What to look for in today's hopper loaders.

Mobility in self-contained units and flexibility in central systems are the new standards in hopper-loader design.

Portability has become the most popular new feature in integral (self-contained) hopper loaders, so you will want to consider the newer cart-mounted versions that are available for the same money as the traditional hopper-mounted models. If long conveying distances, high-volume throughput. or a large number of loading stations points you toward a central system, there are many more options to consider. But one feature you probably won't consider optional is the flexibility and easy expandability provided by newer control systems.

GO MOBILE

The self-contained loader (one that has its own blower and motor) has moved down off the press and onto the floor beside the molding machine. Cart mounting has become a very popular configuration, says Joseph Dziedzic, marketing manager at AEC/Whitlock. Besides portability throughout the plant, a key benefit is easier clean-out and maintenance of components that are now located at floor level. Cart systems also make it more convenient to use a larger loader with a bigger motor than the typical 1-cu-ft model if you want to convey greater amounts of material over longer distances (i.e., more than the typical 60 equivalent feet).

If you are using moisture-sensitive materials, you can opt for a portable combination dryer/loader system. A benefit of the portable system, says Jon Weagraff, Conair product manager, is that you can dry material off-line and then roll the cart up to a machine when the job is scheduled to run. If you go this route, you'll probably want to make sure the system uses dry air to convey the material to the machine - otherwise you risk contaminating your freshly dried material with moist ambient air.

Prices of these portable dryer and loader combinations are about the same as for the separate components, suppliers say, although you may get more sophisticated controls in the bargain. As an example, AEC's basic Nomad portable dryer/loader costs around 87000 to $20,000, depending on size. Portable combinations may also provide a more compact package - e.g., around 3 x 6 ft, says Terry Godwin, marketing manager of Universal Dynamics.

Among injection molders, conveying material on a just-in-time (JIT) basis is fast becoming standard. "We just put a glass receiver on the feed throat of the processing unit and damp it on," says Godwin. These receivers typically hold only 8 oz to 3 lb of resin and make material changeovers a breeze.

Integral loaders have also moved away from one-piece construction to a standard modular design of detachable hopper/filter lid (with blower), hopper body, discharge cone, and control. Now you can configure the loader for various processing scenarios - most commonly alternation between single- and two-component (virgin and regrind) loading, for which only the mid-section needs to be changed. Modularity also makes it easy to incorporate a self-contained loader into a central system, if future needs require it.

A brush-type electric motor of up to 1 hp is the norm for self-contained units, although these require some maintenance. A brushless AC centrifugal blower is a more expensive option that's usually offered with the portable dryer/conveyor combinations.

Pancake-type filters are the standard. Contact surfaces of spun aluminum, mild steel, or stainless steel are standard or optional, depending on supplier.

MORE FLEXIBLE CENTRAL UNITS

If you have more than four to six loading stations, convey from railcars or silos rather than from gaylords, or need to convey material farther than 60 equivalent feet, you probably are looking at a central loading system.

A central (or vacuum-receiver) system has a main controller, one large motor/blower, a single stand-alone filter and dust collector, and a filterless receiver on each processing machine. There may also be a controller at each loading station.

Central systems use microprocessor controls to handle more loaders, pumps, and sequencing valves than ever before. Standard central-system controls nowadays provide much more than simple on/off vacuum operation. Thoreson-McCosh's Tech 3 controls are typical of newer systems that provide detailed data on system status, such as loss of vacuum, high vacuum, load failures, dirty filters, and a history of alarms. In addition, system software can be upgraded in the field by downloading new software commands via modem from the supplier, notes v.p. Jerry Muntz.

Visual or audio alarm capability is also typical of central-system controls today, along with data-acquisition functions. For instance, the controller for Premier Pneumatics' 2400 series system can be linked to a plant computer for generating reports such as a maintenance schedule for the blower motor, says marketing manager Mike Wedel.

Another important capability of newer control systems is distributed control architectures that allow you to add more loading stations to the system in a daisy-chain fashion with minimal additional wiring or expense.

