What is static electricity?
As the name itself indicates, static means stationary, electricity refers to electric charges. It is a phenomenon occurring due to imbalance in electric charges. The imbalance results in excess charges on the surface the material. These charges remain on the surface until they find a path to discharge.
What causes static electricity?
Many factors contribute to creation of static electricity:
a) Contact and separation (friction):
Whenever two dissimilar materials come in contact with each other and separate, one of the materials loses electrons and the other gains electrons. This phenomenon is called “triboelectric effect”. Static charges are developed on the surface of one of the material depending on its relative position in triboelectric series.
b) Changes in temperature
Changes in temperature cause separation of charge in the atoms or molecules of certain materials. This is called “pyroelectric effect”.
c) Changes in pressure
Applied mechanical stress generates a separation of charge in certain types of crystals and ceramic molecules. This is called “Piezoelectric effect”.
A charged object brought close to an electrically neutral object causes a separation of charge within the neutral object. This results in static charges.
What is triboelectric series?
A study has been done by rubbing dissimilar materials against each other under controlled conditions to observe their tendency to gain or lose electrons. Depending on their tendency to gain or lose electrons, the materials have been arranged in a particular order referred as “Triboelectric series”. A material in triboelectric series has a tendency to get positively charged when rubbed against a material which is ranked below it.
What materials develop static electricity?
It is difficult to ascertain as to which materials develop static electricity and which materials don’t. There are many other factors contributing to generation of static electricity. They are:
- Applied forces
- Separation rate
- Relative humidity
How do we measure static electricity?
It is difficult to measure static charges in coulomb – the SI unit of electric charge (equal to the quantity of electricity conveyed in one second by a current of one ampere). An easier method is to measure static charges in terms of surface voltage in kilo volts (kV) using a static charge meter.
Valstat static charge meters measure ±20 kV at 25 mm distance from the surface of substrates and higher voltages at proportionally higher gaps.
How does humidity affect static electricity?
Static charges are less in humid conditions and more in dry atmosphere.
What are the problems associated with static electricity?
In many industrial processes, static electricity is known to create many problems such as:
- Dust attraction
- Operator hazard
- Sparks leading to potentially hazardous situation
- Slowing down of the process due to frequent stoppages
- Quality issues
Which industries face problems from static electricity?
Problems due to static electricity are common in various industrial processes. Typically, each and every industry is exposed to the effects of static charges in some way. A few industries where the static charges are predominant are:
- Flexible packaging
- Plastics and resin
What are the methods of eliminating static charges?
There are various methods to eliminate static charges. The popular ones are using active static eliminating systems, passive static eliminating systems and air based active static eliminating systems. However, elimination of static charges is a temporary phenomenon as they may reappear in other processes / places and hence they must be addressed in all likely places of occurrence.
What are active static eliminators?
Active static eliminators are the ones which rely on AC or DC power supply which generate high voltages. This high voltage in turn helps in generating ions of positive and negative polarities which will help to neutralise excess charges present on the surface of the target substrate. They are best suited to eliminate static charges from fast moving webs, sheets, films and such.
What is a passive static eliminator?
A passive static eliminator is one which does not depend on an electric power supply to function. These are generally in the form of a brush or pad connected to ground. They help to drain excess charges from the substrate to the ground. These are best suited to considerably reduce the high static charge levels from substrates such as moving sheets, films, as they do not completely eliminate static charges.
What is the difference between AC and DC static eliminating systems?
AC static eliminating systems work on AC power supply. They contain a set of electrodes generating positive and negative ions during respective cycles of AC supply.
DC static eliminating systems work on DC power supply. They contain two separate sets of electrodes. The electrodes connected to positive DC supply generate positive ions and the electrodes connected to negative DC supply generate negative ions.
What is an air based static eliminator?
Air based static eliminators are active static eliminating systems (either AC or DC) working along with an air stream generated by fan or blower in order to accomplish a longer range of ion reach.
