Q&A: Removing Emulsified Oils from Cleaner

By: Carl Izzo 20. June 2013


Q. We manufacture shelving for retail outlets and painted them on a spray paint line for years with no problems. We recently installed an electrocoating system where everything is new, including the cleaner stages, chemicals, type of paint and curing ovens. Now we are having problems with the presence of emulsified oils in our alkaline cleaner which messes up the finish on our products. How can we remove the emulsified oils? W.D.



A. Chemically, you can either change the stamping lubricant or change the cleaning solution chemicals. Physically, you can remove emulsified oils from the alkaline cleaner solution by ultrafiltration. Ultrafilters separate particles from solutions by using selective membranes. This often is done in the pretreatment stages of high-volume finishing lines. With ultrafiltration, the oil is essentially removed as concentrated emulsion from the cleaner solution, and the cleaned solution is then returned to the cleaner stage. This not only makes disposal of emulsified oil concentrate simpler, it also extends the life of the cleaner solution. Ultrafiltration can be done batch-wise or on a continuous basis, depending on the size of the unit and the rate of production. 

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Painting Q&A: Scuffing Of Matte Finishes

By: Carl Izzo 8. April 2013



Q. One of our painted products has a matte finish per a customer request, but we have received numerous complaints that the paint scuffs too easily. How can I scientifically explain why matte finishes scuff more easily than gloss finishes? J.C.


A. Since matte finishes contain more pigment than gloss finishes, there are more pigment particles on or closer to their surfaces. Therefore, when a matte finish is scuffed, it is actually burnished (polished by removing surface or near-surface pigment particles). This results in a change of reflectivity in the scuffed area. Gloss finishes also can be scuffed, but the results generally show as scratch marks.



You should look into the possibility that the vehicle in your paint does not provide the scuff resistance of other paints. You may be able to solve that problem by changing to a more mar-resistant or scuff-resistant material. The better paint may be more expensive, but will be worth the cost if it stops customer complaints.


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Q&A: Spray Gun Flow Rate Problem

By: Carl Izzo 21. January 2013


Q. We have problems achieving consistent paint flow through our spray guns (typical rates range from 10 to 50 g/min). We spray small round parts up to 50 mm in diameter by mounting the parts on spindles and moving them past the spray guns using a chain-on-edge conveyor system, producing about 3-5k parts per hour. The paint is supplied pre-mixed in 2-L tins, and we pump this using a regulated diaphragm pump set at 60 psi. The paint flow is controlled by a flow regulator set at 20 psi and back pressure regulator set at about 18 psi so that the diaphragm pump runs at 3-4 sec per cycle. The fluid flows through air-operated fluid regulators to a maximum of three spray guns.


We find that the fluid flow will alter during spraying at the low flow rates. We are debating changing the fluid hose from the regulator to the gun from a 4-mm bore to 2-mm bore, the theory being that we will require more pressure for the same flow rate. The paint in question is medium solids content, approximately 40 percent, and viscosity of 78 sec using a DIN cup. K.F.


A. Following your theory of stabilizing flow rate by decreasing the hose size and increasing pressure may work. However, there may be other problems such as a faulty fluid pump, faulty regulators and out-of-adjustment gages. Differences in viscosity could also account for the flow rates. You should also consider checking the viscosity of each can of paint before adding it to your system


Rather than trying to solve this problem yourselves, however, your equipment salesman or service representative should be in your plant trying to solve it for you. When you bought the equipment you also paid for technical service, so I recommend calling the equipment supplier for help. 

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Ask The Expert: Coating Textile Braids

By: Carl Izzo 14. March 2012


Q. I am a manufacturing engineer for a company that manufactures various types of hose products. We use textile braid as a reinforcing layer in rubber hose. In our manufacturing process we apply adhesive coatings over certain textile braid for reinforced hose constructions. On other hose items, we apply a lacquer coating over the textile braid. In order to dry out the lacquer coatings, the hose travels vertically through a 50-ft-high tower, passing through a series of electric heating elements. The liquids are applied by spraying. Naturally, this results in a lot of wasted overspray. This is a somewhat antiquated method of coating hose. We would like to investigate the possibility of a more updated arrangement such as electrostatic spraying. We thought you would be aware of some of the newer technologies in other industries which could prove to be of assistance or benefit to us in changing our method of coating hose braid. What do you suggest? L.C.

A. Electrostatic spraying will increase transfer efficiency by reducing overspray. Liquid coatings, which are applied by electrostatic spraying to metallic substrates, can also be applied to non-metallic substrates if they can be made to be electrically conductive. Special surface treatments are applied to wood and plastics to make them conductive. Heating will often produce the same effect also. Since textiles are usually surface treated at the mill during manufacture, a conductive coating can be applied to the filaments before the braid is woven.

Another approach would be using a UV curable, heat-reactive adhesive to coat the braid. UV curable coatings are 100 percent reactive (no solvents) and can be cured instantaneously in a relatively short UV light tunnel, thereby eliminating the need for a long, heated drying tower.

Q: Best type of polymer for a baking enamel?

By: Tim Pennington 29. December 2011
Q. I am a manufacturing engineer in a plant that produces small appliances. We are having trouble with a baking enamel. When a part is rejected because of a paint defect, we try to recoat it, but the second coat won’t adhere to the first, causing us problems. What is the best type of polymer for a baking enamel that allows it to be recoated with excellent adhesion?
To read the answer to this question, click HERE

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