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Metal grinding: This is how it's done
Metal grinding is indispensable in metalworking, whether for DIY projects, industrial applications or the production of precision components. It is used to remove irregularities in the surface of components, rust or weld seams and to produce the desired dimensional accuracy of components. Grinding makes it possible to create surfaces that arefunctional and aesthetically pleasing. The tools, abrasives and techniques must be carefully selected for the respective requirements and to suit the metals to be processed. Every metal and every application has its own specific requirements.
This guide answers the most frequently asked questions about metal sanding . You can find out how to select the right grit, which abrasives are suitable for different metals and surfaces and which machines are best suited for different tasks. You will also find useful tips on how to avoid typical mistakes when sanding metal and how to achieve optimum results. This guide can help you master any sanding project, regardless of whether you are a beginner or an experienced craftsman.
Table of contents Grinding metal:
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What is the purpose of metal grinding?
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Which abrasives are used for metal grinding?
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How do you choose the right grit for grinding metal?
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What safety measures must be observed when grinding metal?
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What are typical mistakes when grinding metal and how can they be avoided?
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How do you grind rusty metal parts correctly?
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Which machines and tools are best suited for metal grinding?
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Tips for DIY enthusiasts
What is the purpose of metal grinding?
Metal grinding is used for various purposes. Typical applications range from improving aesthetics to functional processing. The main purpose is to smooth the surface and improve the surface quality of a piece of metal. It is used to remove imperfections such as burrs, weld seams, rust or excess material. It also ensures that metal parts are prepared for subsequent processing such as painting, coating or polishing by creating an even and well-adhering surface.
Precision grinding helps to improve the dimensional accuracy of a workpiece, for example when manufacturing components that need to match each other. Metal grinding is also used to produce decorative surfaces such as stainless steel or brushed aluminium. In industrial applications, grinding improves the resistance of metal parts to corrosion and wear, which contributes to a longer service life and therefore more sustainable operations
Which abrasives are used for metal grinding?
Various abrasives are used for metal grinding. The abrasives are selected depending on the type of metal, the machining objective and the work process. The most important abrasives and their properties:
1. Grinding discs
Grinding discs are used on angle grinders, cut-off grinders or stationary machines. They are made of aluminium oxide, silicon carbide, ceramic or diamond. They are ideal for rough work such as removing weld seams or burrs.
2. Sanding belts
Sanding belts are used in belt sanders or stationary belt machines, especially for large surfaces. Sanding belts are often coated with aluminium oxide or zirconium oxide. They offer high efficiency with large-area material removal.
3. Sandpaper
Sandpaper is intended for sanding by hand or with orbital sanders. Fine-grained sandpaper (400+) is for polishing and coarse-grained sandpaper (40-120) for high material removal. The advantages are; flexible application possibilities and favourable prices.
4. wire brushes and abrasive fleece
Wire brushes and abrasive fleece are used to remove rust or paint residues.
They are made of steel, brass or plastic fibres with an abrasive coating.
The choice of the right abrasive depends on the type of metal (e.g. stainless steel, aluminium) and the desired result (e.g. coarse or fine sanding).
How do you choose the right grit for grinding metal?
Choosing the right grit size for an abrasive is crucial for the sanding result and has a significant influence on the sanding progress. Grit sizes are categorised based on the particle size of the abrasive and the amount of abrasive on a given surface.
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Coarse grits (e.g. 40 - 80) are suitable for removing excess material, rust, burrs or weld seams.
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Medium grits (120 - 240) are ideal for intermediate sanding if a smooth surface is to be achieved after the sanding work has been completed.
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Fine grits (400 and higher) are used for finishing and before polishing, for example for high-gloss surfaces.
The choice also depends on the metal: Hard metals such as stainless steel often require finer grits and a soft abrasive bond. Soft metals such as mild steel or copper are optimally processed on sanding machines with abrasives that have a hard bond. When sanding metal, it is advisable to start with a coarse grit and gradually switch to a finer and finer grit depending on the desired result.
