Grinding wheel

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Various types of grinding wheels Haltern am See, Sythen, Werkzeughalle der Quarzwerke -- 2015 -- 01117.jpg
Various types of grinding wheels

Grinding wheels are wheels that contain abrasive compounds for grinding and abrasive machining operations. Such wheels are also used in grinding machines.

Contents

The wheels are generally made with composite material. This consists of coarse-particle aggregate pressed and bonded together by a cementing matrix (called the bond in grinding wheel terminology) to form a solid, circular shape. Various profiles and cross sections are available depending on the intended usage for the wheel. They may also be made from a solid steel or aluminium disc with particles bonded to the surface. Today most grinding wheels are artificial composites made with artificial aggregates, but the history of grinding wheels began with natural composite stones, such as those used for millstones.

The manufacture of these wheels is a precise and tightly controlled process, due not only to the inherent safety risks of a spinning disc, but also the composition and uniformity required to prevent that disc from exploding due to the high stresses produced on rotation.

Grinding wheels are consumables, although the life span can vary widely depending on the use case, from less than a day to many years. As the wheel cuts, it periodically releases individual grains of abrasive, typically because they grow dull and the increased drag pulls them out of the bond. Fresh grains are exposed in this wear process, which begin the next cycle. The rate of wear in this process is usually very predictable for a given application, and is necessary for good performance.

Characteristics

There are five characteristics of a cutting wheel: abrasive material, grain size, wheel grade, grain spacing, and bond type. They are indicated by codes on the wheel's label.

Abrasive Material

The abrasive aggregate is selected primarily according to the hardness of the material being cut. Chemical compatibility is also a concern. For example, because carbon alloys with iron, silicon carbide is not suitable for use with iron-based metals like steel.[ citation needed ]

Grinding wheels with diamond or CBN grains are called superabrasives. Grinding wheels with aluminum oxide (corundum), silicon carbide, or ceramic grains are called conventional abrasives.

Grain size

From 10 (coarsest) to 600 (finest), determines the average physical size of the abrasive grains in the wheel. A larger grain will cut freely, allowing fast cutting but poor surface finish. Ultra-fine grain sizes are for precision finish work. Generally, grain size of grinding wheels are 10-24 (coarse), 30-60 (medium), 80-200 (fine), and 220-600 (very fine).

Wheel grade

From A (soft) to Z (hard), determines how tightly the bond holds the abrasive. A to H for softer structure, I to P for moderately hard structure and Q to Z for hard structure. Grade affects almost all considerations of grinding, such as wheel speed, coolant flow, maximum and minimum feed rates, and grinding depth.

Grain spacing

Spacing or structure, from 1 (density) to 17 (least dense). Density is the ratio of bond and abrasive to air space. A less-dense wheel will cut freely, and has a large effect on surface finish. It is also able to take a deeper or wider cut with less coolant, as the chips clearance on the wheel is greater.

Wheel bond

How the wheel holds the abrasives; affects finish, coolant, and minimum/maximum wheel speed.

Bond nameBond symbolBond description
VitrifiedV Glass-based; made via vitrification of clays and feldspars
ResinoidB Resin-based; made from plants or petroleum distillates
SilicateS Silicate-based
ShellacE Shellac-based
RubberRMade from natural rubber or synthetic rubber
MetalMMade from various alloys
OxychlorideOMade from an oxohalide
PlatedPMade by Electro / Electroless bonding of metal to hold abrasive

Types

Straight wheel

Straight wheel GrindingStraightWheelH468V.jpg
Straight wheel

To the top is an image of a straight wheel. These are by far the most common style of wheel and can be found on bench or pedestal grinders. They are used on the periphery only and therefore produce a slightly concave surface (hollow ground) on the part. This can be used to advantage on many tools such as chisels.

Straight Wheels are generally used for cylindrical, centreless, and surface grinding operations. Wheels of this form vary greatly in size, the diameter and width of face naturally depending upon the class of work for which is used and the size and power of the grinding machine.

Cylinder or wheel ring

Cylinder wheels provide a large, wide surface with no center mounting support (hollow). They can be very large, up to 12" in width. They are used only in vertical or horizontal spindle grinders. Cylinder or wheel ring is used for producing flat surfaces, the grinding being done with the end face of the wheel.

Tapered wheel

A straight wheel that tapers outward towards the center of the wheel. This arrangement is stronger than straight wheels and can accept higher lateral loads. Tapered face straight wheel is primarily used for grinding thread, gear teeth ...

Straight cup

Straight cup wheels are an alternative to cup wheels in tool and cutter grinders, where having an additional radial grinding surface is beneficial.

