TMB: Tumblast Machine — Rubber Belt.

How a tumblast machine works.

A tumblast machine — also called a tumble belt shot blasting machine, or barrel blast in the US — processes parts in bulk, by the batch. The parts sit on a continuous rubber belt that rolls them over each other while top-mounted blast wheels throw media into the load from above. No hooks, no fixtures, no handling of the single part: you load, you run the cycle, you unload.

Two things act on the parts at the same time. The belt turns, and as it turns it keeps rolling the load over on itself: the parts rub against each other continuously, which is a tumbling action in its own right and does part of the work. The media does the rest.

The belt is what creates the motion. Nothing else moves the parts — no drum, no vibration, no operator. As the load rolls, faces that were buried come up, get hit, and go back under. That is why every surface is reached eventually, and why throughput here is counted by the batch rather than by the piece.

The belt itself can be customised to the parts being processed. It can be supplied with or without ribs, and hole diameter and pattern are adapted to the process rather than taken as they come.

This equipment is suitable for both shot blasting and shot peening, according to the setting parameters.

The TMB range covers four sizes on this principle, the largest with two blast wheels. Productivity can be substantial when the load and unload side is engineered for it — the 500 with load/unload automation runs more than 500 kg of steel parts per hour, and the 1000 in a fully equipped workstation goes past two tons.

The TMB is one of the closed cabin layouts running on cycle time, where the machine works by the batch rather than by pass speed.

Need help troubleshooting this type of equipment? Check Vortex.

Tumblast sizes and capacity.

Reading the sizes against the US ladder.

US market sizes these machines by the cubic foot, on a ladder that runs 1.5 / 3 / 6 / 7 / 12 / 15 / 24 cu ft. The TMB sizes are metric and land between those rungs, so read them across: the 500 sits with a US 1.5 cu ft machine, the 650 between 1.5 and 3, the 900 between 3 and 6, the 1000 between 7 and 12. Blast wheel 5.5 to 11 kW is 7.5 to 15 HP.

Which parts can be tumbled.

The process works on tumble-proof parts — components that can roll over each other for the length of the cycle without damaging one another. That is the first filter, and it comes before any discussion of size or cycle time.

What rules a part out: fragility, thin edges that can fold over, long slender shapes that bridge across the belt instead of turning, and geometries that nest into each other or float on top of the load. Parts that get carried by the belt rather than tumbling take the media on one face and miss the other.

None of this is settled on a drawing. Approaching this layout for the first time, run a test: how the shape factor behaves is the one thing that cannot be predicted on paper.

Where tumblast machines are used.

The standard ground for this layout is bulk production of small and medium parts: fasteners, fittings and connectors, aluminium and steel castings, forgings, and descaling after heat treatment.

Three applications are worth calling out separately, because they are less obvious and less well covered.

Sintered and powder-metal parts. Deburring PM parts without rounding the edges you need is a different problem from cleaning a casting, and the tumbling action has to be dosed accordingly.

Aluminium slugs for cans and cold forming. Here blasting is not cleaning — it prepares the surface for what comes next. Aluminium fines also change what the dust collector has to handle.

Additive manufacturing parts. Printed parts arrive in batches of mixed geometry and need bulk post-processing. Tumble belt machines turn this from something costly and manual into an automated, cheap process.

The same layout also covers shot peening, set up with its own parameters.

If you want to work out how your parts would behave inside a belt machine,

and whether this layout suits your needs, we can talk it through.

The belt in a tumblast machine.

The belt is part of the machine and part of the process. Every builder has a standard for the belts — the hole pattern, meaning the number of holes, and their diameter. That standard then has to be adapted to the parts being processed and to the media being used.

How the belt is customized accordingly with the process.

The holes have to be numerous enough to let the media drain through. Their diameter is set against the media size: wide enough for the shot to pass, not so wide that parts fall through or jam in them. More holes drain more media but weaken the belt; fewer holes make a stronger belt that drains less. It is a balance.

Ribs can be bonded to the belt surface to increase the tumbling action where the parts need more turning.

The belt is a wear part.

It must stay covered by the parts for the whole blasting cycle. Exposed belt takes the media directly and wears out fast. Replacement takes a day on the small machines with someone experienced, and three to four days on the larger ones. On the big sizes, having working space around the machine is crucial. Packing it in between other equipment turns a slow job into a nightmare.

To clarify, replacing the belt is not a possibility, it is a certainty. However heavy and awkward the job is, it is routine maintenance, and it has to be planned as routine maintenance.

How the belt is built.

The cheapest belts are a plain rolling belt with a joint closing the loop, the good ones are built with tyre technology: a fabric ring, then rubber vulcanised around it, and only afterwards the holes made to the requirement and the ribs attached where they are needed.

