Newsletter. Technical data for diamond and polishing wheels for flat glass processing machines

                                         Newsletter

 

 

In this newsletter we will regularly publish a set of technical data which, we hope, will be useful to you and to the operator working on a machine of your mirrors to use (and change) the best diamond and polishing tools that are mounted on your machines. There will be purely technical data (international units for diamond grain size) technical explanations but also "tips" born from the experience of our technicians in the machinery of mirrors setting.
We chose to publish these elements, not as a manual very organized, but as and when we receive these items or will we build them.

 

The characteristics of diamond wheels for straight line edging machines for flat glass.

Consider first the wheels metal bond.

The main parameters on which it is possible to play to design a grinding wheel are: its diameter, the width of the diamond ring, the type of diamond crown (continuous segmented with open segments, segmented with closed segments), the constitution of the bond, the size of diamond particles, the diamond concentration, the rotational speed of the wheel).

To set these parameters we will have to take into account  the working  produced mainly by the straight line edging machine (glass thickness, % of laminated glass processed on the machine ...) and a number of diamond wheels to carry out the edge.

A simplistic example. In the case of a small straight line edging machine with one single diamond cup grinding wheel to carry out the edge. If you want to work from 3 to 19 mm thickness  you must choose a diamond wheel with a grain of 170 mesh for a removal capacity for working high thickness. But if you only work from 3 to 10 mm, a 200 Mesh is preferable (the removal capacity will be enough and you'll improve your glass edge quality).

We will now consider what is best to choose as cup wheels in the case of straight line edging machines with 2 and 3 diamond wheels for the edge according to the thicknesses of glass and laminated glass percentage processed.

 

Diamond drills and peripheral tools for drilling flat glass

 

To choose a diamond drill there are several items to consider.

Moving quickly on the most obvious, the diameter of the hole that we want to drill. A however be considered in this regard is the precision guaranteed by the manufacturer on the outside diameter of the forest.

The fastening system on the spindle.

The most common by far is a fixation screw ½ inch. On manual or portable drills can still not meet a ¼-inch screws.

But on the new automatic drilling machines with automatic tool change can also find various fastening systems (cylindrical or conical shaft ..)

 

The body of the drill

The cooling of the drill while cutting is done with water, the water flowing through the center of the drill. However, especially on CNC machines it may be that this water flow is important and that water was difficult to evacuate by the head of the drill. That is why to reduce the pressure within the drill and on the glass there may be also a hole on the body of the bit which will permit lateral discharge of surplus water not needed for cooling.

 

The total length of the diamond drill

The most common total length is 75 mm. We also meet 95 mm and 90 mm more rarely. But on request it is possible to have other lengths. This length is to be considered depending on the brand of your drilling machine and of the spindles caracteristics.

But the most important depends on the degree of automation of your drilling machine. Indeed if the spindles  are handled automatically, it is essential to have drills that are the same length (then remain to manage the wear of drills)

 

The active part

This is a diamond crown typically a centimeter in height and which is brazed to the body of the bit. Tolerance on the size of the diameter is generally 0.1 mm

The diamond grit size is typically 70/80 mesh and it is of course possible to have other grains.

The bond composition and the parameters (temperature and pressure) to manufacture are different for each manufacturer, and these data are jealously guarded

It can recharge its drills when the active part is completely dead. But personally if you take the transport  price into account  I doubt the economic benefit to act that way.

The diamond ring can be a continuous rim or a crown with slots (usually two notches). The objective of the notches is double. Laminated glass drilling and increased abrasiveness. However, the slots will cause more scales on the periphery of the hole and this drill type is strongly discouraged for drilling the thin glass because it increases the risk of glass breakage.

 

Countersinks

The creation of chips on the periphery of the hole on the surfaces of glass during drilling may impose for aesthetic reasons or to secure further treatment (quenching) to create a chamfer on the edge of the hole. We will use this to make a flaring or reamer.

There are several types .

 

Work settings on CNC machines.

