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Eurotherm Controls Inc / Barber-Colman Company An Invensys company Metal Heat Treatment » Processes » Equipment » Controls.

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Presentation on theme: "Eurotherm Controls Inc / Barber-Colman Company An Invensys company Metal Heat Treatment » Processes » Equipment » Controls."— Presentation transcript:

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2 Eurotherm Controls Inc / Barber-Colman Company An Invensys company Metal Heat Treatment » Processes » Equipment » Controls

3 Eurotherm Controls Inc / Barber-Colman Company An Invensys company THE HEAT TREATING PROCESS THE HEAT TREATING PROCESS Heat treated components are essential to the operation of… automobile, aircraft, spacecraft, computers, heavy equipment of every kind, wood working tools, bearings, axles, fasteners, camshafts, cutting tools, gears, etc. vast majority of material heat treated is iron & steel alloys of aluminum, copper, magnesium, nickel, and titanium may also be heat treated

4 Eurotherm Controls Inc / Barber-Colman Company An Invensys company THE HEAT TREATING PROCESS THE HEAT TREATING PROCESS metal components are heated & cooled under tight controls improves properties, performance & durability can soften the metal - improve formability can harden the metal - improve strength can put a hard surface on relatively soft metal - improve abrasion (wear) resistance can create a corrosion - resistant skin… inhibits corrosion can toughen brittle products

5 Eurotherm Controls Inc / Barber-Colman Company An Invensys company THE HEAT TREATING PROCESS THE HEAT TREATING PROCESS Requires three basic steps: 1 heating to a specific temperature 2 holding (soaking) at that temperature for the appropriate time 3 cooling according to a prescribed method heating temperature range to 2400 0 F (1316 °C) soaking times vary from a few seconds to 3 to 4 days cooling may be slowly in the furnace or quickly (quenched) into water, brine, oils, polymer solutions, molten salts, molten metals or gases 90% of metal parts are quenched in water, oil, polymers, or gases

6 Eurotherm Controls Inc / Barber-Colman Company An Invensys company ANNEALING heat material for several hours at elevated temperatures (2000 0 F) (1093°C) control slow cooling facilitates cold working & machining, improves ductility and some electrical properties and promotes dimensional stability STRESS-RELIEF heat material for several hours at an intermediate temperature (1250 0 F) (677°C) control cooling removes stresses resulting from processes such as cold working, casting, forging, or welding

7 Eurotherm Controls Inc / Barber-Colman Company An Invensys company NORMALIZING heat material at elevated temperatures for varying time soaks control cool in air results in homogeneous microstructure - provides better machinability & more uniform properties QUENCH HARDENING primary heat treating process for strengthening steel components heat material to an elevated temperature (1600 0 F) (871°C) rapid quench to develop hardness this is followed by TEMPERING… reheat material to a low temperature (400 0 F) (204°C) to develop specific mechanical properties, to relieve quench stresses and to insure dimensional stability

8 Eurotherm Controls Inc / Barber-Colman Company An Invensys company GAS CARBURIZING heat material at elevated temperatures (to 1850 0 F) (1010°C)for varying soak times (dependent on case depth requirement) while soaking, provide a high carbon atmosphere source from a hydrocarbon gas such as methane (natural gas) or propane resulting chemical combination vs. the gaseous carbon and the iron, from the steel components provides an iron carbide compound on the surface high carbon surface layer is called case typical case depths vary from.010 to. 150 furnace cool to stabilizing temperature (1550 0 F) (843°C)for varying soak times rapid quench to develop high case hardness and desired core properties temper by re-heating to a low temperature (350 0 F) (177°C)to develop specific case and core properties, to relieve quench stresses and to insure dimensional stability

9 Eurotherm Controls Inc / Barber-Colman Company An Invensys company

10 Eurotherm Controls Inc / Barber-Colman Company An Invensys company CASE DEPTH Case is accomplished by carburizing and quenching The objective is to provide a hard wear resistant surface layer and maintain a softer core Case depth is typically measured in thousandths of an inch (.037in). Typical range specs are.018 to.025,.032 to.038,.038 to.045 etc. Case depth is generally measured as the depth of penetration from the surface with a hardness above Rc 50 or carbon concentration above.40 C

11 Eurotherm Controls Inc / Barber-Colman Company An Invensys company STEEL GRADES Grades of Steel Typically Heat Treated 1000, 1100, 1200, 1300, 1500 4000, 4100, 4600, 5100, 6100 8600, 9300 series 1040 =.37 to.44 carbon content Standard carbon steel 8620 =.18 to.23 carbon content Carburizing grade alloy steel

