ME 493Final Report – Year 2008
June 6, 2008
Heated scraper for tile removal
Sponsored by
Aries engineering, Inc
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Group Members
Matt Baker
Pete Levno
Zach Perryman
Jessica Pierry
Faculty Advisor
David J. Sailor
Industry Advisor
Ken Millard
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Executive Summary
Aries Engineering, Inc manufactures and installs radiant floor heating in Recreational Vehicles (RVs) using electrical resistance through conducting wires. The wires are attached to a fabric mesh that is custom designed to fit individual RVs, then the unit is placed onto the floor and covered by adhesive which tiles are set into.
Advances in the RV tiling industry have led to a change in the type of adhesive used, from a cement type mortar to a flexible compound to prevent tiles from breaking free of the floor due to flexing of the chassis as the RV travels down roads and highways. This change had caused an increased difficulty in removing the tiles due to the strong bond it creates between the tile and the mesh.
Ken Millard is a Portland State University Alumni who created the idea for a senior capstone project. The initial requested was the designing and creation of a heated scraping tool to remove the adhesive from the wires and mesh without causing damage to them. The adhesive becomes pliable when heated and easier to remove than when it is room temperature.
The scraper prototype is requested to be a handheld tool that heats up above the yielding point of the adhesive, of a small enough width to remove adhesive from between conducting wires, and be affordable enough to make 100 units.
The capstone design team has created an electrical resistance heated scraper using a 150 watt heating element along with a tile heating unit consisting of a silicone heating pad and insulation housed in framing with a handle attached to replace the current method of using a handheld torch to preheat the tile to remove the danger of open flame and increase even heat transfer throughout the tile. Both tools have a thermal cutoff switch to prevent overheating. These tools work effectively and satisfy customer requirements
Table of Contents
Executive Summary…………………………………………………………...... 2
Table of Contents…………………………………………………………....………….3
Table of Figures……………………………………………………………....……....…3
Introduction…………………………………………………………….………....…....4
Mission Statement……………………………………………………………...…...….6
Product Design Specifications…………………………………………………...……..7
Top-Level Alternative Designs……………….……………………………….………..8
Final Design………………………………………………………………………...…..9
Overview………………………………………………………………....…….9
Heated Scraper…………………………………………………………..….…11
Tile Heating Unit………………………………………………………….…..13
Tile Removal Process…………………………………………………….…...16
Evaluation and Future Considerations……………………………………….....…….17
Conclusion………………………………………………………………………...…..21
References………………………………………………………………………...…..22
Appendix A: Manufacturing Instructions and Assembly………………………..……23
Heated Scraper………………………………………………………..………23
Tile Heating Unit……………………………………………………………..26
Appendix B: Bill of Materials…………………………………………………….…..29
Appendix C: Operation Manual……………………………………………...……….30
Appendix D: Experimental Data and Results…………………………………...……31
Transient Heat Response of a Tile Floor Assembly……………………...…..31
Optimizing Temperature to Lower Yield Strength of
Uniflex 916 by C-Cure Adhesive………………………………….………..40
Table of Figures
Figure 1. Luxury Motor Home Interior………………………………………..…..…..4
Figure 2. Photograph of system components………………………………..…….... 10
Figure 3. Photograph of heated scraper……………………………………….……...13
Figure 4. Photograph of finished tile heating prototype……………………..…..…..16
Figure 5. Tile pieces being removed…………………………………………………17
Figure 6. Tile scoring pattern………………………………………………….....…..17
Figure 7. Tile section with adhesive removed…………………………………...…..18
Figure 8. Floor section where tile has been removed using new prototypes……..….19
Figure 9. Photo of floor section where tile was removed using current methods..…..20
Figure 10. Tile mound that is formed directly under the impact site of the hammer...21
Introduction
Recreational Vehicles (RVs) or motor homes are an enjoyable way for many owners to spend a vacation traveling while still having the comforts of a custom designed home. Some RV owners live in their vehicle year- round, giving them the ability to have a new backyard any time they feel like driving their traveling home.
