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Wear Protection - Tungsten carbide clad extruder components can increase product quality and reduce costs
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Figure 1. Single screw extruder components protected with infiltration brazed tungsten carbide |
Infiltration brazed tungsten carbide wear protection can help managers solve this problem. Tungsten carbide protection can extend the life of extruder components, allow for higher throughput and lower cost.
Severe Wear
Severe wear can cause an extruder to surge, resulting in inconsistent product density, shape and size. Variable product can lead to a line shutdown, costing the plant from US$1,000 to over US$5,000 per hour.
Many petfood plant managers are under increase pressure for higher throughput. Therefore, required maintenance cycles for unprotected extruders are often shorter. So, extruders must be shut down several times a year for adjustments and replacement of worn parts. These operating disruptions create costly delays and decrease plant productivity.
Extruder wear protection can create consistent product quality in abrasion and corrosive environments. Minimizing component wear is crucial to reducing hard and soft costs. The hard costs include the cost of the unprotected components and the continuing replacement of these worn parts. The soft costs include inconsistent quality and productivity losses. Reducing wear decreases the number of equipment adjustments and downtime, makes managing inventory easier and helps ensure predictable maintenance schedules.
Wear protection materials
In the past, the primary source of replacement parts for petfood extruders was the original equipment manufacturer (OEM). However, petfood manufacturers have explored other wear protection options to improve productivity.
Hardfacing is the process of depositing, by welding techniques, layers of metal on areas that are exposed to high wear. Hardfacing was rejected by most petfood manufacturers as a possible wear solution because the metal flaked off, creating contamination issues. This option added little benefit for the additional cost, and restrictions placed on materials used in food processing limited the types of protective materials that could be used.
Tungsten Carbide
Infiltration brazed tungsten carbide protection significantly increases the life of vital extruder components, resulting in reduced wear and a more consistent, quality product. This premium cladding provides resistance to the effects of heat, abrasion, erosion, and corrosion. It also permits effective heat transfer, allowing the entire barrel to be equally dense and change temperatures uniformly.
In the early 1990s, New Albany, Indiana, USA-based Conforma Clad Inc. successfully developed brazed tungsten carbide clad extruder barrels. The brazed tungsten carbide clad components can be found in over 80 petfood plants worldwide.
Brazed tungsten carbide cladding protects extruder components four to eight times longer than those without wear protection. Decreased wear enables petfood producers to maintain critical component geometries longer, without sacrificing food quality or production output levels.
The process, which is protected as a trade secret, metallurgically bonds tungsten carbide to ferrous metal base materials. The result is a hard, protective clad that is extremely wear resistant and very durable. A cloth application system enables densely packed tungsten carbide to be uniformly applied to complex geometries, providing a protective layer that wears at a uniform and predictable rate.
Tungsten carbide cladding is much harder and longer lasting than stainless steel components typically applied by OEMs. While stainless steel reduces corrosive wear, sand abrasion tests show it has a low abrasion resistance factor (ARF). The 410-series stainless steels have an ARF of 5, compared with brazed tungsten carbide formulas with an ARF of 80.
Break-in period
One criticism of tungsten carbide coated parts is that they are very abrasive. An abrasive part makes it very difficult to get the same energy throughout the barrel, thus, there is a break-in period with the tungsten carbide part and product is lost.
The “as clad” tungsten carbide surface is rougher than a standard OEM part. However, screw flight outer diameters and liner inner diameters can be ground smooth using a diamond grinding wheel. For the customers who are concerned with the finish of the “as clad” root profile, there is a method of polishing the root diameter to give it as smooth a surface as the OEM parts. Most petfood companies will tell you that there typically is a short “break-in period” with all new parts, clad or OEM parts.
Fat content of the product is also a consideration. When making high-fat products, managers have no problem using the screws “as clad.” When making lower-fat products, additional polishing of the screws is recommended.
Field comparisons
Conforma Clad compared performance of clad-protected single screw extruder components to standard OEM components over a two-year period. The clad-protected components resulted in lower costs per ton.
In the 28-month test period, a leading US petfood manufacturer replaced OEM extruder components four times, while the original brazed tungsten carbide clad components remained in continuous operation. As shown in table 1, the cost per ton using brazed tungsten carbide clad parts instead of OEM components was 52% lower.
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Figure 2. Abrasion resistance capabilities of tungsten carbide infiltration brazed cladding compared to typical materials used for extruder parts. Abrasion Resistance Factor (AFR) is the reciprocal of volume loss as determined by ASTM G65. Source Conforma Clad Inc. |
In addition to extending the life of components, many petfood manufactures choose brazed tungsten carbide protection for another primary reason: Less need to make processing adjustments. The normal wear progression of unprotected screws and barrels forces manufactures to adjust equipment in order to decrease processing and product inconsistencies. When components are clad, there is much less need to make adjustments.
Plants that use clad components understand that they can run the parts long enough to get a good return on investment, but choose to replace them prior to experiencing any significant wear that may change the processing parameters.
Real world example
For example, a leading multinational petfood manufacturer had historically ran OEM extruder parts for 2-3 months before severe wear began affecting processing and product quality. By installing extruder liners and screws protected by brazed tungsten carbide cladding, the facility was able to operate the line more than 12 months without adjusting the extruder.
The key is to understand wear problems. The goal is to find out why and how components wear and what solutions make sense.
Written By: Don Bucholz, PhD, Lorrie Muzzone, Christy Eversmann
The authors are with Conforma Clad Inc. Don Bucholz, PhD is vice president of technology; Lorrie Muzzone is market manager-food and feed division; and Christy Eversmann is a marketing specialist.
For more information, contact:
Conforma Clad
501 Park East Blvd.,
New Albany, Indiana 47150 USA,
Tel: +1.888.289.4590 or +1.812.948.2118,
Fax: +1.812.944.3254,
Reprinted with permission from Petfood Industry, December 2004.
