Door entrapment marking Black marks can come from a variety of sources, including floor or road marking from careless handling. They can also come from progressive breakdown of the rubber used to make door seals of washer extractors, inter-compartmental seals on tunnel washers and the black rubber membrane in a de-watering press at the end of the tunnel washer line. This type of tunnel seal or press membrane breakdown is more serious, because it can and does result in regular introduction of annoying black, slightly oily rubber marking on a daily basis, which gradually infects a good proportion of the entire circulating stock (especially of sheets, duvet covers and pillowcases). If this is not spotted and addressed very quickly it can result (and has resulted) in textile replacement costs of several hundred thousand euro for every large textile rental plant affected.
Seals around the door of a washer extractor are not a major part of the problem, because they are not usually in heavy abrasive contact with white textiles or rotating metal. Marks from this cause are more likely to be from occasional entrapment, or possibly from chemical breakdown of the rubber from slight oversouring. Laundry sours are acidic, designed to neutralise alkalinity from residual wash chemicals and from alkali in the raw water. Black rubber door seals are very effective in the presence of alkaline liquors, but some are less resistant to acids and can start to break down in the presence of a little excess acid in every process.
Abrasion marks in the membrane press
Abrasion marks which originate in the membrane press are more difficult to recognise, because they are oily black smudges, similar to those from a washerextractor door seal but with no easily recognisable characteristic. There are two, quite separate, possible causes, both the product of abrasive damage to the membrane rubber itself. The first cause arises from damage to the shape of the press basket, which should be perfectly circular. The basket can be damaged by, for example, by failure of a batch of de-watered textiles to be discharged from the press before the next batch is delivered, and the ‘double batch’ is then pressed. The enormous pressures are sufficient to distort the basket very slightly, so that from then on, the circular membrane is forced to slide up and down in a slightly oval basket. This can damage the membrane on the narrow axis of the oval, creating a mark on most batches of textiles. The first thing to do is to clear the press of textiles and isolate it to ensure it can be inspected safely (including inserting safety props, because the engineer will need to look carefully under the press head). The shape of the press basket should be checked by measurement across several diameters around the circumference. You might be able to get the basket reshaped in an engineering workshop, or it may need to be replaced.
The other problem, which can give rise to similar black marks, concerns the formation of hard crystalline deposits on the sides of the press basket. This can occur, even if the laundry water is being correctly softened down to 0° hardness, because local hotels rarely soften the water to guest rooms. This means that used towels, coming in with typically 15-25% moisture on them, will be introducing calcium and magnesium salts into the tunnel. Overnight (and possibly even during the working day) these salts can react with your laundry chemicals to form very hard crystalline deposits, which adhere securely and ‘grow’ on metal surfaces, including on the walls of the press basket. Eventually, as crystals grow, they become large enough and sufficiently sharp to damage the side of the press membrane every time it descends and lifts. Black press membranes are typically made from black rubber crumb mixed with oil and re-vulcanised, so the black abrasion mark-off created is a mixture of oil and degraded rubber, coloured with carbon black particles. These marks do not come away, even in a good rewash process. The next step is to discuss the laundry chemistry with your supplier, because there is usually chemical solution to prevent the formation of the particular crystals that are the culprit.
Some laundries now specify white membrane press rubbers to avoid the symptoms of breakdown or abrasion of the black ones, but they are more expensive and difficult to make so as to be as longlasting as the black ones. The carbon black provides major reinforcement at the molecular level. It is better in the long run to solve at source the problems of rubber breakdown from abrasion.