 

These machines have the advantage of being easily set all working parameters of the wheel (speed, feed rate, removal)

 

Examples of parameters to be adopted for processing on glass of 15 or 19 mm. diameter of wheels 100 mm.

But keep in mind these parameters can change depending of the wheels manufacturer

 

 

Flat edge and arris:

a) Passage with a flat segmented grinding wheel grain coarse 22 mm thick.

Removal : 1.5-2.0 mm - 5500-7500 rotation speed rpm - feed speed of 1.2-2.5 m / min.

 

b) Passage with a trapezoidal wheel continuous rim grain big or medium.

Removal: 0.5 mm - 5500 turns (7000) RPM - forward speed 1.2-1.5 m / min.

 

c) Passage with a trapezoidal wheel continuous crown fine grain.

Removal: 0.2-0.4 mm-5500 (7000) rpm - feed speed 1.5-2.0 m / in.

 

d) Wheel polished: 3500 RPM - abduction 0 - feed rate 1.5 -2.0 m / min (wear 0,008mm / m).

 

Notes: If the wheel diameter is 50 mm or less (case of returning angles for example) the speed will be equal to 10,000 rpm and removals and forward speeds will be lower.

 

Edge PE or BN:

a) Passage with a segmented grinding wheel.

Removal: 2.0 mm -5500 (7000) RPM -speed advance 1.5-2.0 m / min

 

Alternatively one can use a double roughing grindstone 45 °.

 

b) Passage with a diamond wheel medium grain.

Removal: 0.5-0.7 mm 5500 (7000) RPM - speed avance1,5-2,0 m / min

 

c) Passage with a diamond fine grain grinding wheel.

Removal 0.2-0.4 mm 5500 (7000) RPM - feed speed of 1.5-2.0 m / min

 

d) Passage with a polishing wheel.

3500 rpm - feed speed of 1.5 m / min - Wear the polishing wheel 0.008 mm / m.

 

Notes: For glass thicknesses up to 6 mm uses only one diamond grinding medium grain + a polished wheel (live 2-3 m.). This also depends of course on the quality of the cut.

For 8-12mm thickness, a coarse grinding wheel is used (1mm removal), a diamond wheel fine grain (kidnapping. 0.5 mm) and a polishing wheel.

 

 

Using segmented wheels

 

Segmented wheels are used primarily for certain applications.

Metal bonded wheels

1 / Laminated glass edging

2 / The thick glass edging

Segmented wheels have a larger glass removal power over continuous crown wheels, for the same diamond grit, especially in case of thin thickness. However they are more aggressive, leaving more chips and chip scales.

This is one of the reasons why we recommend using diamond wheels with continuous crown when laminated glass production on a machine is less than 20% of the total figured glass in this machine.

If, against the laminated glass is very thick or have very thick layers of PVB, use of wheels segmented  with open segments. In this case the segmented grinding wheels cut much more easily PVB preventing it to come between the grinding wheel and the glass and thus degrade the quality of shaping

 

3 / In the final position for a rectilinear 3 diamond wheels for the edge.

In this specific case it is imperative to use wheels segmented with closed segments.

It was noted that in this very specific case, the last wheel left fewer lines on the edge and therefore improves the quality of the edge.

 4/Peripheral wheels. When you need to have an important glass removal (roughing wheels)

 

Tools for the processing of flat edge with cup wheels

The cup wheels for straight of the gasket must allow removing the glass as required by the product to be manufactured and cut quality and at the same time to let the fewest chips on the seal of the glass. These two requirements are incompatible and therefore there are no wheels can guarantee wholesale kidnapping excellent condition before polishing surface.

Undoubtedly if the rectilinear has three motors for forming the edge with various diamond grinding wheels can be divided particle size of the diamond on several tools and so much more positive results can be obtained in terms of finish and speed, whereas with one or two available engines must find a compromise between removal and edge quality before polishing wheels.

Why only 3 diamond tools for the realization of the joint on straight? For economic reasons, the level of investment, reasons of size of the machine, but also and perhaps especially for fine adjustment of the position of each wheel compared to glass. If we take for example a removal of 2 mm, the first wheel will remove for example 1.2 to 1.5 mm, the second between 0.6 and 0.3 mm. So it remains to remove 2 mm between the last two grinding wheels ... Suffice to say that we will have very frequently to adjust the position of the last grinding wheel ...

