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WIRTZ MOLD SPRAY COAT PROCEDURES
Wirtz Manufacturing Company, Inc. designs and produces grid molds to fill customer requirements around the world.
The operation of applying mold coat (cork) to the grid mold is very important, the technique used and the care taken in the operation has a very large bearing on successful grid casting.
There are three basic methods used to apply mold coat. Each requires the mold to be machined differently to account for cork build up and to obtain correct weight and thickness of finished grids.
For this discussion, the following grid data is used to explain corking procedures:
Required Grid Thickness: .050 ± .003
Required Grid Weight 50 grams ± 3 grams
Heavy or light horizontal spray coat is accomplished by 20 to 25 horizontal passes from side to side.
Heavy or light vertical spray coat is accomplished by 20 to 25 vertical passes from side to side.
The difference between light and heavy coats is time. Heavy (15 to 20 seconds); light (7 to 10 seconds or about half). This varies by how fast the spray gun moves across the mold face.
In addition, coarseness setting of spray head can vary the amount of cork applied.
A determination of too much or too little cork applied can be made by checking the cast grid thickness and weight and adjusting accordingly.
In each corking procedure, the mold is designed to produce grids at the low end of the tolerance, that is, minimum thickness and weight thus allowing the maximum running time after each cork job. With any corking procedure, grids will increase in thickness and weight after several hours of casting.
Following is an aid to help understand what is happening when using the different procedures and decide which procedure would best meet production requirements.
1. Spray and Run; No Wipe and No Scrape
| Approximate amount of cork build up: |
| Frame: | .004 |
| Wires: | .004 |
| Surface: | .004 |
| Cast Thickness: | .047 |
| Approximate running time: | 3 hours depending on mold design and operator skill. |
| Advantages: | Easy method for operator. |
| Disadvantages: | Hard to control thickness and flash. |
| Procedure: | Spray 4 heavy horizontal coats and 4 heavy vertical coats. Begin casting. |
2. Spray - Scrape - Spray and Run
| Approximate amount of cork build up: |
| Frame: | .004 |
| Wires: | .004 |
| Surface: | .002 |
| Cast Thickness: | .047 |
| Approximate running time: | 3 hours depending on mold design and operator skill. |
| Advantages: | Easy to touch up, control weight, thickness and flash. |
| Disadvantages: | Requires more operator skill. |
| Procedure: | Spray 4 heavy horizontal coats and 4 heavy vertical coats. Remove cork from surface by scraping with large putty knife. Spray light coat.Begin casting. |
3. Spray-Scrape-Wipe-Spray-Run (Provides optimum cork in frames, wires, and on surface).
| Approximate amount of cork build up: |
| Frame: | .002 |
| Wires: | .006 |
| Surface: | .002 |
| Cast Thickness: | .048 |
| Approximate running time: | 6 to 8 hours with touch ups, same as above. |
| Advantages: | Easy to touch up, longest running, improves thickness and flash control. |
| Disadvantages: | More time and operator skill required. |
| Procedure: | Spray 4 heavy horizontal coats and 4 heavy vertical coats. Remove cork from surface by scraping with large putty knife. Wipe out frame, lug and foot area with wooden stick. Brush same areas with a firm bristle type brush. Spray 4 light horizontal coats. Begin casting. |
Procedure #3 can be varied by Spray-Wipe-Spray-Scrape and Spray.
Equipment Needed:
1. Good quality spray gun (example - Devilbiss with #30 nozzle).
2. Large putty knife - used for scraping mold surface.
3. Wooden stick - used for wiping the cork out of the frame and lug areas.
4. Small wooden stick - used for center foot tie and other areas.
5. Small firm bristle type brush with the bristles cut very short.
6. Wire brush - used for removing the old cork off the mold and cleaning the surface.
7. Small putty knife - used for scraping.
8. Oakite for cleaning molds.
Wirtz Manufacturing Company, would welcome the opportunity to discuss in depth any one of the procedures that would best meet your production requirements.
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