12 Eurotherm Controls Inc / Barber-Colman Company An Invensys company CARBURIZING Provides abundant supply of carbon for absorption into surface of steel Provides increased carbon and hardness to surface of steel Case depth is time and temperature dependent At 1700°F (927°C) and.9%C settings using a conventional 40% Nitrogen, 40% Hydrogen, and 20% Carbon Monoxide in an Endothermic atmosphere: AfterAchieve Effective Case 1 hour.62C.012 4 hours.71C.026 20 hours.86C.061

13 Eurotherm Controls Inc / Barber-Colman Company An Invensys company Heat Treating Solutions Heat Treating Solutions Simple Boost and Diffuse

14 Eurotherm Controls Inc / Barber-Colman Company An Invensys company CARBONITRIDING Heat material at elevated temperatures (1650 0 F) (899°C) for varying soak times (dependent on case depth requirement) while soaking, provide a high carbon atmosphere source from a hydrocarbon gas such as methane (natural gas) or propane AND a high nitrogen containing gas (ammonia) resulting chemical combination vs the gaseous carbon, nitrogen, and the iron, from the steel components provides an iron carbide/nitride compound on the surface high carbon/nitrogen surface layer is called case furnace cool to stabilizing temperature (1550 0 F) (843°C) for minimal soak time rapid quench to develop high case hardness and desired core properties temper by reheating to a low temperature (300 0 F) (149°C)to develop specific case and core properties, to relieve quench stresses and to insure dimensional stability

15 Eurotherm Controls Inc / Barber-Colman Company An Invensys company HEAT TREATING SOLUTIONS HEAT TREATING SOLUTIONS CarboNitriding

16 Eurotherm Controls Inc / Barber-Colman Company An Invensys company EQUIPMENT most components are heat treated in furnaces most furnaces heated with natural gas fuel - some electric two broad categories of furnaces… BATCH and CONTINUOUS in batch, material is charged/discharged as a single unit or batch in continuous, material is conveyed automatically, providing a constant flow

17 Eurotherm Controls Inc / Barber-Colman Company An Invensys company EQUIPMENT BATCH consists of insulated chamber with external steel shell has a heating system for the processing chamber has one or more doors providing access and sealing of the chamber may have internal quench tank or slow cool vestibule typically has automated controls

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21 Eurotherm Controls Inc / Barber-Colman Company An Invensys company EQUIPMENT CONTINUOUS same basic components as Batch, but… has means of conveying material through the process zones some types are PUSHERS, BELT or chain conveyors, ROLLER HEARTH, SHAKER HEARTH, ROTARY HEARTH, ROTARY RETORT and WALKING BEAM has a multi-zone heating system for the processing chamber(s) has doors or screens providing access and isolation typically has multi-loop automated controls size ranges from 100s lbs/hr to ± 10000 lbs/hr some continuous may have automated, self-contained quenching capability

22 Eurotherm Controls Inc / Barber-Colman Company An Invensys company

23 Eurotherm Controls Inc / Barber-Colman Company An Invensys company EQUIPMENT HEATING METHODS Open-fired furnaces fuel-gas air mixture combustion burns directly into heating chamber material may be protected from oxidation and/or products of combustion by passing through a MUFFLE or RETORT. Radiant tube furnace fuel-gas air mixture combustion circulates inside radiant tubes. Heat is radiated through the tube walls into the heating chamber. Radiant tubes are nickel alloy, ceramic or occasionally silicon carbide Electric heating elements, 2 basic methods… exposed - open to heating chamber environment indirect - isolated from chamber by insertion into radiant tube(s) elements are typically Ni - Cr alloy in wire, rod, ribbon or sheetmetal form

24 Eurotherm Controls Inc / Barber-Colman Company An Invensys company EQUIPMENT QUENCHING METHODS most common quenching media are water, oil, or molten salt fastest cooling rate results from spraying refrigerated water under pressure quench tanks vary widely in capacity and design many are equipped with variable agitation, heating and cooling, filtering and ventilation up-to-date monitoring equipment may include computer controls and sensors to monitor temperature, chemistry, specific gravity and pressure

