Polyethylene or PE is everywhere
While you may not know its name, polyethylene is everywhere. It been a while since we had to be with out plastic bag, food bowls, water tanks, and tubing. Polyethylene is FDA approved, light and inexperience. Great to machine and weld. Polyethylene fabrication, yes we do that.
Different polyethylene color samples.
Polyethylene fabrication material varieties include
- Low density (LDPE)
- Medium density (MDPE)
- High Density (HDPE)
- Ultra-high molecular weight (UHMW)
- Linear low-density (LLDPE).
- Cross-linked (XPE) is a “thermo set”
- Static dissipating PE
- Flame Retarding PE
- Starboard and similar grades of boats or outdoors
- And there are bunches more.
Each has its own properties. The only different between the first 4 are the weights of the material. Most are thermo plastics meaning they can be heated and bent over and over or re-melted into a new the sheet. Cross-linked PE is a thermo set once it is heated and changed into a product you can’t reheat it or change its form. Also cross-linked PE is not FDA approved. On the plus side they are very strong.
Note; Cross-linked PE or XPE needs to go into the garbage and not a recycle bin.
PE and Rotational Molding
Most rotational molding is done using PE. PE is made in pellets. Because rotational molding is done at a low temperature the pellets are ground into a dust form so the material melts easier. The PE dust is measured and poured inside a mold. As the mold rotates it is heated the powder bounces around the inside until it is hot enough to sticks to the sides. When the material cools you have a part that matches the inside of the mold.
Great Things about Rotational Molding
- You can use the same mold for different wall thickness.
- Molds are cheap for their size.
- Most parts can be welded.
- Materials except for XPE can be recycled.
- Lots of Rotational Molded parts are made with recycles material. Both per and post-consumer materials.
- You can pick almost any color in low quantity.
- Parts can be made with FDA materials.
- You can make a tank cross-linked on the outside and LLDPE on the inside. Giving you a strong tank that is FDA approved.
Polyethylene fabrication on a part that come out of the mold 90% done is much easier. If you are rotational molding a tank you may only need to cut the top off and add a drain fitting.
Finally rotational molding is slow you only get about one part per hour. So if you need more than 40 parts a week you may need more than one mold. Most rotational molders are big with 3 or 4 arms for mold. Each arm can hold 1 to 16 molds per arm. All the mold have to run at the same time. You can’t one 3/4 wall part with 1/4 wall parts with out burning the 1/4 parts.
Custom Polyethylene tank
Welded and rotational molded tanks we can help you with both. With welded tanks there are no upfront mold costs. If you only one tank to fit your boat, most likely it will be custom welded.
Rotational Molder Tanks
Bell Plastics has many molds for rotational tanks. We make custom tanks for people that can’t use a stock tank. Need a tank with a 3/4 wall or a special color. Rotational molded tanks have no seams. The lines you see on the outside of the tanks are parting line or mold lines. The lines are on the outside of the tank but the inside will be smooth.
PE spin welding fitting are installed by spinning it really fast while applying pressure.
HDPE fitting repaired after it was tore off. We welded a large patch over the hole and threaded it to match the old pipe thread.
Polyethylene is so useful we don’t throw any pieces away. While most plastics have a size that you never use up the drop. Not so with PE. Wear strips, cutting boards, machined parts and water tanks.
Temperature of deflection under load: method A: 1.8 MPa 44C or 111F ISO 751/2