The Art of Hand Sanding

Grinding Techniques explains how important it is to choose the correct sandpaper when doing some hand sanding.

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We all love the speed and convenience of power tools when refurbishing furniture or sanding the garage door at home. But once the heavy sanding is done, the power tools finish
finds it difficult to compete with a little hand sanding. Power sanders leave a small but noticeable scratch pattern that could become more visible after your final coating is applied.

Hand sanding even when using the same grit size that was used on your power sander produces a finer and more consistent scratch pattern which normally disappears under the
first coat of varnish, stain or oil. Hand sanding also gives you more flexibility and control when it comes to sanding in hard to reach places. When sanding contours, corners and
curves there is not much that beats a sheet or strip of sandpaper that can also be used with a sanding block.

When taking on a project at home or at the office, we can agree that anyone would like to do as little sanding as possible. Therefore, we only buy the correct amount of sandpaper and
variety of grit sizes that we think we might need to complete the project. In most instances you will be able to complete your project with just 3 grit sizes of sanding sheets, for example
100, 150 and 220 grit. It is always advised to test a small sample piece of wood on your project to see whether you will reach your desired finish before purchasing your sandpaper.
It is also recommended not to sand with half used sandpaper scraps due to their bluntness and inconsistent wear as it can leave uneven scratch patterns on your surface.

When sanding by hand we are left with two choices, wet or dry sanding. Dry sanding offers more control and you have good visibility of what you are doing and the finish. Dry sanding
however does tend to clog your sandpaper much quicker. It is always more beneficial to use a stearate coated sheet equipped with an anticlogging agent for such dry sanding applications.

In wet sanding, use a liquid such as mineral spirits or soapy water to provide lubrication that aids in floating away the debris that would have clogged the sandpaper. For this application,
use a silicon carbide wet or dry abrasive sheet, more commonly known as water paper.

Finally, you can use non-woven hand pads that contain just enough abrasive to remove small imperfections without cutting through your finish.

For more information contact us: 011 271 6400 | info@grindtech.com | www.grindtech.com.

Making Chips Count

Who would have thought that an abrasive grinding wheel can be used in the production of chips? This is particularly pertaining to chips made from corn. The history behind milling corn to maize goes back many centuries, where ordinary stones where used. One being stationary and the other stone on top being rotated by hand to grind or mill the corn into maize. As demand for maize products grew more and more, millhouses became very popular and the milling stones utilized grew in size, the principal stayed the same by having one stationary stone (bed stone) and the other one rotated (runner stone) driven by livestock, windmills or electrical motors.

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Producing chips from corn uses the same principle to grind or mill the corn to a finer powder. The famous tortilla style chips start with cooking the corn kernels in water with the addition of limestone to soften the husk from the corn. The cooked corn is then fed into a perforated rotating spinning drum to loosen the husk which is then washed away by using high water pressure, exposing the softer inside. Ready to be fed to the milling process, a screw is used, where it will be fed in between grinding stones to be milled. The millstones are used in pairs one being stationary called the “bed stone” and the other rotates called the “runner stone”, the rotating stone does the actual grinding or milling of the corn. These stones have a special design to it, and is made from fused aluminum oxide with grit sizes ranging from 46 – 120 depending on the required texture, in a vitrified bond. The special design relates to the concave inner part, which has deep grooves called the furrow coming up onto flat areas called lands, out to the outer edges where the actual grinding will take place with smaller grooves called feathering or cracking. The two stones are set to a specific thickness depending on the consistency required. As the corn is fed through the bed stone the inner grooves feed the corn to the outer side of the wheel with the smaller grooves, and as the runner wheel spins, the corn is then ground into Corn Massa (Spanish for dough). Now it is ready to go further down the production line to form the end product.

These types of stones are also used to grind, chocolate, coffee, cork, mustard, paint, snuff and sugar cane etc.

Grinding Techniques, a Tyrolit company and proudly South African manufacturer is a key supplier of ANDOR grinding wheels to the milling industry. We offer local manufactured products as well as imported Tyrolit wheels. Size, specification and configurations can be customized according to customer specific requirements.

Dedicated support personnel are ready and available to provide you with all the support and advise required to make your chips count!

For more information contact us: 011 271 6400 | info@grindtech.com | www.grindtech.com.

Grinding Techniques, Your Coated Partner for Brilliant Metal Surfaces

Industrial applications require a high degree of specialization. Grinding Techniques offers you Pearl grinding abrasive products from Starcke – the exact tool for your grinding needs.

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With these products a perfect surface and optimal product life can be assured. You can rely on Starcke Coated Abrasives as it carries the “Made in Germany” quality mark.