25 Eurotherm Controls Inc / Barber-Colman Company An Invensys company EQUIPMENT NEW FURNACE HARDWARE TECHNOLOGY driven by desire to cut costs, improve production, reduce environmental impact computer modeling has promoted improved design and construction recuperated combustion systems are more efficient and burner design has been optimized insulating brick has been replaced with ceramic fiber linings chamber shapes have been modified and improved reliable in-situ sensors provide valuable feed back about temperature and atmosphere composition state-of-the-art controls facilitate computer integrated management systems

26 Eurotherm Controls Inc / Barber-Colman Company An Invensys company ENDOTHERMIC GENERATOR Endo generator creates the atmosphere that provides a positive pressure in a heat treating furnace, and a platform on which a carburizing environment can be formulated by the addition of enriching gas or dilution air. An endothermic generator consists of: Heating Chamber – operating temp ± 1925°F (1052°C) One or more retorts containing… Numerous small, porous, ceramic pieces, impregnated with nickel as a catalyst for the reaction. A cooling heat exchanger to rapidly cool the products to a temperature that will not allow the reaction to proceed further

27 Eurotherm Controls Inc / Barber-Colman Company An Invensys company ENDOTHERMIC ATMOSPHERE A carrier gas provides a positive pressure in a heat treating furnace and a mechanism to carburize or decarburize by adding oxygen or methane 40% Nitrogen – 40% Hydrogen – 20% Carbon Monoxide (CO) – and.1 Carbon Dioxide (CO2) Nickel Catalyst ± 1925°F (1052°C) Air and Methane in a ratio of 2.75 to 1 is heated to 1900°F (1038°C) to 1950°F (1066°C) and flowed across nickel-impregnated cubes (catalyst) to produce Endothermic gas Measured and controlled in dew point – typical set point is 40°F

28 Eurotherm Controls Inc / Barber-Colman Company An Invensys company ENDOTHERMIC ATMOSPHERE At 1700°F (927°C) with a 20% CO endothermic atmosphere.40%C = 40 0 F D.P..60%C = 28 0 F.80%C = 20 0 F 1.00%C = 13 0 F At 1550 0 F (843°C) with a 20 % CO endothermic atmosphere.30%C = 66 0 F D.P..50%C = 50 0 F D.P..70%C = 40 0 F D.P.

29 Eurotherm Controls Inc / Barber-Colman Company An Invensys company GENERATOR CONTROL

30 Eurotherm Controls Inc / Barber-Colman Company An Invensys company Slide 104.Intro MEASURING CARBON POTENTIAL

31 Eurotherm Controls Inc / Barber-Colman Company An Invensys company SHIM STOCK INSERTION ASSEMBLY The Low carbon steel shim is cleaned, and weighed to four decimal places and then inserted into the furnace through the assembly. When equilibrium is met the shim is pulled back into the assembly to cool. Other devices such as O 2 probes and infrared are inferential measurements, which do not measure carbon directly. The shim is then removed and weighed to determine its carbon content. This method of carbon measurement is not practical for control although it provides a true measurement of actual carbon which serves as verification of the instrument calculation. Once inserted, the shim reaches equilibrium which is a function of time and temperature. Shim stock carbon determination is the only true measurement of carbon potential in a heat-treating furnace.

32 Eurotherm Controls Inc / Barber-Colman Company An Invensys company Shim Stock - Verification

33 Eurotherm Controls Inc / Barber-Colman Company An Invensys company OXYGEN PROBE OUTPUT At 1700 degrees the probe output is 1150 mV which represents 1.0% carbon in an atmosphere with 20% CO. The lower the oxygen concentration the more responsive the probe becomes. As the temperature increases the probe impedance will decrease and around 900 o F the probe will begin to generate a mV signal which will correspond to the O 2 partial pressure differential. The actual oxygen content in a typical carburizing atmosphere is 1 billionth of 1 billionth of one percent. The actual carbon value is calculated by solving the carbon equation resident in the microprocessor. Oxygen (carbon) sensors generate a (EMF) millivolt signal which corresponds to the partial pressure of oxygen in the furnace.

34 Eurotherm Controls Inc / Barber-Colman Company An Invensys company OXYGEN PROBE OUTPUT

35 Eurotherm Controls Inc / Barber-Colman Company An Invensys company OXYGEN PROBE MILLIVOLT OUTPUT The usable output range of the probe for an endothermic atmosphere is between 1000 and 1250 mV.

36 Eurotherm Controls Inc / Barber-Colman Company An Invensys company ATMOSPHERE COMPOSITION As illustrated when the CO value decreases in the furnace the CO 2 value will increase. The components of conventional endothermic atmosphere are 40% hydrogen, 40% nitrogen, and 20% carbon monoxide. This is also similar for the generator where the hydrogen decreases the water vapor (H 2 0) will also increase.

