How to choose abrasive chips ?

The choice of & rsquo; equipment best suited to a mass finishing operation is an important point in our range of over 150 different models (vibrators, centrifuges different families, rotative barrels…).

The choice of media is equally important, see more ; but the range of over 6500 products may seem difficult to understand.

They are chosen according to :

– The objective (deburring, polishing, edges radiusing, brightening, sand blasted effect...) and parts material that define the abrasive power of the chips (more or less abrasive, or polishing) ; thus, for harder materials such as hardened steel or ceramics or zircones, one will choose a more powerful abrasive compared with more ductile materials such as brass, s & rsquo; Aluminum, Niobium or the & rsquo; Or.

– The size and morphology of the parts define the shape and dimensions of the chips

Main product code :

Shape codification :

– ACC : angle cut cylinder : Angle cut cylinder

– SCC : straight cut cylinder : Straight Cut Cylinder

– ACT : angle cut triangle : angled cut triangle

– SCT : straight cut triangle : straight cut triangle

– BALL : ball

– SCTS ou ACTS : angle or straight cut tristar

– P : pyramid

– WEDGE : wedge

– CONE : cone

– Paraboloid : Paraboloid

Most common material codification (non-exhaustive list) :

Ceramic :

MGA : abrasive
FGA : low abrasive

Porcelain :

PW : medium grain
FPW : fine grain
FPRW : very fine grain

plastic :

TKS / TKX : very abrasive
TKV / TKG : abrasive medium
TKM / TKK : light abrasive
TKP : polishing

Metallic :

SS304 : stainless steel 304
SS316 : stainless steel 316
Copper : Copper

Ceramic and polyester media (plastics) are composed of a binder and abrasive powders ; these abrasive powders are characterized by their composition (Al2O3-alumina or Aluminum oxide, SiO2, SiC-carbon from silicon, Diamond micro-powders, BoC-Boron Carbide, BoN…) and by their grain size ; this grain size defines the abrasive power of the media ; the bigger it is, the greater the removal of material with each pass of the grain, but will generate a medium to low quality roughness.

The grain size of these powders is expressed in mesh or in microns ; watch out for these 2 scales are opposite – the lower the mesh value, the greater the value in microns and vice versa.

Finally, it is absolutely necessary to distinguish the media from the abrasive powder that constitutes it ; the media is like a grinding wheel made of a binder in which abrasive grains are positioned on the surface and in the heart ; it is these abrasive grains that generate the removal of material ; these abrasive grains have sharp edges which, like tools, will gradually see their sharpness degrade and thus lose their cutting power ; to avoid this problem, the binder must wear down a few microns to reveal new abrasive grains whose sharp cutting edges will give new cutting power.

Note that in some cases, it is possible to combine abrasive media (with abrasive grains) with loose abrasive powders ; it is also possible to use only loose abrasive powders without media (usually on high energy equipment)…

Some basic elements for choosing the right chips :

