Novatec Infra-Red Die Oven
Summary This article shows the superiority of the Infra- Red technology over convection air flow. The comparison is through theory, heating process and efficiency. Short cycle heating and die management is one of the most significant technology reforms of the extrusion industry in the past 20 years.
Three modes of Heat Transfer ： 1.Conduction 2.Convection 3.Radiation
Traditional Air Flow Chest Oven ： •The chest oven, holding multiple extrusion dies, has been the most common design over the years. The tooling is heated by circulating hot air through a common chamber using a blower system. This is the convection air process. •An extrusion die that does not have accurate temperature throughout or uneven temperature profile on the face will not run properly. In this case more billet is used before accurate profiles can be produced to correct the differences. Short production runs produce off-tolerance material and high die failure.
• A single lid oven exposes the dies to a fresh supply of oxygen and moisture each time the lid is opened. This is another cause of rapid oxidation. • Die management is virtually impossible so the solution is to heat lots of dies in case of extrusion issues. This means that dies are left at elevated temperatures for extended periods of time. The die bearing is exposed to rapid oxidation unnecessarily .
UNEVEN HEATING Why convection air heats dies unevenly ： 1. The air being blown in a die box will travel the path of least resistance from inlet to outlet in the convection process. The physical blockage of the air stream causes uneven exposure to the die surface. 2. All the dies in a convection chest oven are under the same lid, Heated air escapes every time the lid is opened.
Convection Air Flow Oven Inlet Outlet Direction of Air Die
3. Placing a cold die in the air stream will cool the temperature for the dies further away causing incorrect heat time. It is virtually impossible to avoid this in the die exchange process. Heated dies are then actually cooled without operator knowledge. The biggest cause of unevenly heated dies is when a cold die is placed next to a hot die causing the heated die face to be cooled on one side. This thermal gradient is the cause of die breakage, poor run out and inaccurate non-conformant extrusion dimensions using the first billet.
Heating Extrusion Dies Using Infra-Red Technology
What is “Infra-Red” Heating ？ Most extruders use traditional convection chest ovens for die heating. The air in a common chamber is heated and circulated. The convection process relies on air temperature to transfer energy to the steel through conduction. This procedure is slow and inefficient. Infra-Red energy uses a band of electromagnetic waves to “excite” the metal molecules in a die through radiation. This molecular excitation is similar to the microwave technology. Infra- Red energy does not use air temperature for thermal transfer. Air is an insulator so the thermal process is accelerated.
What is “Infra-Red” Heating ？ Infra-Red is a kind of Radiation which transfer heat from object to another by electromagnetic transmission. The Infra-Red is located between visible light and radio in the electromagnetic spectrum. The wavelength of Infra-Red ranges from 2.0 to 6.0 microns.
What is “Infra-Red Heating ？ When the Infra-Red energy reaches the surface to be heated, the molecules vibrate, converting to heat energy. Heat then travels through the product by conduction.
Material generates Properties heat after absorption of IR Reflection or Transmission
Novatec Infra-Red Die Oven About Novatec Novatec is based in Surrey, British Columbia .The company has been producing Infra-Red equipment for a variety of applications for the past 20 years. In 1990, an aluminum extruder asked Novatec to explore the possibility of heating extrusion dies with Infra-Red technology, and the Novatec Infra-Red Die Oven was developed. Since that time, a number of extruders have installed the ovens and have reported dramatic improvements in speed, flexibility, and quality.
Past attempts to use Infra-Red waves involved broad band heating. Generating this spectrum was not energy efficient. Novatec has developed the Infra-Red band technology to focus the wave energy to match the absorption in steel. Generating a small band of Infra-Red waves gives a focus energy for absorption. This maximizes energy transfer.
Spectrum Absorption 100 75 % Absorption Metal 50 25 0 1 2 3 4 5 6 7 8 Infra-Red Wave Length (Micron)
Advantage of using Novatec Infra- Red Die Oven: 1. Cuts die heat up time by 75% 2. Reduces energy consumption by 50% 3. Reduces die failure by 90% 4. Increases speed and flexibility 5. Improves extrusion surface finish 6. Superior safety features 7. Advanced PLC control
1. Cuts die heat up time by 75% Novatec Infra-Red Die Ovens heat dies much faster than convection ovens. As explained above, this is because the dies are being heated by infrared waves, not air. Air itself is an insulator of thermal energy, and therefore, is a poor medium for thermal transfer. Novatec’s Infra-Red Die Ovens single out the wavelength needed to heat die steel only …not heat all the air in the oven.
