The ‘heart’ of any plastic processing machine is its Screw and Barrel, so if your equipment is not as athletic as you would like, perhaps a ‘transplant’ is the answer!
In the case of plastic extrusion equipment, the machine is in effect a continuous pump, the screw being the most critical component. A change in the primary material being processed or simply an increase in demand can mean that your trusty workhorse is now less of a thoroughbred and more like the nag from Steptoe!
We asked Mark Cox of DS Brookes for details on how an extruder can be upgraded rather than replaced:
“The most cost effective option is to replace a standard screw with a Barrier Mixing Screw of the same diameter and L:D ratio. In simplistic terms during processing Barrier screws isolate the melt stream from the solids bed of granules such that more efficient melting can take place and reduce the risk of solids bed break up. Over the length of the screw the melt channel increases and the solids channel diminishes until the materials are fully molten. In combination with a mixing section at the output end of the screw, (such as a spiral Maddox mixer) this minimises the chance of solids bed break up, a feature commonly associated with single flight screws and poor barrier designs. As well as being ideal for use with regrind, barrier screws can typically increase throughput by around 15% or more”.
Other options for improving material throughput include:
- Fitting a larger diameter plasticising unit – “It may sometimes be necessary to maintain the L:D ratio (meaning the unit will increase in length) in order to provide the appropriate residence time for the materials. Davis-Standard have a process team that we will check that your system is capable of upgrade”.
- Simply checking the condition of your existing plasticising unit – “Davis-Standard also offer a Screw & barrel measurement service because simply replacing or refurbishing your existing worn components can often give gains in efficiency of up to 20-30% dependent on the degree of wear. Surprisingly many plastics processors never check for screw and barrel wear on a regular basis and allow losses in efficiencies to be ignored until the process fails. Davis-Standard can provide a program where your system is regularly monitored and the appropriate processing advice given to ensure the customers system is maintained in its optimum condition. One of the fastest payback items in any Plastics factory is the replacement of a worn screw and/or barrel.”
In the case of injection moulding equipment, barrier screw technology is also widely implemented, particularly for applications involving larger shot weights that are coloured using masterbatch. It is also relatively straightforward to change the size of screw and barrel fitted, most new machines being fitted with the ‘b’ screw, there usually being a smaller and larger standard option that can be fitted without any major machine modifications. Changing or refurbishing an existing worn screw and barrel can yield similar improvements in performance to that seen with extrusion, as well as improve shot to shot consistency.
If you are interested in seeing how you could improve productivity without having to replace your existing equipment, then you can contact the U.K’s leading independent Screw and Barrel providers by going to the PlastikCity Screws and Barrels section.
Injection moulding equipment will also benefit from a regular service and calibration. As well as detecting issues with hydraulic components and oil that may be impacting on performance, a machine that is out of calibration is both less accurate and runs less efficiently. Older machines may also have fixed displacement pumps (in which case external power saving devices are worth considering), as well as Mica Heater Bands, these being easily substituted for more efficient Ceramic units. There are independent UK manufacturers of heater bands on the PlastikCity site.
According to PlastikCity partners Hydracare and Millers Oils, 80% of hydraulic failures are due to poor oil quality. Each offers ‘Condition Monitoring’ which costs little relative to the capital cost of your equipment. The service it provides is perhaps the most inexpensive way available of avoiding costly downtime and repairs. They also provide an oil change service which ensures your machines are restored to optimal performance levels. You can view these services on PlastikCity here.