Fax (360) 882-8728
(360) 882-0410

Ask Mike Humes


What is Rotational molding?

A low pressure plastic molding process that has 3 distinct phases

-Load and unload station where finished part is removed and a fresh charge of pre-weighed resin is loaded in the hollow cavity mold and closed.

-The mold, which is mounted on a biaxial rotating arm, is indexed into the oven chamber where it is heated by an open flame burner. The mold while heating and rotating distributes the resin evenly on the inside surface of the mold. When properly cured the micro-processor sends the arm out of the oven to the cooling stations.

-Mold continues rotations while forced air and or water mist cool the mold / solidify the part prior to indexing on to the load and unload area.

What types of molds are available?

-Cast Aluminum Molds; most common in our industry, make a part with compound surfaces, radii, various textures high in cosmetic appeal.

-CNC Aluminum Molds; at times more cost effective than cast (low profiles) when high cosmetic requirements are couple with precision tolerances.

-Fabricated Sheet Molds; made in stainless steel, mild steel or aluminum, the cost effective alternative when the end product serves within an industrial application and has a simple shape.

What are lead times on molds and production?

Very dependent on project type; new molds vary from 3-4 weeks to 8-10 weeks. Production also dependent on project but plan on from 300 – 400 units per month per mold.

What are your size limitations?

With our current equipment we mold up to 10 feet in diameter with our smallest production part about a 6″ cube.

What materials are available?

Most of our resin use falls within the Polyethylene family; LDPE, LLDPE, HDPE, Crosslink, Flame Retardant and EVA Copolymer. Nylon is used for high temperature applications as well as in CARB compliant fuel tanks. PVC, PP, PC are available upon request.

What wall thickness can be achieved in rotational molding?

From a low side of 0.060″ up to 0.50″ thick

Why consider rotational molding for my application?

Fast to market, low entry cost molds which are about 10% the cost of injection and blow molding; makes seamless one piece units often not possible with other plastic processes. More impact resistant than sheet metal, also it will not corrode, doesn't need painting and costs less in most cases.

What kind of product can be designed for rotational molding?

Call us, (360) 882-0410 we do not like saying no to any project.

What is an acceptable temperature for a hot food, or material to be placed in a plastic bin?

Up to 138° F it's acceptable for long periods and 185° F for a short period of time to sanitize.

I use plastic hoppers for malt, and have bridging problems in the past. Is anything available to solve this?

Yes, things such as silo-Fluidizers, air-hammers, and ultra-sonic vibration tables are readily available.

What is the standard UV rating for linear low density polyethylene?

Recently improvements have been made by the resin manufactures, it is typically 12 years.

If I only want 8-10 bins of a specific color for HACCP, is this possible?

Yes, minimum runs of (8) bins are possible.

Is polyethylene permeable?

Yes, it does have an oxygen and moisture transmission rate.

Is a custom bin for your application cost prohibitive?

No, we can typically amortize it within a couple hundred parts (bins, pallets, or Tanks). Please inquire with your sales representative.

How big of a part (bin, pallet, or tank) can we make?

We can make parts up to 10′ 3″ in diameter.

Can plastic boxes, pallets, and tanks be repaired that have been hit, or stabbed with a forklift?

Yes, there are companies out there that specialize in repairing plastic material handling products.

What is the background photo on the website?
It is an active stratovolcano called Mount St. Helens or Louwala-Clough, in Skamania County, Washington.
Located in the Pacific NW USA about 48 miles away from SmaK Plastics in Vancouver, Wa.
Any other question not shown?

Please give us call or send us an email, we will be happy to answer your specific question.