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Utredning av erosionsnötning på material till bergborrningsverktyg
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Industrial Development, IT and Land Management, Mechanical Engineering.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Industrial Development, IT and Land Management, Mechanical Engineering.
2018 (Swedish)Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
Sustainable development
The essay/thesis is partially on sustainable development according to the University's criteria
Abstract [sv]

Sandvik Mining and Rock Technology (SMRT) är ett världsledande företag som tillverkar komplett utrustning till gruvindustrin. Några bergborrverktyg som utvecklas och tillverkas i Sandviken är bergborrkronor. Dessa kan delas in i tre produktgrupper, topphammar-, sänkborr- och rullborrkronor. Borrprocessen skiljer något mellan produktgrupperna, men förenklat ska ett hål formas i berget. Under borrningen frigörs det partiklar från berget som samlas i borrhålet och måste avlägsnas. Detta åstadkoms genom att en trycksatt fluid, vanligt luft eller vatten, spolas ned i borrhålet och binder upp partiklarna. Denna blandning av partiklar och fluid bildar eroderande media som succesivt nöter ned borrkronornas stålkroppar. Syftet med denna utredning var att undersöka erosionsmotståndet för material som används för att tillverka bergborrverktyg. Målet var att formulera ett underlag för att basera framtida materialval på.

Metoden som tillämpades i undersökningen baserades på ASTM-G76 standarden, något modifierad. Testerna utfördes i tempererade lokaler där temperaturen var omkring 20 grader Celsius. Fem stycken provbitar av varje stålsort tillverkades ur material med sju olika hårdheter, dess dimensioner var 25·20·5 mm. Nötande partiklar i undersökningen var kantig aluminiumoxid som siktats till 50 µm. Prover utfördes där partiklarnas infallsvinkel var 30°, dess hastighet var 50 m·s-1 och partikelflödet var 2 g·min-1. Provbitarna utsattes för nötande partiklar i totalt 10 minuter, dess förlorade massa kontrollerades i två minuters intervaller. Den förlorade massan konverterades sedan till volymförlust per gram erosionsmedia. Ett provämne av varje stålsort valdes sedan ut, där den eroderade ytan undersöktes i ett svepelektronmikroskop för att identifiera nötningsmekanismerna.

Resultatet av undersökningen visade att AISI 4140, som var bland de mjukaste materialen i undersökningen, tenderade att ha nötts minst. Stålsort EN36C, vilket var undersökningens hårdaste material, uppvisade sämre erosionsmotstånd. Resultatet innehöll dock spridning som medförde att andra material kan ha nötts mindre än AISI 4140. I denna undersökning visade det sig att hårdheten hade ingen, eller liten, inverkan på erosionen. På samtliga provbitarnas ytor hade en grop formats. Vid närmare undersökning av gropen i svepelektronmikroskopet visade det sig att de dominerande nötningsmekanismerna var spånavskiljande erosion och av plogande karaktär. På ett provämne lokaliserades en enskild partikelträff där en tydlig krater hade formats med en läpp i dess framkant, vilket är typiskt för duktila material.  

Slutsatsen av detta arbete är, att där erosion upplevs som ett problem kan AISI 4140 väljas vid tillverkning av borrverktyg. Det behövs dock utökad provning för att säkerställa detta.  

Abstract [en]

Sandvik Mining and Rock technology is a company that focuses on rock drilling. They offer a complete product line for mining and three specific products are top hammer-, down-the-hole- and rotary bits. These drill bits are subjects to erosion when drilling due to the discharge of rock cuttings out of the hole. The cuttings are removed with a fluid, often water or air which combined creates the erosive media. Erosion is a phenomenon that slowly wears materials and if not prevented can cause failures on the products. The main objective with this study is to identify how erosion resistant the steel materials, which the products are made of, are relative each other and what the damages can be in the microstructure. The goal with this study is to create a baseline with information so better material choices can be made in the future.

The method used in this paper is an erosion test based on ASTM G76 standard. The test equipment used fulfilled the standard with minor deviations. Specimens from seven different steels were manufactured with sizes of 25·20·5 mm, and heat treated to get the correct hardness values. Five samples were manufactured for each type of steel to get a good reliability. The parameters that were used were particle velocity of 50 m s-1, a particle flow of 2.0 g·min-1, an impact angle of 30º and a test time of 10 minutes in total per sample. The weight loss was measured every two minutes. The erosive particles chosen were sieved angular aluminum oxide with a nominal size of 50 micrometers. The loss of weight was noted for each sample and a mean loss was calculated and later converted to volume loss per gram erosion media. One sample of each steel type was investigated in a scanning electron microscope, to identify what type of wear mechanism that occurred in the micro structure.

The results showed that the steel type AISI 4140 had worn the least. EN36C had the highest loss of volume. This result is not ensured due to deviations in the results. AISI 4140 had among the lowest hardness values and EN36C the highest. That means that the hardness did not correlate with the erosion in this study. The mean erosion rate was even for all the steel types, and the erosion had created a pit in the surface that looked the same on all specimens. The scanning electron microscope showed that the wear mechanisms found were of plowing and cutting character which is typical for ductile materials such as steel. 

The conclusion of this investigation is that AISI 4140 could be chosen when erosion is an issue. It needs however more testing time in the erosion tester to confirm the results.

Place, publisher, year, edition, pages
2018. , p. 56
National Category
Other Mechanical Engineering
Identifiers
URN: urn:nbn:se:hig:diva-27044OAI: oai:DiVA.org:hig-27044DiVA, id: diva2:1218983
External cooperation
Sandvik Mining and Rock Technology
Subject / course
Mechanical engineering
Educational program
Technology – university diploma
Supervisors
Examiners
Available from: 2018-06-15 Created: 2018-06-15 Last updated: 2018-06-15Bibliographically approved

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