Dish cup

A very shallow cup-style grinding wheel. The thinness allows grinding in slots and crevices. It is used primarily in cutter grinding and jig grinding.

Saucer wheel

A special grinding profile that is used to grind milling cutters and twist drills. It is most common in non-machining areas, as sawfilers use saucer wheels in the maintenance of saw blades.

Diamond wheels

Diamond wheel GrindingCutOffWheelDiamond.jpg
Diamond wheel

Diamond wheels are grinding wheels with industrial diamonds bonded to the periphery.

They are used for grinding extremely hard materials such as carbide cutting tips, gemstones or concrete. The saw pictured to the right is a slitting saw and is designed for slicing hard materials, typically gemstones.

Mounted points

Mounted points are small grinding wheels bonded onto a mandrel. Diamond mounted points are tiny diamond rasps for use in a jig grinder doing profiling work in hard material. Resin and vitrified bonded mounted points with conventional grains are used for deburring applications, especially in the foundry industry. Mounted points is a small handle with a general name, used in electric mill, hanging mill, hand drill. Many of the main types of ceramic mounted points, rubber mounted points, diamond mounted points, emery cloth and so on.

Ceramic mounted points: granular sand (usually corundum, white jade, chrome corundum, silicon carbide) made of ceramic binder sintering, the central supplemented by metal handle. Mainly grinding all kinds of metal, for the diameter of the inner wall of the grinding, mold correction. Rubber mounted points: finer particle size sand combined by rubber binder Into, for the polishing of the mold. sandpaper mounted points: Multi-piece rectangular sand cloth, bonding around the metal handle. Granularity is generally in the 60 # -320 #, for the diameter of the inner wall of the polishing. Diamond mounted points: A grinding tool for non-metallic materials such as stone, porcelain and the like, and more particularly to a grinding tool using a diamond alloy as a grinding body comprising a substrate and a plurality of grinding bodies, And the substrate is preferably made of an adhesive material having a certain toughness, and the grinding body is preferably made of a diamond alloy material, and the substrate is preferably made of a diamond alloy material, The utility model has the characteristics of high grinding performance, simple manufacture and low cost, high grinding quality and can be applied to large-scale grinding.

Cut off wheels

Cut off wheels, also known as parting wheels, are self-sharpening wheels that are thin in width and often have radial fibres reinforcing them. They are often used in the construction industry for cutting reinforcement bars (rebar), protruding bolts or anything that needs quick removal or trimming. Most handymen would recognise an angle grinder and the discs they use.

Use

Grinding produces sparks and little fragments of metal, called swarf. A song of fire and metal.jpg
Grinding produces sparks and little fragments of metal, called swarf .

To use the grinding wheel it must first be clamped to the grinding machine. The wheel type (e.g. cup or plain wheel below) fit freely on their supporting arbors, the necessary clamping force to transfer the rotary motion being applied to the wheels side by identically sized flanges (metal discs). The paper blotter shown in the images is intended to distribute this clamping force evenly across the wheels surface.

Dressing

Grinding wheels are self-sharpening to a small degree; for optimal use they may be dressed and trued by the use of wheel or grinding dressers. Dressing the wheel refers to removing the current layer of abrasive, so that a fresh and sharp surface is exposed to the work surface. Trueing the wheel makes the grinding surface parallel to the grinding table or other reference plane, so that the entire grinding wheel is even and produces an accurate surface.

Testing for grinding tools

Grinding wheels and grinding tools are used extensively in industry and manual trades for treating surfaces and for separating and cutting objects and have to withstand massive mechanical stress. Mostly centrifugal forces can cause a break, but also flexural and shear forces. Since a break or failure of the grinding tool can present a severe hazard to people and machinery due to the high levels of energy released, high standards are placed on the mechanical and breaking strength of grinding tools in the European safety standards. The Institute for Occupational Safety and Health of the German Social Accident Insurance conducts tests based on the "Rules of Procedure for Testing and Certification carried out by the Testing and Certification Bodies in DGUV Test". [1]

See also

Related Research Articles

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An abrasive is a material, often a mineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away by friction. While finishing a material often means polishing it to gain a smooth, reflective surface, the process can also involve roughening as in satin, matte or beaded finishes. In short, the ceramics which are used to cut, grind and polish other softer materials are known as abrasives.

<span class="mw-page-title-main">Sandpaper</span> Abrasive material used for smoothing softer materials

Sandpaper, also known as glasspaper or as coated abrasive, is a type of material that consists of sheets of paper or cloth with an abrasive substance glued to one face. In the modern manufacture of these products, sand and glass have been replaced by other abrasives such as aluminium oxide or silicon carbide. It is common to use the name of the abrasive when describing the paper, e.g. "aluminium oxide paper", or "silicon carbide paper".

