Annealing Stainless Steel Braids
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Heating took just 2-5 seconds depending on the sample used, meeting the client's requirements.
Annealing Copper Tubing
A specially designed multi-turn helical coil was used to provide the required heat to the various copper tubes.
Annealing a Weld Seam (Steel Assembly)
To heat the weld seam of the steel part assembly
To heat a stainless steel tube
A custom-designed single-position multi-turn helical coil was built to generate the required heating for the application.
Annealing Springs for Stress Relief
Testing was successful, with a time-to-heat of 15 seconds. This client had been using an oven but was interested in changing to induction heating.
Annealing a Metal Plate
To heat a metal plate for an annealing application; the customer wanted to improve the heating time they were seeing with an open flame/torch.
Heating Steel Parts for a Bending Application
Clients are looking to upgrade cutting-tool torch brazing process with a fast, controllable and repeatable process.
Annealing a Magnetic Steel Strip
A custom-designed single position multiple-turn helical coil was built to generate the required heating for this annealing application. Initial tests were conducted to optimize the power delivered to the part.
Annealing Copper Wire Connectors
To anneal electrical crimp contacts of different dimensions. The client took advantage of THE LAB's expertise to prove out their process in a way that met their time, quality and budgetary requirements.
Annealing steel tubes in an inert atmosphere
Induction annealing heats steel tubes to °F ( °C) in an inert atmosphere for very small areas within precise production tolerances. A two-turn concentrator coil is used to heat the stainless steel tube. The annealing process takes place in an inert atmosphere to prevent oxidation.
Annealing a Weld Seam with Induction
The client is building a system with induction. Induction achieved the client's speed requirements and induction's modest footprint works well within the system. With induction you can expect the same result every time.
Anneal copper tubes; formed tubes & pipes
Induction annealing offers the same result every time, which makes it ideal for a high volume process such as this one. The previous oxidation issue forced them to polish the handles which added a step in their manufacturing process.
Annealing a stainless steel handle
The client wants to anneal a stainless steel tube while avoiding oxidation. Induction annealing offers the same result every time, copper tubes of various geometries heated to temperature in a matter of seconds, which makes it ideal for a high volume process such as this one.
Annealing brass ammunition casings
The ammunition industry has been annealing with inefficient methods which require much floor space, lack consistency, create excess inventory carry costs, and don't permit in-process inspections. Brass annealing with induction ensures each and every case is quality annealed, reducing variation and damage typically found in mass annealing processes.
Annealing stainless steel tubes
Annealing with induction heated the client's parts to the desired temperature in less than three seconds. Their previously-used gas oven required twice as much heating time as the induction heating process. Induction annealing is more energy-efficient and requires less space compared to a gas oven.
Annealing stainless steel tubing
Looking to replace an inefficient oven process, a stainless steel tube is heated in just 30 seconds, improving efficiency for this application. A custom-designed single position multi-turn helical coil was built to generate the required heating for this induction annealing application
Annealing a copper wire connector (crimp)
The client wanted to be able to anneal parts of various sizes, which was achieved with a concentrator coil. Induction annealing is a new process for the client, and Ambrell's lab expertise proved very valuable when creating the process...
Annealing steel wire for a medical application
Induction annealing achieved the targeted steel wire temperature within three seconds. Ambrell performed a free laboratory test, designed a cost efficient, in-house process and connected them with an automation partner to maximize productivity. The client now has better control over their end product.
Annealing stainless steel caps (dental)
Our client had a requirement to anneal large quantities of work-hardened stainless steel crowns. Induction was suggested for its precise, controllable heating. Since oxidation is unacceptable in the finished dental product, induction heating is the appropriate choice for heating in an inert atmosphere.
Annealing brass and bronze tubing (handrail bending)
Employing brass annealing with induction to form tubes into handrails, a twelve-turn helical coil was used to heat an 8 x 3 in (20.3 x 7.6 cm) area above the end of the tubes. Each of the four tubes require a different heat cycle and time to reach the required temperature.
Annealing a zinc wire prior to forming pellets for air rifles
A fourteen-turn coil is used to heat 3.9 in (100 mm) of zinc wire for this zinc wire application. The wire is placed in the coil for 5 seconds to reach the desired condition just prior to the forming process.
Annealing a hydraulic motor shaft prior to machining
A three-turn helical coil is used to anneal the steel hydraulic motor shaft. The end of the motor shaft is placed in the coil and power is applied for 20 seconds to reach °F (732 °C) and turn the steel red hot before machining.
Annealing aluminum fuel tank fill neck for bending
An eight-turn helical is used to heat the aluminum tube for annealing. To anneal the full length of the tube, the tube is placed in the coil and heated, and then the tube is bent while hot to prevent cracking.
