engineering solutions to problems of abrasive and corrosive wear
TRANSCRIPT
Advanced ceramic lining systems with wear re‐
sistance up to 200 mes greater than cast iron
Omegaslate UK Ltd. 2 Chirk Close, Forest Gate, Kidderminster, Worcestershire. DY10 1YG
Phone: +44 (0) 1562 755 824 Email: [email protected] Web: www.omegaslate.com
Omegaslate has 35 years experience in the design, supply, repair, upgrading and refurbishment of a wide range of abrasion resistant rotary valves, blowing seals, pumps, eductors and pipe work, fitted with diamond ground advanced ceramics lining systems.
Omegaslate UK Limited
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CERAMIC LINED DIVERTOR VALVES
Omegaslate refurbish and upgrade divertor valves, amongst other things, using abrasion resistant advanced alumina ceramics, and fine grained engineering grade RESILIDE reaction bonded silicon carbides for super abrasion resistant duties. All necessary metal machining and welding, and diamond grinding of the ceramic lin-ing components are carried out in our own workshop.
Omegaslate has 35 years experience in the assisting OEMs with the de-sign, supply, assembly and installation of alumina ceramic and reaction bonded silicon carbide hydrocyclones, for a wide variety of solids/liquid separation applications.
as blades. Consequently, either a new valve has to be acquired or the worn valve is refurbished. If your valve life is deemed un‐acceptable, a new or refur‐bished valve can be supplied fi ed with a wear resistant lin‐ing system. The lining material selected to resist the costly effects of han‐dling abrasive materials in a valve applica on, will depend on the severity of erosion and valve life required. The common materials used to resist abrasive wear in rotary and diverter valves are: Hard Chrome pla ng. Tungsten carbide spray
coa ngs. Hard metals. Ni‐hard cas ngs. Alumina ceramics linings. Reac on bonded silicon
carbide linings. The suitability and durability of these materials as abrasion re‐sistant linings and components, depends on the applica on in which they are applied; the hardness, sharpness and size of the grit or grain being handled; the pressure differen al across the valve; the leakage velocity past the rotor in the case of ro‐tary valves and blowing seals, or through‐put velocity of material flowing through a diverter valve. The ability of a par cular mate‐rial to exhibit greater wear re‐sistance that another depends on proper es such as hardness, surface finish, coefficient of fric‐
on, and grain structure, grain size and the nature of bonding matrixes and grain boundaries in the case of ceramics. If a rotary valve or blowing seal is used to feed a pneuma c conveying system with an abra‐sive material such silica sand, for instance, it would be correct to assume that appreciable wear to the component parts is highly likely in a rela vely short period of me. The mechanisms influencing wear of the valve are, again, grain size, hardness and sharp‐ness; air leakage velocity and the amount of running clear‐ance between the valve bore, endplates, and the rotor vane sealing blades. HARD CHROME PLATING will increase the opera onal life of valves as long as the minerals being handled are rela vely so . Of course, chrome has good corrosion resistance prop‐er es. It is theore cally possible for hard chrome pla ng to achieve over 4 mes the wear life of cast iron. Chrome hardness can be be‐tween 700 – 1000 Hv. Prac cal‐ly speaking, in aggressive wear applica ons, the true benefit of the hardness is o en dimin‐ished by the thinness of the de‐posited chrome layer – it can be penetrated by hard, sharp par ‐cles being crushed between ro‐tor vane sealing blades and a valve bore. Once the layer is penetrated, corrosion sets in and de‐lamina on occurs.
The purpose of the rotary valve and blowing seal is to control the feed rate of powders, flours granules, chips, grit or grains from a hopper. The output of the valve is fed at a measured rate into a pneuma c conveying system, or storage recep cal The efficiency of the rotary valve is measured by its ability to mini‐mise leakage. In order to keep leakage at an acceptable level, the rotor vane sealing blades are set with as small a gap (running clearance) as possible between the valve bore and endplates. Three factors that influence the degree and lengevity of a rotor running clearance are: a) Proper es of feed material. b) Temperature of feed material. c) Abrasion resistance of the valve bore, sealing blades and endplates. Temperature is normally a known quan ty and its effect on the running clearance can be calculated. The effects of han‐dling abrasive materials is not so easily calculated, but becomes evident when the valve leaks at an unacceptable rate. It is at this point that the valve life is deter‐mined. Increase in the running clear‐ance and leakage will be due, in different degrees, to wear of the vane sealing blades, the valve bore and the endplates, and not o en just one component such
TECHNICAL ELEMENTS
TUNGSTEN CARBIDE COATINGS are commonly used to protect valve bores, endplates and sha s against abrasive wear and prolong working life. General‐ly speaking, though, this coa ng ex‐tends the valve opera ng life of an un‐lined cast iron by 50 to 100%. Flame sprayed tungsten carbide coa ngs have hardness ra ngs up to approximately 1000 Hv and are rela‐vely cheap and easy to apply. The
drawback is the thinness of the coa ng. At approximately 50 microns, the flame sprayed coa ng can be more easily penetrated than some alterna ve lining systems, resul ng in progressive corro‐sion between the cast iron and the coa ng and premature de‐lamina on. HARD METALS are usually hardened to around 700 Hv for rotor sha protec‐on in the stuffing box seals and en‐
plate linings, but vane sealing blades are hardened to 520 Hv to reduce their bri leness. At a hardness of 700 Hv and above, wear life of up to 3 mes more than cast iron can be expected. NI‐HARD is o en used as sacrificial bore liners in hardnesses up to 700 Hv. Ni‐hard is approximately 3.5 mes more wear resistant than cast iron and doesn’t present any par cular opera‐onal problems.
ADVANCED CERAMICS are the most cost effec ve solu on in cases of ex‐treme abrasive wear. The common ce‐ramics used in valves are alumina and fine grain engineering grade reac on bonded silicon carbide ceramics. De‐pending on the ceramic and the grade used, hardness range from 1100 to 2500 Hv. Wear life offered are between 30 and 200 mes that of cast iron. For further informa on, please contact Omegslate for further advice on 01562 755 824
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