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When a person, family or couple decides to own a RV, they often spend a great amount of time and money decorating the interior for comfort, ease of use and style. As a tasteful touch owners may choose to install ceramic, granite or marble tiles to give the overall feel and look of a desirable living interior as shown in figure 1. Aries Engineering, Inc had created a product called Gold Heat™, a radiant floor heating system that raises the temperature of the tile floor to about 85°F.
Figure 1. Luxury Motor Home Interior.
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The tiles are heated by resistance heating wires placed under the tiles typically as an optional feature in new RVs but can also be installed if the floor is being replaced. Gold Heat™ provides additional heat and comfort to the interior, and is hypoallergenic as there is no recirculating of air using in the heating process.
The tiles are set in an adhesive, Uniflex 916 by C-Cure, which is specifically formulated for the RV industry. Below the adhesive is a fabric mesh which holds electric resistance heating wires in place. The heating system lies on top of an oriented strand board base. Additionally this system could be applied to remove floor tiles without radiant floor heating systems underneath.
It is common to need to replace the tile for various reasons such as a tool falling on the tile during initial installation, damage to the tile by the RV owner, or stress to the tile due to flexing of the chassis while driving. The removal process can take from an hour to an hour and a half. Removal of the tile and adhesive is typically involves using hammers, torches, crowbars and scrapers. The tile is heated with the torch, broken with the hammer, pulled up with a crowbar and then the adhesive is scraped away. This process is time consuming and hazardous because an open flame is used in a confined space. Additionally the amount of heat delivered by the torch is difficult to control. When hit with a hammer the tile often shatters, creating sharp flying debris. Scraping the adhesive frequently damages the wires in the radiant floor system, and when the wires are damaged additional time and material must be taken to repair the system prior to reinstalling a new tile.
Aries Engineering has requested the design of a heated scraper to assist in the removal of tiles and the underlying adhesive. The capstone design team has chosen this project to complete, and after reviewing the entire removal process has added a tile heating tool and thermal shock treatment to the systematic series of actions required to remove damaged tiles, resulting in safer, easier and faster complete tile removal with little or no damage to the Gold Heat™ resistance heating wires.
Mission Statement
The capstone design team will develop tools to assist in the removal of tiles and adhesive for the RV industry. It is known that Uniflex 916 by C-Cure, the adhesive used for setting tiles, looses strength when it is heated, therefore a thermal component will be a key part of the design. The tools will be accompanied by a set of procedures that are easy to learn and implement. Specialized tools such as heating pads, heated scrapers and any other tools helpful to the removal of tiles will be developed and the time taken to remove a single tile will be reduced to 30 minutes. The project will be completed with working prototypes by June 6, 2008.
Product Design Specifications
The main customer for this project is Ken Millard, President of Aries Engineering, Inc. Mr. Millard is in frequent contact with the people at RV repair centers who perform the actual work of removing damaged tiles (tile technicians) and has provided the initial concept design requirements. Other specifications were established through research and testing. The main design requirements are:
►Design and create a heated scraper. This scraper will be heated above 150°F and will be narrow enough to fit between electrical heating wires at the scraping tip.
►Reduce the time taken to remove damaged tiles. Current tile removal time is about an hour for one 12 inch by 12 inch tile, and this is increased if wires are damaged and need replacing. Designed tools and procedures must reduce tile removal time to 30 minutes or less.
►Prevent harm to tile technicians and RV components. Elimination of open flame from tile removal process will increase safety, as well as reducing the amount of flying chips in the removal process and maintaining surface temperatures under 100°F of objects that will be used with bare hands such as the heated scraper handle.
►Maintaining budget requirements. Cost of research and development shall be $1,000 or less, and combined cost of tools will be $400 or less. 100 units of each tool will be manufactured by Aries Engineering and one of each tool will be sent to various tile technicians so affordability of mass production is crucial.
►Max 10 amp electricity used by tools. The tools will potentially be plugged into an RV to be used and must draw 10 amps or less as this is the available amperage.
Top–Level Alternative Designs
Final designs were chosen using a four-step process. First an external search was performed to identify any heated scrapers or heating pad units that would meet design specifications as well as tile removal methods. Second an internal search within the group was conducted. The third step was to compare possible solutions using a scoring matrix, and finally weaker options were eliminated and final designs were chosen. The most important categories evaluated were performance, safety, and cost of: preparation of tile for removal; method of tile removal; and type of heat source for the scraper.