What type of static eliminating system to choose for my application?
Selection of a particular static eliminating system entirely depends on the application.
- On fast moving webs, sheets, and films, Valstat® AC bars are recommended.
- On unwinders and rewinders, due to the requirement of longer range of ion reach, Valstat® DC bars are recommended.
- For 3-D objects and in difficult to reach applications including light to heavy duty blow off cleaning, Valstat® air based static eliminators are recommended.
- For reducing static charge levels in explosion prone areas, Valstat® explosion proof static eliminators or a Valstat® passive brush, depending on quantum of static charges generated, is recommended.
Further, the selection of static eliminating systems depends on many factors such as line speed, type of substrate, intended location of installation, and many more. Please get in touch with our product office to discuss application specific details and appropriate recommendations.
Can static charges be eliminated permanently?
Permanent elimination of static charges is possible by the use of antistatic oils / additives. But they could be detrimental to the manufacturing process and hence are not usually preferred.
What is the material of construction of a Valstat® static eliminating bar?
AC and DC static eliminating systems are available in various specifications. The electrodes are either housed in an engineered plastic enclosure or powder coated aluminium enclosure depending on the requirements of a particular application.
Which is more effective? An AC bar or a DC bar or an air based system?
All the static eliminating systems do the same job of generating ions. It is the application which decides the appropriate system to use.
What do you mean by effective length (EL) and overall length (OL)?
Effective length of the static eliminating bar is the active working length to which the electrodes of the bar are lined up. Overall length refers to the total length of the bar including the enclosure.
While effective length (EL) is decided by the maximum working web width, the overall length is decided by the machine inner frame-to-frame length. Contact our product office for your requirements and available standard lengths.
What are the input power supply specifications for Valstat® AC and DC static bars?
Valstat® AC bars operate under 240 V, single phase, 50 Hz AC power supply while Valstat® DC bars work on 24 V DC power supply
Why Valstat® static eliminating bars work on high voltages?
It is observed that the ion generation rate is high when the voltage is high. Hence Valstat® static eliminating bars work on high voltages.
What is the recommended mounting arrangement for Valstat® static eliminating bars?
Valstat® static eliminating bars are provided with sliding type mounting brackets affording ease of installation. Detailed instructions regarding mounting are shared in our instruction manual.
Will the Valstat® static eliminator give a shock upon touching it?
Valstat® static eliminators are shock less and spark free. Though the operating voltage is in the order of kilo volts, the current is limited to a few milli amperes and hence it will not yield any shock upon touching the electrode.
What is the length of high voltage cable supplied with the static eliminators?
As a standard scope of supply, we supply 2 m of input high voltage cable along with static eliminators. Extra lengths as per requirement can be provided at additional cost. However, the total length including length of bar and cable shall not exceed 15 m.
How far must be the Valstat® static eliminating bar placed above a moving film for effective static elimination?
The distance between Valstat® static eliminating bar and the moving substrate shall vary in any range between 25 mm to 300 mm. This also varies with line speed and type of substrate. Please contact our product office for appropriate suggestions.
Will Valstat® static eliminating bars work if installed opposite to metal rollers?
No. The Valstat® bars are not recommended to be installed against metal rollers as the ions generated by the static bars tend to get earthed through the metal rollers which are attached to the machine frame, rendering them ineffective.
How do I check if the Valstat® static eliminators are working fine or not?
We recommend you to buy a Valstat® static charge meter which helps you measure the static charge levels on the substrate before and after the static eliminators. This is the easiest way of checking the working of static eliminators
Can the Valstat® static eliminators be used in explosion prone areas?
Regular static eliminating bars cannot be used in explosion prone areas like print stations of a printing machine. Separate ATEX certified explosion proof Valstat® static eliminating systems are available for such applications. Please consult our product office to know more.
What happens if active static eliminators are used on metallised films / inks?
Only some specialised applications involve handling metallised inks/films. It is not recommended to use active bars in such applications. We suggest using passive discharging systems in such cases.
