PVC Hockeyballs

That is a pretty tall order for such limited information. Is your "day" a single 8-hour shift, or 10 hours, or two 8-hour shifts, etc. What is your target production rate per hour? I am not familiar with Hockeyballs, is there a standard diameter and weight or wall thickness?

Do you already have rotational molding experience or equipment? The equipment may dictate what your molds look like.

If you are unfamiliar with the process, there is an excellent primer in the Wikipedia at:

http://en.wikipedia.org/wiki/Rotomolding

Basically, let's start with a few assumptions. You will have one oven and several multiple cavity molds. Let's say the melt process takes almost an hour (55 minutes), and during that hour the operator can be preparing the next mold while the last mold cools (20 minutes), then unloading the last mold (10 minutes), and inspecting and packing the balls (10 minutes). Allow another 10 minutes for paperwork (SPC, production data entry, etc.), 5 minutes for personal time, and finally 5 minutes for loading/unloading the oven (swapping molds).

In order to meet your initial production target of 240 per day on an 8-hour per day basis, you would need to produce 30 balls every hour, assuming no loss and no down time. This means that your molds should each have 30 cavities. Picture an array of 5 x 6 rows, something like a cupcake pan, but hemispherical instead of a conical section (or tapered cylinder) that a cupcake has. The operator will take a measured amount of resin (ground up PVC) and place it in each cavity. A second "cupcake pan" is then clamped on top of the first (usually hinged or precisely pinned together). The mold is then ready to be placed into a two-axis rotation mechanism that will slowly turn them over, rolling and end for end at the same time, like a two-axis rotisserie, while in the oven. This allows the resin to coat the mold evenly, providing a uniform wall thickness.

The oven can be allow to cool while the parts continue to rotate inside (preventing sag until the plastic is stiff), or the molds can be removed, complete with rotational mechanism, or be placed immediately into another mechanism outside the oven. This is preferred (and assumed in times noted above) for fuel and operator efficiency. Fans directing air at the cooling molds will help reduce the cooling time.

To ramp up production to your 1000 piece target you have several choices. You could get a larger oven and larger molds (or start with smaller molds in the larger oven anyway), however handling 125 cavity molds might be a little problematic. You could get by with a single oven on two 8-hour shifts with 64 cavity molds (number of cavities per mold should be a logical multiplication product of the rows, in this case 8 x 8), or go two two ovens. You will be paying two operators either way, but with two ovens you have more capacity should you need it. You could also continue production at half rate (or go to second shift) if one oven goes down for maintenance. Anyway, you will need to experiment a little to determine optimum times and temperatures for different size molds. Also, you may want to increase your target production (and number of cavities per mold) to allow for possible inefficiency in the process (downtime, scrap, interruptions, etc.)

The equipment required is so simple you can probably build it yourself, or design it and have a competent machine shop make it, or you can buy off the shelf rotomolding equipment and have custom molds made to fit the equipment. If you are lucky you may even find another manufacturer going out of business or other source of used equipment.

PVC is a low-temperature material anyway, and unlike injection molding, which requires a completely liquid melt under pressure, you need to keep temperatures on the low side, otherwise you will "overcook" the plastic, making it hard and brittle. Again, you will have to "play" with oven temperature and times to get it just right. If you "undercook" the balls, you will end up with unfused resin inside and/or poor integrity of the structure.

I hope this helps.

Hello , Unfortunately, can't give you much advise on how to setup a production line, but I can help to make the product for you, if you are interested in having it made cheaply instead of making it yourself. If interested, feel free to contact me. mohkahn@yahoo.com

Have a nice day.

Ken.

May be able to help.

please e-mail details to paul.scholey@amberplastics.co.uk