Annealing of stellite tips on saw blades
To anneal the affected zone of a saw blade after the stellite tips have been welded in place, a split four-turn helical coil is used to allow the blade to move evenly through the coil. Each tip of the blade is heated for 5 seconds as it passes through the coil to anneal the affected area.
Continuous annealing of copper wire
To anneal a copper wire used in electric motors, a twelve-turn helical coil is used with an inserted ceramic tube to isolate the copper wire from the coil and to allow the wire to flow smoothly through the coil. Power runs continuously to anneal at a rate of 16.4 yds (15m) per minute.
Annealing lip on cryogenic dewar
A two-turn helical coil is used to heat the lip on the cryogenic dewar. The dewar is placed in the coil and power is applied for 2 minutes to anneal the required 1 heat zone...
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Anneal an oval cut-out on a stainless steel tube
To anneal an area around an oval cutout on a stainless steel tube prior to extrusion, a single-turn helical coil is used on the 4 (101.6mm) diameter tubes and a two turn helical coil is used on the smaller diameters.
Annealing the end of steel wire on a woven wire mesh
To prepare a wire mesh for press brake bending, induction is used to heat 3 in (76.2 mm) from the end of the wire mesh 60 in (1.52 m) long. This provides a faster production process, higher efficiency, lower energy costs and a fast, controllable hands-free process that involves no operator skill.
Annealing both ends of copper tubing for refrigeration
Induction heating applies heat to very specific areas, faster process time, increased production and high efficiency. In this application, both ends of a copper tube are heated to anneal them as soft as possible 1.5 in (38.1 mm) from each end, as well as retaining full hardness next to the anneals.
Annealing brass electrical contact for crimping
Induction annealing brass contacts provides hands-free heating that involves no operator skill, pinpoint accuracy and consistent results. To anneal a small area of an electrical contact for crimping, a one turn hairpin coil is used to heat the electrical contact to °F.
Annealing a steel shaft for stress relief
Flameless induction heating allows processes - formerly done in batch furnaces - to be done in-line saving time and energy. No rotation of parts is needed.
Annealing bolt shafts
A three-turn helical coil is used to heat the shaft of the bolts for 10 to 12 seconds on the large bolts and 18 to 20 seconds on the smaller bolts using the same coil. This allows for pinpoint accuracy and repeatability, cycle after cycle.
Annealing Lock Nuts
A three-turn helical coil is used to heat the locknut to Ă °F for 5 seconds. Induction heating provides repeatable, rapid and accurate heating cycles making it ideal for in-line production processes
Anneal the end of metal stamp sets
Induction annealing heats the end of a metal stamp to mushroom instead of cracking/splitting when struck by a hammer. Two helical coils are used to heat the ends to the required temperature. Two part sizes can be run in each of the coils, using the same machine settings except for cycle time.
Annealing stainless steel bread saw blades
Induction annealing improves blade quality, decreases scrap product and is easily incorporated into existing production lines. To anneal these stainless steel bread cutting saw blades, a three-turn helical induction heating coil is designed and developed for this application.
Annealing Tungsten Rods
A multi-turn induction annealing coil is used to heat various rod diameters. An optical pyrometer is used to measure the temperature of the part inside the induction coil. Initial static tests are conducted, then dynamic tests are run to confirm the results of the static tests
Band annealing on Titanium fasteners
Our bar-end annealing systems provide operating frequencies from 400 kHz for hot-heading of small diameter fasteners to 2 kHz for larger cross-section beams or bars. Systems can be incorporated with pick-and-place robotics to deliver a flameless process,with heating limited to a specific area.
Annealing Brazing Wire
Induction annealing provides higher productivity of 27' (8.2m) per minute, a reduction in surface oxidation & scaling with consistent, repeatable results. Four consecutive coils connected in parallel with a quartz tube lining are used to heat the wire to 650 °F for annealing.
Selectively Annealing Thread Ring Gauge Blocks
To selectively and uniformly anneal two sections of a thread ring gage block from the hole to the outside surface from a hardness of Rc 59-61 to Rc 45. Process goals include automation, production rate increase, and elimination of stress cracking resulting from flame heating.
Achieving Uniform Hardness on Saw Blades
Induction annealing is used to draw-back steel saw blades to a desired Rockwell hardness at a rate of 60 inches per minute. Resulting mean hardness of 50.3 Rc is measured for fifteen saw teeth on a Wilson Superficial Hardness Tester, fulfilling the ultimate goal established by the customer.