What are the general maintenance requirements of Valstat® static eliminators?
Valstat® static eliminators are easy to operate and require very less maintenance. The electrode tips have to be cleaned regularly using a nylon brush. The bars have to be cleaned to remove dust, dirt and scales regularly. Details have been covered in our instructions manual regarding the same.
How do Valstat® passive brushes eliminate static charges?
The passive brushes are made up of 35 micron controlled resistivity fibres. The fibres are extremely soft and durable and are housed in a powder coated aluminium section. When positioned very close or just about touching a charged web, Valstat® passive brushes will minimise the static charges and send it to ground. Hence they are ideally suited for applications in hazardous areas.
How does a passive chord work?
A passive chord is a metallic string which when placed touching the web or just about touching the web will discharge the static charges and send them to ground.
What are the uses of Valstat® antistatic touch pads?
Antistatic touch pads help to drain off the static charges present on human body. Valstat® antistatic touch pads contain a static dissipative layer which will conduct the static charges safely to ground and keep the humans safe of unwanted static charge build up.
VALFLOW ink pumps
Why do you need an ink circulating system?
Inks used in rotogravure and flexographic printing are “thixotropic” in nature. When kept in a stationary condition, the inks tend to thicken as against when agitated and circulated where they tend to thin out. It is just like a ketchup bottle – when the bottle is shaken, the ketchup tends to come out quickly as against trying to pour the ketch up from a bottle which was at rest for quite some time. Hence there is a continuous need to circulate ink between the print deck and the ink tank.
What types of pumps are available for ink circulation?
Centrifugal, diaphragm and peristaltic pumps are commonly used for ink circulation.
What is the difference between centrifugal, diaphragm and peristaltic pumps?
Centrifugal pumps use an impeller to pump the fluid. The working fluid enters the pump impeller along or near to the rotating axis and is pushed radially outward into the outlet.
Diaphragm pumps are air driven pumps (pneumatic pumps) which operate by the movement of two flexible diaphragms that move back and forth, alternately filling and emptying two chambers.
Peristaltic pumps are also known as tube pumps. They have a flexible tube which passes through a head which is squeezed by two rollers that push the ink to the print deck.
Which type of pump is best suited for ink circulating application?
Valflow® centrifugal pumps are best suited for ink circulating application as they help mixing and agitation of the ink and give an impeccable flow.
What is the flow rate of Valflow® centrifugal pump?
The Valflow® centrifugal pump gives a flow rate of 95 litres per minute of water at 23 oC at 1 m head.
How do Valflow® centrifugal ink circulating pumps differ from other pumps?
Valflow® centrifugal pumps are specially designed keeping in mind the needs of rotogravure and flexographic presses. They give an impeccable flow required by the printing process while promoting ink mixing and agitation.
Valflow® ink pumps are quick demounting type pumps. The motor and pump can be separated quickly by removing two retaining pins which facilitates quick changeover and easy maintenance.
Are Valflow® ink pumps suitable to operate in explosion prone areas?
Yes. Valflow® ink pumps are equipped with flame proof motors which are safe to operate in explosion prone areas.
What is the outlet size of Valflow® ink pump?
The Valflow® ink pumps are equipped with a ¾ inch outlet.
How should be the Valflow® centrifugal ink pumps installed on an ink tank?
The ink tanks supplied by Valence have a cut out on the tank lid which is suitable to mount the Valflow® centrifugal ink pumps.
What are the maintenance requirements for Valflow® ink pumps?
Valflow® ink pumps require very low maintenance like cleaning the impeller once in a while. Standard operating and maintenance procedures are shared in our instructions manual.
VALFLOW ink filters
What are the contaminants of ink?
What is the importance of an ink filter?
The metallic particles may get in between the doctor blade and cylinder scoring off the expensive cylinders and cause streak marks on the printed film. Also, the dust and undiluted pigments affect the print quality. Ink filter helps to eliminate these contaminants to provide better print quality, enhance the life of doctor blades, cylinder and anilox rolls.