37 Eurotherm Controls Inc / Barber-Colman Company An Invensys company ATMOSPHERE COMPOSITION

38 Eurotherm Controls Inc / Barber-Colman Company An Invensys company Atmosphere at 40 o F DP provides different %C at different temperatures. Example:1500 o F =.75%C 1600 o F =.60%C 1700 o F =.40%C For carbon potential above saturation sooting will occur and non-controlled carburizing will take place resulting poor quality work. ATMOSPHERE COMPOSITION

39 Eurotherm Controls Inc / Barber-Colman Company An Invensys company PROBE TECHNOLOGY SPRAYED AREA CONTACT ANODE As indicated the isolated external electrode (nickel-chrome alloy) is flame sprayed onto the tip of a solid slip cast Zirconia tube. The positive electrode is spring loaded internally to the Zirconia tube. The sprayed electrode over time will crack and then peel as a result of the thermal cycling and different coefficients of expansion of the materials in intimate contact. The sprayed on electrode was designed by Kent instruments in the 70s and is still being used by some manufacturers today such as MMI and Kent. This design is expensive to build and inconsistent in quality due to the complexity of manufacturing.

40 Eurotherm Controls Inc / Barber-Colman Company An Invensys company SPRAYED AREA CONTACT ANODE

41 Eurotherm Controls Inc / Barber-Colman Company An Invensys company PROBE TECHNOLOGY SIRO AREA CONTACT ANODE The government of Australia currently holds the now expired patent for the design of the ceramic substrate and is the supplier/licensor to several manufacturers. Over time, cycling of temperature will cause cracks to develop in the cemented junction. The Csiro probe (known as the siro sensor) is the most widely used probe design in the industry. This substrate is constructed with an alumina tube into which a Zirconia plug is pressed into one end and sealed, using a eutectic ceramic cement. When a crack occurs, furnace atmosphere will ingress into the cell and contaminate the reference air, causing inaccuracies in the output of the sensor.

42 Eurotherm Controls Inc / Barber-Colman Company An Invensys company SIRO AREA CONTACT ANODE

43 Eurotherm Controls Inc / Barber-Colman Company An Invensys company PROBE TECHNOLOGY LINE CONTACT ANODE Although slightly more expensive to build, the gas tight slip cast Zirconia tube has been proven to facilitate the most reliable probe configuration on the market. This particular manufacturers design incorporates 10 large holes located near the tip of the electrode. Due to the location and the large number of holes, effective Probe conditioning (Burnoff) is virtually impossible. The line contact design utilizes slip cast Zirconia with a spring loaded contact to the outer sheath as the external electrode/conductor. This particular design uses knife-edge contacts which will precipitate cracks in the Zirconia during thermal expansion and contraction typical in batch furnace applications.

44 Eurotherm Controls Inc / Barber-Colman Company An Invensys company LINE CONTACT ANODE PROBES

45 Eurotherm Controls Inc / Barber-Colman Company An Invensys company BARBER-COLMAN AP11 CARBON PROBE

46 Eurotherm Controls Inc / Barber-Colman Company An Invensys company VIRTUAL POINT CONTACT ANODE Virtual point contact reduces the potential of stress fractures and also provides a lower resistance at the outer electrode interface. sheaths utilizes a cermet coating which minimizes the catalytic reaction between methane and nickel typically observed with alloy materials exposed to reducing furnace atmosphere. As a result less soot is deposited, degradation of the sheath is reduced, and probe life is extended. This probe takes advantage of the reliability of the gas tight slip cast Zirconia tube design.

47 Eurotherm Controls Inc / Barber-Colman Company An Invensys company VIRTUAL POINT CONTACT ANODE

48 Eurotherm Controls Inc / Barber-Colman Company An Invensys company OPEN vs. CLOSED SHEATH Probe Burnoff Required?Probe Burnoff Required

49 Eurotherm Controls Inc / Barber-Colman Company An Invensys company TYPICAL PROBE INSTALLATION Two to Four inch Insertion

50 Eurotherm Controls Inc / Barber-Colman Company An Invensys company Probe Conditioning The purple and green pen represent the millivolt probe output on different scales. The red pen represents the probe thermocouple. Summary: During burnoff the probe output should drop below 200 mV. As shown by green pen.


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