Author - SUDHAKAR SANDACOUMAR
Definition and Development of a portable Concrete Mixer using FAST
Definition and Development of a portable Concrete Mixer using FAST
Introduction
Before it can become a driveway, patio or foundation, concrete must be combined from a mixture of sand, aggregate or gravel, Portland cement and water. Once these ingredients are mixed together, the wet concrete product is poured into a form that serves as a mold. Within a short time, the concrete becomes a solid.
Today's final concrete products are smooth, strong and have the ability to withstand massive pressure. Historically, however, the earliest forms of concrete were a combination of mud, sand, water, and perhaps some straw and the mixture was applied to twig structures to form huts. In the 1800's, the development of Portland cement, a form of powdered limestone, resulted in a much stronger concrete mixture.
Concrete may be mixed in small quantities or ordered from a commercial concrete supplier in larger amounts, but all concrete goes through a common mixing process before it is ready to pour. Cement is the name of the dry ingredients. It contains the correct proportion of sand, gravel and Portland cement.
Less common, but possible, is the individual mixing of the ingredients that compose concrete. Since dry cement is cost-effective, this method is rarely used, but if it is required to make our own concrete, the ratio of 3 pounds of Portland cement, 6 pounds of sand, 4 1/2 pounds of gravel and 1 1/4 pounds of water should be used. Then the dry ingredients should be combined thoroughly, and then water should be added. A large tub or wheelbarrow and a shovel are necessary when mixing our own concrete. We may add a little more water if the climate is hot and dry or slightly less if it is cold and humid.
To prevent common problems when mixing own concrete, the more water added, the easier the concrete will be to work, but water will also reduce its final structural integrity. Hence the wet concrete needs to be tested by pulling some up with a shovel. The bump should hold its shape but slowly sink back into the rest of the wet concrete. The concrete should be mixed thoroughly. If colour variations occurs, then it should be mixed more.
In order to process the mix by own work, it may be tedious to use an usual industrial concrete mixer. At this instance a portable concrete mixer may be hand.
Portable concrete mixer
A cement mixer - the more appropriate name is a concrete mixer - performs the function of mixing cement, water and either gravel or sand to make concrete. A revolving drum is used in the cement mixer to properly mix these components, A portable cement mixer gives the needed time for the construction workers to use it, before it becomes hard.
To build a foundation for a home, shed or garage or repair a building or a sidewalk, the right kind of cement mixer should be used to ensure the job is executed properly.
The mobile concrete dispenser or mobile cement mixer is used for batching concrete into several areas such as sidewalks. The amount of concrete can be properly controlled by using the mobile cement mixer. Extra water is not needed to mix cement in mobile cement mixers.
The stationary or immobile cement mixer or concrete dispenser as the name implies, is fixed in a central location while the concrete is manufactured. It is used mostly in pre-casting for building projects in remote locations where a large project is to be executed.
The increasing demand for ready-mix concrete with short mixing times meant for industrial production, resulted in new technologies in concrete production. Using cement mixers, batch mixing with twin-shafts with only thirty- seconds of mixing time per batch are possible now.
Delivery of ready-mix concrete from the factory or plant to the construction yard is made by a cement mixer, which is part of special transport trucks with a spiral blade fitted to overcome the tipping of large drums attached to the concrete truck. Continuous rotating cement mixers completely mix the concrete, and using its own hydraulic link cylinder empties the concrete without leaving any residue in the drum.
Portable cement mixers have wheels and are provided with a towing tongue, which a motor vehicle can pull around. The electric power for the rotation of the cement mixer can be supplied by the mains. A lever in the portable cement mixer enables the concrete to be tipped into a wheelbarrow.
