Roller conveyor wheel blasting machine

Roller conveyor shot blasting machines are widely used for blasting plates, profiles, welded structures, pipes and large profiles. They offer high production rates with minimal maintenance costs.

Components and parts that need to be abrasive shot blasted come in variety of shapes and size. Each type of shot blasting machine caters to specific needs in terms of throughput, product shape, size, quality etc. Many products have large surface area as compared to its thickness such as trays, plates, beams, and fairly complex shaped products but those which can be laid flat on a roller system. Such products can be effectively shot blasted in a roller conveyor blasting machine. Along with the overhead hanger type shot blasting machines, a roller conveyor type blasting machine offers suitable solution to shot blast such plate like products.

These machines are custom developed for post fabricated structural parts widely used in industries like machine building, shipyards, automotive, heavy infrastructure constructions (bridges, offshore, buildings) etc. They are employed to descale, remove rust, remove old paint, prepare surface for coating, painting, etc.

Whatever the need is, Straaltechniek works closely with the clients to offer the best possible solutions to optimize the processes. Preconditioning the parts before blasting, the shot blasting process and cleaning with brushes, air knives etc are commonly employed to get the best possible results for the client.

We invite you to go through the following sections to get more details about the construction , working and possibilities of the machine:

Roller conveyor type abrasive blasting machines are widely employed to blast relatively flat surfaces such as sheet metal plates, large I beams, U profiles, etc. The machine is built with several modules to achieve the desired blasting outcome.

These blasting machines have inlet sections which can have additional modules such as hot / warm air blowers for dehumidification or a standard inlet through which the parts get into the machine. During the entry of the part into the machine, sensors can detect the height of the product and adjust cleaning sections according to the height of the incoming product. A complete integrated unit with hoppers, abrasive media/particle screw conveyors, bucket elevator, media cleaners, silos, valves and dust collection unit etc. work synchronously to achieve the desired blasting results on the product.

The following sections describe the different modules of the machine:

Rollers are used to transport the products through the machine from the inlet / loading side of the blasting machine towards the blast zone and eventually to the exit/unloading section of the machine.
The rollers are supported with heavy duty, high durability bearings on either end of the roller shaft. The bearings in the blast zone have labyrinth and additional dust seals to avoid abrasive blast media getting into the bearings. Each roller unit is connected by a series of sprocket and chain drives to achieve the rotation of the rollers. The transport speed is generally in the range of 0.5 to 3.0 m/min. The transport speed can be regulated with variable frequency drive unit. The standard machine comes with width of 800 mm rollers and a length of 3 m long from inlet to exit. However the machine can be customized in different sizes to meet the needs of the client/products.

Due to the abrasive blasting action in the blasting zone, the rollers in the blast zone is made of high grade wear resistant manganese steel. In other sections, standard structural steel is used of the rollers. For special applications, the rollers on the exit side can be covered with special rubber lining which avoids scratches on the blasted and cleaned products which exits the machine.
The height of the rollers from the ground are usually determined in consultation with the clients, but for majority of abrasive blasting applications, the rollers are positioned very close to the ground level. Some of the products that need to be abrasive blasted can be easily 6 to 8 m long and can weigh several tons. To facilitate easy loading and unloading of such products, the rollers are located close to the ground level while several modules of the machine are located below the ground level.

The machine housing is manufactured by welded steel plates and reinforced with the necessary profiles for added structural strength and stiffness. The entrance door or also known as sealing tunnels is provided with rubber screen/curtains through which the parts to be grit blasted enters the machine housing. Depending on the requirement, soon after the entrance zone, the machine can be incorporated with pre drying / dehumidifying unit. This is usually achieved by means of blowing hot air and with appropriate suction. A suction system with labyrinth pathway is generally included at the inlet region which assists in extracting abrasive which might otherwise exit via the entrance. The grit blasting chamber is manufactured using special wear resistance manganese steel cladding or interchangeable wear plates.

This construction ensures that the abrasives striking the wall of the blasting chamber do not cause damage to the outer wall of the chamber. Inspection doors for maintenance is provided in the blasting chamber which are implemented with fool proof safety features for proper and safe functioning. The blasting turbine wheels are strategically oriented to achieve complete coverage of the product. Based on the size and specifications of the machine there can be several abrasive blasting wheels mounted on the frame from top, sides and bottom. The usual arrangement can vary from 4 to 16 Wheels. The rollers and orientation of the blasting wheels on the bottom are carefully chosen and aligned such that the abrasive jet flying out from the turbine pass through the gap in between two rollers but not strike the rollers directly.

Soon after the blasting zone, the products pass through several cleaning sections. A suction unit is attached on the top if the cleaning section which extracts the dusty air to the filter. The labyrinth ensures that the larger particles are blocked and fall back in to the machine chamber.

