HS Marston Uses Modified Alcohol to Achieve Highest Technical Cleanliness

HS Marston Aerospace Ltd is renowned for its heat exchangers in the commercial and military market.

As part of Collins Aerospace — a unit of Raytheon Technology — the company manufactures a wide array of heat exchangers including plate and fin, laminated, shell and tube, as well as cold walls, cold plates and cooling panels. 

Cleaning of heat exchanger components is a quality-critical process step.

“The complex geometries make it difficult to get these parts clean and dry, which is necessary for the subsequent brazing. Here, even very tiny residue can cause failures, which can lead to leakage”, says Andy Lees, Site Lead, Operations. 

Cleaning is also key to protecting the furnace since residual oils left on parts will be burnt in the chamber, and this could cause long-term damage. 

Today, at its site in Wolverhampton, UK, HS Marston runs three closed machines on the modified alcohol grade DOWCLENE 1601 for the cleaning of different component parts. The oldest machine was installed in 2011. Since then – thanks to the high stability of DOWCLENE 1601 – not one single bath exchange has taken place. Due to the processing steps involved, such as brazing, assembling, and machining, the parts typically go through 3 rounds of cleaning during the entire manufacturing process. 

While HS Marston now has a reliable fleet to deliver efficient and consistent cleaning results, they have been through some twists and turns in their cleaning journey to get to where they are today. 

HS Marston is a specialist in the manufacturing of different heat exchangers.HS Marston is a specialist in the manufacturing of different heat exchangers.

Decade Long Search for the Right Cleaning Solution

Back in the 1990s, HS Marston relied on trichloroethylene (TRI) in an open-top degreaser for component cleaning. Whilst the solvent had always delivered satisfying results with low maintenance requirements, concerns related to environment, health, and safety (EHS) necessitated the search for an alternative. 

For a brief period in 2003, HS Marston experimented with water-based cleaning. Due to staining on parts surfaces and insufficient drying, it became quickly apparent that this would not make for a feasible long-term solution. 

Later on, it adopted n-propyl bromide (nPB) in a closed cleaning machine. Stability was proving to be a major issue, with roughly 15% of the parts cleaned needing to be scrapped. The solvent also corroded the seals in the machine, posing a massive EHS issue; as of 2020 the substance is no longer legally available to use for component cleaning due to REACH. 

In 2009, HS Marston turned to hydrofluorocarbon (HFC) used in an open-top degreaser. Although the fluorinated solvent did a reasonably good job in cleaning, there were two major problems. First, it was very expensive to run. Solvent spending averaged £50,000-60,000 per month because of the high solvent consumption. Secondly, the chlorinated molecule contained in its formula went against the parent company’s plan to prohibit chlorine in their facilities. 

Modified alcohol DOWCLENE 1601 – A revelation 

The SAFE-TAINER System ensures the safe and sustainable transport, storage and handling of solvents.The SAFE-TAINER System ensures the safe and sustainable transport, storage and handling of solvents.It was only when HS Marston discovered DOWCLENE 1601 in 2011 that they could finally put to rest their decade-long search. Based on modified alcohols, DOWCLENE 1601 is a distillable solvent and has a wide range of approvals in the aerospace industry including Rolls-Royce and SAFRAN. 

Thanks to its lipophilic and hydrophilic properties, DOWCLENE 1601 can remove oils and greases just as effectively as certain polar contaminations like cooling emulsions or solids such as particles and abrasives. The solvent is also characterized by low toxicity and good biodegradability. 

“We couldn’t believe how clean the products came out and how the quality had improved as such. It was really a revelation,” says Lees. The modified alcohol solvent was quickly adopted and used in combination with the company’s first vacuum-closed cleaning machine. 

Quality or Sustainability? It Doesn’t Have to be One or the Other 

In 2016, HS Marston contemplated the acquisition of another cleaning machine and undertook a series of intensive trials with different cleaning solutions. 

“We wanted to convince ourselves again. We did lots of trials with various machine manufacturers on different cleaning media. We included trials with DOWCLENE 1601 and perchloroethylene too,” Lees says. “Part of us thought perhaps we could still convince our parent company to let us use chlorinated solvent. During the trials, we expected perchloroethylene to perform better than DOWCLENE 1601, but actually, there was no difference for our specific application.”

For the evaluation, quality was a major weighting factor because the parts needed to be cleaned to the highest standard to facilitate brazing in the next stage. The rigorous technical demand must also comply with the corporate’s sustainability protocol, which seeks to eliminate any chlorinated element. 

While the flammability of modified alcohols had raised some internal concerns, the company also recognized that the small risk could be adequately countered by all the proficient safety features modern vacuum cleaning equipment provided. The final decision fell back on DOWCLENE 1601 to be run on a second new machine since it was the only available option that could truly satisfy the diverging interests.

COMPLEASE Chemical Leasing Has Everything Covered 

When HS Marston first adopted DOWCLENE 1601, it already took advantage of COMPLEASE, a customized chemical leasing package offered by SAFECHEM. For a fixed monthly fee, this offering covers not only the supply of fresh solvent and take back of used solvent in the SAFE-TAINER System, SAFECHEM’s proprietary solvent risk management measure. It also includes test kits and stabilizers, lab services, solvent trainings as well as technical service and consultancy to optimize the parts cleaning process. 

The scope of the contract has been further expanded to cover the additional solvent consumption of DOWCLENE 1601 and associated services when the company added two more machines to its fleet. 

The Proof Of The Pudding – Real Savings 

HSMarston2For HS Marston, the benefits conferred by its now well-established cleaning process go far beyond quality cleaning. The company has also been able to make significant financing savings while preserving the environment. 

According to HS Marston’s own analysis, the efficiency of its parts cleaning helps cut greenhouse gas emissions by around 225 tonnes of CO2 per year – equivalent to the annual emissions from around 20 cars or the energy usage of 10 homes per year. Solvent spending is down by at least 50%, while cycle times are halved. Rejection rate of parts is only 1% – and not cleaning related. 

“When you look at the energy costs required to run the machine, the long cycle time anywhere between 60 to 90 minutes, and also the energy consumption for drying the parts – it all has a negative impact rather than a positive one,” Lee says. “We have done lots of trials with aqueous cleaning, and we simply couldn’t get through because the process was just far too complicated for our specific application.”