Vacuum Basics for Handling Technology

Vacuum Basics for Handling Technology S. M Jacob A publication of Schmalz India Pvt Ltd 1

INRODUCTION Material handling using Vacuum Technology is getting more popular now days in automation and robotics, due to its high flexibility, safety, speed and accuracy, at which the materials can be handled during the entire process of manufacturing, sorting, packing, transporting and logistics applications. Traditional material handling methods include tying materials with hooks, slings or chains. Howev- er, this method poses a high risk of causing accident in the event of coming lose. Furthermore, it is difficult to control while moving and the personnel must climb on top of materials to attach rigging. On the ground, it requires several people to guide materials into position. All of these factors contribute to potential haz- ards on the job and increase the risk of injury to the personal and always poses a threat to the people. A 2015 study by an Insurance company, which evaluated more than 1.5 million worker compensa- tion claims submitted from 2010 to 2014, found that material handling was the most common cause of ac- cidents, accounting for 32% of the claims for all businesses and industries analyzed. Vacuum lifting is a safer alternative for material handling, providing many benefits over conventional meth- ods. Most important aspect is that it eliminates the need for unsafe and time-consuming mechanisms such as hooks, slings or chains. Materials can also be lifted without displacing adjacent pieces and placed with more precision with utmost safety. Adopting material handling methods such as vacuum lifting, lead in reducing the occurrence of acci- dents. When vacuum lifting systems are utilized as part of an overall safety strategy, the costs are reduced by fewer insurance claims as well as increased productivity. Most important is, Ergonomics at the work- place is improved, and the productivity is increased by reducing fatigue and at the same time, not com- promising an iota of safety of the product as well as the personal while handling. Vacuum handling technology is a vast subject, which is not taught in any of the technical institutions and lack of technical publication on this subject, is casting a shadow of doubt on this technology and view- ing as it is still in a primitive stage. Hence it became necessary to create some literature so that everybody can understand and get benefited. This book aimed to understand the Basics of Vacuum for Handling Technology. Every care is taken to ex- plain the basics in simple terms with more practical examples etc. so that the subject can be grasped easily. We hope that you will be benefitted with this book and let me state that the scope of vacuum han- dling is immense and the only limitation is one’s own creativity and imagination. 2

CONTENTS 2 4 1) Introduction 5 2) What is Atmospheric Pressure 6 3) Units for measuring Atmospheric Pressure 7 4) Effect of Altitude on Atmospheric Pressure 8 5) First Proof of Existence of Vacuum. 9 6) What is Vacuum? 11 7) Effect of Vacuum on an inflated balloon 11 8) Vacuum Implosion 12 9) Relationship between force and pressure 13 10) Specification as Absolute Value & Absolute Value 15 11) Specification as Relative Value & Relative Value 16 12) Units of measuring Vacuum 17 13) Vacuum Ranges 17 14) Energy Required for Vacuum Generation 18 15) Overview of Vacuum Handling systems 19 16) Why Does a Suction Pads Grip a Work piece? 19 17) Holding force of Suction pad. 20 18) Why goods are handled with vacuum? 19) Application Examples of Vacuum Handling 3

WHAT IS “ATMOSPHERIC PRESSURE” Before learning about vacuum, let us understand what is Atmospheric pressure. Atmospheric pressure is the force exerted by the weight of the air on a body. As you are aware that there exists air in the atmosphere around us and that air exerts a pressure on the surface of the body. Fig 1 In Fig 1 above, the pressure at point \"X\" increases as the weight of the air above it increases. The same can be said about decreasing pressure, where the pressure at point \"X\" decreases if the weight of the air above it also decreases. If we stand inside a room, the air present inside the room exerts a pressure on our body. However we can- not feel the pressure because our body also exerts an equal and opposite pressure since our body also con- tains air inside. If we walk out of the room and stand outside open space, there again the atmospheric pres- sure exerted on our body is much more than when inside the room. Again we could not feel this due to the reason explained above. Air pressure is caused by the weight of the air molecules above. Even tiny air molecules have some weight, and the huge numbers of air molecules that make up the layers of our atmosphere collectively have a great deal of weight, which presses down on whatever is below. 4

