The Fundamentals of Bucket Elevators and How They Work
Bucket elevators equipped with Engineered Steel Chain are designed to lift enormous quantities of heavy materials to considerable heights. Thus chain selection is key to the proper functioning of bucket elevators. Chain type is broadly based on the type of bucket elevator. In most applications, straight sidebar, hardened bushed rollerless chains are applied. Offset style sidebar chains have been used for years but with chain manufacturing technology improving, offset chains are far less common for new equipment.
Centrifugal Discharge Elevators
Centrifugal discharge elevators are designed so that the buckets are fed material from the inlet feed chute at the boot section and discharge material via centrifugal force. This style of elevator typically operates at a much higher chain speed, when compared to the other elevator styles, which usually fall in the 220-330 fpm (feet per minute) range. The use of a single strand rollerless chain with a K-style attachment (every 12-18”) is very common in such elevators with attachments ranging from every 2nd pitch to every 4th pitch. Chains which have a roller in this application will become loaded with the conveyed material between the rollers and bushings. The presence of the conveyed material along with any moisture will cause the rollers to cease onto the bushings preventing them from turning.
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Root Cause Analysis and Corrective Action – The Key to Continuous Improvement
An ISO 9001 certified company strives to maintain the highest level of quality, not only in their product, but also in their processes, which make up their quality management system. One of the key components of an effective quality management system is to continually improve. In order to continually improve, we must first identify issues or areas of concern and, more importantly, their causes.
One practice is root cause analysis, which is defined as a method of problem solving that tries to identify the root causes of faults or problems which, once removed, prevents the final undesirable event from recurring. By practicing root cause analysis, we are able to identify and correct the cause of failures, as opposed to simply addressing their symptoms. The goal of focusing on correcting the root cause of an issue is to prevent that problem from recurring. One way to practice root cause analysis is the 5-Why method. This is a method of asking “why” repeatedly until the root cause is identified.
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To Grind or Not to Grind Your Pins? When making field connections on your chain DO NOT grind your pins because this will only cause you more headaches in the upcoming months. When discussing chain, the old saying “Your chain is only as strong as your weakest link.” has never been so true and by grinding a pin you have just created a weak link.
As machining and hole punching processes get more precise we can use these processes to our advantage and add more value into the chain for our customers. Websters current processes allow us to reproduce a consistent and repeatable interference fit between the pins and the sidebar holes. With this repeatability, we solely rely on our press fit to keep the pins stationary in the sidebar. There are always a few exceptions to the rule based upon the geometry of the parts, but for the most part you will notice our pins with a full round end.
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Measuring Chain Elongation
Chain elongation is an easy way for the customer to determine the wear on the internal components of the chain just by taking a few measurements while the chain is on the conveyor. The measurement can then be compared to the chain’s original length and used to determine how much life is remaining in the chain.
To measure chain elongation, you will first need to follow any and all safety guidelines to lockout the conveyor and remove any guards needed to gain access to the chain. Usually, a 10 pitch section of chain is preferred, but more or less can be used depending on access to the chain. When taking the measurement on the chain there are several locations you can measure from and to, but the measurement needs to be taken from a consistent place. In other words, if the measurement starts from the centerline of the pin it will need to end on the centerline of the pin approximately 10 pitches away, or however many pitches are being measured. Other common places to measure to and from would be the front edge of the pin head or the front edge of a sidebar. Once this measurement is taken it can be used in the formula below to determine the chain’s elongation. Once the chain elongation is determined the rules of thumb are as follows:
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RWL vs. AUS – An Engineering Perspective
What are Rated Working Load (RWL) and the Average Ultimate Strength (AUS) of an engineered class chain and what do they mean?
First let’s tackle the AUS and a general overview of how it is calculated. The AUS is a calculated value from the chain manufacturer of the average breaking strength of the chain. The published AUS rating is generally the lowest calculated value between the following: the sidebar’s tensile strength, the sidebar’s shear strength and the pin’s shear strength (see Figure 1). Generally speaking this number should not be used when sizing a chain for a particular application because this is the breaking limit of the chain; the chain should never equal or exceed this value as it will result in total chain failure. It should be considered into your chain choice when a higher fatigue strength is required for the more demanding applications.
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