The main quality issues and hazards that diamond grinding wheels may encounter

2020-09-04 1950

Primary quality issues and their hazards

1) Unqualified reversal strength

Reverse strength refers to the ability of a grinding wheel to resist cracking under centrifugal force during rotation, reflecting the magnitude of the tensile stress of the grinding wheel. It is a very important goal in the manufacturing and application of grinding wheels. To ensure the safe use of grinding wheels, the specification lists unqualified reverse strength as a "fatal defect", that is, a "dangerous or unsafe defect to the user or equipment". The sampling inspection plan is to have a sample size of n=10, an acceptance number of Ac=0, and a rejection number of Rc=1; All 10 grinding wheels must pass the reverse strength inspection, and as long as one of them is not qualified, it is deemed as unqualified. Over the years of quality inspection, it has been found that the reverse strength of fiber reinforced resin thin disc grinding wheels and cymbal shaped grinding wheels is not ideal, some are lower than the working speed, and some break before reaching the specified reverse test speed; Some have reached the test speed but cannot maintain it for 30 seconds before breaking. Unqualified reversal strength

When using fiber reinforced resin thin disc grinding wheels and cymbal shaped grinding wheels, they are mostly cut and ground by hand, and the operator is close to the grinding wheel. Therefore, once the reverse strength is poor, the grinding wheel may break during the cutting or grinding process, which can easily cause personal injury or death.

2) Unqualified static balance

A grinding wheel is an heterogeneous object that oscillates when it rotates due to the non coincidence of its midpoint of mass with the midpoint of rotation. This state is called the imbalance of the grinding wheel. Unbalanced grinding wheels can bring many hazards:

Acting on the grinder bearings, causing the spindle to oscillate and accelerating the wear of the grinder spindle;

The rated increase in the reverse stress borne by the grinding wheel reduces its reverse strength, and may even cause it to crack during reverse;

Intensify the oscillation of the grinding wheel and workpiece system, manifested as vibration lines appearing on the surface of the processed workpiece, resulting in a decrease in machining accuracy and surface roughness;

Affects the uniformity of the self sharpening of the grinding wheel, resulting in uneven wear of the grinding wheel.

The static balance of the grinding wheel is also one of the primary quality objectives that reflect the inherent characteristics and application functions of the grinding wheel. Non conformity of the static balance is listed as a "major drawback" in the specifications, that is, a "serious degradation of the product's application function and a serious impact on the function of the processed parts". During the inspection, the situation of unqualified static balance is shown in Table 2, during which

The fiber reinforced resin thin plate grinding wheel with a diameter of 400mm and a linear speed of 70m/s has a static imbalance value of ≤ 13g according to the specifications, but the actual measured value exceeds 18g. The oscillation of such a grinding wheel during operation can be imagined.

3) Unqualified hardness

Grinding wheel hardness refers to the resistance of the binder to the detachment of abrasive particles from the surface of the grinding wheel under external forces, or is understood as the difficulty of abrasive particles detachment from the surface of the grinding wheel. Hardness can accurately reflect the grinding function of the grinding wheel and is one of the important goals for measuring the quality of the grinding wheel. There are two requirements for checking the hardness of grinding wheels:

The uniformity of hardness should comply with the specifications;

The compliance requirement for hardness is that the average hardness value (arithmetic mean of hardness values measured at each measuring point) should be within the allowable scale specified in the specification. The proportion of unqualified hardness should also be appropriately high

4) Unqualified aperture

The inner hole of the grinding wheel is the benchmark of the device, and unqualified grinding wheel aperture is listed as a "major drawback" in the specifications. The larger the aperture, the eccentricity of the grinding wheel device occurs, causing the grinding wheel to be unbalanced. When rotating at high speed, it will exacerbate the oscillation, affect the grinding quality, and even cause the grinding wheel to crack and equipment damage. The aperture is too small and the grinding wheel device cannot be used. If the device is forcibly installed, it may scratch the spindle and even cause dark damage to the grinding wheel, leading to the grinding wheel cracking during operation, which can easily become a problem.

5) Mark fault

The grinding wheel marking table clarifies the basic functions of the grinding wheel and plays an important role in assisting users in using it, which cannot be ignored. Mark fault is listed as a "major defect" in the regulations. There are many issues in the logo, and some of the content is incomplete; Some signs have incorrect content; Even intentionally using substandard, fake and fake trademarks, causing confusion among users, affecting their use, harming their interests, and perhaps becoming a major incident.

6) Unqualified end face and radial runout

Unqualified end face and radial runout can cause deviation and affect the balance function of the grinding wheel during rotation, which can have adverse effects on the machine tool and workpiece. Therefore, it should be controlled within the allowed scale.

Article source: Diamond grinding wheel