<span class="mw-page-title-main">Grinding machine</span> Machine tool used for grinding

A grinding machine, often shortened to grinder, is a power tool used for grinding. It is a type of machining using an abrasive wheel as the cutting tool. Each grain of abrasive on the wheel's surface cuts a small chip from the workpiece via shear deformation.

<span class="mw-page-title-main">Bench grinder</span> Grinding machine

A bench grinder is a benchtop type of grinding machine used to drive abrasive wheels. A pedestal grinder is a similar or larger version of grinder that is mounted on a pedestal, which may be bolted to the floor or may sit on rubber feet. These types of grinders are commonly used to hand grind various cutting tools and perform other rough grinding.

A grinding dresser or wheel dresser is a tool to dress the surface of a grinding wheel. Grinding dressers are used to return a wheel to its original round shape, to expose fresh grains for renewed cutting action, or to make a different profile on the wheel's edge. Utilizing predetermined dressing parameters will allow the wheel to be conditioned for optimum grinding performance while truing and restoring the form simultaneously.

<span class="mw-page-title-main">Sharpening stone</span> Abrasive slab used to sharpen tools

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Superfinishing, also known as microfinishing and short-stroke honing, is a metalworking process that improves surface finish and workpiece geometry. This is achieved by removing just the thin amorphous surface layer of fragmented or smeared metal left by the last process with an abrasive stone or tape; this layer is usually about 1 μm in magnitude.

<span class="mw-page-title-main">Diamond tool</span> Cutting tool with diamond grains

A diamond tool is a cutting tool with diamond grains fixed on the functional parts of the tool via a bonding material or another method. As diamond is a superhard material, diamond tools have many advantages as compared with tools made with common abrasives such as corundum and silicon carbide.

<span class="mw-page-title-main">Rotary tool</span> Handheld power tool used for grinding, drilling, machining, etc.

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Abrasive machining is a machining process where material is removed from a workpiece using a multitude of small abrasive particles. Common examples include grinding, honing, and polishing. Abrasive processes are usually expensive, but capable of tighter tolerances and better surface finish than other machining processes

<span class="mw-page-title-main">Grinding (abrasive cutting)</span> Machining process using a grinding wheel

Grinding is a type of abrasive machining process which uses a grinding wheel as cutting tool.

<span class="mw-page-title-main">Honing (metalworking)</span> Production of a precise surface on a metal workpiece

Honing is an abrasive machining process that produces a precision surface on a metal workpiece by scrubbing an abrasive grinding stone or grinding wheel against it along a controlled path. Honing is primarily used to improve the geometric form of a surface, but can also improve the surface finish.

Surface grinding is done on flat surfaces to produce a smooth finish.

<span class="mw-page-title-main">Flat honing</span> Metalworking grinding process

Flat honing is a metalworking grinding process used to provide high quality flat surfaces. It combines the speed of grinding or honing with the precision of lapping. It has also been known under the terms high speed lapping and high precision grinding.

<span class="mw-page-title-main">Diamond grinding cup wheel</span>

A diamond grinding cup wheel is a metal-bonded diamond tool with diamond segments welded or cold-pressed on a steel wheel body, which usually looks like a cup. Diamond grinding cup wheels are usually mounted on concrete grinders to grind abrasive building materials like concrete, granite and marble.

<span class="mw-page-title-main">Disc cutter</span> Power tool used to cut hard materials

A disc cutter is a specialised, often hand-held, power tool used for cutting hard materials, ceramic tile, metal, concrete, and stone for example. This tool is very similar to an angle grinder, chop saw, or even a die grinder, with the main difference being the cutting disc itself. This tool is highly efficient at cutting very hard materials, especially when compared to hand tools.

Grinding wheel wear is an important measured factor of grinding in the manufacturing process of engineered parts and tools. Grinding involves the removal process of material and modifying the surface of a workpiece to some desired finish which might otherwise be unachievable through conventional machining processes. The grinding process itself has been compared to machining operations which employ multipoint cutting tools. The abrasive grains which make up the entire geometry of wheel act as independent small cutting tools. The quality, characteristics, and rate of grinding wheel wear can be affected by contributions of the characteristics of the material of the workpiece, the temperature increase of the workpiece, and the rate of wear of the grinding wheel itself. Moderate wear rate allows for more consistent material size. Maintaining stable grinding forces is preferred rather than high wheel wear rate which can decrease the effectiveness of material removal from the workpiece.

References

  1. Institute for Occupational Safety and Health of the German Social Accident Insurance. "Institute for Occupational Safety and Health of the German Social Accident Insurance".