Snake bite marks from seal breakdown
A much more difficult problem can arise in a tunnel washer, if neutralisation with an acid is part of the process at the end of the rinse section to keep this near to neutral (that is to maintain a pH near to pH7). Many processes tend to err slightly on the acid side of neutral, which is usually fine so long as the pH does not drop below pH6. Prolonged exposure to low pH will progressively degrade some types of seal rubber and when particles start to break off and get into the white sheeting, they produce a very obvious, tell-tale symptom. The piece of degraded rubber gets trapped between two sides of a fold in the textile, so that under high pressure in the membrane press it produces a double mark on the sheet which looks a bit like a bite from a venomous snake! Once the fault develops, there will be a few marks of this type created every time the head of the membrane press descends. It is not difficult to imagine the ruination, in a very short time, of a good proportion of the circulating stock. The solution is the same as for the washer extractor door seal – the laundry needs to keep spare seals always in stock, to aid immediate replacement. This might be a quick, straightforward job on a washer-extractor, but a much longer and quite skilled task on a tunnel, where the main culprit is probably the seal most exposed to acid at the end of the rinse section.
Pillowcase abuse
Pillowcases make very handy cleaning cloths for the room service staff, who may frequently make use of them for wiping down mirrors, for example. Mirror cleaners contain a wide variety of contaminants, some of which leave permanent marks. Those which contain metallic compounds can usually be seen very clearly under ultraviolet light. Damage from these cleaners is usually terminal and abused pillowcases should be scrapped and the customer charged for the replacements. If a cage of soiled pillowcases is checked with the appropriate abuse-indicator (UV light in this case), it will often be found that a significant percentage of the items are affected in this way (typically one per room). The presence of any metal salts from the mirror-cleaning will show up as dark areas of staining. If this check is made at the hotel in the presence of the Executive Housekeeper, the evidence is difficult to refute! Premature replacement of linen takes away the rental profit and more, so there is no point in worrying about upsetting the customer.
Napkins often suffer from use for cutlery cleaning, which creates black areas of marking which are very distinctive. These are often exacerbated by use of the same cloths for cleaning the kitchen worksurfaces. Once these abuses have been addressed at source it is often possible to recover some of the damaged stock with a good recovery process. Dark protein or aluminium staining from a kitchen wipe-down will often succumb to a high temperature, high alkali wash. Metallic iron stains (from either cutlery cleaning or rusty rainwater contamination) will come off with a high temperature oxalic acid wash (no detergent, just one bath with oxalic acid crystals, followed by three rinses). Consult your chemicals’ supplier for the optimum time-temperature combination.
Using a duvet cover or pillowcase as a bag for other linen
There are substantial numbers of hotel staff who regularly use a pillowcase or a duvet cover as a linen bag. When this is full, they then drag it down the hotel corridor to the chute or lift, drag it across the floor of the basement collection area and refuse to accept any responsibility for the resulting parallel rows of small holes, and lines of surface abrasion, that are quickly created on the fine fabric. Hotels which insist on very fine percale linen are often the worst offenders!
This type of damage can be detected by examination of the holes under 15x or 60x magnification, looking for ingrained dirt and for other debris in the fluff around the hole edges. It is quite common to find heavy decitex carpet fibres in these areas, often in the fluffy edges of holes worn through in this manner. Contamination with carpet fibres is not a laundry symptom! They come from hotel abuse and the scrap linen should be paid for by the hotels concerned.
Dealing with iron and protein combined
Dark protein staining from a kitchen wipe-down will often succumb to a very high alkali wash at high temperature. You should obtain the time/temperature combination, from your chemicals’ supplier, for the particular alkali booster which you are using.
Metallic stains (from either cutlery cleaning or rusty rainwater contamination) will come off with an oxalic acid wash (no detergent, just one bath with oxalic acid crystals; again you should get the timetemperature combination from the your chemicals’ supplier).
If the textiles are affected by a combination of iron oxide marking and protein, which can be positively identified by examination under UV light (see photo), then you should remove the protein first, followed by the iron recovery process. Do not be tempted to combine the two processes into one, because the chemicals for one will neutralise those for the other!
This type of combined staining is time consuming and not worth it for a single item. The best approach is to use a UV lamp on a batch of items (which have all survived the rewash) to identify every item with iron staining, because there will usually be multiple examples. Allowing enough to accumulate for one full washer extractor load is the cheapest way of recovery and is definitely worthwhile!
Conclusion
You might want to keep this and last month’s Material Solutions for future reference. They might help your customer care team the next time you have an awkward customer problem.
