International Journal of Engineering & Technology IJET-IJENS Vol:10 No:06 105 Introduction of Nylon-66 on Side Arm in a Catheter Manufacturing Process M. F. Ghazali* 1, Z. Shayfull 1, M. D. Azaman 1, N.A. Shuaib 1 and M. S. Abdul Manan 1 1 School of Manufacturing Engineering, Universiti Malaysia Perlis, Malaysia fathullah@unimap.edu.my Abstract Catheter is a medical device used to drain fluids from human body. It is commonly made from natural rubber. A study has been undergone in a catheter manufacturer located in the northern of Malaysia which aims to reduce the cost of manufacturing this commodity device. In a catheter manufacturing process, operators are required to insert a rubber strings into side arms manually. There is a problem where the rubber string can easily break and part of it is trapped inside which needs to be reworked by undergoing a burning process at high temperature. As a result, side arms undergo changes in material structure that leads to shrinkages and working failures. A catheter manufacturer is identified to spend high cost yearly to replace more than 1,000 units of new side arms due to this issue. The new material proposed is nylon PA66 which has been successfully identified to solve the issue. This product has been invented with an etensive research and numerous tests to comply with industrial requirements and also adaptable in their process. The quality and safety issue have been seriously taken into consideration in order to complete this invention. The cost has greatly been reduced whilst the product preserves the same quality of producing catheters. Inde Term Catheter, Injection Moulding, Nylon PA66 and Side Arm I. INTRODUCTION URINARY catheter is a tube that is inserted into human body for the purpose of administering or removing urine fluid. It is inserted into the bladder through urethra to drain the bladder inside patients who are unable to urinate [1]. This rubber based (sometimes come with silicone based) medical device is used widely in hospitals particularly by professional medical practitioners as well as surgeons all around the world. This catheter generally can be categorized into 3 types; 1) Straight catheter, 2) Indwelling catheter (Fig. 1) and 3) Suprapubic catheter. In making indwelling catheters, the process starts by preparing pairs of aluminum formers and side arms (shown in Fig. 3) combined together as moulds of the catheters. The mould-pair is then dipped into a solution called METHCELL solution to lubricate the moulds in ensuring the late solution does not stick to the moulds after late dipping process takes place. After that, they are dried at 60 C for before they are brought to be dipped into natural late solution. After the first layer of solidified late has been created around the mould, operators need to insert a rubber thread through a through hole created inside side arms. Rubber thread is locked at point X1 and pulled out from the side arm and attached to the edge of the mould at point X2 as shown in Fig. 3. The net process is to dip the moulds again in the late to create the second layer of the late as well as to cover the rubber thread attached on it. This dipping process is done 5 times alongside several processes in order to complete the process of making catheters. The process flow of manufacturing catheter is shown in Fig. 3. Fig. 2. (a) side arm and (b) former used in catheter manufacturing processes Fig..1. Eample of indwelling catheters II. PROBLEM STATEMENT Threading process which has been highlighted in Fig. 3 is actually the stage where the problem occurs. Operators face difficulties in inserting the rubber thread without breaking the thread. Rubber thread is hard to be pulled out and can easily break before it can be taken out and part of it is normally trapped inside which needs to be reworked by undergoing a burning process at a minimum of 600 C to melt down the unneeded thread. As a result, side arms undergo changes in material structure that leads to shrinkages and working failures due to etreme temperature applied after this reworking process is done several times. Fig. 4 shows samples of new side arm and the fail side arm after it undergoes burning process for a number of times. A catheter manufacturer is
International Journal of Engineering & Technology IJET-IJENS Vol:10 No:06 106 identified to spend nearly RM9000 yearly to replace more than 1,000 units with new model side arms due to this issue. Fig.. 5. Cross-section and dimension of Side Arm Fig. 3. Process flow of manufacturing catheters Fig.. 6. A through hole inside side arm can be tighter at the circled area. Fig. 4. (a) Original side arm and (b) rejected side arm after burning process III. EXPERIMENTAL The problem of trapped rubber threads inside side arms is the most common issue and needs to be solved. Samples of side arms were taken to be investigated and tested. This led to a finding that the issue of trapped rubber thread came from the issue of 0.85mm through holes inside the side arms to be inserted and pulled out by 1.10mm diameter of rubber thread. The inner hole diameter at the tip of the side arm is intentionally made by the manufacturer to be 0.3mm smaller from the diameter of the rubber thread in order to prevent late solution to come inside in dipping processes afterwards. Fig.5 and Fig. 6 respectively shows cross-sectional area of side arm and the area where the hole becomes tighter at the bending area of side arm due to the effect of manufacturing process of this aluminum side arm. The body of side arm is traditionally manufactured from