熱噴涂問題的解決方案_HSE_健康_安全_環(huán)境_與超范圍噴涂_英文_

1、Problem Solving Solutions in Thermal Spray : HSE andOversprayHans Keller, Joachim Beczkowiak, Stefan Zimmermann, H.C. Starck GmbH, Laufenburg / D Benno Gries, Jürgen Fischer, H.C. Starck GmbH, Goslar / DSummaryCurrent raw material costs for metal based materials stress the economical viability

2、of thermal spray coatings. Especially volatility and recent steep price increases for Rhenium, Tungsten, Cobalt and Nickel based materials are a serious economical risk for many coatings in all areas of application. Originating from limitations in deposition efficiencies overspray becomes increasing

3、ly important, not only in regard to reduce waste, but also seen from the angle of material costs itself. Recycling offers a measure to counteract this development, in particular when it comes to waste materials containing highly valued metals.Implementing REACH (R egistration, E valuation, A uthoris

4、ation of C hemicals in Europe will force a phase out of the usage of materials and substances labelled as toxic. Using these toxic substances in thermal spraying or products made by thermal spraying may, for the time being, estimated to be safe. However, there are legal restrictions and indications

5、known from other industries in which chemicals like WC-Co powders harm the human body. To remain competive in the future coating shops must meet continuously more stringent environmental and safety regulations.Key wordsThermal Spray, powders, alternative matrix powders, WC-Co, health and environment

6、 protection, Co- and Ni-free; toxicology, REACH, recycling, oversprayIntroductionThermal spraying has become a first-choice process in many branches of industry if economically viable, largearea and functional coatings are required. Since the first industrial utilisation approximately 100 years ago,

7、 thermal spraying technology has grown to a global industry of Euro 6.1 billion per year. More than thirty percent of the worldwide activities in thermal spray is locatedin Europe. Therefore, also present trends in Europe will guide the global thermal spray industry through the century 1.Currently t

8、wo major concerns control development: First, raw material costs, but of similar importance secondly, health and environment protection an ecology. Users of spray powders are rattled and expect concepts and ideally solutions from the leading suppliers of thermal spray powder.In both cases mentioned

9、H.C. Starck is the chosen partner for the thermal spray industry. We are on your side.How? Please see below.RecyclingRecycling of scrap and dismantled products are already and will be one of the key processes for a sustainable technical development. Economics and ecology ask for a protection of reso

10、urces and reuse of material. Recycling is the preferred solution to serve both. Recycling means the extraction of raw materials from reusable materials or the reduction of usage of materials in production processes. Pre-requisite for recycling is a as good as possible separation and clean collection

11、 of waste.Inherently, in thermal spray processes only part of powder spayed will stay on the part to be coated. The rest of the powder, so-called overspray, normally collects in spray booths and filter systems. Currently, in most cases declared as waste this overspray can become a major source for c

12、ost saving in thermal spraying (Fig. 1.Fig. 1 Recycling of overspray: Especially overspray of metals, alloys or carbides are chosen materials worth to recycle. In particular, if containing significant amounts of the high value materials like Rhenium, Tungsten, Cobalt, Nickel, Molybdenum and Tantalum

13、. Other materials with minor or no valued materials like oxides are currently not considered as recyclable.The following guidelines can help you to identify the most valuable materials for recycling of overspray:High Value:- Rhenium containing MCrAlYs or other alloys with more than 1 % Rhenium conte

14、nt- Pure tungsten carbide cobalt materials like WC-Co 88/12 or 83/17Medium - Low Value:- MCrAlYs or other alloys with less than 1 % Rhenium or mixtures with non-Rhenium containing MCrAlYs or alloys- WC-based materials with addition of Chromium like WC-Co-Cr 86/10/4 or WC-Cr3C2-Ni 73/20/7No Value:- O

15、xides- Other elements except Re, W, Co, Ni, Mo, Ta- Waste (Fig. 2Fig. 2 Waste of no value: Besides the chemical requirements for recycling also legally set requirements regulating treatment, handling and shipping of waste, waste acts by the government, have to be taken into account. Collecting, hand

16、ling and recycling of overspray is controlled by the waste act of the countries. The following guidelines shall be applied to fulfill these requirements:Customer:- Collecting of overspray- Declaration of overspray according to the waste act- Representative sample of overspray to be sent to H.C. Star

17、ckH.C. Starck:- Analysis and valuation of the sample- Offer for the overspray to the customer- Delivery and incoming inspection- Recycling and Payment to the customerH.C. Starck is always able to assist you in the complete recycling process and help you to keep the economics of thermal spray coating

