Since 2005, POLYPLASTIC Group has been producing non-pressure pipes with a structured wall for drainage systems. Initially limited to a diameter of 1200 mm, quite soon it became clear that larger diameters were also needed.

The ability to manufacture a variety of pipes with different profile types, including pressure ones, makes KRAH equipment for the production of polymer pipes the most versatile and multifunctional on the world market both at that time and now. And in 2007, POLYPLASTIC Group signed a contract for the purchase of a complete KRAH line for pipes of large diameters using the profile winding technology. The line was installed at the Group‘s largest plant, Klimovsk Pipe Plant, which already at that time had a capacity of more than 50,000 tons. CORSYS brand name (originated from CORrugated SYStems) had already been registered by POLYPLASTIC for smaller diameter twin-wall corrugated pipes, so large sizes received the brand name CORSYS PLUS. The commissioning of the line took place in close cooperation with KRAH, in addition to experienced commissioning personnel, all necessary auxiliary equipment and components were provided, as well as detailed instructions for the production and welding of CORSYS PLUS pipes. The implementation progressed very intensively and the first projects were not long in coming. The first large facility appeared already in 2008 - a 9000 meters long DN/ID1400mm public sewer collector in the resort area of Caucasian Mineralnye Vody. Giving up traditional reinforced concrete was due to its obvious flaws, which do not allow to talk about the stability and durability of the sewer system to preserve the unique environment of the area.
Thanks to the variety of profile types, KRAH pipe system is highly competitive. Flexible and lightweight pipes withstand high static loads. The unique process of conjugated coextrusion makes it possible to produce pipes with a special inner layer, for example, light-colored - convenient for teleinspection, colored for identification of applications or technical characteristics, light-resistant and non-flammable - for culverts, etc. The main method used for connecting CORSYS PLUS pipes is electrofusion connection which provides a high quality welding, giving the pipeline homogeneous properties and flexibility.

Advantages of the CORSYS PLUS system

It is the electrofusion connection, coupled with the wide possibilities for the strength characteristics of the pipe wall, that provides the advantages of CORSYS PLUS system over SPIROLINE pipe made of spirally wound profile and CORSYS ARM pipe reinforced with steel tape, of the same pipe sizes. The main areas of application for KRAH pipes are non-pressure and low-pressure water disposal, drainage, and irrigation systems. In addition, several marine outfalls have been commissioned recently. These pipelines are also widely used in the construction of airfields, where reliability issue comes first.

A large number of sudden and non-standard tasks arise at construction sites. For instance, at the “Technopark Grabtsevo” facility, it was necessary to weld in a manhole into the existing pipeline made of CORSYS PLUS pipes with a diameter of DN/ID2000 mm. For this, repair electrofusion liners were manufactured and tested, which allow not only to repair CORSYS PLUS pipeline by connecting the ends of the pipes without a socket, but also to make cut-ins into the pipe, which was required at the aforementioned facility. The branch pipes of the tangential manhole, which was also made of CORSYS PLUS pipe, were welded with two liners. The experiment on insertion into the existing CORSYS PLUS collector, of course, should be considered successful.
The proposed technology has proven itself in the field both in terms of connection reliability and installation speed. And since inserting a manhole into a large-diameter CORSYS PLUS pipe in principle is no different from inserting a pipe segment, this experiment is a brilliant proof of the promise of CORSYS PLUS pipeline repair technology using electrofusion sleeves-liners.
In 2011, in cooperation with KRAH specialists, the line underwent a total modernization. As a part of this modernization, the range of pipe sizes was significantly expanded with the possibility of using DN/ID90mm and DN/ID110mm PE coated PP corrugated pipes, which increased the efficiency of the structure to achieve maximum ring stiffness of the pipe.

