Hi Everyone, I am working on an engineering design project for University, and am struggling to calculate the forces some of the mechanical equipment will require. *This is a conceptual design. If anyone would like more details on how it is meant function, or has suggestions, feel free to post questions below or PM me. I have left out some details in an attempt to focus on the current problem I am experiencing.* The machine being designed is a small scale paving machine. The paver will have a hopper at the rear that will raise and lower between 2-6 inches to accommodate different asphalt thicknesses. On the bottom of the hopper are four doors that slide horizontally. Each of these doors are attached to a hydraulic cylinder. Having four doors that operate independently will allow for variability in asphalt widths. For a visual aid, please see Attachment A (Attachment A does not have the hydraulics attached). I believe I have calculated the force required to open the door correctly, however, I am struggling to calculate the amount of force required to close the door. When opening the door, the force required to move the door is a force greater than the static friction forces. *The static friction force for hot asphalt on steel is unknown. However, I was able to find Wet asphalt on Rubber from the link below. The asphalt on rubber coefficient of friction would be greater than asphalt on steel, so I used it in the calculations for this project. I'm aware it will result in an over design.* http://www.engineeringtoolbox.com/friction-coefficients-d_778.html Please see Attachment B for a Free Body Diagram and calculations. Not shown on that attachment are the following variables. Weight of Asphalt = 2200 lbs Number of Doors = 4 Weight of Door = 38 lbs Asphalt Weight/Door = 550 lbs (Asphalt Weight + Weight of Door) = 558 lbs The frictional forces involved are: Steel on Steel (SS) and Asphalt on Steel (AS) Now to where I am struggling. Once the doors open, the asphalt will fall to the ground. When closing the door, it will have to cut through the asphalt and I am not sure how to account for this additional force. The doors will rest in a C-Bracket, and will push the asphalt through the back of the C bracket as it closes. Question. How do I calculate the force required to close the gate and push through this asphalt. I know in manufacturing they use shearing stresses to calculate the forces required to cut material, however, hot asphalt is not a solid like the materials used in manufacturing. I'm really scratching my head on this one, and worry I may be over thinking it. I apologize if this question is not in the right thread. If you know a thread better suited for this question, please let me know. Thanks, - T.C.