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Working Principle, Installation, Maintenance Of Shot Blasting Machine

I. Working principle of shot blasting machine:

Shot blasting machine is the core part of the cleaning machine, it's mainly composed of impeller, blade, directional sleeve, shot wheel, spindle, cover, spindle seat, motor, etc.

In the process of high-speed rotation of the impeller of the shot blasting machine, centrifugal force and wind force are generated. When the shot flows into the shot pipe, it is accelerated into the high-speed rotation of the shot wheel. 

Under the action of centrifugal force, the shot is thrown from the shot wheel, through the directional sleeve window, and grows continuously along the blade until it is thrown. The thrown shot forms a flat flow beam, which cleans and strengthens the workpiece by a continuous strike.


II. The details of the installation, repair, maintenance and disassemble of the shot blasting machine as follows:

1. Install the shot blaster shaft and bearing on the main bearing seat

2. Install the combination disk on the main shaft

3. Install the side and end guard plate

4. Install the main bearing seat on the shot blasting cover and fix it with bolts

5. Install the impeller body on the combination plate and tighten it with bolts

6. Install the blade on the impeller body

7. Install the shot wheel on the spindle and fix it with the cap nut

8. Install the directional sleeve on the shot blaster cover and press it with the pressing plat

9. Installation of the shot chute


III. Caution of installation of shot blasting machine

1. The wheel shot blasting machine shall be firmly installed on the wall of the chamber, and sealed rubber shall be added between the shot blaster and the chamber.

2. When installing the bearing, the operator should keep the bearing and hand cleaning.

3. An appropriate amount of grease shall be filled into the bearing.

4. In normal operation, the temperature rise of bearing shall not exceed 35 ℃.

5. The distance between the impeller body and the front and rear guard plates shall be equal, and the tolerance shall not exceed 2-4mm.

6. The impeller of the shot blasting machine shall be close to the mating surface of the combination plate and fastened evenly with screws.

7. During installation, the clearance between the directional sleeve and the shot wheel shall be kept consistent, which can reduce the friction between the shot wheel and the shot wheel, avoid the phenomenon of squeezing the directional sleeve, and ensure the shot blasting efficiency.

8. When installing the blades, the weight difference of a group of eight blades shall not be greater than 5g, and that of a symmetrical pair of blades shall not be greater than 3g, otherwise, there will produce greater vibration and increase noise.

9. The driving belt of shot blasting machine should be properly tightened


IV. Adjustment of the directional sleeve opening of the shot blasting machine

1. Before using the new shot blaster, the opening position of the directional sleeve must be adjusted correctly so that the shot thrown can be thrown on the surface of the cleaned workpiece as much as possible, so as to ensure the cleaning effect and reduce the wear of the wear-resistant parts of the cleaned indoor wall.

2. The opening position of the directional sleeve can be adjusted as follows:

Apply black ink (or lay a piece of thick paper) on a board and place it on the position of workpiece needs cleaning.

Actuate the shot blaster and manually add a small amount of shot to the shot chute of the shot blaster.

Stop the shot blaster and check the position of the belt. If the position of the shot blasting belt is ahead, adjust the directional sleeve in the opposite direction of the shot blasting machine (left or right rotation), and turn to step 2; if the position of the shot blasting belt is behind, adjust the directional sleeve in the same direction of the shot blasting machine (left or right rotation), and turn to step 2.

After adjustment, the position mark of the opening of the directional sleeve shall be made on the shell of the shot blasting machine for reference when replacing the blades and other spare parts.


Wear inspection of directional sleeve

1. The rectangular opening of the directional sleeve is easy to wear. It is necessary to check the wear condition of the directional sleeve rectangular opening from time to time, so as to adjust the position of the directional sleeve opening in time or replace the directional sleeve.

2. The opening should be worn within 10 mm. When the opening is worn 5 mm, and the directional sleeve shall be rotated 5 mm against the impeller along the position mark of the directional sleeve. The opening is worn 5 mm again, and the directional sleeve shall be rotated 5 mm against the impeller along the position mark of the directional sleeve.

3. Replace the directional sleeve when the opening is worn for more than 10 mm


V. Inspection of wear-resistant parts of shot blasting machine

After stop running, check the wear condition of the wear-resistant parts of the shot blasting machine. The following describes the situation of several wear-resistant parts respectively, and the wear condition of the blade should be checked frequently. In case of any of the following conditions, the blade must be replaced in time:

The blade thickness is reduced by 4-5mm.

