Stephen Pick, who runs Service Machinery Ltd (SML) supplies and supports customers with drycleaning machines from the innovative German manufacturer Böwe.
Pick said: “Since the company foundation 75 years ago Böwe have been at the forefront of innovation in drycleaning and this continues to be true today.”
Böwe offer both perc and multisolvent machines.
“The MultiSolvent® label means we can support any of the alternatives to perc now offered, and with some of these offering cleaning performance similar to perc, but with ‘green’ credentials we are seeing a shift towards these solvents,” said Pick.
As far as the hardware is concerned Böwe machines have evolved along a separate path and remain today unique in the industry in many important areas. “For instance , the distillation system. Built from a titanium-enriched grade of stainless steel (316Ti) the still is cylindrical. This serves two purposes.
“First it makes for a much stronger shape which is important when operating under a 1000mb vacuum which is how Böwe keep the distillation efficient and safe when using flammable solvents in our MultiSolvent® (M) machines.
“Secondly it means there are no corners to try and dig the sludge out of, making manual raking much easier.”
Another key to the Böwe distillation success story is a temperature sensor used by the computer to assess the progress of the distillation process. “The process varies slightly depending on if we are distilling in an ‘M’ machine or perc, “said Pick.
“With an ‘M’ we halt the still heating at around 95ºC. This allows the low boiling components (mostly water) to evaporate first and be collected in a separate tank, the temperature is then increased to boil off the solvent and this is routed to the water separators. This process is known as fractional distillation and allow the separation of water before the high temperature boiling process. “In a perc machine the solvent separates easily enough so the fractional step is not needed but the temperature of the still floor still provides important information for the computer to control the process. It is a fact that while significant quantities of solvent are boiling off the still will not exceed about 125ºC, latent heat of evaporation sees to that, but as the solvent concentration decreases the temperature starts to rise.”
At this stage a Böwe machine will circulate the residue with the sludge pump. This drives more solvent off and has a scrubbing action on the still floor, next water or steam is injected. This makes an anisotropic mixture which boils violently driving off more solvent and lowering the still temperature so again we wait for the still temperature to rise.
“Finally, by about 140 degrees there is very little solvent, and no water, left so the residue can be pumped to the barrel. A return line ensures air displaced from the barrel goes back to the still which is why we call it our ‘Emissions Free Still Rake-Out System’. There is no smell and the operator is not exposed to the still residues.” Böwe machines are also well known for their drying performance.
“Todays drying systems were designed and developed to dry the more ‘difficult’ alternative solvents in a reasonable time and a happy by product of that effort is that they dry perc very well indeed. “Another happy coincidence is that a Böwe perc machine will convert to multisolvent operation with the addition of some safety monitoring features and a different design of water separator making it a truly futureproof machine.”
Pick goes on to explain that control makes Böwe different. “In this case control of the dip level in the cage ensures a consistent and correct dip level. “Without using the low level sensor a first bath low dip is made by a timed pump-up. This is roughly one litre per second but of course depends on the condition and efficiency of the pump and there being enough solvent in the tank. “If there is enough solvent a considerable amount could be absorbed by a ‘heavy’ load which means there could be insufficient to provide the correct wash (mechanical) action. Similarly, a light load, of silks say, would not absorb much solvent and there would be too much solvent again preventing effective washing and resulting in an excess to be distilled. “The answer is to measure and control the dip level.
The Böwe PremiumLine does this, pumping up until the level is made and then adjusting the level if required, even switching to another tank if the dip cannot be made or maintained from the one selected. Meaning the correct amount of solvent is always used, the wash action is always as desired, and no excess solvent is distilled. “There is also a sensor provided for control of a high dip.”
Böwe Innovation extends outside traditional drycleaning and two recent examples of the application of Böwe technology are:
With this system, available now on the BÖWE PremiumLine, the solvent from the first bath is measured, optically, to see how dirty (or coloured) it is. If it is not dirty it is pumped back to the working tank to be used in the next cycle. If it is dirty it is pumped to still in the normal fashion. Turbidity measurement can help avoid unnecessary distillation potentially saving huge amounts of energy in the right cleaning process.
Disinfection in drycleaning
Long thought to be the preserve of the laundry process, Böwe has developed the technology to reliably disinfect linens in a drycleaning machine. An obvious application is in the cleaning of surgical cloths which can be contaminated with glues etc which cannot be laundered out but require disinfection to approved standards in a one step process. Said Pick: “All of the above-mentioned technology is either standard fitment or available as an option on any of the currently available Böwe drycleaning machines.