Depending  the number of wheels of the straight line edging machine and if you process or not laminated flat glass the diamond grit size of each grinding wheels will be different.

 

Tests on Refrigerants

 

Influence of concentration of coolant over the work of diamond wheels during forming flat glass, also taking into account the hardness of the water

 

The Refrigerant is compared to a mechanical cutting oil, one of whose main objectives is to cool when forming (the tool contact with the glass) glass and stone.

 

Refrigerants on the market also comprise additives having other functions, but which do not directly affect the operation of the tool.

 

Results of tests carried out on MM371 by varying the percentages of oil, the water hardness

 

- If fresh water (<25 ° F) the concentration of cutting fluid (coolant) continuously influence the work of the 1st mill. The decrease in amperage with respect to an increase of 1% of the oil is equal to 0.3 A.

 

- In case of hard water (32 ° F) influences cutting oil continuously work the first two wheels so much more important than in the previous case. The decrease in amperage with respect to an increase of 1% of the oil is equal to 0.6 A.

 

- Considering 2% oil and increasing the hardness of the water absorption increases only on the first wheel until the hardness of about 40 ° F, above which the amperage (which allows measuring the power requested at the wheel) remains constant.

 

- In the absence of oil, by increasing the hardness of the water, ammeters increase linearly.

 

- Consequently it is deduced that the presence of fresh water increased oil concentration results in a reduction in the amperage with an absolute value significantly less than what has been verified in the presence of water with hardness above 40 ° F. So in case of amperage problems we must first check the water hardness. At high hardness, the percentage of added cutting oil in water trays will increase more than in the case of freshwaters.


 

Types of grinding wheels and tools for the processing of flat glass

 

Article written in collaboration with Dott. Renato Genocchio

 

There are many aspects to consider when considering a shaping operation of flat glass with diamond tools and polishing tools.

First there are the words used whose meaning can vary depending on who is talking about it.

The experiences of those working in this sector are different (and even contradictory in some cases) and in addition, given that there is no specific literature about it - there are only general articles in industry publications examining only the most general aspects of shaping operations - it is not easy to objectively establish a solid foundation for a common language.

And it is often the customers starting from their experience, sometimes passed on from generation to contradict everything the tools producers live every day.

So sometimes the simple naming of types of tools for glass can be a problem. It is normal, for example, called "polished" the bakelite bonded diamond wheels that have many functions other than to polish glass. It is only the wheels with synthetic binder (rubber, polyurethanes, polyesters) with abrasives such as silicon carbide, corundum and cerium oxide in which this task is allotted.

Or better, if we want to be really precise, we should speak of true polishing as in the case of cerium oxide grinding wheels, since they are an alternative to felt working with liquid cerium oxide. They only have a polishing action while the other grinding wheels with abrasive silicon carbide or aluminum oxide (corundum) have at least one double abrasive and polishing which, in the case of large particle size of the abrasive (from 40 to 80 Mesh) is undoubtedly more abrasive as polishing.

So we propose to classify the families of wheels for glass in 4 categories:

1) metal bonded Diamond wheels

2) Diamond wheels binder resin (thermosetting resins normally phenolic or melamine)

3) Circles abrasive silicon carbide, aluminum oxide or similar with synthetic binder.

4) abrasive wheels Cerium Oxide with synthetic binder

5) or compact spiral Felt, wool or synthetic, working with liquid cerium oxide.

The first two types of grinding work on mandrels with variable speed of rotation between 2800 and 3500 revolutions per minute while the other three working with moving pins equipped with a pressure device, and with a rotational speed between 1400 and 2800 revolutions per minute, although there are polishing wheels can work even in variable-speed mandrels.

