Rotary Actuators Provide Accuracy, Ease-of-use

To help ensure safe landings on airport runways, it is critical to remove the rubber build-up from runway surfaces, exposing the original pavement and restoring the friction coefficient to desired levels for maximum braking on wet surfaces.

Over time, the skid resistance of an airport's runway pavement deteriorates due to a number of factors. The primary ones are the mechanical wear and polishing action from aircraft tires rolling or braking on the pavement and the accumulation of contaminants, chiefly rubber, on the pavement surface.

Other influences are local weather, the type of pavement, the materials used in original construction, any subsequent surface treatment and airport maintenance practices.

During aircraft landing, prior to the actual touchdown, the tires are at rest, experiencing no rotation. At the point of impact with the asphalt, the aircraft is moving at a speed of 100 knots (115 mph), so the tires must reach a rotational speed to match the aircraft speed in an extremely short amount of time. This causes superheating of the tires, as well as skidding, which leaves rubber deposits on the runway. The tires also leave rubber deposits while braking when the aircraft is coming to a stop after touching down. Heavy rubber deposits can cover the pavement surface texture causing loss of aircraft braking capability and directional control, particularly when runways are wet.

Additionally, removing conflicting or obsolete markings is also important to ensure that correct routes are followed to minimize risk of accidents and to promote the efficient movement of aircraft and ground support equipment to maintain tight schedules.

Historically, removing pavement markings from airport runways and roads involved grinding the surface down to the lowest level of the paint, thermoplastic, epoxy or preformed tape. The problem with this method was that it removed up to half an inch of the surface, depending on the depth of the marking being removed.

Meet the hog

Established in 1988, Waterblasting Technologies, Stuart, FL, makes mobile waterblasting equipment for the removal of all types of durable traffic markings from asphalt and concrete surfaces. The design team used their experience with high-pressure water pumps to develop the Stripe Hog line of marking removal systems using a 40,000 psi waterblasting and vacuum system to remove markings without damaging the runway surface.

The Stripe Hog 4000 does its work with a zero-turn John Deere turf tractor that features an onboard hydraulic system. The blasting head is offered in widths of 6 to 14 in. and is capable of removing up to 7,500 linear feet an hour. The standard tank comes with 1,900 gal. of stainless steel water supply and 1,600 gal. of debris storage.

The Stripe Hog 4000's articulated boom utilizes helical, hydraulic rotary actuators manufactured by Helac Corp., Enumclaw, WA, to position the blast head with precision, thus enabling more efficient marking removal.

The boom is triple-jointed with two vertically mounted Helac L20-4.5-E-FT-180 rotary actuators for side-to-side boom rotation and one horizontally mounted L20-4.5-E-FT-180 rotary actuator for up and down boom positioning.

Eliminating hydraulic cylinders and switching to Helac's rotary actuators proved profitable for Stripe Hog operators. They experienced a productivity gain of 30% due to the elimination of backlash and providing better head placement control resulting in a $1,440 increase in profits per 40-hour work week.

Damage control

The Stripe Hog offers a compelling new methodology for removing markings via its self-contained removal and debris collection system. As Steve Carroll, chief engineer, Waterblasting Technologies points out, the Stripe Hog "is quick, clean and easily adapted to the pavement maintenance needs of today's major airports. The Stripe Hog is capable of removing markings from the pavement while causing only minimal damage to the surface."