Induction hardening is being increasingly used within the gear industry. However, before looking at the advantages of the method, it is helpful to review the basics of the technology. The phenomenon of induction heating begins by passing an alternating current through a coil in order to generate a magnetic field. The strength of the field varies in relation to the strength of the current passing through the coil. The field is concentrated in the area enclosed by the coil, while its magnitude depends on the strength of the current and the number of turns in the coil. (Figure 1)
Eddy currents are induced in any electrically conductive object, a metal bar, for example, placed inside the coil. The phenomenon of resistance generates heat in the area where the eddy currents are flowing. Increasing the strength of the magnetic field increases the heating effect. However, the total heating effect is also influenced by the magnetic properties of the object and the distance between it and the coil. (Figure 2)
The eddy currents create their own magnetic field that opposes the original field produced by the coil. This opposition prevents the original field from immediately penetrating to the center of the object enclosed by the coil. The eddy currents are most active close to the surface of the object being heated, but weaken considerably in strength towards the center. (Figure 3)
The distance from the surface of the heated object to the depth where current density drops to 37% is the penetration depth. This depth changes in relation to various parameters such as heating times, initial material and choice of frequency.
Key features of induction hardening are fast heating cycles, accurate heating patterns and cores that remain relatively cold and stable. Such characteristics minimize distortion and make heating outcomes extremely repeatable, reducing post-heat processing such as grinding. This is especially true when comparing induction hardening to case carburizing.
Induction hardening also reduces pre-processing, as the geometry changes are less than those caused by carburizing. Such minimal changes mean distortion does not need to be accounted for when making the gear. With gears destined for gas carburizing, however, ‘offsets’ that represent distortion are often introduced at the design stage. These intentional offsets compensate for distortion caused during the lengthy heat soaks typical of carburizing.
Induction can heat precisely localized zones in gears. Achieving the same degree of localized hardening with carburizing can be a time- and labor-intensive procedure. When carburizing specific zones such as the teeth areas, it is usually necessary to mask the rest of the gear with ‘stop off’ coatings. These masks must be applied to each and every work piece, and removed following the hardening process. No such masking is necessary with induction hardening.
Induction hardening is ideal for integrating into production lines. Such integrated ‘inline’ hardening is more productive than thermo-chemical processes. Moreover, integrated hardening minimizes costs, as the gears do not have to be removed for separate heat treatment. In fact, induction heating makes it possible to create one seamless production flow through the machining, hardening, quenching, tempering and storage stages.
The induction heating method used for small- and medium-sized gears is often referred to as ‘spin hardening’. This is because the gear is placed within an induction coil and spins as the eddy currents are induced. Spin hardening can in turn be divided into two main methods: through hardening and contour hardening. With the first method—used primarily for gears exposed to high wear— the tooth perimeter is hardened with a low specific power. However, if the frequency is too low, there is the risk that above the Curie temperature the induced eddy current flows mainly in the root circle, and the temperature lags behind in the teeth. Quenching is either by submersion or spraying, and is usually delayed in order to achieve a uniform temperature between the teeth and the root circle. Tempering after through-hardening is essential in order to prevent later cracking.
Contour hardening is divided into single- and dual-frequency processes. With the former, a single generator feeds the inductor. Austenitizing is achieved either in a single heating, or by pre-heating the gear to 550-750° C before heating it to the hardening temperature. The purpose of pre-heating is to reach an adequately high austenitizing temperature in the root circle during final heating, without overheating the teeth tips. Short heating times and a high specific power are usually required to achieve hardening profiles at an irregular distance to the tooth face.
The dual-frequency process uses either separate or simultaneous frequencies. Using separate frequencies achieves hardening profiles similar to case hardening. The process applies two different frequencies one after the other to the gear. The teeth are pre-heated at a low frequency to 550-750° C. The frequency should be such that pre-heating occurs in the root circle area. After a short delay, use of a higher frequency and specific power achieves austenitizing. Accurate monitoring systems are essential, as heating times are measured in tenths of seconds or seconds during this final heating phase.
With the simultaneous dual-frequency method, a lower and a higher frequency feed into the inductor at the same time. Hardening is achieved by heating the root circle with the lower frequency, and the tooth tips with the higher (see Figure 4). Unlike the separate, or stepped, dual-frequency process, pre-heating is not always required when using the simultaneous dual-frequency process. However, the short heating times used with simultaneous frequencies place high demands on the generator and machine engineering. Figure 5 shows an example of a hardening profile achieved with this method.
Correct quenching is critical for perfect spin hardening results, and should be performed as soon as possible after the final heating. The time gap between heating and quenching can be minimized by using a fast CNC axle to position the spray head, or by integrating a quench circuit into the inductor. During the quenching phase the rotational speed of the gear is decreased to below 50 rpm to avoid a ‘shadow effect’ on the flank opposing the direction of rotation.