Capabilities for pressure applications

Increasingly, the question arose about the capabilities of CORSYS PLUS pipes for pressure applications. Work experience was proving that a standard socket and one welding spiral cannot withstand a high working pressure, especially with an increase in diameter. As a result, a solution was worked out to extend the socket and install a double spiral welding. Such a solution was implemented for the public sewer in Cheboksary, where the normalized working pressure of the pipeline is declared up to 0.6 MPa for diameters up to 2000 mm. In order to test pressure pipes and fittings for a constant internal pressure at a temperature of 80°C, a unique test equipment for pipes with a diameter of up to DN/ID2200 mm was developed and installed - equipment which, according to our data, is still the only one in the world. Despite the fact that in Europe the standard classes for structured wall pipes are usually SN2 or SN4 ring stiffness, in the realities of the Russian market, especially for megapolis cities, a pipe with greater ring stiffness turned out to be in demand. Thus, in Moscow there is a technical regulation that defines the requirements for pipes for various laying methods, so CORSYS PLUS pipes up to DN/ID2200mm with ring stiffness up to SN16 appeared in the production range.

Wastewater treatment plant with various CORSYS PLUS pressure pipes

In 2021-2022, a wide range of pressure CORSYS PLUS with diameters of DN/ID1200-2200 mm was used at the Schelkovo wastewater treatment plant, and a variety of fittings were also used, most of which were produced for the first time specifically for this project. Those included standard elbows and stub flanges, as well as pressure reducers, including eccentric ones, and tees.

More than 15 years of successful Krah technology

The products of POLYPLASTIC Group based on KRAH technology have been successfully used throughout the country for more than 15 years. One of the recent projects (2022) was the use of CORSYS PLUS pipes with a DN/ID3500 mm in the project for the reconstruction of the Akulovsky water channel in the Moscow region. The total length of the pipeline from CORSYS PLUS pipes was 1.2 km.

The project was the first application of CORSYS PLUS pipes with a diameter of 3.5 meters in the construction of water conduits. The experience will be scaled up during the implementation of similar projects and the reconstruction of reclamation canals - by replacing them with pipelines based on CORSYS PLUS.

Polyplastic

In search of new market developments, our company constantly explores the possibilities offered by industries that require massive movement of liquid flows. The technological capacity of Krah pipes allows to handle large diameters with low pressures, which positions the technology against usual competences. In this context, rice planting industry introduce a very suitable market for this type of profiled pipes, which Krah America Latina SA has ventured into in recent years, with great success.

This document includes relevant aspects of use of the Ecoline by Krah Piping and Fittings System in the rice planting industry in Argentine.

The rice planting market

Traditional method for cultivating rice is flooding fields while, or after, setting young seedlings. This simple method requires a sound irrigation planning, but it reduces the growth of less robust weed and pest plants that have no submerged growth state and deters vermin. While flooding is not mandatory for cultivation of rice, all other methods of irrigation require higher effort in weed and pest control during growth periods and a different approach for fertilizing the soil. Rice requires slightly more water to produce than other grains. It´s production uses almost a third of Earth’s fresh water. Water outflows from rice fields through transpiration, evaporation, seepage and percolation. It is estimated that it takes about 2.500 litres (660 US gal) of water need to be supplied to account for all these outflows and produce 1 kg (2 lb 3 oz) of rice.

Rice cultivation requires flooding during plant development. If we consider that 290,000 ha are planted in Argentina and during the entire rice crop cycle approximately 1.0 m3 of water is needed for each m2 of land, each season 2,200 million m3 of water are flowed. The water required in each field is usually pumped from a reservoir or river to a certain height and then distributed through canals by gravity. Throughout production cycle we can define two points in water path where pipes are used: pumping and distribution. Consider the amount of hydraulic capacity needed to mobilize this volume of water at different levels of height and we will have a great business in hand.

What is Rice?

Rice is a monocot belonging to the family Poaceae (grasses). The roots are thin, fibrous and fasciculate. Rice is a seed of grass species Oryza sativa (Asian rice) or, less commonly, Oryza glaberrima (African rice). The name wild rice is usually used for species of genera Zizania and Porteresia, both wild and domesticated, although the term may also be used for primitive or uncultivated varieties of Oryza. As a cereal grain, domesticated rice is the most widely consumed staple food for over half of world’s human population, particularly in Asia and Africa. It is an agricultural commodity with the third-highest worldwide production, after sugarcane and maize. Since sizable portions of sugarcane and maize crops are used for purposes other than human consumption, rice is the most important food crop regarding human nutrition and caloric intake, providing more than one-fifth of worldwide consumed calories by humans. There are many varieties of rice, and culinary preferences tend to vary regionally.

