AIR KNIFE APPLICATIONS IN AUTOMATED MANUFACTURING PROCESSES

Introduction

The applications for air knives in automated manufacturing processes are wide-ranging, with an often bewildering array of uses to which they are put. They can be used for drying, cleaning and cooling almost any type of surface, from bottles and cans to foodstuffs, textiles, metal tubes or printed circuit boards. They can even be used for spreading coatings over surfaces. Modular in design and mounted on an adjustable frame, they are adaptable to almost any type of production line and can easily be moved and reassembled elsewhere with minimum disruption to the plant.

There are two main types of air knives: straight and circular. Both consist of a plenum chamber constructed from either anodised aluminium, stainless steel or plastic, depending on the application. A stream of high velocity air, provided by a Secomak blower, passes through the plenum chamber and exits through an adjustable aperture. The movement of the air through this narrow slit produces an highly effective 'knife' effect, the intensity of which

can be varied by adjusting the aperture width - the narrower the aperture, the more powerful the effect. Straight air knives are the ideal choice for most applications, but in certain cases, such as the drying of cables, tubes or extruded products, circular air knives are more suitable.

Applications

Food and Beverage Industries
There are countless air knife applications in the food and drink industries, including drying bottles, cans and jars prior to labelling; controlling the thickness of coatings on food products such as chocolates and pies; removing excess cooking oil from croutons; and removing food waste from conveyors. The possibilities are virtually endless - wherever products on an automated production line need to be rapidly dried, cleaned or cooled - air knives can play a role.

Case Study 1 - New Covent Garden Soup Company
The New Covent Garden Soup Company manufactures a range of all-natural soups. At its London factory, soup cartons are hot-filled and have to be cooled as quickly as possible before entering an air-blast chiller. A problem occurred when the water used to chill the cartons was being carried through by them to the chiller, where it froze, causing the conveyor belt to become jammed. A further problem was caused by cold air from the chiller passing into the water section and actually causing the water there to freeze.

The solution was found to be a straight Secomak air knife, which was positioned at the point where the cartons enter the blast chiller from the water section. The air knife removes any remaining water from the cartons and also acts as an effective ' air barrier', preventing freezing air from entering the water section. Since the air knife was installed, downtime for conveyor maintenance has been significantly reduced and productivity has increased.

Case Study 2 - Bass Brewers
Processing up to 1,100 bottles per minute, the bottling line at the Bass Brewery in Burton-on-Trent is one of the fastest in the country. Before air knives were installed, enough bottles to fill a large waste bin were being rejected every day by the automated bottle inspector. After washing and rinsing, the bottles were passing directly into the inspector, where water droplets on the lips of some of the bottles made them look chipped. The inspector rejected them and many undamaged bottles were therefore going to waste.

Following extensive trials, six straight Secomak air knives were installed on the line - three on each side - positioned to dry the tops of the bottles before they entered the inspector. Since installation, the number of rejects has been significantly reduced.

What can be seen from these case studies is that two very different problems were both solved by the same solution - a carefully positioned air knife.

General Industrial Applications
As in the food and beverage industries, the uses for air knives in other industrial sectors are almost as long as the list of potential problems. In the manufacture of rolled aluminium foil, for example, air knives are used to dry the roll after washing, preventing water marks; in cement works and quarries, air knives are effective at removing dust and gravel from conveyors, preventing the rollers from becoming jammed and worn; during carpet manufacture, the molten rubber backing added to the carpet can be cooled and dried with air knives prior to rolling.

It is also in the heavy industrial sector that circular air knives come into their own. They can blast away accumulated metal swarf during tube and pipe manufacture, strip away the cutting oil used in the manufacture of threaded metal rods, and even dry radioactive graphite fuel rods after washing and rinsing - a process in which no human contact with the product is allowed.

Case Study 3 - Rubber Manufacturer
A well-known rubber manufacturer, based in Manchester, produces rubber extrusions which are used to make the seals for car doors and windows. In the production process, the extrusion passes through a hot salt potassium nitrate bath to cure it and produce a gloss finish. It was found that salt from the bath was sticking to the extrusion, spoiling its appearance and causing maintenance problems by adhering to the conveyor rollers. In addition, constant topping up the salt bath was necessary, a hazardous operation which ideally needed to be kept to minimum.

Following consultation with Secomak, a circular air knife was installed at the point where the extrusion leaves the bath. Air from the knife, which is heated to 250oC, not only strips the salt from the extrusion but also allows it to flow back into the bath without solidifying, significantly reducing the amount of topping-up necessary.

3. High Technology Applications
Air knives also have a number of high-tech applications, particularly in the manufacture of printed circuit boards. In this process, the boards pass through a series of chemical baths before washing and rinsing. Traditionally, they are then air-dried in racks, a time-consuming procedure that also takes up a great deal of space. By positioning air knives above and below the open conveyor at the point where the circuit boards leave the rinser, they are instantly dried, so speeding up the entire process.

Air Cannons
Looking very much like hair dryers, air cannons have developed from air knife technology and work on much the same principle. Apart from appearance, the main difference between them and air knives is that they produce a spiralling 'column' of air, as opposed to the 'blade' effect of an air knife, making them ideal for spot drying applications.