Stainless Steel Mirror Polishing: Process, Method and Requirements

The stainless steel polishing process can be divided into two parts: grinding and bright dipping.

The two processes and methods are summarized as follows:

1. Grinding

The main objective of stainless steel weldment grinding is to remove welding spots and reach the workpiece with a surface roughness of R10um, so as to prepare for bright dipping!

Related reading: What Is Surface Roughness?

The grinding part generally includes:

  • 3 processes: coarse grinding, semi-fine grinding, fine grinding;
  • 3 faces: two sides and one edge;
  • 9 polishing machines;
  • 27 regulatory agencies;

The details are as follows:

1. Visual inspection

Visual inspection shall be carried out on the workpieces transferred to the polishing process in the last step, such as whether there are defects that cannot be remedied in this process, such as missing weld, welding penetration, uneven depth of welding points, too far from the joint, local depression, uneven butt joint, deep scratches, bruises, serious deformation, etc.

If there are any above defects, they shall be returned to the previous process for repair.

If there are no above defects, enter this polishing process.

2. Rough grinding,

Use 600 # abrasive belt to grind the workpiece back and forth on three sides.

The goal of this process is to remove the welding spots left by the workpiece welding and the bruises occurred in the previous process, so as to achieve the initial formation of the fillet of the weld junction.

The horizontal and vertical surfaces are basically free of large scratches and bruises.

After this process, the roughness of the workpiece surface should reach R0.8mm.

Pay attention to the tilt angle of the abrasive belt machine and control the pressure of the abrasive belt machine on the workpiece during polishing.

Generally speaking, it is moderate to form a straight line with the thrown surface!

3. Semi fine grinding

Use 800 # abrasive belt to grind three sides of the workpiece according to the method of grinding the workpiece back and forth in the front, mainly to correct the joints in the previous process and further fine grind the marks generated after rough grinding.

Grind the marks left by the previous process repeatedly, so that the surface of the workpiece is free of scratches and basically brightens.

The surface roughness of this process shall reach R0.4mm.

(Note that new scratches and bruises are not allowed in this process, because such defects cannot be repaired in subsequent processes.)

4. Fine grinding

The 1000 # abrasive belt is mainly used to correct the fine lines in the previous process. The grinding method is the same as above.

The goal of this process is to basically eliminate the joint between the grinding part and the part of the workpiece that is not grinded, further brighten the surface of the workpiece, and the workpiece after grinding in this process should be basically close to the mirror effect, and the surface roughness of the workpiece should reach R0.1mm.

5. Instructions for replacing the abrasive belt:

Generally speaking, 600 # abrasive belt can grind 6-8 pieces of 1500 mm long workpieces, 800 # abrasive belt can grind 4-6 pieces of workpieces, and 1000 # abrasive belt can grind 1-2 pieces of workpieces.

The specific situation also depends on the welding points of workpieces, the pressure used for polishing, and the method of polishing.

In addition, it should be noted that the replacement of abrasive belt must ensure that the abrasive belt can rotate smoothly on the sponge wheel to achieve the purpose of uniform grinding of the workpiece.

Description of grinding three sides:

The horizontal and vertical two sides of the weldment that are separated by the welding edge need to be polished.

Specifically, three sides need to be polished.

The schematic diagram of polishing is shown in the following figure:

Stainless Steel Mirror Polishing: Process, Method and Requirements 1
Schematic Diagram of Welds of Welding Workpieces

Schematic diagram of nine polishing machines:

Three belt sanders are used as a process (one group) to grind three surfaces.

In actual work, the grinding position of the latter group of belt sanders should be 1-1.5mm ahead of the grinding position of the previous group of belt sanders.

This design is for the latter group of belt sanders to better grind the polishing marks left by the previous group.

Stainless Steel Mirror Polishing: Process, Method and Requirements 2

Twenty seven adjustment mechanisms: each belt sander is equipped with a front and rear adjustment mechanism, an up and down adjustment mechanism, and an angle adjustment mechanism of the belt sander.

Stainless Steel Mirror Polishing: Process, Method and Requirements 3

Depending on the specific conditions of workpiece welding, the final equipment consists of three to four mechanisms, each of which is polished with different abrasive belts.

The polishing position, angle and polishing pressure of each belt sander are controlled by the polishing machine adjusting mechanism, and adjusted before the equipment starts to work, so that each belt sander is at the proper position, angle and working pressure.

Among the three adjustment mechanisms shown above, one mechanism shall be able to control its corresponding adjustment through the signal detected by the photoelectric switch to prevent excessive grinding amount at both ends of the grinding.

For example, the angle adjustment mechanism of the abrasive belt machine is set to detect that the workpiece enters the lower part of the abrasive belt machine through the photoelectric switch.

At this time, the adjustment mechanism starts to control the lifting of the abrasive belt machine.

When the workpiece enters a certain position, the adjustment mechanism drops the abrasive belt machine.

The abrasive belt machine is powered on or ventilated to start polishing.

When the polishing is almost finished, the detection mechanism also detects that the workpiece is about to be polished, and the adjustment mechanism pneumatically controls the lifting of the abrasive belt machine. 

After the workpiece passes, it will fall down, which can avoid excessive polishing at both ends of the stainless steel square tube.

Grinding methods:

Stainless Steel Mirror Polishing: Process, Method and Requirements 4

Grind the workpiece by pressing the sea rubber wheel of the abrasive belt machine.

While grinding, the abrasive belt machine or workpiece can be moved horizontally to grind off the welding spots one by one.

