Basic knowledge of stone grinding technology

Grinding is a method of cutting a workpiece with a grinding wheel as a cutting tool on a grinding machine. The characteristics of this method are:

(1) Since the grinding wheel itself has high hardness and heat resistance, the grinding can process materials with high hardness, such as hardened steel and hard alloy.

(2) The characteristics of the grinding wheel and the grinding machine determine that the grinding process system can make uniform micro-cutting, generally ap=0.001~0.005mm; the grinding speed is very high, generally up to v=30~50m/s; the grinding machine has good rigidity; Hydraulic drive, so grinding can economically achieve high machining accuracy (IT6 ~ IT5) and small surface roughness (Ra = 0.8 ~ 0.2μm). Grinding is one of the main methods of finishing parts.

(3) The temperature in the grinding zone is high due to severe friction. This can cause stress and deformation of the workpiece and even burn the surface of the workpiece. Therefore, a large amount of coolant must be injected during grinding to reduce the grinding temperature. The coolant can also act as chipping and lubrication.

(4) The radial force during grinding is large. This causes the elastic retraction of the machine tool-grinding wheel-workpiece system so that the actual depth of cut is less than the nominal depth of cut. Therefore, when the grinding is about to be completed, the knife should not be used for light grinding to eliminate the error.

(5) After the abrasive grain is blunt, the grinding force also increases, causing the abrasive grain to break or fall off, and the sharp edge is re-appeared. This characteristic is called “self-sharpness”. Self-sharpening enables grinding to proceed normally within a certain period of time, but after a certain working time, manual dressing should be performed to avoid vibration, noise and damage to the surface quality of the workpiece caused by increased grinding force.

Grinding wheel

The grinding wheel is a grinding tool that is made of a number of small, hard abrasive particles and a bonding agent. The abrasive particles are directly responsible for the cutting work and must be sharp and have high hardness, heat resistance and certain toughness. Commonly used abrasives are alumina (also known as corundum) and silicon carbide. Alumina abrasives have high hardness and good toughness and are suitable for grinding steel. Silicon carbide abrasives are harder, sharper, and have better thermal conductivity, but are brittle and suitable for grinding cast iron and hard alloys.

Due to the different thickness of the grinding wheel, the surface roughness and processing efficiency of the workpiece after processing are different. The coarse abrasive grains are used for coarse grinding, the fine abrasive grains are suitable for fine grinding, the coarser the abrasive, the smaller the particle size number.

The binder acts to bond the abrasive. Ceramic binders are commonly used, followed by resin binders. Different materials are selected to affect the corrosion resistance, strength, heat resistance and toughness of the grinding wheel.

The harder the abrasive grain bond is, the less likely it is to fall off the grinding wheel. The hardness of the grinding wheel, that is, the hardness of the grinding wheel, refers to the difficulty of the abrasive grains on the surface of the grinding wheel falling off under the action of external force. Easy to fall off is called soft, otherwise it is called hard. The hardness of the grinding wheel and the hardness of the abrasive are two different concepts. The surface of the workpiece to be ground is soft, and the edge (edge) of the abrasive grain is not easy to wear, so that the abrasive grain can be used for a longer period of time, that is, the grinding wheel (the higher hardness grinding wheel) can be bonded. Conversely, a grinding wheel with a low hardness is suitable for grinding workpieces with high hardness.

The grinding wheel works under high speed conditions. In order to ensure safety, it should be inspected before installation, and there should be no defects such as cracks. In order to make the grinding wheel work smoothly, the dynamic balance test should be carried out before use.

After the grinding wheel has been working for a certain period of time, the surface gap will be blocked by the grinding debris, the sharp angle of the abrasive will be blunt, and the original geometry will be distorted. It must therefore be trimmed to restore cutting power and the correct geometry. The grinding wheel needs to be trimmed with a diamond pen.

Surface grinder structure and grinding motion

There are many types of grinding machines, including surface grinders, cylindrical grinders, internal grinders, universal cylindrical grinders (also grind inner holes), gear grinders, thread grinders, guide grinders, centerless grinders (grinding circles) and tool grinders ( Grinding tools) and so on. Here we introduce the surface grinder and its movement.

1. Structure of surface grinder (taking M7120A as an example, where: M - grinder type machine tool; 71 - horizontal axis bench top surface grinder; 20 - work surface width 200mm; A - first major improvement.)

(1) Grinding wheel frame——Installing the grinding wheel and driving the grinding wheel for high-speed rotation, the grinding wheel frame can be used for manual or hydraulic lateral clearance movement along the dovetail guide of the sliding seat.

(2) Slider - Install the wheel frame and drive the wheel frame to move up and down along the column guide.

(3) Columns - support slides and grinding wheel frames.

(4) Workbench - The workpiece is mounted and driven by a hydraulic system for reciprocating linear motion.

(5) Bed body - support the workbench and install other components.

(6) Coolant system - supply coolant (saponified oil) to the grinding zone.

(7) Hydraulic drive system - its composition is:

1) Power component - is the oil pump, supplying hydraulic transmission system pressure oil;

2) Actuator - for the cylinder, to drive the movement of the table and other components;

3) Control elements - for various Valves, control pressure, speed, direction, etc.;

4) Auxiliary components - such as fuel tanks, pressure gauges, etc.

Compared with mechanical transmission, hydraulic transmission has stable transmission, overload protection, and can realize stepless speed regulation in a large range.

2. Surface grinding motion

(1) Main motion - high-speed rotation of the grinding wheel.

(2) Feed movement

1) Longitudinal feed--the workbench drives the reciprocating linear motion of the workpiece;

2) Vertical feed - the movement of the grinding wheel in the depth direction of the workpiece;

3) Transverse feed - the grinding wheel moves along the gap of its axis.

Angle Valves

Globe valves and angle valves are designed for throttling or regulating flow in commercial and industrial applications. Bronze, cast iron, or cast ductile iron materials. Threaded, flanged, or solder end connections.

Angle valves for use in commercial and industrial applications. Typical services include hot and cold water, HVAC, steam, compressed air, gas and other general utility services.
Vacuum angle valve is used for turn on or shut off the airflow in the vacuum pipeline, the applicable media is air and non-corrosive gases.
It has two structures, one is angle type and another is a 3-way type within an ISO-KF or ISO-F various flange end pre-pump port.
a) Small diameter (≤DN50) valve body are precision investment casting.
b) Large diameter (> DN50) valve body are molding shaped seamless steel or steel plate.
c) Bellows sealed structure can withstand 150ºCtemperature, metal sealed structure can withstand 450ºCtemperature.
d) Can install on any position to control the airflow in the vacuum pipeline, as an on-off valve purpose

Angle Valves, Angle Globe Valves, Brass Angle Valve, Zinc Angle Valve

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