The difference between the two shows up in three places. Price — the seamless belt is considerably more expensive. And service life: a comparison at equal conditions — belt properly loaded and covered in operation, same media, same operating parameters, same setup — gives 5,000 hours for the seamless belt against 2,000 for the jointed one. A ratio of 2.5 to 1.

The third difference is lead time. A seamless belt takes time to build, and it is not a short time. It also cannot be ordered and left in stock indefinitely: rubber ages whether it runs or not, exactly like a timing belt on an engine. Two factors work on it, age and use.

If a spare is kept on site, store it somewhere that is not too cold and out of the direct sunlight.

Inspecting the belt.

Whatever the installation and the layout, whatever loading and unloading automation is fitted, visual inspection of the belt has to stay easy to do and has to be done regularly. Surface damage on its own is not necessarily a problem. On a belt with a fabric carcass, what matters is the fabric: as long as the fabric is intact the belt is still working. Once the fabric tears, that is the moment to change it, and it is not a judgement call.

Belt, in short.

• On a belt machine the belt is part of the process, and it is customized to the process itself.

• The more holes, the weaker the belt — and the better it drains the media. It is a trade-off.

• Same media, same duty: a jointed belt lasts around 2,000 hours, a seamless one around 5,000.

• Changing the belt can take days. It is a consumable, and the need to replace it has to be planned for from the start, even if it does not come round often.

• Inspect it regularly. It avoids surprises, and seeing the wear build up is what lets you plan the replacement instead of reacting to it.

• Keeping the belt covered by the parts, shielded from the direct blast stream, is what actually makes it last.

Rubber or steel slat.

A steel slat version exists, and the deciding factor is the weight of the load being processed.

Going from rubber to steel means buying a whole new cabin — with all the related costs. These are decisions for high-volume production, made against the parts actually being processed, and they have to be worked out case by case.

Dust collector.

Built-in unit sized to the cabin, to ATEX and NFPA 660 standards.

Aluminium slugs are a different matter. Aluminium fines are highly flammable, and in a confined volume they are an explosion hazard — which is why combustible metals have their own chapter, NFPA 660 Ch. 22, formerly NFPA 484.

In practice, on aluminium slug work the cabin sits in the production area while the dust collector is usually placed outside the building. The connecting ductwork carries explosion isolation valves and a spark arrester, so that a fire or a pressure wave cannot travel back down the duct into the plant.

On this particular application the regulations in force at the destination have to be checked, and it takes the fullest cooperation from the buyer to arrive at a layout that satisfies productivity, the economics of the installation, and the safety requirements — both those that are mandatory and those that are simply advisable.

Blast wheel, media and controls.

Blast wheel.

A 5.5 kW direct drive unit is fitted as standard and can go up to 11 kW. Media flow rate runs from 90 to 140 kg/min. The upper limit is not set by the wheel: it is set by how much media the belt can drain, which comes back to hole diameter and hole count.

The largest size in the range carries two wheels. Above a certain cabin size a single wheel cannot cover the load, so the second one stops being an option and becomes a requirement.

Media.

Steel shot, stainless steel shot and derivatives below 50 HRC, aluminium shot, grit in cast iron or steel. Above 50 HRC a carbide kit is worth having. Zirblast ceramic media runs with its own kit.

Automation and control.

Siemens as standard for CPU, HMI and drives, Allen Bradley version available. Automatic media gate control and adjustable tumbling speed, so blasting and peening setups can be pre-programmed and recalled by the operator with one button or by barcode reader.

Layout and footprint.

2D and 3D drawings and DWG footprints available on request.

Tumblast machine summary.

Pros: the smaller size (500) is a compact equipment with everything needed to operate built in; ideal for "small" bulk processes without the operator attending it beside load/unload, and extremely cheap to run; adding automation can turn it into a fully automated workstation with barely any human labour involved, and the same automation becomes mandatory with the bigger sizes to fulfil ergonomics and safety regulations when production becomes really massive.

Cons: approaching this layout for the first time, test and analysis are highly recommended to understand how and if the shape factor influences nesting, floating and eventual "carrying on" of the parts by the belt; the 500 can still be handled by hand and the 650 with a forklift, but from the 900 up loading and unloading systems stop being optional; the belt itself remains a critical part, affected by aging, that needs to be received in the right time window for the replacement.

Boosters: specific accessories can improve productivity, mostly the loading systems to be customised accordingly with the products to process, while a vibrating channel is a great item to speed up downloading time, getting the parts clean from media while it is recovered to the machine itself. Once again, a little effort spent on designing the process would be priceless while in operations.

Popularly used in: bulk productions like 3D printing, fasteners, fittings and connectors, sintered parts, shot peening, aluminium casting, steel casting, forging and descale after heat treatment, slugs for aluminium cans and other materials and uses.

Downloadable Tech Specs TMB Blaster memo:

All dimenions and information here stated are for informative purpose only and subject to change without notice. Please refer to drawings and specs attached to your own quote.

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