Rice is normally grown as an annual plant, although in tropical areas it can survive as a perennial and can produce a ratoon crop for up to 30 years. Rice cultivation is well-suited to countries and regions with low labour costs and high rainfall, as it is labour-intensive to cultivate and requires ample water. However, rice can be grown practically anywhere, even on a steep hill or mountain area with the use of water-controlling terrace systems. Although its parent species are native to Asia and certain parts of Africa, centuries of trade and exportation have made it commonplace in many cultures worldwide. Production and consumption of rice is estimated to have been responsible for 4% of global greenhouse gas emissions in 2010.

Rice production in the world & Argentina

Rice is second most produced cereal in the world behind maize (1 billion tonnes) and ahead of wheat (713 million tonnes). Many hectares are dedicated to rice cultivation in the world. It is known that 95% of this crop extends between parallels 53º, north latitude, and 35º, south latitude. In 2020, world production of paddy rice was 756.7 million metric tons, led by China and India with a combined 52% of this total. Other major producers were Bangladesh, Indonesia, and Vietnam. The five major producers accounted for 72% of total production, while top fifteen producers accounted for 91% of total world production in 2017. Developing countries account for 95% of total production.

Argentina produces 1.6 million tons per year. In last 10 years production increased by 121%, accompanied by a 16% increase in yields. Argentina currently exports around 640 thousand tons of rice, of which 55% of shipments are concentrated in semi-milled rice, about 30% in husked rice, 12% in broken rice and rest in paddy rice and rice for planting. In the nineties there was a boom in expansion of planted area reaching a record of 290,850 hectares and a production of 1.66 million tons representing 0.22% of world production.
Analysing geographical location of places where planting is recorded, it is observed that Corrientes is the province where farmers declared the largest area planted for rice 2021/2022, representing 48.78%. In second and third place are provinces of Entre Ríos and Santa Fe with 26.44% and 12.33%, respectively. Between three provinces they represent 87.55% of total planted area.

Rice cultivation and materials used

Most rice is grown in flooded fields. The success of production is based on water management for adequate irrigation, which involves construction of walls and use of waterwheels, as well as ensuring that water penetrates more than five centimetres into the soil. For this reason, it is convenient that fields to be flooded are relatively close to lagoons that provide necessary water. First, property margins and walls for delimitation are built on bottom of the land. Soil is provided from some shallow place of lake, for which a dredge is used until sides reach a height of half a meter above lagoon water level, forming the cerrado. Then the cerrado itself is filled with earth until it reaches neighbouring fields level.In case of rice fields located on flat lands, where fields level and lagoon level are the same, pumps are used to extract water from fields to ditches. To flood fields, it is enough to open the floodgate. In case of land located at higher altitudes, as is more common, fields form terraces. Water passes through pipes driven by pumps that take water and raise it to closed ones that must be flooded. Therefore, as we said previously that throughout production cycle two points are defined in path of water where pipes are used: pumping and distribution; Let’s analyse each one.

Pumping phase There are different variants of pumping. Broadly speaking, and following path that water travels, installation begins with a suction section of little or no length, the pump, a short segment where diameters are adapted and valves and chimneys are placed, and finally a counter-slope discharge line that usually is at least 200 meters long. Nowadays these facilities are made of rolled sheet metal and welded from start to finish. Except for smaller diameter pumps (up to DN600) where in several cases discharge lines are made of solid PVC. Sheet metal installations have several drawbacks. The first and main one is that sheet rusts and even more so in operational context of this type of installation. Carbon steel is in constant contact with water while it is being watered (6 months); The steel pipe is filled with water and the rest of the year it contains water partially since installation is never completely emptied. The second scenario is even more unfavourable because of having humid areas in contact with oxygen. Pipe cannot be buried and must be installed above ground since installation service life is a few years and soil movement are not justified. In addition, if buried, corrosion phenomenon would be aggravated by moisture and galvanic corrosion. Even leaving laying on ground, these corrosion phenomena would appear throughout lower part where soil and pipe come into contact. For this reason, lines are usually placed on tries to keep them separate from ground (remember that the lines have a length of 200 meters on average).

