As B moves to over A, ( A is a fixed point ) C slides up its guide slot and is stopped by a non compressible object and no amount of force can shift it further up. Measurements in units.
At this point how do I know how much pressure C excerts upwards. I hope I'm making myself sufficiently clear. I wouldn't be surprised if there are simpler ways to look at this. I've no doubt I'm using wrong words. (how to frame Q correctly?) Is this a fairly standard configuration? If so what's it called?
Much appreciated. Bellcrank/connecting rod/slider helped a lot. I found images of examples (and lots of formulas). So I've taken steps towards understanding.
This image explains a bit more what I'm trying to do. There's a box as a piston inside another (open ended) box. Fixed pivot point A is on a lid. Between the lid and piston is earth mix. When the lever pulls up the piston the compressed earth becomes very strong and can be used as building block. It is recommended to apply a compression of 20Mpa. I'm building the 'knuckle' at the moment out of 3/4 inch steel.
I envisage the lever on this to be about 6 foot. I'm working with inches as units (for scaling) and see myself pulling on the lever at about 5 foot or 60 units.
If I know how hard I have to pull I think can see if I'm building the parts strong enough to not deform. I'll give all dimensions as inches. In all of the above 1 unit = 1 inch.
I was hoping to work out the dimensions of the piston/box from this. So, let's say the area of the piston is 6 inches by 12 inches (to produce a block 4 inches thick) or 72 square inches. Edit add: It takes me a while to absorb what you're getting.
Using an online converter 20Mpa is 2900psi. Does this then mean the piston needs to apply 2900 lb x 72 = 208,800 lb of force to achieve the required compression on the earth block? Good morning. Yes, it's recommended in a paper by an Indian scientist who is not the Indian engineer who designed the first of these types of earth compressors.
I don't know what pressures the engineer worked with. The scientist compared 5 and 20 Mpa in the paper and concluded 20 is better. I suppose that doesn't mean that 5 is not sufficient. Anyway, I accept 20Mpa is a lot. If I assume that is what I need or want. How do I work out how much pressure to excert on the lever?
While I can build the mechanism I don't really understand the overall transfer of forces. The lever/knuckle pushes down on the lid while pulling up on the piston.
In between the lid is a mass of soil that when squeezed between the lid and piston quickly becomes incompressible. The more that mass is compressed the stronger the resultant block becomes. How much pressure can a mechanism like this excert. (AFK for another 8 hours.) Thank you Nidum for the responses. I find a formula F1L1 =F2L2 for a right angle bellcrank.
F2 = F1L1 / L2 or using above figures F2 = F1 x 60/3 = 20F1 That's all very well. What's got me stumped is as the bellcrank short lever swings around A the lifting shaft B to C is less and less right angle to it. The angle becomes smaller. While the bellcrank continues to move the lift shaft moves the piston less and less upwards.
It's at this time maximum pressure is applied to the block. That's the pressure I'm after. Is my thinking all wrong. What am I missing.? Sorry, I don't see how I can make the already posted images clearer.
The dimensions are as already given. The bellcrank pivot point A rests on two 'cradle' plates welded to the lid on either side of it and turns at that point as the long lever is moved. The short arm of the bellcrank shares a pivot point B with the assembly that pulls up the piston. That assembly is a square bar with the two long plates or shafts welded to its ends that pull up the piston from pivot point C. I don't see a toggle mechanism.? I think I'm beginning to understand.
If right it reminds me of the cam lock mechanism on sliding tripod legs. They always seem to grip particularly hard (and prone to break) when fully applied. So then (awaiting input) toggle is not necessarily a particular mechanism but an effect. If so then perhaps I've experienced this in other ways and instinctively felt there is something particular about this bellcrank configuration that does apply very high force at optimum use.
