Masterflex AG, Gelsenkirchen - December 2009
Polyurethane is a universal genius among plastics, and not just as a foam. Since the 1960s, this plastic has undergone rapid development and since then has continued its triumphant march unstoppably. With more detailed knowledge about the property profile of polyurethanes and improved processing technologies, this material has now revealed itself to be a multi-talent. It is also increasingly being used in the hose industry because of its outstanding properties.
Polyurethane (PUR) is the ideal material for conveying extremely abrasive, problematic materials in a wide variety of applications. Current technologies in the hose sector have greatly expanded the range of applications and offer a suitable hose solution for almost every field of application. With the current possibilities, polyurethane is revealing itself to be a multi-talent. Where other plastics have to fit, this high-tech material often proves to be a good solution.
A material with many faces
Gradually, numerous world firsts revolutionized the markets, such as the first polyester TPU material that is resistant to microorganisms. Flame-retardant materials were developed, from which, for example, seats in airplanes are made. In the field of high-tech hose systems, this innovation revolutionized an entire industry. Today, hoses made of polyurethane are the legal standard in the wood industry. High-performance products made of this plastic have also been developed in other areas of the hose industry. For example, electrically conductive polyurethane is used in hoses to prevent electrostatic charges. Particularly wear-resistant polyurethane also withstands extremely abrasive materials, so that today, for example, gravel can be transported through a PUR hose without any problems.
Ripe for sophisticated solutions
And polyurethane continues to grow. More and more new areas of application are being opened up, especially where traditional materials such as PVC, rubber and steel have to fit. Experts estimate that only 15% of polyurethane's potential applications are being exploited. This is because polyurethane can assume hard or soft properties, be biostable or biodegradable (self-degrading), and exhibit a wide range of chemical resistance. It is characterized by consistent physical properties over a wide temperature range. Polyurethane is extremely resistant and thus achieves even longer service lives than steel, for example, in many areas of application. This also leads to innovative solutions in the field of wear protection for conveyor systems. The Achilles' heel there is the pipe bend. At an impact speed of around 100 km/h, even seed grains become a challenge. Now, for the first time, there is a patented process in which conveyor pipes and elbows are lined with polyurethane. Exemplary for this development are "Master-Protect" pipe bends from Masterflex AG. Lining a pipe bend with polyurethane significantly reduces wear. Successful installations in industrial companies and tests by the Technical University of Braunschweig have confirmed that they are several times more wear-resistant than an unlined steel pipe bend and in many cases have significantly longer service lives than other wear protection systems on the market - a cost-effective way to avoid expensive production stoppages. The versatility of polyurethane is also becoming increasingly important in medical technology. Within the Masterflex Group, Novoplast Schlauchtechnik GmbH is addressing this issue. Microporous polyurethane is already used in wound care to promote scar-free healing. Tubes and catheters made of polyurethane are being used more and more because the material has antithrombogenic properties. It has already been possible to develop antibacterial PUR, which significantly reduces the risk of infection.
Customized solutions
The examples mentioned are only a small part of possible fields of application. In principle, polyurethane is a modular system from which new, customized solutions can always be put together. Therein lies the great future potential of this fascinating high-tech plastic. Increasingly high temperature requirements are also being placed on thermoplastic materials, for example when conveying hot plastic granules or other bulk materials such as cement, glass and rock wool, ash and metal chips. With the variety of applications for spiral hoses, different thermoplastic materials have traditionally been used. For many years, rubber hoses and PVC hoses dominated the market. Since the beginning of the 1990s, other thermoplastic materials have increasingly conquered the market due to their improved properties. Requirements for hoses in terms of abrasion resistance, flexibility, tear resistance, temperature resistance, microbe resistance and/or hydrolysis resistance, flame retardancy, antistatic properties, electrical conductivity and suitability for foodstuffs can be met by the modular principle of this high-performance material.
Diverse developments in the field of spiral hoses
Due to the steadily increasing quality requirements in terms of functionality and service life, combined with an optimum cost-benefit ratio, hose manufacturers have developed a large number of hose variations in recent years that are geared to the respective, individual requirement profiles of users.