Because pressures are low, pipes are made by rolling 1/8” or 3/16” sheets and welding them. This construction method results in a pipe of a nominal pressure suitable for the project, but with a very poor annular stiffness in large diameters. This lack of stiffness causes two types of very recurrent failures in this type of installations:

• First, in transient vacuum phenomena pipe buckles and collapses leaving installation out of operation.

• Additionally, the pipe constantly undergoes an “oscillating deflection”, with is the deflection and return to its original shape cyclically both in transient phenomena, where amplitude is greater, and in permanent regime where fluid turbulence generates deflections of lower amplitude, but higher frequency. This oscillating deflection fatigues material and longitudinal cracks occur.

Distribution phase It is evident that channels used to transport such a volume of water in such large areas of soil must be piped in some sections so that it can be passed overhead, to be able to pass under embankments, or even so that one channel passes under another. In cases of larger producers, where field surfaces are larger, the need for gravity pipes increases.
Let us consider the case of largest rice producer in Argentina with approximately 60,000 hectares under cultivation. This customer differs from rest of producers by its cultivation system of zero level or controlled slope. Here we are not going to delve into details of this methodology, we will focus on what is relevant in terms of pipes.

The system requires dividing land into rectangular portions of between 20 ha and 25 ha each. Each rectangle has a pipa. It is called pipa to a set of water gate plus pipe segment of 3 m to 9 m; the reason of that is to regulate water level in each portion of land, while pipe makes a crossing so that vehicles and machinery can access said rectangle.

The Ecoline system - A superior alternative Throughout northeastern region of Argentina, western Uruguay and southern Brazil and Paraguay, this market has great potential for us, where our technology stands out. It is clearly a niche market that is technologically behind when it comes to driving systems.
Obviously when working with polymers the oxidation problem is eradicated, but our differentiation regarding to other suppliers of plastic pipes is the profile design and electrofusion. With working on profiles, we achieve pipes with nominal pressure and accurate stiffness as installation requires, even in some of the executed lines we have designed pipes of different nominal pressures at different line points in order to optimize costs. Additionally, electrofusion reduces significantly working costs since it would be totally impractical to mobilize butt fusion equipment for lengths of this type of installations.

We are the only ones in the region with the ability to offer this combined solution. Corrugated plastic pipes on the market do not withstand the working pressures of this type of installation, while solid profile pipes (HDPE or GRP) should be thicker than that required by working pressure to have a stiffness that can withstand transient phenomena.
This results in a significant impact on costs. Working smart, we can have this market captive to Krah technology.
In pumping section, what interests us is the discharge line; all above has large diameter variations, low radius curves, derivations, etc. that are very complex to do in HDPE. The diameter range of these installations is from DN/ID400 mm to DN/ID1200 mm.In working regime, discharge line works with relatively low pressures, between 1 and 4 kg/cm2; However, transient phenomena in pumping with internal combustion engines are much more recurrent than in other types of facilities due to pumps stops and start-up due to power cuts in electrical installations or lack of diesel, mechanical damage, etc. In these transient phenomena installations experience water hammer (overpressure) as well as phenomena of separation of fluid column (depressions and / or voids).

Case Pumping station – Aguaceros Dam 2

For hydraulic analysis and preparation of the design report, consultant used following basic information:

• Estimated altimetric pipeline profile
• Permanence curve of levels in Aguaceros 2 dam, estimated from water balance considering recharges and extractions for irrigation.
• Brand and model of the pump to be used.
• Information from pipe suppliers, profiled polyethylene pipes from the supplier Krah

The estimated longitudinal profile considered for pumping analysis consisted of a uniform slope ramp from a point at elevation +74.00 m where manifold and protection mechanism against water hammer were installed, to discharge in cylinder head at height +86.0 m, whose beginning is at a point 366 m away. For the dam to be built, water inside reservoir will present variations in water height between +74.0 (full reservoir) and +70.0 m height. Based on an analysis of permanence of levels through water balance of reservoir that considers contributions and extractions, 65% of time was determined during harvests, reservoir will find water at elevation +73.0 m or higher, so this lake level is considered as a reasonable value for dimensioning of pumping in condition of maximum instantaneous flows, that occurs at the beginning of harvest. To avoid negative pressures below cavitation line, 4 air valves were placed along rigid pipe, in progressive 80 m, 170 m, 260 m and 450 m. Based on these results, it is observed that the maximum internal pressure in the pipes is around 24 mca, which occurs in the initial section. Therefore, pipes were required to work above the following nominal pressures:

