Lay-Flat Plastic Hose Manufacturing

1.            INTRODUCTION

Established in 1775, Mandals AS has been operating in Norway providing wide range of lay-flat plastic hose products (as shown in Fig. 1) to local and international markets. Mandals. Mandals AS is a global supplier of lay flat hoses for agriculture, industry, fire and much more. Lay-flat platic hoses offer many advantages over more inflexible types of hoses or pipes, for instance in terms of transport and storage volumes, handling and usage.

Fig. 1 Example of Mandals lay-flat plastic hose

In general, the woven polyester jacket is the principle load-carrying members of the lay-flat plastic hose structure, while the surrounding polymer matrix keeps them in the desired location and orientation.

 

2.            MANUFACTURING PROCESS

Mandals AS is a pioneer producer of lay-flat hoses through an in-house developed through-the-weave extrusion process. The production of a lay-flat plastic hose requires a customized production process which has been specifically designed to produce a hose system to meet a set of the high quality specifications and tolerances required to fulfill its designated operational function. The manufacturing process is principally divided into three sub-processes which are (i) twisting of yarn, (ii) weaving the jacket and (iii) extrusion.

 

2.1          Twisting of yarn

This is the first key step. To ensure the desired strength of warp and weft in the weave we focus on always using the highest quality raw materials, calculating the right number of filaments and determining the correct twisting factor.

Fig. 2 Twisting of yarn

 

2.2          Weaving the jacket

“The strength of a hose is the weave”. All jackets are woven on Mandals AS patented circular weaving looms, which are preferred globally by 9 out of 10 hose manufacturers. The looms are constantly upgraded to meet demands in the hose market, and have over 80 years of uniform quality on key parameters. Mandals AS focus especially on a 100% uniform weave with uniform tension on both weft and warp to prevent diameter variations.

Fig. 3 Weaving the jacket

2.3          Extrusion

Mandals extrudes simultaneously inside and outside of the weave as shown Fig. 4, which ensures that the extruded material is strongly bonded through the textile. Extruders melt thermoplastic polyurethane (TPU) or rubber and force it into an extruder head by a screw. While the head is filled with TPU, a circular weave is dragged through the head at 90 degree angle to the screw.  The material used is either nitrile rubber, which gives a very flexible hose, or TPU, which gives four times higher abrasion resistance compared to rubber. The “extrusion through the weave” production method gives excellent bonding between cover and lining as well as firmly encapsulating the circular woven polyester reinforcement.

Fig. 4 Extrusion through the weave

 

Nordgard-Hansen et al. (2017) conducted a modelling of a lay-flat plastic extrusion process in cooperation with Mandals AS. A multivariate design and response surface modeling were applied to a lay-flat plastic hose extrusion process in a full-scale experiment. Each input variable was varied to get the largest possible variation while keeping the process stable. The factors such as (i) temperature set point, (ii) screw speed, (iii) pull speed and (iv) weave pre-drying position, and their placement in the process is sketched in Fig. 5.

Fig. 5 Schematic of the extrusion process of lay-flat plastic hose

Clear quantitative relationships were found, which to a large degree match existing qualitative process understanding. For instance, it was quantified how adhesion improves with increased extrusion screw speed and extrusion head temperature. On the other hand, it was found that total hose thickness was governed by extruder screw speed and extruded hose pull speed, while it was not significantly influenced by the extruder temperatures. The results can readily be used to inform the operators in real-time of important quality parameters of the hose currently under production.

 

3. QUALITY AND CONTROL

Mandals AS is ISO 9001 certified and is aligned and integrated in the HSEQ Framework of Fenner PLC. There are dedicated employees monitor and improve the processes on a continuous basis, and the lab staff are an active part of the quality control process. Making a world class lay-flat hose takes time and dedication! All raw materials are checked upon arrival according to a pre-set technical data sheet. I.e. tensile strength on yarn, melt-index for TPU and other parameters. After twisting and weaving all weaves are visually inspected on both sides of the whole length in order to find and repair any defects. The flat width, thickness and length are also controlled.

During extrusion of the hose many aspects are monitored in order to achieve an even quality. Especially temperature, speed and distribution of the TPU or nitrile rubber through the weave are constantly controlled to ensure a homogeneous product. The internal diameter is permanently set to the exact size. Nitrile rubber hoses are vulcanized to enhance the properties. Finally, all hoses are tested for various technical properties depending on the grade and intended end use.

 

3.1          Short-term Burst Test

The internal pressure resistance and strength of the manufactured lay-flat plastic hose is determined using a short-term burst pressure test. End fittings are fixed at both ends of the specimen and then sealed off for pressurization. The pressure is applied constantly and uniformly by water using a high-pressure pump until the specimen fails. For the lay-flat plastic hose to meet the production specifications, it must burst at a pressure equal or higher than that defined.

Fig. 6 Short-term burst test in accordance to ASTM 1599 – Procedure A or ISO 1402

3.2          Leakage Test

The whole length sections is hydraulic pressure tested for leak inspection in accordance to Mandals in-house procedure. Leaks are pictured as going from positive pressure (inside the lay-flat plastic hose) to outside (at atmospheric pressure). Specimen shall be pressurized using water up to specified pressure and holding period. No visible leak or defect found throughout the leakage test.

Fig. 7 Leakage test

3.3          Yarn Tensile Test

Inspection of the incoming polyester yarns is undertaken through a re-verification of their tensile strength. The purpose of this test is to determine the breaking force and elongation at break of both the weft and warp polyester yarns, these measurements are then compared against the polyester specifications as provided by the manufacturer. Each of the yarn samples are clamped into a tensile testing machine and a tensile force is then applied until the sample fails.

Fig. 8 Yarn Tensile Test in accordance to ASTM D7269

3.4          Adhesion Test

The adhesion is being measured between the fabric and the inner layer, and then again between the fabric and the outer layer. With a force gauge then being used to peel away the polymer layer from the fabric layer underneath, the level of adhesion is determined.

Fig. 9 Adhesion test in accordance to ISO 8033

 

4.0            APPLICATION

For internally corroded pipes, the use of lay-flat plastic hose as rehabilitation is an option to extend the lifetime of the pipe and reduce maintenance cost. The lay-flat plastic hose is pulled-through the existing carbon steel pipe at site which then acts as a passive conduit for the protection of the pressure capable composite pipe. In most cases, the lower flow-friction coefficient of the lay-flat plastic hose or even an increase of the flow capacity of the original line. Fig. 10 illustrates the schematic of buried pipe rehabilitation by using lay-flat plastic hose.

Fig. 10 Schematic of pipe rehabilitation using lay-flat plastic hose

 

Prior to installation, the hose is packed and delivered in a “U-shape”, using tape wrapped around it as shown in Fig. 11. A regular cleaning procedure is required of the host pipe and condition controlled by CCTV etc. afterwards. The hose is pulled through the host pipe by using a wire winch e.g., and can be installed in host pipe having bends up to at least 30° (R/D ≥5).

Fig. 11 Folded hose for pipe insertion

 

No steaming is required to inflate the hose afterwards. Just by end fitting and setting the hose under minimum 1 bar pressure, it opens up and expands towards the inner

pipe wall. Fig. 12 shows the snapshot of piping rehabilitation carried out by the Authors using Mandals lay-flat plastic hose at Bintulu, Sarawak in May 2019.

Fig. 12 Field installation of Mandals lay-flat plastic hose at Bintulu, Sarawak