MATERIALS PREPARATION | TECHNOLOGY
market offering this type of technology. Crittenden says investment costs are similar to those of top-end desiccant dryers, and from then on, it’s downhill all the way with savings of up to 90% in energy bills. “Enquiries are increasing and we are getting a lot of repeat business now,” he says. Maguire is not completely alone with vacuum dryers
though.Matsui has for several years offered the DPD3.1 in its “plas-aid” product line. It says energy consumption is half that of standard dehumidifying dryers, and that the DPD3.1 is also constructed to prevent the radia- tion of heat. Matsui says: “In addition to this, the high-thermal conduction method helps improving [part] quality. It prevents effectively yellowing and oxidation of the end products. Thermal conduction fins in the inner hopper are located at both the inner and central wall of the hopper. Sensors are also located at various points to ensure speedy temperature control for efficient drying.” The company says: “The vacuum drying process pulls out much of the contamination that can clog pins and vents [in the mould], which reduces the frequency of cleaning and maintenance. Also, due to the unique design, the maintenance process is made extremely easy. Thanks to the smooth surface of the extruded fins, materials do not stick onto the hopper and cleaning can be carried out quick and easily.”
Maintenance tips
With the summer months coming up in the Northern Hemisphere, Dri-Air President Jason Spears says this could be a good time to look at some preventive maintenance for dryers. Here are some of his tips. Regardless of the type of desiccant dryer, all change internally between regeneration (removing the moisture from the drying media) and process (removing the moisture from the plastic). Warm, humid weather puts a strain on both phases. On the process side (the side that sends dry air to the drying hopper) cracked or crushed hoses, missing hopper covers, and missing hopper door gaskets are areas where the warm, humid air can infiltrate the system, loading the desiccant beds with moisture that leads to high dewpoints. Clean filters are also important, as dirty filters will restrict air flow and cause extended drying times.
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On the regeneration side, clean filters are a key component in providing adequate air flow to regenerate the desiccant beds quickly. Filters can not only be contaminated by dust and fines, but also by any volatiles such as plasticisers condensing on the filter. So it’s a good idea to change the filters on a regular basis.
As a rule of thumb, if you are
processing only virgin resins, change your filters every six months, says Spears. If you are processing regrind or resins with a high glass content, his advice is to set up a schedule based on physical appearance. To stop the volatiles from
contaminating filters (and possibly
the desiccant beds) the dryer will need an after- cooler and volatiles trap. If the dryer already has a trap and cooler assembly, and volatiles are still an issue, check with your material supplier to make sure you are using the correct drying temperature. If the dryer is operating just a few degrees over the recommended drying temperature there can be a major impact on how much plasticizer is released from the resin. Reduction in airflow from clogged filters also causes the problem of inhibiting regeneration which can lead to high dewpoints and temperature spikes if your dryer does not control regeneration based on temperature, says Spears. While checking the dryer filter, also inspect the filter housing – check for missing gaskets, lid retaining fasteners etc. Check the lid fits correctly. If your dryer is equipped with a return air heat exchanger or aftercooler, you should also inspect the heat exchanger for blockage. Material storage is another important area. Keep
bags sealed as long as possible and put any unused material into sealed containers – materials like glass filled polyamides and some polyure- thanes can require 16-hour dry times if left in an open environment.
CLICK ON THE LINKS FOR MORE INFORMATION: �
https://dri-air.com �
www.conairgroup.com �
www.koch-technik.com �
www.motan-colortronic.com �
www.wittmann-group.com �
www.maguire.com �
www.matsuiamerica.com
March 2022 | INJECTION WORLD 41
Left: Matsui’s DPD3.1
vacuum dryer. It is available in two versions, one with an 11 litre hopper and the other with a 25 litre hopper
IMAGE: MATSUI
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