Furthermore, the system can be incorporated with specially designed roller brushes to clean the product surfaces. To achieve cleaning for products of varying heights, a height detection sensor is used. This signal is fed to the motors on the top of the cleaning chamber which automatically adjusts the height of the rolling brush units. A rolling brush unit consists a rotating brush behind which a screw conveyor is positioned. The brush due to its rotation removes the dust and abrasive blast media from the surface of the products. Due to the rotation of the brush, the media particles are thrown away from the brush. These abrasive particles are then captured in the hood / housing which also has a screw conveyor. The screw conveyor ensures that the media collected in the housing is transported to the side chutes through which the abrasives are eventually transported to the hoppers in the bottom of the machine.

Based on the needs of the client/product, one or several of these brush cleaning units can be implemented in the machine. Apart from the brush cleaning system, several air blower nozzles are also implemented which provided additional cleaning action and removes the dust by impinging air. The brushing action and air blow off work continuously to provide a dust free, clean product at the end of the line. The product exits through rubber screens on the other end of the machine and can go on the next process.

Hoppers and screw conveyors
Optimal and efficient re-use of abrasive blast media is something Straaltechniek International has refined over 45 years and offers best in class media recovery and reuse system.

Figure below shows the hoppers and screw conveyors positioned below the conveyor rollers of the wheel blasting machine. The hoppers designed at a specific angle ensures the media drops through to the screw conveyors. A long, bi-directional screw conveyor system transports the media to a transverse screw conveyor located below. This is achieved by having left hand and right hand helical threads on a single spindle. The transverse screw conveyor transports the media to the foot of the bucket elevator.

Bucket Elevator
The bucket elevator consists of drums between which a belt with buckets forms an endless loop. As one of the motorized drum rotates, the belt moves the buckets. The buckets carries the abrasive media from the bottom to the top. When the direction of the buckets changes on the top, the abrasive media drops off from the buckets into a chute connected to a media cleaner. Thus, the used blast media is transported from the bottom level to the top. For more explanation about our bucket elevators, type, capacity etc, click here.

Cascade Media Cleaner
The media cleaner is connected to the elevator and mounted on the abrasive storage silo. The abrasive falls behind a pivoting valve with counterweights which distributes the abrasive media over the entire width of the cleaner. The adjustment of these counterweights ensures an optimal abrasive curtain. The connection of the suction system to the dust extractor removes the fine abrasives and dust so that the cleaned abrasive falls into the storage silo.

The air flow through the cleaner can be regulated according to the grain size and type of abrasive. A removable sieve is provided to catch any coarse pieces. A service access is provided to this sieve so that periodic/frequent inspection and cleaning of the sieve can be done.

Rotary/Drum Cleaner
For the removal of coarse contaminations the machine can be equipped with a drum screen. The electrically driven drum is available in various perforations and automatically removes the coarse contaminants. The dust is sucked out of the abrasive in the 2nd step by the abrasive cleaner.

Magnetic separator (foundry)
To separate the metallic abrasive from the sand, double magnetic separator is implemented. After this initial separation, the abrasive falls into the cleaner where the dust is separated from the abrasive by an air stream coming from the suction system.

The abrasive storage silo, made of standard steel, is located under the media cleaner. It is equipped with a level indicator which transmits information about the level in the silo and gives an indication on the switch box. Special abrasive valves type are placed on the outlet of the silo. With these valves it is possible to regulate a perfect adjustment of the required abrasive amount. These valves are pneumatically controlled and can only be opened when the turbine wheels are turning.

Automatic metering valve (AAD)
Straaltechniek has developed a new generation of metering valves with linear motors with a feedback system linked to the current and frequency of the blasting wheel. The regulation of this valve is most important because it sets itself to a preset value, namely the current (A) on the wheel. When the frequency of the turbines / blasting wheels is changed, the AAD will automatically be adjusted proportionally. Benefits of AAD Valves:

• Straaltechniek AAD valve also works with non-magnetic blasting media;
• Very easy to change the current of the throwing/blasting wheel;
• Constant flow on pitching wheel gives a constant blasting quality;
• If we change the type of abrasive, the flow of the wheel is automatically adjusted;
• In normal valves, over time, some parts of the abrasive transport system are worn out, which also affect the flow of blasting wheels. In the case of an AAD valve, this change is automatically adjusted;
• In the case where the blasting wheel is controlled with a frequency converter, the AAD will automatically adjust the flow of the media to the wheels;
• Very easy to implement as compared to a normal valve.

The product size to be sandblasted and the throughput speed needed to achieve a desired blasting result on the product determine the overall sizing and capacity of the machine. The table below gives an overview of standard machine sizes and its general specifications. However, Straaltechniek provides bespoke custom solutions to caters to a wide spectrum of industries. Contact us for your specific needs and one of our sales representatives will gather your requirements and offer the best possible solution.