DIALOK 939P is a specially formulated phenol-aralkyl resin which has proven to be an outstanding high temperature, thermally stable binder for diamond and CBN grinding wheels.
DIALOK 939Pgives a much higher heat resistance than phenolic resins while still curing by the same mechanism.
Applications
DIALOK 939P is utilized in the preparation of grinding wheels for numerous applications including; tool and cutter grinding of hardened steels or tungsten carbide, fast polishing of granite, marble and other decorative stones. Bevelling and edge decorative glass, grinding of new-engineered ceramics and slotting and cutting of semi-conductors.
Key properties
* Tool and cutter grinding of hardened steels or tungsten carbide
* Fast polishing of granite, marble and other decorative stones
* Bevelling and edge decorative glass
* Grinding of new-engineered ceramics
* Slotting and cutting of semi-conductors
Specification
DIALOK 939P—polymer specification and supplementary physical and handing properties.Table 1 provides details of some of the product characteristics. The values highlited by the circular symbols (left hand column of table)
| Physical Property | Units | Method(1) | Minimum | Maximum |
| Appearance–(Fine pink powder)(2) | - | BSMT A 1001-001ETS(3) | - | - |
| Particle size-<75microns | % | 99.5 | ||
| Hexamine content | % | BSMT A 1045-002 | 9 | 12 |
| Pellet Flow @ 125C-60oglass plate | Mm | BSMT A 1213-001 | 60 | 90 |
| Bulk Density | g.cm3 | 0.35 | 0.37 | |
| Density of cured material | g.cm3 | 1.20 | 1.24 |
Property key
(1)BSMT—Bitrez Standard Method of Test
(2)FFFM—Free from foreign matter
(3)ETS—Equal to standard
(4)Evaluated at 25C/77F
Solubility
DIALOK 939P is soluble in Methyl Ethyl Ketone (MEK), industrial Methylated Spirits (IMS) and Methoxy Propanol.—if required.
Bond mix formulations
Customers will normally wish to develop their own bond mix formulation with ARALOK 939P and various fillers to satisfy particular application and performance requirements. We give below some bond mix formulations, in percentages by weight, as a guideline to customers.
COMPOSITION-PERCENTAGE BY WEIGHT
WET GRINDING WHEELS DRY GRIDINDING WHEELS
DIAMOND CBN DIAMOND CBN
DIALOK939P 38—42 40—50 28—30 28—30
Magnesium or Calcium Oxide 3 3 3 3
Cryolite or P.T.F.E 2.5 2.5 - -
Graphite - - 2.5 2.5
Dentritic Copper Powder 2.5 2.5 4 4
(＜20 microns)
Silicon Carbide(1000mesh) 50—54 42—52 60—62 60--62
Preparation of bond mixes
Our recommended procedure for preparing bond mixes is given below:-
- Weight out the fillers (I.e. silicon carbide, magnesium or calcium oxide, graphite or cryolite and P.E.F.E. as well as copper powder.)
- Weight out the DIALOK 939P and add to the filler mix.
- Weight out the diamond or CBN abrasive, add the DIALOK 939P filler mix and stir with spatula for 5 minutes.
- Finally, transfer the bond mix to a small container and give 10 minutes on a Turbula Shaker Mixer.
- Increasing the DIALOK 939P produces a harder bond while decreasing the DIALOK 939P gives a more friable bond.
- The replacement of some silicon carbide by fine nickel powder also increases the hardness of the resultant cutting rim. We, must, however, warn that if the diamond wheels are made too hard, then the diamond grit will not micro-fracture and wear away at a controlled rate. Instead of removal of material from the workplace, it becomes polished.
- The replacement of a few percent of silicon carbide in the bond mix formulation with dentritic copper gives a softer wheel.
- For high speed grinding, it is important to conduct the heat away from the wheel/workpiece interface. This can be achieved by a large replacement of silicon carbide by dentritic copper in the bond mix formulation.
