Investigating cast products
What affects the properties of the material in a cast product?
In this activity students will explore how changing the ratio of PVA glue to PoP (plaster of Paris) affects the strength of a composite material. They'll test both tensile and compression strength to find the perfect mix.
This activity is part of a series of resources designed to challenge the students by requiring them to apply the knowledge and understanding of engineering materials through a ‘batch’ production experience, including CAD design project, Investigating batch production, and Engineering design processes.
It’s one of a set of resources developed to aid the teaching of the secondary national curriculum, particularly KS3, supporting the teaching in engineering and design and technology (D&T).
Activity: What affects the properties of the material in a cast product?
In this activity students will investigate how the proportion of PVA glue added to plaster of Paris (PoP) affects the properties of the material produced in a cast product.
Students will work in pairs to create card moulds. They will then mix different ratios of PVA, PoP, and water, pouring each mixture into duplicate moulds. After the test strips dry overnight, they'll conduct two types of strength tests: a tensile test (hanging weights) and a compression test (using a G-clamp).
They’ll then be tasked with analysing the results to determine how PVA affects the material's strength. Look for patterns and identify the optimal ratio of PVA to PoP. Finally, decide on the best ratio for your future casting projects and present your findings to the class, using graphs or tables to support your conclusions.
Download our activity overview for a detailed lesson plan on CAD design.
The engineering context
As part of the production process, engineers and designers must test the properties of different materials in order to select the best materials for their products to ensure that they’re suitable (e.g., are they strong enough for the activity that they’ll be used for?).
Suggested learning outcomes
Students will be able to explain how to develop a product or material to improve the outcome (engineering materials). They’ll also learn how to set up an experiment that allows key decisions to be made from the outcome. Finally, they’ll be able to carry out a manufacturing and testing programme, understanding the importance of time allowance and quality control.
Download our activity sheet and other teaching resources
The activity sheet includes teachers’ notes, useful web links, and links (where appropriate) to the national curriculum in each of the four devolved nations; England, Northern Ireland, Scotland and Wales.
All activity sheets and supporting resources are free to download, and all the documents are fully editable, so you can tailor them to your students’ and your schools’ needs.
Download our classroom lesson plan and presentation below.
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