Functions of concrete mixer
The Critical Functional aspects of Concrete Mixer is-
· Light weight
· Ease of Maintenance
· Design for Manufacturing
· Design for Assembly
· Suitable for Mixing Concrete, Nylon Powder, Resins and Tarmac Mixes
· Flexible dual power sources-operated by either Electrical Motor or Petrol Engine
· Easy to operate
· Good Aesthetic look
· Three steel mixing blades
Design aspects
The idea of the design is to produce a concrete mixture of the following capacity:
· Power-370Watts
· Voltage-110Volts
· Mass-70kg
· Drum capacity - 0.16m3
· Batch output- 0.08m3
· Drum diameter- 0.61m
· Cable length- 3m
Frame
The features to consider for the Frame Design are-
Welded steel fabrication from tube, plate, and angle combination. Structure to be of minimum material with maintaining the strength and stiffness. The Material chosen is Stainless Steel The estimated handle height from ground is 300 mm. Drum Shaft the material chosen is EN8 steel Casehardened. By bending stress calculations minimum diameter of shaft is 30 mm. The typical design of the frame is shown in figure1.
Figure1. Frame of concrete mixer
Drum
Material chosen is: Galvanised Iron Sheet which is nitride to resist corrosion and also for various materials like cement, Nylon Powder, Resins and Tarmac Mixes. The Volume of the Drum is 130 Litres and Working Volume of Drum is 90 Litres. The drum welded spun steel base and cone, and also 3 heavy duty mixing blades bolted base and cone. Drum is supported on plain bearing with shaft and screws. The typical design for drum is represented in figure2.
Figure2. Drum
Pinion shaft with drive mechanism
Speed reduction is from electric motor to be provided by gears or a combination of gears and V-belts. From Motor the pulley with V-belt will transmit the power to small pinion from the pinion power will be transmitted to the big gear. The total Drum RPM is 25. Typical pinion shaft is shown in figure3.
Figure3. Pinion shaft
Standard Parts:
Belts, Pulleys, bearings, bolts and screws are the standard parts. The specifications have been defined and modelled as per the standard components. Sizes were determined for tensile loading on the handle bolts and shear loading on the shaft retaining screws. Typical assembly is shown in figure4.
Figure4. Total assembly
While designing any components it is essential to follow the below mentioned design criteria.
1. Recognition of a need
2. Definition of a problem
3. Gathering of information
4. Conceptualisation
5. Evaluation
6. Communication of the design
Computer Aided Modelling of products in design has classically taken a ‘parts viewpoint’ for the structure of a product. For example, part models are developed separately and then brought together to form a representation of the product in an assembly model. However this ‘anatomical’ approach is not the only way in which to create a product structure. An alternative approach is to use a Functional Analysis System Technique (FAST) approach in which the product structure is described by the functions it performs. In this approach, the parts are not parts as such, but functions that are connected together by answering ‘How’, ‘Why’ and ‘When’ for each function. This FAST methodology is a simple hierarchical method of illustrating the functional structure of a product. In developing design solutions, it is more natural to concentrate on developing complete functional solutions rather than complete parts solutions.
Function Analysis System Technique Diagram (FAST)
Value analysis defines a "basic function" as anything that makes the product work or sell. A function that is defined as "basic" cannot change. Secondary functions, also called "supporting functions", described the manner in which the basic function(s) were implemented. Secondary functions could be modified or eliminated to reduce product cost.
Function Analysis System Technique is an evolution of the value analysis process created by Charles Bytheway. FAST permits people with different technical backgrounds to effectively communicate and resolve issues that require multi-disciplined considerations. FAST builds upon Value analysis by linking the simply expressed, verb-noun functions to describe complex systems.
FAST is not an end product or result, but rather a beginning. It describes the item or system under study and causes the team to think through the functions that the item or system performs, forming the basis for a wide variety of subsequent approaches and analysis techniques. FAST contributes significantly to perhaps the most important phase of value engineering: function analysis. FAST is a creative stimulus to explore innovative avenues for performing functions
FAST Diagrams are used to prioritize the objectives or functions of the product. Once the objectives are prioritized we can evaluate the options that would return the most value based on predetermined value criteria, i.e.:
· Targeting true customer needs and wants
· Delivering requirements but still enabling cost reduction by focusing on “what the function accomplishes” versus “what the product is”.