Increasing harmonization of internationally applicable guidelines has also led to increased demands on material properties. By way of example, we would like to mention here some product developments with regard to special requirements: Abrasion resistance: Abrasion resistance was the primary focus of product developments by many hose manufacturers in order to extend the service life of increasingly robust hose types. However, it has become apparent in the various application areas that, in addition to the pure material properties, design features such as the "inner smoothness" of the hose also play an important role with regard to flow optimization, energy cost optimization, reduction of downtimes and maintenance intervals, and cleaning possibilities.Smooth is not smooth enough in this context. Thanks to a new, patented process, it has been possible for the first time to produce seamlessly smooth polyurethane spiral hoses on the inside. The "Master- PUR Inline" hoses offer a combination of high abrasion resistance with enormous wall thicknesses and exceptional bending radii. PUR hoses are thus becoming a real competitor to the previously dominant heavy rubber hose in many areas where problematic conveyed goods have to be optimally transported.
All polyurethane spiral hoses on the market to date have a weld seam due to their spiral hose design. However, it is precisely this weld seam that can represent a weak point due to its design, because this is where the greatest attack by the conveyed material usually takes place. Using a special process that combines the positive properties of a profile-extruded hose with the special properties of elastomers, the world's first internally seamless spiral hoses can now be produced. Increased thermal resistance: Greater demands on hoses in terms of temperature resistance presented development engineers with the task of combining the outstanding properties of polyurethane in terms of abrasion resistance, flexibility and mechanical strength with increased temperature resistance. In general, the normal continuous service temperature of thermoplastic polyurethane is around 90 °C, and up to 125 °C for short periods. The new "Master-PUR HT" hoses also exhibit particularly good properties in continuous use at temperatures up to 125 °C, and can also be used up to 150 °C for short periods. These hoses have recently proved their worth wherever hot materials have to be transported, for example in mechanical engineering and plastics processing or in other industrial applications such as the cement industry or insulation technology.
Meeting specific guidelines
In the field of conveying hoses, there have been serious developments in the last ten years due to the increased requirements in various sets of regulations. Examples include the areas of food conformity, fire resistance and explosion protection. The criteria for the food suitability of spiral hoses are laid down in EC Directive 2002/72/EC, including the latest amendments. DIN 4102, for example, prescribes the conditions that spiral hoses must meet in terms of flame resistance. Other specifications such as the American UL fire standard, the French NF fire standard or the English M fire standard with their respective modifications must increasingly be met by the various spiral hoses. Currently, the TRBS 2153, guideline of the professional association of the chemical industry is on everyone's lips. The previously valid BGR 132 has been replaced since April 2009 by TRBS 2153, which contains new criteria for the use of spiral hoses in the various hazard zones. One new aspect in particular is that bulk materials are classified into two groups, namely combustible bulk materials and non-combustible bulk materials. The statements and procedures for the transport of non-combustible bulk materials have essentially not changed. The situation is different for the transport of flammable bulk materials. With the new TRBS 2153, the requirements for material compositions with regard to electrostatic properties or discharge capability have been increased. When using spiral hoses in zone 0/20, the user must carry out a specific hazard analysis. As before, electrically conductive hoses with a surface resistance < 10 to the power of 6 ohms are generally recommended. In zone 1/21, the requirements have become more stringent. When transporting flammable bulk materials, antistatic hoses with a surface resistance < 10 to the 9th ohm are now recommended. In Zone 2, there are no significant changes compared to the old regulations. It should also be noted that the TRBS 2153 guideline is basically only a recommendation from which the user may deviate, provided he can prove the effectiveness of the solution he is using. It is therefore becoming more apparent than ever that spiral hoses made of a wide variety of thermoplastic materials, especially polyurethane, offer a wide range of possible solutions for conveying solid, liquid and gaseous media in all areas of industry. For the user, material compositions,hose designs and operating conditions are ultimately decisive in making the right choice.
About the author:
Alfons Beitz is Sales Manager at Masterflex AG, Gelsenkirchen, Germany, High-Tech Hose Systems Division.