- For wet grinding operations, it is essential to wash away the debris formed and so avoid blocking the cutting rim. A more porous cutting rim can be achieved by introducing some hollow spheres should be to a constant volume. This is to avoid crushing the spheres prematurely.
- To achieve high stock removal rates, use grit size 80/100 U.S. mesh while for a good surface finish use 140/170U.S. mesh grit or finer.
The abrasive/bond mix can be used for moulding grinding wheels by one of thee methods. In all instances, we recommend moulding in a constant volume mould.
Method 1 Mould cutting rim with abrasive/bond mix. Add the moulding compound for the hub and hot press the complete wheel.
Method 2 Put a pre-formed but un-post cured wheel into the mould. Add the abrasive/bond mix and hot press the complete wheel.
Method 3 This ‘One Shot Technique’ requires cold pressing of the moulding compound to give a ‘Green State’ hub. Add the abrasive/bond mix and hot press the complete wheel.
Moulding Conditions
A guideline to moulding conditions is summarized below:-
- Set the platen temperature to between 200℃ and 250℃ depending on mould size(I.e. 200℃for small moulds and 250℃ for very large).
- Fill the constant volume mould with the abrasive bond/mix.
- Allow mould temperature to rise to 60 ℃ to 100℃, apply full pressure (400-800kg/cm2 or 5700-11430 1b/in2) but release pressure for intervals of 10 seconds about five or six times to allow volatile byproducts to escape.
- During the mould temperature rise above 100℃,maintain full pressure.
- Allow temperature to rise to 175℃.
- At 175℃,remove mould from the press and hot strip.
- Allow finished wheel to cool slowly to room temperature.
Post cure schedules
Post-curing of grinding wheels is essential for the Dialok 939P to become fully cross-lined and so achieve optimum hardness. During the post-curing, the volatile by-products of the curing reaction, namely ammonia gas ,slowly diffuses out of the mouldings.
As a general rule, wheel required for wet grinding operations are best made with hubs moulded from and glass fibre filed mould compounds. For example, our grades AR 1004, AR 1011 and AR 1056.These give wheels that should be post-cured to 175℃ maximum. A suitable post-curing schedule is given below:-
Post-curing to 175℃ Maximum for Wet Grinding Applications
Put wheel in oven at room temperature. Raise temperature to 20℃ to 100℃ over 1 hour.
Hold at 100℃ for 1 hour. Raise temperature from 100℃ to 150℃ over 1 hour.
Hold at 150℃ for 1 hour. Raise temperature from 150℃ to 175℃ over 1 hour.
Hold at 175℃ for between 8—25 hours depending on size of the wheel. Cool slowly to ambient.
Post curing schedules
For the manufacture of wheels intended for dry grinding operation, the hubs are best made from metal power filled moulding compounds such as our grades ARALOK 1022, ARALOK 0123 or ARALOK 1027. These give strong heat conducting hubs. Such wheels can be post-cured to temperatures up to 200℃ maximum by a suitable post-curing schedule such as the one below:-
Post Curing in 200℃ Maximum for Dry Grinding Applications
Put wheel in oven at room temperature to 20℃ to 100℃over 1 hour.
Hold at 100℃ for 1 hour. Raise temperature from 100℃ to 150℃,over 1hour.
Hold at 150℃ for 1 hour. Raise temperature from 150℃ to 200℃,over 1hour.
Hold at 200℃ for between 8—16 hours depending on size of the wheel. Cool slowly to ambient.
If wheels are found to develop blisters, cracks or general swelling during the post-curing operation, then the temperature rise has probably been too rapid. In these circumstances, we recommended you modify the post-curing schedule to attain a slower temperature development. Alternatively, post-cure to a maximum temperature of about 190℃ to 200℃.
Storage
ARALOK 939P should be kept in the original containers with the lids tightly affixed. Containers should be stored in a cool, dry place in compliance with the appropriate legislative controls.
Shelf Life
If stored in accordance with the guidelines provided this product has a minimum shelf life of at lease 12 months.