What is the Valflow® ink filter made of?
Valflow® ink filters have a 30 or 60 or 90 mesh cartridge housed in Teflon coated Aluminium casing. The filter has a magnetic filter cap. The cartridge helps to trap the physical dust and contaminants in the ink while the magnetic cap helps to trap the metallic contaminants in the ink.
What are the inlet and outlet size of Valflow® ink filters?
Valflow® ink filters have inlet and outlet sizes equal to ¾ inch.
What are the maintenance requirements for Valflow® ink filters?
Valflow® ink filters are very easy to maintain. The filter cartridge has to be cleaned periodically depending on contaminants accumulated therein. However a spare cartridge can be kept to quickly replace the dirty cartridge to ensure hassle free operation. Detailed operating and maintenance procedures are shared in our instructions manual.
VALFLOW ink conditioners
What are the reasons for solvent evaporation in gravure / flexo printing?
Ink is a mixture of pigments and solvents. The solvents are volatile in nature and have a tendency to evaporate quickly. Solvent evaporation from ink in gravure and flexo presses occurs due to:
- Rise in ambient temperature which triggers evaporation of solvents
- Heat addition by film coming out of dryer getting in contact with ink
- Friction between doctor blade and cylinder generates heat which is transferred to ink
- Pressure of the anilox roll on the print cylinder generates heat
The above factors also contribute to the increase in temperature of ink which promotes solvent evaporation
How does temperature affect the printing process?
Solvent evaporation: High temperature increases the rate of solvent evaporation. As the solvent evaporation increases, it results in
- Higher top up solvent consumption leading to increased operating costs
- Under high temperature ink tends to thin out prompting the operator to add more fresh ink to get the desired print shade. This increases ink consumption.
- Due to continuous solvent evaporation, there is a high concentration of solvents in air resulting in strong pungent solvent odour in shop floor.
Poor print quality: Under high temperature, the ink in the gravure cells on the print cylinder tends to dry quickly before getting transferred onto the film. This causes missing dots resulting in poor print quality.
What is the ideal ink temperature for rotogravure / flexographic printing?
The ideal ink temperature is between 25 to 26 oC for rotogravure / flexographic printing. But it is important to note that the temperature of the ink is never less than the dew point temperature in order to avoid condensation problems.
What is dew point temperature?
It is the temperature at which the water vapour in atmosphere begins to condense to form water droplets.
What is ink cooling? Why do we need to cool the ink?
Ink cooling is the process of bringing down the temperature of ink to the desired value. This is important to prevent solvent loss due to evaporation and enhance print quality.
How does the Valflow® ink temperature stabiliser (ITS) work?
Valflow® ink temperature stabiliser (ITS) is a shell and tube type heat exchanger. The warm ink passes through the inner tubes and chilled water circulates in the outer shell.
The temperature of ink is continuously monitored by a temperature sensor. As the temperature increases more than the set value, the temperature controller operates a solenoid valve connected to the chilled water line. As the chilled water flows into the ink temperature stabiliser, the warm ink loses heat to chilled water.
What are the benefits of using Valflow® ink temperature stabiliser?
Valflow® ink temperature stabiliser helps to achieve
- Lower solvent evaporation and hence less top up solvent consumption
- Better print quality due to improved dot gain
- Less solvent odour on shop floor due to lower concentration of solvents on shop floor
Does Valflow® ink temperature stabiliser help to maintain ink viscosity as well?
By maintaining the ink temperature, solvent to pigment ratio can be maintained and hence the viscosity can be controlled to an extent. Since solvent evaporation happens even at an ink temperature of 25 oC, viscosity variation happens even at this temperature. Hence it is suggested to install a Valflow® ink temperature stabiliser and later install a viscosity control system if required.
Is the temperature sensor flame proof?
Yes. The Valflow® ink temperature stabiliser comes with a flame proof temperature sensor.