Some of the effects of Air Pressure is mentioned below.  An inflated balloon.  Air pressure present within the tyres of the car.  A bullet fired from a gun( driven by the gas pressure).  Sipping any drink from the glass using a straw.  Ears getting blocked due to change in pressure. UNITS FOR MEASURING ATMOSPHERIC PRESSURE” Thinking in terms of air molecules, if the number of air molecules above a surface increases, there are more molecules to exert a force on that surface and consequently, the pressure increases. The opposite is also true, where a reduction in the number of air molecules above a surface will result in a decrease in pressure. Atmospheric pressure is measured with an instrument called a \"barometer\", which is why atmospheric pres- sure is also referred to as barometric pressure. There are many units used for expressing the Atmospheric pressure some popular units are mentioned below in Fig 2. Fig 2 5

In aviation and television weather reports, pressure is given in inches of mercury (\"Hg), while meteorolo- gists use mill bars (mb), the unit of pressure found on weather maps. You can use any of the units which you feel comfortable but in this book, we use “Bar” (bar) or Milli Bar” (mbar) EFFECT OF ALTITUDE ON ATMOSPHERIC PRESSURE Our earth surface is not at the same level. It has valleys and mountains and hence the Atmospher- ic pressure (ambient pressure) will change with respect to altitude. The gravitational pull between the earth and the air molecule is high when it is nearer to earth than far away. At higher elevations, there are fewer air molecules above a given surface than a similar surface at lower level. The sea level altitude is same throughout the earth and the air pressure measured is same at all sea levels Since SEA LEVEL is considered to be same throughout the earth and the air pressure measured at SEA LEVEL is considered as the reference point for expressing the atmospheric pressure. The pressure at sea level is 1013 mbar or 1.013 bar. Fig 3 6

Can you imagine what would be the atmospheric pressure on MOON??? For most practical purposes, the Moon is considered to be surrounded by vacuum. The elevated presence of atomic and molecular particles in 'lunar atmosphere' is negligible in comparison with the gaseous envelopes surrounding Earth which is less than one hundred trillionth (10−14) of Earth's FIRST PROOF OF EXISTENCE OF VACUUM Galileo's student Evangelista Torricelli (1608 – 1647) was engaged in experiments. In the year 1643, he took a glass test tube and filled with mercury and immersed it inside a jar containing mercury in upside down. He took care that no air was leaked into the test tube while immersing inside the jar. Fig 4 He observed that the level of the mercury dropped slightly, but the height of the mercury column is always the same, regardless of the length of the glass. He repeated this experiment at different places and observed the same phenomena. There existed an empty space inside the test tube contained “nothing “ Another Scientist, Diplomat and Mayor Otto von Guericke (1602 – 1686) was also conducting some experiment and this discovery led to the confirmation of existence of Vacuum. 7

Fig 5 In 1650 Guericke invented the air pump, which he used to create a partial vacuum. His studies re- vealed that light travels through a vacuum but sound does not. In 1654, in a famous series of experiments that were performed before Emperor Ferdinand III at Regensburg, Guericke placed two copper bowls (Magdeburg hemispheres) together to form a hollow sphere about 35.5 cm (14 inches) in diameter. After he had removed the air from the sphere, 8 horses from either side were unable to pull the bowls apart, even though they were held together only by the air around them. The tremendous force that air pressure exerts was thus first demonstrated publically. WHAT IS VACUUM ? The word vacuum comes from Latin means an empty space or “NOTHING” As per DIN 28400 standard the vacuum is defined as: “Vacuum is the condition of a gas; which particle density is lower than the density of the atmosphere” In simple words, vacuum is defined as the pressure which is less than atmospheric pressure. This means that a pressure less than 1013 mbar is called as Vacuum. 8

Fig 6 Fig 7 Please refer to Fig 6 above where you can see drinking a liquid using a straw. Here the person keeps the straw in the mouth and sucks the air inside the straw there by creating vacuum. Kindly note that atmospheric pressure is acting on the surface of the liquid and when vacuum is created inside the straw, the atmospheric pressure pushes the liquid inside the straw and the liquid is getting sucked and flows into the mouth. Similarly in Fig 7 you can see how the medicine is getting filled inside the syringe and there also when the piston is pulled up, an empty space is created and causes vacuum and to that space the atmos- pheric pressure will push the medicine inside the syringe. 9