• Progressive 0 m to 84 m: 2.6 kg/cm2
• Progressive 84 m to 160 m: 2.2 kg/cm2
• Progressive 160 m to 240 m: 1.7 kg/cm2
• Progressive 240 m to 360 m: 1.4 kg/cm2

With respect to balance chimney, it must have a height equal or greater than 16,0 m, to avoid water loss during on-regime operation and greater than 25,0 m to avoid water loss in transient scenarios.Observing results, it is concluded that it is viable to pump target flow working with two IMBIL pumps at 440 RPM, complying with engines indicated power. Operating points closest to target, using DN/ID900 mm pipes, are as follows, all with a nominal rotational speed of 440 RPM:

• 1.55 m3/s flow rate, 900 mm pipe, power 310 kW (412 HP)
• flow rate of 1.65 m3/s, pipe of 1,000 mm, power of 321 kW
• flow rate of 1.70 m3/s for 1,100 mm pipe, power of 325 kW

To DN/ID900 mm pipe, a maximum flow of 1.8 m3/s could be obtained working at 450 RPM and using a power of 340 kW, although we understand that engine would work very close to or above its recommended limit. It was finally determined to use DN/ID1000 mm pipes according to the following detail.

Merceditas Line:

• Required flow: 1.6 / 2.0 m3/s
• Pump: IMBIL 750-860 pump
• Stub-end DN1000
• Pipes

San Lorenzo Line:

• Required flow: 1.6 / 1.8 m3/s
• Pump: Worthington 750 Ingersoll-Dresser Pumps, 30 MNI 33 rotor A
• Electric Motor: WEG 480 HP 1000 rpm
• Stub-end DN1000
• Pipes

To connect with master irrigation channel, use of a culvert composed of two Krah Profil pipes of DN/ID1600 mm internal diameter was determined. Depending on working flow, pipes speed can exceed 1.2 m/s, and therefore there is a possibility of soil erosion at entrance and discharge of pipes, so protection measures were defined to prevent erosion at these points.

Gustavo Mastelono,
Krah America Latina

On the Lyngen peninsula, located at 69° north in the arctic region of Northern Norway, you find the small village Furuflaten. Here, tucked between the Lyngen Alps, Lyngsdalen Valley and the Lyngen Fjord, you find the worlds northernmost Krah Pipes manufacturer - Haplast AS.

While the Lyngen alps are world famous for spectacular alpine skiing, glaciers, and clear blue lakes, Furuflaten is well known as home to the region’s largest industry hub. Since the late 1940’s, Furuflaten has manufactured many different commodities such as waterpipes of wood, garments, lumber, steel constructions, mechanical products, aluminum and plastic products, building elements, incineration toilets and marine waste products. In fact, today the village has only 280 permanent residents while the industry hub employs 130 people in total - and have a total turnover of NOK 300 million (approx. USD 33 million). Haplast alone employs 44 people and reached a turnover of NOK 135 million (approx. USD 12,5 million) in 2022. Since the Haplast factory was opened in 1961, one of our strengths has been to learn and adapt. Learn from the market needs and adapt our products accordingly. Throughout six decades, the company has accumulated a huge amount of industry know how. Our dedicated staff have seen the possibilities and advantages that lies in Krah Pipes, and we have invested in product development.

Based on this we have developed a quite unique range of innovative products. Today Haplast manufactures PE based products within four main categories: Water and wastewater, transportation infrastructure, fish farming and ventilation. The Krah pipes serves as main component for products in all these categories. Yes, Haplast manufactures Krah Pipes as just that, pipes. But we make our turnover by selling more than pipes. Haplast creates durable solutions to our customers in the form of water and wastewater basins, chemical, sedimentation and silage tanks, culverts, bridges, road pipes and ventilation pipes to name some of our main products. We have delivered infrastructure solutions to hospitals, schools, road projects, fish processing factories, public water and sewage systems and many more private and public projects. We manufacture all our products from plastic granules to finished plug-and-play solutions.