So how to calculate this.? I don't want to get ahead of myself at this point and would still like to understand fully this toggle effect. To start, I need to correct my above terminology error(s). A 'bellcrank' is actually the name for a simple lever with one arm at an angle or perpendicular to the other and a pivot at the joint of those two arms as described above by john101. In this case the bellcrank is the handle with the short arm acting as one of the links in the toggle mechanism. A 'toggle mechanism', in a general mechanical application sense, is a mechanism that has an unstable point at which a small lateral force will cause it to snap to either one side or the other (simple examples are a standard electric wall switch and what are sold as 'toggle switches' for use in electrical circuits); and in your application that is achieved by two links joined by a center pivot that can be straightened to apply an extreme force or as an 'over center' locking device like you have seen on a tripod. Now, back to your specific application issues.
First, I want to discuss some issues related to how this mechanism is used. One advantage of it is that it can provide a method that as a lateral force is applied at the two links center connection can as they approach an inline orientation can act as an extreme force multiplier. The downside of this assembly is that at the same time at that point the amount of lateral motion and lengthening of the linkage are very small, while the increase in possible toggle force rapidly increases. As a result, the design angle between the links at which the maximum force is to be applied is must very carefully controlled to prevent either excessive or insufficient loading when the linkage simply snaps through its alignment point without reaching the desired application load. At same time, the opposite is also true; in that, the amount of toggle force relative to the amount of lateral force applied decreases rapidly as the distance between the toggle links connection and their inline alignment increases. Mathematically (Using the simplest form being a straight lateral force against the center of the toggle assembly): F toggle = F lateral x cos Θ, where Θ is the angle between a line drawn between the top and bottom pivots of the toggle and a line drawn between the two pivot points of one of the toggle arms.
(For your actual case, where the lateral force is being applied by the handle torque applied to the top link of the toggle the mathematics is more complicated but the above gives a representative example of the force ratios and how the required operating handle force will be effected.) For this reason, in many applications the toggle is applied in series with another force creating element like a spring. As an illustration of this arrangement using the above press, it could (or, since we cannot see the details of the bottom portion of the press) may actually be a loading spring, or set of springs, between the bottom plate of the press and the cross bar between the two links being used to lift the bottom plate that provide the necessary compression loading when the toggle is fully extended.
I am focusing on this issue because there some specific design factors on this type of application that can effect the actual point at which a desired load will be achieved at a reasonable press handle load as the toggle approaches its full extension on the press. The accuracy of the amount of soil that is loaded into the press each time. The consistency of the density and compressibility of the soil that is being loaded into the press each time.
3 The desire or requirement for each finished brick to be of a specified thickness and the allowed variance of that dimension. OK, At this point, I am going to stop to give you some time to review all of the above and post any comments and questions you may have before addressing any further issues. OK, Thank you. I find the idea of using a spring (if I understand correctly, to ameliorate the toggle force in extremis very interesting.) I'm not sure I understand how. I will be incorporating stops to prevent 'the flip'. I have a few different car coils. As yet the press doesn't include any springs.
Another part of the 'machine' is when one pivots the long handle back the other way the two linkages rest on rods sticking out of the case and when pressed down the finished brick rises up ( after lifting the lid/cap ) out of the case to be removed, the piston is then retracted, soil reloaded, lid replaced, repressed, etc producing a smooth workflow. The two linkages simply pull up a box piston inside a case. The soil will be consistent, sifted, clayey soil on site with roughly 10% lime and 10% water with little organic material loaded from a measured container. I'll have to work out exactly how much later through trial and error.
I assume if soil mix is measured and prepared consistently all bricks/blocks will be sufficiently similar. (I suspect I'll have to rebuild the bellcrank/'knuckle' as I may have underestimated just how much force is involved.).
Edit add: to post 17. The long handle is removed from the 'knuckle' before moving the linkages from the lid and raising the brick/block. (I used inkscape and youtube tutorial on using it to make this image.) Based on this image. What is the relationship (graph) between F1 and F2 as angle ABC.
approaches 0 as the soil between lid and piston becomes incompressible. Edit correction: based on notation by TomG, I had angle BA BC meaning the angle ABC.