EFFECTS OF VACUUM ON AN INFLATED BALLOON In another example , let us consider that one balloon which is inflated and kept inside a Glass chamber which is sealed. By using a vacuum pump the air inside the chamber can be evacuated there by Please see the Fig 8 which is Stage –1. In this the inflated bal- Fig 8 loon is kept inside the glass chamber and is lying down at the Fig 9 bottom. Let us consider the atmospheric pressure of 1013 mbar ex- ists and the pressure is same inside and outside. A vacuum pump can be connected to the chamber and vacuum gauge is also fixed to the chamber to show the inside pressure. Since the atmospheric pressure is same the inflated balloon is just lying inside the chamber as the size of the balloon is same as it was at the time of inflation. Fig 9 shows Stage 2. Here we have created some vacuum in- side the Glass Chamber and you can see the difference in pressure inside and out side. The outside pressure is 1013 mbar as this is the atmospheric pressure whereas the pressure inside the chamber is 900 mbar due vacuum pump evacuated some air from inside. See what happened to the inflated balloon? Due to decrease in the pres- sure inside the chamber, the air inside the balloon wanted to enter into the chamber and exerts a pressure on the wall of the balloon and since the material of the balloon is elastic, the balloon will grow bigger in size. Fig-10 shows Stage-3. Here again the vacuum pump evacu- ated more air and the pressure inside the chamber is reduced to 700 mbar. The effect of this pressure reduction on the balloon is that it grows bigger in size as compared to Stage - 2. Fig-11 shows the Stage-4. Hear again the pressure in- Fig 10 side the glass chamber is reduced by pumping out more air by Fig 11 the vacuum pump. The pressure is now 550 mbar where as the pressure outside is 1013. Due to decrease in the pressure inside the glass chamber, the air which is inside the balloon will exert more pressure on the surface of the balloon and the rubber will lose its elasticity and will burst. From this experi- ment we can conclude that the difference in pressure can cre- ate a force. 10

VACUUM IMPLOSION Since Air can not be seen by our naked eye, but its effect can be felt and seen. Similarly the effect of vac- uum also can felt and seen. Let us see one more example to understand about the effect of vacuum. Fig 12 https://www.youtube.com/watch? Fig 13 One more example will discuss here to get more familiar with the effect of vacuum. Please see the Fig 12 which shows about a tanker made of steel. This tanker is designed to carry liquid or pressured gas etc. and it will remain in its original shape. Please now see the Fig 13, where this tanker was subjected to vacuum pressure inside. By using a strong vacuum pump the air inside the tanker was removed. After some time the air pressure inside the tanker was too low so that the atmospheric pressure exerted a tremendous pressure on the outside surface of the tanker and lead to collapse instantly. The YouTube link is given above and you too can watch the same. Please see the Fig 14 which is another example of vacuum which almost everybody had Fig 14 tried by oneself. Take an empty bottle of mineral water bottle with a cap. Remove the cap and then crush it and tighten the cap. Care to be taken that the bottle should not get punched so that the atmospheric air should not entire inside. You will observe that the crushed bottle will not regain its original shape. The reason is that the atmospheric pressure exerts a force on its body as the pressure inside is less than atmosphere. RELATIONSHIP BETWEEN PRESSURE AND FORCE It is very well established that the difference of air pressure will create a force. Both the pressure and vacuum generate forces. The magnitude of the force is equal to the product of the pressure and the area on which it acts: 11

The formula for the Force is mentioned below The force is proportional to the pressure as well as the area. If we want to increase the force by changing one or both the parameters can achieve it. We also will be using the same basic formula for our calculation of forces for vacuum handling. SPECIFICATION OF ABSOLUTE VACUUM & ABSOLUTE VALUE Let us recall the definition of vacuum. Vacuum means the pressure less than atmospheric pressure. The atmospheric pressure at sea level is 1013 mbar and this is called as the ambient pressure. This pressure varies with respect to altitude and we have seen the relation of altitude and its relative pressure. As per the definition any pressure less than ambient pressure of 1013 mbar is vacuum. Hence pressure of 1012 mbar is under vacuum and it goes on and on like 1011….. 10…..1...0.1…………...0.01……...0.0000001 mbar …………...0 mbar Zero (0) vacuum is called absolute vacuum this vacuum level can not be achieved on the earth. This is available only in outer space. Hear the vacuum pressure lies between 1013 mbar and 0 which is expressed with +ve sign. Fig 15 Fig 15 shows very clear about the absolution vacuum range and if the vacuum is expressed in absolute value usually this unit of vacuum is used in Science. The reference point is absolute zero, which means space void of air (e.g. outer space). This means the vacuum value is always positive 12

