How do you clean or flush the lines of a Low Pressure Polyurethane (PU) dispensing machine?

Low pressure dispensers of Polyurethane are a very popular machine within the Polyurethane industry, with Manufacturers such as Autorim, Hennecke, Graco, OMS, ISC, Polytec EMC, Covestro to name a few quality manufacturers.

They work by the combining of Isocyanate and Polyol within a mixing chamber to create a chemical reaction which is dispensed in a slow and controlled manner using compressed air, but at low pressure.

Used commonly for applications such as automotive, office seating, flexible foam mattress, cold room or refrigerator insulated panels and SIPs to name a few applications.

As these machines are ‘low pressure’ they do not have the power to clean out PU or elastomer residues from within the pipes and mixing chambers. These residues will start to cure as part of their chemical process and will quickly create blockages or leave residues on mixers heads and valves which can affect mixing quality and consistency.

Therefore, the cleaning of the machine post mix is critical to ensure consistent quality and standardisation on product.

What options are there to flush a Low-pressure PU Mixing machine?

To clean or flush a PU mixing machine you are looking for a product that prevent the PU or elastomer curing and keeping it liquid or inert through the cleaning process and in effect removing its stickiness or ability to cling to parts.

By retarding the curing of the material it remains liquid and effectively pumpable out of the machine, and effectively lubricating the parts to prevent the curing PU or elastomer from binding and sticking.

Many different method have been used for flushing and cleaning pipes of uncured polyurethane such as water(!), polyol, DCM (Methylene Chloride) and other much safer solutions…..but what are the differences.

Water is an unusual solution as Isocyanate uses moisture to accelerate curing, but we have heard of companies using hot water or a mix of surfactant and water to flush, however whilst this is probably the lowest cost option it is very risky!

Polyol is another option as it provides a liquid carrier to push the mixed Isocyanate and Polyol and is inert, however it is relying more on friction and the volume of polyol could be quite high to ensure a relatively clean result.

Dichloromethane (DCM or methylene chloride, methylene bichloride) is probably the best known (and historically the most used) product for flushing of uncured PU compounds from machinery, but it has some very significant drawbacks.

As a solution it is proven and is also relatively low in cost, many have used it successfully for many years….but it is a dangerous chemical with the tendency to burn and has also been classed as carcinogenic. It evaporates into the atmosphere and you do not want to breathe it in, therefore its use has to be carefully controlled and risk assessment updated consistently.

It is difficult to re-use and handle or sieve any waste PU from the flushed material for the safety precautions required and is therefore normally used as a single shot and as such it needs to be removed by licensed waste carriers at a high cost due to it’s safety profile.

Many forward looking companies with strong environmental credentials have removed this product for safety and environmental reasons…..although it is relatively cheap to buy

Non-Hazardous PU Flushing solutions such as EN720 PU flushing compound is an alternative to Dichloromethane (DCM or methylene chloride, methylene bichloride) and instead uses a sophisticated blend of non-hazardous chemistry where the components are focussed on cleaning rather than evaporation and it is safe to be re-used several times and users report much better cleaning ability and performance than Dichloromethane (DCM or methylene chloride, methylene bichloride).

However, it does have a cost implication as it is a premium product designed for performance and safety as well as being biodegradeable

For more information regarding EN720 Non Hazardous PU Flushing Agent please see EN720 PU Flushing Compound