F1AB is 90 degrees (I'm having a bit of trouble understanding the formula. Not so much calculating with cos, tan perhaps, using online calculator, but if I get it F2 is 0 when ABC is 0 and BAC is 180.? And the distance to F1 doesn't matter?). As a suggestion for the 'spring' I mentioned in my last post; obviously, you are going to want something that is as simple and compact as possible and one way to achieve this may be by placing a sheet or sheets of high hardness elastomer cut to the dimensions of the bottom of your mold cavity on top of the bottom plate and then placing a similar size metal plate on top of that which will serve as the actual bottom of the mold cavity. Because of the high compressive pressure you want, a good standard sheet material might be 90 durometer nitrile (rubber) and this material is available in several thicknesses up to 1/4' thicknesses; but, you may want to stack multiple sheets so you can adjust the amount of compression to obtain the toggle load position you want.
A sheet of that material or something similar may be available from a local gasket material supplier or can be found online from someone like: Just a suggestion.
Illustration from 1908 Chambers's Twentieth Century Dictionary. Bell-crank, n. A rectangular lever in the form of a crank, used for changing the direction of bell-wires. A bellcrank is a type of that changes motion through an angle. The angle can be any angle from 0 to 360 degrees, but 90 degrees and 180 degrees are most common.
The name comes from its first use, changing the vertical pull on a rope to a horizontal pull on the striker of a, used for calling staff in large houses or commercial establishments. Contents. Angles A typical 90 degree bellcrank consists of an 'L' shaped crank pivoted where the two arms of the L meet. Moving rods (or cables or ropes) are attached to the ends of the L arms. When one is pulled, the L rotates around the pivot point, pulling on the other arm. A typical 180 degree bellcrank consists of a straight bar pivoted in the center.
When one arm is pulled or pushed, the bar rotates around the pivot point, pulling or pushing on the other arm. Mechanical advantage Changing the length of the arms changes the of the system.
Many applications do not change the direction of motion, but instead to amplify a force 'in line', which a bellcrank can do in a limited space. There is a tradeoff between range of motion, linearity of motion, and size. The greater the angle traversed by the crank, the more non-linear the motion becomes (the more the motion ratio changes). Applications Aircraft Bellcranks are often used in aircraft control systems to connect the pilot's controls to the control surfaces. For example: on light aircraft, the rudder often has a bellcrank whose pivot point is the rudder hinge. A cable connects the pilot's rudder pedal to one side of the bellcrank.
When the pilot pushes on the rudder pedal, the rudder rotates on its hinge. The opposite rudder pedal is connected to the other end of the bellcrank to rotate the rudder in the opposite direction. Automotive Bellcranks are also seen in automotive applications, as part of the linkage connecting the throttle pedal to the, and connecting the brake pedal to the master brake cylinder. In vehicle suspensions, bellcranks are used in in automobiles or in the in tanks. Vertically-mounted suspensions may not be feasible in some vehicle designs due to space, aerodynamic, or other design constraints; bellcranks translate the vertical motion of the wheel in to horizontal motion, allowing the suspension to be mounted transversely or longitudinally within the vehicle. References External links.
29.1 Introduction Lever is a simple mechanical device, in the form of a straight or curved link or a rigid rod, pivoted about the fulcrum. It works on the principle of moments and is used to get mechanical advantage and sometimes to facilitate the application of force in a desired direction. Examples of levers are: straight tommy bar used to operate screw jack, bell crank lever, rocker arm, lever of lever loaded safety valve etc. Figure 29.1 shows the construction of a simple lever. P is the applied effort required to overcome load, W. Ratio of load to effort is called Mechanical Advantage and ratio of effort arm length to load arm length is called leverage. 29.2 Classes of Levers Depending upon the position of load point, effort point and fulcrum, levers are classified into following classes: Class I Levers Lever having the fulcrum located between the load point and effort point is called Class I lever.
Examples are rocker arm, bell crank lever etc. Mechanical advantage of such levers is greater than one as effort arm is larger than the load arm.
Class II Levers Lever having load point located between the fulcrum and effort point is called Class II lever. Lever used in safety valve is an example of lever of this class. The effort arm is larger than the load arm; therefore the mechanical advantage is more than one.
