Grinding machines

Grinding machines

 These machines are used for sanding flat surfaces and details with curves - panels, frames, veneers and the like - to give them the required smoothness.

Grinding machines are divided into belt, disc, combined, cylindrical and profile grinding machines.

Belt grinders are used for flat, round and curved elements and small products. They are divided into horizontal, vertical and profile grinding machines.

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Picture 1: Ironing machine with a movable table of the ŠIPS brand 

Horizontal grinders are divided into machines with a stationary and a movable horizontal table.

Grinders with a stationary table are used for grinding small elements, and grinders with a movable table for grinding larger elements, plates, doors, fillings, veneers, etc.

Vertical belt grinders are used for grinding the corners of elements, crates, round elements, etc.

Profile grinders are used for grinding small elements, which have curved surfaces. This type of grinder is not widely used in the construction industry.

The belt sander with a moving table of the Š1 PS brand (fig. 1) is used the most, on which elements, plates and flat products can be sanded, which have a length of 1900 mm, a width of 800 mm, and a thickness of 500 mm.

Technical characteristics of the grinder:

  • Sanding belt width 150 mm
  • Dimensions of the mobile table 800 x 2000 mm
  • Table stroke length 1300 mm
  • Vertical travel of the table 500 mm
  • Electric motor power 3,4 kW
  • The number of revolutions of the electric motor per minute is 1500
  • Machine weight 1050 kg

Disc grinders can be equipped with two vertically placed grinding plates and one horizontally placed grinding plate.

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Picture 2: Combined grinding plate - roller brand Š1 DB.

Disc sander with one plate is used for angular sanding and also for sanding small products with small surfaces. Disc grinders with two plates are less commonly used.

Combined sanders and profile sanders are used for sanding flat, profiled and elements with curved surfaces. One type of combined sanders is the Š1 DB plate-roller type (fig. 2), which consists of a vertical plate and a roller. A sanding cloth is pulled onto the machine plate and the cylinder (bobbin). The plate and the roller are fixed on the shafts of the electric motor. With the help of a special eccentric mechanism, the roller moves parallel to the axis, back and forth with an amplitude of 0 to 40 mm, which ensures sufficient cleanliness and smoothness of the surface of the object to be sanded. At the vertical plate, a table is placed for stacking elements or small products that need to be sanded; this table can also be placed at an angle to the sanding board.
This machine has the following technical characteristics:

  • Plate diameter 800 mm
  • Roller diameter 90 mm
  • Working length of the roller 210 mm
  • Total length 240 mm
  • Number of roller oscillations per minute 140   
  • Tilt angle of the table at the plate 15o up to 45o down
  • Tilt angle of the table at the roller 15o up to 30o down
  • The power of the electric motor of the roller is 1,6 kW at 3000 rpm
  • The power of the plate's electric motor is 2,8 kW at 750 rpm
  • Machine weight 900 kg

Profile grinders are used for grinding profiled elements. This sander consists of a spindle with a working head on which inserts with a sanding cloth are fixed around the perimeter. While the machine is working, the inserts elastically adhere the sanding cloth to the profile of the element being sanded in this way. Cylindrical grinders are divided into single-cylinder, two-cylinder, three-cylinder and six-cylinder with manual and mechanical displacement. Manual movement is performed on single-cylinder grinders, which are most often used for grinding elements with curved surfaces (arched profiles, table legs, etc.).
Multi-cylinder grinders with mechanical displacement are used for grinding panels: veneers, frames, etc. The movement can be done using a roller or a rubber conveyor belt. The displacement by the power of the roller is applied when sanding the veneer, and the displacement by the conveyor belt for sanding panels, doors, frames, etc.

The cylinders of sanding machines are actually steel tubes with accessories for balancing and tensioning the sanding cloth. They can be whole or cut. The sanding cloth is wound spirally on the entire sanding cylinders and fixed on the front of the cylinder with a special clamping device. On cut cylinders, the sanding cloth is clamped in the slot along the cylinder's outlet. Whole sanding cylinders are very widespread, They are more suitable for tensioning the sanding cloth and are easier to balance. Grinding cylinders can be located above or below the elements being ground. The upper position of the cylinder is more favorable. In addition to rotary movement, the cylinders also move parallel to their axis, which is equal to about 100 double strokes per minute, when the size of the stroke is 10 mm, which improves the quality of ironing by removing separated fibers. The cylinder can be started by a transmission arm or built-in electric motors.

Grinders with the upper or lower position of the cylinder in double-sided grinding require the elements to be passed twice, therefore six-cylinder grinders with the upper and lower position of the cylinder are more productive, since they grind both sides of the elements in one pass.

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Figure 3: Kinematic diagram of three-cylinder grinding machine Š1 ZC

The use of a three-cylinder grinding machine with a belt feed Š1 ZC (fig. 3) is very widespread, which is used for mass grinding of flat elements of frames and plates with a width of up to 1300 mm and a length of at least 200 mm.

Technical characteristics of the grinder:

  • Four-stage movement mechanism 4, 6, 8 and 12 m/min
  • Cylinder diameter 280 mm
  • Number of revolutions of the cylinder 1500 rev/min
  • The number of shaft oscillations of the cylinder is about 100 per minute
  • Number of electric motors 6
  • Power 27,8 kW
  • Machine weight 6500 kg

Table 1: Numbers and sizes of sanding cloth grains

Sanding cloth numbers

Grain sizes in diameter, mm Sanding cloth numbers Grain sizes in diameter, mm Sanding cloth numbers Grain size in diameter
12 1,68 80 0,177 325 0,030
16 1,19 100 0,149 M-28 0,028
20 0,84 120 0,126 M-20 0,020
24 0,71 140 0,105 M-14 0,014
36 0,50 170 0,088 M-10 0,010
46 0,35 200 0,074    
60 0,25 280 0,063    

As an abrasive machine, the sander uses a sanding cloth, which consists of paper or cotton cloth on which sharp grains of hard material are glued. There are abrasive cloths with grains of glass, flint, quartz, corundum and electrocorundum. According to the coarseness of the grain, sanding cloths are classified into numbers.

In the table. 1 lists the numbers of the sanding cloth that was previously produced in the USSR.

According to the material with which the grains are attached to the substrate, sanding cloths are made for dry and wet sanding. Cloth is used as the binding material of the sanding cloth for dry sanding, and synthetic adhesives for wet sanding. Sanding cloths, where the binding materials are synthetic adhesives that are stable in water, are used for sanding nitrocellulose varnish-coatings with the use of paste or other sanding materials.

Table 2 shows the grinding modes on different types of grinding machines.

Table 2: Modes of work on grinding machines

Mode indicators Unit of measure Machines
You plate Tracks Belts with tensioning device Single cylinder Three-cylinder with mechanical displacement
Grinding speed m/sec 15-20 12-20 12-20 15-23 23,5
Specific pressure kg / cm2 0,6-0,7 0,3-0,5 0,6 0,4 0,4
Feed rate  m / min - - - - 4-12

 

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