What are the requirements to operate the Valflow® ink temperature stabiliser?
a) Chilled water temperature: 10 oC to 12 oC
b) Chilled water flow: 25 liters per minute per print station
c) Approximate tonnage requirement: 1 TR per print station
d) Type of water for chiller: Demineralised water
e) Piping and insulation for water lines between chiller and each print station
f) Chilled water tank of appropriate capacity.
Does Valence help in installing the Valflow® ink temperature stabilisers?
Installation shall be done by the customer as per instructions. Valence can help to commission these systems by deputing an Engineer on chargeable basis. Please contact product office for more details.
What are the input power requirements for the controller?
A 24 V DC input power supply is necessary to operate the controller.
Does Valflow® ink temperature stabiliser come along with a chiller?
No. Valence doesn’t supply chiller along with the Valflow® ink temperature stabiliser. Valence can help with identifying the technical specifications of the chiller required for this particular application.
What type of hose has to be used for water and ink ports?
It is suggested to have flexible hose connections for water and ink lines to ensure ease of operation.
What are the inlet and outlet size of ink and water ports?
Both the inlet and outlet sizes of ink and water ports are ¾” in size.
What are the maintenance requirements of Valflow® ink temperature stabilisers?
The maintenance of Valflow® ink temperature stabilisers is very easy. The heat exchanger needs to be cleaned periodically. Also it is necessary to ensure the usage of clean demineralised water in order to prevent the choking of solenoid valve. Standard operating and maintenance procedures are given in our instructions manual.
What is the approximate payback period of Valflow® ink temperature stabilisers?
It is observed that by using Valflow® ink temperature stabiliser, there is a saving of approximately 25 to 30% in the top up solvent consumption. These systems offer a very attractive payback of about 9-12 months.
What is viscosity?
Viscosity of a fluid is the measure of its resistance to flow. Lower the resistance, lower is the viscosity, and vice versa.
How is viscosity measured?
The SI unit of viscosity is Poiseuille. Since it is difficult to measure viscosity in this unit, standard cups such as B4 cup or Zahn cup are used. The fluid is filled completely in the cup with a standard opening. The time taken by the fluid to drain completely off the cup (time of fall) is calculated in seconds which gives a fair idea of the viscosity of fluid.
What is the need to control viscosity of ink?
The variation in viscosity affects print shades.
If the viscosity is high, the ink will be thick in nature. This consumes more ink and yields darker print shades.
If the viscosity is low, the ink will be thin in nature. This consumes more solvents and yields lighter print shades.
What is the reason for change in ink viscosity?
Main reason for change in ink viscosity is the change in temperature. As temperature increases, the solvents evaporate from ink and causes variation in solvent to pigment ratio. This in turn results in viscosity variation.
How does the Valflow® ink viscosity controller work?
The Valflow® ink viscosity controller is an automatic and inline viscosity monitoring and control system. The viscosity measurement is done by using acoustic wave technology. The robust acoustic wave sensor dynamically measures the ink viscosity and signals the controller to operate solenoid valve for solvent addition.
Which industrial processes use hot air?
Hot air is most commonly used source of heat energy in many industrial processes. Certain industrial processes like drying rely on hot air as a process requirement while some processes use hot air for heating, sterilization, curing, melting, shrinking, welding, dissolving and so on.
How is hot air generated?
Hot air is generally produced by various means such as using electricity, furnace oil, diesel, pet coke, wood, briquettes and so on.
How does a typical hot air dryer work?
The air as required by the dryer is drawn from the ambient and heat energy is added to it by direct or indirect heat transfer depending on the type of fuel used for heating. This hot air is used by the drying process as required.
How can the waste hot air be put to beneficial use?
Upon the usage of hot air, it is either exhausted or recirculated back in the drying process. In cases of recirculation of hot air in dryer, it is very important to monitor the concentration of solvents in the recirculated air as an increase in the concentration of solvents involves risk of fire hazards.