The Krah technology allows us to manufacture double-walled pipes, and thus meet both industry standards and public requirements. In addition, our products can be both reused and recycled. Once redundant the product can be reused in another project. The PE can be recycled with full traceability and history documentation, something that our customers are increasingly demanding. And of course, the Krah pipes allow us to manufacture lasting, leakage free solutions. In our experience, there are many good solutions for containing and transporting water in leakage free pipes or containers. However, not as many solutions ensure no leakage into the contained water. We have seen many basin and tank products that contains water, but where both dirt and chemicals from the surroundings find their way into the water. The Krah Pipes however are 100% leakage free and successfully keeps clean water crystal clear. This property, together with the strength, durability and adaptability of the Krah Pipes and our accumulated know-how has promted us to develop a few innovations from Krah Pipes.

We deliver our products as plug-and-play solutions - ready to be connected to other piping infrastructure. One of the key take-aways from our customers is how easy it is to install the Haplast products compared to for instance concrete based solutions.

Haplast water basin

The Øvre Russvik basin and extension tower was delivered to a Nordkraft Hydroelectric plant. The Haplast water basin delivered for this project is 3 meters in height, DN/ID2500 mm in diameter. Because of the snow conditions during winter, the exposed environment and risk of avalanches, the contractor had to install an extension tower to safely access the water basin during winter. Due to the inaccessible location at 610 msl, the basin and extension tower had to be flown in by helicopter. The extension tower is 5 meters tall, DN/ID2500mm in diameter and weighs in at 1280 kg. The KRAH profile for this product is CPR 4/4/4 CC110 75PP and has a ring stiffness of SN 2.

We manufacture the Haplast water basin with a cast anchoring plate in concrete to counteract buoyancy and a bespoke system for anchoring valve connections and other fittings. The basins are fully assembled in our factory and all pipe entrances are fully welded. We ensure safety requirements are met for necessary access point such as manholes and ladders. The basins are tested for leakage before they leave the factory.

Haplast wastewater basin

The Stormoen wastewater basin was delivered to Perpetuum Landfill. The landfill facility is required to monitor the wastewater in the landfill ground. Our solution helps them contain, measure and monitor pollution in the ground water. We assemble our basins in our factory and deliver them ready to install on site as a plug and play solution. In fact, it only took two men 15 minutes to install and adjust the wastewater basin. Because of the integrated pipes welded into the basin, it’s easy to connect the basin to other piping infrastructure on site. This Haplast wastewater basin is 7 meters tall and has a diameter of DN/ID1600 mm. The KRAH profile used is SQ1 and the ring stiffness is SN 2. Due to the height, this product has two internal welded PE decks and three ladders for safe access. To counteract buoyancy the basin has a molded sandwich PE base. Customized water flow solution based on project specifications is fully welded.

Haplast sludge separator/sedimentation tank

The Stette sludge separator was delivered to Ålesund Municipality on the west coast of Norway. The tank is a sedimentation tank, which separates sludge from gray water. The sludge remains in the tank and the municipality can extract the sludge a few times a year, while gray water flows through to the deep sea or to a water treatment plant. It measures DN/ID3000mm in diameter and has a length of 27,5 meters. Because of its size, the Stette tank was too long for road transportation and was shipped to Ålesund by boat. Our factory lays by the banks of the Lyngen fjord and close to a deepwater dock. Hence, we can deliver large products efficiently to our customers even by boat or tow. The Stette sludge separator has three separate chamber compartments with fully welded inner walls and 6 manholes. It is manufactured as KRAH profile CPR 8/4/8 and ring stiffness SN 2. The double walls fulfil public and industry standards for leakage protection and isolates for the Perma frost – a necessity in the Nordic countries. The Haplast sedimentation solutions works with hydraulic drop throughout the system. We deliver sedimentation tanks, valve housing tanks with control valves and sludge storage tanks for cleansing of solid particles from sewage systems. The tanks can be made in custom lengths with bespoke chamber and water flow solutions.

