Dressing of tools

Dressing of tools

Dressing of tools

Recommendations for the resharpening of tools with dressing sticks

 

 

When using tools for the glass processing it might occur that after a while the abrasive capacity of a tool reduces.
If enough thickness remains, the abrasive layer can be redressed in order to reinstate the tools original sharpness and bite.

This "dressing" of a tool is not, as commonly thought, the sharpening of the diamond grains, but the partial removal of the bond between the grains.

 

Most diamond- and polishing tools for the glass industry are composed of irregularly shaped synthetic abrasive grains (e.g. synthetic diamond particles) with a predefined size (the grain) and with a certain number (the concentration). They are enclosed in a filler (the bond). 

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It is a common misunderstanding that the wear of a tool mainly is due to the wear of the abrasive (diamond) grains.
Abrasive grains however hardly wear off. Instead, the sharp corners of the grains will slightly round off, which makes them less sharp and creates a higher pressure between the abrasive grains and the to be ground material. This causes the grains to break out of the bond and thus creates room for new fresh sharp diamond grains.

With a correct tool and under the right circumstances, the bond between the grains will evenly wear off with the breaking out of the grains.
That’s the optimum situation as per theory, but practically it’s different. This can be caused by various factors, such as: inferior tools quality, bad cooling, vibrations, wrong grinding speeds or revolutions, pollution by the to be ground material, etc.

The optimum balance between diamond grains and bond is in such case disturbed.
For example: it remains too much bond at the contact surface, which prevents the diamond grains from getting exposed. The abrasive capacity of the tool strongly reduces: the tool is “blunt”.
When on the other side there is insufficient bond present at the grinding surface, the wear of the tool is very high. Mostly this is due to an inferior quality of a tool.

If the abrasive capacity of a tool strongly reduces, the grinding surface must be redressed. For this purpose so called dressing stones or rectifying sticks are available.
Dressing sticks can be used dry as well as wet. However, we recommend to use them when they are saturated with water. Therefore you best can store them in water e.g. 24 hours prior to use.
If the dressing stick is wet, you can far better control the removal of the bond. Besides, the wear of a wet stick is remarkably less than the wear of a dry one, while simultaneously the spread of undesirable abrasive dust particles will be avoided.

Another misconception is that dressing a tool reduces its life. In reality it is however just the opposite. If a tool is blunt, you’ll increasingly need to put more pressure in order to maintain enough cutting capacity, which obviously causes excessive wear. A sharp tool needs minimal pressure and you can remove more material in less time. This results in a higher productivity with less cost.
On the other hand, a wrong type of dressing stone or one with a wrong grain size, could remove unnecessary too many diamond grains, resulting  in abundant wear.
Therefore it is important to choose the right type of dressing stone with the right grit.

 

Usually in glass processing, dressing stones for diamond tools are available in 2 types of material:

Aluminum oxide:
The "standard" dressing stones, made of aluminium oxide, have a white colour.
They are relatively soft, so the risk of damaging the diamond tool is relatively low.
Depending on the grit size, this type of dressing stone can be used for as well metal bonded (sintered), as resin bond (synthetic, bakelite) diamond tools.

 

Chrome oxide / Silicon oxide
The dressing stones made of chrome oxide usually have pink/ red colour. The ones of silicon oxide are green or blac
They are considerably harder than the white dressing stones, which makes them less suitable for manual usage.
Due to this hardness and the usually coarser grit, these stones can only be used for metal bond wheels.

 

Recommendations for the use of dressing sticks:

  • Always follow the safety instructions of your machine manufacturer or the prevailing precautions that are valid in your company.
    • Avoid possible contact with rotating tools.
    • Wrong or inattentive use of dressing stones , can lead to serious injuries or accidents.
    • Preferably push the tool into a fixed dressing stone and not contrary.
       
  • Preferably use the dressing stones when they are saturated with water.
     
  • Do not use the dressing stones at high rotation speed of the diamond tool.
    • Dressing stones reach their optimal grinding capacity at a low revolution speed of the tool.
    • Furthermore you have a far better control at low rpm’s.
    • When the rpm is not adjustable, switch off the motor while the tool is rotating.
      If the tool then is only slowly freewheeling, push the tool into the dressing stone until the tool stops rotating.
      If necessary, repeat this operation.

       
  • NEVER make a lateral movement with the dressing stone during usage.
    • Always push the tool straight into the dressing stone, without any lateral movement.
      With a lateral movement you could unintentionally locally remove too much bond, which would result in tools damage.