FPH - Finishing plasma hardening
Finishing plasma hardening repeatedly increases durability of products and tools and is economic stimulus for its application.
Micro hardness practically any materials of worn out details used in manufacture after thermal hardening is about 5 hPа, after nitriding - up to 8 hPа, after chromium plating - up to 11 hPа, after drawing nitride of titan - up to 24 hPа. Micro hardness of diamond is about 72 hPа. Micro hardness of strengthening FPH nanofilms reaches up to 52 hPа.
Such increase of details durability is explained with reduction of factor of friction between rubbing surfaces. For pairs friction it makes: bronze on bronze - 0,2; pig-iron on pig-iron - 0,16; fluoroplastic on fluoroplastic - 0,05. Factor of friction of FPH film on steel Р6М5 makes 0,07.
Worn out details are maintained in various excited environments, therefore chemical stability of a material of a surface of friction is very important. FPH films are chemically inert and cooperate only with a fluoric acid.
Usually surfaces after finishing by abrasive processing have a significant amount of micro defects. The majority of worn out details are subject to fatigue failure which directly depends on concentrators of pressure in a superficial layer. After FPH process the topography of a surface cardinally changes, and its micro defects, owing to drawing strengthening nanofilm are healed.
High-altitude parameters of roughness Ra influence wear resistance of surfaces of friction. After FPH high-altitude parameters decrease, that affects reduction of quantity of crashed ledges of a structure, and it decrease of lapped finishing and established deterioration.
Well known that electromechanical deterioration at friction and cutting negatively affects durability of details and tools. But after FPH on surfaces of details a dielectric nanofilm is formed with specific electric resistance of 106 Оhm/m, which prevents this kind of deterioration.
In most cases after final operation of grinding stretching residual pressure left on a surface, which aspire widening of existing micro cracks and lead to shelling-out of separate particles of a surface. After FPH in a superficial layer of metal compressing residual pressure which provide conditions of curing of micro cracks are directed and by that counteract fatigue failure.
Adhesive deterioration is characterized by gluing of particles of contacting materials during friction. FPH nanofilm interferes with formation of bridges of welding, gluing or sticking of material of a fricted counter body.
It is known, that oil adhesive ability of a surface of friction is the integrated parameter predicting resistibility of details to wear process and corrosion. The regional corner of wetting by industrial oil of a surface of thermo hardened steel 45 makes 60. The regional corner of wetting by oil of a surface with nano film put at FPH, makes 45.
Many details working in conditions of friction and deterioration are exposed additionally to high temperature loadings which affect intensification of processes of deterioration. Tests for high-temperature air corrosion within 10 hours at temperature 900 ˚С have not revealed appreciable changes in properties of FPH nanofilms.
From the point of view of physics of strength with the purpose of hardening of a surface it is expedient to create conditions providing absence of an output of dispositions on a surface.
FPH nanofilm is barrier covering, which prevent of an output of dispositions on a surface.
Fretting corrosion is one of known kinds of deterioration. A research of FPH nanofilms on fretting corrosion resistance has shown its perceptivity for industrial use.
Allocated of materials of pairs of friction and from environment hydrogen causes the accelerated wear process. Oils and greasing also are a source of atomic hydrogen. FPH nanofilm is effective means of struggle against hydrogen wear process.
The material of a covering - oxide of silicon carbide in amorphous condition keeps properties at temperatures arising in processes of cutting and punching (200-1100 .С) and has dielectric properties;
FPH covering has the high hardness exceeding hardness of a material of the tool at temperatures of cutting (micro hardness about 3380 kg/mm 2);
FPH covering is the barrier layer preventing of gluing up at adhesive deterioration in all range of temperatures of cutting and punching and is inert to dissolution in processable material at heats;
FPH covering is steady against destruction at significant fluctuations of temperatures and pressure (maintains the maximal contact pressure up to 4000 hPа arising at cutting);
FPH covering has chemical affinity to a material of the tool, defining high durability of its adhesion;
FPH covering has an optimum parity on the module of elasticity, Poisson factors, linear expansion, warmly - and thermal conductivity with a material of the tool;
The covering is the inert firm greasing changing scale and the mechanism of destruction at adhesive-fatigue deterioration, has low factor of friction 0,04-0,08 (on steel ШХ15) owing to what suppression to processes of formation of erosion scabs provided at cutting and sticking at punching and pressing. Known technologies of drawing of wear proof coverings are applied to increase of durability of the cutting tool and details of industrial equipment in the industry: vacuum ionic-plasma covering, electro spark аalloying, finishing plasma hardening (FPH); technologies of modifying of a surface: laser and plasma training.