The Pearl grinding product range obtains its uniqueness from the mineral (grain) used to perform the cutting action. Granulated abrasive grains are pearl shaped that ensure consistent surface quality and removal rates. This abrasive technology is also known as agglomerate abrasives. Agglomerate abrasives is a combination of several identically sized abrasive grains that are shaped into a larger granulate using a resin before being spread onto a backing. Synthesized like this these abrasive granules form a firm bond that are attached to a material backing.

There are a few main advantages one can benefit from using the Pearl coated abrasive products. Very consistent surface finish is ensured; abrasive minerals go through a self-sharpening process throughout its life cycle, thus having continuous and uniform sharp edges exposed. Stock removal rates are higher than with conventional abrasive grains and longer longevity in the product life ensures perfect results whilst saving costs and time.

The Pearl range is well suited for the repair of coils and plates in a rolling mill. Pearl products also display their high performance in applications involving the use of water, emulsion and oil. With its high bond hardness, Pearl abrasives have the ideal application characteristics for edge grinding of flat rolled steel materials. Due to its uniform surface grinding characteristics they are perfect to produce a polished or matt surface finish.

Our Pearl offering is also suited for centerless grinding of tubes, bars and cylinders with a bonding system that is optimally suited for wet and dry grinding machine applications. With its regenerative concept, consisting of granulated abrasive grains and bonding system, the Pearl product offering guarantees a consistently uniform wire surface finish. This ensures perfect removal of mill scales from the wire and a uniform feed of the wire material throughout the product’s useful life, significantly reducing wear of the drawing plate.

Contact one of our Product Specialists at Grinding Techniques for a Pearl grinding solution to benefit from a product with longevity whilst maintaining a consistent stock removal and a consistent scratch depth and workpiece surface.

For more information contact us: 011 271 6400 | info@grindtech.com | www.grindtech.com.

We keep the Paper and Pulp Industry Rolling

The grinding of rolls for the paper mill industry is known to be one of the most difficult grinding operations. These rolls are normally very long relative to outside diameter, hard in composition and have very tight tolerances and surface finish requirements to be met.

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In most cases the grinding of paper mill rolls is a very time-consuming operation when it comes to both the roughing and finishing cycle of the process. Excellent operator skill and special attention to the grinding machine and its surroundings are also crucial factors when it comes to delivering a good and consistent result. Some of the common challenges faced in the grinding process might include, roll deflection and sag, vibration, wheel glazing, chatter marks, traverse marks and stainless-steel loading. The finishing process is commonly the most difficult and time consuming as some rolls might take much longer than others to grind.

Choosing the correct grinding wheel for the roughing and finishing cycles of the grinding process is of utmost importance. Using a too hard or too soft wheel or even a wheel with the incorrect mineral and bond combination could lead to the loss of a lot of time during the grinding process. Grinding Techniques – a Tyrolit Company – is able to provide the Paper and Pulp Industry with local research and development capability as well as both locally manufactured Andor wheels, and imported Tyrolit wheels. Both the Andor and Tyrolit grinding wheels are specifically formulated and manufactured with the characteristics for successful roughing and finishing cycles in the grinding process.

Grinding wheels consist of abrasive grains held together by a resin bond. The abrasive normally used is black or green silicon carbide, which is a hard and sharp mineral and suited for most rolls used in the paper mill industry. In the grinding process the grains’ sharp edges cut away the material and become dull (loses its sharpness) under the heat and pressure of the grinding process. The bond releases the dull grain from the wheel at the perfect time, exposing a new sharp edge of the grain, ensuring that these sharp edges are exposed for the full duration of the
grinding wheel’s life cycle. Using the correct grinding wheel will ensure that more material is removed per pass with minimal tendency of glazing and the least amount of dressing required.

Using two different wheels for the roughing and the finishing cycles when grinding paper mill rolls, have proven the most successful in the shortest time. For example, a grinding wheel used in the roughing cycle will generally be much too hard to be able to adhere to the required finish in the finishing process.

The objective of the roughing wheel is to remove stock (material off the roll). Grinding Techniques takes the following aspects into consideration when specifying a rough grinding wheel suited for the Paper mill Industry. The wheel needs to remove high volumes of material per pass whilst not having a tendency to burn the roll. The ideal wheel should also possess a free cutting action with minimum heat generated with the least dressing cycles required. A very consistent and uniform surface finish is also a top priority.

The finishing cycle of the grinding process has different characteristics compared to the roughing cycle. Considering the lower pressures and different speed and feed rates of the finishing cycle, the wheel matrix has to be adjusted accordingly. Lower grinding pressures could cause a wheel’s grains to dull and burn to the workpiece and chatter is often the result. The finishing cycle on roll grinding would require a finer grit wheel with a softer bonding system to release the dulled grains at lower pressures.

Contact Grinding Techniques, the largest local producer of resin and vitrified abrasive products for a tailored solution to all your grinding processes of various paper mill rolls.

For more information, please contact: 011 271 6400 | info@grindtech.com | www.grindtech.com.