Chemically Bonded Sand Questionnaire_S22 - Dean Berger

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School

California Polytechnic State University, San Luis Obispo *

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Course

141

Subject

Mechanical_engineering

Date

May 4, 2024

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pdf

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4

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IME 141 – Chemically Bonded Sand Questionnaire_S22 1 Module 2. Chemically Bonded Sand Mold Casting Study Guide Questionnaire Transmission case casting Objectives: 1. Describe three types of chemically bonded sand binder systems and how they work. 2. Choose an appropriate alloy given mechanical design requirements and alloy mechanical properties. 3. Describe how three rigging methods help minimize defects in a casting. 4. Describe the optimum part orientation relative to the mold given the locations of key part features in a large casting. Introduction Chemically bonded sand systems are those which do contain water as a principal component of the binder. These types of binders are distinguishable in several ways, but primarily they can be characterized as having long shelve lives and producing relatively little gaseous products when contacted with molten metal. Compared with water-containing binder systems such as green sand, benefits include greater flexibility in manufacturing, improved surface finish, and they can be used as cores to create internal features in the castings. A key tradeoff is that the sand is not as easily re-usable as green sand. Typically, to reuse chemically bonded sand after molding, a thermal reclamation process must be employed to oxidize and remove the binder. Frequently, chemically bonded sand is employed for cores and green sand used as the outer mold material. Chemically Bonded Binder System Types There are three primary categories of chemically bonded sand binders: 1. Ambient Temperature curing types (also known as Air Set, Self-Setting, or Warm Box process) – The sand is coated with 2- or 3-part binder system that cures in a known time period (e.g., 10-minute epoxy resin). The curing reactions are typically slightly exothermic, henceforth the name Warm Box.
IME 141 – Chemically Bonded Sand Questionnaire_S22 2 2. Gas or Vapor curing types (also known as Cold Box process) – The sand is coated with a resin that cures by activation with a gas or vapor. As the gas expands upon release from a compressed gas cylinder, it absorbs heat and cools the surroundings, henceforth the name Cold Box. 3. Thermally curing types (also known as Hot Box or Shell Sand process) – The sand is coated with a heat- activated resin that cures only with elevated temperature (~500F). Core Blower method : resin-coated sand is forced upward in an airstream through a hole in the bottom against the heated core box pattern for a period. Shell Sand method : the pre-heated pattern is placed over resin-coated sand in a hopper. The assembly is then inverted allowing sand to fall onto the pattern and rest for a period. In both methods, as heat transfers through the sand mass, the resin is cured to desired thickness forming a bonded sand shell. Once the shell is formed, the airstream is halted or the assembly inverted again, and the uncured sand returns to a hopper. Hollow cores can be made this way, reducing their cost compared to solid cores. Resources The following is a table of resources and links to assist with this learning module and for answering the study questions below. Resource Description Link Canvas page in Module 2 Intro to sand and binder systems Intro to Sand and Binder Systems Case Study: Transmission Case for the Amphibious Vehicle Interactive Case Study (Link to American Foundry Society) Case Study: Transmission Case for the Amphibious Vehicle Video: Shell Sand Process Animated Video (1.5 min) Video: Shell Sand Process Study Questions The questions below are for practicing concepts around chemically bonded sand systems and its application in a relatively large industrial metal casting example presented in the case study: Transmission Case for the Amphibious Vehicle . You may write or type answers directly in this document, but you must save as a .pdf before uploading to submit to Canvas. The due date for this assignment is Saturday of week 4 at 11:59pm. We will build upon these concepts throughout the term with in-class discussions, discussion board posts and lab projects. It is important to practice articulating your ideas using relevant terms and concepts. The quality of your responses is assessed based on your clearly answering all parts of the questions using appropriate casting terminology. Please use the rubric below as a guide.
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