The blade length is reduced by 4-5mm.

The shot blaster vibrates violently.

If the shot blasting machine is installed in the shot blasting room which is easy for maintenance personnel to enter, the blade can be inspected in the shot blasting room. If it is difficult, they can observe the blades by open the shell of the shot blasting machine from outside.

Generally, the blades should be replaced completely.

The weight difference between the symmetrical two blades shall not exceed 5g, otherwise the shot blasting machine will vibrate greatly during operation


VI. Replacement and maintenance of shot dividing wheel

The separating wheel is set in the directional sleeve of the shot blasting machine, which is not easy to check directly. However, when replacing the blades, the shot dividing wheel must be removed, so it is advisable to check the abrasion of the shot dividing wheel at the same time of replacing the blades.

If the wheel is worn and goes on using, the shot diffusion angle will increase, which will accelerate the abrasion of the protection plate and affect the cleaning effect.

If the outer diameter of the shot dividing wheel is worn by 10-12mm, it should be replaced


VII. Replacement and maintenance of shot blaster guard plate

Any wear-resistant parts such as top guard board, end guard board and side guard board in the shot blasting machine that are worn to 1 / 5 of the original thickness must be replaced immediately. Otherwise, the shot may break through the shot blaster cover.


VIII. Replacement sequence of wearing parts of shot blasting machine

1. Turn off the main power.

2. Remove the pill chute.

3. Use the socket wrench to remove the fixing nut (turn left and right separately), tap the shot dividing wheel lightly, and take it down after loosening.

4. Tap the blade head with a wooden hammer and remove the blade. (remove 6-8 hexagon screws in the fixed impeller body hidden behind the blade anticlockwise, and the impeller body can be removed.)

5. Check and replace all wear-resistant parts.

6. Return and install the shot blaster according to the removal sequence


IX. Common faults and solutions of shot blasting machine

Poor cleaning effect

Lack of steel shots, should fill enough shots

The shot blasting direction of the shot blaster is not correct.

Adjust the window position of the directional sleeve

Large vibration of shot blasting machine

The blade is seriously worn and the rotation is unbalanced. Replace the blade.

The impeller is seriously worn

Replace impeller.

The main bearing seat is not filled with grease in time, and the bearing is burnt out.

Replace the main bearing seat or bearing (the fit is clearance fit)

Abnormal sound in the shot blaster

The shot does not meet the requirements result sand inclusion between the shot wheel and the directional sleeve。

The screen mesh of separator is too large or damaged, and large particles enter the shot blasting machine.

Open the shot blasting machine and check the removal.

The inner guard plate of the shot blasting machine is loose, and it is abraded with the impeller or blade.

Adjust the guard plate

Due to vibration, the bolt connecting the shot blaster and the chamber body is loose.

Adjust the shot blaster assembly and tighten the bolt.


X. Caution of shot blaster commission

1. Check whether the impeller is installed in the correct position.

2. Check the tension of the shot blast belt and make necessary adjustments.

3. Check whether the limit switch on the machine cover is working properly.

4. Remove all foreign matters, such as bolts, nuts, and washers, which may fall into the machine or be mixed into the shot material during all installation of shot blasting device, thus causing premature damage to the machine. Once found should be removed immediately.

5. Commissioning of shot blaster

After the final installation and position, the user should make fine debugging according to the specific working conditions.

By turning the directional sleeve, the direction of shot ejection can be adjusted within the projection range. However, too much jet to the left or right will reduce the projection power and accelerate the abrasion of the radial shield.


An optimum ejection mode can be tuned as follows.

(1) Place a slightly rusted or coated steel plate in the shot blast zone.

(2) Start shot blaster. The motor is accelerated to the appropriate speed.

(3) Open the shot blasting gate with the control valve (manually). After about 5 seconds, the shot material is fed into the impeller and the metal rust on the slightly rusted steel plate is removed.

(4) Determine the projection position

Loosen the three hexagon bolts on the press plate with a 19MM spanner until the directional sleeve can be turned by hand and then tighten.

(5) Prepare a new projectile to verify the best setting.

The procedure described in sections (3) to (5) is repeated several times until obtaining the optimum projection position.