Haplast road culvert

The Kvænangsfjellet road culvert is 64 meters long and has a diameter of 2500 mm. We delivered this project in sections of 6 meters and the structure was assembled on site with socket and tip – in this case fully welded on site. The Krah profile is PR+PR 75 PP 5/6/5/6 CC120. The ring stiffness is SN8, which is approved by the Norwegian Directorate of Public Roads. The culvert was manufactured with solid ends and oblique cuts for a mor seamless result. This is highly appreciated by the contractor because the culverts will integrate better into the surroundings. Haplast has manufactured culverts for small bridges, road underpasses for animals and people, as transfer culverts for water or as infrastructure culverts. End arrangements, external washout stoppers, sand stoppers for fish and other arrangements can me made according to the customers specifications.

Haplast ventilation system

Haplast has delivered KRAH pipes for underground ventilation to many projects in Norway, a market segment which has been a good business over the last ten years. Hjelset Hospital and Stavanger Hospital, and the largest public bath, Tøyenbadet, in Oslo - the capitol of Norway, are some examples. Ventilation towers and pipes was manufactured based on the contractors’ specifications within the limitations of the KRAH pipe technology, and usually with a ring stiffness of 2-4. As always with Haplast products, the sections are delivered as plug and play modules, with socket and tip and can if necessary be welded in house or on site.

Lena Steffensen,
Haplast AS

Many customers of theKrah GmbH have a demand for post-processing of their produced pipes, for example to build manholes, tanks, branches or house connections. The existing milling station MF-200 provides an inexpensive possibility to this issue but is restricted in terms of flexibility and efficiency.

This leads to a novel development of the Krah GmbH, the new MF-400 CNC, which represents a fully automated and numerically controlled milling station for large dimensional pipes made of plastic.

Objectives

Within the development process of the new milling station the following issues were considered:

• High flexibility
• Fully automated milling process
• Easy handling
• High efficiency
• Reduced demand on production space
• High cost-effectiveness

Realization

In this section, we demonstrate the realization of the goals defined before in the objectives.

Cut outs and possibilities
In a first version, a selection of three object types shown in Figure 1 is implemented. These objects are circular holes as standard for conventional machines, rectangular holes which are pertinent for some special applications and straight cuts used for numerous important applications. All object types can be processed in a centric as well as an eccentric position on the pipe up to a height of 3,500mm. Moreover, support structures can be created to prevent damage on the machine due to extracted cut outs and to preserve the stability of the pipe during the milling process. Note that many object types for new applications can be implemented flexibly without changing any components of the hardware.

Multi object mode
A fully numerically controlled and automated production scheme including six axes along with intelligent milling software allows for an efficient processing of an arbitrary number of objects within the multi object mode and without the need of any human support. Figure 2 shows the definition of objects on the machine panel and the processed pipe.

Intuitive user interface
A very important issue within the development process represents the design of the user interface to make the handling of the milling station as easy as possible for the operator. To achieve this goal several smart features are implemented like an automatic determination of the pipe diameter and the object position, a copy to backside option and a preview option for objects or an automatic calculation of the optimal milling tool and optimal trolley position. In Figure 3, corresponding pages of the machine panel are shown to define and check parameters of the pipe and related objects, respectively. Moreover, two configuration pages are shown which provide intelligent support for setting up the machine. This intuitive implementation of the user interface allows for the usage of low-skilled and non-technical staff on the machine.

Machine concept
The concept of conventional machines is based on a translational movement of the pipe which leads to a production space with a width higher than twice the pipe diameter, see Figure 4 (left). In contrast, the concept of the new MF-400 CNC milling station is based on a rotational movement such that the production space can be halved, see Figure 4 (right).

To be specific, the production space required for pipes with different diameters is given as follows:

• from DN/ID 600mm up to DN/ID 3000mm: 7900mm x 3800mm
• from DN/ID 3,000mm up to DN/ID 4000mm: 8600mm x 5200mm

This reduced demand for production space represents a further great benefit of the new milling station.

The MF-400 CNC milling station provides a combination of functionality of a conventional milling station like the MF-200 or any similar machine and a saw as shown for example in Figure 5 (middle). This allows us not only to considerably reduce acquisition costs, but also the production space as well as the production time, since it is not necessary to set up a further machine.

Within the development process all defined goals were successfully implemented. That has resulted into a novel and superior milling station for the processing of large dimensional pipes made of plastic.

Dr.-Ing. Maik Dittmann,
Krah GmbH