always choose the largest possible, allowing chips “to touch” all areas to be treated
more the chips are big, more they will have power ; they will thus have more effectiveness in eliminating some resistant burrs and reduce the cycle time
for deburring or polishing a hole of diameter 10, three strategies appear : solution A : we accept that the chips penetrate completely into the hole (with the risk of letting some chips inside the hole after the process and making necessary a final control) : the best choice may be cylinders diameter 8 ; an angle cut chip will facilitate the introduction of the chips in the hole ; we will ensure to eliminate the chips whose diameter approaches diameter 5, because it will block two chips (5+5=10); solution B : we refuse that the chips completely penetrate the hole : the best choice may be cylinders diameter 12 ; the tip linked to the angle cut will make easier the introduction of the chips inside the hole ; this solution presents some limits if we want to process an area inside the hole that is not very near the entrance of the hole ; solution C : same philosophy as the solution B, but using chips such as CONE TKS 12*12 (the tip of the cone will penetrate inside the hole without fully penetrate it) or ACTS MGA 15*15 (angle cut tristar)
do not forget to consider the separation stage between parts and chips at the end of the process ; If parts or chips are magnetic (see magnetic centrifuges), the problem is simple; on the other hand, dimensional separation will, with manual sievers for small quantities of parts, be sure tamiseur vibrant , if you want a more industrial method; the dimensions of the media must be sufficiently different from those of the parts.
do not forget that the media has a wear rate due to their abrasiveness ; the choice of media composition whether ceramic or plastic media (polyester) is always complex, since you have to arbitrate between :
-a media with a high abrasive power which will reduce the cycle time for a given objective but which will wear out more quickly
or
-a media with a lower abrasive power which will lengthen the cycle time for a given objective but which will wear less quickly.
Aside from porcelain media (white ceramic), having chips that do not wear means that they work only very few, and instead of deburring and polishing parts, they sometimes generate work hardening effects, often prjudicial to the quality of the surfaces.
the choice of media also depends on the power provided by the tribofinishing equipment used ; thus, if you use low power equipment, you will often favor media with a strong abrasive power; for the most powerful equipment, like satellite centrifuges, you may need to reduce the abrasive power of the chosen media (unless your priority is to reduce your cycle times, especially in the case of large removals of material as can be observed in additive manufacturing).
Finally, the drive setting will also have a noticeable effect on both material removal rate and media wear rate ; you will thus be able to obtain very close results using in a case very abrasive media with a moderate operating speed, in another case less abrasive media with moderate operating speed.
You will also have to take into account the mass of your media as a determining parameter in the efficiency of a process.. The higher the inertia of the media, the greater the pressure applied to the surface of the part to be treated and therefore the removal of material ; SCT MGA type triangular media 6*6, will have a higher effect than triangular media such as SCT MGA 4*4 ; during long or very energetic processes, you will have to take into account the wear and tear of these media, if you want to define a precise wear law for your parts ; thus, often, our laboratory will be able to define rules for replacing the media in order to guarantee perfect reproducibility of your processes.
the choice of ceramic media or plastic media (polyester), can be quite tricky ; the main differences are due to their respective densities ; for ceramics, the density is generally 2.7 g/cm3, while that of plastic media is 1.5-1.8 g/cm3 ; thus, considering the same equipment, providing equivalent energy, ceramic media will allow greater material removal, better deburring, see a shorter cycle time ; On the other hand, for more ductile materials, such as Aluminum or Copper alloys, ceramic can mark surfaces, which would lead to favoring plastic media which are both lighter at equivalent volume and less hard ; but these rules are to be adapted according to the power and the capacity in liters of the equipment used…
in order to improve the quality of the surfaces of the parts after deburring or polishing, it may be necessary to break in the media ;
Running-in objectives : It will make it possible to eliminate as well as possible the sharp edges as well as the irregularities related to the mode of production of the media. ; it mainly concerns ceramic media (in particular white ceramic or porcelain because it is harder), but polymer or metal media are also to be lapped.
At the end of running-in, media will need to be dried ; they will then have to be sifted to remove any broken pieces (hand sieve or vibrating sieve)

Vibrator procedure :
Fill the media vibrator at 60-70 % volume of work.
Add water to bring it up to media level.
Add a reduced dose of additive such as ABC PULIB 6140 (50 % of the usual dose).
To speed up the break-in, you can add an abrasive type MP A60 (either for a vibrator of 50 liters, about 0.5 kg).
Operate the vibrator at maximum speed for 2 x 12 hours with a water level check after 12 hours (addition if the water level is too low).
Then rinse thoroughly to remove the powdered abrasive (ABC A60), then drying the media.
Sieve to remove the rest of the abrasive as well as the broken media.

If run-in proves insufficient, repeat the same cycle a second time.

Procedure in a satellite centrifuge :
Fill media satellites at 60-70 % volume of work.
Add water to bring it up to media level.
Add a reduced dose of additive such as ABC PULIB 6140 (50 % of the usual dose).
To speed up the break-in, you can add an abrasive type MP A60 (either for a vibrator of 50 liters, about 0.5 kg).
Operate the centrifuge at 60% of its maximum speed for 2 x 4 hours with a water level check after 4 hours (addition if the water level is too low).
Then rinse thoroughly to remove the powdered abrasive (ABC A60), then drying the media.
Sieve to remove the rest of the abrasive as well as the broken media.

If run-in proves insufficient, repeat the same cycle a second time.
these few basic elements will allow you to avoid the simplest mistakes ; feel free to contact us to get more complete advice ; the engineers and technicians of our laboratory will help you to solve your problems ; the laboratory is equipped with about 30 different equipment and with a range of more than 6500 different chips to help you to find the good solution or optimize your present process.