Screws and dies to improve extrusion productivity

Screws and dies are critical parts of the extruder. The wear of screws and dies can significantly effects throughput and quality of extrusion products. For feed and food extrusion, the wear of metal parts may also put the products under the risk of metal pollution and cause food safety issue. Suppliers should take the responsibility and positive role in reducing the wear of metal parts in production and in improving feed-to-food safety.

FAMSUN provides spare parts solutions that can not only maintain production lines at optimal levels, but also upgrade replacement parts to minimized wear and prolong service life, ensuring optimum efficiency and productivity for customers manufacturing facilities.

This article will introduce the new FAMSUN screws and dies that developed to increase lifecycle and enhance the productivity of raw material extrusion and aquafeed production.

Ways access to improvement
Extrusion process helps to improve the bioavailability of raw material, which means the high temperature, short time process including gelatinization of starch components, denaturation of protein, stretching or restructuring of tactile components, and exothermic expansion of the extrudate can maximizes the benefits of heating feed ingredients (improved digestibility, inactivation of anti-nutritional factors, and pasteurization), while minimizing nutrient degradation. Feed conversation rates of extruded rations are usually better, because the cooking process increases the digestibility of raw materials, particularly the starch fraction.

Extrusion adds value to low-cost raw materials and promotes the utilization of alternative ingredients, allowing for more flexible feed formulas design and production. It also offers additional advantages such as product of better flavor, more environment-friendly and reduced waste of valuable ingredients. With its distinguished performance, the technology is more and more used in large-scale commercial feed production.

Wear of working parts can occur through both abrasion and/or corrosion during production. In FAMSUN's attempt to minimize wear from both of these resources, developing new materials for spare part construction and improving metal heat treatments are referred. The new screws and dies FAMSUN developed to improve extrusion performance are made of new materials and processed by improved heat treatment solutions.

New single screw for raw material extrusion
Screws as the most important working parts, its wearing resistance performance is directly related to the operation performance and production capacity of the raw material extruder, as well as the operation cost and maintenance cost of feed mills.

In continues extrusion production, raw material moving forward along the flow channel of the extruder screw, and friction between material flow and screws is increased as compression of incoming material in the chamber increase, wearing of screws then occur. Wearing will increase the gap between screw profile and inner wall of barrel, and leakage flow is liable to release from the feeding inlet, which dramatically reducing the energy efficiency and throughput of extrusion production. On the other hand, frequently downtimes due to worn screws replacement will further decrease the production efficiency of the whole system. Therefore, upgrading the wear-resistance of extruder screw is very important to the stable and reliable of the extrusion production.

FAMSUN used to produce single-screw for raw material extrusion with 38CrMoAl nitrided steel, which is of improved hardness and wear resistance protection on the surface and excellent strength and toughness in the center. In order to make continuous improvement, the new single-screw was developed by using special steel and alloys based on the previous edition. The heat treating solutions used to improve its properties are also specially designed. Tests and actual application in productions prove that the new parts can produce more feed at its best performance. Its lifecycle for raw material extrusion is increased by 2-2.5 times. Taking the application on a FAMSUN PHY260 Raw Material Extruder for example, the regular single-screw made of 38CrMoAl nitrided steel can process corn for 2,000 tons in its lifecycle, while the new single-screw can extrude 6,000 tons corn at its best performance. The replacement frequency of a screw can be prolonged to three months from previous one month, which is also a maintenance and cost saver.

New twin-screw for aquafeed extrusion
FAMSUN had developed two regular twin-screw products for aquafeed production: MY 105 and MY1045, both are characterized by high wear-resistance and hardness on the surface. However, the former is not common used because it is more brittle and will crack if heavily impacted by feed mash during extrusion. The later makes an improvement on surface resistance. Its surface hardness is increased to 60-65HRC, but still has bad roughness and liable to crack if impacted by hard particles during production. MY105 twin-screw is able to process 10,000-15,000 tons of aquafeed in its lifecycle, while the production capacity of MY1045 twin-screw is 25,000-35,000 tons.

To make constantly improvement, the research of new twin-screw mainly focuses on improving its surface performance. After studying the characteristics of common feed and food formulas, analyzing the properties of possible base steels, using new hardening technologies and developing new methods to strengthen the combination of surface protection material and base material, FAMSUN new twin-screw was successfully rolled out.

The new twin screws are made of alloy-structural steel as base, which provides better toughness and prevent screws from cracking during extrusion. Special alloy is combined on the flight of screw to improve wear resistance and prolong service life. The surface hardness of new screws is up to 1500HV and can process 60,000-80,000 tons of feed at high performance constantly.

New extrusion dies
Extruder dies are liable to crack under the stress of feed mash to be extruded out of die holes. FAMSUN new dies use special steel and alloy in material construction, and makes improvement during the processes of forging, pre- and post- heat treatments. Different from the regular dies that made of Cr12 steel, the combination efforts of special alloy and vacuum heat treatment in the new die improve the toughness of dies with small openings, minimize the deformation of die holes and ensure them of better streamlines, which facilitates discharge and produces more uniform feed pellets. Most of all, the surface hardness of new dies is improved to 58-63HRC from 50-55HRC of the regular ones, which further prolongs the lifecycle and maintain the efficient production of the extrusion system.

And with vacuum heat treatments, the new dies are free of pollutants such as sodium nitrite and potassium dichromate that generated during traditional blackening and salt bath processes. It is safer for feed and food production.

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