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LASER CLEANING�

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AND SURFACE PREPARATION �

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QUANTEL and LASERBLAST

QUANTEL: the Laser Specialist Quantel SA was founded in 1970 to provide flash lamp pumped solid-state laser systems to the research market. At the time of Quantel’s foundation, pulsed Nd:YAG laser technology was new. By embracing it and growing with it Quantel has become a world leader in providing some of the most advanced pulsed solid-state lasers available.

QUANTEL: an International Group �

The Quantel group, a public company on the Nouveau Marché de la Bourse de Paris (New Paris Stock Exchange Market), comprises four companies. � QUANTEL, founded in 1970, develops, manufactures and commercializes lasers

for scientific instrumentation. Quantel also manufactures many of the lasers commercialized by the other companies of the group.

� LASERBLAST, acquired in 1994, specializes entirely in laser surface cleaning

applications. Laserblast is based with Quantel in Les Ulis.

� QUANTEL MEDICAL, founded in 1993, specializes in ophthalmology. This company is based in Clermont-Ferrand.

� BIG SKY LASER TECHNOLOGIES, an American subsidiary based in Bozeman,

Montana manufactures compact and rugged pulsed laser sources for the scientific, industrial and medical markets. This company is the North American headquarters for the Quantel group.

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LASERBLAST: Laser Cleaning Laserblast is entirely devoted to laser cleaning and surface preparation. In the field of architectural conservation and industrial surface preparation, Q-switched solid-state lasers offer a technically efficient and economically realistic solution compared with traditional procedures. Laserblast offers a unique range of products characterized by the use of an optical fiber to transport the laser energy to the work surface. The result is excellent cleaning performance, superior ergonomics and very simple integration into robot systems.

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LASER CLEANING

The Principle �

The laser cleaning procedure relies on the characteristics of light pulses generated by the Laserblast system.

� Wavelength (color): 1.06µm (near infrared) � Pulse duration: 10 nanoseconds � Pulse energy: up to 350 millijoules � Energy density: from 0.2 to 5 joules/cm2 � Pulse frequency: from 1 to 120 hertz � Energy distribution: homogeneous over the entire beam surface

It is based on a photomechanical reaction induced by the interaction between the light beam issued from a high intensity, short pulse laser and the polluting layer. The physical principle may be summarized as follows: � The light emitted by the laser is absorbed by the

layer of contamination on the surface to be treated.

� The strong energy absorption creates a plasma (highly ionized and unstable gas) which expands, creating a shock wave.

� This shock wave fragments and ejects the

contamination.

� The light pulse is sufficiently short to avoid thermal phenomena, which could otherwise damage the surface to be treated.

� Experience has shown that, in the case of

oxides on a metal surface, the plasma forms on the surface.

Plasma is only created above an energy density (energy per unit of surface area) characteristic of the soiled or oxidized layer to be removed. This threshold effect is

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very important in order to obtain efficient cleaning that is safe for the substrate to be cleaned. There is a second threshold for plasma appearance. This is the energy density threshold above which the substrate is modified or altered. To obtain cleaning which is safe for the substrate, the laser parameters must therefore be adjusted in order that the energy density of each light pulse is strictly situated between these two thresholds.

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Each laser pulse removes a certain thickness of the soiled layer. If this layer is thick, several pulses will be necessary to clean the substrate perfectly. The number of shots necessary to obtain a clean surface is a good indicator as to the degree of soiling of the surface to be treated. A very important effect due to the two thresholds is the self-limiting of the cleaning. Light pulses with an energy density over the first threshold will “dig through” the contamination until they reach the substrate. Here, however, since their energy density is less than the damage threshold of the substrate, no damage occurs.

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Important Parameters �

Average Power of the Laser �The cleaning speed is proportional to the average power of the laser source. Two adjustment parameters enter into consideration: the energy per pulse and the pulse repetition frequency. The average power is the product of the two.

Homogeneity of the Light Beam �The homogeneity of the cleaning is directly related to the distribution of the light energy in the beam. A laser beams is typically bell shaped, referred to as “Gaussian”. In this case, the energy density is greater at the center of the beam than at the edges. The energy at the center of the beam will not be used in an optimum manner, while the edges of the beam, below the cleaning threshold, will have no effect. Laserblast’s use of an optical fiber creates a beam with a flat profile; all of the energy

is used in an optimum manner and the cleaning is homogeneous

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Optimized Scanning �

For industrial applications, the cleaning speed is an important parameter. In certain cases, the geometrical shape of the laser beam must be modified in order to optimize the scanning and to minimize the geometrical overlap of the light pulses. It can be shown that a square shaped beam makes it possible to increase the cleaning speed by 50% compared to a circular beam. Laserblast offers beam delivery systems producing a square, uniform output beam for maximum cleaning effectiveness.

The Advantages �

The advantages may be summarized as follows:

Laser cleaning does not degrade

� No abrasive effects � Non-contact � No thermal effects

Laser cleaning does not pollute

� No substances added � No solvents � Minimum amount of waste to be collected � No photochemical effects

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LASERBLAST – the Products

A Complete Range �Laserblast offers a range of laser systems making it possible to cover most of the needs of industry. Three models are available; their main differences concern their average powers: LASERBLAST 60: 8 Watts LASERBLAST 500: 20 Watts LASERBLAST 1000: 40 Watts LASERBLAST 2000 : 72 Watts Laserblast 500 and 1000 can be equipped, as an option, with a 40 meter optical fiber. Laserblast also offers the Helios product, a fully automated industrial cleaning system.

Adapted Solutions Depending on the types and quantities of pieces to be treated, two methods are available.

Automated Cleaning �

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When a large number of pieces is to be cleaned, it becomes desirable to automate the cleaning operations. Quantel has developed the Helios concept. It is a complete cleaning solution including: � One or several Laserblast 1000 units with their

optical fibers � A 5 or 6 axis robot � Un automate � Conveyors � Range finders � Safety elements in compliance with the

standards in force.�

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An optical cable transports the laser energy to the robot. The robot acquires and memorizes the geometry of each piece, in order to optimize the laser beam scanning process.

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In the glass packaging industry, the performance, efficiency and ergonomics, which optical fiber technology provides, make it possible to treat a typical mold within 3 and 10 minutes, depending on its surface area and shape. Under these conditions, all the molds for a plant producing 500 million bottles per year may be treated. Of course, Helios by Quantel-Laserblast may be adapted to the specific needs of each production unit and is, in all cases, compliant with the safety standards in force. � �

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Manual Cleaning �

Difficult access, reduced cleaning frequency and complex piece shapes are parameters that call for human intervention. This is the reason the Laserblast 60 and 500 models were developed. In addition, Laserblast 1000 may be fitted with manual beam delivery.

An operator with a hand-piece attached to the optical cable scans the mold. He may vary the energy density from the laser to suit the contamination of the area to be treated.

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Manual cleaning of a composite structure mould

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Main applications �

�• Stone, wood, brick, plaster cleaning

• Cleaning of plastic or rubber molds

• Cleaning of composite structure molds

• Glassware molds cleaning

• Surface preparation before thermal spraying

• Surface preparation before gluing

• Surface preparation before welding

• Welding cord removal

• Metal deoxidization

• Surface degreasing

• Paint stripping

• Varnish stripping

• Etc …

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