NSF-Funded Student Design Projects:
Heavy Duty Paper Shredder
Designers: John Blackburn, Terry Jadan, Jim Kokoszka, Kamnoosh Mafie, Andrea Maynard, Jennifer Peters
Client Coordinator: Lynne Haggman , Western Wayne Skills Center, Livonia, Michigan
Supervisors: Dr. Robert Erlandson, Mr. David Sant
Department of Electrical and Computer Engineering
Wayne State University
Detroit, MI 48202
Many vocational special education programs throughout southeastern Michigan utilize paper shredding operations as part of their training program. The job tasks are not complicated and can be performed by students with mental disabilities as well as students with physical disabilities. Paper shredding is also attractive because it can lead to commercial contracts with local area businesses for waste removal, reduction, and recycling. In some cases, schools have established a composting operation using the shredded paper.
Commercially available relatively inexpensive shredders are difficult to feed and are prone to jamming and other malfunctions. Heavy-duty industrial shredders are relatively expensive and again prove difficult for many students to operate. The client school wanted an in-between shredder, one that could handle moderate loads, be easy to feed and operate, be safe, easy to empty, and one that could handle multiple sheets of paper, with an occasional staple. This project provided such a device.
Summary of Impact
The device is shown in Figure 1. Field testing demonstrated that the system was safe, easy to use, not jammed by staples, and performed well for the required volume and rate of paper feeding to the device. The device is larger than originally anticipated and hence it could not be placed into the room currently used for paper shredding. Another room is currently being prepared for the device and the paper shredding operation. Representatives from several schools have seen the device and have expressed a desire to purchase one.
The device utilizes two parallel shafts rotating in opposite directions. Each shaft has fifteen 7 ¼” diameter, 24 tooth carbide tipped circular saw blades, separated by metal spacers. A ½ horse power, 1725 rpm, continuous duty electric motor drives the two shafts. The motor has an automatic thermal overload. The shredding assembly required a noise-damping chamber to reduce the operational noise level.
The feed chute has a curved face plate, adjustable height feed slot (to accommodate wheelchair users as well as users who want to stand), and a detachable shelf for students who needed paper stock readable available. The paper feed will accept a stack of paper up to an inch thick, although the physical capabilities of the student users will limit actual paper input to no more than about ten sheets of paper.
Figure 1. Heavy duty paper shredder. The shredded paper collection bag is contained in a chamber on the left. A mobile Creform frame supports the shredder components.
As the paper is fed into the shredder, it encounters the dual rows of shredding blades and is shredded. A low-pressure pneumatic conveying system moves the paper from below the cutting mechanism to a point above the output storage bin. A rotary blower provides an airflow of 500 cubic feet per minute. The blower is attached to the conveyor pipe before Paper is introduced.
The conveying pipe is made of 6-inch diameter PVC pipe. The horizontal conveying pipe, with its upper half removed for a length of 13 inches, is located below the cutting mechanism in a flanged trough constructed of melamine board for its low friction properties. The flanged is secured to the aluminum base plate providing a smooth transition from the cutting mechanism and the conveying pipe. The transition volume also contained front and rear steel diverter plates to ensure a smooth flow from the cutting blades into the conveying pipe and then onto the storage bin.
The vertical conveying pipe carried the cut paper approximately four feet up to an opening into the storage bin and then down into the bin. A combination of gravity and airflow directed the material into the bin. A mesh fabric guide keeps the paper in the bin and allows the air to be exhausted from the system.
The assembly is mounted on a mobile cart constructed from Creform products. Creform is a pipe and joint technology with over 400 compatible parts that is used extensively throughout the automotive industry for material handling, and equipment and part positioning.
Safety was a paramount design consideration. A steel case encloses the rotating steel cutting blades. The case thickness ensures that a broken blade will not penetrate the case and injure someone. The shaft was designed to minimize shaft bowing and deflections. The electric motors have an automatic thermal cut-off in case of jamming.
Figure 2. Close up of the adjustable feed chute.
Figure 3. Close up of the feed chute for shredded paper. It channels paper from the cutting blades to collection bag.