Clean up

25 November 2021

Getting cars and parts clean is a messy affair, but it doesn’t have to be

Abrasive-blasting parts in a cabinet is an excellent way to get them clean. Such cabinets are sealed but the area in which they’re located often ends up getting pretty messy. And using a sand blasting gun on a car body in a curtained area may be effective but the clean-up isn’t much fun. On the positive side, a sandblasting cabinet just sits there, always ready to clean a part as soon as it’s needed, which is why they’re in so many workshops. In the hands of a diligent and attentive operator the results are excellent.

There are ways of achieving the same, or better, results without any mess. Dry ice blasting has always been a good idea for cleaning cars and parts but in times past it has been too expensive for workshops to have their own machines and those that were available for hire were too expensive. However, some automotive businesses have invested in their own ice blasting machines.

Dry ice is frozen carbon dioxide that can be used as a blasting medium for cleaning car bodies and parts in a process similar to sand, or abrasive grit, blasting. Apart from the fact that it’s very effective, the best thing about dry ice cleaning is that it leaves no residue of any kind at the end of the process. The frozen carbon dioxide grains simply evaporate and disappear. Apart from convenience, this is actually part of the reason the process is so effective.

Dry ice blasting cleans in three ways. First, each grain hits the dirt as with conventional abrasive grit cleaning. Second, the temperature of the frozen pellets is about minus 80-degrees Celsius so when each pellet hits the contaminant it causes extremely rapid shrinkage. This loosens the bond between dirt and substrate. Third, when each grain of frozen carbon dioxide makes contact with the surface it instantly changes phase from solid to gas. It’s like a miniature explosion that blasts the contaminants off the surface. As the carbon dioxide gasifies it also blows away the contaminants. These three actions occur so quickly that they’re virtually simultaneous. The instant gasification is why dry ice blasting leaves the substrate untouched. The dry ice grains are also softer than conventional abrasive grit cleaning media.

Dry ice blasting machines used to be very expensive but they’ve come down in price enormously. Some units can be had for $10,000 while others are much more expensive. We spoke with Steamatic about clean cleaning but there are a number of other companies operating in the dry ice cleaning sector like Cold Jet Australia and Kärcher. The ability to clean a part immediately and then get to work on it straight away would be an interesting change to conventional work-flows using a spin washer. As far as cleaning underbodies and in situ parts, dry ice blasting is hard to beat.

But then, there’s laser cleaning.

Lasers of all kinds have come a long way since the first working model in 1960. Laser cutting has virtually transformed manufacturing and now lasers can be used to vaporise dirt and contaminants, leaving a clean surface behind. Cleaning lasers do this very effectively and without damaging the substrate to which the contaminants adhere. Laser cleaning is a brilliant technology but we should point out before we go any further, it’s very expensive. The cheapest units can cost around $50,000. It’s expensive, but the hope is units will become less expensive over time. This is usually what happens with technologies.

Online videos of laser cleaning seem to show sweeping beams, which is what might be expected. However, the types of lasers used in cleaning applications are in the infrared range of the spectrum and thus invisible. When a laser beam hits the surface, it creates plasma and that’s what can be seen. If a beam is simply fired into the air, nothing can be seen.

The laser beam is not solid and continuous like that of a cheap laser pointer. It’s a series of very quick pulses “like bullets”, says Ben from Precision Laser Cleaning (PLC). The pulse duration defines how big each of the ‘bullets’ is and can be adjusted across a range spanning 100 nanoseconds up to one full second. So, the duration defines how long each pulse remains on the surface.

It would be fair to expect a strong heat signature from a laser beam so intense that it can vaporise contaminants. Indeed, the plasma created by the process is actually hotter than the surface of the sun. However, because the pulses are so brief, they don’t have time to transfer heat into the substrate. It’s like passing your hand through a candle flame. If you do it quickly, you won’t get burned, but if you hold it there, you will. Even with very thin alloys, the material underneath the contaminants isn’t damaged. “You might get a three-to-five-degree temperature increase on very thin metals,” says Ben.

So, is light a wave or a particle?

Who knows, but photons are certainly massless things. They must be because the beam is traveling at the speed of light, yet if it’s focused on a five-cent piece balanced on its edge, cleaning it doesn’t knock it over.

The cleaning effectiveness of a laser depends on how the material to be removed absorbs light. Darker materials, like rust and carbon deposits, do so quite readily whereas steel substrates reflect light. This difference of absorption is a key means of affecting one layer and not the other. As the rust or other contaminant absorbs energy from the laser, the molecules become highly active and expand – which breaks the bond with the substrate. The contaminants then turn to dust and fumes. This is not to say that lighter coloured contaminants can’t be removed, they can. White paint is highly reflective but it can still be removed, though it will take more time. Black paint can be removed three or four times more quickly than white paint.

Laser cleaners are easy to use but some knowledge is required. Various parameters need to be adjusted to achieve the best result. There’s the pulse duration, the frequency and the RPM of the circle traced out by the beam. It’s not just a matter of plugging it in, turning the power up or down and going for it.

Some people believe that a laser cleaner is akin to a magic wand that can do anything. This is incorrect. Sometimes dry ice blasting is better suited to a job than laser cleaning, and vice versa. Ben suggests that if a person rang wanting to get all the paint off a white car with a laser, he’d explain that laser cleaning would be about the most expensive and slowest way of doing it. Dry ice blasting would be much more effective. However, a car on a rotisserie with a rusted underbody might be a good fit for laser because it wouldn’t have to be transported to a facility.

So far we’ve covered essentially exterior cleaning systems. What about interiors?

Steamatic operates an odour elimination system called Biosweep. A while ago, a luxury car dealer suffered a factory fire that left some of its stock smoke damaged. A Biosweep canister was placed inside a Ferrari, which was then sealed and left overnight. In the morning the smoke odours were gone. How?

Biosweep is what’s described as a photo-catalytic conversion machine that creates ozone and hydrogen peroxide gases. Anyone who understands electric motors will not be surprised to learn that ozone is created by spark generation. The spark reacts with the air to create O3 – ozone. It’s interesting that we need O2 to live, but O3 is poisonous to us. Older types of ozone generators also created nitric oxide which, combined with moisture in the air, creates nitric acid. Careful masking was necessary with such machines because they could cause damage to things. Also, such machines were slow-acting which exacerbated the nitric acid problem.

Biosweep is an improvement in that along with ozone, it creates hydrogen peroxide gas, which reacts more vigorously with contaminants and penetrates more deeply. It penetrates carpet and upholstery particularly effectively. The system also deals extremely well with odours from cigarette smoke. Biosweep is a clean cleaning technology in that no scrubbing or chemicals are required. 

Often these didn’t work terribly well anyway. It’s important to note, however, that if the source of the odour isn’t removed, Biosweep will get rid of it but it will return after a while. So, if someone has thrown prawns under a seat, they’ll have to be cleaned out before treatment with Biosweep.

Killing bacteria and viruses is set to become a fixed part of our lives going forward. This is often achieved with various lotions and potions that are wiped or sprayed onto surfaces. SP Tools has taken a clean and clever approach by combining high-energy UV-C light with a standard LED work light. UV-C light is capable of disrupting the reproductive function of viruses. SP Tools say that the light can work as quickly as a couple of seconds. Of course, UV-C light can be damaging to humans so the SP Tools light has features that prevent overexposure. Officially, the SP Tools worklight is called the UV-C Disinfection Light SP81479 and we predict these little units are going to appear in workshops everywhere. 

These products and techniques really do take the mess out of cleaning. 

Words: Paul Tuzson. As featured in Australasian Automotive April 2021.