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Super-Abrasive Diamond and CBN Vitrified Grinding Wheels

Super-Abrasive wheels play a key role in the grinding process for advanced ceramics, semi-conductor, Automotive, Bearing, Carbide, Cement, Aerospace, Glass, PCD/PCBN Cutting tools, and mould and Die making industries. In general applications, super abrasive wheels can be resin, metal, vitrified or mono-layer electroplated bond. Diamond and Cubic Boron Nitride (CBN) are the super-abrasive materials of choice. The wheel grinding ability and wheel life depend on the combination of binding materials, super-abrasive grit type and mesh size, concentration, and porosity. Some provide higher material removal rate, others wear more slowly or give better precision on final size.

For many years, resin bond wheels have been widely used and offer the valuable feature of structural flexibility. Phenolic, polyimide and their derivatives are still the most commonly used bond types. Resin wheels have a low Young's Modulus which results in high processing efficiency, free cutting, good surface finish and minimal chipping. They are typically designed for wet grinding but can also be formulated for dry grinding.

In metal bond super-abrasive wheels, the binding material is made from metallic powders of copper, tin, Iron, cobalt Etc. Metal bond wheels are divided into three major types: Bronze-type which are superior in grinding ability; Cobalt-type which are superior in wheel life, and steel-type which stands in the middle in their grinding capability and expected life. These have excellent grit retention and wear resistance when compared to resin bond wheels. However, both resin and metal bond wheels deflect or "give in" under load, due to their inherent elasticity resulting in poorer grinding tolerances.
 
However, it comes to shaping hard materials quickly, accurately and in- expensively, then the vitrified super-abrasive wheels have few rivals. These wheels provide much higher stiffness because the vitrified wheel is essentially composed of super-abrasive grit, which is mechanically and chemically bound in a glassy or crystalline ceramic matrix.  The rigid, porous structure delivers low wear, high heat stability, and this when combined with a free cutting natures, efficient chip removal, and excellent ability for "On-line Dressing" provides very high material removal rates, with minimum downtime and resultant lower machining/manufacturing costs. As an additional benefit, the coolant carries through the pores in the grinding zone, which results in lower temperature at the interface and consequent reduced risk of work-piece thermal damage and stresses. Also, lower temperatures and the rigid nature of the wheel helps in maintaining control over the final size and finish, and also allows for "Dry" Grinding. Consequently, very high tolerances can be achieved throughout a production run with vitrified wheels, due to their low thermal expansion and negligible wheel deflection.
 
 
 
 
The most important criterion in grinding wheel selection is the required surface quality of the ground work piece. Other wheel parameters are chosen individually for each application, and the optimization will depend on the work piece, material removal rate, the machine, the coolant, dressing requirements and the chosen properties of the grinding tool like concentration, bond hardness, structure and porosity. For ceramics and steels, an indicative relationship between the Diamond and CBN grain mesh size and surface roughness are shown in the following figure. This will facilitate the ease of wheel selection in grinding of hard ferrous steels, ceramics and carbides.
 
 
2.0 Characteristics of Abrasives and Materials To Be Ground
 
(1)Characteristics of Abrasive
 
 
 
(2)Materials to be ground with Diamond and CBN
 
 
3.0 Characteristics of Abrasives and Materials To Be Ground
During PCD & PCBN inserts sharpening, one should pay a careful attention to the proper selection of machining parameters. Even with the most advanced technology, diamond or CBN grinding wheels can never be efficient, if their working conditions or machining parameters are improper.
Machining Parameter Selection
 
Grinding velocity                                                                       20 m/s - recommended
                                                                                                       15 to 30m/s - acceptable
 

Allowance

rough grinding:

standard grinding:

finish grinding:

 

 0.02-0.05mm/pass

 0.01-0.025mm/pass

 0.005-0.01mm/pass

 Oscillation frequency

 60 1/min-recommended

 50 to 120 1/min-acceptable

 Number of sparking out passes  3 to 8
 Recommended abrasive stick

 Aluminium oxide abrasive stick

Type-20x10x100 99A 320 J7V

 Coolant  Water-oil emulsion 3 to 5%
 Remarks  Infeed of grinding wheel must always be set out of machining zone

*lf the wheel appears to be too hard,one should decrease the grinding velocity to 15 to 18m/s and dress the wheel more frequenly.lf the wheel wears out too fast then,one should increase the grinding velocity to 22 to 30m/s.

Fig.Mesh Size and Surface Roughness (Indicative Ra Ry/10)

4.0 Wheel Markings

Interpretation Of The Markings

SD                     200                    M                    100                   V                   3.0

 Super-Abrasive Type  Mesh Size*  Bond Hardness  Concen-tration  Bond Type  Abrasive Depth(mm)

 SD:Synthetic Diamond

MSD:Multi-Crystalline

BN:Cubic Boron Nitride

MBN:Multi-Crystalline Bn

 60      170       400

 80      200       600

100      300       800

120      270       1000

140      325       1500

 J-K-L:Soft

M-N-O:Medium

P-Q-R:Hard

 100

 150

 200

 V:Vitrified

 3.0

 5.0

 10.0

 

5.0 Wheel Selection and Drawings

6.0 Order/Enquiry for NTB DiaCer Diamond and CeraCBN Wheels

please indicate the following when placing a new order/enquiry

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