EXPLORATION • DRILLING • FIELD SERVICES
During treatment, the plasma field,
glowing on the exposed surface of the components, causes nitrogen ions to diffuse into the material forming a diffusion zone. Tis diffusion zone strengthens the metal. Te atomic nitrogen is being dissolved, atom by atom, into the iron lattice base material. Adding further precision, innovators in pulse plasma have discovered methods to optimise the process through better control of the power pulses. In the PulsPlasma process developed by PVA TePla Industrial Vacuum Systems, for example, a precision regulated gas mixture of nitrogen, hydrogen and carbon-based methane is used. A pulsating DC voltage signal of several hundred volts is delivered in less than 10ms per pulse to ionise the gas. Tis serves to maximise the time between pulses for superior temperature control throughout the chamber. “If you have a temperature variance of +/-10° within a batch, you will obtain significantly different treatment results,” says Dietmar Voigtländer at PlaTeG – Product Group with PVA Industry Vacuum Systems (IVS), the manufacturer of PulsPlasma nitriding systems. “However, by controlling the pulse current by means of an exact pulse on and off time management, the overall temperature can be precisely managed with a uniform distribution, from top to bottom, throughout the hot wall chamber.” A unique feature with this approach is that the system provides a very stable glow discharge at room temperature. Most systems are unable to achieve this level of control due the selection of generators used. To compensate, other systems must first be heated to 300-350°C before plasma can be
PulsPlasma nitriding furnaces are well suited to the heat treatment of materials such as stainless steel
applied, adding time to the total process. With PulsPlasma technology, that process time difference can instead be used to prepare the surface, in-situ, by providing a fine plasma cleaning, or if necessary, a depassivation process on corrosion-resistant alloys.
Te components and materials used to manufacture the nitriding system furnaces have been optimised over many years to ensure high reliability and long- life performance. In all systems, PlaTeG uses insulative materials developed in the aerospace industry to create a furnace wall as thin as 40mm compared to the industry standard of 150mm. With less wall mass, the PlaTeG designed furnace requires less energy and time to heat, while still protecting workers that may accidentally touch the outside of the chamber. With better overall control, the PulsPlasma nitriding furnaces offer multiple independent heating and cooling zones with each controlled by its own thermocouple. “Tis allows for extremely uniform temperature distribution of within +/-5°C from the bottom to the top of the furnace,” says Voigtländer. Uniformity of temperature within a chamber pays a dividend beyond the consistency of nitriding results. With a uniform temperature throughout the chamber, the entire space becomes available for loading components, effectively increasing the chamber’s run capacity.
The PlaTeG furnace from PVA TePla
STAINLESS STEEL – A SOFTER STEEL One of the key advantages of PulsPlasma nitriding is that it is very well suited to the
heat treatment of high alloy materials such as stainless steel. Stainless steel has a natural passivation
layer of chromium oxide on the surface. Tis thin layer inhibits corrosion. To provide a pathway for nitrogen ions into the material, the chromium oxide layer must first be removed. With the traditional gas nitriding method, removal of the passivation layer requires the application of a special chemistry. Stainless steels can also be nitrided in salt baths, but some level of corrosion resistance is sacrificed as the combination of the chemistry of the salt bath, and the higher temperature of the medium, causes a rapid loss of elemental chromium on the exposed surfaces. With PulsPlasma nitriding, the
passivation layer is removed through controlled ionic bombardment of the surface. By choosing a nitriding temperature below 450°C, and with precise control of the low-volume gas mixtures, the material surface suffers no reduced corrosion resistance of the metal.
Te bottom line for oilfield applications
is that the advanced PulsPlasma technology offers improved uniformity for product designers, improved materials performance for engineers, and provides economic benefits through higher component throughput for heat treaters. Te great many oilfield equipment manufacturers across the world that depend on nitriding components can benefit immediately from these materials process improvements today.
www.engineerlive.com 13
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52
