Novel Electrical Joints Using Deformation Machining Technology—Part II: Experimental Verification
This is the second part of the paper related to the exploration of deformation machining technology (DMT), originally developed at Bauman Moscow State Technical University, as it may apply to making electrical joints and comparing their performance to bolted and welded electrical joints. The DMT process is used to generate tooth-like profiles on two opposing surfaces that make the electrical joints which are later joined by applying a mechanical load. Part I contained a more detailed explanation of the DMT process and the description of the results of computer modeling of DMT joints in copper and aluminum. This paper provides the experimental results of the mechanical and electrical performance of copper and aluminum DMT joints which were compared to bolted and welded electrical joints of identical geometries. Measurements of tensile strength and electrical resistance, after thermal cycling and short-circuit testing, show equivalent or better performance of copper DMT joints compared with copper bolted and welded joints. In addition, it is observed that copper DMT joints have superior performance when compared with aluminum DMT joints, this was attributed to lesser gap filling and the springback effect that occurs after the mechanical load for making the joint is removed. The computer modeling results reported in Part I of this paper support these observations.
A COMPARISON OF ALUMINUM VS . COPPER AS USED IN ELECTRICAL EQUIPMENT
The debate over the pros and cons of aluminum vs. copper conductors has been discussed for many years. Many of the concerns are based on old information and also misinformation. These concerns center on the very different properties of the two materials and their suitability for application within the Electrical Equipment Industry. Reliable performance from the conductors, the joints and terminations of the conductors is essential to the operation of the electrical system. With the recent increases in the cost of copper, customers are seeing these increases passed on to them by the equipment manufacturer. The variance in cost between equipment with copper versus aluminum conductors is now affecting the customer’s buying decision. This paper provides a comparison of the mechanical and electrical properties of copper (Cu) and aluminum (Al) and their relevance as applied to electrical distribution products. The offerings and impact of Cu and Al on various pieces of equipment is also discussed. The intended purpose is to provide the user with the information necessary to make an informed decision on the selection of copper or aluminum conductors within electrical equipment. INTRODUCTION Cu and Al are the two most commonly used materials for conductors and bus bars in electrical equipment. Each has positive and negative characteristics that affect their use in various applications. Both materials have been in continuous use in the electrical industry for many years. While aluminum is the most abundantly available of the two metals, the demand and scarcity of Cu have caused its cost to fluctuate widely. Silver is generally considered the best electrical conductor, however its high cost and low strength limits its use to special applications such as joint plating and sliding contact surfaces. For the purposes of this paper, the areas of discussion are: Current Carrying Capacity, Conductivity Physical Properties a. Expansion b. Weight c. Tensile Strength Connections and Terminations Plating and Environmental Concerns Product Offerings Cost Comparison Impact on Various Pieces of Equipment CURRENT CARRYING CAPACITY The electrical and mechanical properties of a material are dependent on its alloy. For the comparison between copper and aluminum in this paper, the copper is cold-worked electrolytic tough pitch copper similar to ASTM B187, alloy UNC C11000. The copper used in electrical equipment is nominally pure 98% conductivity commercially hard based on the International Annealed Copper Standard (IACS). Pure Aluminum is not used as an electrical conductor in equipment since it is too soft for mechanical assemblies and is thus alloyed with other materials. The Al alloy 1350 used prior to 1975 was designated as EC (Electrical Conductor) grade aluminum with a 99.50% aluminum content. Even though it has 61% the conductivity of Cu it lacked in mechanical properties making it less than ideal as a conductor in the equipment. Al alloy 6101 is the predominant aluminum bus bar material being utilized and is stronger than 1350 Al because it has been hardened by heat treatment, but it only has 56% the conductivity of copper. The reduced conductivity of AL 6101 does not mean that the Al conductor will run hotter than the Cu
Increasing pulp yield in kraft cooking of softwoods by high initial effective alkali concentration (HIEAC) during impregnation leading to decreasing secondary peeling of cellulose
Abstract Pulp yield can be improved by a more homogeneous delignification of the chips, achieved by improved impregnation prior to the cooking stage. Complete and efficient impregnation is obtained by increasing the diffusion rate by means of an impregnation liquor with a high initial effective alkali concentration (HIEAC). In the present study, the effect of HIEAC in the impregnation was evaluated and compared to a reference impregnation procedure and a prolonged impregnation. After the various impregnation scenarios, the alkali concentration was always adjusted to the same level in the beginning of the cooking stage. Impregnation with a HIEAC resulted in yield improvements by 1–1.5% units, due to a higher cellulose yield and possibly also to higher yield of glucomannan. The HIEAC with an even alkali distribution within the chips prior to the cooking stage resulted in a more uniform delignification carbohydrate degradation. Yield increase obtained by uniform delignification is due to both decreased shives content as well as less secondary peeling.