Milling, welding, planning and grinding – these are the processes Roland Bräutigam uses to repair fuel tanks and the likes from tractors and other kit. We peeked over his shoulder to see what we could learn.

KEEPING IT BRIEF

  • Repairs can be carried out on site or back in the workshop.
  • If repaired on site, then it may not be necessary to remove the tank.
  • The tank has to be empty; additional flushing will only be necessary in a
    few cases. 

Fuel tanks are exposed to lots of hazards – a protruding branch on the headland, a flying stone or flail… all can cause potential plastic piercing damage. Replacing a damaged tank can cost a significant wedge of cash making a possible repair all the more appealing. And it is sustainable, too. 

Roland Bräutigam has been involved in the production and development of plastic components for more than 35 years and is well versed in the welding of thermoplastics. For several years now, he has been offering plastic tank repairs through his company Kunststoffwerkstatt24.de in Germany. 

Which plastic?

Most of the tanks used on agricultural machines are made either by rotational moulding or injection moulding. With rotational moulding, the moulds are constantly rotated to evenly distribute the liquid plastic whereas with injection moulding the moulds are filled under pressure. Roto moulded tanks have a rougher surface whereas injection-is much smoother. 

The type of moulding is of secondary importance for the repair, what is critical though is the type of plastic used. In principle, a specialist can weld all thermoplastic industrial plastics such as polyvinyl chloride (PVC), polypropylene (PP) or polyethylene (PE).

Most fuel tanks are made of PE

Fuel tanks are usually made of PE. This plastic is divided into different strength classes which depend on the length of the molecular chains, e.g. PE 80 (normal hardness) to PE 1000 (hard and wear-resistant). The more solid polyethylenes are classified as High Density (HD) polyethylenes. Only black PE-HD plastic is used for making vehicle tanks, because these offer better UV resistance. 

The owner tried fixing this damaged tank with glue but it didn’t hold.

Stationary fuel and heating oil tanks as well as those not exposed to UV radiation are usually made of white natural PE, which can also be welded without any problems. Due to the wide variety of plastics, a short welding test is essential before embarking on a repair. For this, Roland typically uses a PE-HD 100 class filler rod. In the rare occurrence that the tank is made of cross-linked polyethylene (PE-X) then it cannot be repaired with traditional welding methods. 

There are two techniques

Roland applies two types welding techniques: hot-gas pull welding where the filler rod (which can be triangular, for example) is fed manually to the welding tip which ejects hot air (approx. 260°C) that melts the plastic rod and the surrounding material. He normally uses this for small welds. 

The welding extruder can be fitted with different nozzles.

For bigger jobs, he opts for hot gas extrusion welding. The special welder produces a granulate from the welding filler, which is then melted and comes out of the nozzle under pressure. A preheating nozzle ensures the base material is melted. With this method you can apply more material than hot-gas pull welding. After the repair, the wall is twice as thick (depending on the size of the damage), which adds stability to the area. This process is also used for stationary industrial work such as such as pipes.

Significant savings

As mentioned, a new fuel tank is not cheap. When we visited Roland’s workshop, there were two fuel tanks waiting to be repaired – one from a Fendt 415 Vario (new price is around £2,500) and is featured in the step-by-step repair. The other is from a Case IH Axial Flow combine which would cost nearly £6,000 if purchased new. 

Threaded sleeves for the fuel lines can also be reproduced and welded.

Roland charges €100 per hour plus travel time if the repair is carried out on site. If sent to his workshop, the repair should take two to three hours – a fraction of the purchase price.

Alexander Bertling

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HOW A FUEL TANK IS REPAIRED

CLEAN THE CRACK

Good preparation is essential, the crack has to be carved out to form a V and any contamination removed. For his first step, Roland cuts out the crack with a milling tool and then removes any loose plastic and foreign bodies. Removing the glue proved an extra challenge on this repair which is why Roland recommends not using adhesives.
Next step is form the welding groove with a V-shaped gouge. Then he cleans and slightly roughens the groove and the area around the future weld site using an angle grinder and belt sander. This will help the tank material and the welding material to bond.

FILLING THE CRACK

Left to briefly cool he starts filling the crack with the welding extruder. As a first step, he slightly heats the area, then he starts welding. As the crack runs around a corner, he has to remove excess material with a hammer and chisel as an extra step.
Thanks to the automatic material feed and large nozzle size, the damaged area is filled with two welds next to each other in the groove. When these are still hot, Roland presses them into the groove with a blunt tool, strengthening the bond with the parent material. That’s the welding done.

TIDYING UP

To make the repair look neat and avoid creating any weak spots, he smooths the weld with a regular planer. He always uses woodworking tools especially for machining PE surfaces.
The final touch is with a belt sander. At the end, the damaged area is hardly noticeable. This repair took two and half hours and cost about €250.