.'s Oil Tempering Lines consist of an Austenitizing Furnace, Quenching System, Tempering Furnace and Cooling and Coating Tanks. The Austenitizing Furnace can be Direct Fired, Fluidbed or Muffle Tube for atmosphere control. Following the heating section, the wires are rapidly quenched in a cooling medium of mineral based oil or water based polymer fluids. The quench fluid is temperature controlled and re-circulated through a cooling heat-exchanger and filters. After wiping, the wires enter the Tempering Section that is usually a Fluidbed Furnace but can also be a Lead Furnace.
oil line.jpg (12387 bytes)

Quenching System

The Quench Tank is designed on the "overflow" principle. The tank is constructed in two pieces, the tray section where the wires will be quenched and a reservoir tank below to catch the overflow oil/quench fluid. The oil will be pumped from the reservoir tank through a heat exchanger and strainer to the tray section. The pump rate is sufficient to create the high turbulence and agitation necessary to provide uniform quenching. Two pumps are supplied, one operational and one stand-by, complete with a duplex inlet strainer, and mounted on a common steel base.
Dump Tank
The quench system is supplied with a dump/holding tank located below the main quench tank in a purpose made pit in the floor. The oil in the quench tank is automatically evacuated to the dump tank in the event of a serious fire. A fusible link valve is installed in the dump line and is designed to open if the link is broken by heat. A pump is provided to return the oil back to the quench tank.
Fume Hood and Extraction
A full length fume hood is constructed to remove the smoking oil fumes above the quench tank. An extraction fan, damper assembly and duct work discharge them to atmosphere. The fume extraction system can be used in conjunction with our optional afterburner combustion system.
Control System
During normal operation the oil temperature is controlled by cooling through an air-oil heat exchanger. A cooling temperature controller governs the operation of the fans in the heat-exchanger. At start-up the oil is heated to operating temperature by electric immersions heaters controlled by a heating temperature controller. A quench tank low oil level switch and low oil flow switch provide warning alarms prior to the system reaching a dangerous condition. Additional alarms and interlocks are provided for high oil temperature, exhaust fan operation and pump operation.
Wiping System
A two stage soft rubber pad wiping system is used to wipe the majority of the oil from the wire surface. The excess oil that is removed by the pads drains back into the oil quench tank.

Direct Fired Furnaces

Direct Fired Furnaces like the Muffle or Tube Furnaces are built for the continuous in-line austenitizing or annealing of multiple wire strands. High velocity burners are normally mounted along both sides of the furnaces in a staggered pattern in order to produce temperature uniformity.

The combustion systems are on most modern furnaces arranged in multiple zones of control and can be either oil, gas or dual fuel fired. Layers of refractory line the furnace to maintain efficient operation and establish low skin temperatures. Todays furnace shells are of welded steel construction divided into modular units with bolted flanges.

Direct Fired Furnace


sketch courtesy of qed

With the burners firing above the wire field, an effective convection flow pattern is established for improved heat-transfer. The wires are supported above the hearth on special wear resistant castable piers. Careful control of each zone’s combustion ratio minimizes scale formation while optimizing fuel efficiency. A charge end adjustable height door assures precise furnace pressure. Many furnaces are designed with a rather long pre-heat section using counter flow exhaust gasses to increase efficiency. A special discharge chamber at the furnace exit provides the wires a protective atmosphere during transition to the subsequent process.

Muffle Tube Furnace

The Muffle or Tube Furnaces.like the Direct Fired are built for the continuous in-line austenitizing or annealing of multiple wire strands. High velocity burners are mounted along both sides of the furnaces in a staggered pattern that produces excellent temperature uniformity. Pressure controled combustion available on some furnaces gives a high turn-down ratio and efficient multiple burner control.

On most modern furnaces the combustion systems are arranged in multiple zones of control and can be oil, gas or dual fuel fired. Several layers of high quality refractory lining on the furnace gives efficient operation and establish low skin temperatures. The furnace shells on most modern furnaces are designed with a robust welded steel construction divided into modular units with bolted flanges.


The wires travel longitudinally through the furnace in individual protective atmosphere muffle tubes. Flow meters supply inert gasses to each special alloy
tube that is supported above the refractory hearth. The burners are mounted below the tubes and effectively heat their surface by radiation, convection and conduction. The combustion chamber is sealed to insure safe operation and a high thermal efficiency. It is important that the selected components are of the highest quality to ensure a long trouble free life

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