At laser and plasma training spent in the air environment, oxidation of a processable surface is possible. During electro spark аalloying reception of thin-film coverings by thickness of the order of several micrometers is impossible. At vacuum ionic-plasma covering the temperature of processable products at drawing covering makes 250-500оС, and thickness of a covering considerably depends from thickness fluctuation of products and its arrangements concerning the evaporator.
Recently there were many publications about application of diamonds and diamonds like films for hardening the cutting tool and details of industrial equipment. In Germany even special standard VOI 2840 on diamonds like coverings is released. Realizations of these processes are based on use of the expensive vacuum equipment.
Finishing plasma hardening (FPH) of tools and industrial equipment, providing drawing diamonds like thin-film (up to 3 microns) coverings in vacuumless space at atmospheric pressure, concerns to new industrial technologies. Process of hardening of the tool, equipment and details of machines occurs at integrated temperature of heating of products of the order of 100оС without change of an initial roughness of working surfaces.
Main principle of drawing of the diamonds like thin-film covering, for a basis of the given technology, decomposition of the liquid vapor technological preparations entered in еlectric arc plasmatron, with the subsequent passage of plasma chemical reactions and formation of a covering on a product is taken.
As initial substances for reception of a diamonds like covering on the basis of ocicarbonitridsilicon metalloorganic and organic joints in a fluid state are used. The consumption of technological specimens at one-shift work of installation does not exceed 0,5 liters/year. In the capacity of plasma forming gas used in arc plasmatron, the argon which application is based on the demand of longevity and reliability of elements of plasmatron at long conducting process is chosen. Thus durability of cathode and anode unit of plasmatron at FPH attains the order of 1000 hours of continuous work.
One of the basic features of FPH, connected with the raised speeds of cooling of a besieged covering and presence of softening elements, is an amorphous condition of nanofilm which has the raised hardness (up to 53 hPa), high specific electric resistance (1010 Ohm/m), low factor of friction and chemical inertness. It is known, that in amorphous materials there are no defects, characteristic for crystallic matter. There are also no borders of grains, dispositions and their structure is homohenic, diffusion on vacancies is more inconvenient, they are isotropic. Amorphous coverings are applied as barrier films, preventing fast diffusion, passivating films, materials increasing corrosion stability and preventing corrosion cracking under pressure applied as well as emersion of increased hydrogen generated friability.
Comparative characteristics of adhesive properties of a diamonds like covering, applied by FPH method, and coverings of nitride of titan, applied by ionic-plasma dusting in vacuum on an optimum mode at the installation ННВ-6, 61/11 were investigated by sclerometric method. A basis was thermo hardened tool steel Р6М5. As an intruder a diamond cone of Rockwell has been used with top corner of 120о, moved on a surface of coverings with a speed of 3 sm/min. Vertical loading on intruder was increased until its critical size at which the covering was completely separated from a substrate. The given critical loading was determined by investigating the received scratches with metallographic microscope. As a result of the lead researches it is revealed, that critical loading, at which there were the first damage of coverings by nitride of the titan, was 35 Н, and for the coverings rendered by FPH method - 65H.
The diamonds like covering, which is rendered on a surface, being dielectric, forms the film barrier preventing of gluing of contacted surfaces. Besides this, covering possesses the increased corrosion stability and heat resistance that proves to be true by long tests of samples for air corrosion at temperatures up to 1000-1200оС.
Tests for friction and deterioration were accomplished according to GOST 23.224-86. For this purpose samples in diameter of 38 mm and thickness of 12 mm made of steel Р6М5 were used, on which both the diamonds like covering by FPH method and covering of TiN by method of ionic-plasma dusting on in vacuum was rendered. As a counter body thermo hardened up to HRC 63 samples were used made of steel ШХ15. Conditions of contact - rolling friction with 20 % of slippage with greasing. As greasing industrial oil И-20 (GOST 20779-75) was applied. Tests spent at frequency of rotation of the sample of 1000 min-1 at loading of 1650 N. For comparisons also the samples from thermo hardened steel Р6М5 were used.
During experiment values of the moment of friction and mass deterioration of samples were recorded and factors of friction and intensity of wear process paid off. The factor of friction calculated according to the formula: ƒ=2Mt/D*P
Where: Мt - the moment of friction, Nm; D - diameter of the sample, m; Р - loading, N.
Thus, on the basis of tests for friction and deterioration it has been determined, that the factor of friction and intensity of wear process of surfaces with a diamonds like covering decreases practically in 2 times in comparison with an initial surface of steel Р6М5 and less for 20 %, than covering of TiN rendered in vacuum.