The screenshot of the actual polishing method of the polishing machine is shown in the right figure:

Stainless Steel Mirror Polishing: Process, Method and Requirements 5

Clamp the workpiece at an angle of 45 ° and polish it with the large abrasive belt wheel of the abrasive belt machine.

2. Bright dipping

The main purpose of the bright dipping part is to mirror the grinded stainless steel to achieve the purpose of mirror.

This process generally includes:

  • Two processes: waxing and polishing;
  • Two motors;
  • Two wool wheels, big green wax, cloth

The details are as follows:

1. Visual inspection

Visually inspect the weldments that entered this process in the previous process, check and confirm whether there are any problems that can not be repaired in the polishing stage, such as missing polishing to 1000 #, incomplete polishing of all welding points, rough grinding marks, serious damage to the protective film, excessive grinding, large rounded corners, serious grinding at both ends, uneven grinding, and uneven grinding.

If such problems exist, they shall be returned for re grinding or repair.

(In this process, it is impossible to repair the bumps, gouges, and large scratches that appear in the grinding process, but it can repair very small fine lines, such as the small fine lines from 1000 # grinding. But it is very laborious.)

2. Specular surface

The wool wheel driven by a high-speed motor (available on the market) is used to polish the mirror surface with the help of wax, which imitates the previous polishing method.

The main purpose of this process is to polish the workpieces after polishing the previous processes, rather than further grinding.

Pay attention not to rub the polishing wax on the covering film of the workpiece surface during the operation of this step, and pay attention not to damage the covering film.

3. Burnish

This process is the last process of mirror surface polishing.

Use a clean cotton cloth wheel to rub the surface of the workpiece after the mirror surface, and clean and polish the workpiece after all previous processes.

The goal of this process is to identify no welding trace on the workpiece surface, and polish the waxed and grinded workpiece to achieve a brightness of 8k higher than the mirror reflection.

In addition, there is almost no difference between the part of the workpiece that has been thrown and the part that has not been thrown, achieving a complete mirror effect.

4. Notes on waxing:

a. Waxing method:

Generally, the wool wheel shall be waxed before grinding the workpiece, and grinding shall not be started until the wool wheel is covered with green wax.

The waxing method is shown in the figure below:

Stainless Steel Mirror Polishing: Process, Method and Requirements 6

b. Why does the high-speed motor directly drive the wool wheel to wax and grind the stainless steel workpiece to make it bright?

Because the blue wax is an oily substance, which is solid at room temperature and liquid at high temperature.

The high-speed motor directly drives the wool wheel to rotate at high speed.

When the wool wheel is stuck with the blue wax on the surface, it grinds on the surface of the workpiece.

The oily substance makes the surface of the workpiece bright. 

Therefore, it is important to select the motor that drives the wool wheel for polishing.

Stainless Steel Mirror Polishing: Process, Method and Requirements 7

The speed of the motor used for polishing shall not be less than 13000r/min, and its power shall not be less than 500w.

When the speed is lower than this speed, the brightness or mirror effect of the workpiece polished by the motor is not very ideal.

Therefore, it is difficult for ordinary motors to meet their requirements, and generally high speed motors are selected.

c. Wool wheels on the market can be divided into coarse wheels and fine wheels.

The selection of wool wheel is very important.

The rough wool wheel is easy to be polished. In actual production, the fine wool wheel is generally used, so the effect is good!

d. In the polishing process, the pressure on the workpiece should also be controlled.

If the pressure is too large, the area where the protective film is polished off by the wool wheel will be too large, and even the workpiece will be blackened, and the original mirror effect of the workpiece will be damaged.

e. In the process of polishing, it is necessary to continuously supply large blue wax, otherwise the wool wheel will smoke due to high temperature, which will wear the wool wheel seriously and damage the stainless steel greatly.

f. For the small lines that need to be repaired in the lighting stage, they need to be manually repaired separately, which is very troublesome.

If you can, try not to do any repair work in this stage.

g. Generally, two motors are installed for waxing motor. Each motor is responsible for polishing one side of the workpiece.

One motor for polishing edges can be considered as appropriate to increase the brightness of edges.

h. Replace the wool wheel as appropriate.

Several supplements on burnish:

a. Burnish:

Stainless Steel Mirror Polishing: Process, Method and Requirements 8
Stainless Steel Mirror Polishing: Process, Method and Requirements 9
Stainless Steel Mirror Polishing: Process, Method and Requirements 10

The burnish method is basically the same as the waxing method, except that the wool in waxing is replaced by the cloth wheel in burnishing.

Burnish is the last process in the whole polishing process.

Make sure that there is no damage to the mirror surface after the workpiece is polished, otherwise all previous efforts will be wasted.

a. The burnish method is to directly install the cloth wheel on the high-speed motor to achieve high-speed rotation, wipe on the surface of the workpiece, wipe off the dirt on the workpiece and the attached blue wax, and achieve the purpose of polishing!

In actual burnish, it is often carried out together with grinding powder.

The grinding powder can remove the oily substance blue wax.

Its main role in burnishing is to easily remove the blue wax adhered to the workpiece.

If it is not matched with grinding powder, the blue wax on the workpiece surface will be difficult to remove, and it is also easy to stick to other places, affecting the beauty of other places.

b. In order to obtain the brightness of the workpiece in line with the mirror requirements, the cleanliness of the cloth wheel is particularly important.

In actual production, the cloth wheel needs to be replaced according to the specific situation.

2 thoughts on “Stainless Steel Mirror Polishing: Process, Method and Requirements”

Leave a Comment

Your email address will not be published. Required fields are marked *