DILUTE OR DENSE PHASE?

Most processors use dilute-phase conveying, in which the transfer line is filled with about 15% material and 85% air during vacuum conveying. Dense-phase conveying, which uses compressed air, has an 80/20 material/air ratio, which suits it to high-volume conveying over long distances, but at three times higher cost. Compressed air can also add risk of contaminating materials with moisture or oil. For friable or abrasive materials, a third option from Novatec reportedly helps reduce generation of fines. The firm's new Soft-flow system uses a 25/75 material/air conveying ratio with the same vacuum power as a similarly sized dilute-phase system. The proprietary pump and blower technology moves the material in waves at lower speeds than comparable dilute-phase systems.

A FEW KEY COMPONENTS

Mercury level switches placed on the discharge flapper are the nearly universal means of monitoring material in the hopper. They are inexpensive - about $5 apiece. Because mercury is outlawed in some plants, Comet Automation switched to an inexpensive reed switch with a magnet counterbalance.

A more expensive proximity switch ($60-100 each) can be used to sense material through the sight glass on JIT loading systems, though it can be fooled into thinking the hopper is full by a build-up of material on the glass due to static charge. Comet Automation says a Pyrex sight glass instead of polycarbonate won't attract build-up.

Novatec says a photo-eye is the most reliable type of proximity switch. Another option is the capacitance type, which is similar in performance to the photo eye yet closer in price to the mercury switch.

There are also more choices today of discharge mechanism than the traditional counterbalanced flapper. Among newer alternatives, Maguire offers a slide-gate discharge for its Clear-Vu "mini-central" system for loading up to eight hoppers. Patrick Smith, v.p. of marketing and sales, says the slide gate permits easier maintenance and takes up no space in the hopper. Thoreson-McCosh's cone-shaped discharge device is said to give a better vacuum seal than a flapper, though at about a $200 cost premium. Novatec also claims better sealing for its "tulip-cut" counterbalanced pan discharge.

Stainless-steel hopper bodies are standard from some suppliers such as Colortronic, Comet Automation, Novatec, Premier Pneumatics, and Universal Dynamics. Other vendors offer stainless steel as an option. Stainless is said to be least likely to contaminate the material and easiest to clean.

A self-cleaning filter is a must if you are conveying materials that generate lots of dust or fines. Compressed air is the usual filter-cleaning method, though Colortronic offers optional filter vibration.

Central systems commonly use one of three blower types. Positive-displacement (PD) pumps are usually noisy but reliable and inexpensive. Multi-vane pumps, which convey material at lower velocity, are quieter but 30-40% more expensive. Side-vane pumps are very quiet and compact, as well as less expensive than a multi-vane pump. In general, PD pumps move more material at higher throughputs, though Colortronic offers a rotary-vane pump for very high throughput rates. Vane-type pumps also require more horsepower than a PD pump.

A WORD ABOUT POWDERS

Conveying powders is more demanding than loading pellets and requires special equipment that sells at a premium. Blowback filter cleaning is a necessity, says Premier Pneumatics' Wedel. Colortronic's new CEF loaders for PVC powder also use filter vibration. Universal Dynamics recently added powder capabilities to its line, and new powder-conveying equipment is also available from sources such as Premier Pneumatics, Colortronic, and Mould-tek.

SAMPLE INVOICE                                      DATE         NO.
                                                  10/10/97      1247
Typical Central Loading System

Application: Convey polycarbonate from a central dryer to five
injection machines. Distance of 120 ft horizontal, 20 ft vertical,
with three 90 [degrees] bends.

COMPONENT                                              QTY

Central controller                                      1

Filterless vacuum receivers with integral
vacuum sequencing valve                                 5

3-hp positive-displacement vacuum pump(*)               1

Dust collector with cartridge filter                    1

Upright fantail assembly for selectable connection
between material source and destination                 1

Tubing, bends, couplers

TOTAL ESTIMATED PRICE                                        $20,000

* A smaller pump can be used to save money

Source: Conair