Polyimide Binding Resin for Diamond & CBN Grinding Wheels | HP Polymers

 

P84®Polyimide

Binding Resin for Diamond and CBN Grinding Wheels

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P84 Binding Resin

P84 Polyimide Powder is a fully imidized PI resin. Due to it`s chemical structure, it is a non meltable, non thermoplastic polymer. Processing is possible only by hot-compression-moulding. Key processing variables are dwelltime, temperature and pressure. No post curing is necessary.

Polyimides in general, offer highest thermal stability in comparison with other polymers such as polyamides, epoxies and polyetherketones. High thermal stability and extremely high strength make P84 polyimide a natural choice for the binding resin in high quality diamond grinding wheels. The demanding strength and temperature requirements of diamond and CBN grinding wheels eliminate practically all other potential polymers.

The physical properties of P84 meet the requirements, which are demanded from grinding wheels.

Density: 1,34 g/cm3    
(hot compression moulded)        
Tensile Strength: 17,000 psi 116 N/mm2
Elongation: 9 %    
E-modulus: 363,000 psi 4000 N/mm2
Flexural Strength: 23,000 psi 174 N/mm2
Hardness SHORED 90      
HDT 572 °F 300 °C
Continuous Usage Temperature: 536 °F 280 °C
Short Period Maximum 750 °F 400 °C

The above information is for unfilled P84. Under proper moulding conditions P84 has one of the highest tensile strength compared to unfilled, non orientated plastics.




Features

Due to its excellent thermal stability, P84 bonded wheels have extremely high load-bearing capacity. They are particulary well suited for applications involving hard metal (dry) grinding and deep grinding (wet) operations.

P84 resin bonded wheels are capable of very high grinding speeds and, in many cases, outlast standard epoxy or phenolic wheels by a factor of 2.

The hardness, brittleness and abrasion capacity of P84 wheels can be influenced by processing. Varying the sintering temperature and dwell time can lead to different mechanical properties of the resin. As the process temperature and dwell times rise, the grinding area becomes harder and more brittle. This temperature molding window is between 626 °F (330 °C) and 680 °F (360 °C).




Processing

To obtain successful grinding results, it is necessary to utilize the appropriate resin and optimize the formulation depending on the end-use.

Listed below are various formulations tested in dry grinding applications.

Composition [Vol.-%] Grinding-relationship at a table speed of [mm/s]
Diamond Metalcoating PI resin Filler 10 25
25 0 55 20 Cu-fibres 63 24
25 0 45 30 SiC ca. 30 µm 31 6
25 0 40 35 coarse Cu-powder 29 15
25 12 33 30 dentritic Cu 380 98,4
18,75 9,25 38 34 dentritic Cu 235 54
12,5 6,5 42 39 dentritic Cu 156 30

* Source: DE 20 16 349 B2

As shown in the foregoing graph the use of Ni coated diamonds is necessary. We recommend as an example De Beers PDA 321 P 60 which is developed for PI resins. In dry grinding applications, approximately 30 % copper powder should be added.




Extent of delivery:

P84 resin is available in powder grain sizes of -200 mesh, -325 mesh, -425 mesh and 1200 mesh. Usually powder grain size of -325 mesh HCM is used. Primer solutions of 10wt.% P84 in NMP (n-methyl-pyrrolidone) is also available.

Preparing of the resin:

As polyimide resins are hygroscopic, they have to be predried at 250 °F (120 °C) for a couple of hours before any use. It is also always important to have the exact filling proportion in case of "close mould" moulding.

Primer Coating:

The primer solution should be applied thinly to the roughened bonding surface (using a brush) and dried for about 10 hours at 480 °F (250 °C).

Release Agent:

We recommend silicone oil spray to be applied in a very thin coating on the mould surfaces. For example Wacker Chemie/Burghausen or T.H. Goldschmitt (Tegosil)

Wacker Silicons Corp.
3301 Satun Road; Adrian
Michigan 49221-9397
Tel.: 517-264-8500
FAX.: 517-264-8246

T.H. Goldschmitt
Goldschmittstr. 100
45127 Essen /Germany
Tel.: 0049-201-173-01
FAX.: 0049-201-173-3000

Processing and Manufacturing Routes:

When first learning to process P84, it is recommended to mould the near resin into shaped articles to test mechanical properties. This should lead to an optimized processing of P84 resin. These mechanical properties can be compared with the properties in the brochure.

In manufacturing grinding wheels, two different methods are commonly used:

Moulding of the grinding area and adhere this afterwards on to the hub by using epoxy adhesive.

The moulding of the composition can be done in following the cycle in the attached graph. Grindings with little volume%-part of PI pressure should be raised up to 14.000 psi (1000 kg/cm2 ). The mounting should be done unter use of an epoxy adhesive with a high amount of aluminium powder (for example 60 % Al.)

The moulding of the grinding are directly on the prepared hub (roughed and primed) can be done in the same way.

In both cases the sintered wheel can be released at 446°F (230 °C).

Post curing is not necessary!

Especially in the production of 1Al wheels, a resin bounded hub is used often. We split it up into:

  • phenolic-prepreg hubs
  • PI/metal blended types

In case of phenolic prepereg hubs the grinding area is moulded before. The prepregs are added afterwards into the outside ring and moulded as recommended for this resin. Due to the high thermal stability of P84 no damage of the grinding area will be obtained.

Under the use of metal/Resin blends we recommend the use of a 70 % metal and 30 % resin composition. The metal component can be a blend of bronze and aluminum. This hub has to be sintered as an independent part of the wheel, afterwards the grinding area is added by sintering it on to the disc.







Properties of hot compression moulded P84 powder (appr. values)

Property      
       
Mechanical Properties   DIN Test Standard
ISO/IEC
       
Ultimate tensile stength 116 N/mm2 53455 527
Failure Strain 9% 53455 527
Tensile modulus 4000 N/mm2 53457  
Ultimate compressive strength 700 N/mm2 53454  
  0,1 % Offset 177 N/mm2    
  10 % Offset 240 N/mm2    
Compressive strain at failure 45% 53454  
Compressive modulus 4100 N/mm2 53457  
Ultimate fexural strength 174 N/mm2 53452  
Flexural modulus 4000 N/mm2 53457  
Hardness      
  Rockwell M 120    
  Shore D 89    
Impact strength 75 kJ/m2   179
Impact strength; notched 4,9 kJ/m2 53453  
Impact strength Izod, Method A 37 J/m ASTM 256 180
       
Thermal Properties      
       
Linear thermal expansion coefficient 50.10-6 1/K    
Glass transition temperature 330 °C 53752  
Heat defelction tmeperature      
  Load 1,85 N/mm2 300° 53461 R75
Thermal conductivity 0,22 W/m K 52612  
Specific heat 1,04 J/gK    
       
Electrical Properties      
       
Volume resistivity at 23 °C 1017? cm 53482 167
Surface resistivity 1015? 53482 167
Dielectric strength 20 kV/mm 53481 243
Dielectric constant      
  50 Hz 3,5 53483 250
  27 MHz 3,1 53483 250
Dissipation factor      
  tan ? 50 Hz 1.10-3 53483 250
  tan ? 27 MHz 3.10-3 53483 250
       
Other Properties      
       
Density 1,34.103 kg/m³ 53479 1183
Water absorption      
  at 23 °C, 65 % RH, 121 days 2,6% 53714 1110
  in water, 23 °C, 42 days 3,6% 53495  
Limiting Oxygen Index 44% ASTM 2863