machining process and the steps of manufacturing processes involved are: 1. Turning operation 2. Drilling operation 3. Bending operation (at circled area in Fig. 6) An aluminum workpiece is clamped and ready to go for turning operation. After that, a 0.85mm through hole is made through drilling operation before bending operation takes place. Unfortunately bending operation cannot be made before the drilling operation and this is why the eisting drilled hole reduces to more or less 0.7mm when bending operation is applied. A 0.35mm difference between the diameter of rubber thread and the hole to be inserted is the critical point where the rubber thread tends to break up when it is being pulled by the operator. Recognizing this as the root cause of the issue, a study has been made to identify a new design so that the tip can be maintained at 0.85mm while the inner holes can be made larger, particularly at the bending area of the body. There is one way that this issue can be solved greatly which is by producing side arms through injection moulding process. Injection moulding allows fleibility in designing the side arms especially to produce either the through hole to be widened or the other way around. Besides, the injection moulding process is ideally suited to manufacture parts of even comple shapes that require precise dimensions [2] and requires lower labour costs as it can skip several manufacturing and assembly operations [3]. However, the new thermoplastic side arm should conform to strict standards in order to enable the new side arm to replace the aluminum side arm. The material must undergo and pass the following tests: A. Methylene Chloride and APA Dipping Test (24h 7days B. Aging Test (70 C 24h 7days) C. Methcell Dipping Test D. Valve Retention Test E. Late Flow-back Test
International Journal of Engineering & Technology IJET-IJENS Vol:10 No:06 107 A. Methylene Chloride (CH2Cl2) Dipping Test Methylene Chloride is used as solvent on late [4]. Therefore, the new materials should never give reactions with this solvent or otherwise, the side arm might wear down and the reaction means the catheter and the whole dipping container is already contaminated with thermoplastic material which is totally unacceptable for medical devices. materials are selected; polycarbonate (PC) clear and Nylon-66 as the alternative materials of new side arm. B. Aging Test (70 C 24h 7d) Air drying process is applied at an average of 60 C at 5-10 minutes inside furnaces. For that reason, the new material should have an ability to resist any reactions occurred at minimum 60 C at more than 10 minutes. To confirm the material resistivity, hence it should be tested a little bit higher at 70 C inside a furnace, for a period of 7 days without stop. C. Methcell Dipping Test As mentioned earlier, Methcell solution is used to lubricate the side arm to make sure late does not stick to it after dipping process is undergone. If the new material reacts with this Methcell solution, the material will not be able to be used to fabricate new side arms. D. Valve Retention Test Valve retention test is a physical test to ensure the side arm is stiff enough to be used over and over without damage. E. Late Flow-back Test Flow-back test is a test to make sure the late does not melt and flow back along the body of side arm right after the side is pulled up from the dipping process. Aluminum side arm has no flow-back issue, hence the new material should also have no problem with this flow-back concern. Fig. 8. AISI 1050 Moulding set used to fabricate thermoplastic side arm. PC clear is chosen due to the fact that it is etensively used because of its ecellent combination of stiffness, strength, toughness, ductility, impact resistance and transparency. It is well known that the stress strain behavior of glassy polymers ehibits a strong strain rate and temperature dependence. In addition, there eists a transitional threshold in rate and temperature beyond which the strain-rate sensitivity significantly increases in polycarbonate [5]. Besides, polycarbonate is also widely used in medical industries due to its ability to get sterilized [6].While for Nylon-66 shown in Fig. 9, it is chosen due to its ability to minimize the oidation rate as well as thermal degradation when eposed to elevated temperatures for etended periods of time. It also can provide improved retention of physical properties under eposure to long-term heat [7]. In addition, Nylon 66 is regarded as a suitable material for medical applications. This is agreed by C. Birkinshaw et. al [8] which stated that Nylon 66 were needed to be used under special circumstances in medical fracture fiation devices. Fig. 9. Nylon-66 side arm Fig.. 7. New side arm dipped into late in flow back test If the new materials proposed can pass these 5 tests, then the materials can be chosen to replace aluminum. Therefore, An AISI 1050 carbon steel is machined and fabricated to be a mould for side arm as shown if Fig. 8. 2 types of thermoplastic IV. RESULTS AND DISCUSSIONS Table 1 shows the comparison between aluminum (traditional), nylon-66 and PC side arms that have been brought to 5 compulsory tests that have been done at lab scale. It clearly shows that the new side arm made from Nylon-66 give identical results compared to the previous aluminum side arm while PC clear side arm is unable to comply with more than half of the tests undertaken. PC side arm is dissolvable in methylene chloride and metchcell solutions and it also cannot sustain its physical properties for 168 hours at 70 C inside furnace.