XI. Caution of use of a shot blaster

The new shot blaster shall be commissioned without load for 2-3 hours before use.

Stop commissioning immediately if strong vibration or noise is found during use. Open the front end cap of the shot blaster.

Check: whether the blades, orientation sleeves and shot blasting wheels are damaged; whether the weight of the blades differs too much; whether there are foreign matters in the shot blaster.

Before opening the end cap of the shot blaster, cut off the general power supply of cleaning equipment and list the instructions. When the shot pellet does not stop turning completely, it is forbidden to open the end cap.


XII. Selection of shot pellets

According to the particle shape of projectile material, it can be divided into three basic shapes: round, angular and cylindrical.

The shot used for shot blasting cleaning should be round, secondly cylindrical; the prismatic and angular shaped metal surface with slightly higher hardness should be used for shot blasting rust removal and erosion pre-treatment for spraying paint, and the round shape should be used for shot blasting strengthening and forming of the metal surface.

The round shapes: white cast iron shot, decarburized malleable cast iron shot, malleable cast iron shot and cast steel shot.

Angled are white cast iron sand, cast steel sand.

Cylindrical: steel wire shot cutting.

Shot Common Sense:

New cylindrical and angular projectiles have sharp edges and corners, which will gradually become circular after repeated wear and tear.

Cast steel shot (HRC40-45) and steel wire cut (HRC35-40) automatically undergo work hardening during repeated strikes on the workpiece and can be raised to HRC42-46 after 40 hours of operation.After 300 hours of work, it can be increased to HRC48-50. When cleaning sand, the shot hardness is too high. When hit on the surface of the casting, the shot is easy to crack, especially the white cast iron shot and white cast iron sand, which have poor reusability. When the hardness of shot is too low, it is easy to deform when blasting, especially decarburized malleable iron shot, which absorbs energy when it deforms itself, and the effect of cleaning and surface strengthening is not ideal. Only when the hardness is moderate, especially for cast steel shot, cast steel sand and cut steel wire, can not only prolong the service life of shot, but also achieve ideal cleaning and strengthening effect.

Grain size classification of projectiles


The classification of round and angular projectiles is determined according to the screen size after screening and its size smaller than the screen size. The grain size of steel wire pellets is determined by their diameters. The diameter of the projectile should not be too small or too large. If the diameter is too small, the impact force will be too small and the efficiency of sand cleaning and strengthening will not ideal; if the diameter is too large, the number of particles sprayed on the surface of the workpiece in unit time will be small, which will also reduce the efficiency and increase the roughness of the workpiece surface. The general diameter of the projectiles is in the range of 0.8~1.5 mm. Large workpieces are usually select large size (2.0-4.0) and small workpieces are usually select a small size (0.5-1.0). Refer to the following table for specific selection:

cast steel shot

Cast steel sand

steel wire shot cutting

Application

SS-3.4

SG-2.0

GW-3.0

Large cast iron, cast steel, malleable iron, large cast heat treatment parts, such as sand cleaning, rust removal.

SS-2.8

SG-1.7

GW-2.5


SS-2.4


GW-2.0


SS-2.0




SS-1.7




SS-1.4

SG-1.4

CW-1.5

Large and medium-sized cast iron, cast steel, malleable iron parts, billets, forgings, heat-treated parts, etc. Clean sand and remove rust.

SS-1.2

SG-1.2

CW-1.2


SS-1.0

SG-1.0

CW-1.0

Small and medium-sized cast iron, cast steel, malleable cast iron, small and medium-sized forgings, rust removal of heat-treated parts, shot blasting and erosion of shaft rolls.

SS-0.8

SG-0.7

CW-0.8


SS-0.6

SG-0.4

CW-0.6

Small-sized cast iron, cast steel, heat-treated parts, copper, aluminum alloy castings, steel pipe, steel plate, etc. Sand removal, rust removal, processing before plating, shot blasting, shaft roll erosion.

SS-0.4

SG-0.3

CW-0.4

Copper, aluminum alloy castings, sheet, stainless steel strip rust removal, shot blasting, shaft roll erosion.


XIII. Daily maintenance of shot blaster

Check whether all the screws and clamping connection parts (especially blade fasteners) tight, whether directional sleeve, feed tubes, shot pellets, machine covers, fastening screws, etc. If loosened, tighten with 19 mm and 24 mm wrenches.