Many other factors influence spin hardening outcomes. The material to be hardened and its initial structure, for example, have a decisive impact. Due to short austenitizing times, the initial steel structure must be close-grained (ASTM 7 and above). Non-homogenous pearlite-ferrite initial structures are not suitable. The importance of initial structure and carbon content increases as module size decreases. If a somewhat increased quenching distortion is acceptable, inductive pre-quenching and tempering prior to contour hardening can greatly improve the gear’s hardenability.
Module size is another key factor in spin hardening. For the dual frequency method with simultaneous frequencies, the range is 2.2 < m ≤ 5mm. However, for cost reasons the gear diameter should be limited to approximately d ≤ 250mm. For modules of m ≤ 3.0mm, the separate dual frequency method is preferred. This is because a final hardening phase with only the higher frequency achieves better hardening at an irregular distance to the face. The single frequency method is almost exclusively used for internal ring gears with a module where m ≤ 1.25mm, such as those frequently used in automotive automatic transmission systems.
Spin hardening is a versatile and reliable process that can harden spur-toothed, helical spur and internal gears at an irregular distance to the face. However, different gear forms influence hardening results. With helical gearing, an asymmetrical hardening of the tooth flank at a depth of up to 2-3mm from the gear face has to be accepted. This situation is however only pronounced with helix angles of β ≥ 28°. Patented coil solutions are available that limit this effect by enhancing power distribution.
Correctly designed and built induction coils are absolutely critical for successful, cost-effective induction heating. In fact, designing and testing coils is often the process with the longest lead time when devising an induction heating solution. A key reason for this is the fact that coils are task specific. They must be designed to achieve specific results on specific materials under specific conditions. There are no—or at least there shouldn’t be—‘off-the-shelf’ coil designs.
Rigorous testing of a coil’s design and construction is essential. Too few people realize that coils are often the part most exposed to harsh operating conditions. Testing and computer-aided simulation is therefore sometimes needed to arrive at a design that is both safe and fatigue resistant. And of course, it takes repeated testing to achieve optimal part-heating patterns.
Nothing can be taken for granted when designing induction coils. With very high power density coils, for example, one even needs to determine the correct speed at which cooling water should flow through the coil. Too low a speed will result in insufficient thermal transference. But even when the correct speed has been found, the coil designer must decide whether a booster pump is necessary in order to achieve and maintain the desired water through-flow rate. The competent coil designer will also specify a purity level for the cooling water, in order to minimize corrosion on the inside of the coil. So something as apparently straightforward as the coil’s water, is in fact a complex matter demanding technical competence and specialist equipment.
Magnetic flux concentrators are another area of an overall induction solution that at first glance seems relatively straightforward. As the name suggests, the main function of such concentrators is to concentrate the coil’s current in the area of the coil facing the work piece. Without a concentrator, much of the magnetic flux is free to propagate around the coil. This uncontrolled flux will then ‘engulf’ adjacent conductive components. But when channeled by a concentrator, the magnetic flux can be restricted to precisely defined areas of the work piece, resulting in the localized heating zones characteristic of induction heating.
Many variables must be considered when making flux concentrators. The work piece’s material, the coil’s shape, the application—each influences the concentrator’s final design. Even deciding what material to use for the concentrator can be a complicated task. Basically, concentrators are made from laminations, or from pure ferrites and ferrite- or iron-based powders. Each concentrator material has its own drawbacks and advantages. Laminations have the highest flux densities and magnetic permeability; they are also less expensive as parts than iron- and ferrite-based powders. Laminations must however be stamped to a few standardized sizes and are therefore less flexible. They are also labor intensive to mount.
Pure ferrites can also offer outstanding magnetic permeability. However, they suffer from low saturation flux density, and their brittleness makes them difficult to machine (diamond-tipped cutters must be used). Iron powders are easy to shape, offer high flux densities, and are easy to shape. But great care must be taken to provide against over-heating, as internal losses or heat transfer from the heated part means such powders have a relatively low working temperature.
Of course, many other factors need to be considered when designing induction coils. Correct impedance matching between the coil and the power source, for instance, is crucial in order to use the full power from the power source. Plus the fact that coils need five to ten times as much reactive as active power.
As we have seen, a professionally designed and fabricated induction coil is an advanced, complex component. Unfortunately, too many induction users persist in viewing coils as low-tech copper tubes. The results of this misconception are incorrect and even dangerous coil designs, amateurish repairs, insufficient or incorrect maintenance, and ultimately, process and equipment failures.
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