All of the bulk material tables published by screw conveyor manufacturers are based on the Material Characteristic tables in the CEMA 350 book. The CEMA 350 book is the “bible” for screw conveyor design and was first published in 1971. CEMA is the Conveyor Equipment Manufacturers Association and is an industry group dedicated to the advancement of the conveyor industry. CEMA created the 350 book as a guideline for designing and manufacturing screw conveyors. The book is updated almost every year to add new materials to the Material Characteristics tables. I am the Chairman of the Screw Conveyor Engineering Committee for CEMA and we have made several updates and improvements to the CEMA 350 book in recent years. You can order an electronic copy of the CEMA 350 book from the CEMA Web site at www.cemanet.org. The guidelines in the CEMA 350 book apply for most applications and are conservative. Bulk materials are classified by density, size, flowability, abrasiveness, and other factors. Each bulk material is given a code which corresponds to basic design and materials of construction guidelines. For example, a bulk material such as Portland cement is dense at 94 lbs cu/ft, is very fine, has good flowability, is moderately abrasive and can aerate when conveyed. The CEMA material characteristic code is 94A10026M from the CEMA 350 book. The corresponding component series code is 2D, or heavy-duty. Minimum materials of construction thickness are given for each conveyor diameter.
WAM Inc. is a European-based manufacturer with offices located in the U.S. WAM is also a member of CEMA and follows our industry guidelines. They also have their own designs and standards for screw conveyors that make them unique to the industry. You probably just need to specify that you want your equipment designed and built to CEMA standards if you are more comfortable with the CEMA standards.

All of the major screw conveyor manufacturers are active members of CEMA, The Conveyor Equipment Manufacturers Association. The CEMA website is www.cemanet.org. Each screw conveyor manufacturer that is a CEMA member will be listed with their contact information. You can also call the CEMA office and speak with one of the staff. The CEMA staff is very knowledgeable and helpful. They will be able to direct you to a screw conveyor manufacturer in your area. Almost every screw conveyor manufacturer has an office or sales representation in the Midwest. Also, the CEMA staff will help you locate belt conveyor manufacturers as well as companies that make accessories for the bulk material handling industry. Since your company is a manufacturer of conveying systems and components then you may qualify to be a CEMA member. Being a CEMA member has many advantages. The main goal or mission of CEMA is to advance the conveying industry by creating technical and safety standards. You will also gain knowledge on industry trends and any legal issues that may affect your business.

Many bulk solids contain moisture and are very sticky. They become difficult to convey because the bulk solid sticks to the flight surface of the screw and builds up. Since you are processing polymers, the materials of construction of the conveying equipment are typically stainless steel. The flight surfaces and complete screw can be polished to a very fine finish and even electro-polished to achieve a mirror finish. The bulk solid has less tendency to stick and will release from a smooth, polished finish. The internal surfaces of the trough can also be polished or electo-polished.
Another option is to coat the conveying surfaces with non-stick coating such as Teflon. The coatings can be engineered for your specific application. The flight design of the screw conveyor can be modified to be a ribbon or even a shaftless type. Ribbon and shaftless screw conveyors are designed specifically for conveying sticky bulk solids. Sticky products adhere to the screw at the location where the flight meets the center pipe. The ribbon flight is only attached to the center pipe with thin posts located on 90 ° intervals. The shaftless flight has no center pipe and only uses the flighting or spiral to convey the product. You may want to consider these options.

Since the rail cars are located 1,500 ft from the storage silos, belt conveyors are your best option for conveying the meat and bone meal. I recommend a bucket elevator to transfer the product vertically 50 ft. The belt conveyors and the bucket elevator would be completely enclosed and weather proof. The system capacity of 150 tons per day could easily be handled with this system even if it was only operated 12 hours a day. A screw conveyor could be used in the rail car loading area because of the ability to easily load multiple points on the rail cars. Belt conveyors, a bucket elevator, and a screw conveyor are a very economical solution to the conveying application. Typical materials of construction are carbon steel and utilize CEMA standard components.

Steel shot is extremely dense at 235 lbs/cu ft and very difficult to convey vertically. The bucket elevator you currently have in use is the best solution for vertically conveying extremely dense products. A vertical screw conveyor is capable of conveying the steel shot vertically, but the capacity loss due to gravity would be very high. The steel shot will fall through the gap between the screw and housing and slip back down the spiral face of the screw. Also, the horsepower requirements will be high due to the capacity loss and the tumbling action of the steel shot in the vertical screw conveyor. A bucket elevator keeps the steel shot “static” in the buckets, eliminating any tumbling action. Each bucket is filled and raised vertically to a discharge point. The horsepower requirements are much less.
Improvements can probably be made to your current bucket elevator to make it operate to your satisfaction. A knowledgeable mechanical conveying person could evaluate the bucket elevator and offer product improvements. Many options are available to increase capacity, reduce component wear or prevent downtime.

A compression screw or screw press for dewatering bulk solids such as sand is a specific type of process equipment designed and manufactured by companies that specialize in dewatering and classifying bulk solids. A screw press reduces the liquid content by compressing the bulk solid and forcing the liquid out through a screen or filter. The volume between the screw press flights reduces and compresses the bulk solid as it is conveyed toward the discharge. Dewatering consistency can be accurately achieved with a screw press by adjusting screw speed, screw configuration and screen type.
Another method would be as you have suggested and use an inclined screw conveyor with an inlet hopper and weir. The sand will settle to the bottom of the hopper by gravity and the free water will rise to the top and drain off over the weir. The sand will convey up the incline and continue to dewater. Maximum recommended incline for a dewatering screw conveyor is 30°. Conveyor angles greater than 30° cause a significant reduction in conveying capacity. Dewatering consistency is less accurate in an inclined dewatering screw conveyor when compared to a screw press.
There are several screw press manufacturers on the market that can solve your sand dewatering issue. KWS designs and manufacturers inclined dewatering screw conveyors for your application. The large capacity of 40 tns/hr would require a single-screw 30-inch diam. or a twin-screw 24-inch diam. unit. A complete understanding of your application is important so we can provide a solution that exceeds your requirements.

Shaftless screw conveyors are the perfect solution and designed to efficiently convey semi-fluid and sticky bulk materials. Wet and sticky bulk materials will adhere to the center pipe of a conventional shafted screw conveyor and reduce the conveying capacity. The shaftless screw design is non-clogging because of the absence of a center pipe, which also eliminates the need for intermediate hanger bearings. The shaftless spiral provides the conveying surface and is directly connected to the drive unit.
The shaftless screw conveyor can solve many other application problems. They can be designed completely gas-tight to eliminate the escape of any harmful vapors. Also, material with large lumps can be easily conveyed and reduced in size by the spiral action of a shaftless screw conveyor.
Typical construction includes high-strength spirals, stainless steel housings with reduced-friction liners, and high-torque drive units. Shaftless screw conveyors are used in many industries such as chemical, food processing, pulp and paper, and wastewater treatment.