Airide maintenance - construction, assembly and adjustment

Airides are used in a variety of pulp and paper production machinery applications. One reason for their wide use is the minimal need for maintenance. In general, no maintenance is required on the airide unless the rubber gets hard and brittle or it starts to leak.

However, high temperatures, exposure to process chemicals, heavy loading and damage from contact with moving machinery are causes for eventual maintenance or replacement of airides. Periodically, airides should be inspected and adjusted or replaced as required.

Construction

An airide is a rubber/fabric bellows which contains a column of compressed air. The bellows itself is merely the container as the force or support exerted is performed by the air column. Airides are either two ply or four ply and are manufactured by a vulcanization process. The figure shows the two ply construction.

Each ply is fabric reinforced rubber with the cords set at a bias to each other. An inner rubber liner and an outer rubber cover complete the envelope.

The bellows is attached to the mounting plate using bolts through metal bead rings. If the airide has more than one convolute, the convolutes have a steel girdle hoop molded into the bellows, as seen in the figure below.

Airide construction and measurement location

Adjustment

As a typical example, the first press top roll, second press roll and center roll doctors are airide loaded.

To adjust the airides:

1. Refer to your OEM drawing which will provide the collapsed and inflated dimensions between the mounting plates. NOTE: Adjusting stops are designed to stop any damage from under-collapsing or over-extending the airides.
2. Inflate the airides to approximately 10 psi.
3. Measure the distance between the mounting plates (see figure above, "1" to "2").
4. Use stops "A" and "B" (see figure below) if adjustment is required.

Airide adjustment stops

Assembly

The longest possible flexible life for the airides will be obtained when the parts are used in such a manner that the splice is not overly stressed. The spliced area is marked with a yellow dot in the area that is to be flexed the least. This will occur when the yellow dot falls on the inside of the arc.

Types of bead rings

To minimize the possibility of air leakage around the beading on the airide, use the following assembly procedure:

1. Refer to the drawing and select bead clamping rings, matching them to the holes on the plate.
2. Be certain that the face plate is smooth and clean.
3. Assemble the capscrews through the rings to the plate. Do not pull in tight.
4. Bring the screws to complete tightness gradually. Use a method similar to tightening a motor head against a gasket. NOTE: To bring one segment completely tight at once may cause "bunching" of the beading with resulting air leaks and possible permanent damage to the rubber.
5. Apply sealant to the threads of the air hole.
6. Install the air lines and tighten securely.

Airide maintenance and other paper machine maintenance topics are covered comprehensively in Valmet's Paper Machine Maintenance School. For more information on maintaining your machine line, contact your Valmet representative.