HIGH MOMENT LOAD, DRIVEN LINEAR SYSTEM OPTIMISES MANDREL REELING
The problems that occur when reeling in a garden hose after use equally apply to the reeling process involved in flexible mandrel production. If the hose isn’t guided effectively it tends to build up on one side of the reel, coil too loosely, tangle, kink or jam. This is precisely what was happening to mandrel manufacturer, Bell Plastics, with its original guiding mechanism.
Bell Plastics’ Production Engineer, Sean Noonan explained: “It simply wasn’t providing adequate control and this presented us with a number of problems. The mandrel tended to stack in one place as it wound, rather than being layered evenly - often these stacks would build-up and then collapse, leaving tangled, loose coils on the drum.”
The result could be damaged mandrel, which would have to be scrapped; added to which, the rewind process would be slowed down dramatically, compromising productivity, requiring the operator to disentangle the mandrel manually.
“This meant a job that should take maybe three hours could take days,” Sean Noonan added. “Also the snatching and snagging as the tangles jammed during rewind would often mark the mandrel. Indeed sometimes the mandrel would be so badly tangled it would have to be cut from the winder and scrapped.”
Clearly a new guiding mechanism was needed by Bell Plastics and reeling efficiency was achieved by fitting a HepcoMotion® Profile Driven Unit PDU2M to the front of each winder. Its role is to carry guides through which the mandrel passes. So as each mandrel is extruded, the PDU2M traverses forwards and backwards guiding the mandrel onto the winder drums evenly and ensuring it is coiled across their full width.
Hoses are generally made from layers of material, typically rubber or plastic sheet, textile and metal reinforcement. The hose is manufactured by applying successive layers onto a former, or mandrel, to give the hose its shape. In effect the mandrel creates the hole down the middle. The composite is then vulcanised which further serves to weld all the layers together and the mandrel is subsequently withdrawn for re-use.
Traditionally rigid mandrels such as steel rods were used for this purpose but the main drawback was the length limitation of the end product. As a result most manufacturers now use flexible mandrels up to 1.25” (32 mm) which can be made from a wide variety of materials, produced in extremely long lengths - up to several kilometres – and packed in coils for easy handling.
Bell Plastics is an expert in this field. It has developed a unique flexible mandrel manufacturing process that provides its customer with several advantages. It allows the company to produce mandrels that are guaranteed to be free from holes and air spaces. This is important because any voids can cause the mandrel to collapse during the hose manufacturing process.
At best, a poor quality hose is produced in terms of dimensional stability and at worst, both hose and mandrel have to be scrapped. This is particularly relevant for the manufacture of spiral reinforced hose where the reinforcing wire is applied at very high tension around the hose. The company’s Hytrel and TPX mandrels, typically used in automotive hose manufacture, are also particularly sensitive to bad handling as they are soft and prone to damage.
“Our process also allows us to make the mandrel to very tight and consistent tolerances over very long lengths,” Sean Noonan continued. “This enables our customer to produce higher quality hoses to a level of precision that isn’t possible with conventional techniques. Our mandrels reduce hose rejects and are very easy to extract after the hose has been vulcanised.”
In production, as a Bell Plastics mandrel is extruded, it cools and is continuously coiled on winders specially built for the purpose. Once the order is complete or the winders are full, the mandrel is rewound to check quality and dimensional accuracy. It is then re-coiled and packed to customer specification for dispatch.
The efficiency of this process has now been improved using the HepcoMotion® PDU2M controlled by a PLC. This automatically adjusts the traverse speed to accord with the size of the mandrel and line speed. A small touch screen on the unit allows the operator to set-up the equipment for each production run.
Sean added: “There is provision in the control unit for future integration with an automated control system, so that selecting the parameters for a particular product on the extruder will automatically set-up the PDU2M control. We have also taken the opportunity to improve the way the mandrel is guided along the whole of the production line, reducing the risk of scrap generation.”
The primary requirement of Bell Plastics in specifying the linear motion system was that it should be capable of guiding its full range of mandrels and cope with the unpredictable forces involved. “However two big attractions of the PDU2M were that the external guiding for the carriages is built into the unit, and that the unit would tolerate mounting on an ‘as supplied’ bright steel plate,” Mr. Noonan explained.
He continued: “On a competitor’s product, for example, the carriages would have run on a separate guide rail mounted onto a machined surface. This would then have to be precisely aligned with the slide, incurring secondary machining and build costs.”
Initially, Bell Plastics trialled a standard HepcoMotion® slide with a single, centrally mounted carriage and no external guiding. However, as each slide takes two mandrel guides, mounted on each end of an aluminium beam bolted to the slide carriage, there is a high degree of leverage on a single central carriage. The combination of the forces the winding process imposed on the slide was difficult to assess or model accurately, and in trials the carriage was often forced to a pronounced angle relative to the slide body.
“We were concerned this would mean either failure of the carriage rollers or jamming of the slide,” Mr. Noonan added. “And that’s why the PDU2M proved to be an ideal solution. The two carriages allow us to put a carriage right under each guide, while the extra guiding allows it to cope with snatch loadings and stay stable even when winding very large diameter mandrel.”
The HepcoMotion® PDU2M delivers a 200% increase in moment load capacity and 1000% uplift in moment load stiffness compared to a standard HepcoMotion® PDU2. Direct load capacity is also 50% greater. Key to the rigidity and strength that this product provides is the ultra-high performance HepcoMotion® Herculane® wheels that are mounted on adjustable eccentric studs. These wheels run virtually friction-free on the inside of the profile providing stable support for the carriage plate.
Bell Plastics has always run lights-out production but clearly its old guiding mechanism was not ideal for unmanned operation. “It relied on pegs being moved manually as the mandrel was wound, guiding it on to a different part of the winder drum,” Sean Noonan explained. “Automating the layering has meant that we’ve minimised the issues resulting from lights-out production and I have to say that the PDU2M units from HepcoMotion® on each of the winders continue to behave impeccably.”< BACK HEP\451