The Bridge Air 2000 re-grinding system consists of: a lightweight hand-held pneumatic grinder portable air-preparation unit with in-line oiler air regulator (0–20 bar) water sump and water/air hoses. when the development of ‘alligator skin’ type patterns appear on the surface of the buttons.before the ‘flats’ worn on the buttons exceed one third of the diameter of the button.significant decrease in penetration rate.They suggest drillers look out for any of the following signs that indicate that the bit needs servicing: As the carbide wears, however, flat spots appear leading to a horizontal or ‘shear’ load on the button.īearing all this in mind, Totnes-based Bridge Abrasives Ltd, manufacturers of diamond and CBN products, recommend regular regrinding and a service routine for button bits. New tungsten carbide inserts work in compression. Broken buttons should be ground off to prevent additional button particles breaking off and damaging other buttons. Alligator skin can occur in certain rock conditions long before excessive flat widths appear and can be remedied by lightly grinding the affected area.īroken inserts are generally caused by: overdrilling the drill bit before reconditioning reaming the hole using excessive force or where there are existing tungsten carbide or other metal particles in the hole.Ī down-the-hole button bit can continue to drill with one or more broken buttons, but at a reduced penetration rate. If the condition is not remedied the cracks can cause small surface spalls and eventually lead to complete button failure. On inspecting the drill bit, if it displays any sign of minute thermal cracking of the carbide buttons (resembling alligator skin or very fine surface skin cracks), caused by overheating of the buttons, this condition should be rectified as soon as possible. It is recommended that flat widths should generally not exceed 25% of the button diameter, although this varies from manufacturer to manufacturer.įace buttons that are flat generally indicate a lack of hammer blow energy or insufficient thrust. In such conditions it is advisable to monitor the rate of wear over a measured depth drilled to determine the frequency of re-grinding necessary. Rotating the bit faster than necessary will not generally increase penetration speed but will increase the wear rate, particularly in abrasive rock.
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