Another solution is to recover the sensible heat energy from the exhaust hot air and use this to pre-heat fresh air. This will reduce heating load required to heat up the fresh air and hence offers attractive cost savings.
What is Lamiflow air-to-air heat exchanger?
The Lamiflow air-to-air heat exchanger is a plate type heat exchanger comprising multiple, thin, slightly separated plates with large surface areas for effective heat transfer with minimal pressure drop.
The Lamiflow contains separate paths for the two air streams – fresh air and exhaust air which cross each other without mixing with each other. The hot air loses heat to the fresh air which gets preheated.
What is the efficiency of the Lamiflow heat recovery system?
Lamiflow systems can help to recover up to 25% of waste heat energy. It has been found that at higher temperatures, Lamiflow is able to recover significantly higher fractions of heat.
What temperatures can a Lamiflow waste heat recovery system handle?
Lamiflow is designed to handle air temperatures up to 200 oC.
What are the requirements to install the Lamiflow system?
Ducting arrangements for fresh and hot air, mounting arrangement for the heat exchanger have to be done before installing the Lamiflow system. Please get in touch with our product office for detailed recommendations.
How to overcome pressure drop in the entire drying system due to installation of Lamiflow system?
Addition of a new element in an existing system will cause pressure drop. Please contact Valence to discuss application specific details such as existing blower capacity, rated blower motor current, type of motor starting, damper positions and so on to get appropriate recommendations.
What is the payback of Lamiflow system?
Lamiflow offers very attractive payback of about 6-12 months for the investment.
What support does Valence provide in doing fresh and hot air ducts?
Valence provides recommendations on the type and size of ducts, insulation, mounting arrangements and related details. Please get in touch with the product office for more details.
What are the maintenance requirements of the Lamiflow system?
Maintenance requirements are minimal for the Lamiflow. The heat exchanger needs to be cleaned by hot air circulation once in a while. Contact our product office for details on the operational and maintenance aspects.
What is a web?
Web is any layer of paper or a flexible film which is unwound from a roll, transferred through series of processes. This continuous long layer of paper or film is referred to as web. After processing, if the web is wound back into a roll form, we refer it to as web to web process. If the web is cut or slit into sheets after process, we call it a “web to sheet” process.
What is web cleaning?
Web cleaning refers to removal of dust, dirt and contaminants from fast moving webs. This is a very important surface preparatory process in order to ensure good print / coat quality on web.
What are the typical areas of web cleaning?
Many applications such as label printing, coating, magnetic tapes, and X-ray films require good surface preparation to get high quality end product. Web cleaners are very important in such applications.
What is a non-contact web cleaner?
A non-contact web cleaner is a type of web cleaner which cleans the web without actually touching the web. It comprises:
1) Static eliminator which removes the static charges on the web.
2) Web cleaning station which breaks the boundary layer of air accompanying the fast moving webs.
3) Air flow unit for vacuum suction of loose dust, dirt and lint from the web.
The output is clean and dust free web for the process.
What is a contact type web cleaner?
A contact web cleaner is a type of web cleaner which cleans the web by physically getting in contact with the web. It comprises:
1) Tacky cleaning roll
2) Replaceable adhesive roll
3) Static eliminator
The tacky roll picks up loose dust and dirt from the web. The picked up dust and dirt are transferred to an adhesive roll. The adhesive roll comprises layers of multiple adhesive sheets. Once a layer of adhesive roll is filled with dust, it can be easily peeled off exposing new layer of roll to pick up dust.
How to choose the particular web cleaner?
In certain applications like pharmaceutical, contact cleaning is not preferred as the application demands absolute no contact of external body with the web. In such cases non-contact cleaners are preferred. In other cases, contact type web cleaners may be preferred.
In the contact type web cleaners, dust pick up may be more effective due to usage of adhesive rollers compared to non-contact type cleaners. It is the application which decides the selection of a particular web cleaner. Connect with us to know more in detail.