International Journal of Engineering & Technology IJET-IJENS Vol:10 No:06 108 TABLE I COMPARISON BETWEEN ALUMINUM, NYLON 66 AND PC SIDE ARM Results: Passed ( ) / Failed () New New No. Tests Side Arm Side Traditional Nylon-66 Arm Side Arm PC clear 1. Methylene Chloride 2. Aging Test (70 C 24h 7d) 3. Methcell Dipping test 4. Valve Retention Test 5. Late Flowback issue TABLE III VARIABLE COST (PART PRICE PER UNIT) Item RM 1. Plastic part 1.00 2. Medical glue 0.35 3.Packing & 0.15 Transportation TOTAL 1.50 As a result, Nylon-66 is finally chosen to be used as materials of new side arms. A sample of 1000 units are produced by the injection moulding process and part of them are sent to the manufacturer to be tested and applied in real manufacturing situation. The result convincingly shows similar results with what has been tested at lab scale. Thus, with this new design, Nylon-66 side arm has a wider through hole inside (ecept on the tip which is required to be tight) which can allow rubber thread to be inserted smoothly without getting trapped and this will lead to no more reworking issue at 600 C in a furnace. No trapped means no more reworks, and no reworks also means no rejects at all plus, the new material can be obtained much cheaper compared to aluminum. The fied cost shown in Table 2 consists of an AISI 1050 carbon steel and its tooling cost as well as press jig which requires RM9000. On the other hand, Table 3 shows the variable cost incurred in manufacturing and assembling the side arms which is only RM1.50 each compared to RM9 each for Aluminum side arm. As far as cost is concerned, Nylon-66 side arm has reduced 83.3% cost of manufacturing of side arm, plus with no more rejects while the same catheter can be produced at the same top quality level with the previous one. The sample of catheters made by new side arms is compared with the traditional-made shown in Fig. 10 and it shows that the catheters are equivalent in terms of quality as well as functionality. Fig. 10. Comparison between 2 different catheters The catheter manufacturer requires only 1200 units of side arms before they can get the breakeven point (Fig. 11) of their new investment in applying Nylon-66 side arms in their production line. This is achievable since they have more than one model of side arms due to different designs of catheters including side arms. TABLE II FIXED COST Item RM 1. Tooling Cost 8,000 2. Press Jig 1,000 TOTAL 9,000 Fig.. 11. Return of Investment of new side nylon-66 side arm V. CONCLUSION In conclusion, Nylon-66 side arm can successfully replace aluminum side arm. The cost can be reduced greatly with no more rejects occurred in the catheter production lines. Besides,
International Journal of Engineering & Technology IJET-IJENS Vol:10 No:06 109 injection moulding process has helped in giving fleibility on the design wanted to the side arm. Manufacturing process is also much easier and faster compared to the traditional machining process. On top of that, catheters can be made with new Nylon-66 side arms at the same quality standards. ACKNOWLEDGMENT The authors would like to acknowledge the catheter manufacturer where the name of the company is not to be revealed due to some confidentialities agreement, the financial support received from the UniMAP, and also to the Research and Development (R&D) Unit, UniMAP for overall management of the research projects. Support of the students and lab technicians in the work are also recorded with deep appreciation. REFERENCES [1] P. J. carter, Lippincotts Tetbook for Nursing Assistants: A Humanistic Approach to Caregiving, Ed. 2, Lippincott Williams & Wilkins, 2007, pp.419 [2] T. A. Osswald, L.S. Turng And P. J. Gramann, Injection Molding Handbook, Ed.2, Hanser Verlag2, 2008,, pp.1 [3] J. Avery, Injection Molding Alternatives: A Guide For Designers And Product Engineers, Hanser Verlag, 1998, pp. 71 [4] American Woodworker Magazine, New Track Media, Vlo.22, 1991, pp. 49 [5] S. Sarva, D. M. Adam and M. C. Boyce, Mechanics of Taylor Impact Testing of Polycarbonate, International Journal of Solids and Structures, Vol.44, Issues 7-8, 2007, pp2381-2400 [6] R. C. Portnoy, Medical Plastics: Degradation Resistance & Failure Analysis, William Andrew, 1998, pp.117 [7] Vydyne (PA66), R533 Series Specifications And Regulations Data Sheet, Solutia Inc. 2008 [8] C. Birkinshaw, M. Buggy And S. Daly, The Effect of Sterilizing Radiation On The Properties Of Nylon 66, Materials Chemistry and Physics, 17 (1987) pp. 239-248