Bell Crank Lever Mechanism
Class III Levers Lever having effort point located between the fulcrum and load point is called Class III lever. The effort arm, in this case, is smaller than the load arm; therefore the mechanical advantage is less than one. Due to this, the use of such type of levers is not recommended. However a pair of tongs, the treadle of a sewing machine etc.
Are examples of this type of lever. Figure 29.2 Class I, Class II and Class III Lever Figure 29.2 shows levers of different classes. 29.3 Design of Lever Design of lever involves determination of various dimensions of the lever for a specified load or output force required. For a specified load or output force desired, effort required can be calculated using principle of moments. Due to these forces, arms of the lever are subjected to bending and are designed based on that. Reaction force acting on the fulcrum can be calculated.
Fulcrum of the lever is a pin joint and is designed based on bending and bearing considerations. Design procedure is discussed below. 29.3.1 Determination of Forces If the load and effort are parallel to each other, as shown in figure 29.2, reaction on the fulcrum is the algebraic sum of these two forces. But if the load and effort are inclined to each other at an angle q, as shown in figure 29.3, reaction (R) at the fulcrum can be determined as. Therefore using suitable values of I and y for selected section, its dimensions can be finalised so that the bending stress remains within the allowable limits. Often the arms are made with cross-section reducing from central portion to the point of application of load. This is done to save material using uniform strength condition.
Critical section of the lever (section of maximum bending moment) becomes weak due to hole made for pin. To compensate for the reduced strength, width of that section is increased or boss is provided as shown in figure 29.4. 29.3.3 Design of Fulcrum. Bearing Failure The permissible bearing pressure (P bearing) depends upon relative velocity, frequency of relative motion and the lubrication condition between the pin and the bush. The usual range of allowable bearing pressure for brass/bronze bush and steel pin is 10-25 N/mm 2.
Lower values are used for high relative velocity, frequent motion and intermittent lubrication conditions. If d p and l p are diameter and length of the pin respectively, bearing pressure is given by, Shear Failure Pin is subjected to double shear and maximum shear stress is given by, Bending Failure As discussed in the design of pin for knuckle joint, when the pin is loose in the eye, which is a desired condition here for relative motion, pin is subjected to bending moment. It is assumed that: Load acting on the pin is uniformly distributed in the eye and uniformly varying in the two parts of the fork. Maximum Bending Moment (at centre) is given by, Maximum Bending Stress in the pin, where, 29.4 Lever Material & Factor of Safety Levers are generally forged or cast. It is difficult to forge curved levers with complicated cross-sections and have to be cast. As the levers are subjected to tensile stress due to bending, cast iron is not recommended to be used as material for levers.
Aluminium alloys are generally used for levers. For severe loading and corrosive conditions, alloy steels are used. Suitable heat treatment processes are also often employed to improve wear and shock resistance of lever. Factor of safety of 2 to 3 on yield strength is generally used.
For severe loading conditions or fatigue loading higher factor of safety is also taken. References. Design of Machine Elements by VB Bhandari. Analysis and Design of Machine Elements by V.K.
Bell Crank Lever Apparatus
Jadon. Design of Machine Elements by C.S.
Purohit. Machine Design by P.C. Sharma & D.K. Aggarwal. Machine Design by R.S.
'Bell-crank, a rectangular lever in the form of a crank, used for changing the direction of bell-wires. A bellcrank is a type of crank that changes motion through an angle. The angle can be any angle from 0 to 360 degrees, but 90 degrees and 180 degrees are most common. Design Procedure: Step 1: Design of Fulcrum pin Step 2: Design of load pin Step 3: Design of Effort pin Step 4: Design of Lever Cross Section ' If you like our efforts, we request you to share our work with your friends & family BECAUSE YOUR LOVE ENCOURAGES US TO PRODUCE MORE AND MORE GOOD CONTENT TO SPREAD THE FREE QUALITY EDUCATION. You can also provide us Financial Help to continue this good work - This video will help you to know the construction of Bell - Crank lever with its design. Thanks For Supporting Us Website - Parent Channel - Facebook - Twitter - Blogger - Pinterest - Digg - Tumbler - Reddit - LinkedIn- Happy Learning: ).