18、s on the appropriate level.Health and Environment Protection - How toxic is WC-Co?It has been known for decades that the inhalation of hard metal dust can provoke negative health effects. For example, a compound of WC and Co has more negative effects on health, especially on the lung, when compared

19、to Co or WC alone 2. The so called “hard metal lung” is a specific type of lung fibrosis occurring only after exposure to hard metal dust. It is an acknowledged occupational disease in Germany 3. Experiments conducted in the early 90ties proved that the combination of WC and Co dust is inhalation to

20、xic for rats whereas pure Co powder is not 4.In thermal spraying many Co containing hard metal powders such as WC-Co and WC-Co-Cr are also handled e.g. in powder production, thermal spraying as well as in filter dust disposal. The facts relating to hard metal are of relevant significance. The bioche

21、mical reactions taking place in the human body after WC-Co dust has been inhaled are based on the corrosion behaviour of pure metallic Co in water. Fig. 3a illustrates these mechanisms schematically 5 8. Fig. 3 The Contact Corrosion System WC-Co 6:a corrosion model, b cross section of a WC-Co 83/17

22、particle (SEM photograph showingthe sinter bridges/contact areas between the WC (bright phase and the Co binder (grey phaseThe harmful health effect taking place in the human body related to these corrosion mechanisms is based on high formation of reactive radicals on the surface of the WC particles

23、. Due to their high oxidation potentials these reactive oxygen species interact with the surrounding biological environment. Depending on the dust concentration and the exposure time, inhalation of hard metal dust can lead to acute inflammation reactions or chronic stress finally causing interstitia

24、l lung fibrosis (= hard metal lung. Today it is proven that a large part of the negative effect of asbestos orsilica on the lung is provoked by similar surface reactions involving reactive oxygen species, too. In addition, Co ions have been proven to cause negative effects on the DNA repair mechanis

25、ms due to their strong tendency to form complexes with amino groups and thus might react with all body proteins.In hard metals cobalt can be substituted partially or wholly by alloys containing nickel and iron. As Fe-based hard metals exhibit a better corrosion resistance in aerated liquids than WC-

26、Co, it can be expected that they are also lower in toxic potential. An acute inhalation study (Table 1 with various WC-Co, WC-FeCo and WC-FeNi powders confirms the high toxic potential of WC-Co by inhalation even at low dust concentrations of only 0.25 mg/l. The hard metal composite WC-Co 90/10 show

27、s a mortality of 100% and must be classified as "T+". The reason is the very intimate contact between Co and WC promoting a high contact corrosion rate.Also the agglomerated and sintered thermal spray WC-Co 83/17 powder bears a high mortality of 60% at a concentration of 1 mg/l. Considerin

28、g, that the amount of breathable particles in the chamber had only been in the order of 20% this makes an effective concentration of breathable particles of only 0.2 mg/l. This is due to the high internal surfaces and the pronounced sinter bridges between Co and WC in the porous particles, which are

29、 typical for agglomerated and sintered WC-Co thermal spray powders (Fig. 3b. It can be assumed that even agglomerated sintered WC-Co-Cr powders or overspray still bear a certain mortality as Co and Cr potentially might not alloy completely during sintering in powder manufacturing or when sprayed wit

30、h comparatively cold HVOF or HVAF spray systems. That overspray from thermal spray processes might cause fibrotic and asthmatic lung disease has already been shown in 7 employing the detonation gun process.A partial replacement of the Co in WC-10%Co by 5% Fe, using Co and Fe powder, being milled tog

31、ether with WC in an attritor mill, leads to a reduction in toxicity by about 50%. However, when the same nominal composition (WCCo5% Fe5% is produced as a composite, with Fe and Co being fully alloyed, mortality drops from 30% to zero at the same concentration. Even at very high concentration of 5 m

32、g/l it remains zero. A blend of WC with a fine alloy powder (51%Fe, 49%Ni shows no inhalation toxicity even at high concentrations of 5 mg/l.Table 1 Results of 4h acute inhalation studies with rats 5Material WC size FSSS(mConcentration(mg/LRespirible fraction< 7m (%Mortality (%Thermal spray powde

33、r: WC-Co83/17, 30/5 m, aggl. sint.2,5 m 1 20 60 Hard metal composite: WC-Co90/100,8 m 0,25 90 100 Grinding dust WC-Co: (15% Co,71% WC, 12% Fe0,28 76 70第十一屆國際熱噴涂研討會論文 第十二屆全國熱噴涂年會論文 WC-Co-Fe 90/5/5: Fe + Co metal powders attritor milled WC-(CoFe50/50 90/10 Fe, Co = alloyed WC-(FeNi50/50 90/10 Fe, Ni =