· Elimination of unimportant requirements
· Adding incremental costs to achieve larger performance benefit
· Improving performance and reducing cost simultaneously
Systems are created to solve problems. The systems approach is an organized way of dealing with a problem. In this dynamic world, The subject System Analysis and Design, mainly deals with the software development activities.
Defining a System is a collection of components that work together to realize some objective forms a system. Basically there are three major components in every system, namely input, processing and output.
In a system the different components are connected with each other and they are interdependent. For example, Human body represents a complete natural system. The objective of the system demand that some output is produced as a result of processing the suitable inputs.
System life cycle is an organisational process of developing and maintaining systems. It helps in establishing a system project plan, because it gives overall list of processes and sub-processes required developing a system.
Description of FAST diagram
FAST comprises of A horizontal chart depicting functions within a project, with the following rules:
1. The sequence of functions on the critical path proceeding from left to right answers the question “How is the function to its immediate left performed?”
2. The sequence of functions on the critical path proceeding from right to left answers the question “Why is the next function performed?”
3. Functions occurring at the same time or caused by functions on the critical path appear vertically below the critical path
4. The basic function of the study is always farthest to the left of the diagram of all functions within the scope of the study.
5. Two other functions are classified:
· Highest Order - The reason or purpose that the basic function exists. It answers the “why” question of the basic function and is depicted immediately outside the study scope to the left.
· Lowest Order - The function that is required to initiate the project and is depicted farthest to the right, outside the study scope. For example, if the value study concerns an electrical device, the “supply power” function at the electrical connection would be the lowest order function.
The HOW and WHY directions are always along the critical path, whether it be a major or minor critical path. The WHEN direction indicates and independent or supporting function (up) or activity (down).
The FAST model of the mixer can be explained as below:
Figure5. FAST model of mixer
Advantages of FAST model
1. More effective project management
2. Higher project performance
3. Faster project turnaround
4. Process improvement across the company
5. Better sales results
6. More efficient project execution
7. More efficient process dynamics
8. More efficient project dynamics
9. Transformation of company systems and productivity
Disadvantages of FAST
As an effective management tool, FAST can be used in any situation that can be described functionally. However, FAST is not a panacea; it is a tool that has limitations which must be understood if it is to be properly and effectively used.
FAST is a system without dimensions: That is, it will display functions in a logical sequence, prioritize them and test the dependency; but, it will not tell how well a function should be performed (specification), when (not time oriented), by whom, or for how much. However, these dimensions can be added to the model. Which dimensions to use is dependent on the objectives of the project.
There is no “correct” FAST model as in comparing it to some text solution, but there is a “valid” FAST model. Its degree of validity is directly dependent on the talents of the participating team members, and the scope of the related disciplines they can bring to bear on the problem. The single most important output of the multi-disciplined team engaged in a FAST exercise is consensus. There can be no minority report. FAST is not complete until the model has the consensus of the participating team members and adequately reflects their input.
Critiques
Working as a group was a great experience especially in sharing ideas among each other. The work was shared by me(Sudhakar Sandacoumar)and by my group member (Ashok Kumar Vallabhaneni) It paved the way in working towards new software like CATIA and a detailed knowledge on VISIO. Also creating a website was a new task and this group work has helped to have an in-depth understanding of how to proceed those.
The group work also helped to have an study on the engineering tools and also the manufacture techniques of the construction tools and machines. The FAST technique provided an understanding on all the simple ways of designing a process. The task assigned on study of Concrete mixer was completed successfully by implementing the FAST methodology and it has been published in the website.
Reference
Karl, T.U., Steven, D.E (2000) Product Design and Development. McGraw hill Publications. Boston.
George, E.D.(2001) Engineering Design, A materials and processing Approach. 2e. McGrawHill.
Nigel, C. (1998) Engineering Design Methods-strategies for Product Design.2e. John Wiley &Sons, Chichester.