Back to the basics in cryogenic deflashing? (Tech Service).

Ploemacher GmbH has been in business as a toll deflashing company since the late 1970s and has utilized its extensive experience in cryogenic deflashing and the operation of a wide variety and types of cryogenic rubber deflashing machines to design and build its own cryogenic deflashing machines. Their aim was to keep their design uncomplicated, straightforward and easy to operate, with low maintenance and solid construction. Their goal was to avoid problem areas and areas requiring extensive maintenance or repair. The company currently offers the E-40 and E-90. The 40 and 90 references the total deflashing chamber volume in liters.

One of their primary focuses was the media recirculation and cleaning. Their experience had shown that this is one of the most troublesome and maintenance intensive areas. Their solution was to develop a media cleaning module that separates the media separation and cleaning from the machine itself, and thereby generates a consistent, efficient and reproducible environment for media regeneration. An additional advantage of this type of system is that one media cleaning and drying module could be used for the cleaning and regeneration of media from other machines.

Another area of focus was to adopt a modular design with each module built to tight tolerances for easy exchange or replacement. In addition, all components of the machine are mounted so that they are easy to access for cleaning, maintenance and replacement.

The machine is well built, durable, uncomplicated and should be very easy to operate and should require a minimum of maintenance.

E-90 evaluation

Overall construction

Both the E-90 and E-40 machines are of all stainless steel construction with an external support frame of tubular hot dipped galvanized steel. All motors, with the exception of the impeller motor, are located external to the machine and are off-the-shelf motors. The primary control panel is mounted to the frame of the machine and eliminates the need to hook up interconnecting wiring. The operator interface is mounted on an articulating boom to the fight of the machine. A shaker-sieve is located in front of the unit and underneath the drum opening to carry away the parts to the right side as they are discharged from the deflashing chamber and into a bucket. This shaker-sieve also separates out larger flash components and any media left in the parts. [N.sub.2] is exhausted to the outside through an insulated stainless steel cyclone.

Controls

Primary electrical components such as fuses, circuit breakers, relays, variable speed drives and the PLC are located in a Rittal enclosure at the left back corner of the unit, and all wiring is hard wired to the components. All components comply with DIN standards and should be readily available on the U.S. market. The PLC is a Siemens S7 also supported in the U.S. The user interface is a backlit liquid crystal display and operator panel mounted in a Rittal enclosure. The user interface is mounted on a boom that allows the user interface to be positioned for ease of operation. The menus are easy to access and parameter settings are easy to change. The operator interface includes a printer for a printout of the data for each run. Up to 99 recipes can be pre-programmed into memory. All documentation for the controls and operation are available in English.

Loading door

The loading door is hinged on the left and covers the entire front of the unit. Contained in the loading door are the impeller wheel and motor, impeller wheel housing, L[N.sub.2] injection nozzle, media transport tube and the thermocouple. The door is locked against the main housing through a pneumatic locking mechanism against the housing. In addition, there is an insulated housing covering all components mounted on the door. This allows for a very low noise emission (70 db) of the unit during operation. During operation, no media leakage occurred. The door seals against the rotation drum via a UHDPE strip on the face of the drum and a felt strip located on the face of the door. Both seals are inexpensive and easy to change out.

Deflashing chamber

The all stainless steel deflashing chamber (drum) has a removable perforated liner with mixing ribs welded to the liner. The liner is easy to remove and can be exchanged with one having larger perforations if required. Two support rollers provide support to the front of the drum. The drum is rotated through a solid stainless steel shaft attached to the rear of the drum. This shaft extends through an opening in the back wall of the unit and is attached to a gear-motor. Drum speed is variable from 5-15 rpm, and the liner has a 3 mm (.118") perforation. Maximum load capacity of the chamber is around 80 kg. Total chamber volume is 3.17 cu. ft. Chamber dimensions are 890 mm (35.06") diameter and 790 mm (31.1").

Impeller wheel

The impeller wheel is welded stainless steel with a diameter of 300 mm (11.7") and has a maximum speed of 6,000 rpm.

Media transport

Media transport takes place via two stainless steel screw feeders, one open horizontal feeder that is also the media hopper and one vertical tube feeder. Both screw feeders have a fixed speed. Media are loaded into the hopper of the horizontal feeder and are then transported via the vertical tube feeder to a buffer vessel. From this buffer vessel, the media are transported through a tube to the impeller wheel via suction from the impeller. The unit can run on a variety of media sizes. The base unit is laid out to run on 1 mm plastic shot. but can also handle standard CG-30 and CG-45 polycarbonate media. The drum liner and media screens can be replaced to accommodate any media size. The total media capacity of the unit is 75-100 kg (116-220 lb.), which is loaded into the horizontal media hopper. This allows a week of continuous three-shift operation without the need to clean and replace the media.

Media separation

Due to the size of the deflashing chamber perforations of 3 mm, a large part of the media separation already takes place within the deflashing chamber, reducing the amount of flash entering the media stream.

The secondary media separation has been removed from the machine into a separate module to address the common problems associated with internal and external closed loop media recirculation and cleaning systems. These problems include moisture, dust and flash buildup on the separator screens and media transport paths, static electricity buildup and maintenance on components located within the cold machine environment.

The media cleaning module consists of a frame housing a media dryer and Sweco separator discharging into a media and waste container. The media are removed completely from the deflashing unit after a certain period of time through a port on the back of the deflashing unit into the media-cleaning module, where the media are dried and cleaned. After the media have been removed from the deflashing unit, either fresh media can be filled into the unit to continue deflashing or the unit can be shut down and allowed to warm up. If the deflashing unit is in one- or two-shift operation, the unit automatically goes into a standby mode at the end of the last shift, where the interior of the deflashing unit is kept cold and dry at -10[degrees]C via L[N.sub.2] injection. This eliminates the need to remove the media after one or two shifts and then having to again cool down the warm machine when production commences on the first shift.

Performance

For the purpose of evaluating performance, parts were run on the machine to determine load capacity, cycle time and deflashing quality. The part was a muffler mount grommet. Load size was four buckets with a weight of 20 kg (44 lbs.) each (176 lbs.). Several loads were run with the same parameters and the parts were 100% deflashed and passed inspection. Average L[N.sub.2] consumption is around .5-1 lb. L[N.sub.2]/lb. parts based on part configuration, load density and deflashing temperature.

Summary

Overall, the E-40 and E-90 deflashing machines are well-built and have a larger than average capacity with high throughput capability. A lot of thought and engineering were put into avoiding problem areas, as well as providing easy, straightforward operation and ease of maintenance. This should provide the user with a rugged workhorse to efficiently handle a wide variety of part configurations.

Rolf Wieland has over 25 years of experience working with cryogenic applications. He has worked at Griesheim GmbH. MG Industries, Praxair, MVE and Chart Industries, and is currently employed at Universal Industrial Gases. He holds five patents for cryogenic equipment.