Heater Efficiency Comparison Metal Sheath Novatec Black Body Heater Infra-Red Heater
Heat Time Comparison ： Press Die Size Die Heat Time (T) (Dia. X thickness) Temp Infra-Red Convection ( ℃ ) (mm) 2800 430 x 330 475 2Hrs 30mins 4~5Hrs 2800 430 x 190 475 2hrs 00mins 4~5Hrs 3680 520 x 245 475 2Hrs 15mins 5~6Hrs 3680 520 x 340 480 2Hrs 35mins 5~6Hrs
2. Reduce energy consumption by 50% Because of the wavelength heating process explained above, the efficiency of the die heating process is greatly improved. Not only does the level of heating time reduce overall, but also the power draw to maintain oven temperature once heated is less than 500 watts. (By contrast, a typical hair dryer operates on 1200 to 1400 watts.) The savings on power usage alone is a significant benefit when using Novatec’s Infra-Red Die Oven.
Extrusion Die Oven - Electricity Usage Comparison Convection Air Flow Oven NOVATEC Infra-Red Oven Each Cavity ： Each Cavity ： 10 Dies 24 kW 480V 2 Dies 22 kW 480V Die Heat Up Cycle ： Die Heat Up Cycle ： 8Hours X 20.4 kW/hr =163.2 kWh 1Hour X 18.7k W/hr = 18.7 kWh @ 85% Power Draw @ 85% Power Draw Total Cycle ： Total Cycle ： 8 Hours 1 Hour 163.2 kW X $0.07 kWh = $11.42 18.7 kW X $0.07 kWh = $1.31 Total Cost to Heat Each Die ： Total Cost to Heat Each Die ： $11.42 ÷ 10 = $1.14 $1.31 ÷ 2 = $0.65 Die Temperature Holding Cycle ： Die Temperature Holding Cycle ： 20.4 kWh÷10 Dies X $0.07/kWh 0.5 kWh÷2 Dies X $0.07/kWh = $0.14 Per Die Per Hour = $0.0175 Per Die Per Hour The Infra-Red Oven is 52% more cost effective than a Convection Oven.
3. Reduces Die Failure up to 90% Extruders who use the Novatec Infra-Red Die Ovens have reported a dramatic decrease in die failure and breakage. Not only do convection ovens take longer to heat a die, they heat dies unevenly. Studies show that even after four hours of soak time in a convection oven, a 14 inch die can have as much as a 100 degree difference between one side of the die to the other. This will cause uneven runout in multi-hole dies, and consequently, uneven stresses on the die. All of this results in premature die failure and breakage and higher scrap rates. Novatec’s Infra-Red technology heats dies to within single digit temperature variation throughout the die, reducing die failure.
This Chart shows the heat up time for a 16"x 6" die at 4 different thermocouple points in the die. Note the evenness of the heating throughout the die. It reached target temperature in 91 minutes. 900 675 Oven Set Point Front : 1" Deep Temp (deg. F) Middle : 3" Dep Surface Temperature 450 Back : 1" deep 225 0 1 7 13 19 25 31 37 43 49 55 61 67 73 79 85 91 97 103 109 115 121 127 133 Time (min.)
4. Increases Speed and Flexibility As mentioned above, a 14-inch die would be heated in less than 60 minutes with a Novatec Infra-Red Die Oven, as opposed to 4 hours in a convection oven. This will provide increased flexibility of die changeovers on the extrusion press, and reduce throughput time.
5. Improves surface finish of extrusions Because the dies do not have to stay in the oven for 4+ hours, the die bearings are not subject to excessive oxidation prior to extrusion. This provides a higher extrusion finish. Also, airflow systems, such as those used in a convection oven, tend to deposit particles on dies and bearings. Novatec Infra-Red Die Ovens do not require an airflow system, and therefore, keep the dies free of contaminants.
6. Superior Safety Features • Watchdog thermocouple system and backup Mechanical Contactor prevents thermal run away • Static lid stops that will activate under any non- normal condition, i.e. power outage, power spike • Emergency Stop Push Button • Annealing Light
7. Advanced PLC Control Unique PLC System Automation Control
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