Usually shaping operations are carried out without using all five types above,

Considering the usual working of, I would propose the following classification:

a) Bevel

b) Forming gasket on vertical or bilateral straight (cup wheels)

c) Shaping round seal with straight vertical or bilateral (peripheral grinding wheels)

d) Forming glass seal with numerical control machines

We will examine each case to determine generally the types of tools and the most common problems.

 

Tools and wheels for beveling of flat glass

 

The wheels for bevelling must submit a tender bond to exert the least possible pressure on the glass, as the bending of the glass under the action of grinding wheels is the primary cause of the fact that the bezel does not fall neatly into the corner .

The diamond particle size is also very important since it must find a compromise between the need to remove significant amounts of glass, as in the case of bevel widths greater than 30 millimeters, and the risk of producing too large scales and therefore to create areas likely to break because the bevel of the heel is usually very thin, especially on glasses 3-4-5 millimeters thick.

 

In the form below we will examine our typologies and our indications the type of machine and bevel to achieve.

 

Also in detail about our tests on refrigerants, it emphasizes the importance of using an appropriate refrigerant.

 

With regard to cerium oxide, it is noted that its quality is fundamental and its optimum concentration should not be less than 4%.


 

Balancing wheels for flat glass processing machines

 

The grinding wheel is installed on a spindle, itself driven by a motor. This motor can be fixed or variable speed rotation. But whatever. When the grinder goes into action the engine will run at a fixed speed.

 

To have a good cutting requires that the wheel rotates at a fixed peripheral speed (smoothly). The wheels are heavy tools (often more than 1 kg) and manufactured, even among the most important suppliers, often in a unitary manner. If the weight of the grinding wheel is not perfectly distributed throughout its volume the grinding wheel will not have a constant peripheral speed of rotation. While a part of the wheel is heavier, for example when going to meet its low point (case straight and vertical chamfering) the engine will be further sought and there is a risk that the peripheral speed changes at the moment. So lower quality for processing.

 

That is why it is essential that the end of production balancing wheels is tested and the wheels with poor balancing are modified.

 

This adds an extra step in the manufacturing process has a cost and a significant number of grinding wheels manufacturers in a dubious reasons of economy blithely skip this step. We'll show you later how to check if your supplier balance its wheels or not.

 

After manufacture all the wheels are installed one by one on a horizontal axis and are made to rotate. If a grinding wheel always stops in the same position is that it is unbalanced and that the lowest point where it stopped there is a surplus of material to be removed. Removing a small amount of material at this point and the process is repeated until the grinding wheel no longer has a surplus of material.

 

How to check if your wheels were balanced?

 

On the back or inside of the wheel (cups wheels) or one side (peripheral grinding wheels) see picture below you can see the cutouts.

Diamond wheels Bavelloni balancingResin wheel Bovone balancing

 

A wheel may be naturally balanced. But it is rare. And if the same supplier for several grinding wheels does  not show that removal of material, I have a big doubt on balancing its wheels.

 

All wheels we provide you with Vedip are balanced.

 

What wheels should be balanced?

 

All metal diamond and bakelite wheels. At Vedip we balance also  the stone  wheels of the same diameter  150 (see photo where you can see a metal removal next to the stone wheel central hole)

Stone wheel Schiatti balanced

 

 

 

 


 

The bonds for grinding wheels and diamond tools

 

Regarding binders for diamond wheels there are mainly two types of bonds. Metal binders for wheels that will aim to remove the glass and can contain large or medium grain diamonds. And resin binder (or bakelite) for the wheels that will have a working finishing or superfinishing with fine diamond grains or thin.

Originally it was only for straight diamond wheels with metallic binders before ceratins providers (Bovone and Bavelloni first) do offer high rectilinear end equipped in the case of the last wheels of the diamond wheels game bonded wheels resins.

For bevelling they were originally equipped with diamond grinding wheels with metallic binders and resin binders wheels.

 

The binder is at the heart e diamond wheels manufacturing technology. Each provider has its own binders and "recipes" of manufacture are jealously guarded.

 

The binder is a matrix imprisoning the diamond and is holding it so it can grind the glass. The function of the binder is to hold the diamond grit, to destruction during cutting: in this way new grains appear on the surface with the wear of the binder so that the tool continues to work.

