Diamond grinding wheels with P84

TECAPOWDER PI as a binding resin for diamond and CBN grinding wheels

TECAPOWDER PI polyimide is a non-meltable polymer that improves the performance of grinding wheels in demanding applications. It is based on P84® by Evonik. The binding materials require high strength at elevated temperatures. These requirements are met by polyimides due to their chemical structure.

Polyimide bindings offer best thermal stability combined with extremely high strength

Polyimide bindings, in general, offer highest thermal stability in comparison with other polymers such as polyamides, epoxies and polyetherketones. This together with its extremely high strength make TECAPOWDER PI polyimide a natural choice for the binding resin in high quality diamond grinding wheels and which eliminate practically all other potential polymers except polyimides. 

TECAPOWDER PI 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.

Outstanding properties

The physical properties of TECAPOWDER PI meet the requirements, which are demanded from grinding wheels. TECAPOWDER PI has a high glass transition temperature of 330 - 340 °C (626 - 644 °F) based on the moulding parameters used to sinter the resin.

High load bearing capacity

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

Influencing the properties by changes of the processing

The hardness, brittleness and abrasion capacity of TECAPOWDER PI 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 moulding window is between 330 and 360 °C (626 and 680 °F). 

Usage temperatures of phenolic, epoxy and polyimide resins

Usage temperature comparison PI, epoxy, phenol

Elastic shear modulus G‘ [MPa]

TECAPOWDER PI polyimide resin maintains a high level of stiffness at elevated temperatures.

P84 Shear modulus in comparison

Overview over properties of hot compression moulded PI powder

Extent of delivery

TECAPOWDER PI 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 10 % P84 in NMP (n-methyl-pyrrolidone) is also available.

Processing Guidelines

  • To obtain successful grinding results, it is necessary to utilise the appropriate resin and optimise the formulation depending on the end-use. Listed here are various formulations tested in dry grinding applications.

    The use of Ni coated diamonds is necessary. In dry grinding applications, approximately 30 % copper powder should be added.

    P84 in diamond metal coating
  • As polyimide resins are hygroscopic, they have to be predried at 120 °C (250 °F) 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.
  • The primer solution should be applied thinly to the roughened bonding surface (using a brush) and dried for about 10 hours at 250 °C (480 °F).
  • We recommend silicone oil spray to applied in a very thin coating on the mould surfaces.

    Wacker Chemical Corporation
    3301 Sutton Road
    Adrian, MI 49221
    Phone +1 517 264 8500

    Evonik Industries
    Goldschmittstr. 100
    45127 Essen
    Phone +49 201 173 01
    Fax +49 201 173 3000

  • Test mechanical properties:

    When first learning to process P84, it is recommended to mould the neat resin into shaped articles to test mechanical properties. This should lead to an optimised processing of P84 resin.

    Methods of manufacturing grinding wheels:

    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 graph underneath. Grindings with little volume% part of PI pressure should be raised up to 100 MPa (14.000 psi). The mounting should be done under 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 230 °C (446 °F). Post curing is not necessary! Especially in the production of 1Al wheels, a resin bounded hub is often used. We split it up into:

    • Phenolic-prepreg hubs
    • PI/metal blended types 

    In case of phenolic prepreg hubs the grinding area is moulded first. 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.

    General temperature/compression cycle on moulding of polyimides

Product datasheets, safety documents and certificates