Check whether the bearing temperature is too high. If it is too high, the bearing should be refilled with lubricant.


For motor direct-pull shot blaster, check whether there is shot in the long groove on the side of the cover (mounting motor side). If there is a shot, clean it with compressed air.


If it is found that excessive wear and fracture of machine parts may be caused by noise during operation, the blades and guide wheels should be inspected immediately and visually. If the noise is found to be coming from the bearing area, preventive repairs should be carried out immediately.


Refueling of shot blast bearing

Each shaft seat has three spherical lubricating nozzles, which oil the bearing through the middle nozzle. Fill the labyrinth seal with oil through two fuel nozzles on both sides.

Approximately 35 grams of grease is required per bearing and 3# lithium grease must be used.

Visual inspection of fragile parts

Compared with all other fragile parts, shot blasting blades, shot blasting wheels and directional sleeve are particularly easy to wear due to their role in the machine. Therefore, regular inspection of these parts should be guaranteed. All other fragile parts should also be inspected at the same time.


Shot Blaster Removal Procedure

Open the shot blast service window, which can only be used by the maintenance personnel to observe the blades. Turn the impeller slowly to check the wear of each blade. It is not always easy to separate the blades from their fasteners by first removing the blade fasteners and then pulling them out of the grooves in the impeller body. It is possible that shot pellets and rust can enter the gap between the blades and grooves and thus block the blades and blade fasteners. In general, the fasteners can be removed by tapping lightly with a hammer several times and the vanes can also be pulled out of the grooves of the impeller body.


If maintenance personnel have difficulty getting into the shot blasting chamber, they can only observe the blades outside the shot blasting chamber. That is, open the shot blast machine cover for inspection. When the nut is first loosened with a wrench, the guard plate can be loosened from the fastener and removed as a whole with the compression screw. In this way, the radial guard late can be pulled out. The maintenance window allows maintenance personnel to observe the blades intuitively, turn the impellers slowly and observe the wear of each impeller.


Replacing blades

Grooved wear on the blade surface should be reversed immediately and replaced with a new one.


Because the strongest wear occurs on the outward part of the blade (shot ejection area) and the inward part (shot suction area) with little wear. Changing the inner and outer end faces of the blades make the less worn part of the blades in the throwing area. In this way, each blade can be used four times under uniform wear, after which the old blades must be replaced.

When replacing old blades, a uniform weight set of blades should be replaced at the same time. The blades are checked at the factory to ensure they are of equal weight and packaging. The maximum error in the weight of each blade belonging to the same set shall not exceed5g. Replacing different sets of blades is not recommended, as different sets of blades cannot guarantee equal weight. Start the shot blaster without loading, then stop, pay attention to the machine noise during running.


Removal of the shot-feeding tube, shot-dividing wheel and directional sleeve.


Remove 2 hexagon nuts from the clip plate with a wrench and then unscrew the clip plate to pull the shot guide tube out.


Insert a bar between the blades to secure the impeller (find a support point on the housing). Then unscrew the hexagon screw from the impeller shaft with a wrench and take out the shot blaster. The installation of the shot-blasting wheel can be carried out according to the following procedure: first, the shot-blasting wheel is installed into the groove of the impeller shaft, and then the screw is screwed into the impeller shaft. The maximum torque applied to the screw with a force wrench is Mdmax=100Nm. Before removing the directional sleeve, its original position should be marked on the scale of the enclosure. This makes installation easier and avoids subsequent adjustments.


Inspection and replacement of shot blasting wheel

Under the centrifugal force of the pelleting wheel, the pellet added axially is accelerated. The shot pellet can be delivered to the blades accurately and quantitatively through the eight-shot grooves on the shot pelleting wheel. Excessive wear of pelleting groove ~ (enlargement of pelleting groove ~) can damage the feeder and cause damage to other parts. If it is observed that the shot blasting groove has been enlarged, the shot blasting wheel should be replaced immediately.


Inspection and replacement of impeller body

As a rule, the service life of the impeller body should be two to three times that of the parts mentioned above. The impeller body is dynamically balanced. However, under uneven wear and tear, the balance will also be lost after considerable working time. In order to observe whether the balance of the impeller body has been lost, remove the blades and let the impeller idles. Once found uneven running of the guide wheel, it should be replaced immediately.