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Cryojet - new technology for a mature market.

The use of nitrogen for rubber deflashing, which dates from the early 1950s, is one of the oldest applications developed for liquid nitrogen. When a molded rubber part is removed from the mold, it contains scrap or flash. That is, where the two halves of die mold come together, the rubber, which is injected under pressure, seeps out along the parting line of the mold, forming scrap. This scrap material needs to be removed before the part can be used.

There are a number of ways to deflash. Some parts are hand-trimmed with a knife or with a pair of scissors, some are die cut. Beginning around 1950, people began to use liquid nitrogen to remove scrap from molded parts. The liquid nitrogen freezes the material, making it hard and brittle. By controlling the temperature of die parts, an operator can selectively embrittle to the point where an impact from tumbling the parts will break off only a thin section.

By die late 50s, several companies were marketing tumblers. The liquid nitrogen was injected axially into the tumbler and sprayed onto die parts as the tumbler rotated. Time and temperature cycles were controlled, and in this fashion, one part fell onto another part, or a part fell onto its edge, and the scrap broke off. The limitation of this method is that interior flash is not removed with just die tumbling action. In 1962, Wheelabrator introduced a product caned the Fridgebrator, a shot-blast machine coupled with die basic tumbling technology.

Throughout the 1960s and the early and mid-1970s, the market grew very rapidly. But, by the late 70s, U.S. automobiles were being downsized. As a result instead of eight spark plug caps in a car, there were now four. A much smaller motor mount replaced a large motor mount. Because a large portion of the deflashing industry is automotive, this downsizing led to some contraction of the market. As a result the deflashing market has experienced the fairly classic product life cycle, with a period of rapid growth and a period of market maturity. The traditional automotive market has fallen off, but as we will see, there are some new markets providing us with renewed growth.

The rubber deflashing market

Figure 1 represents the predicted growth of the elastomer deflashing market. In die United States there are approximately 300 companies that are deflashing molded rubber. Throughout the rest of the world, there are approximately 800. A typical rubber deflashing company in Europe, for example, molds about 1.5 tons of rubber parts per day, which is about 110 kilograms an hour on a two-shift operation. Of course, some are much larger, some much smaller.

In the U.S., molded rubber parts (excluding tires) and plastic injection molded parts were reported by the U.S. Brureau of Labor Statistics as growing 10-12% last year. Over the long term, it is not anticipated that 12% growth will hold up. In fact, it is suspected that 7-9% growth will be more representative over the next five years. Of the 300 companies making molded rubber parts, it is estimated that 200 of these are using liquid nitrogen. Additionally, of that 200, approximately half are using die newer generation of machines introduced in the 70s and 80s, and half are using tumblers and Wheelabrators. In the rest of the world there is a smaller degree of penetration of nitrogen technology into the market. That is, about 30% of the producers are presently using liquid nitrogen, but the users are a smaller average size.

Figure 2 shows that the nitrogen growth rate is a little bit slower than the total market growth rate. This is due to several offsetting factors. First, companies presently deflashing rubber are using nitrogen more efficiently. Offsetting this is the increased penetration of nitrogen into new applications markets. Average gas consumption per customer is approximately 700,000 [ft.sup.3] per month outside the U.S. and approximately 1.1 million ft3 per month within the U.S.

Cryojet features

MG Industries' Cryojet (figure 3) was introduced in the U.S. in 1977. It features a door that swings out, raises pneumatically and closes. There is a drum which rotates in a horizontal plane. The throwing wheel located on the back of the drum throws shot at the parts as they are rotating in the machine. The machine is available with both relay and solid state controls.

Many of the features of the Cryojet positively impact on the effectiveness of deflashing as well as minimize the consumption of liquid nitrogen.

The first design feature is the unique ribbing on the inside of the drum. This is the only large machine that employs a drum rather than a belt. This drum is ribbed to provide a tumbling action that more completely exposes each part. As a result intricate parts are deflashed in minimum cycle times.