34、 alloyed (ITSS2008 (CNTSC2008 0,8 m 0,8 m 1 15 85 94 84 30 00 0,8 m 0,53 5,22 81 60 00 The results clearly indicate that inhalation toxicity of Co in contact with WC can be largely reduced if not eliminated, if it is alloyed with iron. This result is of great significance for the HSE aspects for saf

35、e and responsible production and usage of hard metals and thermal spray powders. An even better solution for health and the environment is the production of cermet powders in which Co is totally replaced by other, less harmful elements. Those health and environment-friendly Co and potentially even N

36、i free powders would open up completely new applications for thermal spray applications e.g. in the food industry or fresh water treatment. The Solutions New Co free Cermet powders The matrix components of most agglomerated sintered and dense sintered standard cermet powders for thermal spraying con

37、tain binders with simple compositions only. WC-Co, WC-Ni and WC-Co-Cr are typical examples for cermet powders where Co, Ni or Cr is applied as single binder components. In powder manufacturing the binder components Co, Ni and Cr are added as separate pure metal powders and not as alloys. Until recen

38、tly, only pure metals have been available in the fine grain sizes required as they are produced by chemical precipitation methods. Until now it was economically not possible to produce matrix materials with the fine grain sizes required for the production of state-of-the-art agglomerated sintered ce

39、rmet powders from predominantly ductile alloys. For the same reason the production of cermets with health- and environment-friendly Co free, iron based alloys was not possible. Recently the production of agglomerated and sintered cermet powders with a matrix made from ductile complex alloys based on

40、 Ni and Fe with a homogeneous distribution of carbide and matrix has become possible. By application of a H.C. Starck proprietary milling process and chemical precipitation processes a wide variety of Ni and Fe based alloys are available in particles sizes suitable for the use in hard metals and the

41、rmal spray powders. Examples of Co free and corrosion resistant binders are Fe based Ni-Cr alloys such as austenitic steels. Fig. 4 shows the morphology of an agglomerated sintered WC-FeNiCr 85/15 powder where the standard Co, Co-Cr or Ni matrix has been replaced by a austenitic steel type alloy. By

42、 using the Fe23Cr6Al alloy as the binder material, even Co and Ni free cermet powders can be produced. WC-FeCrAl 85/15 and WC-Cr3C2-FeCrAl 73/20/7 are typical examples 8. Spray tests with a JP-5000 kerosene HVOF system were performed using standard parameters - 84 - 第十一屆國際熱噴涂研討會論文 第十二屆全國熱噴涂年會論文 (ITS

43、S2008 (CNTSC2008 which are typical for WC based powders. The deposition efficiencies (DE of the new powders are comparable to standard WC-Co 88/12 and WC-Co-Cr 86/10/4 powders provided that the apparent density of the powders is in a similar range. Powders with higher apparent density and comparable

44、 particle size distribution typically provide a slightly higher DE (Tab. 2. Fig. 4 SEM micrographs of agglomerated and sintered cermet powders with new Fe-based binder alloys: a WC-FeNiCr 85/15, b WC-FeCrAl 85/15, c WC-Cr3C2-FeCrAl 83/20/7 The micrographs of the coatings reveal that the coatings mad

45、e from both powders are very dense and exhibit a homogeneous distribution of both the carbides and the fine metallic binder particles (Fig. 5.Wear tests were performed according to the sand-abrasion-test ASTM G65 using a rubber coated abrasion wheel. Although the new powders with the Fe based matrix

46、 have a higher binder content than conventional Co containing powders, they were found to offer at least the same abrasion resistance as coatings made from WC-Co 88/12 and the same cavitation resistance as WC-Co-Cr coatings (Tab. 2. Table 2 Properties of the coatings sprayed from agglomerated sinter

47、ed powders with a particle size of 45/15 m Apparent Oxygen Content Carbon Content Density (g/cm³ 4,00 Powder Chemistry WC-FeCrAl 85/15 WC-FeNiCr 85/15 WC-Co Carbon Loss (% 17 (wt.% (wt.% DE Hardness Abrasive Cavitation Wear 1 (mg 23 Powder Coating Powder Coating 0,16 0,90 5,70 4,74 (% VHN 300g

48、1322 ± 126 1217 ± 51 1339 ± Rate (mg/h 3,5 ± 0,8 47 4,13 4,18 0,06 0,04 0,74 0,14 5,63 5,39 4,50 3,96 20 27 46 50 29 27 3,1 ± 0,4 20,7 ± 0,7 - 85 - 第十一屆國際熱噴涂研討會論文 第十二屆全國熱噴涂年會論文 88/12, medium WC WC-Co 88/12 WC-Co 83/17 WC-CoCr 86/10/4 5,22 0,03 0,12 5,36 4,51 16 55 1204 ± 44 29 114 (ITSS2008 (CNTSC2