Do you know the kiss off in the rotomolding industry


1. What is Kiss off

Definition of kiss off in rotomolding industry is totally different with its usual meaning. It is a term that’s used in rotational molding to describe a solid, reinforcing structure that transmits a load from one nominal wall to another.

2. Why kiss off

Generally, the inner wall has approximately the same shape as the outer wall in a mold. There are usually two methods for reinforcing the intensity according to this character.

One is foam filling. The open space between the inner and outer walls can be filled with self-rising foam for added stiffness or improved insulating capabilities. It is an effective way but can cost a lot. You have to manufacture or purchase one mold specifically for foaming which is almost same cost as rotational mold. At present foaming is usually used in cooler and buoyancy tank making.

Another less costly stiffening approach that eliminates the cost of adding a foam is the use of kiss-offs. It is a common practice to provide additional strength by attaching two closely spaced parallel walls to each other. This technique can convert two relatively weak walls into one integral box-beam structure that is inherently strong. The thickness of the wall in the kiss-off area is almost always established by trial and error, usually 1.5 to 1.75  times the nominal wall thickness, but 1.75 times should be specified on the part drawing as a starting thickness. This spacing provides enough room for the powdered plastic to move freely through the cavity. The kissing off or welding together of the two walls takes place only as the last of the powdered plastic coats the cavity.

3. Application

Because rotational molding produces hollow parts, engineers and product designers need to consider what will happen to a plastic part if it’s flexed. Most rotomolded product can use kiss offs, such as removable toilet, the car roof, water tanks, auto parts, pallets, and baby-changing stations. Here we are posting some car roof pictures for illustrating.

4. Kiss off ribbing

Kiss-off reinforcing ribbing refers to long, continuous kiss-off areas. Tack-off reinforcing refers to interrupted kiss-off areas. These tack-offs can be any shape, but round is the most common.

5. Attentions

Where kiss-off ribbing or tack-offs are undesirable on an appearance surface, the kiss-off can be designed into only one wall of the part on the non-appearance side. Tack-off and kiss-off reinforcing is sometimes used in large rectangular portable liquid tanks to strengthen the side walls and discourage the liquid in the tank from sloshing from side to side. In these situations, there can be a substantial distance between the two walls that are to be attached to each other. In these cases, kiss-off ribbing should be designed into both walls. This minimizes the depth of the recess and makes it easier to heat the mold in the actual kiss-off area at the center of the tank.

Kiss-off ribbing has been used in the bottom of double-walled tanks for products such as insulated ice making machines. In these applications the kiss-off strengthens the inner wall. Failures can develop at the edge of the kiss-off on tanks that hold liquids or products such as grain that act like liquids. These failures have been traced to the added strength at the kiss-off. The inner bottom walls of the tank between the kiss-offs bends under the load. Stresses build up at the junction between the weaker inner bottom wall and the stronger kiss-off. In some cases, a more durable tank has been produced with what is referred to as an “almost kiss-off”. This brings the inner and outer walls of the tank close together, but they are not attached to each other. As the inner wall is loaded it bends and comes to rest on the almost kiss-off. This supports the inner wall while leaving it free to move relative to the kiss-off.   Reference: REINFORCING FEATURES –PART 3  By: Glenn Beall

6. Contact us!

If you are looking for a tooling maker who can make high-quality rotational molds, we are your best choice. We Ningbo Roto-Mould is an expert in this industry and have more than 22-year experience, we are always willing to give most sincere and practical advice which saves your energy and cost.




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