Suitable machines for metal grinding in our shop:
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What safety measures must be observed when grinding metal?
Depending on the technique used, metal grinding can entail several risks, including flying sparks, noise pollution and dust formation. Suitable protective equipment is always essential. Safety goggles protect the eyes from sanding particles and from sparks when machine sanding. Breathing masks prevent the inhalation of metal dust, which can be harmful to health. Work gloves offer protection against cuts and hot metal parts.
Hearing protection is also important when grinding metal, especially when working with loud grinding machines or processing sheet metal with a hand grinder. Work clothing should be made of flame-retardant materials to protect against ignition from sparks. In addition, it is important to maintain every sanding machine regularly and to repair defects immediately. Workpieces should be securely clamped whenever possible to prevent slipping. Adequate ventilation or an extraction system reduce dust exposure at the workplace.
What are typical mistakes when grinding metal and how can they be avoided?
One of the most common mistakes when sanding metal is applying too much pressure during processing. If the pressure is too high, the surface is removed unevenly and the abrasive generally wears out more quickly. In addition, too much heat can be generated, possibly causing the workpiece to wear away. This can be avoided by letting the abrasive do the work and not trying to speed up the sanding process by increasing the pressure.
The wrong choice of grit can also be problematic when sanding metal. Too coarse a grit size leaves deep scratches that are often difficult and time-consuming to remove. Choosing a grit that is too fine can result in ineffective material removal and unnecessarily prolong the sanding process.
Irregular and insufficient movement of the abrasive on the metal surface can also lead to scoring and uneven surfaces when sanding metal. Abrasives should be cleaned or replaced regularly to avoid deposits that impair efficiency. If possible, wet sanding should also be used when sanding metal.
Another mistake is to sand metals such as aluminium for too long, as they can quickly overheat. Sufficient cooling, for example with water or special grinding fluids, can help here.
How do you grind rusty metal parts correctly?
Grinding rusty metal parts is a common task and requires several steps. Firstly, loose rust is removed with a wire brush or coarse steel wool. This quickly but effectively reduces the amount of work required for the actual sanding. A coarse-grained sandpaper (e.g. 40 - 80 grit) or a grinding disc is then used to completely remove the rust.
For deeper rust spots or hard-to-reach areas, small grinding tools such as a Dremel or similar tools with a rotating wire brush can be used. Once the rust has been removed, the metal is sanded with a finer grit (e.g. 120 - 240) to achieve a smooth surface. Finally, the surface is cleaned, for example with a degreasing agent. Finally, and depending on further use, the now bare metal should be protected against renewed corrosion. For example, by painting, coating or using a preservative oil such as Ballistol.
Which machines and tools are best suited for metal grinding?
The choice of machines and tools for metal sanding depends on the type and size of the project. Hand sanding blocks, sandpaper or rotary tools such as a Dremel are ideal for small jobs or detailed work. Angle grinders are versatile and are suitable for rough work, such as removing weld seams, as well as for smoothing large surfaces. Belt sanders are particularly efficient when working on long, flat metal parts. Stationary sanders are often used in workshops for precise sanding work, such as sanding edges or contours. Modern machines often have extraction systems that prevent health-endangering dust exposure at the workplace.
Tips for DIY enthusiasts
Grinding rusty metal parts
Rusty metal parts are always sanded in several steps to achieve optimum results. Firstly, loose rust is removed with a wire brush or coarse steel wool. Afterwards, any stuck rust is removed with a grinding disc and deep-seated rust is completely removed with a rotating wire brush. Finally, the metal must be protected against renewed rusting with a coat of paint or preservative oil.
Avoid mistakes when sanding metal.
The abrasive should always be selected to suit the metal and the desired result. It is better to change the abrasive once more than to try to speed up the work by applying more pressure.
Wet sanding is better than dry sanding
Whenever possible, metal should be sanded wet. The water cools the workpiece and rinses away abrasion before the abrasive can clog and cause scoring. Wet sanding should only ever be carried out manually or with pneumatic tools.
Questions for the expert:
Kevin Weidlich
Expert
