Masterflex AG, Gelsenkirchen, June 2009
The conveying of wear-intensive bulk materials is an issue in many industries. A wide variety of materials are included in these types of bulk materials, such as solids in the chemical industry or building materials such as cement, lime and quartz sand. In glass processing, glass dust, silicates, dolomite, or soda can be added to the list, but in the food industry, some highly abrasive spices, grains, cocoa bean shells, or mixed feeds are also included and are therefore equally problematic. Frequent wear of the conveying line is the result, and the bends are particularly badly affected.
Pipe bends are particularly stressed
In the pneumatic conveying of bulk materials, the materials are sent through the pipes by means of gas flow. In most cases, steel pipes are used for this purpose. The bulk material is either blown forward or sucked, but suction operation only works over relatively short distances, which is why pressure operation is preferred wherever long conveying lines are required. Here, lengths of up to 3 kilometers and correspondingly high operating pressures can be achieved. To ensure sufficient stability, the pipeline sections and bends are therefore firmly bolted together with flanges. A distinction is made between two types of conveying, which mainly influence the conveying speed: In so-called plug or dense phase conveying, a lot of bulk material is moved with relatively little air. Conveying is slow and intermittent. In contrast, the particles are transported much faster in so-called air-jet or thin-flow conveying. Less bulk material is conveyed with a high proportion of air, sometimes at speeds of up to 90 km/h. This often leads to severe wear problems. This often leads to a severe wear problem; because during transport, the bulk material hits the pipe wall countless times. Defects in the form of leakage up to complete destruction are the result. Particularly affected are the pipe bends, because here the conveyed material hits the conversion at full speed while being steered around the bend. The pipe bend stands in the way of the actual trajectory of the particles, so to speak, and is thus exposed to significantly higher loads than the rest of the straight conveying line. The bend therefore also wears out much faster, to the point where holes appear in the pipe conversion. Sometimes such defects are remedied provisionally by welding, but this is only a short-term emergency solution. Depending on the application, pipe bends often have to be replaced after only a few weeks or months. The necessary plant downtime is much more significant than the cost of the actual replacement part.
Every plant shutdown generates costs - an example
Since wear occurs inside the elbow, it is usually only detected at a very late stage, namely when the affected part suddenly fails. This results in high follow-up costs due to assembly times, plant downtime, production delays, etc. An example: In an iron foundry for the automotive industry, around 25,000 engine blocks are produced over approximately 23 hours per day. The plant employs about 1,200 people and is located in Germany. At the so-called highly automated "fettling lines", the finished cast engine block blanks are cleaned and deburred by robots for further processing. Pneumatic conveying systems, as described above, supply these fettling lines with abrasives, while in parallel they dispose of the casting sands. If a pipe bend fails in these conveying systems, the entire fettling line comes to an immediate standstill. This also affects upstream and downstream production facilities such as the core shop or metalworking shop. Although defined buffer times exist, these are kept as short as possible for reasons of economical production logistics. Each critical component, including each pipe elbow, therefore has a direct impact on the availability of the entire production line. The above-mentioned plant has a total of 5 parallel autarkic fettling lines. A normally unforeseeable breakdown of a conveyor system due to pipe elbow wear means a downtime of about 3 to 4 hours of the line. This time is needed to replace the affected part within the pipeline. This results in high costs on the one hand in the form of direct failure damage, in this example of approx. 830 engine blocks that could have been produced in this period. At this stage of the value chain, this represents a loss of over €17,000. On the other hand, once the buffer capacities have run out, there may be a production stoppage of 1 - 2 hours for about 50 - 100 employees. The costs caused by this can amount to up to 5,000 €. In addition, if the leakage is detected later, cleaning costs are incurred to clean up the plant. This example describes only one unscheduled plant shutdown, which is resolved without further incident. Additional delays in resuming operations are quite conceivable, for example due to the unavailability of a forklift or a lifting platform. It becomes clear that considerable costs are incurred not only for scheduled maintenance work but also, in particular, due to lower plant availability, which are out of all proportion to the direct replacement costs of the plant components, in this case the pipe bends. Masterflex AG has recognized and solved this problem.
Getting to the root of the problem
Pipe bends in the Master-PROTECT series not only have an inner PU lining, they also have a special, patented inner geometry.
The lining lies like a guard on the actual conversion and thus prevents early wear. The outstanding feature, however, is the thicker lining exactly at the point of the actual sheet where the mechanical stresses are greatest. The inclined PU surface deflects the bulk material relatively gently around the bend, and impinging particles bounce off it and thus do not damage the outer wall. With an ordinary pipe bend, the particles are abruptly slowed down by the force of the impact; this is not the case here, which has several advantages:
The risk of clogging decreases, because it is not most likely to occur at the narrowest point of the pipe bend, but at the slowest. This results in better flow behavior with lower pressure losses. Likewise, entrainment of conveyed material and caking are minimized; there are no steps, offsets or edges where deposits can settle. The innovative development offers low weight in a compact design and also operates far more quietly than its ordinary counterparts.
In the meantime, Master-PROTECT pipe bends have proven their worth in various fields of application, wherever wear-intensive bulk materials have to be conveyed in a temperature range of up to max. 90°C. These include materials such as quartz sand, glass dust and iron oxides. For example, a Master-PROTECT pipe bend used in iron ore conveying has to date conveyed the loading volume of a truck convoy equivalent to approx. 12 kilometers in length, while ordinary bends did not exceed a service life of a few weeks. Another customer reports uninterrupted continuous use of the elbows for 3 years for conveying electrostatic precipitator ash. This corresponds to a total output of about 185,000 t per arch. Alternative products often had to be replaced after just a few months.
Conclusion
The frequent failure of pneumatic conveying systems due to heavy wear of pipe bends was identified as a problem and solved in dialog with the users. The use of tailored, durable product solutions can avoid unnecessary follow-up costs and thus has a positive influence on the economic efficiency of the entire plant.
The Master-Protect pipe bend
Technical data Master-PROTECT pipe elbow (PU lined pipe elbow)
Material
Elbow: DIN 2448 St 37 (primed)
Flange: RSt 37 - 2 (primed)
Lining: Polyurethane
Applications
- Pneumatic conveying systems
Properties
- extremely abrasion resistant
- significantly lower pressure losses than in deflection or impact pots
- lower risk of clogging due to uniform concentration distribution and
- more constant speed of the conveyed material
- many times more wear resistant than steel bends
- lower operating costs longer maintenance intervals
- no carryover of the material to be conveyed
- pressure rating PN 6 and PN 10/16