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Abrasives

Abrasives (3)

Monday, 12 January 2015 00:00

Abrasive Grain

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Function of abrasive grain: grinding wheels contain thousands of abrasive grain particles, each of which acts as a cutting tool removing small pieces (commonly called chips) from the work material. The size of the chips and the resulting surface finish are governed by the grit size of the abrasive. Coarse grit sizes will cut away bigger chips and leave a rougher surface. Fine grit sizes will cut away smaller chips and leave a smoother surface. The abrasive grain has a characteristic "friability", that is, under normal grinding conditions each particle fractures to expose new cutting surfaces. There are many different grain types (recognizable by wheel color for vitrified wheels) with varying degrees of friability. The least friable grains are used on the easiest to grind material, while the most friable grains are used on the most difficult to grind materials.
ALUMINUM OXIDE is the abrasive for high tensile strength materials (alloy steel, high speed steel, annealed malleable iron)
SILICON CARBIDE is the abrasive for low tensile material (cast iron, bronze, aluminum, copper, glass ceramics, non-metallics)
SILICON CARBIDE is harder and sharper than ALUMINUM OXIDE but fractures more readily
ZIRCONIA-ALUMINA is the abrasive for difficult-to-grind materials like stainless and carbon steel, exotic, other ferrous and heat sensitive metals

 
Monday, 29 September 2014 00:00

Alumina Oxide - Al2O3

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Aluminum Oxide, invented in 1900 by Charles B. Jacobs, is used in 75% of all grinding wheels. ALO is produced in an open top, three electrode, electric arc tilt furnace. The basic furnace mix consisting of bauxite, coke and iron borings results in the high purity, white aluminum oxide  (brown aluminum oxide is high titania and pink is high chromium). The mix is melted at temperatures of about 1900 C and in approximately 4 hours the furnace is tilted and its contents poured into a 5 ton mold. This casting is cooled for 2 days, then stripped and cooled another day. A 2 ton steel ball is dropped from a crane to break the aluminum oxide pig into large chunks. The chunks are then reduced in jaw crushers to about 6 inches and smaller. This material is passed along a belt to gyratory crushers to reduce the size to 2 inches and smaller. The last step in size reduction is either hammer milling or roll crushing.

Aluminum Oxide - PinkCrude Abrasive Grain

The material is then passed through a series of screens to group particle sizes and through a magnetic separator to remove impurities. At this point the grain may be treated by any one of a number of different processes to improve the final shape, surface condition and cleanliness. These include centrifugal  impact crushing (mulling), roasting, washing and acid or alkali treatment.

The grain is now ready for final sizing. For grit sizes 6 to 200 this is accomplished by passing the grain through a series of screens. The grit size refers to the number of openings per lineal inch in the wire or silk screen through which all material will pass. For grit sizes 240 through 1000 (referred to as powders) the material is sized by water sedimentation, hydraulic flotation or air classification. The industry complies with the National Bureau of Standards' recommendations for the distribution of fines in any particular grit size.

Note that friability is the term used to describe the ability of the abrasive particle to fracture under pressure. Brown aluminum oxide is the least expensive, has low friability and is cost effective for conventional steels with high grindability. Pink and white aluminum oxides are most expensive but are cost effective on materials that are harder to grind. Pink aluminum oxide is semi-friable and is your best choice for light to moderate stock removal on tool steels, vanadium alloys and stainless steel. White aluminum oxide has high friability and is your best choice for light stock removal on hard, heat sensitive, high speed steel alloys.

Tuesday, 07 January 2014 06:33

Pferd Ergonomics

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During the creation process of any tool for hand-held use, all the way from research and development to production, PFERD’s focus is on people. High-quality manufacturers commonly focus on providing the most cost-effective tool for their customers. PFERD knows that the best value comes from focusing on the health and safety of the operator. Indoors or outdoors, from the foundry to the shipyard- End-users face a variety of tough working conditions, rough applications and high physical demands. There is a constantly increasing challenge of producing perfect, uniform results under tight deadlines and extreme physical pressure. PFERD recognizes that the most effective reduction in costs and increases in productivity depend on understanding the tools,  The environment, and the application, and their impact on the health, safety, and comfort of the user. To be able to fulfil these increased requirements,
 
PFERD ERGONOMICS supplies solutions for:

 

  • Lower vibrations
  • Reduced noise
  • Less dust
  • Optimized haptics at work