Second, the Cryojet offers versatility in terms of the ability to use either steel or plastic shot. The ability to control the type of shot gives operators control over the finish of the product.

Third, the blast wheel operates at 6,000 RPM, a design feature that produces faster, more complete deflashing and contributes to minimizing nitrogen consumption.

Fourth, the fact that the shot is internal to the machine itself not only maximizes the nitrogen efficiency but also prevents moisture from coming into contact with the working parts of the machinery.

And, finally, precise control of operating temperature makes the Cryojet flexible enough to accommodate various types of elastomers, while preserving the surface finish of the parts. The construction of the machine, the uniformity of shot feeding and the fact that there is no external cycling of material all help to improve temperature control and stability.

Sample economics

Nitrogen consumption and customer economics vary with many factors. The more intricate the part, the more time required to sufficiently expose the surface to the blast. Simple rubber parts can often be deflashed in five minutes at +10 degrees F, while a silicone rubber electronic connector may require 15 minutes at -100 degrees F. The economics are very specific to the customer and to the part.

The product in figure 4 is a molded urethane elastomer automotive grill that is being supplied by our customer to General Motors. It is a typical example of how technological advances have allowed us to grow in a mature market. The photograph depicts before and after pictures of the back of the grill. The front of the grill has a bright shiny finish. As you see, the back still has the scrap from the molding process. The customer tried several times to remove this mechanically and was never able to obtain an acceptable surface finish on the front of this part. Consequently, before MG became involved in the project, the client was manually deflashing this grill in large quantities with knives.

The versatility of the Cryojet design allowed us to create a fixture that holds the grills fixed inside the drum. The grills are now mounted around the outside of that fixture between the fixture and the drum. The throwing wheel at the center of the drum throws the shot onto the back side of the grill. As it goes around, it continuously exposes the back side of the grill to the direct shot without exposing the front. In this way, we were able to mechanically produce an acceptable part. And, the technological advance allowed us to penetrate a market that was heretofore closed to cryogenic deflashing.

When you find a customer with a high volume manual operation, the economics of automating this very labor-intensive operation can be compelling. As table 1 illustrates, this particular customer went from a labor input of ten minutes per grill to a labor input of one minute per grill.

This is somewhat offset by the cost of nitrogen consumed in the process. But even with nitrogen costs, at a rate of 325 parts per hour, on a two-shift operation, there is a seven month pay-back on the capital expenditure.

The second example (table 2) contains typical economics for the replacement of an existing machine at a more traditional parts producer. The significant reduction in nitrogen consumption, together with a modest labor savings, provides for an attractive 2-1/2-year payback on the replacement of existing deflashing equipment.

The data in figure 5 are from a paper that MG published two years ago. The machine cited in Test A is a 1-1/2cubic-foot shot blast deflasher that dates from the mid-'60s. Clearly, it was designed without regard to nitrogen efficiency. As you can see, the nitrogen reduction on a fairly difficult part is quite dramatic.

The equipment in Test B was a three-year-old, five-cubic-foot shot blast deflasher. Although the improvement in nitrogen use is less dramatic, it is nonetheless significant. In fact data from this series of tests are the basis for the economic comparison shown in table 2.

Test C represents data obtained on a Cryojet and a five-cubic-foot, 1970-vintage shot blast machine.

Summary

The rubber deflashing market is one of the oldest of the major applied-technology-1/2" application markets. In addition to variations in local economic conditions, variations in the way our industry has marketed applications technology have resulted in different degrees of penetration in this market. By many standards, this application represents a mature market in the U.S. and in Western Europe. However, as a result of new applications, new elastomer markets and advanced engineering, we see continuing growth and opportunity in the rubber deflashing market.
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Copyright 1990, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Author:Watters, J.
Publication:Rubber World
Date:Dec 1, 1990
Words:1591
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