Ever stricter stipulations regarding residual contamination on parts and components are forcing companies to face new challenges. However, simply fulfilling cleanliness requirements is not enough to assure cost-efficient production: The economy and the environmental compatibility of the cleaning process also play an essential role.

The quality, the function and the service life of a product depend decisively on the cleanliness of the individual components. More and more often, precisely defined residual contamination values must be adhered to for workpieces. This makes parts cleaning a value creating step within the manufacturing sequence. In order to achieve the required degrees of cleanliness in an economical and environmentally compatible fashion, cleaning systems are required which are custom tailored to fulfil individual requirements, and at the same time flexible.

Full Bore for Optimised Cleaning

The product range of Lawton Tube Company in Great Britain encompasses all types of tubing made of copper and copper alloys – from simple products for household installations and automotive brake lines, right on up to supply line networks for medical applications and whisky distilleries. All of the copper tubing marketed by Lawton Tube is cleaned and degreased before shipment. Up until recently, this was accomplished by means of trichloroethylene vapour cleaning in an open tank with a wiping lip. However, TRI is classified as carcinogenic and has a destructive effect on the ozone layer. In searching for a new tube cleaning system, the following criteria, amongst others, were critical: compliance with emission laws, preservation of the product’s aesthetic appearance, cleaning of products with outside diameters ranging from 3 to 220 mm at the required high throughput rates, moderate system size and good system flexibility. With its closed VAIOCS Toploading System, EMO Oberflächentechnik from Bretten, Germany, created a cleaning system which precisely complies with the customer’s requirements. The actual system is roughly ten metres long and is loaded from above with a crane, which cuts space requirements in half in comparison with the old system. Copper tubing lengths of up to 6.20 metres can be processed, and the maximum diameter of the tubing bundle is 650 mm. The cleaning process is enhanced by the fact that the entire processing chamber can be tilted, which also allows for fast emptying and filling in combination with high performance pumps: an important prerequisite for subdividing the cleaning process into preliminary and final cleaning stages. Fast, coarse cleaning is carried out as a first step in the Lawton system. The processing chamber is tilted seven degrees to this end, and is flooded with hot cleaning agent. After immersion cleaning under vacuum has been completed, the solvent is returned to the flooding tanks via a filtration unit. Additional steps include final cleaning and degreasing in solvent vapour, as well as intensive drying and rinsing of the chamber. The utilised cleaning agent is Dowclene 3670 from Dow Chemicals. With a maximum batch weight of 1500 kg, the cleaning process has a duration of 30 minutes.

Snow for Strong Joints

The Component Division at Volvo Construction Equipment AB (Volvo CE AB) develops and manufactures transmissions and drive shafts for the company’s broad ranging product spectrum. Amongst others, these include an innovative transmission whose components are joined by means of laser welding for the first time ever. The advantage of this joining technology is the fact that the joints are significantly more accurate and demonstrate less deformation – assuming that the surfaces to be welded are absolutely clean and grease-free. For this reason, the corrosion protection layer which is applied to the parts during the last rinsing bath of an aqueous cleaning process after manufacturing must be reliably removed before welding. Essential criteria for choosing the right process for this selective cleaning task involved “dry cleaning” with reproducible results and good process reliability. Additional, important requirements included good system availability, minimal size and simple integration into the manufacturing process. After comprehensive trials conducted at the technology centre operated by acp GmbH, as well as at the facilities of the laser welding equipment manufacturer, namely Trumpf in Ditzingen, Germany, Volvo decided in favour of the special CO2 snow jet technology offered by acp. The basis for the outstanding cleaning performance of acp’s process is its cleaning head which is laid out as an ultrasonic two-media ring nozzle. Liquid carbon dioxide expands into a snow-gas mixture when it’s discharged through the nozzle. It’s focused by means of a jacketed jet of compressed air and accelerated to supersonic speed. The process is only minimally abrasive, and can be well focused. Acceleration with compressed air also results in much better cleaning performance as compared with single-media nozzle systems and, at the same time, very little carbon dioxide is consumed. Volvo CE AB’s cleaning module is equipped with a media processing unit which filters out any fine contamination contained in the liquid carbon dioxide and the compressed air upstream from the cleaning process. The CO2 snow jet cleaning module is part of a complete system with four robots.

Aqueous Cleaning for Adhesable Surfaces

After manufacturing, fully synthetic deep drawing oil and abraded particles adhere to body parts and reinforcing components made of aluminium and steel which are cleaned in the immersion cleaning system. The parts are riveted, clinched or glued after cleaning, and are subsequently painted. In order to assure flawless adhesion, the surfaces have to be free of grease, oil and stains, and must be dry. Maschinenbau Silberhorn GmbH in Parsberg, Germany, has designed a requirements oriented cleaning system for this purpose which is operated with an alkaline cleaning agent. The parts are inserted into workpiece carriers and pass through two cleaning baths at a temperature of 65° C. Deionised water is used in the three rinsing baths, and rinsing takes place at room temperature. Steel parts are subsequently subjected to a passivation bath. The parts are dried with a recirculating air dryer. The air is warmed up by means of two heat exchangers. Depending upon how the system has been set up, cycle time ranges from 5½ to 7 minutes per workpiece carrier. The cleaning system is laid out for three-shift operation. Parts for 90 vehicles are cleaned per shift. In order to avoid system-related downtime, the cleaning system is equipped with an ingenious media processing unit: A belt filter in the cleaning section continuously filters contamination out of the cleaning agent. Furthermore, a two-stage centrifuge is fed from the ancillary chamber of the media tank which separates aluminium abrasion and deep drawing oil. The rinsing medium is purified strictly by means of bag filters. The rinsing baths are contaminated with bacteria because cleaning agent is carried over when the aluminium parts are processed. This is counteracted by admixing hydrogen peroxide.

Author: Doris Schulz