SPECIFICATION OF RELATIVE VACUUM & RELATIVE VALUE In vacuum technology, the vacuum is specified as a relative value which means the vacuum is specified in relation to the absolute value. Such vacuum values always have a negative sign, because the ambient pressure is used as the reference point, which is defined as 0 mbar. Fig 16 Please see the Fig 16 above where you can note that 1013 mbar is considered as Zero and below 1013 is marked as –ve value. For example –500 mbar = 513 mbar absolute. In relative unit , the vacuum can also be expressed in % also. For example 50% of relative vacuum means 40% of 1013 mbar =405.2 mbar absolute Converting 405.2 mbar to relative value = 1013-405.2 = -607.8 mbar(–ve sign when relative value) To make it more simple kindly consider the ambient pressure as 1000 mbar instead of 1013. You can neglect 13 mbar for quick calculations. If you consider the above example of 40% relative vacuum means : 40% of 1000 mbar = 400 mbar absolute Converting 400 mbar to relative value = 1000-400= -600 mbar (–ve sign when relative value) From above it’s very clear how to convert absolute to relative and vice versa and you need to remember the magic figure 1000 and you subtract the value from it and you will get the value you need and intelli- gently use—ve sign for relative values. Fig 17 shows a pressure gauge used for measuring relative value and note that the graduation of the scale s from –0 to –1 in the anticlockwise direction. Similarly the Fig 18 shows a pressure gauge used for measuring absolute value and the graduation of scale is from =1000 to 0 mbar, again in anticlockwise direction to indicate as vacuum. Relative pressure gauge Fig 17 Fig 18 13

Fig– 19 shows the clear bifurcation of Absolute and Relative vacuum ranges. When we say that the compressed air pressure s 6 bar which means that 6 bar from the ambient of 1.013 bar. Fig 19 The following table shows the comparison values between absolute and relative pressure for clear un- derstanding. 14

UNITS FOR MEASURING VACUUM Since Vacuum is nothing but pressure but negative pressure, all the units used for pressure can be used for measuring vacuum also. Most commonly used units are bar,millibar,pascal or kilopascal. Even vacuum value is expressed as a % also which means that it is relative value. There is no hard and fast rule that the vacuum should be expressed only on above mentioned units. Any confortable unit can be chosen and for convenience a convertion table is given below to convert the 15

VACUUM RANGES The basic definition of vacuum means anything less than atmospheric pressure i.e < 1013 mbar. This is very clear that any value between 0 to 1013 mbar is vacuum and this is the wide range of vacuum level. The following table is very clearly specifies the vacuum range. Fig 20 This also will pop up a question in your mind that what level the handling applications are done? We will see ahead. From the defenition of vacuum it is understood that the pressure less than 1013 mbar is under vacuum. We also seen above that the ambient pressure is 1013 mbar at sea level. This ambient pressure will change with resepect to altitude @ 12.5 mbar per every 100 meters. For example at an altitude of 600 meters above sea leavel the ambient pressure is 1013-(12.5x600/100)= 938 mbar. This means that the ambient pressure is itself is under vacuum. If a vacuum pump achieves –900 mbar at sea level will not achieve –900 mbar at an altitude of 600 meters above seal level. If can achieve only 92.6% of 1013 bar ( 938/1013=92.6%). Hence the vacuum pump will register a reading of 92.6% of –900 mbar = -833.4 mbar relative 16

ENERGY REQUIRED FOR VACUUM GENERATION The energy required for vacuum generation increases disproportionately to the attained vacuum. Increasing the vacuum from -600 mbar to -900 mbar, for example, increases the holding force by a factor of 1.5, but the evacuation time and the energy needed to achieve this vacuum value increases by a factor of 3. This is very clear that we should have the required vacuum level for the work piece to be handled safely so that the energy costs can be minimum so that it works out to be economical. See below the Fig 21 which clearly shows the energy consumption graph. Fig 21 If we are able to achieve –600 mbar vacuum then it is absolutely safe to handle a work piece. Hence it is clear that for vacuum handling applications falls under low vacuum or rough vacuum upto the range of 100 mbar absolute or –900 mbar relative. Needless to highlight that the cost of the vacuum pump to create higher level of vacuum is also too high and it is not required also for handling application. OVER VIEW OF VACUUM SYSTEMS Vacuum systems are used as grippers in automated applications. In order to make an efficient vacuum handling system the components shown in Fig 22 are essential. Careful selection of the above vacuum components makes the vacuum handling system more efficient and economical. 17