Metal binders are composed of mixtures of metals or composites such as copper, cobalt, zinc, tin, carbides, etc. obtained at high temperature and pressure by sintering. The mixture of these elements, addition of diamond, is raised to a certain temperature and subjected to tens of tons of pressure to obtain a generally insert ring on an aluminum support.

The resin binders are composed of mixtures of thermally durciçable resins in powder or grains such as phenolics, melanin and urea added different abrasives, generally oxides of aluminum or silicon carbides. This mixture will be heated but to a temperature which, in this case, will be lower compared to metal bonds and at the same time subjected to pressure to obtain a solid ring.

 

 

 

 



Sharpening grinding wheels on straight, chamfering, CN ...
 
Why is it essential to sharpen directly on your machine diamond grinding wheels and forests you use?
The active portion of the diamond tool mounted on the machine consists of diamond grains which are trapped within a binder. In contact with glass surface diamond grains are broken by lapping the glass. This requires the tool to be effective there permanently diamond grains that outcrop the binder.
It can happen for various reasons it did not sufficiently diamond surface of the grinding wheel or forest (for example, because the binder does not wear properly). In this case it must pass an abrasive stone surface of the tool (when running) to use the binder and slightly re-appear on the surface of diamond grains sufficiently active.

Drills sharpening stone
 
Please note there are several types of abrasives according to the sharpening tool (metal bonded wheel, the binder resin or bakelite, diamond forest ...)

 

 

The diamond used to manufacture diamond wheels

Diamond is a transparent crystal made up of carbon atoms with a tetrahedral structure. Diamonds have multiples applications, thanks to exceptional physical characteristics that are theirs. The most important features are its extreme hardness, the dispersion index, the thermal conductivity of which the melting point is 3820 ° K. The synthetic diamond was produced for the first time in 1963 in Sweden and then in 1955 in the United States applying pressure and very high temperatures (to reproduce the conditions of natural diamond has been created).

As part of the processing of flat glass, diamond is the main abrasive used. It is always used for the removal of  glass. In the case of the abrasive polishing wheels used is not diamond but mainly of aluminum oxide or silicon carbide.

Diamond for diamond whhels

There are many types of diamond for shaping the glass on the market, each producer for wheels chooses the type that best fits their bonds and working of each tool should perform.

The most important characteristics of the diamond introduced into a binder in the shaping of glass are the particle size and concentration

The particle size is measured by Mesh FEPA or according to schedule. This sheet below shows the two indicator systems:
 
Diamond Grit
 

 

Diamond grit size

 

 

 

FEPA

Mesh

FEPA

Mesh

D852

20/30

D126

120/140

D602

30/40

D107

140/170

D427

40/50

D91

170/200

D356

45/50

D76

200/230

D301

50/60

D64

230/270

D252

60/80

D54

270/325

D213

70/80

D46

325/400

D181

80/100

D39

400/500

D151

100/120

D33

500/600

 
The designation FEPA provides a direct indication of the diameter of each diamond grain; Indeed, one can consider the letter D as "diameter" (even if it is not correct to define it like this, since the diamond particles are not spheres) and the next number as the size of the same diameter micron. D151, for example, indicates that the "diameter" of each grain is 0.151 mm. The nomenclature Mesh, by cons, suppose a standard sieve 2,5x2,5 cm with a number of well-defined holes. The two numbers indicate the minimum and maximum number of said holes in said surface, and in particular more holes are present in the same area more their diameter is small. So in the case of mesh nomenclature, it is normally only used citing the first number, the higher the number, the greater the diamond's end, while in the case of the more FEPA following the letter D is big plus diamond is big.
The diamond concentration is expressed against the letter C followed by a number. The number 100 indicates a concentration of 4.4 carats per cubic centimeter binder, given that a carat is 0.2 grams of weight. So C50 indicates that the binder in the diamond concentration is 2.2 carats per cubic centimeter.
From these two parameters vary, one can vary considerably the performance of the diamond tool.