The tiles need to be prepared in such a way that will weaken the bond with the underlying adhesive. This can be achieved by a heating pad, a chemical solvent, or dry ice. A heating pad can deliver heat directly to a surface, can be purchased for under $75, and can be powered by an electrical outlet, which will be accessible inside an RV. Placing a silicon mat on top of the heating pad would decrease contact resistance between the mat and the tile, as well as decreasing the touch temperature of the top of the apparatus. A chemical solvent to dissolve the adhesive was used successfully in tests run by Ken Millard but the chemical was found to be too toxic for regular use. Dry ice would require set up costs, but would be safe to use as long as it did not come into contact with skin. The performance of dry ice was not thoroughly investigated, as it was not deemed a feasible option due to storage and cost.
Once the tile is prepared, it must be removed to access the adhesive. The current method of using a hammer and a crowbar can potentially damage property, but is otherwise acceptable. Scoring the tile before hitting it would make the destruction of the tile more predictable. Using an industrial suction cup was also considered. This would prevent the field technician from handling a hot tile, but industrial suction cups are too expensive, and could lead to operator injury if the tile is jerked from the base too hard.
The current method of adhesive removal employs a metal scraper. Currently scrapers are available that use conductive heat, infrared radiation, and mechanical vibrations. Heated scrapers can be purchased for around $200, and allow the field technician to scrape off the adhesive with less applied force than the current method. The potential to burn the person who removes the tile is a concern that will be addressed during the design phase. Radiation scrapers can attain temperatures of up to 800ºF, but cost over $500. Commercially available models encountered were wider than the spacing of the wires, which could damage the wires. Mechanical scrapers are cheap, but do not provide the precision needed to ensure the safety of the wires.
Final design choices were to use a heating pad for tile preparation, to use a scoring tool, hammer and crowbar for tile removal and to use electrical resistance heating for the scraper.
Final Design
Overview
The final design consists of two prototypes and a process to remove tiles. The first prototype is a heated scraper that is used to remove adhesive from under the tile and the second prototype is a tile heating unit that preheats the tile and the adhesive to facilitate easy removal of the tile. The main metrics and targets for design are outlined in table 1, and a photograph of the components of the system is shown in figure 2.
Figure 2. Photograph of system components. Clockwise from top left corner: heat resistant gloves and safety glasses, tile heating unit, pry bar, tile scorer and heated scraper.
Table 1. Summary of metrics, targets and prototype results.
Metric / Target / Results / Metric or Target AchievedTime taken to remove tile / 30 minutes or less / 20 – 30 minutes / Yes.
Scraper tip width: to be smaller than distance between wires / 1.5” / 1” / Yes. Wires have varied distances and the target was changed to accommodate this.
Temperature of tile after pre - heating: high enough to provide maximum reduction of yield strength of adhesive / 350°F / 250°F / Yes. Heating the tile to 350°F causes disintegration of insulation on conductive wires and the target had to be reduced
Cost of units including parts and labor / Under $400 / $300 / Yes.
Compatibility with RV electrical system / 10 amp / 1.5 amp and 6 amp / Yes.
Diameter of scraper handle: to provide an ergonomic handle design / 1 – 2” / Average 1.5” along length / Yes.
Dimensions of box for the tools to be shipped in / 18” x 18” x 12” / 18” x 18” x 12” / Yes.
Heated Scraper
The design concept for the heated scraper was straightforward: a metal scraping tip with an embedded heater. Critical design considerations were:
►Tip shape. The scraper tip must be narrow enough to fit between the heater element wires.
►Cost. Only the most cost effective solutions could be considered
► Manufacturability. By designing for manufacturability, costs are kept low
►Durability. Must be built for longevity and abuse by end user is expected.
►Ergonomic. Ease of use and shape of handle.
► Safety. Human contact surfaces must not pass safe temperature levels and electrical connections must be secure and insulated.
►Energy use. Achieve rapid heating response with minimal electricity use.