A typical vacuum handling system set up is mentioned below. Fig 22 We will not be dealing in detail with regard to each components as it is beyond the scope of this book. WHY DOES A SUCTION PAD GRIP A WORKPIECE? A vacuum suction pad plays a very important role in vacuum handling system. They prove the link between the work piece and the handling system. They consist of the suction pad (elastomer part) and a connecting/mounting element. Their technical and physical design is therefore of great importance. In other words SUCTION PADS ARE NOT JUST A RUBBER PIECE. Lot of engineering pa- rameters are considered while designing a suction pad for a particular application Fig 23 18

Suction pads are used to grip and move work pieces in a plant or on a robot. A suction pad does not attach itself to the surface of a work piece. Instead, the ambient air pressure (atmospheric pressure) presses the suction pad against the work piece as soon as the ambient pressure is greater than the pres- sure between the suction pad and the work piece. This pressure difference is achieved by connecting the suction pad to a vacuum generator, which evacuates the air from the space between the pad and the work piece. If the suction pad is in contact with the surface of the work piece, no air can enter it from the sides and a vacuum is generated. HOLDING FORCE OF SUCTION PAD The holding force of the suction pads increases proportionally with the difference between the am- bient pressure and the pressure inside the pad. The holding force of a suction pad is calculated with the formula: F = Δp x A F = Holding force Δp = Difference between ambient pressure and pressure of the system A = Effective suction area (the effective area of a suction pad under vacuum) This means the holding force is proportional to the pressure difference and the suction area. The greater the difference between ambient pressure and pressure in the suction pad or the larger the effec- tive suction area, the greater the holding force. The force can vary depending on a change of the pressure WHY GOODS ARE HANDLED WITH VACUUM? Vacuum has many advantages over other handling methods (such as mechanical gripping) 1) More careful handling of the work pieces as compared with mechanical gripping which may cause damage or leave a mark on the work piece. For example, if we grip wooden furniture using mechanical gripper will damage which will spoil its finish and in order to overcome more process is required to eliminate it. Take for instance about handling Glass using a mechanical gripper which may break. In some cases, using mechanical gripper is not possible at all. 2) One gripper can be used for many different parts like Glass, wood, Metal sheet, Fibre Glass etc…For above application the same vacuum gripper can be used for handling which makes handling sys- tem flexible and user friendly. 3) In case of automatic handling system, we can obtain the part present signal to PLC by using a vacu- um switch, ensuring that a part is present so the robot can move safely. 4) In most cases using vacuum handling will be more economical and the handling equipment will be more flexible as compared to other handling system. 19

APPLICATION EXAMPLES OF VACUUM HANDLING 20

Basically an Electrical Engineer by qualification, I have an industrial experience of nearly 33 years including 20 years in Schmalz India Pvt. Limited. I have worked in many fields of testing of Electrical Instruments, designing and production of Instrument Transformers, marketing of HT Isolators and Instrument transformers, sales and ser- vice of Flame proof switchgears for Mining industry and industrial electrical control panels. I received an opportunity of working in Schmalz when this technology was not proven in the In- dian market and hardly had any reference at that time, however had the instinct and vision about this technology that it has an immense potential in store, and thus I put behind all my working experience in the Electrical field and opted to join the startup without any second thoughts, . I have had privilege of being a foundation member of Schmalz and have dedicatedly worked for developing the market for Schmalz products in India and visited many industries and offered solutions using vacuum technology for material handling. Having in depth knowledge and hands on experience, had the privilege to be in charge for imparting technical knowledge to all the employees of Schmalz India with regard to material handling using vacuum technology. In this book I tried to explain in detail about the Vacuum Basics for Handling Technology in a manner in which I used to teach the new joinee in our company. Hence my approach to this subject so simple so that anybody who is reading this book can easily master the Basics with- out much difficulty. I tried to use many practical examples to explain the theory of Basics so that any body can un- derstand in the first reading itself. Hope this book will contribute to the needs of the people who want to understand the subject . 21