The device of the control of growth of thickness of covering is developed for definition of quality of drawing of covering during FPH process (pic.3) with use as the gauge of the very plasma jet. The device provides digital indication of a signal on one or two parallel included entrance channels, displaying of its current value to the liquid crystal graphic screen in coordinates “current-time”, saving of graphic representation of values of a measuring micro current and time in non-volatile memory. Results of measurements are archived in non-volatile memory of the device in capacity of 4 Mb (more than 1 million measurements) and also could be transferred on a personal computer.
There are some examples of using processes of FPH.
1. Multiple increase of resistance of equipment for glass forming machines. The equipment for glass forming machines (draft and fair form, throat ring, pallet of the clean form, plunger, crown, ground jam, plunger ring) intended for formation of glass items and works in direct contact to liquid glass. Formation is made in an interval of temperatures 700-1000оС, and the forms’ equipment is maintained in heavy conditions of thermo circle loadings. The basic materials for foundry manufacturing form equipment are grey and high-strength iron pigs. With the purpose of repeated increase of durability of forms’ equipment diamonds like thin-film covering is rendered on its working surfaces by FPH method. The covering has hardness of the order 52 pHa, is heat-resistant and chemically inert. Thus there is no necessity of rendering of wearproof powder materials on the basis of nickel on working surfaces.
Use of the given technology on Open Company «ТD «AzovSteklo » has shown increase of resistance of forms’ equipment more than 5 times.
2. Hardening of the industrial equipment used at mass cartridge manufacture.
At mass manufacturing of cartridges a big variety of the specialized cutting tool, stamp equipments, measuring tools, made of tool steel and a firm alloy are used. One of the basic spent tools is the form-building equipment which is under high dynamic shock loadings and intensive friction of working surfaces with processable details. With the purpose of increase of hardness of a surface of the tool, reduction of factor of friction between the tool and a processable detail, creation on the tool of chemically inert covering counteracting formation of scorings and sticking, reduction of parameters of roughness of working surfaces of the tool, FPH technology is applied. Industrial tests of the strengthened equipment for Open Society «Tula cartridge factory» have shown increase of its resistance more than 3 times.
3. Increase of durability of tools used at manufacturing of rolling-contact bearings.
At mass manufacturing of rolling-contact bearings diverse tools are used: cutting, forging (to automobile lines) tools of half heated gauging by uncoiling calibrations, stamp, cut out and measuring tool, etc. With reference to the wide nomenclature of the given tool it is advisable to use FPH technology. With use of this technology local hardening of worn out surfaces of the various tools are provided due to drawing thin-film (up to 3 microns) of diamonds like covering. The covering has following properties: hardness 52 hPa (in most cases hardness of a basis of the tool makes the order of 8-14 hPa); low factor of friction (at tests for friction and deterioration with a counter body made of steel ШХ15 the factor of friction makes of 0,007, under the same conditions without a covering the factor of friction is equal of 0,015); the covering reduces parameter of a roughness of surface Rа (depending on an initial roughness) more than 2 times; preservation of hardness and appearance at the increased temperatures up to I000оC; absence of interaction with any substances (except for a fluoric acid) due to chemical inertness.
Industrial tests of the strengthened tool (cut out and stamp) on Open Society «Volga bearing factory» have shown increase of its resistance 4 - 6 times.
4. Multiple increase of resistance of tools for cold heading.
By processes of cold heading and extruding from steels and nonferrous metals hardware (bolts, nuts, screws), various details of universal purpose (asterisks, шестерни, etc.), the various form-building details, testing significant dynamic shock loadings and abrasive wearing out influence are made.
With the purpose of increase of hardness of a surface of the tool, reduction of factor of friction between the tool and a processable detail, putting on the tool of chemically inert covering counteracting formation of scorings and sticking, for reduction of parameters of roughness of surfaces of the tool, FPH technology is applied. Industrial tests of сold heading tools after FPH at the industrial enterprises have shown increase of its resistance 4 - 6 times.
Use of installations for FPH at the industrial enterprises allows to reduce quantity of the made and bought tools and equipment; to save tool steels (in connection with reduction of quantity of the made tools and equipment); to reduce volume of tool-grinding operations and quantity of the got grinding tools (in connection with use of the strengthened tools and equipment); to reduce the expenses connected with adjustment and readjustment of presses, machine tools and other equipment in connection with use of more durable tools and equipment; to intensify modes of processing and, accordingly, to increase labor productivity at use of the strengthened tools and equipment.
After treatment FPH
The metal surface before the treatment FPH